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TOMOYO Linux Cross Reference
Linux/kernel/rcu/tree.c

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  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License as published by
  6  * the Free Software Foundation; either version 2 of the License, or
  7  * (at your option) any later version.
  8  *
  9  * This program is distributed in the hope that it will be useful,
 10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12  * GNU General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program; if not, you can access it online at
 16  * http://www.gnu.org/licenses/gpl-2.0.html.
 17  *
 18  * Copyright IBM Corporation, 2008
 19  *
 20  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 21  *          Manfred Spraul <manfred@colorfullife.com>
 22  *          Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
 23  *
 24  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 25  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 26  *
 27  * For detailed explanation of Read-Copy Update mechanism see -
 28  *      Documentation/RCU
 29  */
 30 #include <linux/types.h>
 31 #include <linux/kernel.h>
 32 #include <linux/init.h>
 33 #include <linux/spinlock.h>
 34 #include <linux/smp.h>
 35 #include <linux/rcupdate_wait.h>
 36 #include <linux/interrupt.h>
 37 #include <linux/sched.h>
 38 #include <linux/sched/debug.h>
 39 #include <linux/nmi.h>
 40 #include <linux/atomic.h>
 41 #include <linux/bitops.h>
 42 #include <linux/export.h>
 43 #include <linux/completion.h>
 44 #include <linux/moduleparam.h>
 45 #include <linux/percpu.h>
 46 #include <linux/notifier.h>
 47 #include <linux/cpu.h>
 48 #include <linux/mutex.h>
 49 #include <linux/time.h>
 50 #include <linux/kernel_stat.h>
 51 #include <linux/wait.h>
 52 #include <linux/kthread.h>
 53 #include <uapi/linux/sched/types.h>
 54 #include <linux/prefetch.h>
 55 #include <linux/delay.h>
 56 #include <linux/stop_machine.h>
 57 #include <linux/random.h>
 58 #include <linux/trace_events.h>
 59 #include <linux/suspend.h>
 60 #include <linux/ftrace.h>
 61 
 62 #include "tree.h"
 63 #include "rcu.h"
 64 
 65 #ifdef MODULE_PARAM_PREFIX
 66 #undef MODULE_PARAM_PREFIX
 67 #endif
 68 #define MODULE_PARAM_PREFIX "rcutree."
 69 
 70 /* Data structures. */
 71 
 72 /*
 73  * In order to export the rcu_state name to the tracing tools, it
 74  * needs to be added in the __tracepoint_string section.
 75  * This requires defining a separate variable tp_<sname>_varname
 76  * that points to the string being used, and this will allow
 77  * the tracing userspace tools to be able to decipher the string
 78  * address to the matching string.
 79  */
 80 #ifdef CONFIG_TRACING
 81 # define DEFINE_RCU_TPS(sname) \
 82 static char sname##_varname[] = #sname; \
 83 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
 84 # define RCU_STATE_NAME(sname) sname##_varname
 85 #else
 86 # define DEFINE_RCU_TPS(sname)
 87 # define RCU_STATE_NAME(sname) __stringify(sname)
 88 #endif
 89 
 90 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
 91 DEFINE_RCU_TPS(sname) \
 92 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
 93 struct rcu_state sname##_state = { \
 94         .level = { &sname##_state.node[0] }, \
 95         .rda = &sname##_data, \
 96         .call = cr, \
 97         .gp_state = RCU_GP_IDLE, \
 98         .gpnum = 0UL - 300UL, \
 99         .completed = 0UL - 300UL, \
100         .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
101         .name = RCU_STATE_NAME(sname), \
102         .abbr = sabbr, \
103         .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
104         .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
105 }
106 
107 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
108 RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
109 
110 static struct rcu_state *const rcu_state_p;
111 LIST_HEAD(rcu_struct_flavors);
112 
113 /* Dump rcu_node combining tree at boot to verify correct setup. */
114 static bool dump_tree;
115 module_param(dump_tree, bool, 0444);
116 /* Control rcu_node-tree auto-balancing at boot time. */
117 static bool rcu_fanout_exact;
118 module_param(rcu_fanout_exact, bool, 0444);
119 /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
120 static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
121 module_param(rcu_fanout_leaf, int, 0444);
122 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
123 /* Number of rcu_nodes at specified level. */
124 int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
125 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
126 /* panic() on RCU Stall sysctl. */
127 int sysctl_panic_on_rcu_stall __read_mostly;
128 
129 /*
130  * The rcu_scheduler_active variable is initialized to the value
131  * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
132  * first task is spawned.  So when this variable is RCU_SCHEDULER_INACTIVE,
133  * RCU can assume that there is but one task, allowing RCU to (for example)
134  * optimize synchronize_rcu() to a simple barrier().  When this variable
135  * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
136  * to detect real grace periods.  This variable is also used to suppress
137  * boot-time false positives from lockdep-RCU error checking.  Finally, it
138  * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
139  * is fully initialized, including all of its kthreads having been spawned.
140  */
141 int rcu_scheduler_active __read_mostly;
142 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
143 
144 /*
145  * The rcu_scheduler_fully_active variable transitions from zero to one
146  * during the early_initcall() processing, which is after the scheduler
147  * is capable of creating new tasks.  So RCU processing (for example,
148  * creating tasks for RCU priority boosting) must be delayed until after
149  * rcu_scheduler_fully_active transitions from zero to one.  We also
150  * currently delay invocation of any RCU callbacks until after this point.
151  *
152  * It might later prove better for people registering RCU callbacks during
153  * early boot to take responsibility for these callbacks, but one step at
154  * a time.
155  */
156 static int rcu_scheduler_fully_active __read_mostly;
157 
158 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
159 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
160 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
161 static void invoke_rcu_core(void);
162 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
163 static void rcu_report_exp_rdp(struct rcu_state *rsp,
164                                struct rcu_data *rdp, bool wake);
165 static void sync_sched_exp_online_cleanup(int cpu);
166 
167 /* rcuc/rcub kthread realtime priority */
168 static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
169 module_param(kthread_prio, int, 0644);
170 
171 /* Delay in jiffies for grace-period initialization delays, debug only. */
172 
173 static int gp_preinit_delay;
174 module_param(gp_preinit_delay, int, 0444);
175 static int gp_init_delay;
176 module_param(gp_init_delay, int, 0444);
177 static int gp_cleanup_delay;
178 module_param(gp_cleanup_delay, int, 0444);
179 
180 /*
181  * Number of grace periods between delays, normalized by the duration of
182  * the delay.  The longer the delay, the more the grace periods between
183  * each delay.  The reason for this normalization is that it means that,
184  * for non-zero delays, the overall slowdown of grace periods is constant
185  * regardless of the duration of the delay.  This arrangement balances
186  * the need for long delays to increase some race probabilities with the
187  * need for fast grace periods to increase other race probabilities.
188  */
189 #define PER_RCU_NODE_PERIOD 3   /* Number of grace periods between delays. */
190 
191 /*
192  * Track the rcutorture test sequence number and the update version
193  * number within a given test.  The rcutorture_testseq is incremented
194  * on every rcutorture module load and unload, so has an odd value
195  * when a test is running.  The rcutorture_vernum is set to zero
196  * when rcutorture starts and is incremented on each rcutorture update.
197  * These variables enable correlating rcutorture output with the
198  * RCU tracing information.
199  */
200 unsigned long rcutorture_testseq;
201 unsigned long rcutorture_vernum;
202 
203 /*
204  * Compute the mask of online CPUs for the specified rcu_node structure.
205  * This will not be stable unless the rcu_node structure's ->lock is
206  * held, but the bit corresponding to the current CPU will be stable
207  * in most contexts.
208  */
209 unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
210 {
211         return READ_ONCE(rnp->qsmaskinitnext);
212 }
213 
214 /*
215  * Return true if an RCU grace period is in progress.  The READ_ONCE()s
216  * permit this function to be invoked without holding the root rcu_node
217  * structure's ->lock, but of course results can be subject to change.
218  */
219 static int rcu_gp_in_progress(struct rcu_state *rsp)
220 {
221         return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
222 }
223 
224 /*
225  * Note a quiescent state.  Because we do not need to know
226  * how many quiescent states passed, just if there was at least
227  * one since the start of the grace period, this just sets a flag.
228  * The caller must have disabled preemption.
229  */
230 void rcu_sched_qs(void)
231 {
232         RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!");
233         if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
234                 return;
235         trace_rcu_grace_period(TPS("rcu_sched"),
236                                __this_cpu_read(rcu_sched_data.gpnum),
237                                TPS("cpuqs"));
238         __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
239         if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
240                 return;
241         __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
242         rcu_report_exp_rdp(&rcu_sched_state,
243                            this_cpu_ptr(&rcu_sched_data), true);
244 }
245 
246 void rcu_bh_qs(void)
247 {
248         RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
249         if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
250                 trace_rcu_grace_period(TPS("rcu_bh"),
251                                        __this_cpu_read(rcu_bh_data.gpnum),
252                                        TPS("cpuqs"));
253                 __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
254         }
255 }
256 
257 /*
258  * Steal a bit from the bottom of ->dynticks for idle entry/exit
259  * control.  Initially this is for TLB flushing.
260  */
261 #define RCU_DYNTICK_CTRL_MASK 0x1
262 #define RCU_DYNTICK_CTRL_CTR  (RCU_DYNTICK_CTRL_MASK + 1)
263 #ifndef rcu_eqs_special_exit
264 #define rcu_eqs_special_exit() do { } while (0)
265 #endif
266 
267 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
268         .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
269         .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
270 };
271 
272 /*
273  * There's a few places, currently just in the tracing infrastructure,
274  * that uses rcu_irq_enter() to make sure RCU is watching. But there's
275  * a small location where that will not even work. In those cases
276  * rcu_irq_enter_disabled() needs to be checked to make sure rcu_irq_enter()
277  * can be called.
278  */
279 static DEFINE_PER_CPU(bool, disable_rcu_irq_enter);
280 
281 bool rcu_irq_enter_disabled(void)
282 {
283         return this_cpu_read(disable_rcu_irq_enter);
284 }
285 
286 /*
287  * Record entry into an extended quiescent state.  This is only to be
288  * called when not already in an extended quiescent state.
289  */
290 static void rcu_dynticks_eqs_enter(void)
291 {
292         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
293         int seq;
294 
295         /*
296          * CPUs seeing atomic_add_return() must see prior RCU read-side
297          * critical sections, and we also must force ordering with the
298          * next idle sojourn.
299          */
300         seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
301         /* Better be in an extended quiescent state! */
302         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
303                      (seq & RCU_DYNTICK_CTRL_CTR));
304         /* Better not have special action (TLB flush) pending! */
305         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
306                      (seq & RCU_DYNTICK_CTRL_MASK));
307 }
308 
309 /*
310  * Record exit from an extended quiescent state.  This is only to be
311  * called from an extended quiescent state.
312  */
313 static void rcu_dynticks_eqs_exit(void)
314 {
315         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
316         int seq;
317 
318         /*
319          * CPUs seeing atomic_add_return() must see prior idle sojourns,
320          * and we also must force ordering with the next RCU read-side
321          * critical section.
322          */
323         seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
324         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
325                      !(seq & RCU_DYNTICK_CTRL_CTR));
326         if (seq & RCU_DYNTICK_CTRL_MASK) {
327                 atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
328                 smp_mb__after_atomic(); /* _exit after clearing mask. */
329                 /* Prefer duplicate flushes to losing a flush. */
330                 rcu_eqs_special_exit();
331         }
332 }
333 
334 /*
335  * Reset the current CPU's ->dynticks counter to indicate that the
336  * newly onlined CPU is no longer in an extended quiescent state.
337  * This will either leave the counter unchanged, or increment it
338  * to the next non-quiescent value.
339  *
340  * The non-atomic test/increment sequence works because the upper bits
341  * of the ->dynticks counter are manipulated only by the corresponding CPU,
342  * or when the corresponding CPU is offline.
343  */
344 static void rcu_dynticks_eqs_online(void)
345 {
346         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
347 
348         if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
349                 return;
350         atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
351 }
352 
353 /*
354  * Is the current CPU in an extended quiescent state?
355  *
356  * No ordering, as we are sampling CPU-local information.
357  */
358 bool rcu_dynticks_curr_cpu_in_eqs(void)
359 {
360         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
361 
362         return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
363 }
364 
365 /*
366  * Snapshot the ->dynticks counter with full ordering so as to allow
367  * stable comparison of this counter with past and future snapshots.
368  */
369 int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
370 {
371         int snap = atomic_add_return(0, &rdtp->dynticks);
372 
373         return snap & ~RCU_DYNTICK_CTRL_MASK;
374 }
375 
376 /*
377  * Return true if the snapshot returned from rcu_dynticks_snap()
378  * indicates that RCU is in an extended quiescent state.
379  */
380 static bool rcu_dynticks_in_eqs(int snap)
381 {
382         return !(snap & RCU_DYNTICK_CTRL_CTR);
383 }
384 
385 /*
386  * Return true if the CPU corresponding to the specified rcu_dynticks
387  * structure has spent some time in an extended quiescent state since
388  * rcu_dynticks_snap() returned the specified snapshot.
389  */
390 static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
391 {
392         return snap != rcu_dynticks_snap(rdtp);
393 }
394 
395 /*
396  * Do a double-increment of the ->dynticks counter to emulate a
397  * momentary idle-CPU quiescent state.
398  */
399 static void rcu_dynticks_momentary_idle(void)
400 {
401         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
402         int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
403                                         &rdtp->dynticks);
404 
405         /* It is illegal to call this from idle state. */
406         WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
407 }
408 
409 /*
410  * Set the special (bottom) bit of the specified CPU so that it
411  * will take special action (such as flushing its TLB) on the
412  * next exit from an extended quiescent state.  Returns true if
413  * the bit was successfully set, or false if the CPU was not in
414  * an extended quiescent state.
415  */
416 bool rcu_eqs_special_set(int cpu)
417 {
418         int old;
419         int new;
420         struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
421 
422         do {
423                 old = atomic_read(&rdtp->dynticks);
424                 if (old & RCU_DYNTICK_CTRL_CTR)
425                         return false;
426                 new = old | RCU_DYNTICK_CTRL_MASK;
427         } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
428         return true;
429 }
430 
431 /*
432  * Let the RCU core know that this CPU has gone through the scheduler,
433  * which is a quiescent state.  This is called when the need for a
434  * quiescent state is urgent, so we burn an atomic operation and full
435  * memory barriers to let the RCU core know about it, regardless of what
436  * this CPU might (or might not) do in the near future.
437  *
438  * We inform the RCU core by emulating a zero-duration dyntick-idle period.
439  *
440  * The caller must have disabled interrupts.
441  */
442 static void rcu_momentary_dyntick_idle(void)
443 {
444         raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
445         rcu_dynticks_momentary_idle();
446 }
447 
448 /*
449  * Note a context switch.  This is a quiescent state for RCU-sched,
450  * and requires special handling for preemptible RCU.
451  * The caller must have disabled interrupts.
452  */
453 void rcu_note_context_switch(bool preempt)
454 {
455         barrier(); /* Avoid RCU read-side critical sections leaking down. */
456         trace_rcu_utilization(TPS("Start context switch"));
457         rcu_sched_qs();
458         rcu_preempt_note_context_switch(preempt);
459         /* Load rcu_urgent_qs before other flags. */
460         if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
461                 goto out;
462         this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
463         if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
464                 rcu_momentary_dyntick_idle();
465         this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
466         if (!preempt)
467                 rcu_note_voluntary_context_switch_lite(current);
468 out:
469         trace_rcu_utilization(TPS("End context switch"));
470         barrier(); /* Avoid RCU read-side critical sections leaking up. */
471 }
472 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
473 
474 /*
475  * Register a quiescent state for all RCU flavors.  If there is an
476  * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
477  * dyntick-idle quiescent state visible to other CPUs (but only for those
478  * RCU flavors in desperate need of a quiescent state, which will normally
479  * be none of them).  Either way, do a lightweight quiescent state for
480  * all RCU flavors.
481  *
482  * The barrier() calls are redundant in the common case when this is
483  * called externally, but just in case this is called from within this
484  * file.
485  *
486  */
487 void rcu_all_qs(void)
488 {
489         unsigned long flags;
490 
491         if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
492                 return;
493         preempt_disable();
494         /* Load rcu_urgent_qs before other flags. */
495         if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
496                 preempt_enable();
497                 return;
498         }
499         this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
500         barrier(); /* Avoid RCU read-side critical sections leaking down. */
501         if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
502                 local_irq_save(flags);
503                 rcu_momentary_dyntick_idle();
504                 local_irq_restore(flags);
505         }
506         if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
507                 rcu_sched_qs();
508         this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
509         barrier(); /* Avoid RCU read-side critical sections leaking up. */
510         preempt_enable();
511 }
512 EXPORT_SYMBOL_GPL(rcu_all_qs);
513 
514 #define DEFAULT_RCU_BLIMIT 10     /* Maximum callbacks per rcu_do_batch. */
515 static long blimit = DEFAULT_RCU_BLIMIT;
516 #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
517 static long qhimark = DEFAULT_RCU_QHIMARK;
518 #define DEFAULT_RCU_QLOMARK 100   /* Once only this many pending, use blimit. */
519 static long qlowmark = DEFAULT_RCU_QLOMARK;
520 
521 module_param(blimit, long, 0444);
522 module_param(qhimark, long, 0444);
523 module_param(qlowmark, long, 0444);
524 
525 static ulong jiffies_till_first_fqs = ULONG_MAX;
526 static ulong jiffies_till_next_fqs = ULONG_MAX;
527 static bool rcu_kick_kthreads;
528 
529 module_param(jiffies_till_first_fqs, ulong, 0644);
530 module_param(jiffies_till_next_fqs, ulong, 0644);
531 module_param(rcu_kick_kthreads, bool, 0644);
532 
533 /*
534  * How long the grace period must be before we start recruiting
535  * quiescent-state help from rcu_note_context_switch().
536  */
537 static ulong jiffies_till_sched_qs = HZ / 10;
538 module_param(jiffies_till_sched_qs, ulong, 0444);
539 
540 static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
541                                   struct rcu_data *rdp);
542 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp));
543 static void force_quiescent_state(struct rcu_state *rsp);
544 static int rcu_pending(void);
545 
546 /*
547  * Return the number of RCU batches started thus far for debug & stats.
548  */
549 unsigned long rcu_batches_started(void)
550 {
551         return rcu_state_p->gpnum;
552 }
553 EXPORT_SYMBOL_GPL(rcu_batches_started);
554 
555 /*
556  * Return the number of RCU-sched batches started thus far for debug & stats.
557  */
558 unsigned long rcu_batches_started_sched(void)
559 {
560         return rcu_sched_state.gpnum;
561 }
562 EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
563 
564 /*
565  * Return the number of RCU BH batches started thus far for debug & stats.
566  */
567 unsigned long rcu_batches_started_bh(void)
568 {
569         return rcu_bh_state.gpnum;
570 }
571 EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
572 
573 /*
574  * Return the number of RCU batches completed thus far for debug & stats.
575  */
576 unsigned long rcu_batches_completed(void)
577 {
578         return rcu_state_p->completed;
579 }
580 EXPORT_SYMBOL_GPL(rcu_batches_completed);
581 
582 /*
583  * Return the number of RCU-sched batches completed thus far for debug & stats.
584  */
585 unsigned long rcu_batches_completed_sched(void)
586 {
587         return rcu_sched_state.completed;
588 }
589 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
590 
591 /*
592  * Return the number of RCU BH batches completed thus far for debug & stats.
593  */
594 unsigned long rcu_batches_completed_bh(void)
595 {
596         return rcu_bh_state.completed;
597 }
598 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
599 
600 /*
601  * Return the number of RCU expedited batches completed thus far for
602  * debug & stats.  Odd numbers mean that a batch is in progress, even
603  * numbers mean idle.  The value returned will thus be roughly double
604  * the cumulative batches since boot.
605  */
606 unsigned long rcu_exp_batches_completed(void)
607 {
608         return rcu_state_p->expedited_sequence;
609 }
610 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
611 
612 /*
613  * Return the number of RCU-sched expedited batches completed thus far
614  * for debug & stats.  Similar to rcu_exp_batches_completed().
615  */
616 unsigned long rcu_exp_batches_completed_sched(void)
617 {
618         return rcu_sched_state.expedited_sequence;
619 }
620 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);
621 
622 /*
623  * Force a quiescent state.
624  */
625 void rcu_force_quiescent_state(void)
626 {
627         force_quiescent_state(rcu_state_p);
628 }
629 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
630 
631 /*
632  * Force a quiescent state for RCU BH.
633  */
634 void rcu_bh_force_quiescent_state(void)
635 {
636         force_quiescent_state(&rcu_bh_state);
637 }
638 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
639 
640 /*
641  * Force a quiescent state for RCU-sched.
642  */
643 void rcu_sched_force_quiescent_state(void)
644 {
645         force_quiescent_state(&rcu_sched_state);
646 }
647 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
648 
649 /*
650  * Show the state of the grace-period kthreads.
651  */
652 void show_rcu_gp_kthreads(void)
653 {
654         struct rcu_state *rsp;
655 
656         for_each_rcu_flavor(rsp) {
657                 pr_info("%s: wait state: %d ->state: %#lx\n",
658                         rsp->name, rsp->gp_state, rsp->gp_kthread->state);
659                 /* sched_show_task(rsp->gp_kthread); */
660         }
661 }
662 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
663 
664 /*
665  * Record the number of times rcutorture tests have been initiated and
666  * terminated.  This information allows the debugfs tracing stats to be
667  * correlated to the rcutorture messages, even when the rcutorture module
668  * is being repeatedly loaded and unloaded.  In other words, we cannot
669  * store this state in rcutorture itself.
670  */
671 void rcutorture_record_test_transition(void)
672 {
673         rcutorture_testseq++;
674         rcutorture_vernum = 0;
675 }
676 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
677 
678 /*
679  * Send along grace-period-related data for rcutorture diagnostics.
680  */
681 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
682                             unsigned long *gpnum, unsigned long *completed)
683 {
684         struct rcu_state *rsp = NULL;
685 
686         switch (test_type) {
687         case RCU_FLAVOR:
688                 rsp = rcu_state_p;
689                 break;
690         case RCU_BH_FLAVOR:
691                 rsp = &rcu_bh_state;
692                 break;
693         case RCU_SCHED_FLAVOR:
694                 rsp = &rcu_sched_state;
695                 break;
696         default:
697                 break;
698         }
699         if (rsp == NULL)
700                 return;
701         *flags = READ_ONCE(rsp->gp_flags);
702         *gpnum = READ_ONCE(rsp->gpnum);
703         *completed = READ_ONCE(rsp->completed);
704 }
705 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
706 
707 /*
708  * Record the number of writer passes through the current rcutorture test.
709  * This is also used to correlate debugfs tracing stats with the rcutorture
710  * messages.
711  */
712 void rcutorture_record_progress(unsigned long vernum)
713 {
714         rcutorture_vernum++;
715 }
716 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
717 
718 /*
719  * Return the root node of the specified rcu_state structure.
720  */
721 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
722 {
723         return &rsp->node[0];
724 }
725 
726 /*
727  * Is there any need for future grace periods?
728  * Interrupts must be disabled.  If the caller does not hold the root
729  * rnp_node structure's ->lock, the results are advisory only.
730  */
731 static int rcu_future_needs_gp(struct rcu_state *rsp)
732 {
733         struct rcu_node *rnp = rcu_get_root(rsp);
734         int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
735         int *fp = &rnp->need_future_gp[idx];
736 
737         lockdep_assert_irqs_disabled();
738         return READ_ONCE(*fp);
739 }
740 
741 /*
742  * Does the current CPU require a not-yet-started grace period?
743  * The caller must have disabled interrupts to prevent races with
744  * normal callback registry.
745  */
746 static bool
747 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
748 {
749         lockdep_assert_irqs_disabled();
750         if (rcu_gp_in_progress(rsp))
751                 return false;  /* No, a grace period is already in progress. */
752         if (rcu_future_needs_gp(rsp))
753                 return true;  /* Yes, a no-CBs CPU needs one. */
754         if (!rcu_segcblist_is_enabled(&rdp->cblist))
755                 return false;  /* No, this is a no-CBs (or offline) CPU. */
756         if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
757                 return true;  /* Yes, CPU has newly registered callbacks. */
758         if (rcu_segcblist_future_gp_needed(&rdp->cblist,
759                                            READ_ONCE(rsp->completed)))
760                 return true;  /* Yes, CBs for future grace period. */
761         return false; /* No grace period needed. */
762 }
763 
764 /*
765  * rcu_eqs_enter_common - current CPU is entering an extended quiescent state
766  *
767  * Enter idle, doing appropriate accounting.  The caller must have
768  * disabled interrupts.
769  */
770 static void rcu_eqs_enter_common(bool user)
771 {
772         struct rcu_state *rsp;
773         struct rcu_data *rdp;
774         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
775 
776         lockdep_assert_irqs_disabled();
777         trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0);
778         if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
779             !user && !is_idle_task(current)) {
780                 struct task_struct *idle __maybe_unused =
781                         idle_task(smp_processor_id());
782 
783                 trace_rcu_dyntick(TPS("Error on entry: not idle task"), rdtp->dynticks_nesting, 0);
784                 rcu_ftrace_dump(DUMP_ORIG);
785                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
786                           current->pid, current->comm,
787                           idle->pid, idle->comm); /* must be idle task! */
788         }
789         for_each_rcu_flavor(rsp) {
790                 rdp = this_cpu_ptr(rsp->rda);
791                 do_nocb_deferred_wakeup(rdp);
792         }
793         rcu_prepare_for_idle();
794         __this_cpu_inc(disable_rcu_irq_enter);
795         rdtp->dynticks_nesting = 0; /* Breaks tracing momentarily. */
796         rcu_dynticks_eqs_enter(); /* After this, tracing works again. */
797         __this_cpu_dec(disable_rcu_irq_enter);
798         rcu_dynticks_task_enter();
799 
800         /*
801          * It is illegal to enter an extended quiescent state while
802          * in an RCU read-side critical section.
803          */
804         RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
805                          "Illegal idle entry in RCU read-side critical section.");
806         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
807                          "Illegal idle entry in RCU-bh read-side critical section.");
808         RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
809                          "Illegal idle entry in RCU-sched read-side critical section.");
810 }
811 
812 /*
813  * Enter an RCU extended quiescent state, which can be either the
814  * idle loop or adaptive-tickless usermode execution.
815  */
816 static void rcu_eqs_enter(bool user)
817 {
818         struct rcu_dynticks *rdtp;
819 
820         rdtp = this_cpu_ptr(&rcu_dynticks);
821         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
822                      (rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
823         if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
824                 rcu_eqs_enter_common(user);
825         else
826                 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
827 }
828 
829 /**
830  * rcu_idle_enter - inform RCU that current CPU is entering idle
831  *
832  * Enter idle mode, in other words, -leave- the mode in which RCU
833  * read-side critical sections can occur.  (Though RCU read-side
834  * critical sections can occur in irq handlers in idle, a possibility
835  * handled by irq_enter() and irq_exit().)
836  *
837  * We crowbar the ->dynticks_nesting field to zero to allow for
838  * the possibility of usermode upcalls having messed up our count
839  * of interrupt nesting level during the prior busy period.
840  *
841  * If you add or remove a call to rcu_idle_enter(), be sure to test with
842  * CONFIG_RCU_EQS_DEBUG=y.
843  */
844 void rcu_idle_enter(void)
845 {
846         lockdep_assert_irqs_disabled();
847         rcu_eqs_enter(false);
848 }
849 
850 #ifdef CONFIG_NO_HZ_FULL
851 /**
852  * rcu_user_enter - inform RCU that we are resuming userspace.
853  *
854  * Enter RCU idle mode right before resuming userspace.  No use of RCU
855  * is permitted between this call and rcu_user_exit(). This way the
856  * CPU doesn't need to maintain the tick for RCU maintenance purposes
857  * when the CPU runs in userspace.
858  *
859  * If you add or remove a call to rcu_user_enter(), be sure to test with
860  * CONFIG_RCU_EQS_DEBUG=y.
861  */
862 void rcu_user_enter(void)
863 {
864         lockdep_assert_irqs_disabled();
865         rcu_eqs_enter(true);
866 }
867 #endif /* CONFIG_NO_HZ_FULL */
868 
869 /**
870  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
871  *
872  * Exit from an interrupt handler, which might possibly result in entering
873  * idle mode, in other words, leaving the mode in which read-side critical
874  * sections can occur.  The caller must have disabled interrupts.
875  *
876  * This code assumes that the idle loop never does anything that might
877  * result in unbalanced calls to irq_enter() and irq_exit().  If your
878  * architecture violates this assumption, RCU will give you what you
879  * deserve, good and hard.  But very infrequently and irreproducibly.
880  *
881  * Use things like work queues to work around this limitation.
882  *
883  * You have been warned.
884  *
885  * If you add or remove a call to rcu_irq_exit(), be sure to test with
886  * CONFIG_RCU_EQS_DEBUG=y.
887  */
888 void rcu_irq_exit(void)
889 {
890         struct rcu_dynticks *rdtp;
891 
892         lockdep_assert_irqs_disabled();
893         rdtp = this_cpu_ptr(&rcu_dynticks);
894 
895         /* Page faults can happen in NMI handlers, so check... */
896         if (rdtp->dynticks_nmi_nesting)
897                 return;
898 
899         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
900                      rdtp->dynticks_nesting < 1);
901         if (rdtp->dynticks_nesting <= 1) {
902                 rcu_eqs_enter_common(true);
903         } else {
904                 trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nesting, rdtp->dynticks_nesting - 1);
905                 rdtp->dynticks_nesting--;
906         }
907 }
908 
909 /*
910  * Wrapper for rcu_irq_exit() where interrupts are enabled.
911  *
912  * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
913  * with CONFIG_RCU_EQS_DEBUG=y.
914  */
915 void rcu_irq_exit_irqson(void)
916 {
917         unsigned long flags;
918 
919         local_irq_save(flags);
920         rcu_irq_exit();
921         local_irq_restore(flags);
922 }
923 
924 /*
925  * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
926  *
927  * If the new value of the ->dynticks_nesting counter was previously zero,
928  * we really have exited idle, and must do the appropriate accounting.
929  * The caller must have disabled interrupts.
930  */
931 static void rcu_eqs_exit_common(long long oldval, int user)
932 {
933         RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
934 
935         rcu_dynticks_task_exit();
936         rcu_dynticks_eqs_exit();
937         rcu_cleanup_after_idle();
938         trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
939         if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
940             !user && !is_idle_task(current)) {
941                 struct task_struct *idle __maybe_unused =
942                         idle_task(smp_processor_id());
943 
944                 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
945                                   oldval, rdtp->dynticks_nesting);
946                 rcu_ftrace_dump(DUMP_ORIG);
947                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
948                           current->pid, current->comm,
949                           idle->pid, idle->comm); /* must be idle task! */
950         }
951 }
952 
953 /*
954  * Exit an RCU extended quiescent state, which can be either the
955  * idle loop or adaptive-tickless usermode execution.
956  */
957 static void rcu_eqs_exit(bool user)
958 {
959         struct rcu_dynticks *rdtp;
960         long long oldval;
961 
962         lockdep_assert_irqs_disabled();
963         rdtp = this_cpu_ptr(&rcu_dynticks);
964         oldval = rdtp->dynticks_nesting;
965         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
966         if (oldval & DYNTICK_TASK_NEST_MASK) {
967                 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
968         } else {
969                 __this_cpu_inc(disable_rcu_irq_enter);
970                 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
971                 rcu_eqs_exit_common(oldval, user);
972                 __this_cpu_dec(disable_rcu_irq_enter);
973         }
974 }
975 
976 /**
977  * rcu_idle_exit - inform RCU that current CPU is leaving idle
978  *
979  * Exit idle mode, in other words, -enter- the mode in which RCU
980  * read-side critical sections can occur.
981  *
982  * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
983  * allow for the possibility of usermode upcalls messing up our count
984  * of interrupt nesting level during the busy period that is just
985  * now starting.
986  *
987  * If you add or remove a call to rcu_idle_exit(), be sure to test with
988  * CONFIG_RCU_EQS_DEBUG=y.
989  */
990 void rcu_idle_exit(void)
991 {
992         unsigned long flags;
993 
994         local_irq_save(flags);
995         rcu_eqs_exit(false);
996         local_irq_restore(flags);
997 }
998 
999 #ifdef CONFIG_NO_HZ_FULL
1000 /**
1001  * rcu_user_exit - inform RCU that we are exiting userspace.
1002  *
1003  * Exit RCU idle mode while entering the kernel because it can
1004  * run a RCU read side critical section anytime.
1005  *
1006  * If you add or remove a call to rcu_user_exit(), be sure to test with
1007  * CONFIG_RCU_EQS_DEBUG=y.
1008  */
1009 void rcu_user_exit(void)
1010 {
1011         rcu_eqs_exit(1);
1012 }
1013 #endif /* CONFIG_NO_HZ_FULL */
1014 
1015 /**
1016  * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
1017  *
1018  * Enter an interrupt handler, which might possibly result in exiting
1019  * idle mode, in other words, entering the mode in which read-side critical
1020  * sections can occur.  The caller must have disabled interrupts.
1021  *
1022  * Note that the Linux kernel is fully capable of entering an interrupt
1023  * handler that it never exits, for example when doing upcalls to
1024  * user mode!  This code assumes that the idle loop never does upcalls to
1025  * user mode.  If your architecture does do upcalls from the idle loop (or
1026  * does anything else that results in unbalanced calls to the irq_enter()
1027  * and irq_exit() functions), RCU will give you what you deserve, good
1028  * and hard.  But very infrequently and irreproducibly.
1029  *
1030  * Use things like work queues to work around this limitation.
1031  *
1032  * You have been warned.
1033  *
1034  * If you add or remove a call to rcu_irq_enter(), be sure to test with
1035  * CONFIG_RCU_EQS_DEBUG=y.
1036  */
1037 void rcu_irq_enter(void)
1038 {
1039         struct rcu_dynticks *rdtp;
1040         long long oldval;
1041 
1042         lockdep_assert_irqs_disabled();
1043         rdtp = this_cpu_ptr(&rcu_dynticks);
1044 
1045         /* Page faults can happen in NMI handlers, so check... */
1046         if (rdtp->dynticks_nmi_nesting)
1047                 return;
1048 
1049         oldval = rdtp->dynticks_nesting;
1050         rdtp->dynticks_nesting++;
1051         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
1052                      rdtp->dynticks_nesting == 0);
1053         if (oldval)
1054                 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
1055         else
1056                 rcu_eqs_exit_common(oldval, true);
1057 }
1058 
1059 /*
1060  * Wrapper for rcu_irq_enter() where interrupts are enabled.
1061  *
1062  * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
1063  * with CONFIG_RCU_EQS_DEBUG=y.
1064  */
1065 void rcu_irq_enter_irqson(void)
1066 {
1067         unsigned long flags;
1068 
1069         local_irq_save(flags);
1070         rcu_irq_enter();
1071         local_irq_restore(flags);
1072 }
1073 
1074 /**
1075  * rcu_nmi_enter - inform RCU of entry to NMI context
1076  *
1077  * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
1078  * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
1079  * that the CPU is active.  This implementation permits nested NMIs, as
1080  * long as the nesting level does not overflow an int.  (You will probably
1081  * run out of stack space first.)
1082  *
1083  * If you add or remove a call to rcu_nmi_enter(), be sure to test
1084  * with CONFIG_RCU_EQS_DEBUG=y.
1085  */
1086 void rcu_nmi_enter(void)
1087 {
1088         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1089         int incby = 2;
1090 
1091         /* Complain about underflow. */
1092         WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
1093 
1094         /*
1095          * If idle from RCU viewpoint, atomically increment ->dynticks
1096          * to mark non-idle and increment ->dynticks_nmi_nesting by one.
1097          * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
1098          * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
1099          * to be in the outermost NMI handler that interrupted an RCU-idle
1100          * period (observation due to Andy Lutomirski).
1101          */
1102         if (rcu_dynticks_curr_cpu_in_eqs()) {
1103                 rcu_dynticks_eqs_exit();
1104                 incby = 1;
1105         }
1106         rdtp->dynticks_nmi_nesting += incby;
1107         barrier();
1108 }
1109 
1110 /**
1111  * rcu_nmi_exit - inform RCU of exit from NMI context
1112  *
1113  * If we are returning from the outermost NMI handler that interrupted an
1114  * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
1115  * to let the RCU grace-period handling know that the CPU is back to
1116  * being RCU-idle.
1117  *
1118  * If you add or remove a call to rcu_nmi_exit(), be sure to test
1119  * with CONFIG_RCU_EQS_DEBUG=y.
1120  */
1121 void rcu_nmi_exit(void)
1122 {
1123         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1124 
1125         /*
1126          * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
1127          * (We are exiting an NMI handler, so RCU better be paying attention
1128          * to us!)
1129          */
1130         WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
1131         WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
1132 
1133         /*
1134          * If the nesting level is not 1, the CPU wasn't RCU-idle, so
1135          * leave it in non-RCU-idle state.
1136          */
1137         if (rdtp->dynticks_nmi_nesting != 1) {
1138                 rdtp->dynticks_nmi_nesting -= 2;
1139                 return;
1140         }
1141 
1142         /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
1143         rdtp->dynticks_nmi_nesting = 0;
1144         rcu_dynticks_eqs_enter();
1145 }
1146 
1147 /**
1148  * rcu_is_watching - see if RCU thinks that the current CPU is idle
1149  *
1150  * Return true if RCU is watching the running CPU, which means that this
1151  * CPU can safely enter RCU read-side critical sections.  In other words,
1152  * if the current CPU is in its idle loop and is neither in an interrupt
1153  * or NMI handler, return true.
1154  */
1155 bool notrace rcu_is_watching(void)
1156 {
1157         bool ret;
1158 
1159         preempt_disable_notrace();
1160         ret = !rcu_dynticks_curr_cpu_in_eqs();
1161         preempt_enable_notrace();
1162         return ret;
1163 }
1164 EXPORT_SYMBOL_GPL(rcu_is_watching);
1165 
1166 /*
1167  * If a holdout task is actually running, request an urgent quiescent
1168  * state from its CPU.  This is unsynchronized, so migrations can cause
1169  * the request to go to the wrong CPU.  Which is OK, all that will happen
1170  * is that the CPU's next context switch will be a bit slower and next
1171  * time around this task will generate another request.
1172  */
1173 void rcu_request_urgent_qs_task(struct task_struct *t)
1174 {
1175         int cpu;
1176 
1177         barrier();
1178         cpu = task_cpu(t);
1179         if (!task_curr(t))
1180                 return; /* This task is not running on that CPU. */
1181         smp_store_release(per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, cpu), true);
1182 }
1183 
1184 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1185 
1186 /*
1187  * Is the current CPU online?  Disable preemption to avoid false positives
1188  * that could otherwise happen due to the current CPU number being sampled,
1189  * this task being preempted, its old CPU being taken offline, resuming
1190  * on some other CPU, then determining that its old CPU is now offline.
1191  * It is OK to use RCU on an offline processor during initial boot, hence
1192  * the check for rcu_scheduler_fully_active.  Note also that it is OK
1193  * for a CPU coming online to use RCU for one jiffy prior to marking itself
1194  * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
1195  * offline to continue to use RCU for one jiffy after marking itself
1196  * offline in the cpu_online_mask.  This leniency is necessary given the
1197  * non-atomic nature of the online and offline processing, for example,
1198  * the fact that a CPU enters the scheduler after completing the teardown
1199  * of the CPU.
1200  *
1201  * This is also why RCU internally marks CPUs online during in the
1202  * preparation phase and offline after the CPU has been taken down.
1203  *
1204  * Disable checking if in an NMI handler because we cannot safely report
1205  * errors from NMI handlers anyway.
1206  */
1207 bool rcu_lockdep_current_cpu_online(void)
1208 {
1209         struct rcu_data *rdp;
1210         struct rcu_node *rnp;
1211         bool ret;
1212 
1213         if (in_nmi())
1214                 return true;
1215         preempt_disable();
1216         rdp = this_cpu_ptr(&rcu_sched_data);
1217         rnp = rdp->mynode;
1218         ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1219               !rcu_scheduler_fully_active;
1220         preempt_enable();
1221         return ret;
1222 }
1223 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1224 
1225 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1226 
1227 /**
1228  * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1229  *
1230  * If the current CPU is idle or running at a first-level (not nested)
1231  * interrupt from idle, return true.  The caller must have at least
1232  * disabled preemption.
1233  */
1234 static int rcu_is_cpu_rrupt_from_idle(void)
1235 {
1236         return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
1237 }
1238 
1239 /*
1240  * We are reporting a quiescent state on behalf of some other CPU, so
1241  * it is our responsibility to check for and handle potential overflow
1242  * of the rcu_node ->gpnum counter with respect to the rcu_data counters.
1243  * After all, the CPU might be in deep idle state, and thus executing no
1244  * code whatsoever.
1245  */
1246 static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
1247 {
1248         lockdep_assert_held(&rnp->lock);
1249         if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, rnp->gpnum))
1250                 WRITE_ONCE(rdp->gpwrap, true);
1251         if (ULONG_CMP_LT(rdp->rcu_iw_gpnum + ULONG_MAX / 4, rnp->gpnum))
1252                 rdp->rcu_iw_gpnum = rnp->gpnum + ULONG_MAX / 4;
1253 }
1254 
1255 /*
1256  * Snapshot the specified CPU's dynticks counter so that we can later
1257  * credit them with an implicit quiescent state.  Return 1 if this CPU
1258  * is in dynticks idle mode, which is an extended quiescent state.
1259  */
1260 static int dyntick_save_progress_counter(struct rcu_data *rdp)
1261 {
1262         rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
1263         if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
1264                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1265                 rcu_gpnum_ovf(rdp->mynode, rdp);
1266                 return 1;
1267         }
1268         return 0;
1269 }
1270 
1271 /*
1272  * Handler for the irq_work request posted when a grace period has
1273  * gone on for too long, but not yet long enough for an RCU CPU
1274  * stall warning.  Set state appropriately, but just complain if
1275  * there is unexpected state on entry.
1276  */
1277 static void rcu_iw_handler(struct irq_work *iwp)
1278 {
1279         struct rcu_data *rdp;
1280         struct rcu_node *rnp;
1281 
1282         rdp = container_of(iwp, struct rcu_data, rcu_iw);
1283         rnp = rdp->mynode;
1284         raw_spin_lock_rcu_node(rnp);
1285         if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
1286                 rdp->rcu_iw_gpnum = rnp->gpnum;
1287                 rdp->rcu_iw_pending = false;
1288         }
1289         raw_spin_unlock_rcu_node(rnp);
1290 }
1291 
1292 /*
1293  * Return true if the specified CPU has passed through a quiescent
1294  * state by virtue of being in or having passed through an dynticks
1295  * idle state since the last call to dyntick_save_progress_counter()
1296  * for this same CPU, or by virtue of having been offline.
1297  */
1298 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1299 {
1300         unsigned long jtsq;
1301         bool *rnhqp;
1302         bool *ruqp;
1303         struct rcu_node *rnp = rdp->mynode;
1304 
1305         /*
1306          * If the CPU passed through or entered a dynticks idle phase with
1307          * no active irq/NMI handlers, then we can safely pretend that the CPU
1308          * already acknowledged the request to pass through a quiescent
1309          * state.  Either way, that CPU cannot possibly be in an RCU
1310          * read-side critical section that started before the beginning
1311          * of the current RCU grace period.
1312          */
1313         if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
1314                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1315                 rdp->dynticks_fqs++;
1316                 rcu_gpnum_ovf(rnp, rdp);
1317                 return 1;
1318         }
1319 
1320         /*
1321          * Has this CPU encountered a cond_resched_rcu_qs() since the
1322          * beginning of the grace period?  For this to be the case,
1323          * the CPU has to have noticed the current grace period.  This
1324          * might not be the case for nohz_full CPUs looping in the kernel.
1325          */
1326         jtsq = jiffies_till_sched_qs;
1327         ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
1328         if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
1329             READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
1330             READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
1331                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
1332                 rcu_gpnum_ovf(rnp, rdp);
1333                 return 1;
1334         } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) {
1335                 /* Load rcu_qs_ctr before store to rcu_urgent_qs. */
1336                 smp_store_release(ruqp, true);
1337         }
1338 
1339         /* Check for the CPU being offline. */
1340         if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
1341                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1342                 rdp->offline_fqs++;
1343                 rcu_gpnum_ovf(rnp, rdp);
1344                 return 1;
1345         }
1346 
1347         /*
1348          * A CPU running for an extended time within the kernel can
1349          * delay RCU grace periods.  When the CPU is in NO_HZ_FULL mode,
1350          * even context-switching back and forth between a pair of
1351          * in-kernel CPU-bound tasks cannot advance grace periods.
1352          * So if the grace period is old enough, make the CPU pay attention.
1353          * Note that the unsynchronized assignments to the per-CPU
1354          * rcu_need_heavy_qs variable are safe.  Yes, setting of
1355          * bits can be lost, but they will be set again on the next
1356          * force-quiescent-state pass.  So lost bit sets do not result
1357          * in incorrect behavior, merely in a grace period lasting
1358          * a few jiffies longer than it might otherwise.  Because
1359          * there are at most four threads involved, and because the
1360          * updates are only once every few jiffies, the probability of
1361          * lossage (and thus of slight grace-period extension) is
1362          * quite low.
1363          */
1364         rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
1365         if (!READ_ONCE(*rnhqp) &&
1366             (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
1367              time_after(jiffies, rdp->rsp->jiffies_resched))) {
1368                 WRITE_ONCE(*rnhqp, true);
1369                 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1370                 smp_store_release(ruqp, true);
1371                 rdp->rsp->jiffies_resched += jtsq; /* Re-enable beating. */
1372         }
1373 
1374         /*
1375          * If more than halfway to RCU CPU stall-warning time, do a
1376          * resched_cpu() to try to loosen things up a bit.  Also check to
1377          * see if the CPU is getting hammered with interrupts, but only
1378          * once per grace period, just to keep the IPIs down to a dull roar.
1379          */
1380         if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) {
1381                 resched_cpu(rdp->cpu);
1382                 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1383                     !rdp->rcu_iw_pending && rdp->rcu_iw_gpnum != rnp->gpnum &&
1384                     (rnp->ffmask & rdp->grpmask)) {
1385                         init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
1386                         rdp->rcu_iw_pending = true;
1387                         rdp->rcu_iw_gpnum = rnp->gpnum;
1388                         irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1389                 }
1390         }
1391 
1392         return 0;
1393 }
1394 
1395 static void record_gp_stall_check_time(struct rcu_state *rsp)
1396 {
1397         unsigned long j = jiffies;
1398         unsigned long j1;
1399 
1400         rsp->gp_start = j;
1401         smp_wmb(); /* Record start time before stall time. */
1402         j1 = rcu_jiffies_till_stall_check();
1403         WRITE_ONCE(rsp->jiffies_stall, j + j1);
1404         rsp->jiffies_resched = j + j1 / 2;
1405         rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1406 }
1407 
1408 /*
1409  * Convert a ->gp_state value to a character string.
1410  */
1411 static const char *gp_state_getname(short gs)
1412 {
1413         if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
1414                 return "???";
1415         return gp_state_names[gs];
1416 }
1417 
1418 /*
1419  * Complain about starvation of grace-period kthread.
1420  */
1421 static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1422 {
1423         unsigned long gpa;
1424         unsigned long j;
1425 
1426         j = jiffies;
1427         gpa = READ_ONCE(rsp->gp_activity);
1428         if (j - gpa > 2 * HZ) {
1429                 pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
1430                        rsp->name, j - gpa,
1431                        rsp->gpnum, rsp->completed,
1432                        rsp->gp_flags,
1433                        gp_state_getname(rsp->gp_state), rsp->gp_state,
1434                        rsp->gp_kthread ? rsp->gp_kthread->state : ~0,
1435                        rsp->gp_kthread ? task_cpu(rsp->gp_kthread) : -1);
1436                 if (rsp->gp_kthread) {
1437                         sched_show_task(rsp->gp_kthread);
1438                         wake_up_process(rsp->gp_kthread);
1439                 }
1440         }
1441 }
1442 
1443 /*
1444  * Dump stacks of all tasks running on stalled CPUs.  First try using
1445  * NMIs, but fall back to manual remote stack tracing on architectures
1446  * that don't support NMI-based stack dumps.  The NMI-triggered stack
1447  * traces are more accurate because they are printed by the target CPU.
1448  */
1449 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1450 {
1451         int cpu;
1452         unsigned long flags;
1453         struct rcu_node *rnp;
1454 
1455         rcu_for_each_leaf_node(rsp, rnp) {
1456                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1457                 for_each_leaf_node_possible_cpu(rnp, cpu)
1458                         if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
1459                                 if (!trigger_single_cpu_backtrace(cpu))
1460                                         dump_cpu_task(cpu);
1461                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1462         }
1463 }
1464 
1465 /*
1466  * If too much time has passed in the current grace period, and if
1467  * so configured, go kick the relevant kthreads.
1468  */
1469 static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
1470 {
1471         unsigned long j;
1472 
1473         if (!rcu_kick_kthreads)
1474                 return;
1475         j = READ_ONCE(rsp->jiffies_kick_kthreads);
1476         if (time_after(jiffies, j) && rsp->gp_kthread &&
1477             (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
1478                 WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
1479                 rcu_ftrace_dump(DUMP_ALL);
1480                 wake_up_process(rsp->gp_kthread);
1481                 WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
1482         }
1483 }
1484 
1485 static inline void panic_on_rcu_stall(void)
1486 {
1487         if (sysctl_panic_on_rcu_stall)
1488                 panic("RCU Stall\n");
1489 }
1490 
1491 static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1492 {
1493         int cpu;
1494         long delta;
1495         unsigned long flags;
1496         unsigned long gpa;
1497         unsigned long j;
1498         int ndetected = 0;
1499         struct rcu_node *rnp = rcu_get_root(rsp);
1500         long totqlen = 0;
1501 
1502         /* Kick and suppress, if so configured. */
1503         rcu_stall_kick_kthreads(rsp);
1504         if (rcu_cpu_stall_suppress)
1505                 return;
1506 
1507         /* Only let one CPU complain about others per time interval. */
1508 
1509         raw_spin_lock_irqsave_rcu_node(rnp, flags);
1510         delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1511         if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
1512                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1513                 return;
1514         }
1515         WRITE_ONCE(rsp->jiffies_stall,
1516                    jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1517         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1518 
1519         /*
1520          * OK, time to rat on our buddy...
1521          * See Documentation/RCU/stallwarn.txt for info on how to debug
1522          * RCU CPU stall warnings.
1523          */
1524         pr_err("INFO: %s detected stalls on CPUs/tasks:",
1525                rsp->name);
1526         print_cpu_stall_info_begin();
1527         rcu_for_each_leaf_node(rsp, rnp) {
1528                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1529                 ndetected += rcu_print_task_stall(rnp);
1530                 if (rnp->qsmask != 0) {
1531                         for_each_leaf_node_possible_cpu(rnp, cpu)
1532                                 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
1533                                         print_cpu_stall_info(rsp, cpu);
1534                                         ndetected++;
1535                                 }
1536                 }
1537                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1538         }
1539 
1540         print_cpu_stall_info_end();
1541         for_each_possible_cpu(cpu)
1542                 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1543                                                             cpu)->cblist);
1544         pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1545                smp_processor_id(), (long)(jiffies - rsp->gp_start),
1546                (long)rsp->gpnum, (long)rsp->completed, totqlen);
1547         if (ndetected) {
1548                 rcu_dump_cpu_stacks(rsp);
1549 
1550                 /* Complain about tasks blocking the grace period. */
1551                 rcu_print_detail_task_stall(rsp);
1552         } else {
1553                 if (READ_ONCE(rsp->gpnum) != gpnum ||
1554                     READ_ONCE(rsp->completed) == gpnum) {
1555                         pr_err("INFO: Stall ended before state dump start\n");
1556                 } else {
1557                         j = jiffies;
1558                         gpa = READ_ONCE(rsp->gp_activity);
1559                         pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1560                                rsp->name, j - gpa, j, gpa,
1561                                jiffies_till_next_fqs,
1562                                rcu_get_root(rsp)->qsmask);
1563                         /* In this case, the current CPU might be at fault. */
1564                         sched_show_task(current);
1565                 }
1566         }
1567 
1568         rcu_check_gp_kthread_starvation(rsp);
1569 
1570         panic_on_rcu_stall();
1571 
1572         force_quiescent_state(rsp);  /* Kick them all. */
1573 }
1574 
1575 static void print_cpu_stall(struct rcu_state *rsp)
1576 {
1577         int cpu;
1578         unsigned long flags;
1579         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1580         struct rcu_node *rnp = rcu_get_root(rsp);
1581         long totqlen = 0;
1582 
1583         /* Kick and suppress, if so configured. */
1584         rcu_stall_kick_kthreads(rsp);
1585         if (rcu_cpu_stall_suppress)
1586                 return;
1587 
1588         /*
1589          * OK, time to rat on ourselves...
1590          * See Documentation/RCU/stallwarn.txt for info on how to debug
1591          * RCU CPU stall warnings.
1592          */
1593         pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1594         print_cpu_stall_info_begin();
1595         raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
1596         print_cpu_stall_info(rsp, smp_processor_id());
1597         raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
1598         print_cpu_stall_info_end();
1599         for_each_possible_cpu(cpu)
1600                 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1601                                                             cpu)->cblist);
1602         pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
1603                 jiffies - rsp->gp_start,
1604                 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1605 
1606         rcu_check_gp_kthread_starvation(rsp);
1607 
1608         rcu_dump_cpu_stacks(rsp);
1609 
1610         raw_spin_lock_irqsave_rcu_node(rnp, flags);
1611         if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1612                 WRITE_ONCE(rsp->jiffies_stall,
1613                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1614         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1615 
1616         panic_on_rcu_stall();
1617 
1618         /*
1619          * Attempt to revive the RCU machinery by forcing a context switch.
1620          *
1621          * A context switch would normally allow the RCU state machine to make
1622          * progress and it could be we're stuck in kernel space without context
1623          * switches for an entirely unreasonable amount of time.
1624          */
1625         resched_cpu(smp_processor_id());
1626 }
1627 
1628 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1629 {
1630         unsigned long completed;
1631         unsigned long gpnum;
1632         unsigned long gps;
1633         unsigned long j;
1634         unsigned long js;
1635         struct rcu_node *rnp;
1636 
1637         if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
1638             !rcu_gp_in_progress(rsp))
1639                 return;
1640         rcu_stall_kick_kthreads(rsp);
1641         j = jiffies;
1642 
1643         /*
1644          * Lots of memory barriers to reject false positives.
1645          *
1646          * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1647          * then rsp->gp_start, and finally rsp->completed.  These values
1648          * are updated in the opposite order with memory barriers (or
1649          * equivalent) during grace-period initialization and cleanup.
1650          * Now, a false positive can occur if we get an new value of
1651          * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
1652          * the memory barriers, the only way that this can happen is if one
1653          * grace period ends and another starts between these two fetches.
1654          * Detect this by comparing rsp->completed with the previous fetch
1655          * from rsp->gpnum.
1656          *
1657          * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1658          * and rsp->gp_start suffice to forestall false positives.
1659          */
1660         gpnum = READ_ONCE(rsp->gpnum);
1661         smp_rmb(); /* Pick up ->gpnum first... */
1662         js = READ_ONCE(rsp->jiffies_stall);
1663         smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1664         gps = READ_ONCE(rsp->gp_start);
1665         smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1666         completed = READ_ONCE(rsp->completed);
1667         if (ULONG_CMP_GE(completed, gpnum) ||
1668             ULONG_CMP_LT(j, js) ||
1669             ULONG_CMP_GE(gps, js))
1670                 return; /* No stall or GP completed since entering function. */
1671         rnp = rdp->mynode;
1672         if (rcu_gp_in_progress(rsp) &&
1673             (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1674 
1675                 /* We haven't checked in, so go dump stack. */
1676                 print_cpu_stall(rsp);
1677 
1678         } else if (rcu_gp_in_progress(rsp) &&
1679                    ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1680 
1681                 /* They had a few time units to dump stack, so complain. */
1682                 print_other_cpu_stall(rsp, gpnum);
1683         }
1684 }
1685 
1686 /**
1687  * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1688  *
1689  * Set the stall-warning timeout way off into the future, thus preventing
1690  * any RCU CPU stall-warning messages from appearing in the current set of
1691  * RCU grace periods.
1692  *
1693  * The caller must disable hard irqs.
1694  */
1695 void rcu_cpu_stall_reset(void)
1696 {
1697         struct rcu_state *rsp;
1698 
1699         for_each_rcu_flavor(rsp)
1700                 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1701 }
1702 
1703 /*
1704  * Determine the value that ->completed will have at the end of the
1705  * next subsequent grace period.  This is used to tag callbacks so that
1706  * a CPU can invoke callbacks in a timely fashion even if that CPU has
1707  * been dyntick-idle for an extended period with callbacks under the
1708  * influence of RCU_FAST_NO_HZ.
1709  *
1710  * The caller must hold rnp->lock with interrupts disabled.
1711  */
1712 static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1713                                        struct rcu_node *rnp)
1714 {
1715         lockdep_assert_held(&rnp->lock);
1716 
1717         /*
1718          * If RCU is idle, we just wait for the next grace period.
1719          * But we can only be sure that RCU is idle if we are looking
1720          * at the root rcu_node structure -- otherwise, a new grace
1721          * period might have started, but just not yet gotten around
1722          * to initializing the current non-root rcu_node structure.
1723          */
1724         if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1725                 return rnp->completed + 1;
1726 
1727         /*
1728          * Otherwise, wait for a possible partial grace period and
1729          * then the subsequent full grace period.
1730          */
1731         return rnp->completed + 2;
1732 }
1733 
1734 /*
1735  * Trace-event helper function for rcu_start_future_gp() and
1736  * rcu_nocb_wait_gp().
1737  */
1738 static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1739                                 unsigned long c, const char *s)
1740 {
1741         trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1742                                       rnp->completed, c, rnp->level,
1743                                       rnp->grplo, rnp->grphi, s);
1744 }
1745 
1746 /*
1747  * Start some future grace period, as needed to handle newly arrived
1748  * callbacks.  The required future grace periods are recorded in each
1749  * rcu_node structure's ->need_future_gp field.  Returns true if there
1750  * is reason to awaken the grace-period kthread.
1751  *
1752  * The caller must hold the specified rcu_node structure's ->lock.
1753  */
1754 static bool __maybe_unused
1755 rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1756                     unsigned long *c_out)
1757 {
1758         unsigned long c;
1759         bool ret = false;
1760         struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1761 
1762         lockdep_assert_held(&rnp->lock);
1763 
1764         /*
1765          * Pick up grace-period number for new callbacks.  If this
1766          * grace period is already marked as needed, return to the caller.
1767          */
1768         c = rcu_cbs_completed(rdp->rsp, rnp);
1769         trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1770         if (rnp->need_future_gp[c & 0x1]) {
1771                 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1772                 goto out;
1773         }
1774 
1775         /*
1776          * If either this rcu_node structure or the root rcu_node structure
1777          * believe that a grace period is in progress, then we must wait
1778          * for the one following, which is in "c".  Because our request
1779          * will be noticed at the end of the current grace period, we don't
1780          * need to explicitly start one.  We only do the lockless check
1781          * of rnp_root's fields if the current rcu_node structure thinks
1782          * there is no grace period in flight, and because we hold rnp->lock,
1783          * the only possible change is when rnp_root's two fields are
1784          * equal, in which case rnp_root->gpnum might be concurrently
1785          * incremented.  But that is OK, as it will just result in our
1786          * doing some extra useless work.
1787          */
1788         if (rnp->gpnum != rnp->completed ||
1789             READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1790                 rnp->need_future_gp[c & 0x1]++;
1791                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1792                 goto out;
1793         }
1794 
1795         /*
1796          * There might be no grace period in progress.  If we don't already
1797          * hold it, acquire the root rcu_node structure's lock in order to
1798          * start one (if needed).
1799          */
1800         if (rnp != rnp_root)
1801                 raw_spin_lock_rcu_node(rnp_root);
1802 
1803         /*
1804          * Get a new grace-period number.  If there really is no grace
1805          * period in progress, it will be smaller than the one we obtained
1806          * earlier.  Adjust callbacks as needed.
1807          */
1808         c = rcu_cbs_completed(rdp->rsp, rnp_root);
1809         if (!rcu_is_nocb_cpu(rdp->cpu))
1810                 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1811 
1812         /*
1813          * If the needed for the required grace period is already
1814          * recorded, trace and leave.
1815          */
1816         if (rnp_root->need_future_gp[c & 0x1]) {
1817                 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1818                 goto unlock_out;
1819         }
1820 
1821         /* Record the need for the future grace period. */
1822         rnp_root->need_future_gp[c & 0x1]++;
1823 
1824         /* If a grace period is not already in progress, start one. */
1825         if (rnp_root->gpnum != rnp_root->completed) {
1826                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1827         } else {
1828                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1829                 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1830         }
1831 unlock_out:
1832         if (rnp != rnp_root)
1833                 raw_spin_unlock_rcu_node(rnp_root);
1834 out:
1835         if (c_out != NULL)
1836                 *c_out = c;
1837         return ret;
1838 }
1839 
1840 /*
1841  * Clean up any old requests for the just-ended grace period.  Also return
1842  * whether any additional grace periods have been requested.
1843  */
1844 static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1845 {
1846         int c = rnp->completed;
1847         int needmore;
1848         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1849 
1850         rnp->need_future_gp[c & 0x1] = 0;
1851         needmore = rnp->need_future_gp[(c + 1) & 0x1];
1852         trace_rcu_future_gp(rnp, rdp, c,
1853                             needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1854         return needmore;
1855 }
1856 
1857 /*
1858  * Awaken the grace-period kthread for the specified flavor of RCU.
1859  * Don't do a self-awaken, and don't bother awakening when there is
1860  * nothing for the grace-period kthread to do (as in several CPUs
1861  * raced to awaken, and we lost), and finally don't try to awaken
1862  * a kthread that has not yet been created.
1863  */
1864 static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1865 {
1866         if (current == rsp->gp_kthread ||
1867             !READ_ONCE(rsp->gp_flags) ||
1868             !rsp->gp_kthread)
1869                 return;
1870         swake_up(&rsp->gp_wq);
1871 }
1872 
1873 /*
1874  * If there is room, assign a ->completed number to any callbacks on
1875  * this CPU that have not already been assigned.  Also accelerate any
1876  * callbacks that were previously assigned a ->completed number that has
1877  * since proven to be too conservative, which can happen if callbacks get
1878  * assigned a ->completed number while RCU is idle, but with reference to
1879  * a non-root rcu_node structure.  This function is idempotent, so it does
1880  * not hurt to call it repeatedly.  Returns an flag saying that we should
1881  * awaken the RCU grace-period kthread.
1882  *
1883  * The caller must hold rnp->lock with interrupts disabled.
1884  */
1885 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1886                                struct rcu_data *rdp)
1887 {
1888         bool ret = false;
1889 
1890         lockdep_assert_held(&rnp->lock);
1891 
1892         /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1893         if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1894                 return false;
1895 
1896         /*
1897          * Callbacks are often registered with incomplete grace-period
1898          * information.  Something about the fact that getting exact
1899          * information requires acquiring a global lock...  RCU therefore
1900          * makes a conservative estimate of the grace period number at which
1901          * a given callback will become ready to invoke.        The following
1902          * code checks this estimate and improves it when possible, thus
1903          * accelerating callback invocation to an earlier grace-period
1904          * number.
1905          */
1906         if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
1907                 ret = rcu_start_future_gp(rnp, rdp, NULL);
1908 
1909         /* Trace depending on how much we were able to accelerate. */
1910         if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1911                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1912         else
1913                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1914         return ret;
1915 }
1916 
1917 /*
1918  * Move any callbacks whose grace period has completed to the
1919  * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1920  * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1921  * sublist.  This function is idempotent, so it does not hurt to
1922  * invoke it repeatedly.  As long as it is not invoked -too- often...
1923  * Returns true if the RCU grace-period kthread needs to be awakened.
1924  *
1925  * The caller must hold rnp->lock with interrupts disabled.
1926  */
1927 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1928                             struct rcu_data *rdp)
1929 {
1930         lockdep_assert_held(&rnp->lock);
1931 
1932         /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1933         if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1934                 return false;
1935 
1936         /*
1937          * Find all callbacks whose ->completed numbers indicate that they
1938          * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1939          */
1940         rcu_segcblist_advance(&rdp->cblist, rnp->completed);
1941 
1942         /* Classify any remaining callbacks. */
1943         return rcu_accelerate_cbs(rsp, rnp, rdp);
1944 }
1945 
1946 /*
1947  * Update CPU-local rcu_data state to record the beginnings and ends of
1948  * grace periods.  The caller must hold the ->lock of the leaf rcu_node
1949  * structure corresponding to the current CPU, and must have irqs disabled.
1950  * Returns true if the grace-period kthread needs to be awakened.
1951  */
1952 static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1953                               struct rcu_data *rdp)
1954 {
1955         bool ret;
1956         bool need_gp;
1957 
1958         lockdep_assert_held(&rnp->lock);
1959 
1960         /* Handle the ends of any preceding grace periods first. */
1961         if (rdp->completed == rnp->completed &&
1962             !unlikely(READ_ONCE(rdp->gpwrap))) {
1963 
1964                 /* No grace period end, so just accelerate recent callbacks. */
1965                 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1966 
1967         } else {
1968 
1969                 /* Advance callbacks. */
1970                 ret = rcu_advance_cbs(rsp, rnp, rdp);
1971 
1972                 /* Remember that we saw this grace-period completion. */
1973                 rdp->completed = rnp->completed;
1974                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1975         }
1976 
1977         if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1978                 /*
1979                  * If the current grace period is waiting for this CPU,
1980                  * set up to detect a quiescent state, otherwise don't
1981                  * go looking for one.
1982                  */
1983                 rdp->gpnum = rnp->gpnum;
1984                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1985                 need_gp = !!(rnp->qsmask & rdp->grpmask);
1986                 rdp->cpu_no_qs.b.norm = need_gp;
1987                 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
1988                 rdp->core_needs_qs = need_gp;
1989                 zero_cpu_stall_ticks(rdp);
1990                 WRITE_ONCE(rdp->gpwrap, false);
1991                 rcu_gpnum_ovf(rnp, rdp);
1992         }
1993         return ret;
1994 }
1995 
1996 static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1997 {
1998         unsigned long flags;
1999         bool needwake;
2000         struct rcu_node *rnp;
2001 
2002         local_irq_save(flags);
2003         rnp = rdp->mynode;
2004         if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
2005              rdp->completed == READ_ONCE(rnp->completed) &&
2006              !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
2007             !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
2008                 local_irq_restore(flags);
2009                 return;
2010         }
2011         needwake = __note_gp_changes(rsp, rnp, rdp);
2012         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2013         if (needwake)
2014                 rcu_gp_kthread_wake(rsp);
2015 }
2016 
2017 static void rcu_gp_slow(struct rcu_state *rsp, int delay)
2018 {
2019         if (delay > 0 &&
2020             !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
2021                 schedule_timeout_uninterruptible(delay);
2022 }
2023 
2024 /*
2025  * Initialize a new grace period.  Return false if no grace period required.
2026  */
2027 static bool rcu_gp_init(struct rcu_state *rsp)
2028 {
2029         unsigned long oldmask;
2030         struct rcu_data *rdp;
2031         struct rcu_node *rnp = rcu_get_root(rsp);
2032 
2033         WRITE_ONCE(rsp->gp_activity, jiffies);
2034         raw_spin_lock_irq_rcu_node(rnp);
2035         if (!READ_ONCE(rsp->gp_flags)) {
2036                 /* Spurious wakeup, tell caller to go back to sleep.  */
2037                 raw_spin_unlock_irq_rcu_node(rnp);
2038                 return false;
2039         }
2040         WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
2041 
2042         if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
2043                 /*
2044                  * Grace period already in progress, don't start another.
2045                  * Not supposed to be able to happen.
2046                  */
2047                 raw_spin_unlock_irq_rcu_node(rnp);
2048                 return false;
2049         }
2050 
2051         /* Advance to a new grace period and initialize state. */
2052         record_gp_stall_check_time(rsp);
2053         /* Record GP times before starting GP, hence smp_store_release(). */
2054         smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
2055         trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
2056         raw_spin_unlock_irq_rcu_node(rnp);
2057 
2058         /*
2059          * Apply per-leaf buffered online and offline operations to the
2060          * rcu_node tree.  Note that this new grace period need not wait
2061          * for subsequent online CPUs, and that quiescent-state forcing
2062          * will handle subsequent offline CPUs.
2063          */
2064         rcu_for_each_leaf_node(rsp, rnp) {
2065                 rcu_gp_slow(rsp, gp_preinit_delay);
2066                 raw_spin_lock_irq_rcu_node(rnp);
2067                 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
2068                     !rnp->wait_blkd_tasks) {
2069                         /* Nothing to do on this leaf rcu_node structure. */
2070                         raw_spin_unlock_irq_rcu_node(rnp);
2071                         continue;
2072                 }
2073 
2074                 /* Record old state, apply changes to ->qsmaskinit field. */
2075                 oldmask = rnp->qsmaskinit;
2076                 rnp->qsmaskinit = rnp->qsmaskinitnext;
2077 
2078                 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
2079                 if (!oldmask != !rnp->qsmaskinit) {
2080                         if (!oldmask) /* First online CPU for this rcu_node. */
2081                                 rcu_init_new_rnp(rnp);
2082                         else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
2083                                 rnp->wait_blkd_tasks = true;
2084                         else /* Last offline CPU and can propagate. */
2085                                 rcu_cleanup_dead_rnp(rnp);
2086                 }
2087 
2088                 /*
2089                  * If all waited-on tasks from prior grace period are
2090                  * done, and if all this rcu_node structure's CPUs are
2091                  * still offline, propagate up the rcu_node tree and
2092                  * clear ->wait_blkd_tasks.  Otherwise, if one of this
2093                  * rcu_node structure's CPUs has since come back online,
2094                  * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
2095                  * checks for this, so just call it unconditionally).
2096                  */
2097                 if (rnp->wait_blkd_tasks &&
2098                     (!rcu_preempt_has_tasks(rnp) ||
2099                      rnp->qsmaskinit)) {
2100                         rnp->wait_blkd_tasks = false;
2101                         rcu_cleanup_dead_rnp(rnp);
2102                 }
2103 
2104                 raw_spin_unlock_irq_rcu_node(rnp);
2105         }
2106 
2107         /*
2108          * Set the quiescent-state-needed bits in all the rcu_node
2109          * structures for all currently online CPUs in breadth-first order,
2110          * starting from the root rcu_node structure, relying on the layout
2111          * of the tree within the rsp->node[] array.  Note that other CPUs
2112          * will access only the leaves of the hierarchy, thus seeing that no
2113          * grace period is in progress, at least until the corresponding
2114          * leaf node has been initialized.
2115          *
2116          * The grace period cannot complete until the initialization
2117          * process finishes, because this kthread handles both.
2118          */
2119         rcu_for_each_node_breadth_first(rsp, rnp) {
2120                 rcu_gp_slow(rsp, gp_init_delay);
2121                 raw_spin_lock_irq_rcu_node(rnp);
2122                 rdp = this_cpu_ptr(rsp->rda);
2123                 rcu_preempt_check_blocked_tasks(rnp);
2124                 rnp->qsmask = rnp->qsmaskinit;
2125                 WRITE_ONCE(rnp->gpnum, rsp->gpnum);
2126                 if (WARN_ON_ONCE(rnp->completed != rsp->completed))
2127                         WRITE_ONCE(rnp->completed, rsp->completed);
2128                 if (rnp == rdp->mynode)
2129                         (void)__note_gp_changes(rsp, rnp, rdp);
2130                 rcu_preempt_boost_start_gp(rnp);
2131                 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
2132                                             rnp->level, rnp->grplo,
2133                                             rnp->grphi, rnp->qsmask);
2134                 raw_spin_unlock_irq_rcu_node(rnp);
2135                 cond_resched_rcu_qs();
2136                 WRITE_ONCE(rsp->gp_activity, jiffies);
2137         }
2138 
2139         return true;
2140 }
2141 
2142 /*
2143  * Helper function for swait_event_idle() wakeup at force-quiescent-state
2144  * time.
2145  */
2146 static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
2147 {
2148         struct rcu_node *rnp = rcu_get_root(rsp);
2149 
2150         /* Someone like call_rcu() requested a force-quiescent-state scan. */
2151         *gfp = READ_ONCE(rsp->gp_flags);
2152         if (*gfp & RCU_GP_FLAG_FQS)
2153                 return true;
2154 
2155         /* The current grace period has completed. */
2156         if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
2157                 return true;
2158 
2159         return false;
2160 }
2161 
2162 /*
2163  * Do one round of quiescent-state forcing.
2164  */
2165 static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
2166 {
2167         struct rcu_node *rnp = rcu_get_root(rsp);
2168 
2169         WRITE_ONCE(rsp->gp_activity, jiffies);
2170         rsp->n_force_qs++;
2171         if (first_time) {
2172                 /* Collect dyntick-idle snapshots. */
2173                 force_qs_rnp(rsp, dyntick_save_progress_counter);
2174         } else {
2175                 /* Handle dyntick-idle and offline CPUs. */
2176                 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
2177         }
2178         /* Clear flag to prevent immediate re-entry. */
2179         if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2180                 raw_spin_lock_irq_rcu_node(rnp);
2181                 WRITE_ONCE(rsp->gp_flags,
2182                            READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
2183                 raw_spin_unlock_irq_rcu_node(rnp);
2184         }
2185 }
2186 
2187 /*
2188  * Clean up after the old grace period.
2189  */
2190 static void rcu_gp_cleanup(struct rcu_state *rsp)
2191 {
2192         unsigned long gp_duration;
2193         bool needgp = false;
2194         int nocb = 0;
2195         struct rcu_data *rdp;
2196         struct rcu_node *rnp = rcu_get_root(rsp);
2197         struct swait_queue_head *sq;
2198 
2199         WRITE_ONCE(rsp->gp_activity, jiffies);
2200         raw_spin_lock_irq_rcu_node(rnp);
2201         gp_duration = jiffies - rsp->gp_start;
2202         if (gp_duration > rsp->gp_max)
2203                 rsp->gp_max = gp_duration;
2204 
2205         /*
2206          * We know the grace period is complete, but to everyone else
2207          * it appears to still be ongoing.  But it is also the case
2208          * that to everyone else it looks like there is nothing that
2209          * they can do to advance the grace period.  It is therefore
2210          * safe for us to drop the lock in order to mark the grace
2211          * period as completed in all of the rcu_node structures.
2212          */
2213         raw_spin_unlock_irq_rcu_node(rnp);
2214 
2215         /*
2216          * Propagate new ->completed value to rcu_node structures so
2217          * that other CPUs don't have to wait until the start of the next
2218          * grace period to process their callbacks.  This also avoids
2219          * some nasty RCU grace-period initialization races by forcing
2220          * the end of the current grace period to be completely recorded in
2221          * all of the rcu_node structures before the beginning of the next
2222          * grace period is recorded in any of the rcu_node structures.
2223          */
2224         rcu_for_each_node_breadth_first(rsp, rnp) {
2225                 raw_spin_lock_irq_rcu_node(rnp);
2226                 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
2227                 WARN_ON_ONCE(rnp->qsmask);
2228                 WRITE_ONCE(rnp->completed, rsp->gpnum);
2229                 rdp = this_cpu_ptr(rsp->rda);
2230                 if (rnp == rdp->mynode)
2231                         needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
2232                 /* smp_mb() provided by prior unlock-lock pair. */
2233                 nocb += rcu_future_gp_cleanup(rsp, rnp);
2234                 sq = rcu_nocb_gp_get(rnp);
2235                 raw_spin_unlock_irq_rcu_node(rnp);
2236                 rcu_nocb_gp_cleanup(sq);
2237                 cond_resched_rcu_qs();
2238                 WRITE_ONCE(rsp->gp_activity, jiffies);
2239                 rcu_gp_slow(rsp, gp_cleanup_delay);
2240         }
2241         rnp = rcu_get_root(rsp);
2242         raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
2243         rcu_nocb_gp_set(rnp, nocb);
2244 
2245         /* Declare grace period done. */
2246         WRITE_ONCE(rsp->completed, rsp->gpnum);
2247         trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
2248         rsp->gp_state = RCU_GP_IDLE;
2249         rdp = this_cpu_ptr(rsp->rda);
2250         /* Advance CBs to reduce false positives below. */
2251         needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
2252         if (needgp || cpu_needs_another_gp(rsp, rdp)) {
2253                 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2254                 trace_rcu_grace_period(rsp->name,
2255                                        READ_ONCE(rsp->gpnum),
2256                                        TPS("newreq"));
2257         }
2258         raw_spin_unlock_irq_rcu_node(rnp);
2259 }
2260 
2261 /*
2262  * Body of kthread that handles grace periods.
2263  */
2264 static int __noreturn rcu_gp_kthread(void *arg)
2265 {
2266         bool first_gp_fqs;
2267         int gf;
2268         unsigned long j;
2269         int ret;
2270         struct rcu_state *rsp = arg;
2271         struct rcu_node *rnp = rcu_get_root(rsp);
2272 
2273         rcu_bind_gp_kthread();
2274         for (;;) {
2275 
2276                 /* Handle grace-period start. */
2277                 for (;;) {
2278                         trace_rcu_grace_period(rsp->name,
2279                                                READ_ONCE(rsp->gpnum),
2280                                                TPS("reqwait"));
2281                         rsp->gp_state = RCU_GP_WAIT_GPS;
2282                         swait_event_idle(rsp->gp_wq, READ_ONCE(rsp->gp_flags) &
2283                                                      RCU_GP_FLAG_INIT);
2284                         rsp->gp_state = RCU_GP_DONE_GPS;
2285                         /* Locking provides needed memory barrier. */
2286                         if (rcu_gp_init(rsp))
2287                                 break;
2288                         cond_resched_rcu_qs();
2289                         WRITE_ONCE(rsp->gp_activity, jiffies);
2290                         WARN_ON(signal_pending(current));
2291                         trace_rcu_grace_period(rsp->name,
2292                                                READ_ONCE(rsp->gpnum),
2293                                                TPS("reqwaitsig"));
2294                 }
2295 
2296                 /* Handle quiescent-state forcing. */
2297                 first_gp_fqs = true;
2298                 j = jiffies_till_first_fqs;
2299                 if (j > HZ) {
2300                         j = HZ;
2301                         jiffies_till_first_fqs = HZ;
2302                 }
2303                 ret = 0;
2304                 for (;;) {
2305                         if (!ret) {
2306                                 rsp->jiffies_force_qs = jiffies + j;
2307                                 WRITE_ONCE(rsp->jiffies_kick_kthreads,
2308                                            jiffies + 3 * j);
2309                         }
2310                         trace_rcu_grace_period(rsp->name,
2311                                                READ_ONCE(rsp->gpnum),
2312                                                TPS("fqswait"));
2313                         rsp->gp_state = RCU_GP_WAIT_FQS;
2314                         ret = swait_event_idle_timeout(rsp->gp_wq,
2315                                         rcu_gp_fqs_check_wake(rsp, &gf), j);
2316                         rsp->gp_state = RCU_GP_DOING_FQS;
2317                         /* Locking provides needed memory barriers. */
2318                         /* If grace period done, leave loop. */
2319                         if (!READ_ONCE(rnp->qsmask) &&
2320                             !rcu_preempt_blocked_readers_cgp(rnp))
2321                                 break;
2322                         /* If time for quiescent-state forcing, do it. */
2323                         if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2324                             (gf & RCU_GP_FLAG_FQS)) {
2325                                 trace_rcu_grace_period(rsp->name,
2326                                                        READ_ONCE(rsp->gpnum),
2327                                                        TPS("fqsstart"));
2328                                 rcu_gp_fqs(rsp, first_gp_fqs);
2329                                 first_gp_fqs = false;
2330                                 trace_rcu_grace_period(rsp->name,
2331                                                        READ_ONCE(rsp->gpnum),
2332                                                        TPS("fqsend"));
2333                                 cond_resched_rcu_qs();
2334                                 WRITE_ONCE(rsp->gp_activity, jiffies);
2335                                 ret = 0; /* Force full wait till next FQS. */
2336                                 j = jiffies_till_next_fqs;
2337                                 if (j > HZ) {
2338                                         j = HZ;
2339                                         jiffies_till_next_fqs = HZ;
2340                                 } else if (j < 1) {
2341                                         j = 1;
2342                                         jiffies_till_next_fqs = 1;
2343                                 }
2344                         } else {
2345                                 /* Deal with stray signal. */
2346                                 cond_resched_rcu_qs();
2347                                 WRITE_ONCE(rsp->gp_activity, jiffies);
2348                                 WARN_ON(signal_pending(current));
2349                                 trace_rcu_grace_period(rsp->name,
2350                                                        READ_ONCE(rsp->gpnum),
2351                                                        TPS("fqswaitsig"));
2352                                 ret = 1; /* Keep old FQS timing. */
2353                                 j = jiffies;
2354                                 if (time_after(jiffies, rsp->jiffies_force_qs))
2355                                         j = 1;
2356                                 else
2357                                         j = rsp->jiffies_force_qs - j;
2358                         }
2359                 }
2360 
2361                 /* Handle grace-period end. */
2362                 rsp->gp_state = RCU_GP_CLEANUP;
2363                 rcu_gp_cleanup(rsp);
2364                 rsp->gp_state = RCU_GP_CLEANED;
2365         }
2366 }
2367 
2368 /*
2369  * Start a new RCU grace period if warranted, re-initializing the hierarchy
2370  * in preparation for detecting the next grace period.  The caller must hold
2371  * the root node's ->lock and hard irqs must be disabled.
2372  *
2373  * Note that it is legal for a dying CPU (which is marked as offline) to
2374  * invoke this function.  This can happen when the dying CPU reports its
2375  * quiescent state.
2376  *
2377  * Returns true if the grace-period kthread must be awakened.
2378  */
2379 static bool
2380 rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
2381                       struct rcu_data *rdp)
2382 {
2383         lockdep_assert_held(&rnp->lock);
2384         if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2385                 /*
2386                  * Either we have not yet spawned the grace-period
2387                  * task, this CPU does not need another grace period,
2388                  * or a grace period is already in progress.
2389                  * Either way, don't start a new grace period.
2390                  */
2391                 return false;
2392         }
2393         WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2394         trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2395                                TPS("newreq"));
2396 
2397         /*
2398          * We can't do wakeups while holding the rnp->lock, as that
2399          * could cause possible deadlocks with the rq->lock. Defer
2400          * the wakeup to our caller.
2401          */
2402         return true;
2403 }
2404 
2405 /*
2406  * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
2407  * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
2408  * is invoked indirectly from rcu_advance_cbs(), which would result in
2409  * endless recursion -- or would do so if it wasn't for the self-deadlock
2410  * that is encountered beforehand.
2411  *
2412  * Returns true if the grace-period kthread needs to be awakened.
2413  */
2414 static bool rcu_start_gp(struct rcu_state *rsp)
2415 {
2416         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
2417         struct rcu_node *rnp = rcu_get_root(rsp);
2418         bool ret = false;
2419 
2420         /*
2421          * If there is no grace period in progress right now, any
2422          * callbacks we have up to this point will be satisfied by the
2423          * next grace period.  Also, advancing the callbacks reduces the
2424          * probability of false positives from cpu_needs_another_gp()
2425          * resulting in pointless grace periods.  So, advance callbacks
2426          * then start the grace period!
2427          */
2428         ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
2429         ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
2430         return ret;
2431 }
2432 
2433 /*
2434  * Report a full set of quiescent states to the specified rcu_state data
2435  * structure.  Invoke rcu_gp_kthread_wake() to awaken the grace-period
2436  * kthread if another grace period is required.  Whether we wake
2437  * the grace-period kthread or it awakens itself for the next round
2438  * of quiescent-state forcing, that kthread will clean up after the
2439  * just-completed grace period.  Note that the caller must hold rnp->lock,
2440  * which is released before return.
2441  */
2442 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2443         __releases(rcu_get_root(rsp)->lock)
2444 {
2445         lockdep_assert_held(&rcu_get_root(rsp)->lock);
2446         WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2447         WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2448         raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2449         rcu_gp_kthread_wake(rsp);
2450 }
2451 
2452 /*
2453  * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2454  * Allows quiescent states for a group of CPUs to be reported at one go
2455  * to the specified rcu_node structure, though all the CPUs in the group
2456  * must be represented by the same rcu_node structure (which need not be a
2457  * leaf rcu_node structure, though it often will be).  The gps parameter
2458  * is the grace-period snapshot, which means that the quiescent states
2459  * are valid only if rnp->gpnum is equal to gps.  That structure's lock
2460  * must be held upon entry, and it is released before return.
2461  */
2462 static void
2463 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2464                   struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2465         __releases(rnp->lock)
2466 {
2467         unsigned long oldmask = 0;
2468         struct rcu_node *rnp_c;
2469 
2470         lockdep_assert_held(&rnp->lock);
2471 
2472         /* Walk up the rcu_node hierarchy. */
2473         for (;;) {
2474                 if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2475 
2476                         /*
2477                          * Our bit has already been cleared, or the
2478                          * relevant grace period is already over, so done.
2479                          */
2480                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2481                         return;
2482                 }
2483                 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2484                 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1 &&
2485                              rcu_preempt_blocked_readers_cgp(rnp));
2486                 rnp->qsmask &= ~mask;
2487                 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
2488                                                  mask, rnp->qsmask, rnp->level,
2489                                                  rnp->grplo, rnp->grphi,
2490                                                  !!rnp->gp_tasks);
2491                 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2492 
2493                         /* Other bits still set at this level, so done. */
2494                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2495                         return;
2496                 }
2497                 mask = rnp->grpmask;
2498                 if (rnp->parent == NULL) {
2499 
2500                         /* No more levels.  Exit loop holding root lock. */
2501 
2502                         break;
2503                 }
2504                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2505                 rnp_c = rnp;
2506                 rnp = rnp->parent;
2507                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2508                 oldmask = rnp_c->qsmask;
2509         }
2510 
2511         /*
2512          * Get here if we are the last CPU to pass through a quiescent
2513          * state for this grace period.  Invoke rcu_report_qs_rsp()
2514          * to clean up and start the next grace period if one is needed.
2515          */
2516         rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2517 }
2518 
2519 /*
2520  * Record a quiescent state for all tasks that were previously queued
2521  * on the specified rcu_node structure and that were blocking the current
2522  * RCU grace period.  The caller must hold the specified rnp->lock with
2523  * irqs disabled, and this lock is released upon return, but irqs remain
2524  * disabled.
2525  */
2526 static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2527                                       struct rcu_node *rnp, unsigned long flags)
2528         __releases(rnp->lock)
2529 {
2530         unsigned long gps;
2531         unsigned long mask;
2532         struct rcu_node *rnp_p;
2533 
2534         lockdep_assert_held(&rnp->lock);
2535         if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2536             rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2537                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2538                 return;  /* Still need more quiescent states! */
2539         }
2540 
2541         rnp_p = rnp->parent;
2542         if (rnp_p == NULL) {
2543                 /*
2544                  * Only one rcu_node structure in the tree, so don't
2545                  * try to report up to its nonexistent parent!
2546                  */
2547                 rcu_report_qs_rsp(rsp, flags);
2548                 return;
2549         }
2550 
2551         /* Report up the rest of the hierarchy, tracking current ->gpnum. */
2552         gps = rnp->gpnum;
2553         mask = rnp->grpmask;
2554         raw_spin_unlock_rcu_node(rnp);  /* irqs remain disabled. */
2555         raw_spin_lock_rcu_node(rnp_p);  /* irqs already disabled. */
2556         rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2557 }
2558 
2559 /*
2560  * Record a quiescent state for the specified CPU to that CPU's rcu_data
2561  * structure.  This must be called from the specified CPU.
2562  */
2563 static void
2564 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2565 {
2566         unsigned long flags;
2567         unsigned long mask;
2568         bool needwake;
2569         struct rcu_node *rnp;
2570 
2571         rnp = rdp->mynode;
2572         raw_spin_lock_irqsave_rcu_node(rnp, flags);
2573         if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum ||
2574             rnp->completed == rnp->gpnum || rdp->gpwrap) {
2575 
2576                 /*
2577                  * The grace period in which this quiescent state was
2578                  * recorded has ended, so don't report it upwards.
2579                  * We will instead need a new quiescent state that lies
2580                  * within the current grace period.
2581                  */
2582                 rdp->cpu_no_qs.b.norm = true;   /* need qs for new gp. */
2583                 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
2584                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2585                 return;
2586         }
2587         mask = rdp->grpmask;
2588         if ((rnp->qsmask & mask) == 0) {
2589                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2590         } else {
2591                 rdp->core_needs_qs = false;
2592 
2593                 /*
2594                  * This GP can't end until cpu checks in, so all of our
2595                  * callbacks can be processed during the next GP.
2596                  */
2597                 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2598 
2599                 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2600                 /* ^^^ Released rnp->lock */
2601                 if (needwake)
2602                         rcu_gp_kthread_wake(rsp);
2603         }
2604 }
2605 
2606 /*
2607  * Check to see if there is a new grace period of which this CPU
2608  * is not yet aware, and if so, set up local rcu_data state for it.
2609  * Otherwise, see if this CPU has just passed through its first
2610  * quiescent state for this grace period, and record that fact if so.
2611  */
2612 static void
2613 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2614 {
2615         /* Check for grace-period ends and beginnings. */
2616         note_gp_changes(rsp, rdp);
2617 
2618         /*
2619          * Does this CPU still need to do its part for current grace period?
2620          * If no, return and let the other CPUs do their part as well.
2621          */
2622         if (!rdp->core_needs_qs)
2623                 return;
2624 
2625         /*
2626          * Was there a quiescent state since the beginning of the grace
2627          * period? If no, then exit and wait for the next call.
2628          */
2629         if (rdp->cpu_no_qs.b.norm)
2630                 return;
2631 
2632         /*
2633          * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2634          * judge of that).
2635          */
2636         rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2637 }
2638 
2639 /*
2640  * Trace the fact that this CPU is going offline.
2641  */
2642 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2643 {
2644         RCU_TRACE(unsigned long mask;)
2645         RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
2646         RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
2647 
2648         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2649                 return;
2650 
2651         RCU_TRACE(mask = rdp->grpmask;)
2652         trace_rcu_grace_period(rsp->name,
2653                                rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2654                                TPS("cpuofl"));
2655 }
2656 
2657 /*
2658  * All CPUs for the specified rcu_node structure have gone offline,
2659  * and all tasks that were preempted within an RCU read-side critical
2660  * section while running on one of those CPUs have since exited their RCU
2661  * read-side critical section.  Some other CPU is reporting this fact with
2662  * the specified rcu_node structure's ->lock held and interrupts disabled.
2663  * This function therefore goes up the tree of rcu_node structures,
2664  * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
2665  * the leaf rcu_node structure's ->qsmaskinit field has already been
2666  * updated
2667  *
2668  * This function does check that the specified rcu_node structure has
2669  * all CPUs offline and no blocked tasks, so it is OK to invoke it
2670  * prematurely.  That said, invoking it after the fact will cost you
2671  * a needless lock acquisition.  So once it has done its work, don't
2672  * invoke it again.
2673  */
2674 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2675 {
2676         long mask;
2677         struct rcu_node *rnp = rnp_leaf;
2678 
2679         lockdep_assert_held(&rnp->lock);
2680         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2681             rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2682                 return;
2683         for (;;) {
2684                 mask = rnp->grpmask;
2685                 rnp = rnp->parent;
2686                 if (!rnp)
2687                         break;
2688                 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2689                 rnp->qsmaskinit &= ~mask;
2690                 rnp->qsmask &= ~mask;
2691                 if (rnp->qsmaskinit) {
2692                         raw_spin_unlock_rcu_node(rnp);
2693                         /* irqs remain disabled. */
2694                         return;
2695                 }
2696                 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2697         }
2698 }
2699 
2700 /*
2701  * The CPU has been completely removed, and some other CPU is reporting
2702  * this fact from process context.  Do the remainder of the cleanup.
2703  * There can only be one CPU hotplug operation at a time, so no need for
2704  * explicit locking.
2705  */
2706 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2707 {
2708         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2709         struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2710 
2711         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2712                 return;
2713 
2714         /* Adjust any no-longer-needed kthreads. */
2715         rcu_boost_kthread_setaffinity(rnp, -1);
2716 }
2717 
2718 /*
2719  * Invoke any RCU callbacks that have made it to the end of their grace
2720  * period.  Thottle as specified by rdp->blimit.
2721  */
2722 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2723 {
2724         unsigned long flags;
2725         struct rcu_head *rhp;
2726         struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2727         long bl, count;
2728 
2729         /* If no callbacks are ready, just return. */
2730         if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2731                 trace_rcu_batch_start(rsp->name,
2732                                       rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2733                                       rcu_segcblist_n_cbs(&rdp->cblist), 0);
2734                 trace_rcu_batch_end(rsp->name, 0,
2735                                     !rcu_segcblist_empty(&rdp->cblist),
2736                                     need_resched(), is_idle_task(current),
2737                                     rcu_is_callbacks_kthread());
2738                 return;
2739         }
2740 
2741         /*
2742          * Extract the list of ready callbacks, disabling to prevent
2743          * races with call_rcu() from interrupt handlers.  Leave the
2744          * callback counts, as rcu_barrier() needs to be conservative.
2745          */
2746         local_irq_save(flags);
2747         WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2748         bl = rdp->blimit;
2749         trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2750                               rcu_segcblist_n_cbs(&rdp->cblist), bl);
2751         rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2752         local_irq_restore(flags);
2753 
2754         /* Invoke callbacks. */
2755         rhp = rcu_cblist_dequeue(&rcl);
2756         for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2757                 debug_rcu_head_unqueue(rhp);
2758                 if (__rcu_reclaim(rsp->name, rhp))
2759                         rcu_cblist_dequeued_lazy(&rcl);
2760                 /*
2761                  * Stop only if limit reached and CPU has something to do.
2762                  * Note: The rcl structure counts down from zero.
2763                  */
2764                 if (-rcl.len >= bl &&
2765                     (need_resched() ||
2766                      (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2767                         break;
2768         }
2769 
2770         local_irq_save(flags);
2771         count = -rcl.len;
2772         trace_rcu_batch_end(rsp->name, count, !!rcl.head, need_resched(),
2773                             is_idle_task(current), rcu_is_callbacks_kthread());
2774 
2775         /* Update counts and requeue any remaining callbacks. */
2776         rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2777         smp_mb(); /* List handling before counting for rcu_barrier(). */
2778         rdp->n_cbs_invoked += count;
2779         rcu_segcblist_insert_count(&rdp->cblist, &rcl);
2780 
2781         /* Reinstate batch limit if we have worked down the excess. */
2782         count = rcu_segcblist_n_cbs(&rdp->cblist);
2783         if (rdp->blimit == LONG_MAX && count <= qlowmark)
2784                 rdp->blimit = blimit;
2785 
2786         /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2787         if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2788                 rdp->qlen_last_fqs_check = 0;
2789                 rdp->n_force_qs_snap = rsp->n_force_qs;
2790         } else if (count < rdp->qlen_last_fqs_check - qhimark)
2791                 rdp->qlen_last_fqs_check = count;
2792         WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
2793 
2794         local_irq_restore(flags);
2795 
2796         /* Re-invoke RCU core processing if there are callbacks remaining. */
2797         if (rcu_segcblist_ready_cbs(&rdp->cblist))
2798                 invoke_rcu_core();
2799 }
2800 
2801 /*
2802  * Check to see if this CPU is in a non-context-switch quiescent state
2803  * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2804  * Also schedule RCU core processing.
2805  *
2806  * This function must be called from hardirq context.  It is normally
2807  * invoked from the scheduling-clock interrupt.
2808  */
2809 void rcu_check_callbacks(int user)
2810 {
2811         trace_rcu_utilization(TPS("Start scheduler-tick"));
2812         increment_cpu_stall_ticks();
2813         if (user || rcu_is_cpu_rrupt_from_idle()) {
2814 
2815                 /*
2816                  * Get here if this CPU took its interrupt from user
2817                  * mode or from the idle loop, and if this is not a
2818                  * nested interrupt.  In this case, the CPU is in
2819                  * a quiescent state, so note it.
2820                  *
2821                  * No memory barrier is required here because both
2822                  * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2823                  * variables that other CPUs neither access nor modify,
2824                  * at least not while the corresponding CPU is online.
2825                  */
2826 
2827                 rcu_sched_qs();
2828                 rcu_bh_qs();
2829 
2830         } else if (!in_softirq()) {
2831 
2832                 /*
2833                  * Get here if this CPU did not take its interrupt from
2834                  * softirq, in other words, if it is not interrupting
2835                  * a rcu_bh read-side critical section.  This is an _bh
2836                  * critical section, so note it.
2837                  */
2838 
2839                 rcu_bh_qs();
2840         }
2841         rcu_preempt_check_callbacks();
2842         if (rcu_pending())
2843                 invoke_rcu_core();
2844         if (user)
2845                 rcu_note_voluntary_context_switch(current);
2846         trace_rcu_utilization(TPS("End scheduler-tick"));
2847 }
2848 
2849 /*
2850  * Scan the leaf rcu_node structures, processing dyntick state for any that
2851  * have not yet encountered a quiescent state, using the function specified.
2852  * Also initiate boosting for any threads blocked on the root rcu_node.
2853  *
2854  * The caller must have suppressed start of new grace periods.
2855  */
2856 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
2857 {
2858         int cpu;
2859         unsigned long flags;
2860         unsigned long mask;
2861         struct rcu_node *rnp;
2862 
2863         rcu_for_each_leaf_node(rsp, rnp) {
2864                 cond_resched_rcu_qs();
2865                 mask = 0;
2866                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2867                 if (rnp->qsmask == 0) {
2868                         if (rcu_state_p == &rcu_sched_state ||
2869                             rsp != rcu_state_p ||
2870                             rcu_preempt_blocked_readers_cgp(rnp)) {
2871                                 /*
2872                                  * No point in scanning bits because they
2873                                  * are all zero.  But we might need to
2874                                  * priority-boost blocked readers.
2875                                  */
2876                                 rcu_initiate_boost(rnp, flags);
2877                                 /* rcu_initiate_boost() releases rnp->lock */
2878                                 continue;
2879                         }
2880                         if (rnp->parent &&
2881                             (rnp->parent->qsmask & rnp->grpmask)) {
2882                                 /*
2883                                  * Race between grace-period
2884                                  * initialization and task exiting RCU
2885                                  * read-side critical section: Report.
2886                                  */
2887                                 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2888                                 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2889                                 continue;
2890                         }
2891                 }
2892                 for_each_leaf_node_possible_cpu(rnp, cpu) {
2893                         unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
2894                         if ((rnp->qsmask & bit) != 0) {
2895                                 if (f(per_cpu_ptr(rsp->rda, cpu)))
2896                                         mask |= bit;
2897                         }
2898                 }
2899                 if (mask != 0) {
2900                         /* Idle/offline CPUs, report (releases rnp->lock. */
2901                         rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2902                 } else {
2903                         /* Nothing to do here, so just drop the lock. */
2904                         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2905                 }
2906         }
2907 }
2908 
2909 /*
2910  * Force quiescent states on reluctant CPUs, and also detect which
2911  * CPUs are in dyntick-idle mode.
2912  */
2913 static void force_quiescent_state(struct rcu_state *rsp)
2914 {
2915         unsigned long flags;
2916         bool ret;
2917         struct rcu_node *rnp;
2918         struct rcu_node *rnp_old = NULL;
2919 
2920         /* Funnel through hierarchy to reduce memory contention. */
2921         rnp = __this_cpu_read(rsp->rda->mynode);
2922         for (; rnp != NULL; rnp = rnp->parent) {
2923                 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2924                       !raw_spin_trylock(&rnp->fqslock);
2925                 if (rnp_old != NULL)
2926                         raw_spin_unlock(&rnp_old->fqslock);
2927                 if (ret) {
2928                         rsp->n_force_qs_lh++;
2929                         return;
2930                 }
2931                 rnp_old = rnp;
2932         }
2933         /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2934 
2935         /* Reached the root of the rcu_node tree, acquire lock. */
2936         raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2937         raw_spin_unlock(&rnp_old->fqslock);
2938         if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2939                 rsp->n_force_qs_lh++;
2940                 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2941                 return;  /* Someone beat us to it. */
2942         }
2943         WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2944         raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2945         rcu_gp_kthread_wake(rsp);
2946 }
2947 
2948 /*
2949  * This does the RCU core processing work for the specified rcu_state
2950  * and rcu_data structures.  This may be called only from the CPU to
2951  * whom the rdp belongs.
2952  */
2953 static void
2954 __rcu_process_callbacks(struct rcu_state *rsp)
2955 {
2956         unsigned long flags;
2957         bool needwake;
2958         struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2959 
2960         WARN_ON_ONCE(!rdp->beenonline);
2961 
2962         /* Update RCU state based on any recent quiescent states. */
2963         rcu_check_quiescent_state(rsp, rdp);
2964 
2965         /* Does this CPU require a not-yet-started grace period? */
2966         local_irq_save(flags);
2967         if (cpu_needs_another_gp(rsp, rdp)) {
2968                 raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
2969                 needwake = rcu_start_gp(rsp);
2970                 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2971                 if (needwake)
2972                         rcu_gp_kthread_wake(rsp);
2973         } else {
2974                 local_irq_restore(flags);
2975         }
2976 
2977         /* If there are callbacks ready, invoke them. */
2978         if (rcu_segcblist_ready_cbs(&rdp->cblist))
2979                 invoke_rcu_callbacks(rsp, rdp);
2980 
2981         /* Do any needed deferred wakeups of rcuo kthreads. */
2982         do_nocb_deferred_wakeup(rdp);
2983 }
2984 
2985 /*
2986  * Do RCU core processing for the current CPU.
2987  */
2988 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
2989 {
2990         struct rcu_state *rsp;
2991 
2992         if (cpu_is_offline(smp_processor_id()))
2993                 return;
2994         trace_rcu_utilization(TPS("Start RCU core"));
2995         for_each_rcu_flavor(rsp)
2996                 __rcu_process_callbacks(rsp);
2997         trace_rcu_utilization(TPS("End RCU core"));
2998 }
2999 
3000 /*
3001  * Schedule RCU callback invocation.  If the specified type of RCU
3002  * does not support RCU priority boosting, just do a direct call,
3003  * otherwise wake up the per-CPU kernel kthread.  Note that because we
3004  * are running on the current CPU with softirqs disabled, the
3005  * rcu_cpu_kthread_task cannot disappear out from under us.
3006  */
3007 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
3008 {
3009         if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
3010                 return;
3011         if (likely(!rsp->boost)) {
3012                 rcu_do_batch(rsp, rdp);
3013                 return;
3014         }
3015         invoke_rcu_callbacks_kthread();
3016 }
3017 
3018 static void invoke_rcu_core(void)
3019 {
3020         if (cpu_online(smp_processor_id()))
3021                 raise_softirq(RCU_SOFTIRQ);
3022 }
3023 
3024 /*
3025  * Handle any core-RCU processing required by a call_rcu() invocation.
3026  */
3027 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
3028                             struct rcu_head *head, unsigned long flags)
3029 {
3030         bool needwake;
3031 
3032         /*
3033          * If called from an extended quiescent state, invoke the RCU
3034          * core in order to force a re-evaluation of RCU's idleness.
3035          */
3036         if (!rcu_is_watching())
3037                 invoke_rcu_core();
3038 
3039         /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
3040         if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
3041                 return;
3042 
3043         /*
3044          * Force the grace period if too many callbacks or too long waiting.
3045          * Enforce hysteresis, and don't invoke force_quiescent_state()
3046          * if some other CPU has recently done so.  Also, don't bother
3047          * invoking force_quiescent_state() if the newly enqueued callback
3048          * is the only one waiting for a grace period to complete.
3049          */
3050         if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
3051                      rdp->qlen_last_fqs_check + qhimark)) {
3052 
3053                 /* Are we ignoring a completed grace period? */
3054                 note_gp_changes(rsp, rdp);
3055 
3056                 /* Start a new grace period if one not already started. */
3057                 if (!rcu_gp_in_progress(rsp)) {
3058                         struct rcu_node *rnp_root = rcu_get_root(rsp);
3059 
3060                         raw_spin_lock_rcu_node(rnp_root);
3061                         needwake = rcu_start_gp(rsp);
3062                         raw_spin_unlock_rcu_node(rnp_root);
3063                         if (needwake)
3064                                 rcu_gp_kthread_wake(rsp);
3065                 } else {
3066                         /* Give the grace period a kick. */
3067                         rdp->blimit = LONG_MAX;
3068                         if (rsp->n_force_qs == rdp->n_force_qs_snap &&
3069                             rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
3070                                 force_quiescent_state(rsp);
3071                         rdp->n_force_qs_snap = rsp->n_force_qs;
3072                         rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
3073                 }
3074         }
3075 }
3076 
3077 /*
3078  * RCU callback function to leak a callback.
3079  */
3080 static void rcu_leak_callback(struct rcu_head *rhp)
3081 {
3082 }
3083 
3084 /*
3085  * Helper function for call_rcu() and friends.  The cpu argument will
3086  * normally be -1, indicating "currently running CPU".  It may specify
3087  * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
3088  * is expected to specify a CPU.
3089  */
3090 static void
3091 __call_rcu(struct rcu_head *head, rcu_callback_t func,
3092            struct rcu_state *rsp, int cpu, bool lazy)
3093 {
3094         unsigned long flags;
3095         struct rcu_data *rdp;
3096 
3097         /* Misaligned rcu_head! */
3098         WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
3099 
3100         if (debug_rcu_head_queue(head)) {
3101                 /*
3102                  * Probable double call_rcu(), so leak the callback.
3103                  * Use rcu:rcu_callback trace event to find the previous
3104                  * time callback was passed to __call_rcu().
3105                  */
3106                 WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pF()!!!\n",
3107                           head, head->func);
3108                 WRITE_ONCE(head->func, rcu_leak_callback);
3109                 return;
3110         }
3111         head->func = func;
3112         head->next = NULL;
3113         local_irq_save(flags);
3114         rdp = this_cpu_ptr(rsp->rda);
3115 
3116         /* Add the callback to our list. */
3117         if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
3118                 int offline;
3119 
3120                 if (cpu != -1)
3121                         rdp = per_cpu_ptr(rsp->rda, cpu);
3122                 if (likely(rdp->mynode)) {
3123                         /* Post-boot, so this should be for a no-CBs CPU. */
3124                         offline = !__call_rcu_nocb(rdp, head, lazy, flags);
3125                         WARN_ON_ONCE(offline);
3126                         /* Offline CPU, _call_rcu() illegal, leak callback.  */
3127                         local_irq_restore(flags);
3128                         return;
3129                 }
3130                 /*
3131                  * Very early boot, before rcu_init().  Initialize if needed
3132                  * and then drop through to queue the callback.
3133                  */
3134                 BUG_ON(cpu != -1);
3135                 WARN_ON_ONCE(!rcu_is_watching());
3136                 if (rcu_segcblist_empty(&rdp->cblist))
3137                         rcu_segcblist_init(&rdp->cblist);
3138         }
3139         rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
3140         if (!lazy)
3141                 rcu_idle_count_callbacks_posted();
3142 
3143         if (__is_kfree_rcu_offset((unsigned long)func))
3144                 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3145                                          rcu_segcblist_n_lazy_cbs(&rdp->cblist),
3146                                          rcu_segcblist_n_cbs(&rdp->cblist));
3147         else
3148                 trace_rcu_callback(rsp->name, head,
3149                                    rcu_segcblist_n_lazy_cbs(&rdp->cblist),
3150                                    rcu_segcblist_n_cbs(&rdp->cblist));
3151 
3152         /* Go handle any RCU core processing required. */
3153         __call_rcu_core(rsp, rdp, head, flags);
3154         local_irq_restore(flags);
3155 }
3156 
3157 /**
3158  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
3159  * @head: structure to be used for queueing the RCU updates.
3160  * @func: actual callback function to be invoked after the grace period
3161  *
3162  * The callback function will be invoked some time after a full grace
3163  * period elapses, in other words after all currently executing RCU
3164  * read-side critical sections have completed. call_rcu_sched() assumes
3165  * that the read-side critical sections end on enabling of preemption
3166  * or on voluntary preemption.
3167  * RCU read-side critical sections are delimited by:
3168  *
3169  * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR
3170  * - anything that disables preemption.
3171  *
3172  *  These may be nested.
3173  *
3174  * See the description of call_rcu() for more detailed information on
3175  * memory ordering guarantees.
3176  */
3177 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
3178 {
3179         __call_rcu(head, func, &rcu_sched_state, -1, 0);
3180 }
3181 EXPORT_SYMBOL_GPL(call_rcu_sched);
3182 
3183 /**
3184  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
3185  * @head: structure to be used for queueing the RCU updates.
3186  * @func: actual callback function to be invoked after the grace period
3187  *
3188  * The callback function will be invoked some time after a full grace
3189  * period elapses, in other words after all currently executing RCU
3190  * read-side critical sections have completed. call_rcu_bh() assumes
3191  * that the read-side critical sections end on completion of a softirq
3192  * handler. This means that read-side critical sections in process
3193  * context must not be interrupted by softirqs. This interface is to be
3194  * used when most of the read-side critical sections are in softirq context.
3195  * RCU read-side critical sections are delimited by:
3196  *
3197  * - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context, OR
3198  * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
3199  *
3200  * These may be nested.
3201  *
3202  * See the description of call_rcu() for more detailed information on
3203  * memory ordering guarantees.
3204  */
3205 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
3206 {
3207         __call_rcu(head, func, &rcu_bh_state, -1, 0);
3208 }
3209 EXPORT_SYMBOL_GPL(call_rcu_bh);
3210 
3211 /*
3212  * Queue an RCU callback for lazy invocation after a grace period.
3213  * This will likely be later named something like "call_rcu_lazy()",
3214  * but this change will require some way of tagging the lazy RCU
3215  * callbacks in the list of pending callbacks. Until then, this
3216  * function may only be called from __kfree_rcu().
3217  */
3218 void kfree_call_rcu(struct rcu_head *head,
3219                     rcu_callback_t func)
3220 {
3221         __call_rcu(head, func, rcu_state_p, -1, 1);
3222 }
3223 EXPORT_SYMBOL_GPL(kfree_call_rcu);
3224 
3225 /*
3226  * Because a context switch is a grace period for RCU-sched and RCU-bh,
3227  * any blocking grace-period wait automatically implies a grace period
3228  * if there is only one CPU online at any point time during execution
3229  * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
3230  * occasionally incorrectly indicate that there are multiple CPUs online
3231  * when there was in fact only one the whole time, as this just adds
3232  * some overhead: RCU still operates correctly.
3233  */
3234 static inline int rcu_blocking_is_gp(void)
3235 {
3236         int ret;
3237 
3238         might_sleep();  /* Check for RCU read-side critical section. */
3239         preempt_disable();
3240         ret = num_online_cpus() <= 1;
3241         preempt_enable();
3242         return ret;
3243 }
3244 
3245 /**
3246  * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3247  *
3248  * Control will return to the caller some time after a full rcu-sched
3249  * grace period has elapsed, in other words after all currently executing
3250  * rcu-sched read-side critical sections have completed.   These read-side
3251  * critical sections are delimited by rcu_read_lock_sched() and
3252  * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
3253  * local_irq_disable(), and so on may be used in place of
3254  * rcu_read_lock_sched().
3255  *
3256  * This means that all preempt_disable code sequences, including NMI and
3257  * non-threaded hardware-interrupt handlers, in progress on entry will
3258  * have completed before this primitive returns.  However, this does not
3259  * guarantee that softirq handlers will have completed, since in some
3260  * kernels, these handlers can run in process context, and can block.
3261  *
3262  * Note that this guarantee implies further memory-ordering guarantees.
3263  * On systems with more than one CPU, when synchronize_sched() returns,
3264  * each CPU is guaranteed to have executed a full memory barrier since the
3265  * end of its last RCU-sched read-side critical section whose beginning
3266  * preceded the call to synchronize_sched().  In addition, each CPU having
3267  * an RCU read-side critical section that extends beyond the return from
3268  * synchronize_sched() is guaranteed to have executed a full memory barrier
3269  * after the beginning of synchronize_sched() and before the beginning of
3270  * that RCU read-side critical section.  Note that these guarantees include
3271  * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3272  * that are executing in the kernel.
3273  *
3274  * Furthermore, if CPU A invoked synchronize_sched(), which returned
3275  * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3276  * to have executed a full memory barrier during the execution of
3277  * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3278  * again only if the system has more than one CPU).
3279  */
3280 void synchronize_sched(void)
3281 {
3282         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3283                          lock_is_held(&rcu_lock_map) ||
3284                          lock_is_held(&rcu_sched_lock_map),
3285                          "Illegal synchronize_sched() in RCU-sched read-side critical section");
3286         if (rcu_blocking_is_gp())
3287                 return;
3288         if (rcu_gp_is_expedited())
3289                 synchronize_sched_expedited();
3290         else
3291                 wait_rcu_gp(call_rcu_sched);
3292 }
3293 EXPORT_SYMBOL_GPL(synchronize_sched);
3294 
3295 /**
3296  * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3297  *
3298  * Control will return to the caller some time after a full rcu_bh grace
3299  * period has elapsed, in other words after all currently executing rcu_bh
3300  * read-side critical sections have completed.  RCU read-side critical
3301  * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3302  * and may be nested.
3303  *
3304  * See the description of synchronize_sched() for more detailed information
3305  * on memory ordering guarantees.
3306  */
3307 void synchronize_rcu_bh(void)
3308 {
3309         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3310                          lock_is_held(&rcu_lock_map) ||
3311                          lock_is_held(&rcu_sched_lock_map),
3312                          "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3313         if (rcu_blocking_is_gp())
3314                 return;
3315         if (rcu_gp_is_expedited())
3316                 synchronize_rcu_bh_expedited();
3317         else
3318                 wait_rcu_gp(call_rcu_bh);
3319 }
3320 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3321 
3322 /**
3323  * get_state_synchronize_rcu - Snapshot current RCU state
3324  *
3325  * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3326  * to determine whether or not a full grace period has elapsed in the
3327  * meantime.
3328  */
3329 unsigned long get_state_synchronize_rcu(void)
3330 {
3331         /*
3332          * Any prior manipulation of RCU-protected data must happen
3333          * before the load from ->gpnum.
3334          */
3335         smp_mb();  /* ^^^ */
3336 
3337         /*
3338          * Make sure this load happens before the purportedly
3339          * time-consuming work between get_state_synchronize_rcu()
3340          * and cond_synchronize_rcu().
3341          */
3342         return smp_load_acquire(&rcu_state_p->gpnum);
3343 }
3344 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3345 
3346 /**
3347  * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3348  *
3349  * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3350  *
3351  * If a full RCU grace period has elapsed since the earlier call to
3352  * get_state_synchronize_rcu(), just return.  Otherwise, invoke
3353  * synchronize_rcu() to wait for a full grace period.
3354  *
3355  * Yes, this function does not take counter wrap into account.  But
3356  * counter wrap is harmless.  If the counter wraps, we have waited for
3357  * more than 2 billion grace periods (and way more on a 64-bit system!),
3358  * so waiting for one additional grace period should be just fine.
3359  */
3360 void cond_synchronize_rcu(unsigned long oldstate)
3361 {
3362         unsigned long newstate;
3363 
3364         /*
3365          * Ensure that this load happens before any RCU-destructive
3366          * actions the caller might carry out after we return.
3367          */
3368         newstate = smp_load_acquire(&rcu_state_p->completed);
3369         if (ULONG_CMP_GE(oldstate, newstate))
3370                 synchronize_rcu();
3371 }
3372 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3373 
3374 /**
3375  * get_state_synchronize_sched - Snapshot current RCU-sched state
3376  *
3377  * Returns a cookie that is used by a later call to cond_synchronize_sched()
3378  * to determine whether or not a full grace period has elapsed in the
3379  * meantime.
3380  */
3381 unsigned long get_state_synchronize_sched(void)
3382 {
3383         /*
3384          * Any prior manipulation of RCU-protected data must happen
3385          * before the load from ->gpnum.
3386          */
3387         smp_mb();  /* ^^^ */
3388 
3389         /*
3390          * Make sure this load happens before the purportedly
3391          * time-consuming work between get_state_synchronize_sched()
3392          * and cond_synchronize_sched().
3393          */
3394         return smp_load_acquire(&rcu_sched_state.gpnum);
3395 }
3396 EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
3397 
3398 /**
3399  * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
3400  *
3401  * @oldstate: return value from earlier call to get_state_synchronize_sched()
3402  *
3403  * If a full RCU-sched grace period has elapsed since the earlier call to
3404  * get_state_synchronize_sched(), just return.  Otherwise, invoke
3405  * synchronize_sched() to wait for a full grace period.
3406  *
3407  * Yes, this function does not take counter wrap into account.  But
3408  * counter wrap is harmless.  If the counter wraps, we have waited for
3409  * more than 2 billion grace periods (and way more on a 64-bit system!),
3410  * so waiting for one additional grace period should be just fine.
3411  */
3412 void cond_synchronize_sched(unsigned long oldstate)
3413 {
3414         unsigned long newstate;
3415 
3416         /*
3417          * Ensure that this load happens before any RCU-destructive
3418          * actions the caller might carry out after we return.
3419          */
3420         newstate = smp_load_acquire(&rcu_sched_state.completed);
3421         if (ULONG_CMP_GE(oldstate, newstate))
3422                 synchronize_sched();
3423 }
3424 EXPORT_SYMBOL_GPL(cond_synchronize_sched);
3425 
3426 /*
3427  * Check to see if there is any immediate RCU-related work to be done
3428  * by the current CPU, for the specified type of RCU, returning 1 if so.
3429  * The checks are in order of increasing expense: checks that can be
3430  * carried out against CPU-local state are performed first.  However,
3431  * we must check for CPU stalls first, else we might not get a chance.
3432  */
3433 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3434 {
3435         struct rcu_node *rnp = rdp->mynode;
3436 
3437         rdp->n_rcu_pending++;
3438 
3439         /* Check for CPU stalls, if enabled. */
3440         check_cpu_stall(rsp, rdp);
3441 
3442         /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3443         if (rcu_nohz_full_cpu(rsp))
3444                 return 0;
3445 
3446         /* Is the RCU core waiting for a quiescent state from this CPU? */
3447         if (rcu_scheduler_fully_active &&
3448             rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
3449             rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_dynticks.rcu_qs_ctr)) {
3450                 rdp->n_rp_core_needs_qs++;
3451         } else if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm) {
3452                 rdp->n_rp_report_qs++;
3453                 return 1;
3454         }
3455 
3456         /* Does this CPU have callbacks ready to invoke? */
3457         if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
3458                 rdp->n_rp_cb_ready++;
3459                 return 1;
3460         }
3461 
3462         /* Has RCU gone idle with this CPU needing another grace period? */
3463         if (cpu_needs_another_gp(rsp, rdp)) {
3464                 rdp->n_rp_cpu_needs_gp++;
3465                 return 1;
3466         }
3467 
3468         /* Has another RCU grace period completed?  */
3469         if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3470                 rdp->n_rp_gp_completed++;
3471                 return 1;
3472         }
3473 
3474         /* Has a new RCU grace period started? */
3475         if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
3476             unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
3477                 rdp->n_rp_gp_started++;
3478                 return 1;
3479         }
3480 
3481         /* Does this CPU need a deferred NOCB wakeup? */
3482         if (rcu_nocb_need_deferred_wakeup(rdp)) {
3483                 rdp->n_rp_nocb_defer_wakeup++;
3484                 return 1;
3485         }
3486 
3487         /* nothing to do */
3488         rdp->n_rp_need_nothing++;
3489         return 0;
3490 }
3491 
3492 /*
3493  * Check to see if there is any immediate RCU-related work to be done
3494  * by the current CPU, returning 1 if so.  This function is part of the
3495  * RCU implementation; it is -not- an exported member of the RCU API.
3496  */
3497 static int rcu_pending(void)
3498 {
3499         struct rcu_state *rsp;
3500 
3501         for_each_rcu_flavor(rsp)
3502                 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3503                         return 1;
3504         return 0;
3505 }
3506 
3507 /*
3508  * Return true if the specified CPU has any callback.  If all_lazy is
3509  * non-NULL, store an indication of whether all callbacks are lazy.
3510  * (If there are no callbacks, all of them are deemed to be lazy.)
3511  */
3512 static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3513 {
3514         bool al = true;
3515         bool hc = false;
3516         struct rcu_data *rdp;
3517         struct rcu_state *rsp;
3518 
3519         for_each_rcu_flavor(rsp) {
3520                 rdp = this_cpu_ptr(rsp->rda);
3521                 if (rcu_segcblist_empty(&rdp->cblist))
3522                         continue;
3523                 hc = true;
3524                 if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
3525                         al = false;
3526                         break;
3527                 }
3528         }
3529         if (all_lazy)
3530                 *all_lazy = al;
3531         return hc;
3532 }
3533 
3534 /*
3535  * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
3536  * the compiler is expected to optimize this away.
3537  */
3538 static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3539                                int cpu, unsigned long done)
3540 {
3541         trace_rcu_barrier(rsp->name, s, cpu,
3542                           atomic_read(&rsp->barrier_cpu_count), done);
3543 }
3544 
3545 /*
3546  * RCU callback function for _rcu_barrier().  If we are last, wake
3547  * up the task executing _rcu_barrier().
3548  */
3549 static void rcu_barrier_callback(struct rcu_head *rhp)
3550 {
3551         struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3552         struct rcu_state *rsp = rdp->rsp;
3553 
3554         if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
3555                 _rcu_barrier_trace(rsp, TPS("LastCB"), -1,
3556                                    rsp->barrier_sequence);
3557                 complete(&rsp->barrier_completion);
3558         } else {
3559                 _rcu_barrier_trace(rsp, TPS("CB"), -1, rsp->barrier_sequence);
3560         }
3561 }
3562 
3563 /*
3564  * Called with preemption disabled, and from cross-cpu IRQ context.
3565  */
3566 static void rcu_barrier_func(void *type)
3567 {
3568         struct rcu_state *rsp = type;
3569         struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3570 
3571         _rcu_barrier_trace(rsp, TPS("IRQ"), -1, rsp->barrier_sequence);
3572         rdp->barrier_head.func = rcu_barrier_callback;
3573         debug_rcu_head_queue(&rdp->barrier_head);
3574         if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
3575                 atomic_inc(&rsp->barrier_cpu_count);
3576         } else {
3577                 debug_rcu_head_unqueue(&rdp->barrier_head);
3578                 _rcu_barrier_trace(rsp, TPS("IRQNQ"), -1,
3579                                    rsp->barrier_sequence);
3580         }
3581 }
3582 
3583 /*
3584  * Orchestrate the specified type of RCU barrier, waiting for all
3585  * RCU callbacks of the specified type to complete.
3586  */
3587 static void _rcu_barrier(struct rcu_state *rsp)
3588 {
3589         int cpu;
3590         struct rcu_data *rdp;
3591         unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
3592 
3593         _rcu_barrier_trace(rsp, TPS("Begin"), -1, s);
3594 
3595         /* Take mutex to serialize concurrent rcu_barrier() requests. */
3596         mutex_lock(&rsp->barrier_mutex);
3597 
3598         /* Did someone else do our work for us? */
3599         if (rcu_seq_done(&rsp->barrier_sequence, s)) {
3600                 _rcu_barrier_trace(rsp, TPS("EarlyExit"), -1,
3601                                    rsp->barrier_sequence);
3602                 smp_mb(); /* caller's subsequent code after above check. */
3603                 mutex_unlock(&rsp->barrier_mutex);
3604                 return;
3605         }
3606 
3607         /* Mark the start of the barrier operation. */
3608         rcu_seq_start(&rsp->barrier_sequence);
3609         _rcu_barrier_trace(rsp, TPS("Inc1"), -1, rsp->barrier_sequence);
3610 
3611         /*
3612          * Initialize the count to one rather than to zero in order to
3613          * avoid a too-soon return to zero in case of a short grace period
3614          * (or preemption of this task).  Exclude CPU-hotplug operations
3615          * to ensure that no offline CPU has callbacks queued.
3616          */
3617         init_completion(&rsp->barrier_completion);
3618         atomic_set(&rsp->barrier_cpu_count, 1);
3619         get_online_cpus();
3620 
3621         /*
3622          * Force each CPU with callbacks to register a new callback.
3623          * When that callback is invoked, we will know that all of the
3624          * corresponding CPU's preceding callbacks have been invoked.
3625          */
3626         for_each_possible_cpu(cpu) {
3627                 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3628                         continue;
3629                 rdp = per_cpu_ptr(rsp->rda, cpu);
3630                 if (rcu_is_nocb_cpu(cpu)) {
3631                         if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
3632                                 _rcu_barrier_trace(rsp, TPS("OfflineNoCB"), cpu,
3633                                                    rsp->barrier_sequence);
3634                         } else {
3635                                 _rcu_barrier_trace(rsp, TPS("OnlineNoCB"), cpu,
3636                                                    rsp->barrier_sequence);
3637                                 smp_mb__before_atomic();
3638                                 atomic_inc(&rsp->barrier_cpu_count);
3639                                 __call_rcu(&rdp->barrier_head,
3640                                            rcu_barrier_callback, rsp, cpu, 0);
3641                         }
3642                 } else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
3643                         _rcu_barrier_trace(rsp, TPS("OnlineQ"), cpu,
3644                                            rsp->barrier_sequence);
3645                         smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3646                 } else {
3647                         _rcu_barrier_trace(rsp, TPS("OnlineNQ"), cpu,
3648                                            rsp->barrier_sequence);
3649                 }
3650         }
3651         put_online_cpus();
3652 
3653         /*
3654          * Now that we have an rcu_barrier_callback() callback on each
3655          * CPU, and thus each counted, remove the initial count.
3656          */
3657         if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3658                 complete(&rsp->barrier_completion);
3659 
3660         /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3661         wait_for_completion(&rsp->barrier_completion);
3662 
3663         /* Mark the end of the barrier operation. */
3664         _rcu_barrier_trace(rsp, TPS("Inc2"), -1, rsp->barrier_sequence);
3665         rcu_seq_end(&rsp->barrier_sequence);
3666 
3667         /* Other rcu_barrier() invocations can now safely proceed. */
3668         mutex_unlock(&rsp->barrier_mutex);
3669 }
3670 
3671 /**
3672  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3673  */
3674 void rcu_barrier_bh(void)
3675 {
3676         _rcu_barrier(&rcu_bh_state);
3677 }
3678 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3679 
3680 /**
3681  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3682  */
3683 void rcu_barrier_sched(void)
3684 {
3685         _rcu_barrier(&rcu_sched_state);
3686 }
3687 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3688 
3689 /*
3690  * Propagate ->qsinitmask bits up the rcu_node tree to account for the
3691  * first CPU in a given leaf rcu_node structure coming online.  The caller
3692  * must hold the corresponding leaf rcu_node ->lock with interrrupts
3693  * disabled.
3694  */
3695 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
3696 {
3697         long mask;
3698         struct rcu_node *rnp = rnp_leaf;
3699 
3700         lockdep_assert_held(&rnp->lock);
3701         for (;;) {
3702                 mask = rnp->grpmask;
3703                 rnp = rnp->parent;
3704                 if (rnp == NULL)
3705                         return;
3706                 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
3707                 rnp->qsmaskinit |= mask;
3708                 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
3709         }
3710 }
3711 
3712 /*
3713  * Do boot-time initialization of a CPU's per-CPU RCU data.
3714  */
3715 static void __init
3716 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3717 {
3718         unsigned long flags;
3719         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3720         struct rcu_node *rnp = rcu_get_root(rsp);
3721 
3722         /* Set up local state, ensuring consistent view of global state. */
3723         raw_spin_lock_irqsave_rcu_node(rnp, flags);
3724         rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
3725         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3726         WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3727         WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
3728         rdp->cpu = cpu;
3729         rdp->rsp = rsp;
3730         rcu_boot_init_nocb_percpu_data(rdp);
3731         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3732 }
3733 
3734 /*
3735  * Initialize a CPU's per-CPU RCU data.  Note that only one online or
3736  * offline event can be happening at a given time.  Note also that we
3737  * can accept some slop in the rsp->completed access due to the fact
3738  * that this CPU cannot possibly have any RCU callbacks in flight yet.
3739  */
3740 static void
3741 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3742 {
3743         unsigned long flags;
3744         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3745         struct rcu_node *rnp = rcu_get_root(rsp);
3746 
3747         /* Set up local state, ensuring consistent view of global state. */
3748         raw_spin_lock_irqsave_rcu_node(rnp, flags);
3749         rdp->qlen_last_fqs_check = 0;
3750         rdp->n_force_qs_snap = rsp->n_force_qs;
3751         rdp->blimit = blimit;
3752         if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
3753             !init_nocb_callback_list(rdp))
3754                 rcu_segcblist_init(&rdp->cblist);  /* Re-enable callbacks. */
3755         rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3756         rcu_dynticks_eqs_online();
3757         raw_spin_unlock_rcu_node(rnp);          /* irqs remain disabled. */
3758 
3759         /*
3760          * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
3761          * propagation up the rcu_node tree will happen at the beginning
3762          * of the next grace period.
3763          */
3764         rnp = rdp->mynode;
3765         raw_spin_lock_rcu_node(rnp);            /* irqs already disabled. */
3766         rdp->beenonline = true;  /* We have now been online. */
3767         rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
3768         rdp->completed = rnp->completed;
3769         rdp->cpu_no_qs.b.norm = true;
3770         rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
3771         rdp->core_needs_qs = false;
3772         rdp->rcu_iw_pending = false;
3773         rdp->rcu_iw_gpnum = rnp->gpnum - 1;
3774         trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3775         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3776 }
3777 
3778 /*
3779  * Invoked early in the CPU-online process, when pretty much all
3780  * services are available.  The incoming CPU is not present.
3781  */
3782 int rcutree_prepare_cpu(unsigned int cpu)
3783 {
3784         struct rcu_state *rsp;
3785 
3786         for_each_rcu_flavor(rsp)
3787                 rcu_init_percpu_data(cpu, rsp);
3788 
3789         rcu_prepare_kthreads(cpu);
3790         rcu_spawn_all_nocb_kthreads(cpu);
3791 
3792         return 0;
3793 }
3794 
3795 /*
3796  * Update RCU priority boot kthread affinity for CPU-hotplug changes.
3797  */
3798 static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
3799 {
3800         struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3801 
3802         rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
3803 }
3804 
3805 /*
3806  * Near the end of the CPU-online process.  Pretty much all services
3807  * enabled, and the CPU is now very much alive.
3808  */
3809 int rcutree_online_cpu(unsigned int cpu)
3810 {
3811         unsigned long flags;
3812         struct rcu_data *rdp;
3813         struct rcu_node *rnp;
3814         struct rcu_state *rsp;
3815 
3816         for_each_rcu_flavor(rsp) {
3817                 rdp = per_cpu_ptr(rsp->rda, cpu);
3818                 rnp = rdp->mynode;
3819                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3820                 rnp->ffmask |= rdp->grpmask;
3821                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3822         }
3823         if (IS_ENABLED(CONFIG_TREE_SRCU))
3824                 srcu_online_cpu(cpu);
3825         if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
3826                 return 0; /* Too early in boot for scheduler work. */
3827         sync_sched_exp_online_cleanup(cpu);
3828         rcutree_affinity_setting(cpu, -1);
3829         return 0;
3830 }
3831 
3832 /*
3833  * Near the beginning of the process.  The CPU is still very much alive
3834  * with pretty much all services enabled.
3835  */
3836 int rcutree_offline_cpu(unsigned int cpu)
3837 {
3838         unsigned long flags;
3839         struct rcu_data *rdp;
3840         struct rcu_node *rnp;
3841         struct rcu_state *rsp;
3842 
3843         for_each_rcu_flavor(rsp) {
3844                 rdp = per_cpu_ptr(rsp->rda, cpu);
3845                 rnp = rdp->mynode;
3846                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3847                 rnp->ffmask &= ~rdp->grpmask;
3848                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3849         }
3850 
3851         rcutree_affinity_setting(cpu, cpu);
3852         if (IS_ENABLED(CONFIG_TREE_SRCU))
3853                 srcu_offline_cpu(cpu);
3854         return 0;
3855 }
3856 
3857 /*
3858  * Near the end of the offline process.  We do only tracing here.
3859  */
3860 int rcutree_dying_cpu(unsigned int cpu)
3861 {
3862         struct rcu_state *rsp;
3863 
3864         for_each_rcu_flavor(rsp)
3865                 rcu_cleanup_dying_cpu(rsp);
3866         return 0;
3867 }
3868 
3869 /*
3870  * The outgoing CPU is gone and we are running elsewhere.
3871  */
3872 int rcutree_dead_cpu(unsigned int cpu)
3873 {
3874         struct rcu_state *rsp;
3875 
3876         for_each_rcu_flavor(rsp) {
3877                 rcu_cleanup_dead_cpu(cpu, rsp);
3878                 do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
3879         }
3880         return 0;
3881 }
3882 
3883 /*
3884  * Mark the specified CPU as being online so that subsequent grace periods
3885  * (both expedited and normal) will wait on it.  Note that this means that
3886  * incoming CPUs are not allowed to use RCU read-side critical sections
3887  * until this function is called.  Failing to observe this restriction
3888  * will result in lockdep splats.
3889  *
3890  * Note that this function is special in that it is invoked directly
3891  * from the incoming CPU rather than from the cpuhp_step mechanism.
3892  * This is because this function must be invoked at a precise location.
3893  */
3894 void rcu_cpu_starting(unsigned int cpu)
3895 {
3896         unsigned long flags;
3897         unsigned long mask;
3898         int nbits;
3899         unsigned long oldmask;
3900         struct rcu_data *rdp;
3901         struct rcu_node *rnp;
3902         struct rcu_state *rsp;
3903 
3904         for_each_rcu_flavor(rsp) {
3905                 rdp = per_cpu_ptr(rsp->rda, cpu);
3906                 rnp = rdp->mynode;
3907                 mask = rdp->grpmask;
3908                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3909                 rnp->qsmaskinitnext |= mask;
3910                 oldmask = rnp->expmaskinitnext;
3911                 rnp->expmaskinitnext |= mask;
3912                 oldmask ^= rnp->expmaskinitnext;
3913                 nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
3914                 /* Allow lockless access for expedited grace periods. */
3915                 smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */
3916                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3917         }
3918         smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
3919 }
3920 
3921 #ifdef CONFIG_HOTPLUG_CPU
3922 /*
3923  * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
3924  * function.  We now remove it from the rcu_node tree's ->qsmaskinit
3925  * bit masks.
3926  */
3927 static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
3928 {
3929         unsigned long flags;
3930         unsigned long mask;
3931         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3932         struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
3933 
3934         /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
3935         mask = rdp->grpmask;
3936         raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
3937         rnp->qsmaskinitnext &= ~mask;
3938         raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3939 }
3940 
3941 /*
3942  * The outgoing function has no further need of RCU, so remove it from
3943  * the list of CPUs that RCU must track.
3944  *
3945  * Note that this function is special in that it is invoked directly
3946  * from the outgoing CPU rather than from the cpuhp_step mechanism.
3947  * This is because this function must be invoked at a precise location.
3948  */
3949 void rcu_report_dead(unsigned int cpu)
3950 {
3951         struct rcu_state *rsp;
3952 
3953         /* QS for any half-done expedited RCU-sched GP. */
3954         preempt_disable();
3955         rcu_report_exp_rdp(&rcu_sched_state,
3956                            this_cpu_ptr(rcu_sched_state.rda), true);
3957         preempt_enable();
3958         for_each_rcu_flavor(rsp)
3959                 rcu_cleanup_dying_idle_cpu(cpu, rsp);
3960 }
3961 
3962 /* Migrate the dead CPU's callbacks to the current CPU. */
3963 static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
3964 {
3965         unsigned long flags;
3966         struct rcu_data *my_rdp;
3967         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3968         struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
3969 
3970         if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
3971                 return;  /* No callbacks to migrate. */
3972 
3973         local_irq_save(flags);
3974         my_rdp = this_cpu_ptr(rsp->rda);
3975         if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) {
3976                 local_irq_restore(flags);
3977                 return;
3978         }
3979         raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
3980         rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */
3981         rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */
3982         rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
3983         WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
3984                      !rcu_segcblist_n_cbs(&my_rdp->cblist));
3985         raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
3986         WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
3987                   !rcu_segcblist_empty(&rdp->cblist),
3988                   "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
3989                   cpu, rcu_segcblist_n_cbs(&rdp->cblist),
3990                   rcu_segcblist_first_cb(&rdp->cblist));
3991 }
3992 
3993 /*
3994  * The outgoing CPU has just passed through the dying-idle state,
3995  * and we are being invoked from the CPU that was IPIed to continue the
3996  * offline operation.  We need to migrate the outgoing CPU's callbacks.
3997  */
3998 void rcutree_migrate_callbacks(int cpu)
3999 {
4000         struct rcu_state *rsp;
4001 
4002         for_each_rcu_flavor(rsp)
4003                 rcu_migrate_callbacks(cpu, rsp);
4004 }
4005 #endif
4006 
4007 /*
4008  * On non-huge systems, use expedited RCU grace periods to make suspend
4009  * and hibernation run faster.
4010  */
4011 static int rcu_pm_notify(struct notifier_block *self,
4012                          unsigned long action, void *hcpu)
4013 {
4014         switch (action) {
4015         case PM_HIBERNATION_PREPARE:
4016         case PM_SUSPEND_PREPARE:
4017                 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4018                         rcu_expedite_gp();
4019                 break;
4020         case PM_POST_HIBERNATION:
4021         case PM_POST_SUSPEND:
4022                 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4023                         rcu_unexpedite_gp();
4024                 break;
4025         default:
4026                 break;
4027         }
4028         return NOTIFY_OK;
4029 }
4030 
4031 /*
4032  * Spawn the kthreads that handle each RCU flavor's grace periods.
4033  */
4034 static int __init rcu_spawn_gp_kthread(void)
4035 {
4036         unsigned long flags;
4037         int kthread_prio_in = kthread_prio;
4038         struct rcu_node *rnp;
4039         struct rcu_state *rsp;
4040         struct sched_param sp;
4041         struct task_struct *t;
4042 
4043         /* Force priority into range. */
4044         if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
4045                 kthread_prio = 1;
4046         else if (kthread_prio < 0)
4047                 kthread_prio = 0;
4048         else if (kthread_prio > 99)
4049                 kthread_prio = 99;
4050         if (kthread_prio != kthread_prio_in)
4051                 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
4052                          kthread_prio, kthread_prio_in);
4053 
4054         rcu_scheduler_fully_active = 1;
4055         for_each_rcu_flavor(rsp) {
4056                 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
4057                 BUG_ON(IS_ERR(t));
4058                 rnp = rcu_get_root(rsp);
4059                 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4060                 rsp->gp_kthread = t;
4061                 if (kthread_prio) {
4062                         sp.sched_priority = kthread_prio;
4063                         sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4064                 }
4065                 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4066                 wake_up_process(t);
4067         }
4068         rcu_spawn_nocb_kthreads();
4069         rcu_spawn_boost_kthreads();
4070         return 0;
4071 }
4072 early_initcall(rcu_spawn_gp_kthread);
4073 
4074 /*
4075  * This function is invoked towards the end of the scheduler's
4076  * initialization process.  Before this is called, the idle task might
4077  * contain synchronous grace-period primitives (during which time, this idle
4078  * task is booting the system, and such primitives are no-ops).  After this
4079  * function is called, any synchronous grace-period primitives are run as
4080  * expedited, with the requesting task driving the grace period forward.
4081  * A later core_initcall() rcu_set_runtime_mode() will switch to full
4082  * runtime RCU functionality.
4083  */
4084 void rcu_scheduler_starting(void)
4085 {
4086         WARN_ON(num_online_cpus() != 1);
4087         WARN_ON(nr_context_switches() > 0);
4088         rcu_test_sync_prims();
4089         rcu_scheduler_active = RCU_SCHEDULER_INIT;
4090         rcu_test_sync_prims();
4091 }
4092 
4093 /*
4094  * Helper function for rcu_init() that initializes one rcu_state structure.
4095  */
4096 static void __init rcu_init_one(struct rcu_state *rsp)
4097 {
4098         static const char * const buf[] = RCU_NODE_NAME_INIT;
4099         static const char * const fqs[] = RCU_FQS_NAME_INIT;
4100         static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4101         static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4102 
4103         int levelspread[RCU_NUM_LVLS];          /* kids/node in each level. */
4104         int cpustride = 1;
4105         int i;
4106         int j;
4107         struct rcu_node *rnp;
4108 
4109         BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
4110 
4111         /* Silence gcc 4.8 false positive about array index out of range. */
4112         if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4113                 panic("rcu_init_one: rcu_num_lvls out of range");
4114 
4115         /* Initialize the level-tracking arrays. */
4116 
4117         for (i = 1; i < rcu_num_lvls; i++)
4118                 rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
4119         rcu_init_levelspread(levelspread, num_rcu_lvl);
4120 
4121         /* Initialize the elements themselves, starting from the leaves. */
4122 
4123         for (i = rcu_num_lvls - 1; i >= 0; i--) {
4124                 cpustride *= levelspread[i];
4125                 rnp = rsp->level[i];
4126                 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
4127                         raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4128                         lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4129                                                    &rcu_node_class[i], buf[i]);
4130                         raw_spin_lock_init(&rnp->fqslock);
4131                         lockdep_set_class_and_name(&rnp->fqslock,
4132                                                    &rcu_fqs_class[i], fqs[i]);
4133                         rnp->gpnum = rsp->gpnum;
4134                         rnp->completed = rsp->completed;
4135                         rnp->qsmask = 0;
4136                         rnp->qsmaskinit = 0;
4137                         rnp->grplo = j * cpustride;
4138                         rnp->grphi = (j + 1) * cpustride - 1;
4139                         if (rnp->grphi >= nr_cpu_ids)
4140                                 rnp->grphi = nr_cpu_ids - 1;
4141                         if (i == 0) {
4142                                 rnp->grpnum = 0;
4143                                 rnp->grpmask = 0;
4144                                 rnp->parent = NULL;
4145                         } else {
4146                                 rnp->grpnum = j % levelspread[i - 1];
4147                                 rnp->grpmask = 1UL << rnp->grpnum;
4148                                 rnp->parent = rsp->level[i - 1] +
4149                                               j / levelspread[i - 1];
4150                         }
4151                         rnp->level = i;
4152                         INIT_LIST_HEAD(&rnp->blkd_tasks);
4153                         rcu_init_one_nocb(rnp);
4154                         init_waitqueue_head(&rnp->exp_wq[0]);
4155                         init_waitqueue_head(&rnp->exp_wq[1]);
4156                         init_waitqueue_head(&rnp->exp_wq[2]);
4157                         init_waitqueue_head(&rnp->exp_wq[3]);
4158                         spin_lock_init(&rnp->exp_lock);
4159                 }
4160         }
4161 
4162         init_swait_queue_head(&rsp->gp_wq);
4163         init_swait_queue_head(&rsp->expedited_wq);
4164         rnp = rsp->level[rcu_num_lvls - 1];
4165         for_each_possible_cpu(i) {
4166                 while (i > rnp->grphi)
4167                         rnp++;
4168                 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4169                 rcu_boot_init_percpu_data(i, rsp);
4170         }
4171         list_add(&rsp->flavors, &rcu_struct_flavors);
4172 }
4173 
4174 /*
4175  * Compute the rcu_node tree geometry from kernel parameters.  This cannot
4176  * replace the definitions in tree.h because those are needed to size
4177  * the ->node array in the rcu_state structure.
4178  */
4179 static void __init rcu_init_geometry(void)
4180 {
4181         ulong d;
4182         int i;
4183         int rcu_capacity[RCU_NUM_LVLS];
4184 
4185         /*
4186          * Initialize any unspecified boot parameters.
4187          * The default values of jiffies_till_first_fqs and
4188          * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4189          * value, which is a function of HZ, then adding one for each
4190          * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4191          */
4192         d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4193         if (jiffies_till_first_fqs == ULONG_MAX)
4194                 jiffies_till_first_fqs = d;
4195         if (jiffies_till_next_fqs == ULONG_MAX)
4196                 jiffies_till_next_fqs = d;
4197 
4198         /* If the compile-time values are accurate, just leave. */
4199         if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4200             nr_cpu_ids == NR_CPUS)
4201                 return;
4202         pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
4203                 rcu_fanout_leaf, nr_cpu_ids);
4204 
4205         /*
4206          * The boot-time rcu_fanout_leaf parameter must be at least two
4207          * and cannot exceed the number of bits in the rcu_node masks.
4208          * Complain and fall back to the compile-time values if this
4209          * limit is exceeded.
4210          */
4211         if (rcu_fanout_leaf < 2 ||
4212             rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4213                 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4214                 WARN_ON(1);
4215                 return;
4216         }
4217 
4218         /*
4219          * Compute number of nodes that can be handled an rcu_node tree
4220          * with the given number of levels.
4221          */
4222         rcu_capacity[0] = rcu_fanout_leaf;
4223         for (i = 1; i < RCU_NUM_LVLS; i++)
4224                 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4225 
4226         /*
4227          * The tree must be able to accommodate the configured number of CPUs.
4228          * If this limit is exceeded, fall back to the compile-time values.
4229          */
4230         if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4231                 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4232                 WARN_ON(1);
4233                 return;
4234         }
4235 
4236         /* Calculate the number of levels in the tree. */
4237         for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4238         }
4239         rcu_num_lvls = i + 1;
4240 
4241         /* Calculate the number of rcu_nodes at each level of the tree. */
4242         for (i = 0; i < rcu_num_lvls; i++) {
4243                 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4244                 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4245         }
4246 
4247         /* Calculate the total number of rcu_node structures. */
4248         rcu_num_nodes = 0;
4249         for (i = 0; i < rcu_num_lvls; i++)
4250                 rcu_num_nodes += num_rcu_lvl[i];
4251 }
4252 
4253 /*
4254  * Dump out the structure of the rcu_node combining tree associated
4255  * with the rcu_state structure referenced by rsp.
4256  */
4257 static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4258 {
4259         int level = 0;
4260         struct rcu_node *rnp;
4261 
4262         pr_info("rcu_node tree layout dump\n");
4263         pr_info(" ");
4264         rcu_for_each_node_breadth_first(rsp, rnp) {
4265                 if (rnp->level != level) {
4266                         pr_cont("\n");
4267                         pr_info(" ");
4268                         level = rnp->level;
4269                 }
4270                 pr_cont("%d:%d ^%d  ", rnp->grplo, rnp->grphi, rnp->grpnum);
4271         }
4272         pr_cont("\n");
4273 }
4274 
4275 void __init rcu_init(void)
4276 {
4277         int cpu;
4278 
4279         rcu_early_boot_tests();
4280 
4281         rcu_bootup_announce();
4282         rcu_init_geometry();
4283         rcu_init_one(&rcu_bh_state);
4284         rcu_init_one(&rcu_sched_state);
4285         if (dump_tree)
4286                 rcu_dump_rcu_node_tree(&rcu_sched_state);
4287         __rcu_init_preempt();
4288         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4289 
4290         /*
4291          * We don't need protection against CPU-hotplug here because
4292          * this is called early in boot, before either interrupts
4293          * or the scheduler are operational.
4294          */
4295         pm_notifier(rcu_pm_notify, 0);
4296         for_each_online_cpu(cpu) {
4297                 rcutree_prepare_cpu(cpu);
4298                 rcu_cpu_starting(cpu);
4299                 rcutree_online_cpu(cpu);
4300         }
4301 }
4302 
4303 #include "tree_exp.h"
4304 #include "tree_plugin.h"
4305 

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