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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.h>
 36 #include <linux/interrupt.h>
 37 #include <linux/sched.h>
 38 #include <linux/nmi.h>
 39 #include <linux/atomic.h>
 40 #include <linux/bitops.h>
 41 #include <linux/export.h>
 42 #include <linux/completion.h>
 43 #include <linux/moduleparam.h>
 44 #include <linux/module.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 <linux/prefetch.h>
 54 #include <linux/delay.h>
 55 #include <linux/stop_machine.h>
 56 #include <linux/random.h>
 57 #include <linux/trace_events.h>
 58 #include <linux/suspend.h>
 59 
 60 #include "tree.h"
 61 #include "rcu.h"
 62 
 63 MODULE_ALIAS("rcutree");
 64 #ifdef MODULE_PARAM_PREFIX
 65 #undef MODULE_PARAM_PREFIX
 66 #endif
 67 #define MODULE_PARAM_PREFIX "rcutree."
 68 
 69 /* Data structures. */
 70 
 71 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
 72 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
 73 
 74 /*
 75  * In order to export the rcu_state name to the tracing tools, it
 76  * needs to be added in the __tracepoint_string section.
 77  * This requires defining a separate variable tp_<sname>_varname
 78  * that points to the string being used, and this will allow
 79  * the tracing userspace tools to be able to decipher the string
 80  * address to the matching string.
 81  */
 82 #ifdef CONFIG_TRACING
 83 # define DEFINE_RCU_TPS(sname) \
 84 static char sname##_varname[] = #sname; \
 85 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
 86 # define RCU_STATE_NAME(sname) sname##_varname
 87 #else
 88 # define DEFINE_RCU_TPS(sname)
 89 # define RCU_STATE_NAME(sname) __stringify(sname)
 90 #endif
 91 
 92 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
 93 DEFINE_RCU_TPS(sname) \
 94 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
 95 struct rcu_state sname##_state = { \
 96         .level = { &sname##_state.node[0] }, \
 97         .rda = &sname##_data, \
 98         .call = cr, \
 99         .fqs_state = RCU_GP_IDLE, \
100         .gpnum = 0UL - 300UL, \
101         .completed = 0UL - 300UL, \
102         .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
103         .orphan_nxttail = &sname##_state.orphan_nxtlist, \
104         .orphan_donetail = &sname##_state.orphan_donelist, \
105         .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
106         .name = RCU_STATE_NAME(sname), \
107         .abbr = sabbr, \
108 }
109 
110 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
111 RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
112 
113 static struct rcu_state *const rcu_state_p;
114 static struct rcu_data __percpu *const rcu_data_p;
115 LIST_HEAD(rcu_struct_flavors);
116 
117 /* Dump rcu_node combining tree at boot to verify correct setup. */
118 static bool dump_tree;
119 module_param(dump_tree, bool, 0444);
120 /* Control rcu_node-tree auto-balancing at boot time. */
121 static bool rcu_fanout_exact;
122 module_param(rcu_fanout_exact, bool, 0444);
123 /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
124 static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
125 module_param(rcu_fanout_leaf, int, 0444);
126 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
127 static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
128         NUM_RCU_LVL_0,
129         NUM_RCU_LVL_1,
130         NUM_RCU_LVL_2,
131         NUM_RCU_LVL_3,
132         NUM_RCU_LVL_4,
133 };
134 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
135 
136 /*
137  * The rcu_scheduler_active variable transitions from zero to one just
138  * before the first task is spawned.  So when this variable is zero, RCU
139  * can assume that there is but one task, allowing RCU to (for example)
140  * optimize synchronize_sched() to a simple barrier().  When this variable
141  * is one, RCU must actually do all the hard work required to detect real
142  * grace periods.  This variable is also used to suppress boot-time false
143  * positives from lockdep-RCU error checking.
144  */
145 int rcu_scheduler_active __read_mostly;
146 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
147 
148 /*
149  * The rcu_scheduler_fully_active variable transitions from zero to one
150  * during the early_initcall() processing, which is after the scheduler
151  * is capable of creating new tasks.  So RCU processing (for example,
152  * creating tasks for RCU priority boosting) must be delayed until after
153  * rcu_scheduler_fully_active transitions from zero to one.  We also
154  * currently delay invocation of any RCU callbacks until after this point.
155  *
156  * It might later prove better for people registering RCU callbacks during
157  * early boot to take responsibility for these callbacks, but one step at
158  * a time.
159  */
160 static int rcu_scheduler_fully_active __read_mostly;
161 
162 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
163 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
164 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
165 static void invoke_rcu_core(void);
166 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
167 
168 /* rcuc/rcub kthread realtime priority */
169 #ifdef CONFIG_RCU_KTHREAD_PRIO
170 static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
171 #else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
172 static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
173 #endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
174 module_param(kthread_prio, int, 0644);
175 
176 /* Delay in jiffies for grace-period initialization delays, debug only. */
177 
178 #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT
179 static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY;
180 module_param(gp_preinit_delay, int, 0644);
181 #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
182 static const int gp_preinit_delay;
183 #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
184 
185 #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
186 static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
187 module_param(gp_init_delay, int, 0644);
188 #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
189 static const int gp_init_delay;
190 #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
191 
192 #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP
193 static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY;
194 module_param(gp_cleanup_delay, int, 0644);
195 #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
196 static const int gp_cleanup_delay;
197 #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
198 
199 /*
200  * Number of grace periods between delays, normalized by the duration of
201  * the delay.  The longer the the delay, the more the grace periods between
202  * each delay.  The reason for this normalization is that it means that,
203  * for non-zero delays, the overall slowdown of grace periods is constant
204  * regardless of the duration of the delay.  This arrangement balances
205  * the need for long delays to increase some race probabilities with the
206  * need for fast grace periods to increase other race probabilities.
207  */
208 #define PER_RCU_NODE_PERIOD 3   /* Number of grace periods between delays. */
209 
210 /*
211  * Track the rcutorture test sequence number and the update version
212  * number within a given test.  The rcutorture_testseq is incremented
213  * on every rcutorture module load and unload, so has an odd value
214  * when a test is running.  The rcutorture_vernum is set to zero
215  * when rcutorture starts and is incremented on each rcutorture update.
216  * These variables enable correlating rcutorture output with the
217  * RCU tracing information.
218  */
219 unsigned long rcutorture_testseq;
220 unsigned long rcutorture_vernum;
221 
222 /*
223  * Compute the mask of online CPUs for the specified rcu_node structure.
224  * This will not be stable unless the rcu_node structure's ->lock is
225  * held, but the bit corresponding to the current CPU will be stable
226  * in most contexts.
227  */
228 unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
229 {
230         return READ_ONCE(rnp->qsmaskinitnext);
231 }
232 
233 /*
234  * Return true if an RCU grace period is in progress.  The READ_ONCE()s
235  * permit this function to be invoked without holding the root rcu_node
236  * structure's ->lock, but of course results can be subject to change.
237  */
238 static int rcu_gp_in_progress(struct rcu_state *rsp)
239 {
240         return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
241 }
242 
243 /*
244  * Note a quiescent state.  Because we do not need to know
245  * how many quiescent states passed, just if there was at least
246  * one since the start of the grace period, this just sets a flag.
247  * The caller must have disabled preemption.
248  */
249 void rcu_sched_qs(void)
250 {
251         if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) {
252                 trace_rcu_grace_period(TPS("rcu_sched"),
253                                        __this_cpu_read(rcu_sched_data.gpnum),
254                                        TPS("cpuqs"));
255                 __this_cpu_write(rcu_sched_data.passed_quiesce, 1);
256         }
257 }
258 
259 void rcu_bh_qs(void)
260 {
261         if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) {
262                 trace_rcu_grace_period(TPS("rcu_bh"),
263                                        __this_cpu_read(rcu_bh_data.gpnum),
264                                        TPS("cpuqs"));
265                 __this_cpu_write(rcu_bh_data.passed_quiesce, 1);
266         }
267 }
268 
269 static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
270 
271 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
272         .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
273         .dynticks = ATOMIC_INIT(1),
274 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
275         .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
276         .dynticks_idle = ATOMIC_INIT(1),
277 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
278 };
279 
280 DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
281 EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
282 
283 /*
284  * Let the RCU core know that this CPU has gone through the scheduler,
285  * which is a quiescent state.  This is called when the need for a
286  * quiescent state is urgent, so we burn an atomic operation and full
287  * memory barriers to let the RCU core know about it, regardless of what
288  * this CPU might (or might not) do in the near future.
289  *
290  * We inform the RCU core by emulating a zero-duration dyntick-idle
291  * period, which we in turn do by incrementing the ->dynticks counter
292  * by two.
293  */
294 static void rcu_momentary_dyntick_idle(void)
295 {
296         unsigned long flags;
297         struct rcu_data *rdp;
298         struct rcu_dynticks *rdtp;
299         int resched_mask;
300         struct rcu_state *rsp;
301 
302         local_irq_save(flags);
303 
304         /*
305          * Yes, we can lose flag-setting operations.  This is OK, because
306          * the flag will be set again after some delay.
307          */
308         resched_mask = raw_cpu_read(rcu_sched_qs_mask);
309         raw_cpu_write(rcu_sched_qs_mask, 0);
310 
311         /* Find the flavor that needs a quiescent state. */
312         for_each_rcu_flavor(rsp) {
313                 rdp = raw_cpu_ptr(rsp->rda);
314                 if (!(resched_mask & rsp->flavor_mask))
315                         continue;
316                 smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
317                 if (READ_ONCE(rdp->mynode->completed) !=
318                     READ_ONCE(rdp->cond_resched_completed))
319                         continue;
320 
321                 /*
322                  * Pretend to be momentarily idle for the quiescent state.
323                  * This allows the grace-period kthread to record the
324                  * quiescent state, with no need for this CPU to do anything
325                  * further.
326                  */
327                 rdtp = this_cpu_ptr(&rcu_dynticks);
328                 smp_mb__before_atomic(); /* Earlier stuff before QS. */
329                 atomic_add(2, &rdtp->dynticks);  /* QS. */
330                 smp_mb__after_atomic(); /* Later stuff after QS. */
331                 break;
332         }
333         local_irq_restore(flags);
334 }
335 
336 /*
337  * Note a context switch.  This is a quiescent state for RCU-sched,
338  * and requires special handling for preemptible RCU.
339  * The caller must have disabled preemption.
340  */
341 void rcu_note_context_switch(void)
342 {
343         trace_rcu_utilization(TPS("Start context switch"));
344         rcu_sched_qs();
345         rcu_preempt_note_context_switch();
346         if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
347                 rcu_momentary_dyntick_idle();
348         trace_rcu_utilization(TPS("End context switch"));
349 }
350 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
351 
352 /*
353  * Register a quiescent state for all RCU flavors.  If there is an
354  * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
355  * dyntick-idle quiescent state visible to other CPUs (but only for those
356  * RCU flavors in desperate need of a quiescent state, which will normally
357  * be none of them).  Either way, do a lightweight quiescent state for
358  * all RCU flavors.
359  */
360 void rcu_all_qs(void)
361 {
362         if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
363                 rcu_momentary_dyntick_idle();
364         this_cpu_inc(rcu_qs_ctr);
365 }
366 EXPORT_SYMBOL_GPL(rcu_all_qs);
367 
368 static long blimit = 10;        /* Maximum callbacks per rcu_do_batch. */
369 static long qhimark = 10000;    /* If this many pending, ignore blimit. */
370 static long qlowmark = 100;     /* Once only this many pending, use blimit. */
371 
372 module_param(blimit, long, 0444);
373 module_param(qhimark, long, 0444);
374 module_param(qlowmark, long, 0444);
375 
376 static ulong jiffies_till_first_fqs = ULONG_MAX;
377 static ulong jiffies_till_next_fqs = ULONG_MAX;
378 
379 module_param(jiffies_till_first_fqs, ulong, 0644);
380 module_param(jiffies_till_next_fqs, ulong, 0644);
381 
382 /*
383  * How long the grace period must be before we start recruiting
384  * quiescent-state help from rcu_note_context_switch().
385  */
386 static ulong jiffies_till_sched_qs = HZ / 20;
387 module_param(jiffies_till_sched_qs, ulong, 0644);
388 
389 static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
390                                   struct rcu_data *rdp);
391 static void force_qs_rnp(struct rcu_state *rsp,
392                          int (*f)(struct rcu_data *rsp, bool *isidle,
393                                   unsigned long *maxj),
394                          bool *isidle, unsigned long *maxj);
395 static void force_quiescent_state(struct rcu_state *rsp);
396 static int rcu_pending(void);
397 
398 /*
399  * Return the number of RCU batches started thus far for debug & stats.
400  */
401 unsigned long rcu_batches_started(void)
402 {
403         return rcu_state_p->gpnum;
404 }
405 EXPORT_SYMBOL_GPL(rcu_batches_started);
406 
407 /*
408  * Return the number of RCU-sched batches started thus far for debug & stats.
409  */
410 unsigned long rcu_batches_started_sched(void)
411 {
412         return rcu_sched_state.gpnum;
413 }
414 EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
415 
416 /*
417  * Return the number of RCU BH batches started thus far for debug & stats.
418  */
419 unsigned long rcu_batches_started_bh(void)
420 {
421         return rcu_bh_state.gpnum;
422 }
423 EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
424 
425 /*
426  * Return the number of RCU batches completed thus far for debug & stats.
427  */
428 unsigned long rcu_batches_completed(void)
429 {
430         return rcu_state_p->completed;
431 }
432 EXPORT_SYMBOL_GPL(rcu_batches_completed);
433 
434 /*
435  * Return the number of RCU-sched batches completed thus far for debug & stats.
436  */
437 unsigned long rcu_batches_completed_sched(void)
438 {
439         return rcu_sched_state.completed;
440 }
441 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
442 
443 /*
444  * Return the number of RCU BH batches completed thus far for debug & stats.
445  */
446 unsigned long rcu_batches_completed_bh(void)
447 {
448         return rcu_bh_state.completed;
449 }
450 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
451 
452 /*
453  * Force a quiescent state.
454  */
455 void rcu_force_quiescent_state(void)
456 {
457         force_quiescent_state(rcu_state_p);
458 }
459 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
460 
461 /*
462  * Force a quiescent state for RCU BH.
463  */
464 void rcu_bh_force_quiescent_state(void)
465 {
466         force_quiescent_state(&rcu_bh_state);
467 }
468 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
469 
470 /*
471  * Force a quiescent state for RCU-sched.
472  */
473 void rcu_sched_force_quiescent_state(void)
474 {
475         force_quiescent_state(&rcu_sched_state);
476 }
477 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
478 
479 /*
480  * Show the state of the grace-period kthreads.
481  */
482 void show_rcu_gp_kthreads(void)
483 {
484         struct rcu_state *rsp;
485 
486         for_each_rcu_flavor(rsp) {
487                 pr_info("%s: wait state: %d ->state: %#lx\n",
488                         rsp->name, rsp->gp_state, rsp->gp_kthread->state);
489                 /* sched_show_task(rsp->gp_kthread); */
490         }
491 }
492 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
493 
494 /*
495  * Record the number of times rcutorture tests have been initiated and
496  * terminated.  This information allows the debugfs tracing stats to be
497  * correlated to the rcutorture messages, even when the rcutorture module
498  * is being repeatedly loaded and unloaded.  In other words, we cannot
499  * store this state in rcutorture itself.
500  */
501 void rcutorture_record_test_transition(void)
502 {
503         rcutorture_testseq++;
504         rcutorture_vernum = 0;
505 }
506 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
507 
508 /*
509  * Send along grace-period-related data for rcutorture diagnostics.
510  */
511 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
512                             unsigned long *gpnum, unsigned long *completed)
513 {
514         struct rcu_state *rsp = NULL;
515 
516         switch (test_type) {
517         case RCU_FLAVOR:
518                 rsp = rcu_state_p;
519                 break;
520         case RCU_BH_FLAVOR:
521                 rsp = &rcu_bh_state;
522                 break;
523         case RCU_SCHED_FLAVOR:
524                 rsp = &rcu_sched_state;
525                 break;
526         default:
527                 break;
528         }
529         if (rsp != NULL) {
530                 *flags = READ_ONCE(rsp->gp_flags);
531                 *gpnum = READ_ONCE(rsp->gpnum);
532                 *completed = READ_ONCE(rsp->completed);
533                 return;
534         }
535         *flags = 0;
536         *gpnum = 0;
537         *completed = 0;
538 }
539 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
540 
541 /*
542  * Record the number of writer passes through the current rcutorture test.
543  * This is also used to correlate debugfs tracing stats with the rcutorture
544  * messages.
545  */
546 void rcutorture_record_progress(unsigned long vernum)
547 {
548         rcutorture_vernum++;
549 }
550 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
551 
552 /*
553  * Does the CPU have callbacks ready to be invoked?
554  */
555 static int
556 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
557 {
558         return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
559                rdp->nxttail[RCU_DONE_TAIL] != NULL;
560 }
561 
562 /*
563  * Return the root node of the specified rcu_state structure.
564  */
565 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
566 {
567         return &rsp->node[0];
568 }
569 
570 /*
571  * Is there any need for future grace periods?
572  * Interrupts must be disabled.  If the caller does not hold the root
573  * rnp_node structure's ->lock, the results are advisory only.
574  */
575 static int rcu_future_needs_gp(struct rcu_state *rsp)
576 {
577         struct rcu_node *rnp = rcu_get_root(rsp);
578         int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
579         int *fp = &rnp->need_future_gp[idx];
580 
581         return READ_ONCE(*fp);
582 }
583 
584 /*
585  * Does the current CPU require a not-yet-started grace period?
586  * The caller must have disabled interrupts to prevent races with
587  * normal callback registry.
588  */
589 static int
590 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
591 {
592         int i;
593 
594         if (rcu_gp_in_progress(rsp))
595                 return 0;  /* No, a grace period is already in progress. */
596         if (rcu_future_needs_gp(rsp))
597                 return 1;  /* Yes, a no-CBs CPU needs one. */
598         if (!rdp->nxttail[RCU_NEXT_TAIL])
599                 return 0;  /* No, this is a no-CBs (or offline) CPU. */
600         if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
601                 return 1;  /* Yes, this CPU has newly registered callbacks. */
602         for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
603                 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
604                     ULONG_CMP_LT(READ_ONCE(rsp->completed),
605                                  rdp->nxtcompleted[i]))
606                         return 1;  /* Yes, CBs for future grace period. */
607         return 0; /* No grace period needed. */
608 }
609 
610 /*
611  * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
612  *
613  * If the new value of the ->dynticks_nesting counter now is zero,
614  * we really have entered idle, and must do the appropriate accounting.
615  * The caller must have disabled interrupts.
616  */
617 static void rcu_eqs_enter_common(long long oldval, bool user)
618 {
619         struct rcu_state *rsp;
620         struct rcu_data *rdp;
621         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
622 
623         trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
624         if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
625             !user && !is_idle_task(current)) {
626                 struct task_struct *idle __maybe_unused =
627                         idle_task(smp_processor_id());
628 
629                 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
630                 ftrace_dump(DUMP_ORIG);
631                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
632                           current->pid, current->comm,
633                           idle->pid, idle->comm); /* must be idle task! */
634         }
635         for_each_rcu_flavor(rsp) {
636                 rdp = this_cpu_ptr(rsp->rda);
637                 do_nocb_deferred_wakeup(rdp);
638         }
639         rcu_prepare_for_idle();
640         /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
641         smp_mb__before_atomic();  /* See above. */
642         atomic_inc(&rdtp->dynticks);
643         smp_mb__after_atomic();  /* Force ordering with next sojourn. */
644         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
645                      atomic_read(&rdtp->dynticks) & 0x1);
646         rcu_dynticks_task_enter();
647 
648         /*
649          * It is illegal to enter an extended quiescent state while
650          * in an RCU read-side critical section.
651          */
652         rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
653                            "Illegal idle entry in RCU read-side critical section.");
654         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
655                            "Illegal idle entry in RCU-bh read-side critical section.");
656         rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
657                            "Illegal idle entry in RCU-sched read-side critical section.");
658 }
659 
660 /*
661  * Enter an RCU extended quiescent state, which can be either the
662  * idle loop or adaptive-tickless usermode execution.
663  */
664 static void rcu_eqs_enter(bool user)
665 {
666         long long oldval;
667         struct rcu_dynticks *rdtp;
668 
669         rdtp = this_cpu_ptr(&rcu_dynticks);
670         oldval = rdtp->dynticks_nesting;
671         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
672                      (oldval & DYNTICK_TASK_NEST_MASK) == 0);
673         if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
674                 rdtp->dynticks_nesting = 0;
675                 rcu_eqs_enter_common(oldval, user);
676         } else {
677                 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
678         }
679 }
680 
681 /**
682  * rcu_idle_enter - inform RCU that current CPU is entering idle
683  *
684  * Enter idle mode, in other words, -leave- the mode in which RCU
685  * read-side critical sections can occur.  (Though RCU read-side
686  * critical sections can occur in irq handlers in idle, a possibility
687  * handled by irq_enter() and irq_exit().)
688  *
689  * We crowbar the ->dynticks_nesting field to zero to allow for
690  * the possibility of usermode upcalls having messed up our count
691  * of interrupt nesting level during the prior busy period.
692  */
693 void rcu_idle_enter(void)
694 {
695         unsigned long flags;
696 
697         local_irq_save(flags);
698         rcu_eqs_enter(false);
699         rcu_sysidle_enter(0);
700         local_irq_restore(flags);
701 }
702 EXPORT_SYMBOL_GPL(rcu_idle_enter);
703 
704 #ifdef CONFIG_RCU_USER_QS
705 /**
706  * rcu_user_enter - inform RCU that we are resuming userspace.
707  *
708  * Enter RCU idle mode right before resuming userspace.  No use of RCU
709  * is permitted between this call and rcu_user_exit(). This way the
710  * CPU doesn't need to maintain the tick for RCU maintenance purposes
711  * when the CPU runs in userspace.
712  */
713 void rcu_user_enter(void)
714 {
715         rcu_eqs_enter(1);
716 }
717 #endif /* CONFIG_RCU_USER_QS */
718 
719 /**
720  * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
721  *
722  * Exit from an interrupt handler, which might possibly result in entering
723  * idle mode, in other words, leaving the mode in which read-side critical
724  * sections can occur.
725  *
726  * This code assumes that the idle loop never does anything that might
727  * result in unbalanced calls to irq_enter() and irq_exit().  If your
728  * architecture violates this assumption, RCU will give you what you
729  * deserve, good and hard.  But very infrequently and irreproducibly.
730  *
731  * Use things like work queues to work around this limitation.
732  *
733  * You have been warned.
734  */
735 void rcu_irq_exit(void)
736 {
737         unsigned long flags;
738         long long oldval;
739         struct rcu_dynticks *rdtp;
740 
741         local_irq_save(flags);
742         rdtp = this_cpu_ptr(&rcu_dynticks);
743         oldval = rdtp->dynticks_nesting;
744         rdtp->dynticks_nesting--;
745         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
746                      rdtp->dynticks_nesting < 0);
747         if (rdtp->dynticks_nesting)
748                 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
749         else
750                 rcu_eqs_enter_common(oldval, true);
751         rcu_sysidle_enter(1);
752         local_irq_restore(flags);
753 }
754 
755 /*
756  * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
757  *
758  * If the new value of the ->dynticks_nesting counter was previously zero,
759  * we really have exited idle, and must do the appropriate accounting.
760  * The caller must have disabled interrupts.
761  */
762 static void rcu_eqs_exit_common(long long oldval, int user)
763 {
764         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
765 
766         rcu_dynticks_task_exit();
767         smp_mb__before_atomic();  /* Force ordering w/previous sojourn. */
768         atomic_inc(&rdtp->dynticks);
769         /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
770         smp_mb__after_atomic();  /* See above. */
771         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
772                      !(atomic_read(&rdtp->dynticks) & 0x1));
773         rcu_cleanup_after_idle();
774         trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
775         if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
776             !user && !is_idle_task(current)) {
777                 struct task_struct *idle __maybe_unused =
778                         idle_task(smp_processor_id());
779 
780                 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
781                                   oldval, rdtp->dynticks_nesting);
782                 ftrace_dump(DUMP_ORIG);
783                 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
784                           current->pid, current->comm,
785                           idle->pid, idle->comm); /* must be idle task! */
786         }
787 }
788 
789 /*
790  * Exit an RCU extended quiescent state, which can be either the
791  * idle loop or adaptive-tickless usermode execution.
792  */
793 static void rcu_eqs_exit(bool user)
794 {
795         struct rcu_dynticks *rdtp;
796         long long oldval;
797 
798         rdtp = this_cpu_ptr(&rcu_dynticks);
799         oldval = rdtp->dynticks_nesting;
800         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
801         if (oldval & DYNTICK_TASK_NEST_MASK) {
802                 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
803         } else {
804                 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
805                 rcu_eqs_exit_common(oldval, user);
806         }
807 }
808 
809 /**
810  * rcu_idle_exit - inform RCU that current CPU is leaving idle
811  *
812  * Exit idle mode, in other words, -enter- the mode in which RCU
813  * read-side critical sections can occur.
814  *
815  * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
816  * allow for the possibility of usermode upcalls messing up our count
817  * of interrupt nesting level during the busy period that is just
818  * now starting.
819  */
820 void rcu_idle_exit(void)
821 {
822         unsigned long flags;
823 
824         local_irq_save(flags);
825         rcu_eqs_exit(false);
826         rcu_sysidle_exit(0);
827         local_irq_restore(flags);
828 }
829 EXPORT_SYMBOL_GPL(rcu_idle_exit);
830 
831 #ifdef CONFIG_RCU_USER_QS
832 /**
833  * rcu_user_exit - inform RCU that we are exiting userspace.
834  *
835  * Exit RCU idle mode while entering the kernel because it can
836  * run a RCU read side critical section anytime.
837  */
838 void rcu_user_exit(void)
839 {
840         rcu_eqs_exit(1);
841 }
842 #endif /* CONFIG_RCU_USER_QS */
843 
844 /**
845  * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
846  *
847  * Enter an interrupt handler, which might possibly result in exiting
848  * idle mode, in other words, entering the mode in which read-side critical
849  * sections can occur.
850  *
851  * Note that the Linux kernel is fully capable of entering an interrupt
852  * handler that it never exits, for example when doing upcalls to
853  * user mode!  This code assumes that the idle loop never does upcalls to
854  * user mode.  If your architecture does do upcalls from the idle loop (or
855  * does anything else that results in unbalanced calls to the irq_enter()
856  * and irq_exit() functions), RCU will give you what you deserve, good
857  * and hard.  But very infrequently and irreproducibly.
858  *
859  * Use things like work queues to work around this limitation.
860  *
861  * You have been warned.
862  */
863 void rcu_irq_enter(void)
864 {
865         unsigned long flags;
866         struct rcu_dynticks *rdtp;
867         long long oldval;
868 
869         local_irq_save(flags);
870         rdtp = this_cpu_ptr(&rcu_dynticks);
871         oldval = rdtp->dynticks_nesting;
872         rdtp->dynticks_nesting++;
873         WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
874                      rdtp->dynticks_nesting == 0);
875         if (oldval)
876                 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
877         else
878                 rcu_eqs_exit_common(oldval, true);
879         rcu_sysidle_exit(1);
880         local_irq_restore(flags);
881 }
882 
883 /**
884  * rcu_nmi_enter - inform RCU of entry to NMI context
885  *
886  * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
887  * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
888  * that the CPU is active.  This implementation permits nested NMIs, as
889  * long as the nesting level does not overflow an int.  (You will probably
890  * run out of stack space first.)
891  */
892 void rcu_nmi_enter(void)
893 {
894         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
895         int incby = 2;
896 
897         /* Complain about underflow. */
898         WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
899 
900         /*
901          * If idle from RCU viewpoint, atomically increment ->dynticks
902          * to mark non-idle and increment ->dynticks_nmi_nesting by one.
903          * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
904          * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
905          * to be in the outermost NMI handler that interrupted an RCU-idle
906          * period (observation due to Andy Lutomirski).
907          */
908         if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
909                 smp_mb__before_atomic();  /* Force delay from prior write. */
910                 atomic_inc(&rdtp->dynticks);
911                 /* atomic_inc() before later RCU read-side crit sects */
912                 smp_mb__after_atomic();  /* See above. */
913                 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
914                 incby = 1;
915         }
916         rdtp->dynticks_nmi_nesting += incby;
917         barrier();
918 }
919 
920 /**
921  * rcu_nmi_exit - inform RCU of exit from NMI context
922  *
923  * If we are returning from the outermost NMI handler that interrupted an
924  * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
925  * to let the RCU grace-period handling know that the CPU is back to
926  * being RCU-idle.
927  */
928 void rcu_nmi_exit(void)
929 {
930         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
931 
932         /*
933          * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
934          * (We are exiting an NMI handler, so RCU better be paying attention
935          * to us!)
936          */
937         WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
938         WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
939 
940         /*
941          * If the nesting level is not 1, the CPU wasn't RCU-idle, so
942          * leave it in non-RCU-idle state.
943          */
944         if (rdtp->dynticks_nmi_nesting != 1) {
945                 rdtp->dynticks_nmi_nesting -= 2;
946                 return;
947         }
948 
949         /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
950         rdtp->dynticks_nmi_nesting = 0;
951         /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
952         smp_mb__before_atomic();  /* See above. */
953         atomic_inc(&rdtp->dynticks);
954         smp_mb__after_atomic();  /* Force delay to next write. */
955         WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
956 }
957 
958 /**
959  * __rcu_is_watching - are RCU read-side critical sections safe?
960  *
961  * Return true if RCU is watching the running CPU, which means that
962  * this CPU can safely enter RCU read-side critical sections.  Unlike
963  * rcu_is_watching(), the caller of __rcu_is_watching() must have at
964  * least disabled preemption.
965  */
966 bool notrace __rcu_is_watching(void)
967 {
968         return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
969 }
970 
971 /**
972  * rcu_is_watching - see if RCU thinks that the current CPU is idle
973  *
974  * If the current CPU is in its idle loop and is neither in an interrupt
975  * or NMI handler, return true.
976  */
977 bool notrace rcu_is_watching(void)
978 {
979         bool ret;
980 
981         preempt_disable();
982         ret = __rcu_is_watching();
983         preempt_enable();
984         return ret;
985 }
986 EXPORT_SYMBOL_GPL(rcu_is_watching);
987 
988 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
989 
990 /*
991  * Is the current CPU online?  Disable preemption to avoid false positives
992  * that could otherwise happen due to the current CPU number being sampled,
993  * this task being preempted, its old CPU being taken offline, resuming
994  * on some other CPU, then determining that its old CPU is now offline.
995  * It is OK to use RCU on an offline processor during initial boot, hence
996  * the check for rcu_scheduler_fully_active.  Note also that it is OK
997  * for a CPU coming online to use RCU for one jiffy prior to marking itself
998  * online in the cpu_online_mask.  Similarly, it is OK for a CPU going
999  * offline to continue to use RCU for one jiffy after marking itself
1000  * offline in the cpu_online_mask.  This leniency is necessary given the
1001  * non-atomic nature of the online and offline processing, for example,
1002  * the fact that a CPU enters the scheduler after completing the CPU_DYING
1003  * notifiers.
1004  *
1005  * This is also why RCU internally marks CPUs online during the
1006  * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
1007  *
1008  * Disable checking if in an NMI handler because we cannot safely report
1009  * errors from NMI handlers anyway.
1010  */
1011 bool rcu_lockdep_current_cpu_online(void)
1012 {
1013         struct rcu_data *rdp;
1014         struct rcu_node *rnp;
1015         bool ret;
1016 
1017         if (in_nmi())
1018                 return true;
1019         preempt_disable();
1020         rdp = this_cpu_ptr(&rcu_sched_data);
1021         rnp = rdp->mynode;
1022         ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1023               !rcu_scheduler_fully_active;
1024         preempt_enable();
1025         return ret;
1026 }
1027 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1028 
1029 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1030 
1031 /**
1032  * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1033  *
1034  * If the current CPU is idle or running at a first-level (not nested)
1035  * interrupt from idle, return true.  The caller must have at least
1036  * disabled preemption.
1037  */
1038 static int rcu_is_cpu_rrupt_from_idle(void)
1039 {
1040         return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
1041 }
1042 
1043 /*
1044  * Snapshot the specified CPU's dynticks counter so that we can later
1045  * credit them with an implicit quiescent state.  Return 1 if this CPU
1046  * is in dynticks idle mode, which is an extended quiescent state.
1047  */
1048 static int dyntick_save_progress_counter(struct rcu_data *rdp,
1049                                          bool *isidle, unsigned long *maxj)
1050 {
1051         rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
1052         rcu_sysidle_check_cpu(rdp, isidle, maxj);
1053         if ((rdp->dynticks_snap & 0x1) == 0) {
1054                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1055                 return 1;
1056         } else {
1057                 if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
1058                                  rdp->mynode->gpnum))
1059                         WRITE_ONCE(rdp->gpwrap, true);
1060                 return 0;
1061         }
1062 }
1063 
1064 /*
1065  * Return true if the specified CPU has passed through a quiescent
1066  * state by virtue of being in or having passed through an dynticks
1067  * idle state since the last call to dyntick_save_progress_counter()
1068  * for this same CPU, or by virtue of having been offline.
1069  */
1070 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
1071                                     bool *isidle, unsigned long *maxj)
1072 {
1073         unsigned int curr;
1074         int *rcrmp;
1075         unsigned int snap;
1076 
1077         curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
1078         snap = (unsigned int)rdp->dynticks_snap;
1079 
1080         /*
1081          * If the CPU passed through or entered a dynticks idle phase with
1082          * no active irq/NMI handlers, then we can safely pretend that the CPU
1083          * already acknowledged the request to pass through a quiescent
1084          * state.  Either way, that CPU cannot possibly be in an RCU
1085          * read-side critical section that started before the beginning
1086          * of the current RCU grace period.
1087          */
1088         if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
1089                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1090                 rdp->dynticks_fqs++;
1091                 return 1;
1092         }
1093 
1094         /*
1095          * Check for the CPU being offline, but only if the grace period
1096          * is old enough.  We don't need to worry about the CPU changing
1097          * state: If we see it offline even once, it has been through a
1098          * quiescent state.
1099          *
1100          * The reason for insisting that the grace period be at least
1101          * one jiffy old is that CPUs that are not quite online and that
1102          * have just gone offline can still execute RCU read-side critical
1103          * sections.
1104          */
1105         if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
1106                 return 0;  /* Grace period is not old enough. */
1107         barrier();
1108         if (cpu_is_offline(rdp->cpu)) {
1109                 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1110                 rdp->offline_fqs++;
1111                 return 1;
1112         }
1113 
1114         /*
1115          * A CPU running for an extended time within the kernel can
1116          * delay RCU grace periods.  When the CPU is in NO_HZ_FULL mode,
1117          * even context-switching back and forth between a pair of
1118          * in-kernel CPU-bound tasks cannot advance grace periods.
1119          * So if the grace period is old enough, make the CPU pay attention.
1120          * Note that the unsynchronized assignments to the per-CPU
1121          * rcu_sched_qs_mask variable are safe.  Yes, setting of
1122          * bits can be lost, but they will be set again on the next
1123          * force-quiescent-state pass.  So lost bit sets do not result
1124          * in incorrect behavior, merely in a grace period lasting
1125          * a few jiffies longer than it might otherwise.  Because
1126          * there are at most four threads involved, and because the
1127          * updates are only once every few jiffies, the probability of
1128          * lossage (and thus of slight grace-period extension) is
1129          * quite low.
1130          *
1131          * Note that if the jiffies_till_sched_qs boot/sysfs parameter
1132          * is set too high, we override with half of the RCU CPU stall
1133          * warning delay.
1134          */
1135         rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
1136         if (ULONG_CMP_GE(jiffies,
1137                          rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1138             ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1139                 if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
1140                         WRITE_ONCE(rdp->cond_resched_completed,
1141                                    READ_ONCE(rdp->mynode->completed));
1142                         smp_mb(); /* ->cond_resched_completed before *rcrmp. */
1143                         WRITE_ONCE(*rcrmp,
1144                                    READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
1145                         resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
1146                         rdp->rsp->jiffies_resched += 5; /* Enable beating. */
1147                 } else if (ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1148                         /* Time to beat on that CPU again! */
1149                         resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
1150                         rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
1151                 }
1152         }
1153 
1154         return 0;
1155 }
1156 
1157 static void record_gp_stall_check_time(struct rcu_state *rsp)
1158 {
1159         unsigned long j = jiffies;
1160         unsigned long j1;
1161 
1162         rsp->gp_start = j;
1163         smp_wmb(); /* Record start time before stall time. */
1164         j1 = rcu_jiffies_till_stall_check();
1165         WRITE_ONCE(rsp->jiffies_stall, j + j1);
1166         rsp->jiffies_resched = j + j1 / 2;
1167         rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1168 }
1169 
1170 /*
1171  * Complain about starvation of grace-period kthread.
1172  */
1173 static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1174 {
1175         unsigned long gpa;
1176         unsigned long j;
1177 
1178         j = jiffies;
1179         gpa = READ_ONCE(rsp->gp_activity);
1180         if (j - gpa > 2 * HZ)
1181                 pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x\n",
1182                        rsp->name, j - gpa,
1183                        rsp->gpnum, rsp->completed, rsp->gp_flags);
1184 }
1185 
1186 /*
1187  * Dump stacks of all tasks running on stalled CPUs.
1188  */
1189 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1190 {
1191         int cpu;
1192         unsigned long flags;
1193         struct rcu_node *rnp;
1194 
1195         rcu_for_each_leaf_node(rsp, rnp) {
1196                 raw_spin_lock_irqsave(&rnp->lock, flags);
1197                 if (rnp->qsmask != 0) {
1198                         for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1199                                 if (rnp->qsmask & (1UL << cpu))
1200                                         dump_cpu_task(rnp->grplo + cpu);
1201                 }
1202                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1203         }
1204 }
1205 
1206 static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1207 {
1208         int cpu;
1209         long delta;
1210         unsigned long flags;
1211         unsigned long gpa;
1212         unsigned long j;
1213         int ndetected = 0;
1214         struct rcu_node *rnp = rcu_get_root(rsp);
1215         long totqlen = 0;
1216 
1217         /* Only let one CPU complain about others per time interval. */
1218 
1219         raw_spin_lock_irqsave(&rnp->lock, flags);
1220         delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1221         if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
1222                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1223                 return;
1224         }
1225         WRITE_ONCE(rsp->jiffies_stall,
1226                    jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1227         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1228 
1229         /*
1230          * OK, time to rat on our buddy...
1231          * See Documentation/RCU/stallwarn.txt for info on how to debug
1232          * RCU CPU stall warnings.
1233          */
1234         pr_err("INFO: %s detected stalls on CPUs/tasks:",
1235                rsp->name);
1236         print_cpu_stall_info_begin();
1237         rcu_for_each_leaf_node(rsp, rnp) {
1238                 raw_spin_lock_irqsave(&rnp->lock, flags);
1239                 ndetected += rcu_print_task_stall(rnp);
1240                 if (rnp->qsmask != 0) {
1241                         for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1242                                 if (rnp->qsmask & (1UL << cpu)) {
1243                                         print_cpu_stall_info(rsp,
1244                                                              rnp->grplo + cpu);
1245                                         ndetected++;
1246                                 }
1247                 }
1248                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1249         }
1250 
1251         print_cpu_stall_info_end();
1252         for_each_possible_cpu(cpu)
1253                 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1254         pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1255                smp_processor_id(), (long)(jiffies - rsp->gp_start),
1256                (long)rsp->gpnum, (long)rsp->completed, totqlen);
1257         if (ndetected) {
1258                 rcu_dump_cpu_stacks(rsp);
1259         } else {
1260                 if (READ_ONCE(rsp->gpnum) != gpnum ||
1261                     READ_ONCE(rsp->completed) == gpnum) {
1262                         pr_err("INFO: Stall ended before state dump start\n");
1263                 } else {
1264                         j = jiffies;
1265                         gpa = READ_ONCE(rsp->gp_activity);
1266                         pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1267                                rsp->name, j - gpa, j, gpa,
1268                                jiffies_till_next_fqs,
1269                                rcu_get_root(rsp)->qsmask);
1270                         /* In this case, the current CPU might be at fault. */
1271                         sched_show_task(current);
1272                 }
1273         }
1274 
1275         /* Complain about tasks blocking the grace period. */
1276         rcu_print_detail_task_stall(rsp);
1277 
1278         rcu_check_gp_kthread_starvation(rsp);
1279 
1280         force_quiescent_state(rsp);  /* Kick them all. */
1281 }
1282 
1283 static void print_cpu_stall(struct rcu_state *rsp)
1284 {
1285         int cpu;
1286         unsigned long flags;
1287         struct rcu_node *rnp = rcu_get_root(rsp);
1288         long totqlen = 0;
1289 
1290         /*
1291          * OK, time to rat on ourselves...
1292          * See Documentation/RCU/stallwarn.txt for info on how to debug
1293          * RCU CPU stall warnings.
1294          */
1295         pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1296         print_cpu_stall_info_begin();
1297         print_cpu_stall_info(rsp, smp_processor_id());
1298         print_cpu_stall_info_end();
1299         for_each_possible_cpu(cpu)
1300                 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1301         pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
1302                 jiffies - rsp->gp_start,
1303                 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1304 
1305         rcu_check_gp_kthread_starvation(rsp);
1306 
1307         rcu_dump_cpu_stacks(rsp);
1308 
1309         raw_spin_lock_irqsave(&rnp->lock, flags);
1310         if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1311                 WRITE_ONCE(rsp->jiffies_stall,
1312                            jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1313         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1314 
1315         /*
1316          * Attempt to revive the RCU machinery by forcing a context switch.
1317          *
1318          * A context switch would normally allow the RCU state machine to make
1319          * progress and it could be we're stuck in kernel space without context
1320          * switches for an entirely unreasonable amount of time.
1321          */
1322         resched_cpu(smp_processor_id());
1323 }
1324 
1325 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1326 {
1327         unsigned long completed;
1328         unsigned long gpnum;
1329         unsigned long gps;
1330         unsigned long j;
1331         unsigned long js;
1332         struct rcu_node *rnp;
1333 
1334         if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1335                 return;
1336         j = jiffies;
1337 
1338         /*
1339          * Lots of memory barriers to reject false positives.
1340          *
1341          * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1342          * then rsp->gp_start, and finally rsp->completed.  These values
1343          * are updated in the opposite order with memory barriers (or
1344          * equivalent) during grace-period initialization and cleanup.
1345          * Now, a false positive can occur if we get an new value of
1346          * rsp->gp_start and a old value of rsp->jiffies_stall.  But given
1347          * the memory barriers, the only way that this can happen is if one
1348          * grace period ends and another starts between these two fetches.
1349          * Detect this by comparing rsp->completed with the previous fetch
1350          * from rsp->gpnum.
1351          *
1352          * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1353          * and rsp->gp_start suffice to forestall false positives.
1354          */
1355         gpnum = READ_ONCE(rsp->gpnum);
1356         smp_rmb(); /* Pick up ->gpnum first... */
1357         js = READ_ONCE(rsp->jiffies_stall);
1358         smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1359         gps = READ_ONCE(rsp->gp_start);
1360         smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1361         completed = READ_ONCE(rsp->completed);
1362         if (ULONG_CMP_GE(completed, gpnum) ||
1363             ULONG_CMP_LT(j, js) ||
1364             ULONG_CMP_GE(gps, js))
1365                 return; /* No stall or GP completed since entering function. */
1366         rnp = rdp->mynode;
1367         if (rcu_gp_in_progress(rsp) &&
1368             (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1369 
1370                 /* We haven't checked in, so go dump stack. */
1371                 print_cpu_stall(rsp);
1372 
1373         } else if (rcu_gp_in_progress(rsp) &&
1374                    ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1375 
1376                 /* They had a few time units to dump stack, so complain. */
1377                 print_other_cpu_stall(rsp, gpnum);
1378         }
1379 }
1380 
1381 /**
1382  * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1383  *
1384  * Set the stall-warning timeout way off into the future, thus preventing
1385  * any RCU CPU stall-warning messages from appearing in the current set of
1386  * RCU grace periods.
1387  *
1388  * The caller must disable hard irqs.
1389  */
1390 void rcu_cpu_stall_reset(void)
1391 {
1392         struct rcu_state *rsp;
1393 
1394         for_each_rcu_flavor(rsp)
1395                 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1396 }
1397 
1398 /*
1399  * Initialize the specified rcu_data structure's default callback list
1400  * to empty.  The default callback list is the one that is not used by
1401  * no-callbacks CPUs.
1402  */
1403 static void init_default_callback_list(struct rcu_data *rdp)
1404 {
1405         int i;
1406 
1407         rdp->nxtlist = NULL;
1408         for (i = 0; i < RCU_NEXT_SIZE; i++)
1409                 rdp->nxttail[i] = &rdp->nxtlist;
1410 }
1411 
1412 /*
1413  * Initialize the specified rcu_data structure's callback list to empty.
1414  */
1415 static void init_callback_list(struct rcu_data *rdp)
1416 {
1417         if (init_nocb_callback_list(rdp))
1418                 return;
1419         init_default_callback_list(rdp);
1420 }
1421 
1422 /*
1423  * Determine the value that ->completed will have at the end of the
1424  * next subsequent grace period.  This is used to tag callbacks so that
1425  * a CPU can invoke callbacks in a timely fashion even if that CPU has
1426  * been dyntick-idle for an extended period with callbacks under the
1427  * influence of RCU_FAST_NO_HZ.
1428  *
1429  * The caller must hold rnp->lock with interrupts disabled.
1430  */
1431 static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1432                                        struct rcu_node *rnp)
1433 {
1434         /*
1435          * If RCU is idle, we just wait for the next grace period.
1436          * But we can only be sure that RCU is idle if we are looking
1437          * at the root rcu_node structure -- otherwise, a new grace
1438          * period might have started, but just not yet gotten around
1439          * to initializing the current non-root rcu_node structure.
1440          */
1441         if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1442                 return rnp->completed + 1;
1443 
1444         /*
1445          * Otherwise, wait for a possible partial grace period and
1446          * then the subsequent full grace period.
1447          */
1448         return rnp->completed + 2;
1449 }
1450 
1451 /*
1452  * Trace-event helper function for rcu_start_future_gp() and
1453  * rcu_nocb_wait_gp().
1454  */
1455 static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1456                                 unsigned long c, const char *s)
1457 {
1458         trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1459                                       rnp->completed, c, rnp->level,
1460                                       rnp->grplo, rnp->grphi, s);
1461 }
1462 
1463 /*
1464  * Start some future grace period, as needed to handle newly arrived
1465  * callbacks.  The required future grace periods are recorded in each
1466  * rcu_node structure's ->need_future_gp field.  Returns true if there
1467  * is reason to awaken the grace-period kthread.
1468  *
1469  * The caller must hold the specified rcu_node structure's ->lock.
1470  */
1471 static bool __maybe_unused
1472 rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1473                     unsigned long *c_out)
1474 {
1475         unsigned long c;
1476         int i;
1477         bool ret = false;
1478         struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1479 
1480         /*
1481          * Pick up grace-period number for new callbacks.  If this
1482          * grace period is already marked as needed, return to the caller.
1483          */
1484         c = rcu_cbs_completed(rdp->rsp, rnp);
1485         trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1486         if (rnp->need_future_gp[c & 0x1]) {
1487                 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1488                 goto out;
1489         }
1490 
1491         /*
1492          * If either this rcu_node structure or the root rcu_node structure
1493          * believe that a grace period is in progress, then we must wait
1494          * for the one following, which is in "c".  Because our request
1495          * will be noticed at the end of the current grace period, we don't
1496          * need to explicitly start one.  We only do the lockless check
1497          * of rnp_root's fields if the current rcu_node structure thinks
1498          * there is no grace period in flight, and because we hold rnp->lock,
1499          * the only possible change is when rnp_root's two fields are
1500          * equal, in which case rnp_root->gpnum might be concurrently
1501          * incremented.  But that is OK, as it will just result in our
1502          * doing some extra useless work.
1503          */
1504         if (rnp->gpnum != rnp->completed ||
1505             READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1506                 rnp->need_future_gp[c & 0x1]++;
1507                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1508                 goto out;
1509         }
1510 
1511         /*
1512          * There might be no grace period in progress.  If we don't already
1513          * hold it, acquire the root rcu_node structure's lock in order to
1514          * start one (if needed).
1515          */
1516         if (rnp != rnp_root) {
1517                 raw_spin_lock(&rnp_root->lock);
1518                 smp_mb__after_unlock_lock();
1519         }
1520 
1521         /*
1522          * Get a new grace-period number.  If there really is no grace
1523          * period in progress, it will be smaller than the one we obtained
1524          * earlier.  Adjust callbacks as needed.  Note that even no-CBs
1525          * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1526          */
1527         c = rcu_cbs_completed(rdp->rsp, rnp_root);
1528         for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1529                 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1530                         rdp->nxtcompleted[i] = c;
1531 
1532         /*
1533          * If the needed for the required grace period is already
1534          * recorded, trace and leave.
1535          */
1536         if (rnp_root->need_future_gp[c & 0x1]) {
1537                 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1538                 goto unlock_out;
1539         }
1540 
1541         /* Record the need for the future grace period. */
1542         rnp_root->need_future_gp[c & 0x1]++;
1543 
1544         /* If a grace period is not already in progress, start one. */
1545         if (rnp_root->gpnum != rnp_root->completed) {
1546                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1547         } else {
1548                 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1549                 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1550         }
1551 unlock_out:
1552         if (rnp != rnp_root)
1553                 raw_spin_unlock(&rnp_root->lock);
1554 out:
1555         if (c_out != NULL)
1556                 *c_out = c;
1557         return ret;
1558 }
1559 
1560 /*
1561  * Clean up any old requests for the just-ended grace period.  Also return
1562  * whether any additional grace periods have been requested.  Also invoke
1563  * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1564  * waiting for this grace period to complete.
1565  */
1566 static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1567 {
1568         int c = rnp->completed;
1569         int needmore;
1570         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1571 
1572         rcu_nocb_gp_cleanup(rsp, rnp);
1573         rnp->need_future_gp[c & 0x1] = 0;
1574         needmore = rnp->need_future_gp[(c + 1) & 0x1];
1575         trace_rcu_future_gp(rnp, rdp, c,
1576                             needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1577         return needmore;
1578 }
1579 
1580 /*
1581  * Awaken the grace-period kthread for the specified flavor of RCU.
1582  * Don't do a self-awaken, and don't bother awakening when there is
1583  * nothing for the grace-period kthread to do (as in several CPUs
1584  * raced to awaken, and we lost), and finally don't try to awaken
1585  * a kthread that has not yet been created.
1586  */
1587 static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1588 {
1589         if (current == rsp->gp_kthread ||
1590             !READ_ONCE(rsp->gp_flags) ||
1591             !rsp->gp_kthread)
1592                 return;
1593         wake_up(&rsp->gp_wq);
1594 }
1595 
1596 /*
1597  * If there is room, assign a ->completed number to any callbacks on
1598  * this CPU that have not already been assigned.  Also accelerate any
1599  * callbacks that were previously assigned a ->completed number that has
1600  * since proven to be too conservative, which can happen if callbacks get
1601  * assigned a ->completed number while RCU is idle, but with reference to
1602  * a non-root rcu_node structure.  This function is idempotent, so it does
1603  * not hurt to call it repeatedly.  Returns an flag saying that we should
1604  * awaken the RCU grace-period kthread.
1605  *
1606  * The caller must hold rnp->lock with interrupts disabled.
1607  */
1608 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1609                                struct rcu_data *rdp)
1610 {
1611         unsigned long c;
1612         int i;
1613         bool ret;
1614 
1615         /* If the CPU has no callbacks, nothing to do. */
1616         if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1617                 return false;
1618 
1619         /*
1620          * Starting from the sublist containing the callbacks most
1621          * recently assigned a ->completed number and working down, find the
1622          * first sublist that is not assignable to an upcoming grace period.
1623          * Such a sublist has something in it (first two tests) and has
1624          * a ->completed number assigned that will complete sooner than
1625          * the ->completed number for newly arrived callbacks (last test).
1626          *
1627          * The key point is that any later sublist can be assigned the
1628          * same ->completed number as the newly arrived callbacks, which
1629          * means that the callbacks in any of these later sublist can be
1630          * grouped into a single sublist, whether or not they have already
1631          * been assigned a ->completed number.
1632          */
1633         c = rcu_cbs_completed(rsp, rnp);
1634         for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1635                 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1636                     !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1637                         break;
1638 
1639         /*
1640          * If there are no sublist for unassigned callbacks, leave.
1641          * At the same time, advance "i" one sublist, so that "i" will
1642          * index into the sublist where all the remaining callbacks should
1643          * be grouped into.
1644          */
1645         if (++i >= RCU_NEXT_TAIL)
1646                 return false;
1647 
1648         /*
1649          * Assign all subsequent callbacks' ->completed number to the next
1650          * full grace period and group them all in the sublist initially
1651          * indexed by "i".
1652          */
1653         for (; i <= RCU_NEXT_TAIL; i++) {
1654                 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1655                 rdp->nxtcompleted[i] = c;
1656         }
1657         /* Record any needed additional grace periods. */
1658         ret = rcu_start_future_gp(rnp, rdp, NULL);
1659 
1660         /* Trace depending on how much we were able to accelerate. */
1661         if (!*rdp->nxttail[RCU_WAIT_TAIL])
1662                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1663         else
1664                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1665         return ret;
1666 }
1667 
1668 /*
1669  * Move any callbacks whose grace period has completed to the
1670  * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1671  * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1672  * sublist.  This function is idempotent, so it does not hurt to
1673  * invoke it repeatedly.  As long as it is not invoked -too- often...
1674  * Returns true if the RCU grace-period kthread needs to be awakened.
1675  *
1676  * The caller must hold rnp->lock with interrupts disabled.
1677  */
1678 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1679                             struct rcu_data *rdp)
1680 {
1681         int i, j;
1682 
1683         /* If the CPU has no callbacks, nothing to do. */
1684         if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1685                 return false;
1686 
1687         /*
1688          * Find all callbacks whose ->completed numbers indicate that they
1689          * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1690          */
1691         for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1692                 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1693                         break;
1694                 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1695         }
1696         /* Clean up any sublist tail pointers that were misordered above. */
1697         for (j = RCU_WAIT_TAIL; j < i; j++)
1698                 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1699 
1700         /* Copy down callbacks to fill in empty sublists. */
1701         for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1702                 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1703                         break;
1704                 rdp->nxttail[j] = rdp->nxttail[i];
1705                 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1706         }
1707 
1708         /* Classify any remaining callbacks. */
1709         return rcu_accelerate_cbs(rsp, rnp, rdp);
1710 }
1711 
1712 /*
1713  * Update CPU-local rcu_data state to record the beginnings and ends of
1714  * grace periods.  The caller must hold the ->lock of the leaf rcu_node
1715  * structure corresponding to the current CPU, and must have irqs disabled.
1716  * Returns true if the grace-period kthread needs to be awakened.
1717  */
1718 static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1719                               struct rcu_data *rdp)
1720 {
1721         bool ret;
1722 
1723         /* Handle the ends of any preceding grace periods first. */
1724         if (rdp->completed == rnp->completed &&
1725             !unlikely(READ_ONCE(rdp->gpwrap))) {
1726 
1727                 /* No grace period end, so just accelerate recent callbacks. */
1728                 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1729 
1730         } else {
1731 
1732                 /* Advance callbacks. */
1733                 ret = rcu_advance_cbs(rsp, rnp, rdp);
1734 
1735                 /* Remember that we saw this grace-period completion. */
1736                 rdp->completed = rnp->completed;
1737                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1738         }
1739 
1740         if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1741                 /*
1742                  * If the current grace period is waiting for this CPU,
1743                  * set up to detect a quiescent state, otherwise don't
1744                  * go looking for one.
1745                  */
1746                 rdp->gpnum = rnp->gpnum;
1747                 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1748                 rdp->passed_quiesce = 0;
1749                 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
1750                 rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
1751                 zero_cpu_stall_ticks(rdp);
1752                 WRITE_ONCE(rdp->gpwrap, false);
1753         }
1754         return ret;
1755 }
1756 
1757 static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1758 {
1759         unsigned long flags;
1760         bool needwake;
1761         struct rcu_node *rnp;
1762 
1763         local_irq_save(flags);
1764         rnp = rdp->mynode;
1765         if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
1766              rdp->completed == READ_ONCE(rnp->completed) &&
1767              !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1768             !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
1769                 local_irq_restore(flags);
1770                 return;
1771         }
1772         smp_mb__after_unlock_lock();
1773         needwake = __note_gp_changes(rsp, rnp, rdp);
1774         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1775         if (needwake)
1776                 rcu_gp_kthread_wake(rsp);
1777 }
1778 
1779 static void rcu_gp_slow(struct rcu_state *rsp, int delay)
1780 {
1781         if (delay > 0 &&
1782             !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1783                 schedule_timeout_uninterruptible(delay);
1784 }
1785 
1786 /*
1787  * Initialize a new grace period.  Return 0 if no grace period required.
1788  */
1789 static int rcu_gp_init(struct rcu_state *rsp)
1790 {
1791         unsigned long oldmask;
1792         struct rcu_data *rdp;
1793         struct rcu_node *rnp = rcu_get_root(rsp);
1794 
1795         WRITE_ONCE(rsp->gp_activity, jiffies);
1796         raw_spin_lock_irq(&rnp->lock);
1797         smp_mb__after_unlock_lock();
1798         if (!READ_ONCE(rsp->gp_flags)) {
1799                 /* Spurious wakeup, tell caller to go back to sleep.  */
1800                 raw_spin_unlock_irq(&rnp->lock);
1801                 return 0;
1802         }
1803         WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1804 
1805         if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1806                 /*
1807                  * Grace period already in progress, don't start another.
1808                  * Not supposed to be able to happen.
1809                  */
1810                 raw_spin_unlock_irq(&rnp->lock);
1811                 return 0;
1812         }
1813 
1814         /* Advance to a new grace period and initialize state. */
1815         record_gp_stall_check_time(rsp);
1816         /* Record GP times before starting GP, hence smp_store_release(). */
1817         smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1818         trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1819         raw_spin_unlock_irq(&rnp->lock);
1820 
1821         /*
1822          * Apply per-leaf buffered online and offline operations to the
1823          * rcu_node tree.  Note that this new grace period need not wait
1824          * for subsequent online CPUs, and that quiescent-state forcing
1825          * will handle subsequent offline CPUs.
1826          */
1827         rcu_for_each_leaf_node(rsp, rnp) {
1828                 rcu_gp_slow(rsp, gp_preinit_delay);
1829                 raw_spin_lock_irq(&rnp->lock);
1830                 smp_mb__after_unlock_lock();
1831                 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1832                     !rnp->wait_blkd_tasks) {
1833                         /* Nothing to do on this leaf rcu_node structure. */
1834                         raw_spin_unlock_irq(&rnp->lock);
1835                         continue;
1836                 }
1837 
1838                 /* Record old state, apply changes to ->qsmaskinit field. */
1839                 oldmask = rnp->qsmaskinit;
1840                 rnp->qsmaskinit = rnp->qsmaskinitnext;
1841 
1842                 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1843                 if (!oldmask != !rnp->qsmaskinit) {
1844                         if (!oldmask) /* First online CPU for this rcu_node. */
1845                                 rcu_init_new_rnp(rnp);
1846                         else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
1847                                 rnp->wait_blkd_tasks = true;
1848                         else /* Last offline CPU and can propagate. */
1849                                 rcu_cleanup_dead_rnp(rnp);
1850                 }
1851 
1852                 /*
1853                  * If all waited-on tasks from prior grace period are
1854                  * done, and if all this rcu_node structure's CPUs are
1855                  * still offline, propagate up the rcu_node tree and
1856                  * clear ->wait_blkd_tasks.  Otherwise, if one of this
1857                  * rcu_node structure's CPUs has since come back online,
1858                  * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
1859                  * checks for this, so just call it unconditionally).
1860                  */
1861                 if (rnp->wait_blkd_tasks &&
1862                     (!rcu_preempt_has_tasks(rnp) ||
1863                      rnp->qsmaskinit)) {
1864                         rnp->wait_blkd_tasks = false;
1865                         rcu_cleanup_dead_rnp(rnp);
1866                 }
1867 
1868                 raw_spin_unlock_irq(&rnp->lock);
1869         }
1870 
1871         /*
1872          * Set the quiescent-state-needed bits in all the rcu_node
1873          * structures for all currently online CPUs in breadth-first order,
1874          * starting from the root rcu_node structure, relying on the layout
1875          * of the tree within the rsp->node[] array.  Note that other CPUs
1876          * will access only the leaves of the hierarchy, thus seeing that no
1877          * grace period is in progress, at least until the corresponding
1878          * leaf node has been initialized.  In addition, we have excluded
1879          * CPU-hotplug operations.
1880          *
1881          * The grace period cannot complete until the initialization
1882          * process finishes, because this kthread handles both.
1883          */
1884         rcu_for_each_node_breadth_first(rsp, rnp) {
1885                 rcu_gp_slow(rsp, gp_init_delay);
1886                 raw_spin_lock_irq(&rnp->lock);
1887                 smp_mb__after_unlock_lock();
1888                 rdp = this_cpu_ptr(rsp->rda);
1889                 rcu_preempt_check_blocked_tasks(rnp);
1890                 rnp->qsmask = rnp->qsmaskinit;
1891                 WRITE_ONCE(rnp->gpnum, rsp->gpnum);
1892                 if (WARN_ON_ONCE(rnp->completed != rsp->completed))
1893                         WRITE_ONCE(rnp->completed, rsp->completed);
1894                 if (rnp == rdp->mynode)
1895                         (void)__note_gp_changes(rsp, rnp, rdp);
1896                 rcu_preempt_boost_start_gp(rnp);
1897                 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1898                                             rnp->level, rnp->grplo,
1899                                             rnp->grphi, rnp->qsmask);
1900                 raw_spin_unlock_irq(&rnp->lock);
1901                 cond_resched_rcu_qs();
1902                 WRITE_ONCE(rsp->gp_activity, jiffies);
1903         }
1904 
1905         return 1;
1906 }
1907 
1908 /*
1909  * Do one round of quiescent-state forcing.
1910  */
1911 static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1912 {
1913         int fqs_state = fqs_state_in;
1914         bool isidle = false;
1915         unsigned long maxj;
1916         struct rcu_node *rnp = rcu_get_root(rsp);
1917 
1918         WRITE_ONCE(rsp->gp_activity, jiffies);
1919         rsp->n_force_qs++;
1920         if (fqs_state == RCU_SAVE_DYNTICK) {
1921                 /* Collect dyntick-idle snapshots. */
1922                 if (is_sysidle_rcu_state(rsp)) {
1923                         isidle = true;
1924                         maxj = jiffies - ULONG_MAX / 4;
1925                 }
1926                 force_qs_rnp(rsp, dyntick_save_progress_counter,
1927                              &isidle, &maxj);
1928                 rcu_sysidle_report_gp(rsp, isidle, maxj);
1929                 fqs_state = RCU_FORCE_QS;
1930         } else {
1931                 /* Handle dyntick-idle and offline CPUs. */
1932                 isidle = true;
1933                 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1934         }
1935         /* Clear flag to prevent immediate re-entry. */
1936         if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1937                 raw_spin_lock_irq(&rnp->lock);
1938                 smp_mb__after_unlock_lock();
1939                 WRITE_ONCE(rsp->gp_flags,
1940                            READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
1941                 raw_spin_unlock_irq(&rnp->lock);
1942         }
1943         return fqs_state;
1944 }
1945 
1946 /*
1947  * Clean up after the old grace period.
1948  */
1949 static void rcu_gp_cleanup(struct rcu_state *rsp)
1950 {
1951         unsigned long gp_duration;
1952         bool needgp = false;
1953         int nocb = 0;
1954         struct rcu_data *rdp;
1955         struct rcu_node *rnp = rcu_get_root(rsp);
1956 
1957         WRITE_ONCE(rsp->gp_activity, jiffies);
1958         raw_spin_lock_irq(&rnp->lock);
1959         smp_mb__after_unlock_lock();
1960         gp_duration = jiffies - rsp->gp_start;
1961         if (gp_duration > rsp->gp_max)
1962                 rsp->gp_max = gp_duration;
1963 
1964         /*
1965          * We know the grace period is complete, but to everyone else
1966          * it appears to still be ongoing.  But it is also the case
1967          * that to everyone else it looks like there is nothing that
1968          * they can do to advance the grace period.  It is therefore
1969          * safe for us to drop the lock in order to mark the grace
1970          * period as completed in all of the rcu_node structures.
1971          */
1972         raw_spin_unlock_irq(&rnp->lock);
1973 
1974         /*
1975          * Propagate new ->completed value to rcu_node structures so
1976          * that other CPUs don't have to wait until the start of the next
1977          * grace period to process their callbacks.  This also avoids
1978          * some nasty RCU grace-period initialization races by forcing
1979          * the end of the current grace period to be completely recorded in
1980          * all of the rcu_node structures before the beginning of the next
1981          * grace period is recorded in any of the rcu_node structures.
1982          */
1983         rcu_for_each_node_breadth_first(rsp, rnp) {
1984                 raw_spin_lock_irq(&rnp->lock);
1985                 smp_mb__after_unlock_lock();
1986                 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
1987                 WARN_ON_ONCE(rnp->qsmask);
1988                 WRITE_ONCE(rnp->completed, rsp->gpnum);
1989                 rdp = this_cpu_ptr(rsp->rda);
1990                 if (rnp == rdp->mynode)
1991                         needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
1992                 /* smp_mb() provided by prior unlock-lock pair. */
1993                 nocb += rcu_future_gp_cleanup(rsp, rnp);
1994                 raw_spin_unlock_irq(&rnp->lock);
1995                 cond_resched_rcu_qs();
1996                 WRITE_ONCE(rsp->gp_activity, jiffies);
1997                 rcu_gp_slow(rsp, gp_cleanup_delay);
1998         }
1999         rnp = rcu_get_root(rsp);
2000         raw_spin_lock_irq(&rnp->lock);
2001         smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
2002         rcu_nocb_gp_set(rnp, nocb);
2003 
2004         /* Declare grace period done. */
2005         WRITE_ONCE(rsp->completed, rsp->gpnum);
2006         trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
2007         rsp->fqs_state = RCU_GP_IDLE;
2008         rdp = this_cpu_ptr(rsp->rda);
2009         /* Advance CBs to reduce false positives below. */
2010         needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
2011         if (needgp || cpu_needs_another_gp(rsp, rdp)) {
2012                 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2013                 trace_rcu_grace_period(rsp->name,
2014                                        READ_ONCE(rsp->gpnum),
2015                                        TPS("newreq"));
2016         }
2017         raw_spin_unlock_irq(&rnp->lock);
2018 }
2019 
2020 /*
2021  * Body of kthread that handles grace periods.
2022  */
2023 static int __noreturn rcu_gp_kthread(void *arg)
2024 {
2025         int fqs_state;
2026         int gf;
2027         unsigned long j;
2028         int ret;
2029         struct rcu_state *rsp = arg;
2030         struct rcu_node *rnp = rcu_get_root(rsp);
2031 
2032         rcu_bind_gp_kthread();
2033         for (;;) {
2034 
2035                 /* Handle grace-period start. */
2036                 for (;;) {
2037                         trace_rcu_grace_period(rsp->name,
2038                                                READ_ONCE(rsp->gpnum),
2039                                                TPS("reqwait"));
2040                         rsp->gp_state = RCU_GP_WAIT_GPS;
2041                         wait_event_interruptible(rsp->gp_wq,
2042                                                  READ_ONCE(rsp->gp_flags) &
2043                                                  RCU_GP_FLAG_INIT);
2044                         /* Locking provides needed memory barrier. */
2045                         if (rcu_gp_init(rsp))
2046                                 break;
2047                         cond_resched_rcu_qs();
2048                         WRITE_ONCE(rsp->gp_activity, jiffies);
2049                         WARN_ON(signal_pending(current));
2050                         trace_rcu_grace_period(rsp->name,
2051                                                READ_ONCE(rsp->gpnum),
2052                                                TPS("reqwaitsig"));
2053                 }
2054 
2055                 /* Handle quiescent-state forcing. */
2056                 fqs_state = RCU_SAVE_DYNTICK;
2057                 j = jiffies_till_first_fqs;
2058                 if (j > HZ) {
2059                         j = HZ;
2060                         jiffies_till_first_fqs = HZ;
2061                 }
2062                 ret = 0;
2063                 for (;;) {
2064                         if (!ret)
2065                                 rsp->jiffies_force_qs = jiffies + j;
2066                         trace_rcu_grace_period(rsp->name,
2067                                                READ_ONCE(rsp->gpnum),
2068                                                TPS("fqswait"));
2069                         rsp->gp_state = RCU_GP_WAIT_FQS;
2070                         ret = wait_event_interruptible_timeout(rsp->gp_wq,
2071                                         ((gf = READ_ONCE(rsp->gp_flags)) &
2072                                          RCU_GP_FLAG_FQS) ||
2073                                         (!READ_ONCE(rnp->qsmask) &&
2074                                          !rcu_preempt_blocked_readers_cgp(rnp)),
2075                                         j);
2076                         /* Locking provides needed memory barriers. */
2077                         /* If grace period done, leave loop. */
2078                         if (!READ_ONCE(rnp->qsmask) &&
2079                             !rcu_preempt_blocked_readers_cgp(rnp))
2080                                 break;
2081                         /* If time for quiescent-state forcing, do it. */
2082                         if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2083                             (gf & RCU_GP_FLAG_FQS)) {
2084                                 trace_rcu_grace_period(rsp->name,
2085                                                        READ_ONCE(rsp->gpnum),
2086                                                        TPS("fqsstart"));
2087                                 fqs_state = rcu_gp_fqs(rsp, fqs_state);
2088                                 trace_rcu_grace_period(rsp->name,
2089                                                        READ_ONCE(rsp->gpnum),
2090                                                        TPS("fqsend"));
2091                                 cond_resched_rcu_qs();
2092                                 WRITE_ONCE(rsp->gp_activity, jiffies);
2093                         } else {
2094                                 /* Deal with stray signal. */
2095                                 cond_resched_rcu_qs();
2096                                 WRITE_ONCE(rsp->gp_activity, jiffies);
2097                                 WARN_ON(signal_pending(current));
2098                                 trace_rcu_grace_period(rsp->name,
2099                                                        READ_ONCE(rsp->gpnum),
2100                                                        TPS("fqswaitsig"));
2101                         }
2102                         j = jiffies_till_next_fqs;
2103                         if (j > HZ) {
2104                                 j = HZ;
2105                                 jiffies_till_next_fqs = HZ;
2106                         } else if (j < 1) {
2107                                 j = 1;
2108                                 jiffies_till_next_fqs = 1;
2109                         }
2110                 }
2111 
2112                 /* Handle grace-period end. */
2113                 rcu_gp_cleanup(rsp);
2114         }
2115 }
2116 
2117 /*
2118  * Start a new RCU grace period if warranted, re-initializing the hierarchy
2119  * in preparation for detecting the next grace period.  The caller must hold
2120  * the root node's ->lock and hard irqs must be disabled.
2121  *
2122  * Note that it is legal for a dying CPU (which is marked as offline) to
2123  * invoke this function.  This can happen when the dying CPU reports its
2124  * quiescent state.
2125  *
2126  * Returns true if the grace-period kthread must be awakened.
2127  */
2128 static bool
2129 rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
2130                       struct rcu_data *rdp)
2131 {
2132         if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2133                 /*
2134                  * Either we have not yet spawned the grace-period
2135                  * task, this CPU does not need another grace period,
2136                  * or a grace period is already in progress.
2137                  * Either way, don't start a new grace period.
2138                  */
2139                 return false;
2140         }
2141         WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2142         trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2143                                TPS("newreq"));
2144 
2145         /*
2146          * We can't do wakeups while holding the rnp->lock, as that
2147          * could cause possible deadlocks with the rq->lock. Defer
2148          * the wakeup to our caller.
2149          */
2150         return true;
2151 }
2152 
2153 /*
2154  * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
2155  * callbacks.  Note that rcu_start_gp_advanced() cannot do this because it
2156  * is invoked indirectly from rcu_advance_cbs(), which would result in
2157  * endless recursion -- or would do so if it wasn't for the self-deadlock
2158  * that is encountered beforehand.
2159  *
2160  * Returns true if the grace-period kthread needs to be awakened.
2161  */
2162 static bool rcu_start_gp(struct rcu_state *rsp)
2163 {
2164         struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
2165         struct rcu_node *rnp = rcu_get_root(rsp);
2166         bool ret = false;
2167 
2168         /*
2169          * If there is no grace period in progress right now, any
2170          * callbacks we have up to this point will be satisfied by the
2171          * next grace period.  Also, advancing the callbacks reduces the
2172          * probability of false positives from cpu_needs_another_gp()
2173          * resulting in pointless grace periods.  So, advance callbacks
2174          * then start the grace period!
2175          */
2176         ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
2177         ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
2178         return ret;
2179 }
2180 
2181 /*
2182  * Report a full set of quiescent states to the specified rcu_state
2183  * data structure.  This involves cleaning up after the prior grace
2184  * period and letting rcu_start_gp() start up the next grace period
2185  * if one is needed.  Note that the caller must hold rnp->lock, which
2186  * is released before return.
2187  */
2188 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2189         __releases(rcu_get_root(rsp)->lock)
2190 {
2191         WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2192         WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2193         raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2194         rcu_gp_kthread_wake(rsp);
2195 }
2196 
2197 /*
2198  * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2199  * Allows quiescent states for a group of CPUs to be reported at one go
2200  * to the specified rcu_node structure, though all the CPUs in the group
2201  * must be represented by the same rcu_node structure (which need not be a
2202  * leaf rcu_node structure, though it often will be).  The gps parameter
2203  * is the grace-period snapshot, which means that the quiescent states
2204  * are valid only if rnp->gpnum is equal to gps.  That structure's lock
2205  * must be held upon entry, and it is released before return.
2206  */
2207 static void
2208 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2209                   struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2210         __releases(rnp->lock)
2211 {
2212         unsigned long oldmask = 0;
2213         struct rcu_node *rnp_c;
2214 
2215         /* Walk up the rcu_node hierarchy. */
2216         for (;;) {
2217                 if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2218 
2219                         /*
2220                          * Our bit has already been cleared, or the
2221                          * relevant grace period is already over, so done.
2222                          */
2223                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
2224                         return;
2225                 }
2226                 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2227                 rnp->qsmask &= ~mask;
2228                 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
2229                                                  mask, rnp->qsmask, rnp->level,
2230                                                  rnp->grplo, rnp->grphi,
2231                                                  !!rnp->gp_tasks);
2232                 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2233 
2234                         /* Other bits still set at this level, so done. */
2235                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
2236                         return;
2237                 }
2238                 mask = rnp->grpmask;
2239                 if (rnp->parent == NULL) {
2240 
2241                         /* No more levels.  Exit loop holding root lock. */
2242 
2243                         break;
2244                 }
2245                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2246                 rnp_c = rnp;
2247                 rnp = rnp->parent;
2248                 raw_spin_lock_irqsave(&rnp->lock, flags);
2249                 smp_mb__after_unlock_lock();
2250                 oldmask = rnp_c->qsmask;
2251         }
2252 
2253         /*
2254          * Get here if we are the last CPU to pass through a quiescent
2255          * state for this grace period.  Invoke rcu_report_qs_rsp()
2256          * to clean up and start the next grace period if one is needed.
2257          */
2258         rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2259 }
2260 
2261 /*
2262  * Record a quiescent state for all tasks that were previously queued
2263  * on the specified rcu_node structure and that were blocking the current
2264  * RCU grace period.  The caller must hold the specified rnp->lock with
2265  * irqs disabled, and this lock is released upon return, but irqs remain
2266  * disabled.
2267  */
2268 static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2269                                       struct rcu_node *rnp, unsigned long flags)
2270         __releases(rnp->lock)
2271 {
2272         unsigned long gps;
2273         unsigned long mask;
2274         struct rcu_node *rnp_p;
2275 
2276         if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2277             rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2278                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2279                 return;  /* Still need more quiescent states! */
2280         }
2281 
2282         rnp_p = rnp->parent;
2283         if (rnp_p == NULL) {
2284                 /*
2285                  * Only one rcu_node structure in the tree, so don't
2286                  * try to report up to its nonexistent parent!
2287                  */
2288                 rcu_report_qs_rsp(rsp, flags);
2289                 return;
2290         }
2291 
2292         /* Report up the rest of the hierarchy, tracking current ->gpnum. */
2293         gps = rnp->gpnum;
2294         mask = rnp->grpmask;
2295         raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
2296         raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
2297         smp_mb__after_unlock_lock();
2298         rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2299 }
2300 
2301 /*
2302  * Record a quiescent state for the specified CPU to that CPU's rcu_data
2303  * structure.  This must be either called from the specified CPU, or
2304  * called when the specified CPU is known to be offline (and when it is
2305  * also known that no other CPU is concurrently trying to help the offline
2306  * CPU).  The lastcomp argument is used to make sure we are still in the
2307  * grace period of interest.  We don't want to end the current grace period
2308  * based on quiescent states detected in an earlier grace period!
2309  */
2310 static void
2311 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2312 {
2313         unsigned long flags;
2314         unsigned long mask;
2315         bool needwake;
2316         struct rcu_node *rnp;
2317 
2318         rnp = rdp->mynode;
2319         raw_spin_lock_irqsave(&rnp->lock, flags);
2320         smp_mb__after_unlock_lock();
2321         if ((rdp->passed_quiesce == 0 &&
2322              rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
2323             rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
2324             rdp->gpwrap) {
2325 
2326                 /*
2327                  * The grace period in which this quiescent state was
2328                  * recorded has ended, so don't report it upwards.
2329                  * We will instead need a new quiescent state that lies
2330                  * within the current grace period.
2331                  */
2332                 rdp->passed_quiesce = 0;        /* need qs for new gp. */
2333                 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
2334                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2335                 return;
2336         }
2337         mask = rdp->grpmask;
2338         if ((rnp->qsmask & mask) == 0) {
2339                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2340         } else {
2341                 rdp->qs_pending = 0;
2342 
2343                 /*
2344                  * This GP can't end until cpu checks in, so all of our
2345                  * callbacks can be processed during the next GP.
2346                  */
2347                 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2348 
2349                 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2350                 /* ^^^ Released rnp->lock */
2351                 if (needwake)
2352                         rcu_gp_kthread_wake(rsp);
2353         }
2354 }
2355 
2356 /*
2357  * Check to see if there is a new grace period of which this CPU
2358  * is not yet aware, and if so, set up local rcu_data state for it.
2359  * Otherwise, see if this CPU has just passed through its first
2360  * quiescent state for this grace period, and record that fact if so.
2361  */
2362 static void
2363 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2364 {
2365         /* Check for grace-period ends and beginnings. */
2366         note_gp_changes(rsp, rdp);
2367 
2368         /*
2369          * Does this CPU still need to do its part for current grace period?
2370          * If no, return and let the other CPUs do their part as well.
2371          */
2372         if (!rdp->qs_pending)
2373                 return;
2374 
2375         /*
2376          * Was there a quiescent state since the beginning of the grace
2377          * period? If no, then exit and wait for the next call.
2378          */
2379         if (!rdp->passed_quiesce &&
2380             rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
2381                 return;
2382 
2383         /*
2384          * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2385          * judge of that).
2386          */
2387         rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2388 }
2389 
2390 /*
2391  * Send the specified CPU's RCU callbacks to the orphanage.  The
2392  * specified CPU must be offline, and the caller must hold the
2393  * ->orphan_lock.
2394  */
2395 static void
2396 rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
2397                           struct rcu_node *rnp, struct rcu_data *rdp)
2398 {
2399         /* No-CBs CPUs do not have orphanable callbacks. */
2400         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
2401                 return;
2402 
2403         /*
2404          * Orphan the callbacks.  First adjust the counts.  This is safe
2405          * because _rcu_barrier() excludes CPU-hotplug operations, so it
2406          * cannot be running now.  Thus no memory barrier is required.
2407          */
2408         if (rdp->nxtlist != NULL) {
2409                 rsp->qlen_lazy += rdp->qlen_lazy;
2410                 rsp->qlen += rdp->qlen;
2411                 rdp->n_cbs_orphaned += rdp->qlen;
2412                 rdp->qlen_lazy = 0;
2413                 WRITE_ONCE(rdp->qlen, 0);
2414         }
2415 
2416         /*
2417          * Next, move those callbacks still needing a grace period to
2418          * the orphanage, where some other CPU will pick them up.
2419          * Some of the callbacks might have gone partway through a grace
2420          * period, but that is too bad.  They get to start over because we
2421          * cannot assume that grace periods are synchronized across CPUs.
2422          * We don't bother updating the ->nxttail[] array yet, instead
2423          * we just reset the whole thing later on.
2424          */
2425         if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
2426                 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
2427                 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
2428                 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2429         }
2430 
2431         /*
2432          * Then move the ready-to-invoke callbacks to the orphanage,
2433          * where some other CPU will pick them up.  These will not be
2434          * required to pass though another grace period: They are done.
2435          */
2436         if (rdp->nxtlist != NULL) {
2437                 *rsp->orphan_donetail = rdp->nxtlist;
2438                 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2439         }
2440 
2441         /*
2442          * Finally, initialize the rcu_data structure's list to empty and
2443          * disallow further callbacks on this CPU.
2444          */
2445         init_callback_list(rdp);
2446         rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2447 }
2448 
2449 /*
2450  * Adopt the RCU callbacks from the specified rcu_state structure's
2451  * orphanage.  The caller must hold the ->orphan_lock.
2452  */
2453 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2454 {
2455         int i;
2456         struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2457 
2458         /* No-CBs CPUs are handled specially. */
2459         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2460             rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
2461                 return;
2462 
2463         /* Do the accounting first. */
2464         rdp->qlen_lazy += rsp->qlen_lazy;
2465         rdp->qlen += rsp->qlen;
2466         rdp->n_cbs_adopted += rsp->qlen;
2467         if (rsp->qlen_lazy != rsp->qlen)
2468                 rcu_idle_count_callbacks_posted();
2469         rsp->qlen_lazy = 0;
2470         rsp->qlen = 0;
2471 
2472         /*
2473          * We do not need a memory barrier here because the only way we
2474          * can get here if there is an rcu_barrier() in flight is if
2475          * we are the task doing the rcu_barrier().
2476          */
2477 
2478         /* First adopt the ready-to-invoke callbacks. */
2479         if (rsp->orphan_donelist != NULL) {
2480                 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
2481                 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
2482                 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
2483                         if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2484                                 rdp->nxttail[i] = rsp->orphan_donetail;
2485                 rsp->orphan_donelist = NULL;
2486                 rsp->orphan_donetail = &rsp->orphan_donelist;
2487         }
2488 
2489         /* And then adopt the callbacks that still need a grace period. */
2490         if (rsp->orphan_nxtlist != NULL) {
2491                 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
2492                 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
2493                 rsp->orphan_nxtlist = NULL;
2494                 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2495         }
2496 }
2497 
2498 /*
2499  * Trace the fact that this CPU is going offline.
2500  */
2501 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2502 {
2503         RCU_TRACE(unsigned long mask);
2504         RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
2505         RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
2506 
2507         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2508                 return;
2509 
2510         RCU_TRACE(mask = rdp->grpmask);
2511         trace_rcu_grace_period(rsp->name,
2512                                rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2513                                TPS("cpuofl"));
2514 }
2515 
2516 /*
2517  * All CPUs for the specified rcu_node structure have gone offline,
2518  * and all tasks that were preempted within an RCU read-side critical
2519  * section while running on one of those CPUs have since exited their RCU
2520  * read-side critical section.  Some other CPU is reporting this fact with
2521  * the specified rcu_node structure's ->lock held and interrupts disabled.
2522  * This function therefore goes up the tree of rcu_node structures,
2523  * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
2524  * the leaf rcu_node structure's ->qsmaskinit field has already been
2525  * updated
2526  *
2527  * This function does check that the specified rcu_node structure has
2528  * all CPUs offline and no blocked tasks, so it is OK to invoke it
2529  * prematurely.  That said, invoking it after the fact will cost you
2530  * a needless lock acquisition.  So once it has done its work, don't
2531  * invoke it again.
2532  */
2533 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2534 {
2535         long mask;
2536         struct rcu_node *rnp = rnp_leaf;
2537 
2538         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2539             rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2540                 return;
2541         for (;;) {
2542                 mask = rnp->grpmask;
2543                 rnp = rnp->parent;
2544                 if (!rnp)
2545                         break;
2546                 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
2547                 smp_mb__after_unlock_lock(); /* GP memory ordering. */
2548                 rnp->qsmaskinit &= ~mask;
2549                 rnp->qsmask &= ~mask;
2550                 if (rnp->qsmaskinit) {
2551                         raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2552                         return;
2553                 }
2554                 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2555         }
2556 }
2557 
2558 /*
2559  * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
2560  * function.  We now remove it from the rcu_node tree's ->qsmaskinit
2561  * bit masks.
2562  */
2563 static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
2564 {
2565         unsigned long flags;
2566         unsigned long mask;
2567         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2568         struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2569 
2570         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2571                 return;
2572 
2573         /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
2574         mask = rdp->grpmask;
2575         raw_spin_lock_irqsave(&rnp->lock, flags);
2576         smp_mb__after_unlock_lock();    /* Enforce GP memory-order guarantee. */
2577         rnp->qsmaskinitnext &= ~mask;
2578         raw_spin_unlock_irqrestore(&rnp->lock, flags);
2579 }
2580 
2581 /*
2582  * The CPU has been completely removed, and some other CPU is reporting
2583  * this fact from process context.  Do the remainder of the cleanup,
2584  * including orphaning the outgoing CPU's RCU callbacks, and also
2585  * adopting them.  There can only be one CPU hotplug operation at a time,
2586  * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2587  */
2588 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2589 {
2590         unsigned long flags;
2591         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2592         struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */
2593 
2594         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2595                 return;
2596 
2597         /* Adjust any no-longer-needed kthreads. */
2598         rcu_boost_kthread_setaffinity(rnp, -1);
2599 
2600         /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2601         raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2602         rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2603         rcu_adopt_orphan_cbs(rsp, flags);
2604         raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
2605 
2606         WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2607                   "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2608                   cpu, rdp->qlen, rdp->nxtlist);
2609 }
2610 
2611 /*
2612  * Invoke any RCU callbacks that have made it to the end of their grace
2613  * period.  Thottle as specified by rdp->blimit.
2614  */
2615 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2616 {
2617         unsigned long flags;
2618         struct rcu_head *next, *list, **tail;
2619         long bl, count, count_lazy;
2620         int i;
2621 
2622         /* If no callbacks are ready, just return. */
2623         if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2624                 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2625                 trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
2626                                     need_resched(), is_idle_task(current),
2627                                     rcu_is_callbacks_kthread());
2628                 return;
2629         }
2630 
2631         /*
2632          * Extract the list of ready callbacks, disabling to prevent
2633          * races with call_rcu() from interrupt handlers.
2634          */
2635         local_irq_save(flags);
2636         WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2637         bl = rdp->blimit;
2638         trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2639         list = rdp->nxtlist;
2640         rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2641         *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2642         tail = rdp->nxttail[RCU_DONE_TAIL];
2643         for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2644                 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2645                         rdp->nxttail[i] = &rdp->nxtlist;
2646         local_irq_restore(flags);
2647 
2648         /* Invoke callbacks. */
2649         count = count_lazy = 0;
2650         while (list) {
2651                 next = list->next;
2652                 prefetch(next);
2653                 debug_rcu_head_unqueue(list);
2654                 if (__rcu_reclaim(rsp->name, list))
2655                         count_lazy++;
2656                 list = next;
2657                 /* Stop only if limit reached and CPU has something to do. */
2658                 if (++count >= bl &&
2659                     (need_resched() ||
2660                      (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2661                         break;
2662         }
2663 
2664         local_irq_save(flags);
2665         trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2666                             is_idle_task(current),
2667                             rcu_is_callbacks_kthread());
2668 
2669         /* Update count, and requeue any remaining callbacks. */
2670         if (list != NULL) {
2671                 *tail = rdp->nxtlist;
2672                 rdp->nxtlist = list;
2673                 for (i = 0; i < RCU_NEXT_SIZE; i++)
2674                         if (&rdp->nxtlist == rdp->nxttail[i])
2675                                 rdp->nxttail[i] = tail;
2676                         else
2677                                 break;
2678         }
2679         smp_mb(); /* List handling before counting for rcu_barrier(). */
2680         rdp->qlen_lazy -= count_lazy;
2681         WRITE_ONCE(rdp->qlen, rdp->qlen - count);
2682         rdp->n_cbs_invoked += count;
2683 
2684         /* Reinstate batch limit if we have worked down the excess. */
2685         if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2686                 rdp->blimit = blimit;
2687 
2688         /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2689         if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2690                 rdp->qlen_last_fqs_check = 0;
2691                 rdp->n_force_qs_snap = rsp->n_force_qs;
2692         } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2693                 rdp->qlen_last_fqs_check = rdp->qlen;
2694         WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2695 
2696         local_irq_restore(flags);
2697 
2698         /* Re-invoke RCU core processing if there are callbacks remaining. */
2699         if (cpu_has_callbacks_ready_to_invoke(rdp))
2700                 invoke_rcu_core();
2701 }
2702 
2703 /*
2704  * Check to see if this CPU is in a non-context-switch quiescent state
2705  * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2706  * Also schedule RCU core processing.
2707  *
2708  * This function must be called from hardirq context.  It is normally
2709  * invoked from the scheduling-clock interrupt.  If rcu_pending returns
2710  * false, there is no point in invoking rcu_check_callbacks().
2711  */
2712 void rcu_check_callbacks(int user)
2713 {
2714         trace_rcu_utilization(TPS("Start scheduler-tick"));
2715         increment_cpu_stall_ticks();
2716         if (user || rcu_is_cpu_rrupt_from_idle()) {
2717 
2718                 /*
2719                  * Get here if this CPU took its interrupt from user
2720                  * mode or from the idle loop, and if this is not a
2721                  * nested interrupt.  In this case, the CPU is in
2722                  * a quiescent state, so note it.
2723                  *
2724                  * No memory barrier is required here because both
2725                  * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2726                  * variables that other CPUs neither access nor modify,
2727                  * at least not while the corresponding CPU is online.
2728                  */
2729 
2730                 rcu_sched_qs();
2731                 rcu_bh_qs();
2732 
2733         } else if (!in_softirq()) {
2734 
2735                 /*
2736                  * Get here if this CPU did not take its interrupt from
2737                  * softirq, in other words, if it is not interrupting
2738                  * a rcu_bh read-side critical section.  This is an _bh
2739                  * critical section, so note it.
2740                  */
2741 
2742                 rcu_bh_qs();
2743         }
2744         rcu_preempt_check_callbacks();
2745         if (rcu_pending())
2746                 invoke_rcu_core();
2747         if (user)
2748                 rcu_note_voluntary_context_switch(current);
2749         trace_rcu_utilization(TPS("End scheduler-tick"));
2750 }
2751 
2752 /*
2753  * Scan the leaf rcu_node structures, processing dyntick state for any that
2754  * have not yet encountered a quiescent state, using the function specified.
2755  * Also initiate boosting for any threads blocked on the root rcu_node.
2756  *
2757  * The caller must have suppressed start of new grace periods.
2758  */
2759 static void force_qs_rnp(struct rcu_state *rsp,
2760                          int (*f)(struct rcu_data *rsp, bool *isidle,
2761                                   unsigned long *maxj),
2762                          bool *isidle, unsigned long *maxj)
2763 {
2764         unsigned long bit;
2765         int cpu;
2766         unsigned long flags;
2767         unsigned long mask;
2768         struct rcu_node *rnp;
2769 
2770         rcu_for_each_leaf_node(rsp, rnp) {
2771                 cond_resched_rcu_qs();
2772                 mask = 0;
2773                 raw_spin_lock_irqsave(&rnp->lock, flags);
2774                 smp_mb__after_unlock_lock();
2775                 if (rnp->qsmask == 0) {
2776                         if (rcu_state_p == &rcu_sched_state ||
2777                             rsp != rcu_state_p ||
2778                             rcu_preempt_blocked_readers_cgp(rnp)) {
2779                                 /*
2780                                  * No point in scanning bits because they
2781                                  * are all zero.  But we might need to
2782                                  * priority-boost blocked readers.
2783                                  */
2784                                 rcu_initiate_boost(rnp, flags);
2785                                 /* rcu_initiate_boost() releases rnp->lock */
2786                                 continue;
2787                         }
2788                         if (rnp->parent &&
2789                             (rnp->parent->qsmask & rnp->grpmask)) {
2790                                 /*
2791                                  * Race between grace-period
2792                                  * initialization and task exiting RCU
2793                                  * read-side critical section: Report.
2794                                  */
2795                                 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2796                                 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2797                                 continue;
2798                         }
2799                 }
2800                 cpu = rnp->grplo;
2801                 bit = 1;
2802                 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2803                         if ((rnp->qsmask & bit) != 0) {
2804                                 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2805                                         mask |= bit;
2806                         }
2807                 }
2808                 if (mask != 0) {
2809                         /* Idle/offline CPUs, report (releases rnp->lock. */
2810                         rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2811                 } else {
2812                         /* Nothing to do here, so just drop the lock. */
2813                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
2814                 }
2815         }
2816 }
2817 
2818 /*
2819  * Force quiescent states on reluctant CPUs, and also detect which
2820  * CPUs are in dyntick-idle mode.
2821  */
2822 static void force_quiescent_state(struct rcu_state *rsp)
2823 {
2824         unsigned long flags;
2825         bool ret;
2826         struct rcu_node *rnp;
2827         struct rcu_node *rnp_old = NULL;
2828 
2829         /* Funnel through hierarchy to reduce memory contention. */
2830         rnp = __this_cpu_read(rsp->rda->mynode);
2831         for (; rnp != NULL; rnp = rnp->parent) {
2832                 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2833                       !raw_spin_trylock(&rnp->fqslock);
2834                 if (rnp_old != NULL)
2835                         raw_spin_unlock(&rnp_old->fqslock);
2836                 if (ret) {
2837                         rsp->n_force_qs_lh++;
2838                         return;
2839                 }
2840                 rnp_old = rnp;
2841         }
2842         /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2843 
2844         /* Reached the root of the rcu_node tree, acquire lock. */
2845         raw_spin_lock_irqsave(&rnp_old->lock, flags);
2846         smp_mb__after_unlock_lock();
2847         raw_spin_unlock(&rnp_old->fqslock);
2848         if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2849                 rsp->n_force_qs_lh++;
2850                 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2851                 return;  /* Someone beat us to it. */
2852         }
2853         WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2854         raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2855         rcu_gp_kthread_wake(rsp);
2856 }
2857 
2858 /*
2859  * This does the RCU core processing work for the specified rcu_state
2860  * and rcu_data structures.  This may be called only from the CPU to
2861  * whom the rdp belongs.
2862  */
2863 static void
2864 __rcu_process_callbacks(struct rcu_state *rsp)
2865 {
2866         unsigned long flags;
2867         bool needwake;
2868         struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2869 
2870         WARN_ON_ONCE(rdp->beenonline == 0);
2871 
2872         /* Update RCU state based on any recent quiescent states. */
2873         rcu_check_quiescent_state(rsp, rdp);
2874 
2875         /* Does this CPU require a not-yet-started grace period? */
2876         local_irq_save(flags);
2877         if (cpu_needs_another_gp(rsp, rdp)) {
2878                 raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2879                 needwake = rcu_start_gp(rsp);
2880                 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2881                 if (needwake)
2882                         rcu_gp_kthread_wake(rsp);
2883         } else {
2884                 local_irq_restore(flags);
2885         }
2886 
2887         /* If there are callbacks ready, invoke them. */
2888         if (cpu_has_callbacks_ready_to_invoke(rdp))
2889                 invoke_rcu_callbacks(rsp, rdp);
2890 
2891         /* Do any needed deferred wakeups of rcuo kthreads. */
2892         do_nocb_deferred_wakeup(rdp);
2893 }
2894 
2895 /*
2896  * Do RCU core processing for the current CPU.
2897  */
2898 static void rcu_process_callbacks(struct softirq_action *unused)
2899 {
2900         struct rcu_state *rsp;
2901 
2902         if (cpu_is_offline(smp_processor_id()))
2903                 return;
2904         trace_rcu_utilization(TPS("Start RCU core"));
2905         for_each_rcu_flavor(rsp)
2906                 __rcu_process_callbacks(rsp);
2907         trace_rcu_utilization(TPS("End RCU core"));
2908 }
2909 
2910 /*
2911  * Schedule RCU callback invocation.  If the specified type of RCU
2912  * does not support RCU priority boosting, just do a direct call,
2913  * otherwise wake up the per-CPU kernel kthread.  Note that because we
2914  * are running on the current CPU with softirqs disabled, the
2915  * rcu_cpu_kthread_task cannot disappear out from under us.
2916  */
2917 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2918 {
2919         if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2920                 return;
2921         if (likely(!rsp->boost)) {
2922                 rcu_do_batch(rsp, rdp);
2923                 return;
2924         }
2925         invoke_rcu_callbacks_kthread();
2926 }
2927 
2928 static void invoke_rcu_core(void)
2929 {
2930         if (cpu_online(smp_processor_id()))
2931                 raise_softirq(RCU_SOFTIRQ);
2932 }
2933 
2934 /*
2935  * Handle any core-RCU processing required by a call_rcu() invocation.
2936  */
2937 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2938                             struct rcu_head *head, unsigned long flags)
2939 {
2940         bool needwake;
2941 
2942         /*
2943          * If called from an extended quiescent state, invoke the RCU
2944          * core in order to force a re-evaluation of RCU's idleness.
2945          */
2946         if (!rcu_is_watching())
2947                 invoke_rcu_core();
2948 
2949         /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2950         if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2951                 return;
2952 
2953         /*
2954          * Force the grace period if too many callbacks or too long waiting.
2955          * Enforce hysteresis, and don't invoke force_quiescent_state()
2956          * if some other CPU has recently done so.  Also, don't bother
2957          * invoking force_quiescent_state() if the newly enqueued callback
2958          * is the only one waiting for a grace period to complete.
2959          */
2960         if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2961 
2962                 /* Are we ignoring a completed grace period? */
2963                 note_gp_changes(rsp, rdp);
2964 
2965                 /* Start a new grace period if one not already started. */
2966                 if (!rcu_gp_in_progress(rsp)) {
2967                         struct rcu_node *rnp_root = rcu_get_root(rsp);
2968 
2969                         raw_spin_lock(&rnp_root->lock);
2970                         smp_mb__after_unlock_lock();
2971                         needwake = rcu_start_gp(rsp);
2972                         raw_spin_unlock(&rnp_root->lock);
2973                         if (needwake)
2974                                 rcu_gp_kthread_wake(rsp);
2975                 } else {
2976                         /* Give the grace period a kick. */
2977                         rdp->blimit = LONG_MAX;
2978                         if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2979                             *rdp->nxttail[RCU_DONE_TAIL] != head)
2980                                 force_quiescent_state(rsp);
2981                         rdp->n_force_qs_snap = rsp->n_force_qs;
2982                         rdp->qlen_last_fqs_check = rdp->qlen;
2983                 }
2984         }
2985 }
2986 
2987 /*
2988  * RCU callback function to leak a callback.
2989  */
2990 static void rcu_leak_callback(struct rcu_head *rhp)
2991 {
2992 }
2993 
2994 /*
2995  * Helper function for call_rcu() and friends.  The cpu argument will
2996  * normally be -1, indicating "currently running CPU".  It may specify
2997  * a CPU only if that CPU is a no-CBs CPU.  Currently, only _rcu_barrier()
2998  * is expected to specify a CPU.
2999  */
3000 static void
3001 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
3002            struct rcu_state *rsp, int cpu, bool lazy)
3003 {
3004         unsigned long flags;
3005         struct rcu_data *rdp;
3006 
3007         WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
3008         if (debug_rcu_head_queue(head)) {
3009                 /* Probable double call_rcu(), so leak the callback. */
3010                 WRITE_ONCE(head->func, rcu_leak_callback);
3011                 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
3012                 return;
3013         }
3014         head->func = func;
3015         head->next = NULL;
3016 
3017         /*
3018          * Opportunistically note grace-period endings and beginnings.
3019          * Note that we might see a beginning right after we see an
3020          * end, but never vice versa, since this CPU has to pass through
3021          * a quiescent state betweentimes.
3022          */
3023         local_irq_save(flags);
3024         rdp = this_cpu_ptr(rsp->rda);
3025 
3026         /* Add the callback to our list. */
3027         if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
3028                 int offline;
3029 
3030                 if (cpu != -1)
3031                         rdp = per_cpu_ptr(rsp->rda, cpu);
3032                 if (likely(rdp->mynode)) {
3033                         /* Post-boot, so this should be for a no-CBs CPU. */
3034                         offline = !__call_rcu_nocb(rdp, head, lazy, flags);
3035                         WARN_ON_ONCE(offline);
3036                         /* Offline CPU, _call_rcu() illegal, leak callback.  */
3037                         local_irq_restore(flags);
3038                         return;
3039                 }
3040                 /*
3041                  * Very early boot, before rcu_init().  Initialize if needed
3042                  * and then drop through to queue the callback.
3043                  */
3044                 BUG_ON(cpu != -1);
3045                 WARN_ON_ONCE(!rcu_is_watching());
3046                 if (!likely(rdp->nxtlist))
3047                         init_default_callback_list(rdp);
3048         }
3049         WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
3050         if (lazy)
3051                 rdp->qlen_lazy++;
3052         else
3053                 rcu_idle_count_callbacks_posted();
3054         smp_mb();  /* Count before adding callback for rcu_barrier(). */
3055         *rdp->nxttail[RCU_NEXT_TAIL] = head;
3056         rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
3057 
3058         if (__is_kfree_rcu_offset((unsigned long)func))
3059                 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3060                                          rdp->qlen_lazy, rdp->qlen);
3061         else
3062                 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
3063 
3064         /* Go handle any RCU core processing required. */
3065         __call_rcu_core(rsp, rdp, head, flags);
3066         local_irq_restore(flags);
3067 }
3068 
3069 /*
3070  * Queue an RCU-sched callback for invocation after a grace period.
3071  */
3072 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
3073 {
3074         __call_rcu(head, func, &rcu_sched_state, -1, 0);
3075 }
3076 EXPORT_SYMBOL_GPL(call_rcu_sched);
3077 
3078 /*
3079  * Queue an RCU callback for invocation after a quicker grace period.
3080  */
3081 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
3082 {
3083         __call_rcu(head, func, &rcu_bh_state, -1, 0);
3084 }
3085 EXPORT_SYMBOL_GPL(call_rcu_bh);
3086 
3087 /*
3088  * Queue an RCU callback for lazy invocation after a grace period.
3089  * This will likely be later named something like "call_rcu_lazy()",
3090  * but this change will require some way of tagging the lazy RCU
3091  * callbacks in the list of pending callbacks. Until then, this
3092  * function may only be called from __kfree_rcu().
3093  */
3094 void kfree_call_rcu(struct rcu_head *head,
3095                     void (*func)(struct rcu_head *rcu))
3096 {
3097         __call_rcu(head, func, rcu_state_p, -1, 1);
3098 }
3099 EXPORT_SYMBOL_GPL(kfree_call_rcu);
3100 
3101 /*
3102  * Because a context switch is a grace period for RCU-sched and RCU-bh,
3103  * any blocking grace-period wait automatically implies a grace period
3104  * if there is only one CPU online at any point time during execution
3105  * of either synchronize_sched() or synchronize_rcu_bh().  It is OK to
3106  * occasionally incorrectly indicate that there are multiple CPUs online
3107  * when there was in fact only one the whole time, as this just adds
3108  * some overhead: RCU still operates correctly.
3109  */
3110 static inline int rcu_blocking_is_gp(void)
3111 {
3112         int ret;
3113 
3114         might_sleep();  /* Check for RCU read-side critical section. */
3115         preempt_disable();
3116         ret = num_online_cpus() <= 1;
3117         preempt_enable();
3118         return ret;
3119 }
3120 
3121 /**
3122  * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3123  *
3124  * Control will return to the caller some time after a full rcu-sched
3125  * grace period has elapsed, in other words after all currently executing
3126  * rcu-sched read-side critical sections have completed.   These read-side
3127  * critical sections are delimited by rcu_read_lock_sched() and
3128  * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
3129  * local_irq_disable(), and so on may be used in place of
3130  * rcu_read_lock_sched().
3131  *
3132  * This means that all preempt_disable code sequences, including NMI and
3133  * non-threaded hardware-interrupt handlers, in progress on entry will
3134  * have completed before this primitive returns.  However, this does not
3135  * guarantee that softirq handlers will have completed, since in some
3136  * kernels, these handlers can run in process context, and can block.
3137  *
3138  * Note that this guarantee implies further memory-ordering guarantees.
3139  * On systems with more than one CPU, when synchronize_sched() returns,
3140  * each CPU is guaranteed to have executed a full memory barrier since the
3141  * end of its last RCU-sched read-side critical section whose beginning
3142  * preceded the call to synchronize_sched().  In addition, each CPU having
3143  * an RCU read-side critical section that extends beyond the return from
3144  * synchronize_sched() is guaranteed to have executed a full memory barrier
3145  * after the beginning of synchronize_sched() and before the beginning of
3146  * that RCU read-side critical section.  Note that these guarantees include
3147  * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3148  * that are executing in the kernel.
3149  *
3150  * Furthermore, if CPU A invoked synchronize_sched(), which returned
3151  * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3152  * to have executed a full memory barrier during the execution of
3153  * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3154  * again only if the system has more than one CPU).
3155  *
3156  * This primitive provides the guarantees made by the (now removed)
3157  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
3158  * guarantees that rcu_read_lock() sections will have completed.
3159  * In "classic RCU", these two guarantees happen to be one and
3160  * the same, but can differ in realtime RCU implementations.
3161  */
3162 void synchronize_sched(void)
3163 {
3164         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
3165                            !lock_is_held(&rcu_lock_map) &&
3166                            !lock_is_held(&rcu_sched_lock_map),
3167                            "Illegal synchronize_sched() in RCU-sched read-side critical section");
3168         if (rcu_blocking_is_gp())
3169                 return;
3170         if (rcu_gp_is_expedited())
3171                 synchronize_sched_expedited();
3172         else
3173                 wait_rcu_gp(call_rcu_sched);
3174 }
3175 EXPORT_SYMBOL_GPL(synchronize_sched);
3176 
3177 /**
3178  * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3179  *
3180  * Control will return to the caller some time after a full rcu_bh grace
3181  * period has elapsed, in other words after all currently executing rcu_bh
3182  * read-side critical sections have completed.  RCU read-side critical
3183  * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3184  * and may be nested.
3185  *
3186  * See the description of synchronize_sched() for more detailed information
3187  * on memory ordering guarantees.
3188  */
3189 void synchronize_rcu_bh(void)
3190 {
3191         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
3192                            !lock_is_held(&rcu_lock_map) &&
3193                            !lock_is_held(&rcu_sched_lock_map),
3194                            "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3195         if (rcu_blocking_is_gp())
3196                 return;
3197         if (rcu_gp_is_expedited())
3198                 synchronize_rcu_bh_expedited();
3199         else
3200                 wait_rcu_gp(call_rcu_bh);
3201 }
3202 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3203 
3204 /**
3205  * get_state_synchronize_rcu - Snapshot current RCU state
3206  *
3207  * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3208  * to determine whether or not a full grace period has elapsed in the
3209  * meantime.
3210  */
3211 unsigned long get_state_synchronize_rcu(void)
3212 {
3213         /*
3214          * Any prior manipulation of RCU-protected data must happen
3215          * before the load from ->gpnum.
3216          */
3217         smp_mb();  /* ^^^ */
3218 
3219         /*
3220          * Make sure this load happens before the purportedly
3221          * time-consuming work between get_state_synchronize_rcu()
3222          * and cond_synchronize_rcu().
3223          */
3224         return smp_load_acquire(&rcu_state_p->gpnum);
3225 }
3226 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3227 
3228 /**
3229  * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3230  *
3231  * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3232  *
3233  * If a full RCU grace period has elapsed since the earlier call to
3234  * get_state_synchronize_rcu(), just return.  Otherwise, invoke
3235  * synchronize_rcu() to wait for a full grace period.
3236  *
3237  * Yes, this function does not take counter wrap into account.  But
3238  * counter wrap is harmless.  If the counter wraps, we have waited for
3239  * more than 2 billion grace periods (and way more on a 64-bit system!),
3240  * so waiting for one additional grace period should be just fine.
3241  */
3242 void cond_synchronize_rcu(unsigned long oldstate)
3243 {
3244         unsigned long newstate;
3245 
3246         /*
3247          * Ensure that this load happens before any RCU-destructive
3248          * actions the caller might carry out after we return.
3249          */
3250         newstate = smp_load_acquire(&rcu_state_p->completed);
3251         if (ULONG_CMP_GE(oldstate, newstate))
3252                 synchronize_rcu();
3253 }
3254 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3255 
3256 static int synchronize_sched_expedited_cpu_stop(void *data)
3257 {
3258         /*
3259          * There must be a full memory barrier on each affected CPU
3260          * between the time that try_stop_cpus() is called and the
3261          * time that it returns.
3262          *
3263          * In the current initial implementation of cpu_stop, the
3264          * above condition is already met when the control reaches
3265          * this point and the following smp_mb() is not strictly
3266          * necessary.  Do smp_mb() anyway for documentation and
3267          * robustness against future implementation changes.
3268          */
3269         smp_mb(); /* See above comment block. */
3270         return 0;
3271 }
3272 
3273 /**
3274  * synchronize_sched_expedited - Brute-force RCU-sched grace period
3275  *
3276  * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
3277  * approach to force the grace period to end quickly.  This consumes
3278  * significant time on all CPUs and is unfriendly to real-time workloads,
3279  * so is thus not recommended for any sort of common-case code.  In fact,
3280  * if you are using synchronize_sched_expedited() in a loop, please
3281  * restructure your code to batch your updates, and then use a single
3282  * synchronize_sched() instead.
3283  *
3284  * This implementation can be thought of as an application of ticket
3285  * locking to RCU, with sync_sched_expedited_started and
3286  * sync_sched_expedited_done taking on the roles of the halves
3287  * of the ticket-lock word.  Each task atomically increments
3288  * sync_sched_expedited_started upon entry, snapshotting the old value,
3289  * then attempts to stop all the CPUs.  If this succeeds, then each
3290  * CPU will have executed a context switch, resulting in an RCU-sched
3291  * grace period.  We are then done, so we use atomic_cmpxchg() to
3292  * update sync_sched_expedited_done to match our snapshot -- but
3293  * only if someone else has not already advanced past our snapshot.
3294  *
3295  * On the other hand, if try_stop_cpus() fails, we check the value
3296  * of sync_sched_expedited_done.  If it has advanced past our
3297  * initial snapshot, then someone else must have forced a grace period
3298  * some time after we took our snapshot.  In this case, our work is
3299  * done for us, and we can simply return.  Otherwise, we try again,
3300  * but keep our initial snapshot for purposes of checking for someone
3301  * doing our work for us.
3302  *
3303  * If we fail too many times in a row, we fall back to synchronize_sched().
3304  */
3305 void synchronize_sched_expedited(void)
3306 {
3307         cpumask_var_t cm;
3308         bool cma = false;
3309         int cpu;
3310         long firstsnap, s, snap;
3311         int trycount = 0;
3312         struct rcu_state *rsp = &rcu_sched_state;
3313 
3314         /*
3315          * If we are in danger of counter wrap, just do synchronize_sched().
3316          * By allowing sync_sched_expedited_started to advance no more than
3317          * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
3318          * that more than 3.5 billion CPUs would be required to force a
3319          * counter wrap on a 32-bit system.  Quite a few more CPUs would of
3320          * course be required on a 64-bit system.
3321          */
3322         if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
3323                          (ulong)atomic_long_read(&rsp->expedited_done) +
3324                          ULONG_MAX / 8)) {
3325                 wait_rcu_gp(call_rcu_sched);
3326                 atomic_long_inc(&rsp->expedited_wrap);
3327                 return;
3328         }
3329 
3330         /*
3331          * Take a ticket.  Note that atomic_inc_return() implies a
3332          * full memory barrier.
3333          */
3334         snap = atomic_long_inc_return(&rsp->expedited_start);
3335         firstsnap = snap;
3336         if (!try_get_online_cpus()) {
3337                 /* CPU hotplug operation in flight, fall back to normal GP. */
3338                 wait_rcu_gp(call_rcu_sched);
3339                 atomic_long_inc(&rsp->expedited_normal);
3340                 return;
3341         }
3342         WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
3343 
3344         /* Offline CPUs, idle CPUs, and any CPU we run on are quiescent. */
3345         cma = zalloc_cpumask_var(&cm, GFP_KERNEL);
3346         if (cma) {
3347                 cpumask_copy(cm, cpu_online_mask);
3348                 cpumask_clear_cpu(raw_smp_processor_id(), cm);
3349                 for_each_cpu(cpu, cm) {
3350                         struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
3351 
3352                         if (!(atomic_add_return(0, &rdtp->dynticks) & 0x1))
3353                                 cpumask_clear_cpu(cpu, cm);
3354                 }
3355                 if (cpumask_weight(cm) == 0)
3356                         goto all_cpus_idle;
3357         }
3358 
3359         /*
3360          * Each pass through the following loop attempts to force a
3361          * context switch on each CPU.
3362          */
3363         while (try_stop_cpus(cma ? cm : cpu_online_mask,
3364                              synchronize_sched_expedited_cpu_stop,
3365                              NULL) == -EAGAIN) {
3366                 put_online_cpus();
3367                 atomic_long_inc(&rsp->expedited_tryfail);
3368 
3369                 /* Check to see if someone else did our work for us. */
3370                 s = atomic_long_read(&rsp->expedited_done);
3371                 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3372                         /* ensure test happens before caller kfree */
3373                         smp_mb__before_atomic(); /* ^^^ */
3374                         atomic_long_inc(&rsp->expedited_workdone1);
3375                         free_cpumask_var(cm);
3376                         return;
3377                 }
3378 
3379                 /* No joy, try again later.  Or just synchronize_sched(). */
3380                 if (trycount++ < 10) {
3381                         udelay(trycount * num_online_cpus());
3382                 } else {
3383                         wait_rcu_gp(call_rcu_sched);
3384                         atomic_long_inc(&rsp->expedited_normal);
3385                         free_cpumask_var(cm);
3386                         return;
3387                 }
3388 
3389                 /* Recheck to see if someone else did our work for us. */
3390                 s = atomic_long_read(&rsp->expedited_done);
3391                 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
3392                         /* ensure test happens before caller kfree */
3393                         smp_mb__before_atomic(); /* ^^^ */
3394                         atomic_long_inc(&rsp->expedited_workdone2);
3395                         free_cpumask_var(cm);
3396                         return;
3397                 }
3398 
3399                 /*
3400                  * Refetching sync_sched_expedited_started allows later
3401                  * callers to piggyback on our grace period.  We retry
3402                  * after they started, so our grace period works for them,
3403                  * and they started after our first try, so their grace
3404                  * period works for us.
3405                  */
3406                 if (!try_get_online_cpus()) {
3407                         /* CPU hotplug operation in flight, use normal GP. */
3408                         wait_rcu_gp(call_rcu_sched);
3409                         atomic_long_inc(&rsp->expedited_normal);
3410                         free_cpumask_var(cm);
3411                         return;
3412                 }
3413                 snap = atomic_long_read(&rsp->expedited_start);
3414                 smp_mb(); /* ensure read is before try_stop_cpus(). */
3415         }
3416         atomic_long_inc(&rsp->expedited_stoppedcpus);
3417 
3418 all_cpus_idle:
3419         free_cpumask_var(cm);
3420 
3421         /*
3422          * Everyone up to our most recent fetch is covered by our grace
3423          * period.  Update the counter, but only if our work is still
3424          * relevant -- which it won't be if someone who started later
3425          * than we did already did their update.
3426          */
3427         do {
3428                 atomic_long_inc(&rsp->expedited_done_tries);
3429                 s = atomic_long_read(&rsp->expedited_done);
3430                 if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
3431                         /* ensure test happens before caller kfree */
3432                         smp_mb__before_atomic(); /* ^^^ */
3433                         atomic_long_inc(&rsp->expedited_done_lost);
3434                         break;
3435                 }
3436         } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
3437         atomic_long_inc(&rsp->expedited_done_exit);
3438 
3439         put_online_cpus();
3440 }
3441 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
3442 
3443 /*
3444  * Check to see if there is any immediate RCU-related work to be done
3445  * by the current CPU, for the specified type of RCU, returning 1 if so.
3446  * The checks are in order of increasing expense: checks that can be
3447  * carried out against CPU-local state are performed first.  However,
3448  * we must check for CPU stalls first, else we might not get a chance.
3449  */
3450 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3451 {
3452         struct rcu_node *rnp = rdp->mynode;
3453 
3454         rdp->n_rcu_pending++;
3455 
3456         /* Check for CPU stalls, if enabled. */
3457         check_cpu_stall(rsp, rdp);
3458 
3459         /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3460         if (rcu_nohz_full_cpu(rsp))
3461                 return 0;
3462 
3463         /* Is the RCU core waiting for a quiescent state from this CPU? */
3464         if (rcu_scheduler_fully_active &&
3465             rdp->qs_pending && !rdp->passed_quiesce &&
3466             rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
3467                 rdp->n_rp_qs_pending++;
3468         } else if (rdp->qs_pending &&
3469                    (rdp->passed_quiesce ||
3470                     rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
3471                 rdp->n_rp_report_qs++;
3472                 return 1;
3473         }
3474 
3475         /* Does this CPU have callbacks ready to invoke? */
3476         if (cpu_has_callbacks_ready_to_invoke(rdp)) {
3477                 rdp->n_rp_cb_ready++;
3478                 return 1;
3479         }
3480 
3481         /* Has RCU gone idle with this CPU needing another grace period? */
3482         if (cpu_needs_another_gp(rsp, rdp)) {
3483                 rdp->n_rp_cpu_needs_gp++;
3484                 return 1;
3485         }
3486 
3487         /* Has another RCU grace period completed?  */
3488         if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3489                 rdp->n_rp_gp_completed++;
3490                 return 1;
3491         }
3492 
3493         /* Has a new RCU grace period started? */
3494         if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
3495             unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
3496                 rdp->n_rp_gp_started++;
3497                 return 1;
3498         }
3499 
3500         /* Does this CPU need a deferred NOCB wakeup? */
3501         if (rcu_nocb_need_deferred_wakeup(rdp)) {
3502                 rdp->n_rp_nocb_defer_wakeup++;
3503                 return 1;
3504         }
3505 
3506         /* nothing to do */
3507         rdp->n_rp_need_nothing++;
3508         return 0;
3509 }
3510 
3511 /*
3512  * Check to see if there is any immediate RCU-related work to be done
3513  * by the current CPU, returning 1 if so.  This function is part of the
3514  * RCU implementation; it is -not- an exported member of the RCU API.
3515  */
3516 static int rcu_pending(void)
3517 {
3518         struct rcu_state *rsp;
3519 
3520         for_each_rcu_flavor(rsp)
3521                 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3522                         return 1;
3523         return 0;
3524 }
3525 
3526 /*
3527  * Return true if the specified CPU has any callback.  If all_lazy is
3528  * non-NULL, store an indication of whether all callbacks are lazy.
3529  * (If there are no callbacks, all of them are deemed to be lazy.)
3530  */
3531 static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3532 {
3533         bool al = true;
3534         bool hc = false;
3535         struct rcu_data *rdp;
3536         struct rcu_state *rsp;
3537 
3538         for_each_rcu_flavor(rsp) {
3539                 rdp = this_cpu_ptr(rsp->rda);
3540                 if (!rdp->nxtlist)
3541                         continue;
3542                 hc = true;
3543                 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3544                         al = false;
3545                         break;
3546                 }
3547         }
3548         if (all_lazy)
3549                 *all_lazy = al;
3550         return hc;
3551 }
3552 
3553 /*
3554  * Helper function for _rcu_barrier() tracing.  If tracing is disabled,
3555  * the compiler is expected to optimize this away.
3556  */
3557 static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3558                                int cpu, unsigned long done)
3559 {
3560         trace_rcu_barrier(rsp->name, s, cpu,
3561                           atomic_read(&rsp->barrier_cpu_count), done);
3562 }
3563 
3564 /*
3565  * RCU callback function for _rcu_barrier().  If we are last, wake
3566  * up the task executing _rcu_barrier().
3567  */
3568 static void rcu_barrier_callback(struct rcu_head *rhp)
3569 {
3570         struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3571         struct rcu_state *rsp = rdp->rsp;
3572 
3573         if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
3574                 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
3575                 complete(&rsp->barrier_completion);
3576         } else {
3577                 _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
3578         }
3579 }
3580 
3581 /*
3582  * Called with preemption disabled, and from cross-cpu IRQ context.
3583  */
3584 static void rcu_barrier_func(void *type)
3585 {
3586         struct rcu_state *rsp = type;
3587         struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3588 
3589         _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3590         atomic_inc(&rsp->barrier_cpu_count);
3591         rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3592 }
3593 
3594 /*
3595  * Orchestrate the specified type of RCU barrier, waiting for all
3596  * RCU callbacks of the specified type to complete.
3597  */
3598 static void _rcu_barrier(struct rcu_state *rsp)
3599 {
3600         int cpu;
3601         struct rcu_data *rdp;
3602         unsigned long snap = READ_ONCE(rsp->n_barrier_done);
3603         unsigned long snap_done;
3604 
3605         _rcu_barrier_trace(rsp, "Begin", -1, snap);
3606 
3607         /* Take mutex to serialize concurrent rcu_barrier() requests. */
3608         mutex_lock(&rsp->barrier_mutex);
3609 
3610         /*
3611          * Ensure that all prior references, including to ->n_barrier_done,
3612          * are ordered before the _rcu_barrier() machinery.
3613          */
3614         smp_mb();  /* See above block comment. */
3615 
3616         /*
3617          * Recheck ->n_barrier_done to see if others did our work for us.
3618          * This means checking ->n_barrier_done for an even-to-odd-to-even
3619          * transition.  The "if" expression below therefore rounds the old
3620          * value up to the next even number and adds two before comparing.
3621          */
3622         snap_done = rsp->n_barrier_done;
3623         _rcu_barrier_trace(rsp, "Check", -1, snap_done);
3624 
3625         /*
3626          * If the value in snap is odd, we needed to wait for the current
3627          * rcu_barrier() to complete, then wait for the next one, in other
3628          * words, we need the value of snap_done to be three larger than
3629          * the value of snap.  On the other hand, if the value in snap is
3630          * even, we only had to wait for the next rcu_barrier() to complete,
3631          * in other words, we need the value of snap_done to be only two
3632          * greater than the value of snap.  The "(snap + 3) & ~0x1" computes
3633          * this for us (thank you, Linus!).
3634          */
3635         if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
3636                 _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3637                 smp_mb(); /* caller's subsequent code after above check. */
3638                 mutex_unlock(&rsp->barrier_mutex);
3639                 return;
3640         }
3641 
3642         /*
3643          * Increment ->n_barrier_done to avoid duplicate work.  Use
3644          * WRITE_ONCE() to prevent the compiler from speculating
3645          * the increment to precede the early-exit check.
3646          */
3647         WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1);
3648         WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3649         _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3650         smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3651 
3652         /*
3653          * Initialize the count to one rather than to zero in order to
3654          * avoid a too-soon return to zero in case of a short grace period
3655          * (or preemption of this task).  Exclude CPU-hotplug operations
3656          * to ensure that no offline CPU has callbacks queued.
3657          */
3658         init_completion(&rsp->barrier_completion);
3659         atomic_set(&rsp->barrier_cpu_count, 1);
3660         get_online_cpus();
3661 
3662         /*
3663          * Force each CPU with callbacks to register a new callback.
3664          * When that callback is invoked, we will know that all of the
3665          * corresponding CPU's preceding callbacks have been invoked.
3666          */
3667         for_each_possible_cpu(cpu) {
3668                 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3669                         continue;
3670                 rdp = per_cpu_ptr(rsp->rda, cpu);
3671                 if (rcu_is_nocb_cpu(cpu)) {
3672                         if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
3673                                 _rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
3674                                                    rsp->n_barrier_done);
3675                         } else {
3676                                 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
3677                                                    rsp->n_barrier_done);
3678                                 smp_mb__before_atomic();
3679                                 atomic_inc(&rsp->barrier_cpu_count);
3680                                 __call_rcu(&rdp->barrier_head,
3681                                            rcu_barrier_callback, rsp, cpu, 0);
3682                         }
3683                 } else if (READ_ONCE(rdp->qlen)) {
3684                         _rcu_barrier_trace(rsp, "OnlineQ", cpu,
3685                                            rsp->n_barrier_done);
3686                         smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3687                 } else {
3688                         _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
3689                                            rsp->n_barrier_done);
3690                 }
3691         }
3692         put_online_cpus();
3693 
3694         /*
3695          * Now that we have an rcu_barrier_callback() callback on each
3696          * CPU, and thus each counted, remove the initial count.
3697          */
3698         if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3699                 complete(&rsp->barrier_completion);
3700 
3701         /* Increment ->n_barrier_done to prevent duplicate work. */
3702         smp_mb(); /* Keep increment after above mechanism. */
3703         WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1);
3704         WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3705         _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3706         smp_mb(); /* Keep increment before caller's subsequent code. */
3707 
3708         /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3709         wait_for_completion(&rsp->barrier_completion);
3710 
3711         /* Other rcu_barrier() invocations can now safely proceed. */
3712         mutex_unlock(&rsp->barrier_mutex);
3713 }
3714 
3715 /**
3716  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3717  */
3718 void rcu_barrier_bh(void)
3719 {
3720         _rcu_barrier(&rcu_bh_state);
3721 }
3722 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3723 
3724 /**
3725  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3726  */
3727 void rcu_barrier_sched(void)
3728 {
3729         _rcu_barrier(&rcu_sched_state);
3730 }
3731 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3732 
3733 /*
3734  * Propagate ->qsinitmask bits up the rcu_node tree to account for the
3735  * first CPU in a given leaf rcu_node structure coming online.  The caller
3736  * must hold the corresponding leaf rcu_node ->lock with interrrupts
3737  * disabled.
3738  */
3739 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
3740 {
3741         long mask;
3742         struct rcu_node *rnp = rnp_leaf;
3743 
3744         for (;;) {
3745                 mask = rnp->grpmask;
3746                 rnp = rnp->parent;
3747                 if (rnp == NULL)
3748                         return;
3749                 raw_spin_lock(&rnp->lock); /* Interrupts already disabled. */
3750                 rnp->qsmaskinit |= mask;
3751                 raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */
3752         }
3753 }
3754 
3755 /*
3756  * Do boot-time initialization of a CPU's per-CPU RCU data.
3757  */
3758 static void __init
3759 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3760 {
3761         unsigned long flags;
3762         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3763         struct rcu_node *rnp = rcu_get_root(rsp);
3764 
3765         /* Set up local state, ensuring consistent view of global state. */
3766         raw_spin_lock_irqsave(&rnp->lock, flags);
3767         rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3768         rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3769         WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3770         WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3771         rdp->cpu = cpu;
3772         rdp->rsp = rsp;
3773         rcu_boot_init_nocb_percpu_data(rdp);
3774         raw_spin_unlock_irqrestore(&rnp->lock, flags);
3775 }
3776 
3777 /*
3778  * Initialize a CPU's per-CPU RCU data.  Note that only one online or
3779  * offline event can be happening at a given time.  Note also that we
3780  * can accept some slop in the rsp->completed access due to the fact
3781  * that this CPU cannot possibly have any RCU callbacks in flight yet.
3782  */
3783 static void
3784 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3785 {
3786         unsigned long flags;
3787         unsigned long mask;
3788         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3789         struct rcu_node *rnp = rcu_get_root(rsp);
3790 
3791         /* Set up local state, ensuring consistent view of global state. */
3792         raw_spin_lock_irqsave(&rnp->lock, flags);
3793         rdp->beenonline = 1;     /* We have now been online. */
3794         rdp->qlen_last_fqs_check = 0;
3795         rdp->n_force_qs_snap = rsp->n_force_qs;
3796         rdp->blimit = blimit;
3797         if (!rdp->nxtlist)
3798                 init_callback_list(rdp);  /* Re-enable callbacks on this CPU. */
3799         rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3800         rcu_sysidle_init_percpu_data(rdp->dynticks);
3801         atomic_set(&rdp->dynticks->dynticks,
3802                    (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
3803         raw_spin_unlock(&rnp->lock);            /* irqs remain disabled. */
3804 
3805         /*
3806          * Add CPU to leaf rcu_node pending-online bitmask.  Any needed
3807          * propagation up the rcu_node tree will happen at the beginning
3808          * of the next grace period.
3809          */
3810         rnp = rdp->mynode;
3811         mask = rdp->grpmask;
3812         raw_spin_lock(&rnp->lock);              /* irqs already disabled. */
3813         smp_mb__after_unlock_lock();
3814         rnp->qsmaskinitnext |= mask;
3815         rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
3816         rdp->completed = rnp->completed;
3817         rdp->passed_quiesce = false;
3818         rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
3819         rdp->qs_pending = false;
3820         trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3821         raw_spin_unlock_irqrestore(&rnp->lock, flags);
3822 }
3823 
3824 static void rcu_prepare_cpu(int cpu)
3825 {
3826         struct rcu_state *rsp;
3827 
3828         for_each_rcu_flavor(rsp)
3829                 rcu_init_percpu_data(cpu, rsp);
3830 }
3831 
3832 /*
3833  * Handle CPU online/offline notification events.
3834  */
3835 int rcu_cpu_notify(struct notifier_block *self,
3836                    unsigned long action, void *hcpu)
3837 {
3838         long cpu = (long)hcpu;
3839         struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3840         struct rcu_node *rnp = rdp->mynode;
3841         struct rcu_state *rsp;
3842 
3843         switch (action) {
3844         case CPU_UP_PREPARE:
3845         case CPU_UP_PREPARE_FROZEN:
3846                 rcu_prepare_cpu(cpu);
3847                 rcu_prepare_kthreads(cpu);
3848                 rcu_spawn_all_nocb_kthreads(cpu);
3849                 break;
3850         case CPU_ONLINE:
3851         case CPU_DOWN_FAILED:
3852                 rcu_boost_kthread_setaffinity(rnp, -1);
3853                 break;
3854         case CPU_DOWN_PREPARE:
3855                 rcu_boost_kthread_setaffinity(rnp, cpu);
3856                 break;
3857         case CPU_DYING:
3858         case CPU_DYING_FROZEN:
3859                 for_each_rcu_flavor(rsp)
3860                         rcu_cleanup_dying_cpu(rsp);
3861                 break;
3862         case CPU_DYING_IDLE:
3863                 for_each_rcu_flavor(rsp) {
3864                         rcu_cleanup_dying_idle_cpu(cpu, rsp);
3865                 }
3866                 break;
3867         case CPU_DEAD:
3868         case CPU_DEAD_FROZEN:
3869         case CPU_UP_CANCELED:
3870         case CPU_UP_CANCELED_FROZEN:
3871                 for_each_rcu_flavor(rsp) {
3872                         rcu_cleanup_dead_cpu(cpu, rsp);
3873                         do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
3874                 }
3875                 break;
3876         default:
3877                 break;
3878         }
3879         return NOTIFY_OK;
3880 }
3881 
3882 static int rcu_pm_notify(struct notifier_block *self,
3883                          unsigned long action, void *hcpu)
3884 {
3885         switch (action) {
3886         case PM_HIBERNATION_PREPARE:
3887         case PM_SUSPEND_PREPARE:
3888                 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3889                         rcu_expedite_gp();
3890                 break;
3891         case PM_POST_HIBERNATION:
3892         case PM_POST_SUSPEND:
3893                 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3894                         rcu_unexpedite_gp();
3895                 break;
3896         default:
3897                 break;
3898         }
3899         return NOTIFY_OK;
3900 }
3901 
3902 /*
3903  * Spawn the kthreads that handle each RCU flavor's grace periods.
3904  */
3905 static int __init rcu_spawn_gp_kthread(void)
3906 {
3907         unsigned long flags;
3908         int kthread_prio_in = kthread_prio;
3909         struct rcu_node *rnp;
3910         struct rcu_state *rsp;
3911         struct sched_param sp;
3912         struct task_struct *t;
3913 
3914         /* Force priority into range. */
3915         if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
3916                 kthread_prio = 1;
3917         else if (kthread_prio < 0)
3918                 kthread_prio = 0;
3919         else if (kthread_prio > 99)
3920                 kthread_prio = 99;
3921         if (kthread_prio != kthread_prio_in)
3922                 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
3923                          kthread_prio, kthread_prio_in);
3924 
3925         rcu_scheduler_fully_active = 1;
3926         for_each_rcu_flavor(rsp) {
3927                 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
3928                 BUG_ON(IS_ERR(t));
3929                 rnp = rcu_get_root(rsp);
3930                 raw_spin_lock_irqsave(&rnp->lock, flags);
3931                 rsp->gp_kthread = t;
3932                 if (kthread_prio) {
3933                         sp.sched_priority = kthread_prio;
3934                         sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
3935                 }
3936                 wake_up_process(t);
3937                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3938         }
3939         rcu_spawn_nocb_kthreads();
3940         rcu_spawn_boost_kthreads();
3941         return 0;
3942 }
3943 early_initcall(rcu_spawn_gp_kthread);
3944 
3945 /*
3946  * This function is invoked towards the end of the scheduler's initialization
3947  * process.  Before this is called, the idle task might contain
3948  * RCU read-side critical sections (during which time, this idle
3949  * task is booting the system).  After this function is called, the
3950  * idle tasks are prohibited from containing RCU read-side critical
3951  * sections.  This function also enables RCU lockdep checking.
3952  */
3953 void rcu_scheduler_starting(void)
3954 {
3955         WARN_ON(num_online_cpus() != 1);
3956         WARN_ON(nr_context_switches() > 0);
3957         rcu_scheduler_active = 1;
3958 }
3959 
3960 /*
3961  * Compute the per-level fanout, either using the exact fanout specified
3962  * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
3963  */
3964 static void __init rcu_init_levelspread(struct rcu_state *rsp)
3965 {
3966         int i;
3967 
3968         if (rcu_fanout_exact) {
3969                 rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
3970                 for (i = rcu_num_lvls - 2; i >= 0; i--)
3971                         rsp->levelspread[i] = RCU_FANOUT;
3972         } else {
3973                 int ccur;
3974                 int cprv;
3975 
3976                 cprv = nr_cpu_ids;
3977                 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3978                         ccur = rsp->levelcnt[i];
3979                         rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
3980                         cprv = ccur;
3981                 }
3982         }
3983 }
3984 
3985 /*
3986  * Helper function for rcu_init() that initializes one rcu_state structure.
3987  */
3988 static void __init rcu_init_one(struct rcu_state *rsp,
3989                 struct rcu_data __percpu *rda)
3990 {
3991         static const char * const buf[] = {
3992                 "rcu_node_0",
3993                 "rcu_node_1",
3994                 "rcu_node_2",
3995                 "rcu_node_3" };  /* Match MAX_RCU_LVLS */
3996         static const char * const fqs[] = {
3997                 "rcu_node_fqs_0",
3998                 "rcu_node_fqs_1",
3999                 "rcu_node_fqs_2",
4000                 "rcu_node_fqs_3" };  /* Match MAX_RCU_LVLS */
4001         static u8 fl_mask = 0x1;
4002         int cpustride = 1;
4003         int i;
4004         int j;
4005         struct rcu_node *rnp;
4006 
4007         BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
4008 
4009         /* Silence gcc 4.8 false positive about array index out of range. */
4010         if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4011                 panic("rcu_init_one: rcu_num_lvls out of range");
4012 
4013         /* Initialize the level-tracking arrays. */
4014 
4015         for (i = 0; i < rcu_num_lvls; i++)
4016                 rsp->levelcnt[i] = num_rcu_lvl[i];
4017         for (i = 1; i < rcu_num_lvls; i++)
4018                 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
4019         rcu_init_levelspread(rsp);
4020         rsp->flavor_mask = fl_mask;
4021         fl_mask <<= 1;
4022 
4023         /* Initialize the elements themselves, starting from the leaves. */
4024 
4025         for (i = rcu_num_lvls - 1; i >= 0; i--) {
4026                 cpustride *= rsp->levelspread[i];
4027                 rnp = rsp->level[i];
4028                 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
4029                         raw_spin_lock_init(&rnp->lock);
4030                         lockdep_set_class_and_name(&rnp->lock,
4031                                                    &rcu_node_class[i], buf[i]);
4032                         raw_spin_lock_init(&rnp->fqslock);
4033                         lockdep_set_class_and_name(&rnp->fqslock,
4034                                                    &rcu_fqs_class[i], fqs[i]);
4035                         rnp->gpnum = rsp->gpnum;
4036                         rnp->completed = rsp->completed;
4037                         rnp->qsmask = 0;
4038                         rnp->qsmaskinit = 0;
4039                         rnp->grplo = j * cpustride;
4040                         rnp->grphi = (j + 1) * cpustride - 1;
4041                         if (rnp->grphi >= nr_cpu_ids)
4042                                 rnp->grphi = nr_cpu_ids - 1;
4043                         if (i == 0) {
4044                                 rnp->grpnum = 0;
4045                                 rnp->grpmask = 0;
4046                                 rnp->parent = NULL;
4047                         } else {
4048                                 rnp->grpnum = j % rsp->levelspread[i - 1];
4049                                 rnp->grpmask = 1UL << rnp->grpnum;
4050                                 rnp->parent = rsp->level[i - 1] +
4051                                               j / rsp->levelspread[i - 1];
4052                         }
4053                         rnp->level = i;
4054                         INIT_LIST_HEAD(&rnp->blkd_tasks);
4055                         rcu_init_one_nocb(rnp);
4056                 }
4057         }
4058 
4059         init_waitqueue_head(&rsp->gp_wq);
4060         rnp = rsp->level[rcu_num_lvls - 1];
4061         for_each_possible_cpu(i) {
4062                 while (i > rnp->grphi)
4063                         rnp++;
4064                 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4065                 rcu_boot_init_percpu_data(i, rsp);
4066         }
4067         list_add(&rsp->flavors, &rcu_struct_flavors);
4068 }
4069 
4070 /*
4071  * Compute the rcu_node tree geometry from kernel parameters.  This cannot
4072  * replace the definitions in tree.h because those are needed to size
4073  * the ->node array in the rcu_state structure.
4074  */
4075 static void __init rcu_init_geometry(void)
4076 {
4077         ulong d;
4078         int i;
4079         int j;
4080         int n = nr_cpu_ids;
4081         int rcu_capacity[MAX_RCU_LVLS + 1];
4082 
4083         /*
4084          * Initialize any unspecified boot parameters.
4085          * The default values of jiffies_till_first_fqs and
4086          * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4087          * value, which is a function of HZ, then adding one for each
4088          * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4089          */
4090         d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4091         if (jiffies_till_first_fqs == ULONG_MAX)
4092                 jiffies_till_first_fqs = d;
4093         if (jiffies_till_next_fqs == ULONG_MAX)
4094                 jiffies_till_next_fqs = d;
4095 
4096         /* If the compile-time values are accurate, just leave. */
4097         if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4098             nr_cpu_ids == NR_CPUS)
4099                 return;
4100         pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
4101                 rcu_fanout_leaf, nr_cpu_ids);
4102 
4103         /*
4104          * Compute number of nodes that can be handled an rcu_node tree
4105          * with the given number of levels.  Setting rcu_capacity[0] makes
4106          * some of the arithmetic easier.
4107          */
4108         rcu_capacity[0] = 1;
4109         rcu_capacity[1] = rcu_fanout_leaf;
4110         for (i = 2; i <= MAX_RCU_LVLS; i++)
4111                 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4112 
4113         /*
4114          * The boot-time rcu_fanout_leaf parameter is only permitted
4115          * to increase the leaf-level fanout, not decrease it.  Of course,
4116          * the leaf-level fanout cannot exceed the number of bits in
4117          * the rcu_node masks.  Finally, the tree must be able to accommodate
4118          * the configured number of CPUs.  Complain and fall back to the
4119          * compile-time values if these limits are exceeded.
4120          */
4121         if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
4122             rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
4123             n > rcu_capacity[MAX_RCU_LVLS]) {
4124                 WARN_ON(1);
4125                 return;
4126         }
4127 
4128         /* Calculate the number of rcu_nodes at each level of the tree. */
4129         for (i = 1; i <= MAX_RCU_LVLS; i++)
4130                 if (n <= rcu_capacity[i]) {
4131                         for (j = 0; j <= i; j++)
4132                                 num_rcu_lvl[j] =
4133                                         DIV_ROUND_UP(n, rcu_capacity[i - j]);
4134                         rcu_num_lvls = i;
4135                         for (j = i + 1; j <= MAX_RCU_LVLS; j++)
4136                                 num_rcu_lvl[j] = 0;
4137                         break;
4138                 }
4139 
4140         /* Calculate the total number of rcu_node structures. */
4141         rcu_num_nodes = 0;
4142         for (i = 0; i <= MAX_RCU_LVLS; i++)
4143                 rcu_num_nodes += num_rcu_lvl[i];
4144         rcu_num_nodes -= n;
4145 }
4146 
4147 /*
4148  * Dump out the structure of the rcu_node combining tree associated
4149  * with the rcu_state structure referenced by rsp.
4150  */
4151 static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4152 {
4153         int level = 0;
4154         struct rcu_node *rnp;
4155 
4156         pr_info("rcu_node tree layout dump\n");
4157         pr_info(" ");
4158         rcu_for_each_node_breadth_first(rsp, rnp) {
4159                 if (rnp->level != level) {
4160                         pr_cont("\n");
4161                         pr_info(" ");
4162                         level = rnp->level;
4163                 }
4164                 pr_cont("%d:%d ^%d  ", rnp->grplo, rnp->grphi, rnp->grpnum);
4165         }
4166         pr_cont("\n");
4167 }
4168 
4169 void __init rcu_init(void)
4170 {
4171         int cpu;
4172 
4173         rcu_early_boot_tests();
4174 
4175         rcu_bootup_announce();
4176         rcu_init_geometry();
4177         rcu_init_one(&rcu_bh_state, &rcu_bh_data);
4178         rcu_init_one(&rcu_sched_state, &rcu_sched_data);
4179         if (dump_tree)
4180                 rcu_dump_rcu_node_tree(&rcu_sched_state);
4181         __rcu_init_preempt();
4182         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4183 
4184         /*
4185          * We don't need protection against CPU-hotplug here because
4186          * this is called early in boot, before either interrupts
4187          * or the scheduler are operational.
4188          */
4189         cpu_notifier(rcu_cpu_notify, 0);
4190         pm_notifier(rcu_pm_notify, 0);
4191         for_each_online_cpu(cpu)
4192                 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
4193 }
4194 
4195 #include "tree_plugin.h"
4196 

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