~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

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

Version: ~ [ linux-5.17-rc1 ] ~ [ linux-5.16.2 ] ~ [ linux-5.15.16 ] ~ [ linux-5.14.21 ] ~ [ linux-5.13.19 ] ~ [ linux-5.12.19 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.93 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.173 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.225 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.262 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.297 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.299 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

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

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp