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TOMOYO Linux Cross Reference
Linux/kernel/rcu/tree_plugin.h

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  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
  3  * Internal non-public definitions that provide either classic
  4  * or preemptible semantics.
  5  *
  6  * This program is free software; you can redistribute it and/or modify
  7  * it under the terms of the GNU General Public License as published by
  8  * the Free Software Foundation; either version 2 of the License, or
  9  * (at your option) any later version.
 10  *
 11  * This program is distributed in the hope that it will be useful,
 12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14  * GNU General Public License for more details.
 15  *
 16  * You should have received a copy of the GNU General Public License
 17  * along with this program; if not, you can access it online at
 18  * http://www.gnu.org/licenses/gpl-2.0.html.
 19  *
 20  * Copyright Red Hat, 2009
 21  * Copyright IBM Corporation, 2009
 22  *
 23  * Author: Ingo Molnar <mingo@elte.hu>
 24  *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 25  */
 26 
 27 #include <linux/delay.h>
 28 #include <linux/gfp.h>
 29 #include <linux/oom.h>
 30 #include <linux/smpboot.h>
 31 #include "../time/tick-internal.h"
 32 
 33 #define RCU_KTHREAD_PRIO 1
 34 
 35 #ifdef CONFIG_RCU_BOOST
 36 #include "../locking/rtmutex_common.h"
 37 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
 38 #else
 39 #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
 40 #endif
 41 
 42 #ifdef CONFIG_RCU_NOCB_CPU
 43 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
 44 static bool have_rcu_nocb_mask;     /* Was rcu_nocb_mask allocated? */
 45 static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
 46 static char __initdata nocb_buf[NR_CPUS * 5];
 47 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 48 
 49 /*
 50  * Check the RCU kernel configuration parameters and print informative
 51  * messages about anything out of the ordinary.  If you like #ifdef, you
 52  * will love this function.
 53  */
 54 static void __init rcu_bootup_announce_oddness(void)
 55 {
 56 #ifdef CONFIG_RCU_TRACE
 57         pr_info("\tRCU debugfs-based tracing is enabled.\n");
 58 #endif
 59 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
 60         pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
 61                CONFIG_RCU_FANOUT);
 62 #endif
 63 #ifdef CONFIG_RCU_FANOUT_EXACT
 64         pr_info("\tHierarchical RCU autobalancing is disabled.\n");
 65 #endif
 66 #ifdef CONFIG_RCU_FAST_NO_HZ
 67         pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
 68 #endif
 69 #ifdef CONFIG_PROVE_RCU
 70         pr_info("\tRCU lockdep checking is enabled.\n");
 71 #endif
 72 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
 73         pr_info("\tRCU torture testing starts during boot.\n");
 74 #endif
 75 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
 76         pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
 77 #endif
 78 #if defined(CONFIG_RCU_CPU_STALL_INFO)
 79         pr_info("\tAdditional per-CPU info printed with stalls.\n");
 80 #endif
 81 #if NUM_RCU_LVL_4 != 0
 82         pr_info("\tFour-level hierarchy is enabled.\n");
 83 #endif
 84         if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
 85                 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
 86         if (nr_cpu_ids != NR_CPUS)
 87                 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
 88 #ifdef CONFIG_RCU_NOCB_CPU
 89 #ifndef CONFIG_RCU_NOCB_CPU_NONE
 90         if (!have_rcu_nocb_mask) {
 91                 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
 92                 have_rcu_nocb_mask = true;
 93         }
 94 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
 95         pr_info("\tOffload RCU callbacks from CPU 0\n");
 96         cpumask_set_cpu(0, rcu_nocb_mask);
 97 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
 98 #ifdef CONFIG_RCU_NOCB_CPU_ALL
 99         pr_info("\tOffload RCU callbacks from all CPUs\n");
100         cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
101 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
102 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
103         if (have_rcu_nocb_mask) {
104                 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
105                         pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
106                         cpumask_and(rcu_nocb_mask, cpu_possible_mask,
107                                     rcu_nocb_mask);
108                 }
109                 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
110                 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
111                 if (rcu_nocb_poll)
112                         pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
113         }
114 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
115 }
116 
117 #ifdef CONFIG_TREE_PREEMPT_RCU
118 
119 RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
120 static struct rcu_state *rcu_state_p = &rcu_preempt_state;
121 
122 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
123 
124 /*
125  * Tell them what RCU they are running.
126  */
127 static void __init rcu_bootup_announce(void)
128 {
129         pr_info("Preemptible hierarchical RCU implementation.\n");
130         rcu_bootup_announce_oddness();
131 }
132 
133 /*
134  * Return the number of RCU-preempt batches processed thus far
135  * for debug and statistics.
136  */
137 long rcu_batches_completed_preempt(void)
138 {
139         return rcu_preempt_state.completed;
140 }
141 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
142 
143 /*
144  * Return the number of RCU batches processed thus far for debug & stats.
145  */
146 long rcu_batches_completed(void)
147 {
148         return rcu_batches_completed_preempt();
149 }
150 EXPORT_SYMBOL_GPL(rcu_batches_completed);
151 
152 /*
153  * Record a preemptible-RCU quiescent state for the specified CPU.  Note
154  * that this just means that the task currently running on the CPU is
155  * not in a quiescent state.  There might be any number of tasks blocked
156  * while in an RCU read-side critical section.
157  *
158  * Unlike the other rcu_*_qs() functions, callers to this function
159  * must disable irqs in order to protect the assignment to
160  * ->rcu_read_unlock_special.
161  */
162 static void rcu_preempt_qs(int cpu)
163 {
164         struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
165 
166         if (rdp->passed_quiesce == 0)
167                 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
168         rdp->passed_quiesce = 1;
169         current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
170 }
171 
172 /*
173  * We have entered the scheduler, and the current task might soon be
174  * context-switched away from.  If this task is in an RCU read-side
175  * critical section, we will no longer be able to rely on the CPU to
176  * record that fact, so we enqueue the task on the blkd_tasks list.
177  * The task will dequeue itself when it exits the outermost enclosing
178  * RCU read-side critical section.  Therefore, the current grace period
179  * cannot be permitted to complete until the blkd_tasks list entries
180  * predating the current grace period drain, in other words, until
181  * rnp->gp_tasks becomes NULL.
182  *
183  * Caller must disable preemption.
184  */
185 static void rcu_preempt_note_context_switch(int cpu)
186 {
187         struct task_struct *t = current;
188         unsigned long flags;
189         struct rcu_data *rdp;
190         struct rcu_node *rnp;
191 
192         if (t->rcu_read_lock_nesting > 0 &&
193             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
194 
195                 /* Possibly blocking in an RCU read-side critical section. */
196                 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
197                 rnp = rdp->mynode;
198                 raw_spin_lock_irqsave(&rnp->lock, flags);
199                 smp_mb__after_unlock_lock();
200                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
201                 t->rcu_blocked_node = rnp;
202 
203                 /*
204                  * If this CPU has already checked in, then this task
205                  * will hold up the next grace period rather than the
206                  * current grace period.  Queue the task accordingly.
207                  * If the task is queued for the current grace period
208                  * (i.e., this CPU has not yet passed through a quiescent
209                  * state for the current grace period), then as long
210                  * as that task remains queued, the current grace period
211                  * cannot end.  Note that there is some uncertainty as
212                  * to exactly when the current grace period started.
213                  * We take a conservative approach, which can result
214                  * in unnecessarily waiting on tasks that started very
215                  * slightly after the current grace period began.  C'est
216                  * la vie!!!
217                  *
218                  * But first, note that the current CPU must still be
219                  * on line!
220                  */
221                 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
222                 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
223                 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
224                         list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
225                         rnp->gp_tasks = &t->rcu_node_entry;
226 #ifdef CONFIG_RCU_BOOST
227                         if (rnp->boost_tasks != NULL)
228                                 rnp->boost_tasks = rnp->gp_tasks;
229 #endif /* #ifdef CONFIG_RCU_BOOST */
230                 } else {
231                         list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
232                         if (rnp->qsmask & rdp->grpmask)
233                                 rnp->gp_tasks = &t->rcu_node_entry;
234                 }
235                 trace_rcu_preempt_task(rdp->rsp->name,
236                                        t->pid,
237                                        (rnp->qsmask & rdp->grpmask)
238                                        ? rnp->gpnum
239                                        : rnp->gpnum + 1);
240                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
241         } else if (t->rcu_read_lock_nesting < 0 &&
242                    t->rcu_read_unlock_special) {
243 
244                 /*
245                  * Complete exit from RCU read-side critical section on
246                  * behalf of preempted instance of __rcu_read_unlock().
247                  */
248                 rcu_read_unlock_special(t);
249         }
250 
251         /*
252          * Either we were not in an RCU read-side critical section to
253          * begin with, or we have now recorded that critical section
254          * globally.  Either way, we can now note a quiescent state
255          * for this CPU.  Again, if we were in an RCU read-side critical
256          * section, and if that critical section was blocking the current
257          * grace period, then the fact that the task has been enqueued
258          * means that we continue to block the current grace period.
259          */
260         local_irq_save(flags);
261         rcu_preempt_qs(cpu);
262         local_irq_restore(flags);
263 }
264 
265 /*
266  * Check for preempted RCU readers blocking the current grace period
267  * for the specified rcu_node structure.  If the caller needs a reliable
268  * answer, it must hold the rcu_node's ->lock.
269  */
270 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
271 {
272         return rnp->gp_tasks != NULL;
273 }
274 
275 /*
276  * Record a quiescent state for all tasks that were previously queued
277  * on the specified rcu_node structure and that were blocking the current
278  * RCU grace period.  The caller must hold the specified rnp->lock with
279  * irqs disabled, and this lock is released upon return, but irqs remain
280  * disabled.
281  */
282 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
283         __releases(rnp->lock)
284 {
285         unsigned long mask;
286         struct rcu_node *rnp_p;
287 
288         if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
289                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
290                 return;  /* Still need more quiescent states! */
291         }
292 
293         rnp_p = rnp->parent;
294         if (rnp_p == NULL) {
295                 /*
296                  * Either there is only one rcu_node in the tree,
297                  * or tasks were kicked up to root rcu_node due to
298                  * CPUs going offline.
299                  */
300                 rcu_report_qs_rsp(&rcu_preempt_state, flags);
301                 return;
302         }
303 
304         /* Report up the rest of the hierarchy. */
305         mask = rnp->grpmask;
306         raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
307         raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
308         smp_mb__after_unlock_lock();
309         rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
310 }
311 
312 /*
313  * Advance a ->blkd_tasks-list pointer to the next entry, instead
314  * returning NULL if at the end of the list.
315  */
316 static struct list_head *rcu_next_node_entry(struct task_struct *t,
317                                              struct rcu_node *rnp)
318 {
319         struct list_head *np;
320 
321         np = t->rcu_node_entry.next;
322         if (np == &rnp->blkd_tasks)
323                 np = NULL;
324         return np;
325 }
326 
327 /*
328  * Handle special cases during rcu_read_unlock(), such as needing to
329  * notify RCU core processing or task having blocked during the RCU
330  * read-side critical section.
331  */
332 void rcu_read_unlock_special(struct task_struct *t)
333 {
334         int empty;
335         int empty_exp;
336         int empty_exp_now;
337         unsigned long flags;
338         struct list_head *np;
339 #ifdef CONFIG_RCU_BOOST
340         bool drop_boost_mutex = false;
341 #endif /* #ifdef CONFIG_RCU_BOOST */
342         struct rcu_node *rnp;
343         int special;
344 
345         /* NMI handlers cannot block and cannot safely manipulate state. */
346         if (in_nmi())
347                 return;
348 
349         local_irq_save(flags);
350 
351         /*
352          * If RCU core is waiting for this CPU to exit critical section,
353          * let it know that we have done so.
354          */
355         special = t->rcu_read_unlock_special;
356         if (special & RCU_READ_UNLOCK_NEED_QS) {
357                 rcu_preempt_qs(smp_processor_id());
358                 if (!t->rcu_read_unlock_special) {
359                         local_irq_restore(flags);
360                         return;
361                 }
362         }
363 
364         /* Hardware IRQ handlers cannot block, complain if they get here. */
365         if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
366                 local_irq_restore(flags);
367                 return;
368         }
369 
370         /* Clean up if blocked during RCU read-side critical section. */
371         if (special & RCU_READ_UNLOCK_BLOCKED) {
372                 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
373 
374                 /*
375                  * Remove this task from the list it blocked on.  The
376                  * task can migrate while we acquire the lock, but at
377                  * most one time.  So at most two passes through loop.
378                  */
379                 for (;;) {
380                         rnp = t->rcu_blocked_node;
381                         raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
382                         smp_mb__after_unlock_lock();
383                         if (rnp == t->rcu_blocked_node)
384                                 break;
385                         raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
386                 }
387                 empty = !rcu_preempt_blocked_readers_cgp(rnp);
388                 empty_exp = !rcu_preempted_readers_exp(rnp);
389                 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
390                 np = rcu_next_node_entry(t, rnp);
391                 list_del_init(&t->rcu_node_entry);
392                 t->rcu_blocked_node = NULL;
393                 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
394                                                 rnp->gpnum, t->pid);
395                 if (&t->rcu_node_entry == rnp->gp_tasks)
396                         rnp->gp_tasks = np;
397                 if (&t->rcu_node_entry == rnp->exp_tasks)
398                         rnp->exp_tasks = np;
399 #ifdef CONFIG_RCU_BOOST
400                 if (&t->rcu_node_entry == rnp->boost_tasks)
401                         rnp->boost_tasks = np;
402                 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
403                 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
404 #endif /* #ifdef CONFIG_RCU_BOOST */
405 
406                 /*
407                  * If this was the last task on the current list, and if
408                  * we aren't waiting on any CPUs, report the quiescent state.
409                  * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
410                  * so we must take a snapshot of the expedited state.
411                  */
412                 empty_exp_now = !rcu_preempted_readers_exp(rnp);
413                 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
414                         trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
415                                                          rnp->gpnum,
416                                                          0, rnp->qsmask,
417                                                          rnp->level,
418                                                          rnp->grplo,
419                                                          rnp->grphi,
420                                                          !!rnp->gp_tasks);
421                         rcu_report_unblock_qs_rnp(rnp, flags);
422                 } else {
423                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
424                 }
425 
426 #ifdef CONFIG_RCU_BOOST
427                 /* Unboost if we were boosted. */
428                 if (drop_boost_mutex) {
429                         rt_mutex_unlock(&rnp->boost_mtx);
430                         complete(&rnp->boost_completion);
431                 }
432 #endif /* #ifdef CONFIG_RCU_BOOST */
433 
434                 /*
435                  * If this was the last task on the expedited lists,
436                  * then we need to report up the rcu_node hierarchy.
437                  */
438                 if (!empty_exp && empty_exp_now)
439                         rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
440         } else {
441                 local_irq_restore(flags);
442         }
443 }
444 
445 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
446 
447 /*
448  * Dump detailed information for all tasks blocking the current RCU
449  * grace period on the specified rcu_node structure.
450  */
451 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
452 {
453         unsigned long flags;
454         struct task_struct *t;
455 
456         raw_spin_lock_irqsave(&rnp->lock, flags);
457         if (!rcu_preempt_blocked_readers_cgp(rnp)) {
458                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
459                 return;
460         }
461         t = list_entry(rnp->gp_tasks,
462                        struct task_struct, rcu_node_entry);
463         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
464                 sched_show_task(t);
465         raw_spin_unlock_irqrestore(&rnp->lock, flags);
466 }
467 
468 /*
469  * Dump detailed information for all tasks blocking the current RCU
470  * grace period.
471  */
472 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
473 {
474         struct rcu_node *rnp = rcu_get_root(rsp);
475 
476         rcu_print_detail_task_stall_rnp(rnp);
477         rcu_for_each_leaf_node(rsp, rnp)
478                 rcu_print_detail_task_stall_rnp(rnp);
479 }
480 
481 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
482 
483 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
484 {
485 }
486 
487 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
488 
489 #ifdef CONFIG_RCU_CPU_STALL_INFO
490 
491 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
492 {
493         pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
494                rnp->level, rnp->grplo, rnp->grphi);
495 }
496 
497 static void rcu_print_task_stall_end(void)
498 {
499         pr_cont("\n");
500 }
501 
502 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
503 
504 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
505 {
506 }
507 
508 static void rcu_print_task_stall_end(void)
509 {
510 }
511 
512 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
513 
514 /*
515  * Scan the current list of tasks blocked within RCU read-side critical
516  * sections, printing out the tid of each.
517  */
518 static int rcu_print_task_stall(struct rcu_node *rnp)
519 {
520         struct task_struct *t;
521         int ndetected = 0;
522 
523         if (!rcu_preempt_blocked_readers_cgp(rnp))
524                 return 0;
525         rcu_print_task_stall_begin(rnp);
526         t = list_entry(rnp->gp_tasks,
527                        struct task_struct, rcu_node_entry);
528         list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
529                 pr_cont(" P%d", t->pid);
530                 ndetected++;
531         }
532         rcu_print_task_stall_end();
533         return ndetected;
534 }
535 
536 /*
537  * Check that the list of blocked tasks for the newly completed grace
538  * period is in fact empty.  It is a serious bug to complete a grace
539  * period that still has RCU readers blocked!  This function must be
540  * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
541  * must be held by the caller.
542  *
543  * Also, if there are blocked tasks on the list, they automatically
544  * block the newly created grace period, so set up ->gp_tasks accordingly.
545  */
546 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
547 {
548         WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
549         if (!list_empty(&rnp->blkd_tasks))
550                 rnp->gp_tasks = rnp->blkd_tasks.next;
551         WARN_ON_ONCE(rnp->qsmask);
552 }
553 
554 #ifdef CONFIG_HOTPLUG_CPU
555 
556 /*
557  * Handle tasklist migration for case in which all CPUs covered by the
558  * specified rcu_node have gone offline.  Move them up to the root
559  * rcu_node.  The reason for not just moving them to the immediate
560  * parent is to remove the need for rcu_read_unlock_special() to
561  * make more than two attempts to acquire the target rcu_node's lock.
562  * Returns true if there were tasks blocking the current RCU grace
563  * period.
564  *
565  * Returns 1 if there was previously a task blocking the current grace
566  * period on the specified rcu_node structure.
567  *
568  * The caller must hold rnp->lock with irqs disabled.
569  */
570 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
571                                      struct rcu_node *rnp,
572                                      struct rcu_data *rdp)
573 {
574         struct list_head *lp;
575         struct list_head *lp_root;
576         int retval = 0;
577         struct rcu_node *rnp_root = rcu_get_root(rsp);
578         struct task_struct *t;
579 
580         if (rnp == rnp_root) {
581                 WARN_ONCE(1, "Last CPU thought to be offlined?");
582                 return 0;  /* Shouldn't happen: at least one CPU online. */
583         }
584 
585         /* If we are on an internal node, complain bitterly. */
586         WARN_ON_ONCE(rnp != rdp->mynode);
587 
588         /*
589          * Move tasks up to root rcu_node.  Don't try to get fancy for
590          * this corner-case operation -- just put this node's tasks
591          * at the head of the root node's list, and update the root node's
592          * ->gp_tasks and ->exp_tasks pointers to those of this node's,
593          * if non-NULL.  This might result in waiting for more tasks than
594          * absolutely necessary, but this is a good performance/complexity
595          * tradeoff.
596          */
597         if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
598                 retval |= RCU_OFL_TASKS_NORM_GP;
599         if (rcu_preempted_readers_exp(rnp))
600                 retval |= RCU_OFL_TASKS_EXP_GP;
601         lp = &rnp->blkd_tasks;
602         lp_root = &rnp_root->blkd_tasks;
603         while (!list_empty(lp)) {
604                 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
605                 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
606                 smp_mb__after_unlock_lock();
607                 list_del(&t->rcu_node_entry);
608                 t->rcu_blocked_node = rnp_root;
609                 list_add(&t->rcu_node_entry, lp_root);
610                 if (&t->rcu_node_entry == rnp->gp_tasks)
611                         rnp_root->gp_tasks = rnp->gp_tasks;
612                 if (&t->rcu_node_entry == rnp->exp_tasks)
613                         rnp_root->exp_tasks = rnp->exp_tasks;
614 #ifdef CONFIG_RCU_BOOST
615                 if (&t->rcu_node_entry == rnp->boost_tasks)
616                         rnp_root->boost_tasks = rnp->boost_tasks;
617 #endif /* #ifdef CONFIG_RCU_BOOST */
618                 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
619         }
620 
621         rnp->gp_tasks = NULL;
622         rnp->exp_tasks = NULL;
623 #ifdef CONFIG_RCU_BOOST
624         rnp->boost_tasks = NULL;
625         /*
626          * In case root is being boosted and leaf was not.  Make sure
627          * that we boost the tasks blocking the current grace period
628          * in this case.
629          */
630         raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
631         smp_mb__after_unlock_lock();
632         if (rnp_root->boost_tasks != NULL &&
633             rnp_root->boost_tasks != rnp_root->gp_tasks &&
634             rnp_root->boost_tasks != rnp_root->exp_tasks)
635                 rnp_root->boost_tasks = rnp_root->gp_tasks;
636         raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
637 #endif /* #ifdef CONFIG_RCU_BOOST */
638 
639         return retval;
640 }
641 
642 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
643 
644 /*
645  * Check for a quiescent state from the current CPU.  When a task blocks,
646  * the task is recorded in the corresponding CPU's rcu_node structure,
647  * which is checked elsewhere.
648  *
649  * Caller must disable hard irqs.
650  */
651 static void rcu_preempt_check_callbacks(int cpu)
652 {
653         struct task_struct *t = current;
654 
655         if (t->rcu_read_lock_nesting == 0) {
656                 rcu_preempt_qs(cpu);
657                 return;
658         }
659         if (t->rcu_read_lock_nesting > 0 &&
660             per_cpu(rcu_preempt_data, cpu).qs_pending)
661                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
662 }
663 
664 #ifdef CONFIG_RCU_BOOST
665 
666 static void rcu_preempt_do_callbacks(void)
667 {
668         rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
669 }
670 
671 #endif /* #ifdef CONFIG_RCU_BOOST */
672 
673 /*
674  * Queue a preemptible-RCU callback for invocation after a grace period.
675  */
676 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
677 {
678         __call_rcu(head, func, &rcu_preempt_state, -1, 0);
679 }
680 EXPORT_SYMBOL_GPL(call_rcu);
681 
682 /**
683  * synchronize_rcu - wait until a grace period has elapsed.
684  *
685  * Control will return to the caller some time after a full grace
686  * period has elapsed, in other words after all currently executing RCU
687  * read-side critical sections have completed.  Note, however, that
688  * upon return from synchronize_rcu(), the caller might well be executing
689  * concurrently with new RCU read-side critical sections that began while
690  * synchronize_rcu() was waiting.  RCU read-side critical sections are
691  * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
692  *
693  * See the description of synchronize_sched() for more detailed information
694  * on memory ordering guarantees.
695  */
696 void synchronize_rcu(void)
697 {
698         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
699                            !lock_is_held(&rcu_lock_map) &&
700                            !lock_is_held(&rcu_sched_lock_map),
701                            "Illegal synchronize_rcu() in RCU read-side critical section");
702         if (!rcu_scheduler_active)
703                 return;
704         if (rcu_expedited)
705                 synchronize_rcu_expedited();
706         else
707                 wait_rcu_gp(call_rcu);
708 }
709 EXPORT_SYMBOL_GPL(synchronize_rcu);
710 
711 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
712 static unsigned long sync_rcu_preempt_exp_count;
713 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
714 
715 /*
716  * Return non-zero if there are any tasks in RCU read-side critical
717  * sections blocking the current preemptible-RCU expedited grace period.
718  * If there is no preemptible-RCU expedited grace period currently in
719  * progress, returns zero unconditionally.
720  */
721 static int rcu_preempted_readers_exp(struct rcu_node *rnp)
722 {
723         return rnp->exp_tasks != NULL;
724 }
725 
726 /*
727  * return non-zero if there is no RCU expedited grace period in progress
728  * for the specified rcu_node structure, in other words, if all CPUs and
729  * tasks covered by the specified rcu_node structure have done their bit
730  * for the current expedited grace period.  Works only for preemptible
731  * RCU -- other RCU implementation use other means.
732  *
733  * Caller must hold sync_rcu_preempt_exp_mutex.
734  */
735 static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
736 {
737         return !rcu_preempted_readers_exp(rnp) &&
738                ACCESS_ONCE(rnp->expmask) == 0;
739 }
740 
741 /*
742  * Report the exit from RCU read-side critical section for the last task
743  * that queued itself during or before the current expedited preemptible-RCU
744  * grace period.  This event is reported either to the rcu_node structure on
745  * which the task was queued or to one of that rcu_node structure's ancestors,
746  * recursively up the tree.  (Calm down, calm down, we do the recursion
747  * iteratively!)
748  *
749  * Most callers will set the "wake" flag, but the task initiating the
750  * expedited grace period need not wake itself.
751  *
752  * Caller must hold sync_rcu_preempt_exp_mutex.
753  */
754 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
755                                bool wake)
756 {
757         unsigned long flags;
758         unsigned long mask;
759 
760         raw_spin_lock_irqsave(&rnp->lock, flags);
761         smp_mb__after_unlock_lock();
762         for (;;) {
763                 if (!sync_rcu_preempt_exp_done(rnp)) {
764                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
765                         break;
766                 }
767                 if (rnp->parent == NULL) {
768                         raw_spin_unlock_irqrestore(&rnp->lock, flags);
769                         if (wake) {
770                                 smp_mb(); /* EGP done before wake_up(). */
771                                 wake_up(&sync_rcu_preempt_exp_wq);
772                         }
773                         break;
774                 }
775                 mask = rnp->grpmask;
776                 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
777                 rnp = rnp->parent;
778                 raw_spin_lock(&rnp->lock); /* irqs already disabled */
779                 smp_mb__after_unlock_lock();
780                 rnp->expmask &= ~mask;
781         }
782 }
783 
784 /*
785  * Snapshot the tasks blocking the newly started preemptible-RCU expedited
786  * grace period for the specified rcu_node structure.  If there are no such
787  * tasks, report it up the rcu_node hierarchy.
788  *
789  * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
790  * CPU hotplug operations.
791  */
792 static void
793 sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
794 {
795         unsigned long flags;
796         int must_wait = 0;
797 
798         raw_spin_lock_irqsave(&rnp->lock, flags);
799         smp_mb__after_unlock_lock();
800         if (list_empty(&rnp->blkd_tasks)) {
801                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
802         } else {
803                 rnp->exp_tasks = rnp->blkd_tasks.next;
804                 rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
805                 must_wait = 1;
806         }
807         if (!must_wait)
808                 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
809 }
810 
811 /**
812  * synchronize_rcu_expedited - Brute-force RCU grace period
813  *
814  * Wait for an RCU-preempt grace period, but expedite it.  The basic
815  * idea is to invoke synchronize_sched_expedited() to push all the tasks to
816  * the ->blkd_tasks lists and wait for this list to drain.  This consumes
817  * significant time on all CPUs and is unfriendly to real-time workloads,
818  * so is thus not recommended for any sort of common-case code.
819  * In fact, if you are using synchronize_rcu_expedited() in a loop,
820  * please restructure your code to batch your updates, and then Use a
821  * single synchronize_rcu() instead.
822  *
823  * Note that it is illegal to call this function while holding any lock
824  * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
825  * to call this function from a CPU-hotplug notifier.  Failing to observe
826  * these restriction will result in deadlock.
827  */
828 void synchronize_rcu_expedited(void)
829 {
830         unsigned long flags;
831         struct rcu_node *rnp;
832         struct rcu_state *rsp = &rcu_preempt_state;
833         unsigned long snap;
834         int trycount = 0;
835 
836         smp_mb(); /* Caller's modifications seen first by other CPUs. */
837         snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
838         smp_mb(); /* Above access cannot bleed into critical section. */
839 
840         /*
841          * Block CPU-hotplug operations.  This means that any CPU-hotplug
842          * operation that finds an rcu_node structure with tasks in the
843          * process of being boosted will know that all tasks blocking
844          * this expedited grace period will already be in the process of
845          * being boosted.  This simplifies the process of moving tasks
846          * from leaf to root rcu_node structures.
847          */
848         get_online_cpus();
849 
850         /*
851          * Acquire lock, falling back to synchronize_rcu() if too many
852          * lock-acquisition failures.  Of course, if someone does the
853          * expedited grace period for us, just leave.
854          */
855         while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
856                 if (ULONG_CMP_LT(snap,
857                     ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
858                         put_online_cpus();
859                         goto mb_ret; /* Others did our work for us. */
860                 }
861                 if (trycount++ < 10) {
862                         udelay(trycount * num_online_cpus());
863                 } else {
864                         put_online_cpus();
865                         wait_rcu_gp(call_rcu);
866                         return;
867                 }
868         }
869         if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
870                 put_online_cpus();
871                 goto unlock_mb_ret; /* Others did our work for us. */
872         }
873 
874         /* force all RCU readers onto ->blkd_tasks lists. */
875         synchronize_sched_expedited();
876 
877         /* Initialize ->expmask for all non-leaf rcu_node structures. */
878         rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
879                 raw_spin_lock_irqsave(&rnp->lock, flags);
880                 smp_mb__after_unlock_lock();
881                 rnp->expmask = rnp->qsmaskinit;
882                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
883         }
884 
885         /* Snapshot current state of ->blkd_tasks lists. */
886         rcu_for_each_leaf_node(rsp, rnp)
887                 sync_rcu_preempt_exp_init(rsp, rnp);
888         if (NUM_RCU_NODES > 1)
889                 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
890 
891         put_online_cpus();
892 
893         /* Wait for snapshotted ->blkd_tasks lists to drain. */
894         rnp = rcu_get_root(rsp);
895         wait_event(sync_rcu_preempt_exp_wq,
896                    sync_rcu_preempt_exp_done(rnp));
897 
898         /* Clean up and exit. */
899         smp_mb(); /* ensure expedited GP seen before counter increment. */
900         ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
901 unlock_mb_ret:
902         mutex_unlock(&sync_rcu_preempt_exp_mutex);
903 mb_ret:
904         smp_mb(); /* ensure subsequent action seen after grace period. */
905 }
906 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
907 
908 /**
909  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
910  *
911  * Note that this primitive does not necessarily wait for an RCU grace period
912  * to complete.  For example, if there are no RCU callbacks queued anywhere
913  * in the system, then rcu_barrier() is within its rights to return
914  * immediately, without waiting for anything, much less an RCU grace period.
915  */
916 void rcu_barrier(void)
917 {
918         _rcu_barrier(&rcu_preempt_state);
919 }
920 EXPORT_SYMBOL_GPL(rcu_barrier);
921 
922 /*
923  * Initialize preemptible RCU's state structures.
924  */
925 static void __init __rcu_init_preempt(void)
926 {
927         rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
928 }
929 
930 /*
931  * Check for a task exiting while in a preemptible-RCU read-side
932  * critical section, clean up if so.  No need to issue warnings,
933  * as debug_check_no_locks_held() already does this if lockdep
934  * is enabled.
935  */
936 void exit_rcu(void)
937 {
938         struct task_struct *t = current;
939 
940         if (likely(list_empty(&current->rcu_node_entry)))
941                 return;
942         t->rcu_read_lock_nesting = 1;
943         barrier();
944         t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
945         __rcu_read_unlock();
946 }
947 
948 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
949 
950 static struct rcu_state *rcu_state_p = &rcu_sched_state;
951 
952 /*
953  * Tell them what RCU they are running.
954  */
955 static void __init rcu_bootup_announce(void)
956 {
957         pr_info("Hierarchical RCU implementation.\n");
958         rcu_bootup_announce_oddness();
959 }
960 
961 /*
962  * Return the number of RCU batches processed thus far for debug & stats.
963  */
964 long rcu_batches_completed(void)
965 {
966         return rcu_batches_completed_sched();
967 }
968 EXPORT_SYMBOL_GPL(rcu_batches_completed);
969 
970 /*
971  * Because preemptible RCU does not exist, we never have to check for
972  * CPUs being in quiescent states.
973  */
974 static void rcu_preempt_note_context_switch(int cpu)
975 {
976 }
977 
978 /*
979  * Because preemptible RCU does not exist, there are never any preempted
980  * RCU readers.
981  */
982 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
983 {
984         return 0;
985 }
986 
987 #ifdef CONFIG_HOTPLUG_CPU
988 
989 /* Because preemptible RCU does not exist, no quieting of tasks. */
990 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
991         __releases(rnp->lock)
992 {
993         raw_spin_unlock_irqrestore(&rnp->lock, flags);
994 }
995 
996 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
997 
998 /*
999  * Because preemptible RCU does not exist, we never have to check for
1000  * tasks blocked within RCU read-side critical sections.
1001  */
1002 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1003 {
1004 }
1005 
1006 /*
1007  * Because preemptible RCU does not exist, we never have to check for
1008  * tasks blocked within RCU read-side critical sections.
1009  */
1010 static int rcu_print_task_stall(struct rcu_node *rnp)
1011 {
1012         return 0;
1013 }
1014 
1015 /*
1016  * Because there is no preemptible RCU, there can be no readers blocked,
1017  * so there is no need to check for blocked tasks.  So check only for
1018  * bogus qsmask values.
1019  */
1020 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1021 {
1022         WARN_ON_ONCE(rnp->qsmask);
1023 }
1024 
1025 #ifdef CONFIG_HOTPLUG_CPU
1026 
1027 /*
1028  * Because preemptible RCU does not exist, it never needs to migrate
1029  * tasks that were blocked within RCU read-side critical sections, and
1030  * such non-existent tasks cannot possibly have been blocking the current
1031  * grace period.
1032  */
1033 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1034                                      struct rcu_node *rnp,
1035                                      struct rcu_data *rdp)
1036 {
1037         return 0;
1038 }
1039 
1040 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1041 
1042 /*
1043  * Because preemptible RCU does not exist, it never has any callbacks
1044  * to check.
1045  */
1046 static void rcu_preempt_check_callbacks(int cpu)
1047 {
1048 }
1049 
1050 /*
1051  * Wait for an rcu-preempt grace period, but make it happen quickly.
1052  * But because preemptible RCU does not exist, map to rcu-sched.
1053  */
1054 void synchronize_rcu_expedited(void)
1055 {
1056         synchronize_sched_expedited();
1057 }
1058 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1059 
1060 #ifdef CONFIG_HOTPLUG_CPU
1061 
1062 /*
1063  * Because preemptible RCU does not exist, there is never any need to
1064  * report on tasks preempted in RCU read-side critical sections during
1065  * expedited RCU grace periods.
1066  */
1067 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1068                                bool wake)
1069 {
1070 }
1071 
1072 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1073 
1074 /*
1075  * Because preemptible RCU does not exist, rcu_barrier() is just
1076  * another name for rcu_barrier_sched().
1077  */
1078 void rcu_barrier(void)
1079 {
1080         rcu_barrier_sched();
1081 }
1082 EXPORT_SYMBOL_GPL(rcu_barrier);
1083 
1084 /*
1085  * Because preemptible RCU does not exist, it need not be initialized.
1086  */
1087 static void __init __rcu_init_preempt(void)
1088 {
1089 }
1090 
1091 /*
1092  * Because preemptible RCU does not exist, tasks cannot possibly exit
1093  * while in preemptible RCU read-side critical sections.
1094  */
1095 void exit_rcu(void)
1096 {
1097 }
1098 
1099 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1100 
1101 #ifdef CONFIG_RCU_BOOST
1102 
1103 #include "../locking/rtmutex_common.h"
1104 
1105 #ifdef CONFIG_RCU_TRACE
1106 
1107 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1108 {
1109         if (list_empty(&rnp->blkd_tasks))
1110                 rnp->n_balk_blkd_tasks++;
1111         else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1112                 rnp->n_balk_exp_gp_tasks++;
1113         else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1114                 rnp->n_balk_boost_tasks++;
1115         else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1116                 rnp->n_balk_notblocked++;
1117         else if (rnp->gp_tasks != NULL &&
1118                  ULONG_CMP_LT(jiffies, rnp->boost_time))
1119                 rnp->n_balk_notyet++;
1120         else
1121                 rnp->n_balk_nos++;
1122 }
1123 
1124 #else /* #ifdef CONFIG_RCU_TRACE */
1125 
1126 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1127 {
1128 }
1129 
1130 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1131 
1132 static void rcu_wake_cond(struct task_struct *t, int status)
1133 {
1134         /*
1135          * If the thread is yielding, only wake it when this
1136          * is invoked from idle
1137          */
1138         if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1139                 wake_up_process(t);
1140 }
1141 
1142 /*
1143  * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1144  * or ->boost_tasks, advancing the pointer to the next task in the
1145  * ->blkd_tasks list.
1146  *
1147  * Note that irqs must be enabled: boosting the task can block.
1148  * Returns 1 if there are more tasks needing to be boosted.
1149  */
1150 static int rcu_boost(struct rcu_node *rnp)
1151 {
1152         unsigned long flags;
1153         struct task_struct *t;
1154         struct list_head *tb;
1155 
1156         if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1157                 return 0;  /* Nothing left to boost. */
1158 
1159         raw_spin_lock_irqsave(&rnp->lock, flags);
1160         smp_mb__after_unlock_lock();
1161 
1162         /*
1163          * Recheck under the lock: all tasks in need of boosting
1164          * might exit their RCU read-side critical sections on their own.
1165          */
1166         if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1167                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1168                 return 0;
1169         }
1170 
1171         /*
1172          * Preferentially boost tasks blocking expedited grace periods.
1173          * This cannot starve the normal grace periods because a second
1174          * expedited grace period must boost all blocked tasks, including
1175          * those blocking the pre-existing normal grace period.
1176          */
1177         if (rnp->exp_tasks != NULL) {
1178                 tb = rnp->exp_tasks;
1179                 rnp->n_exp_boosts++;
1180         } else {
1181                 tb = rnp->boost_tasks;
1182                 rnp->n_normal_boosts++;
1183         }
1184         rnp->n_tasks_boosted++;
1185 
1186         /*
1187          * We boost task t by manufacturing an rt_mutex that appears to
1188          * be held by task t.  We leave a pointer to that rt_mutex where
1189          * task t can find it, and task t will release the mutex when it
1190          * exits its outermost RCU read-side critical section.  Then
1191          * simply acquiring this artificial rt_mutex will boost task
1192          * t's priority.  (Thanks to tglx for suggesting this approach!)
1193          *
1194          * Note that task t must acquire rnp->lock to remove itself from
1195          * the ->blkd_tasks list, which it will do from exit() if from
1196          * nowhere else.  We therefore are guaranteed that task t will
1197          * stay around at least until we drop rnp->lock.  Note that
1198          * rnp->lock also resolves races between our priority boosting
1199          * and task t's exiting its outermost RCU read-side critical
1200          * section.
1201          */
1202         t = container_of(tb, struct task_struct, rcu_node_entry);
1203         rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1204         init_completion(&rnp->boost_completion);
1205         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1206         /* Lock only for side effect: boosts task t's priority. */
1207         rt_mutex_lock(&rnp->boost_mtx);
1208         rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */
1209 
1210         /* Wait for boostee to be done w/boost_mtx before reinitializing. */
1211         wait_for_completion(&rnp->boost_completion);
1212 
1213         return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1214                ACCESS_ONCE(rnp->boost_tasks) != NULL;
1215 }
1216 
1217 /*
1218  * Priority-boosting kthread.  One per leaf rcu_node and one for the
1219  * root rcu_node.
1220  */
1221 static int rcu_boost_kthread(void *arg)
1222 {
1223         struct rcu_node *rnp = (struct rcu_node *)arg;
1224         int spincnt = 0;
1225         int more2boost;
1226 
1227         trace_rcu_utilization(TPS("Start boost kthread@init"));
1228         for (;;) {
1229                 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1230                 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1231                 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1232                 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1233                 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1234                 more2boost = rcu_boost(rnp);
1235                 if (more2boost)
1236                         spincnt++;
1237                 else
1238                         spincnt = 0;
1239                 if (spincnt > 10) {
1240                         rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1241                         trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1242                         schedule_timeout_interruptible(2);
1243                         trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1244                         spincnt = 0;
1245                 }
1246         }
1247         /* NOTREACHED */
1248         trace_rcu_utilization(TPS("End boost kthread@notreached"));
1249         return 0;
1250 }
1251 
1252 /*
1253  * Check to see if it is time to start boosting RCU readers that are
1254  * blocking the current grace period, and, if so, tell the per-rcu_node
1255  * kthread to start boosting them.  If there is an expedited grace
1256  * period in progress, it is always time to boost.
1257  *
1258  * The caller must hold rnp->lock, which this function releases.
1259  * The ->boost_kthread_task is immortal, so we don't need to worry
1260  * about it going away.
1261  */
1262 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1263         __releases(rnp->lock)
1264 {
1265         struct task_struct *t;
1266 
1267         if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1268                 rnp->n_balk_exp_gp_tasks++;
1269                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1270                 return;
1271         }
1272         if (rnp->exp_tasks != NULL ||
1273             (rnp->gp_tasks != NULL &&
1274              rnp->boost_tasks == NULL &&
1275              rnp->qsmask == 0 &&
1276              ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1277                 if (rnp->exp_tasks == NULL)
1278                         rnp->boost_tasks = rnp->gp_tasks;
1279                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1280                 t = rnp->boost_kthread_task;
1281                 if (t)
1282                         rcu_wake_cond(t, rnp->boost_kthread_status);
1283         } else {
1284                 rcu_initiate_boost_trace(rnp);
1285                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1286         }
1287 }
1288 
1289 /*
1290  * Wake up the per-CPU kthread to invoke RCU callbacks.
1291  */
1292 static void invoke_rcu_callbacks_kthread(void)
1293 {
1294         unsigned long flags;
1295 
1296         local_irq_save(flags);
1297         __this_cpu_write(rcu_cpu_has_work, 1);
1298         if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1299             current != __this_cpu_read(rcu_cpu_kthread_task)) {
1300                 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1301                               __this_cpu_read(rcu_cpu_kthread_status));
1302         }
1303         local_irq_restore(flags);
1304 }
1305 
1306 /*
1307  * Is the current CPU running the RCU-callbacks kthread?
1308  * Caller must have preemption disabled.
1309  */
1310 static bool rcu_is_callbacks_kthread(void)
1311 {
1312         return __this_cpu_read(rcu_cpu_kthread_task) == current;
1313 }
1314 
1315 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1316 
1317 /*
1318  * Do priority-boost accounting for the start of a new grace period.
1319  */
1320 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1321 {
1322         rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1323 }
1324 
1325 /*
1326  * Create an RCU-boost kthread for the specified node if one does not
1327  * already exist.  We only create this kthread for preemptible RCU.
1328  * Returns zero if all is well, a negated errno otherwise.
1329  */
1330 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1331                                                  struct rcu_node *rnp)
1332 {
1333         int rnp_index = rnp - &rsp->node[0];
1334         unsigned long flags;
1335         struct sched_param sp;
1336         struct task_struct *t;
1337 
1338         if (&rcu_preempt_state != rsp)
1339                 return 0;
1340 
1341         if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1342                 return 0;
1343 
1344         rsp->boost = 1;
1345         if (rnp->boost_kthread_task != NULL)
1346                 return 0;
1347         t = kthread_create(rcu_boost_kthread, (void *)rnp,
1348                            "rcub/%d", rnp_index);
1349         if (IS_ERR(t))
1350                 return PTR_ERR(t);
1351         raw_spin_lock_irqsave(&rnp->lock, flags);
1352         smp_mb__after_unlock_lock();
1353         rnp->boost_kthread_task = t;
1354         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1355         sp.sched_priority = RCU_BOOST_PRIO;
1356         sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1357         wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1358         return 0;
1359 }
1360 
1361 static void rcu_kthread_do_work(void)
1362 {
1363         rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1364         rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1365         rcu_preempt_do_callbacks();
1366 }
1367 
1368 static void rcu_cpu_kthread_setup(unsigned int cpu)
1369 {
1370         struct sched_param sp;
1371 
1372         sp.sched_priority = RCU_KTHREAD_PRIO;
1373         sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1374 }
1375 
1376 static void rcu_cpu_kthread_park(unsigned int cpu)
1377 {
1378         per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1379 }
1380 
1381 static int rcu_cpu_kthread_should_run(unsigned int cpu)
1382 {
1383         return __this_cpu_read(rcu_cpu_has_work);
1384 }
1385 
1386 /*
1387  * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1388  * RCU softirq used in flavors and configurations of RCU that do not
1389  * support RCU priority boosting.
1390  */
1391 static void rcu_cpu_kthread(unsigned int cpu)
1392 {
1393         unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1394         char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1395         int spincnt;
1396 
1397         for (spincnt = 0; spincnt < 10; spincnt++) {
1398                 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1399                 local_bh_disable();
1400                 *statusp = RCU_KTHREAD_RUNNING;
1401                 this_cpu_inc(rcu_cpu_kthread_loops);
1402                 local_irq_disable();
1403                 work = *workp;
1404                 *workp = 0;
1405                 local_irq_enable();
1406                 if (work)
1407                         rcu_kthread_do_work();
1408                 local_bh_enable();
1409                 if (*workp == 0) {
1410                         trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1411                         *statusp = RCU_KTHREAD_WAITING;
1412                         return;
1413                 }
1414         }
1415         *statusp = RCU_KTHREAD_YIELDING;
1416         trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1417         schedule_timeout_interruptible(2);
1418         trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1419         *statusp = RCU_KTHREAD_WAITING;
1420 }
1421 
1422 /*
1423  * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1424  * served by the rcu_node in question.  The CPU hotplug lock is still
1425  * held, so the value of rnp->qsmaskinit will be stable.
1426  *
1427  * We don't include outgoingcpu in the affinity set, use -1 if there is
1428  * no outgoing CPU.  If there are no CPUs left in the affinity set,
1429  * this function allows the kthread to execute on any CPU.
1430  */
1431 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1432 {
1433         struct task_struct *t = rnp->boost_kthread_task;
1434         unsigned long mask = rnp->qsmaskinit;
1435         cpumask_var_t cm;
1436         int cpu;
1437 
1438         if (!t)
1439                 return;
1440         if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1441                 return;
1442         for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1443                 if ((mask & 0x1) && cpu != outgoingcpu)
1444                         cpumask_set_cpu(cpu, cm);
1445         if (cpumask_weight(cm) == 0) {
1446                 cpumask_setall(cm);
1447                 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1448                         cpumask_clear_cpu(cpu, cm);
1449                 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1450         }
1451         set_cpus_allowed_ptr(t, cm);
1452         free_cpumask_var(cm);
1453 }
1454 
1455 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1456         .store                  = &rcu_cpu_kthread_task,
1457         .thread_should_run      = rcu_cpu_kthread_should_run,
1458         .thread_fn              = rcu_cpu_kthread,
1459         .thread_comm            = "rcuc/%u",
1460         .setup                  = rcu_cpu_kthread_setup,
1461         .park                   = rcu_cpu_kthread_park,
1462 };
1463 
1464 /*
1465  * Spawn all kthreads -- called as soon as the scheduler is running.
1466  */
1467 static int __init rcu_spawn_kthreads(void)
1468 {
1469         struct rcu_node *rnp;
1470         int cpu;
1471 
1472         rcu_scheduler_fully_active = 1;
1473         for_each_possible_cpu(cpu)
1474                 per_cpu(rcu_cpu_has_work, cpu) = 0;
1475         BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1476         rnp = rcu_get_root(rcu_state_p);
1477         (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1478         if (NUM_RCU_NODES > 1) {
1479                 rcu_for_each_leaf_node(rcu_state_p, rnp)
1480                         (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1481         }
1482         return 0;
1483 }
1484 early_initcall(rcu_spawn_kthreads);
1485 
1486 static void rcu_prepare_kthreads(int cpu)
1487 {
1488         struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1489         struct rcu_node *rnp = rdp->mynode;
1490 
1491         /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1492         if (rcu_scheduler_fully_active)
1493                 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1494 }
1495 
1496 #else /* #ifdef CONFIG_RCU_BOOST */
1497 
1498 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1499         __releases(rnp->lock)
1500 {
1501         raw_spin_unlock_irqrestore(&rnp->lock, flags);
1502 }
1503 
1504 static void invoke_rcu_callbacks_kthread(void)
1505 {
1506         WARN_ON_ONCE(1);
1507 }
1508 
1509 static bool rcu_is_callbacks_kthread(void)
1510 {
1511         return false;
1512 }
1513 
1514 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1515 {
1516 }
1517 
1518 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1519 {
1520 }
1521 
1522 static int __init rcu_scheduler_really_started(void)
1523 {
1524         rcu_scheduler_fully_active = 1;
1525         return 0;
1526 }
1527 early_initcall(rcu_scheduler_really_started);
1528 
1529 static void rcu_prepare_kthreads(int cpu)
1530 {
1531 }
1532 
1533 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1534 
1535 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1536 
1537 /*
1538  * Check to see if any future RCU-related work will need to be done
1539  * by the current CPU, even if none need be done immediately, returning
1540  * 1 if so.  This function is part of the RCU implementation; it is -not-
1541  * an exported member of the RCU API.
1542  *
1543  * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1544  * any flavor of RCU.
1545  */
1546 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1547 int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1548 {
1549         *delta_jiffies = ULONG_MAX;
1550         return rcu_cpu_has_callbacks(cpu, NULL);
1551 }
1552 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1553 
1554 /*
1555  * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1556  * after it.
1557  */
1558 static void rcu_cleanup_after_idle(int cpu)
1559 {
1560 }
1561 
1562 /*
1563  * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1564  * is nothing.
1565  */
1566 static void rcu_prepare_for_idle(int cpu)
1567 {
1568 }
1569 
1570 /*
1571  * Don't bother keeping a running count of the number of RCU callbacks
1572  * posted because CONFIG_RCU_FAST_NO_HZ=n.
1573  */
1574 static void rcu_idle_count_callbacks_posted(void)
1575 {
1576 }
1577 
1578 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1579 
1580 /*
1581  * This code is invoked when a CPU goes idle, at which point we want
1582  * to have the CPU do everything required for RCU so that it can enter
1583  * the energy-efficient dyntick-idle mode.  This is handled by a
1584  * state machine implemented by rcu_prepare_for_idle() below.
1585  *
1586  * The following three proprocessor symbols control this state machine:
1587  *
1588  * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1589  *      to sleep in dyntick-idle mode with RCU callbacks pending.  This
1590  *      is sized to be roughly one RCU grace period.  Those energy-efficiency
1591  *      benchmarkers who might otherwise be tempted to set this to a large
1592  *      number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1593  *      system.  And if you are -that- concerned about energy efficiency,
1594  *      just power the system down and be done with it!
1595  * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1596  *      permitted to sleep in dyntick-idle mode with only lazy RCU
1597  *      callbacks pending.  Setting this too high can OOM your system.
1598  *
1599  * The values below work well in practice.  If future workloads require
1600  * adjustment, they can be converted into kernel config parameters, though
1601  * making the state machine smarter might be a better option.
1602  */
1603 #define RCU_IDLE_GP_DELAY 4             /* Roughly one grace period. */
1604 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1605 
1606 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1607 module_param(rcu_idle_gp_delay, int, 0644);
1608 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1609 module_param(rcu_idle_lazy_gp_delay, int, 0644);
1610 
1611 extern int tick_nohz_active;
1612 
1613 /*
1614  * Try to advance callbacks for all flavors of RCU on the current CPU, but
1615  * only if it has been awhile since the last time we did so.  Afterwards,
1616  * if there are any callbacks ready for immediate invocation, return true.
1617  */
1618 static bool __maybe_unused rcu_try_advance_all_cbs(void)
1619 {
1620         bool cbs_ready = false;
1621         struct rcu_data *rdp;
1622         struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1623         struct rcu_node *rnp;
1624         struct rcu_state *rsp;
1625 
1626         /* Exit early if we advanced recently. */
1627         if (jiffies == rdtp->last_advance_all)
1628                 return 0;
1629         rdtp->last_advance_all = jiffies;
1630 
1631         for_each_rcu_flavor(rsp) {
1632                 rdp = this_cpu_ptr(rsp->rda);
1633                 rnp = rdp->mynode;
1634 
1635                 /*
1636                  * Don't bother checking unless a grace period has
1637                  * completed since we last checked and there are
1638                  * callbacks not yet ready to invoke.
1639                  */
1640                 if (rdp->completed != rnp->completed &&
1641                     rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1642                         note_gp_changes(rsp, rdp);
1643 
1644                 if (cpu_has_callbacks_ready_to_invoke(rdp))
1645                         cbs_ready = true;
1646         }
1647         return cbs_ready;
1648 }
1649 
1650 /*
1651  * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1652  * to invoke.  If the CPU has callbacks, try to advance them.  Tell the
1653  * caller to set the timeout based on whether or not there are non-lazy
1654  * callbacks.
1655  *
1656  * The caller must have disabled interrupts.
1657  */
1658 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1659 int rcu_needs_cpu(int cpu, unsigned long *dj)
1660 {
1661         struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1662 
1663         /* Snapshot to detect later posting of non-lazy callback. */
1664         rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1665 
1666         /* If no callbacks, RCU doesn't need the CPU. */
1667         if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1668                 *dj = ULONG_MAX;
1669                 return 0;
1670         }
1671 
1672         /* Attempt to advance callbacks. */
1673         if (rcu_try_advance_all_cbs()) {
1674                 /* Some ready to invoke, so initiate later invocation. */
1675                 invoke_rcu_core();
1676                 return 1;
1677         }
1678         rdtp->last_accelerate = jiffies;
1679 
1680         /* Request timer delay depending on laziness, and round. */
1681         if (!rdtp->all_lazy) {
1682                 *dj = round_up(rcu_idle_gp_delay + jiffies,
1683                                rcu_idle_gp_delay) - jiffies;
1684         } else {
1685                 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1686         }
1687         return 0;
1688 }
1689 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1690 
1691 /*
1692  * Prepare a CPU for idle from an RCU perspective.  The first major task
1693  * is to sense whether nohz mode has been enabled or disabled via sysfs.
1694  * The second major task is to check to see if a non-lazy callback has
1695  * arrived at a CPU that previously had only lazy callbacks.  The third
1696  * major task is to accelerate (that is, assign grace-period numbers to)
1697  * any recently arrived callbacks.
1698  *
1699  * The caller must have disabled interrupts.
1700  */
1701 static void rcu_prepare_for_idle(int cpu)
1702 {
1703 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1704         bool needwake;
1705         struct rcu_data *rdp;
1706         struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1707         struct rcu_node *rnp;
1708         struct rcu_state *rsp;
1709         int tne;
1710 
1711         /* Handle nohz enablement switches conservatively. */
1712         tne = ACCESS_ONCE(tick_nohz_active);
1713         if (tne != rdtp->tick_nohz_enabled_snap) {
1714                 if (rcu_cpu_has_callbacks(cpu, NULL))
1715                         invoke_rcu_core(); /* force nohz to see update. */
1716                 rdtp->tick_nohz_enabled_snap = tne;
1717                 return;
1718         }
1719         if (!tne)
1720                 return;
1721 
1722         /* If this is a no-CBs CPU, no callbacks, just return. */
1723         if (rcu_is_nocb_cpu(cpu))
1724                 return;
1725 
1726         /*
1727          * If a non-lazy callback arrived at a CPU having only lazy
1728          * callbacks, invoke RCU core for the side-effect of recalculating
1729          * idle duration on re-entry to idle.
1730          */
1731         if (rdtp->all_lazy &&
1732             rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1733                 rdtp->all_lazy = false;
1734                 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1735                 invoke_rcu_core();
1736                 return;
1737         }
1738 
1739         /*
1740          * If we have not yet accelerated this jiffy, accelerate all
1741          * callbacks on this CPU.
1742          */
1743         if (rdtp->last_accelerate == jiffies)
1744                 return;
1745         rdtp->last_accelerate = jiffies;
1746         for_each_rcu_flavor(rsp) {
1747                 rdp = per_cpu_ptr(rsp->rda, cpu);
1748                 if (!*rdp->nxttail[RCU_DONE_TAIL])
1749                         continue;
1750                 rnp = rdp->mynode;
1751                 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1752                 smp_mb__after_unlock_lock();
1753                 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1754                 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1755                 if (needwake)
1756                         rcu_gp_kthread_wake(rsp);
1757         }
1758 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1759 }
1760 
1761 /*
1762  * Clean up for exit from idle.  Attempt to advance callbacks based on
1763  * any grace periods that elapsed while the CPU was idle, and if any
1764  * callbacks are now ready to invoke, initiate invocation.
1765  */
1766 static void rcu_cleanup_after_idle(int cpu)
1767 {
1768 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1769         if (rcu_is_nocb_cpu(cpu))
1770                 return;
1771         if (rcu_try_advance_all_cbs())
1772                 invoke_rcu_core();
1773 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1774 }
1775 
1776 /*
1777  * Keep a running count of the number of non-lazy callbacks posted
1778  * on this CPU.  This running counter (which is never decremented) allows
1779  * rcu_prepare_for_idle() to detect when something out of the idle loop
1780  * posts a callback, even if an equal number of callbacks are invoked.
1781  * Of course, callbacks should only be posted from within a trace event
1782  * designed to be called from idle or from within RCU_NONIDLE().
1783  */
1784 static void rcu_idle_count_callbacks_posted(void)
1785 {
1786         __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1787 }
1788 
1789 /*
1790  * Data for flushing lazy RCU callbacks at OOM time.
1791  */
1792 static atomic_t oom_callback_count;
1793 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1794 
1795 /*
1796  * RCU OOM callback -- decrement the outstanding count and deliver the
1797  * wake-up if we are the last one.
1798  */
1799 static void rcu_oom_callback(struct rcu_head *rhp)
1800 {
1801         if (atomic_dec_and_test(&oom_callback_count))
1802                 wake_up(&oom_callback_wq);
1803 }
1804 
1805 /*
1806  * Post an rcu_oom_notify callback on the current CPU if it has at
1807  * least one lazy callback.  This will unnecessarily post callbacks
1808  * to CPUs that already have a non-lazy callback at the end of their
1809  * callback list, but this is an infrequent operation, so accept some
1810  * extra overhead to keep things simple.
1811  */
1812 static void rcu_oom_notify_cpu(void *unused)
1813 {
1814         struct rcu_state *rsp;
1815         struct rcu_data *rdp;
1816 
1817         for_each_rcu_flavor(rsp) {
1818                 rdp = raw_cpu_ptr(rsp->rda);
1819                 if (rdp->qlen_lazy != 0) {
1820                         atomic_inc(&oom_callback_count);
1821                         rsp->call(&rdp->oom_head, rcu_oom_callback);
1822                 }
1823         }
1824 }
1825 
1826 /*
1827  * If low on memory, ensure that each CPU has a non-lazy callback.
1828  * This will wake up CPUs that have only lazy callbacks, in turn
1829  * ensuring that they free up the corresponding memory in a timely manner.
1830  * Because an uncertain amount of memory will be freed in some uncertain
1831  * timeframe, we do not claim to have freed anything.
1832  */
1833 static int rcu_oom_notify(struct notifier_block *self,
1834                           unsigned long notused, void *nfreed)
1835 {
1836         int cpu;
1837 
1838         /* Wait for callbacks from earlier instance to complete. */
1839         wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1840         smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1841 
1842         /*
1843          * Prevent premature wakeup: ensure that all increments happen
1844          * before there is a chance of the counter reaching zero.
1845          */
1846         atomic_set(&oom_callback_count, 1);
1847 
1848         get_online_cpus();
1849         for_each_online_cpu(cpu) {
1850                 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1851                 cond_resched();
1852         }
1853         put_online_cpus();
1854 
1855         /* Unconditionally decrement: no need to wake ourselves up. */
1856         atomic_dec(&oom_callback_count);
1857 
1858         return NOTIFY_OK;
1859 }
1860 
1861 static struct notifier_block rcu_oom_nb = {
1862         .notifier_call = rcu_oom_notify
1863 };
1864 
1865 static int __init rcu_register_oom_notifier(void)
1866 {
1867         register_oom_notifier(&rcu_oom_nb);
1868         return 0;
1869 }
1870 early_initcall(rcu_register_oom_notifier);
1871 
1872 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1873 
1874 #ifdef CONFIG_RCU_CPU_STALL_INFO
1875 
1876 #ifdef CONFIG_RCU_FAST_NO_HZ
1877 
1878 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1879 {
1880         struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1881         unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1882 
1883         sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1884                 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1885                 ulong2long(nlpd),
1886                 rdtp->all_lazy ? 'L' : '.',
1887                 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1888 }
1889 
1890 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1891 
1892 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1893 {
1894         *cp = '\0';
1895 }
1896 
1897 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1898 
1899 /* Initiate the stall-info list. */
1900 static void print_cpu_stall_info_begin(void)
1901 {
1902         pr_cont("\n");
1903 }
1904 
1905 /*
1906  * Print out diagnostic information for the specified stalled CPU.
1907  *
1908  * If the specified CPU is aware of the current RCU grace period
1909  * (flavor specified by rsp), then print the number of scheduling
1910  * clock interrupts the CPU has taken during the time that it has
1911  * been aware.  Otherwise, print the number of RCU grace periods
1912  * that this CPU is ignorant of, for example, "1" if the CPU was
1913  * aware of the previous grace period.
1914  *
1915  * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1916  */
1917 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1918 {
1919         char fast_no_hz[72];
1920         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1921         struct rcu_dynticks *rdtp = rdp->dynticks;
1922         char *ticks_title;
1923         unsigned long ticks_value;
1924 
1925         if (rsp->gpnum == rdp->gpnum) {
1926                 ticks_title = "ticks this GP";
1927                 ticks_value = rdp->ticks_this_gp;
1928         } else {
1929                 ticks_title = "GPs behind";
1930                 ticks_value = rsp->gpnum - rdp->gpnum;
1931         }
1932         print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1933         pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1934                cpu, ticks_value, ticks_title,
1935                atomic_read(&rdtp->dynticks) & 0xfff,
1936                rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1937                rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1938                fast_no_hz);
1939 }
1940 
1941 /* Terminate the stall-info list. */
1942 static void print_cpu_stall_info_end(void)
1943 {
1944         pr_err("\t");
1945 }
1946 
1947 /* Zero ->ticks_this_gp for all flavors of RCU. */
1948 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1949 {
1950         rdp->ticks_this_gp = 0;
1951         rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1952 }
1953 
1954 /* Increment ->ticks_this_gp for all flavors of RCU. */
1955 static void increment_cpu_stall_ticks(void)
1956 {
1957         struct rcu_state *rsp;
1958 
1959         for_each_rcu_flavor(rsp)
1960                 raw_cpu_inc(rsp->rda->ticks_this_gp);
1961 }
1962 
1963 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1964 
1965 static void print_cpu_stall_info_begin(void)
1966 {
1967         pr_cont(" {");
1968 }
1969 
1970 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1971 {
1972         pr_cont(" %d", cpu);
1973 }
1974 
1975 static void print_cpu_stall_info_end(void)
1976 {
1977         pr_cont("} ");
1978 }
1979 
1980 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1981 {
1982 }
1983 
1984 static void increment_cpu_stall_ticks(void)
1985 {
1986 }
1987 
1988 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
1989 
1990 #ifdef CONFIG_RCU_NOCB_CPU
1991 
1992 /*
1993  * Offload callback processing from the boot-time-specified set of CPUs
1994  * specified by rcu_nocb_mask.  For each CPU in the set, there is a
1995  * kthread created that pulls the callbacks from the corresponding CPU,
1996  * waits for a grace period to elapse, and invokes the callbacks.
1997  * The no-CBs CPUs do a wake_up() on their kthread when they insert
1998  * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1999  * has been specified, in which case each kthread actively polls its
2000  * CPU.  (Which isn't so great for energy efficiency, but which does
2001  * reduce RCU's overhead on that CPU.)
2002  *
2003  * This is intended to be used in conjunction with Frederic Weisbecker's
2004  * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2005  * running CPU-bound user-mode computations.
2006  *
2007  * Offloading of callback processing could also in theory be used as
2008  * an energy-efficiency measure because CPUs with no RCU callbacks
2009  * queued are more aggressive about entering dyntick-idle mode.
2010  */
2011 
2012 
2013 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2014 static int __init rcu_nocb_setup(char *str)
2015 {
2016         alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2017         have_rcu_nocb_mask = true;
2018         cpulist_parse(str, rcu_nocb_mask);
2019         return 1;
2020 }
2021 __setup("rcu_nocbs=", rcu_nocb_setup);
2022 
2023 static int __init parse_rcu_nocb_poll(char *arg)
2024 {
2025         rcu_nocb_poll = 1;
2026         return 0;
2027 }
2028 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2029 
2030 /*
2031  * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2032  * grace period.
2033  */
2034 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2035 {
2036         wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2037 }
2038 
2039 /*
2040  * Set the root rcu_node structure's ->need_future_gp field
2041  * based on the sum of those of all rcu_node structures.  This does
2042  * double-count the root rcu_node structure's requests, but this
2043  * is necessary to handle the possibility of a rcu_nocb_kthread()
2044  * having awakened during the time that the rcu_node structures
2045  * were being updated for the end of the previous grace period.
2046  */
2047 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2048 {
2049         rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2050 }
2051 
2052 static void rcu_init_one_nocb(struct rcu_node *rnp)
2053 {
2054         init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2055         init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2056 }
2057 
2058 #ifndef CONFIG_RCU_NOCB_CPU_ALL
2059 /* Is the specified CPU a no-CBs CPU? */
2060 bool rcu_is_nocb_cpu(int cpu)
2061 {
2062         if (have_rcu_nocb_mask)
2063                 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2064         return false;
2065 }
2066 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
2067 
2068 /*
2069  * Kick the leader kthread for this NOCB group.
2070  */
2071 static void wake_nocb_leader(struct rcu_data *rdp, bool force)
2072 {
2073         struct rcu_data *rdp_leader = rdp->nocb_leader;
2074 
2075         if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
2076                 return;
2077         if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
2078                 /* Prior xchg orders against prior callback enqueue. */
2079                 ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
2080                 wake_up(&rdp_leader->nocb_wq);
2081         }
2082 }
2083 
2084 /*
2085  * Enqueue the specified string of rcu_head structures onto the specified
2086  * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
2087  * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
2088  * counts are supplied by rhcount and rhcount_lazy.
2089  *
2090  * If warranted, also wake up the kthread servicing this CPUs queues.
2091  */
2092 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2093                                     struct rcu_head *rhp,
2094                                     struct rcu_head **rhtp,
2095                                     int rhcount, int rhcount_lazy,
2096                                     unsigned long flags)
2097 {
2098         int len;
2099         struct rcu_head **old_rhpp;
2100         struct task_struct *t;
2101 
2102         /* Enqueue the callback on the nocb list and update counts. */
2103         old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2104         ACCESS_ONCE(*old_rhpp) = rhp;
2105         atomic_long_add(rhcount, &rdp->nocb_q_count);
2106         atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2107 
2108         /* If we are not being polled and there is a kthread, awaken it ... */
2109         t = ACCESS_ONCE(rdp->nocb_kthread);
2110         if (rcu_nocb_poll || !t) {
2111                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2112                                     TPS("WakeNotPoll"));
2113                 return;
2114         }
2115         len = atomic_long_read(&rdp->nocb_q_count);
2116         if (old_rhpp == &rdp->nocb_head) {
2117                 if (!irqs_disabled_flags(flags)) {
2118                         /* ... if queue was empty ... */
2119                         wake_nocb_leader(rdp, false);
2120                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2121                                             TPS("WakeEmpty"));
2122                 } else {
2123                         rdp->nocb_defer_wakeup = true;
2124                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2125                                             TPS("WakeEmptyIsDeferred"));
2126                 }
2127                 rdp->qlen_last_fqs_check = 0;
2128         } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2129                 /* ... or if many callbacks queued. */
2130                 wake_nocb_leader(rdp, true);
2131                 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2132                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2133         } else {
2134                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2135         }
2136         return;
2137 }
2138 
2139 /*
2140  * This is a helper for __call_rcu(), which invokes this when the normal
2141  * callback queue is inoperable.  If this is not a no-CBs CPU, this
2142  * function returns failure back to __call_rcu(), which can complain
2143  * appropriately.
2144  *
2145  * Otherwise, this function queues the callback where the corresponding
2146  * "rcuo" kthread can find it.
2147  */
2148 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2149                             bool lazy, unsigned long flags)
2150 {
2151 
2152         if (!rcu_is_nocb_cpu(rdp->cpu))
2153                 return 0;
2154         __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2155         if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2156                 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2157                                          (unsigned long)rhp->func,
2158                                          -atomic_long_read(&rdp->nocb_q_count_lazy),
2159                                          -atomic_long_read(&rdp->nocb_q_count));
2160         else
2161                 trace_rcu_callback(rdp->rsp->name, rhp,
2162                                    -atomic_long_read(&rdp->nocb_q_count_lazy),
2163                                    -atomic_long_read(&rdp->nocb_q_count));
2164         return 1;
2165 }
2166 
2167 /*
2168  * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2169  * not a no-CBs CPU.
2170  */
2171 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2172                                                      struct rcu_data *rdp,
2173                                                      unsigned long flags)
2174 {
2175         long ql = rsp->qlen;
2176         long qll = rsp->qlen_lazy;
2177 
2178         /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2179         if (!rcu_is_nocb_cpu(smp_processor_id()))
2180                 return 0;
2181         rsp->qlen = 0;
2182         rsp->qlen_lazy = 0;
2183 
2184         /* First, enqueue the donelist, if any.  This preserves CB ordering. */
2185         if (rsp->orphan_donelist != NULL) {
2186                 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2187                                         rsp->orphan_donetail, ql, qll, flags);
2188                 ql = qll = 0;
2189                 rsp->orphan_donelist = NULL;
2190                 rsp->orphan_donetail = &rsp->orphan_donelist;
2191         }
2192         if (rsp->orphan_nxtlist != NULL) {
2193                 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2194                                         rsp->orphan_nxttail, ql, qll, flags);
2195                 ql = qll = 0;
2196                 rsp->orphan_nxtlist = NULL;
2197                 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2198         }
2199         return 1;
2200 }
2201 
2202 /*
2203  * If necessary, kick off a new grace period, and either way wait
2204  * for a subsequent grace period to complete.
2205  */
2206 static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2207 {
2208         unsigned long c;
2209         bool d;
2210         unsigned long flags;
2211         bool needwake;
2212         struct rcu_node *rnp = rdp->mynode;
2213 
2214         raw_spin_lock_irqsave(&rnp->lock, flags);
2215         smp_mb__after_unlock_lock();
2216         needwake = rcu_start_future_gp(rnp, rdp, &c);
2217         raw_spin_unlock_irqrestore(&rnp->lock, flags);
2218         if (needwake)
2219                 rcu_gp_kthread_wake(rdp->rsp);
2220 
2221         /*
2222          * Wait for the grace period.  Do so interruptibly to avoid messing
2223          * up the load average.
2224          */
2225         trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2226         for (;;) {
2227                 wait_event_interruptible(
2228                         rnp->nocb_gp_wq[c & 0x1],
2229                         (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2230                 if (likely(d))
2231                         break;
2232                 flush_signals(current);
2233                 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2234         }
2235         trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2236         smp_mb(); /* Ensure that CB invocation happens after GP end. */
2237 }
2238 
2239 /*
2240  * Leaders come here to wait for additional callbacks to show up.
2241  * This function does not return until callbacks appear.
2242  */
2243 static void nocb_leader_wait(struct rcu_data *my_rdp)
2244 {
2245         bool firsttime = true;
2246         bool gotcbs;
2247         struct rcu_data *rdp;
2248         struct rcu_head **tail;
2249 
2250 wait_again:
2251 
2252         /* Wait for callbacks to appear. */
2253         if (!rcu_nocb_poll) {
2254                 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
2255                 wait_event_interruptible(my_rdp->nocb_wq,
2256                                 !ACCESS_ONCE(my_rdp->nocb_leader_sleep));
2257                 /* Memory barrier handled by smp_mb() calls below and repoll. */
2258         } else if (firsttime) {
2259                 firsttime = false; /* Don't drown trace log with "Poll"! */
2260                 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
2261         }
2262 
2263         /*
2264          * Each pass through the following loop checks a follower for CBs.
2265          * We are our own first follower.  Any CBs found are moved to
2266          * nocb_gp_head, where they await a grace period.
2267          */
2268         gotcbs = false;
2269         for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2270                 rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head);
2271                 if (!rdp->nocb_gp_head)
2272                         continue;  /* No CBs here, try next follower. */
2273 
2274                 /* Move callbacks to wait-for-GP list, which is empty. */
2275                 ACCESS_ONCE(rdp->nocb_head) = NULL;
2276                 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2277                 rdp->nocb_gp_count = atomic_long_xchg(&rdp->nocb_q_count, 0);
2278                 rdp->nocb_gp_count_lazy =
2279                         atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2280                 gotcbs = true;
2281         }
2282 
2283         /*
2284          * If there were no callbacks, sleep a bit, rescan after a
2285          * memory barrier, and go retry.
2286          */
2287         if (unlikely(!gotcbs)) {
2288                 if (!rcu_nocb_poll)
2289                         trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2290                                             "WokeEmpty");
2291                 flush_signals(current);
2292                 schedule_timeout_interruptible(1);
2293 
2294                 /* Rescan in case we were a victim of memory ordering. */
2295                 my_rdp->nocb_leader_sleep = true;
2296                 smp_mb();  /* Ensure _sleep true before scan. */
2297                 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
2298                         if (ACCESS_ONCE(rdp->nocb_head)) {
2299                                 /* Found CB, so short-circuit next wait. */
2300                                 my_rdp->nocb_leader_sleep = false;
2301                                 break;
2302                         }
2303                 goto wait_again;
2304         }
2305 
2306         /* Wait for one grace period. */
2307         rcu_nocb_wait_gp(my_rdp);
2308 
2309         /*
2310          * We left ->nocb_leader_sleep unset to reduce cache thrashing.
2311          * We set it now, but recheck for new callbacks while
2312          * traversing our follower list.
2313          */
2314         my_rdp->nocb_leader_sleep = true;
2315         smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2316 
2317         /* Each pass through the following loop wakes a follower, if needed. */
2318         for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2319                 if (ACCESS_ONCE(rdp->nocb_head))
2320                         my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2321                 if (!rdp->nocb_gp_head)
2322                         continue; /* No CBs, so no need to wake follower. */
2323 
2324                 /* Append callbacks to follower's "done" list. */
2325                 tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
2326                 *tail = rdp->nocb_gp_head;
2327                 atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count);
2328                 atomic_long_add(rdp->nocb_gp_count_lazy,
2329                                 &rdp->nocb_follower_count_lazy);
2330                 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
2331                         /*
2332                          * List was empty, wake up the follower.
2333                          * Memory barriers supplied by atomic_long_add().
2334                          */
2335                         wake_up(&rdp->nocb_wq);
2336                 }
2337         }
2338 
2339         /* If we (the leader) don't have CBs, go wait some more. */
2340         if (!my_rdp->nocb_follower_head)
2341                 goto wait_again;
2342 }
2343 
2344 /*
2345  * Followers come here to wait for additional callbacks to show up.
2346  * This function does not return until callbacks appear.
2347  */
2348 static void nocb_follower_wait(struct rcu_data *rdp)
2349 {
2350         bool firsttime = true;
2351 
2352         for (;;) {
2353                 if (!rcu_nocb_poll) {
2354                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2355                                             "FollowerSleep");
2356                         wait_event_interruptible(rdp->nocb_wq,
2357                                                  ACCESS_ONCE(rdp->nocb_follower_head));
2358                 } else if (firsttime) {
2359                         /* Don't drown trace log with "Poll"! */
2360                         firsttime = false;
2361                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
2362                 }
2363                 if (smp_load_acquire(&rdp->nocb_follower_head)) {
2364                         /* ^^^ Ensure CB invocation follows _head test. */
2365                         return;
2366                 }
2367                 if (!rcu_nocb_poll)
2368                         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2369                                             "WokeEmpty");
2370                 flush_signals(current);
2371                 schedule_timeout_interruptible(1);
2372         }
2373 }
2374 
2375 /*
2376  * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
2377  * callbacks queued by the corresponding no-CBs CPU, however, there is
2378  * an optional leader-follower relationship so that the grace-period
2379  * kthreads don't have to do quite so many wakeups.
2380  */
2381 static int rcu_nocb_kthread(void *arg)
2382 {
2383         int c, cl;
2384         struct rcu_head *list;
2385         struct rcu_head *next;
2386         struct rcu_head **tail;
2387         struct rcu_data *rdp = arg;
2388 
2389         /* Each pass through this loop invokes one batch of callbacks */
2390         for (;;) {
2391                 /* Wait for callbacks. */
2392                 if (rdp->nocb_leader == rdp)
2393                         nocb_leader_wait(rdp);
2394                 else
2395                         nocb_follower_wait(rdp);
2396 
2397                 /* Pull the ready-to-invoke callbacks onto local list. */
2398                 list = ACCESS_ONCE(rdp->nocb_follower_head);
2399                 BUG_ON(!list);
2400                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
2401                 ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
2402                 tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
2403                 c = atomic_long_xchg(&rdp->nocb_follower_count, 0);
2404                 cl = atomic_long_xchg(&rdp->nocb_follower_count_lazy, 0);
2405                 rdp->nocb_p_count += c;
2406                 rdp->nocb_p_count_lazy += cl;
2407 
2408                 /* Each pass through the following loop invokes a callback. */
2409                 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2410                 c = cl = 0;
2411                 while (list) {
2412                         next = list->next;
2413                         /* Wait for enqueuing to complete, if needed. */
2414                         while (next == NULL && &list->next != tail) {
2415                                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2416                                                     TPS("WaitQueue"));
2417                                 schedule_timeout_interruptible(1);
2418                                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2419                                                     TPS("WokeQueue"));
2420                                 next = list->next;
2421                         }
2422                         debug_rcu_head_unqueue(list);
2423                         local_bh_disable();
2424                         if (__rcu_reclaim(rdp->rsp->name, list))
2425                                 cl++;
2426                         c++;
2427                         local_bh_enable();
2428                         list = next;
2429                 }
2430                 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2431                 ACCESS_ONCE(rdp->nocb_p_count) -= c;
2432                 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2433                 rdp->n_nocbs_invoked += c;
2434         }
2435         return 0;
2436 }
2437 
2438 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2439 static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2440 {
2441         return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2442 }
2443 
2444 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2445 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2446 {
2447         if (!rcu_nocb_need_deferred_wakeup(rdp))
2448                 return;
2449         ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2450         wake_nocb_leader(rdp, false);
2451         trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
2452 }
2453 
2454 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2455 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2456 {
2457         rdp->nocb_tail = &rdp->nocb_head;
2458         init_waitqueue_head(&rdp->nocb_wq);
2459         rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2460 }
2461 
2462 /* How many follower CPU IDs per leader?  Default of -1 for sqrt(nr_cpu_ids). */
2463 static int rcu_nocb_leader_stride = -1;
2464 module_param(rcu_nocb_leader_stride, int, 0444);
2465 
2466 /*
2467  * Create a kthread for each RCU flavor for each no-CBs CPU.
2468  * Also initialize leader-follower relationships.
2469  */
2470 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2471 {
2472         int cpu;
2473         int ls = rcu_nocb_leader_stride;
2474         int nl = 0;  /* Next leader. */
2475         struct rcu_data *rdp;
2476         struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
2477         struct rcu_data *rdp_prev = NULL;
2478         struct task_struct *t;
2479 
2480         if (rcu_nocb_mask == NULL)
2481                 return;
2482 #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
2483         if (tick_nohz_full_running)
2484                 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2485 #endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
2486         if (ls == -1) {
2487                 ls = int_sqrt(nr_cpu_ids);
2488                 rcu_nocb_leader_stride = ls;
2489         }
2490 
2491         /*
2492          * Each pass through this loop sets up one rcu_data structure and
2493          * spawns one rcu_nocb_kthread().
2494          */
2495         for_each_cpu(cpu, rcu_nocb_mask) {
2496                 rdp = per_cpu_ptr(rsp->rda, cpu);
2497                 if (rdp->cpu >= nl) {
2498                         /* New leader, set up for followers & next leader. */
2499                         nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2500                         rdp->nocb_leader = rdp;
2501                         rdp_leader = rdp;
2502                 } else {
2503                         /* Another follower, link to previous leader. */
2504                         rdp->nocb_leader = rdp_leader;
2505                         rdp_prev->nocb_next_follower = rdp;
2506                 }
2507                 rdp_prev = rdp;
2508 
2509                 /* Spawn the kthread for this CPU. */
2510                 t = kthread_run(rcu_nocb_kthread, rdp,
2511                                 "rcuo%c/%d", rsp->abbr, cpu);
2512                 BUG_ON(IS_ERR(t));
2513                 ACCESS_ONCE(rdp->nocb_kthread) = t;
2514         }
2515 }
2516 
2517 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2518 static bool init_nocb_callback_list(struct rcu_data *rdp)
2519 {
2520         if (rcu_nocb_mask == NULL ||
2521             !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2522                 return false;
2523         rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2524         return true;
2525 }
2526 
2527 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2528 
2529 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2530 {
2531 }
2532 
2533 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2534 {
2535 }
2536 
2537 static void rcu_init_one_nocb(struct rcu_node *rnp)
2538 {
2539 }
2540 
2541 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2542                             bool lazy, unsigned long flags)
2543 {
2544         return 0;
2545 }
2546 
2547 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2548                                                      struct rcu_data *rdp,
2549                                                      unsigned long flags)
2550 {
2551         return 0;
2552 }
2553 
2554 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2555 {
2556 }
2557 
2558 static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2559 {
2560         return false;
2561 }
2562 
2563 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2564 {
2565 }
2566 
2567 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2568 {
2569 }
2570 
2571 static bool init_nocb_callback_list(struct rcu_data *rdp)
2572 {
2573         return false;
2574 }
2575 
2576 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2577 
2578 /*
2579  * An adaptive-ticks CPU can potentially execute in kernel mode for an
2580  * arbitrarily long period of time with the scheduling-clock tick turned
2581  * off.  RCU will be paying attention to this CPU because it is in the
2582  * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2583  * machine because the scheduling-clock tick has been disabled.  Therefore,
2584  * if an adaptive-ticks CPU is failing to respond to the current grace
2585  * period and has not be idle from an RCU perspective, kick it.
2586  */
2587 static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2588 {
2589 #ifdef CONFIG_NO_HZ_FULL
2590         if (tick_nohz_full_cpu(cpu))
2591                 smp_send_reschedule(cpu);
2592 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2593 }
2594 
2595 
2596 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2597 
2598 /*
2599  * Define RCU flavor that holds sysidle state.  This needs to be the
2600  * most active flavor of RCU.
2601  */
2602 #ifdef CONFIG_PREEMPT_RCU
2603 static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2604 #else /* #ifdef CONFIG_PREEMPT_RCU */
2605 static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2606 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2607 
2608 static int full_sysidle_state;          /* Current system-idle state. */
2609 #define RCU_SYSIDLE_NOT         0       /* Some CPU is not idle. */
2610 #define RCU_SYSIDLE_SHORT       1       /* All CPUs idle for brief period. */
2611 #define RCU_SYSIDLE_LONG        2       /* All CPUs idle for long enough. */
2612 #define RCU_SYSIDLE_FULL        3       /* All CPUs idle, ready for sysidle. */
2613 #define RCU_SYSIDLE_FULL_NOTED  4       /* Actually entered sysidle state. */
2614 
2615 /*
2616  * Invoked to note exit from irq or task transition to idle.  Note that
2617  * usermode execution does -not- count as idle here!  After all, we want
2618  * to detect full-system idle states, not RCU quiescent states and grace
2619  * periods.  The caller must have disabled interrupts.
2620  */
2621 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2622 {
2623         unsigned long j;
2624 
2625         /* Adjust nesting, check for fully idle. */
2626         if (irq) {
2627                 rdtp->dynticks_idle_nesting--;
2628                 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2629                 if (rdtp->dynticks_idle_nesting != 0)
2630                         return;  /* Still not fully idle. */
2631         } else {
2632                 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2633                     DYNTICK_TASK_NEST_VALUE) {
2634                         rdtp->dynticks_idle_nesting = 0;
2635                 } else {
2636                         rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2637                         WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2638                         return;  /* Still not fully idle. */
2639                 }
2640         }
2641 
2642         /* Record start of fully idle period. */
2643         j = jiffies;
2644         ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2645         smp_mb__before_atomic();
2646         atomic_inc(&rdtp->dynticks_idle);
2647         smp_mb__after_atomic();
2648         WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2649 }
2650 
2651 /*
2652  * Unconditionally force exit from full system-idle state.  This is
2653  * invoked when a normal CPU exits idle, but must be called separately
2654  * for the timekeeping CPU (tick_do_timer_cpu).  The reason for this
2655  * is that the timekeeping CPU is permitted to take scheduling-clock
2656  * interrupts while the system is in system-idle state, and of course
2657  * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2658  * interrupt from any other type of interrupt.
2659  */
2660 void rcu_sysidle_force_exit(void)
2661 {
2662         int oldstate = ACCESS_ONCE(full_sysidle_state);
2663         int newoldstate;
2664 
2665         /*
2666          * Each pass through the following loop attempts to exit full
2667          * system-idle state.  If contention proves to be a problem,
2668          * a trylock-based contention tree could be used here.
2669          */
2670         while (oldstate > RCU_SYSIDLE_SHORT) {
2671                 newoldstate = cmpxchg(&full_sysidle_state,
2672                                       oldstate, RCU_SYSIDLE_NOT);
2673                 if (oldstate == newoldstate &&
2674                     oldstate == RCU_SYSIDLE_FULL_NOTED) {
2675                         rcu_kick_nohz_cpu(tick_do_timer_cpu);
2676                         return; /* We cleared it, done! */
2677                 }
2678                 oldstate = newoldstate;
2679         }
2680         smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2681 }
2682 
2683 /*
2684  * Invoked to note entry to irq or task transition from idle.  Note that
2685  * usermode execution does -not- count as idle here!  The caller must
2686  * have disabled interrupts.
2687  */
2688 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2689 {
2690         /* Adjust nesting, check for already non-idle. */
2691         if (irq) {
2692                 rdtp->dynticks_idle_nesting++;
2693                 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2694                 if (rdtp->dynticks_idle_nesting != 1)
2695                         return; /* Already non-idle. */
2696         } else {
2697                 /*
2698                  * Allow for irq misnesting.  Yes, it really is possible
2699                  * to enter an irq handler then never leave it, and maybe
2700                  * also vice versa.  Handle both possibilities.
2701                  */
2702                 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2703                         rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2704                         WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2705                         return; /* Already non-idle. */
2706                 } else {
2707                         rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2708                 }
2709         }
2710 
2711         /* Record end of idle period. */
2712         smp_mb__before_atomic();
2713         atomic_inc(&rdtp->dynticks_idle);
2714         smp_mb__after_atomic();
2715         WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2716 
2717         /*
2718          * If we are the timekeeping CPU, we are permitted to be non-idle
2719          * during a system-idle state.  This must be the case, because
2720          * the timekeeping CPU has to take scheduling-clock interrupts
2721          * during the time that the system is transitioning to full
2722          * system-idle state.  This means that the timekeeping CPU must
2723          * invoke rcu_sysidle_force_exit() directly if it does anything
2724          * more than take a scheduling-clock interrupt.
2725          */
2726         if (smp_processor_id() == tick_do_timer_cpu)
2727                 return;
2728 
2729         /* Update system-idle state: We are clearly no longer fully idle! */
2730         rcu_sysidle_force_exit();
2731 }
2732 
2733 /*
2734  * Check to see if the current CPU is idle.  Note that usermode execution
2735  * does not count as idle.  The caller must have disabled interrupts.
2736  */
2737 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2738                                   unsigned long *maxj)
2739 {
2740         int cur;
2741         unsigned long j;
2742         struct rcu_dynticks *rdtp = rdp->dynticks;
2743 
2744         /*
2745          * If some other CPU has already reported non-idle, if this is
2746          * not the flavor of RCU that tracks sysidle state, or if this
2747          * is an offline or the timekeeping CPU, nothing to do.
2748          */
2749         if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2750             cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2751                 return;
2752         if (rcu_gp_in_progress(rdp->rsp))
2753                 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2754 
2755         /* Pick up current idle and NMI-nesting counter and check. */
2756         cur = atomic_read(&rdtp->dynticks_idle);
2757         if (cur & 0x1) {
2758                 *isidle = false; /* We are not idle! */
2759                 return;
2760         }
2761         smp_mb(); /* Read counters before timestamps. */
2762 
2763         /* Pick up timestamps. */
2764         j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2765         /* If this CPU entered idle more recently, update maxj timestamp. */
2766         if (ULONG_CMP_LT(*maxj, j))
2767                 *maxj = j;
2768 }
2769 
2770 /*
2771  * Is this the flavor of RCU that is handling full-system idle?
2772  */
2773 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2774 {
2775         return rsp == rcu_sysidle_state;
2776 }
2777 
2778 /*
2779  * Return a delay in jiffies based on the number of CPUs, rcu_node
2780  * leaf fanout, and jiffies tick rate.  The idea is to allow larger
2781  * systems more time to transition to full-idle state in order to
2782  * avoid the cache thrashing that otherwise occur on the state variable.
2783  * Really small systems (less than a couple of tens of CPUs) should
2784  * instead use a single global atomically incremented counter, and later
2785  * versions of this will automatically reconfigure themselves accordingly.
2786  */
2787 static unsigned long rcu_sysidle_delay(void)
2788 {
2789         if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2790                 return 0;
2791         return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2792 }
2793 
2794 /*
2795  * Advance the full-system-idle state.  This is invoked when all of
2796  * the non-timekeeping CPUs are idle.
2797  */
2798 static void rcu_sysidle(unsigned long j)
2799 {
2800         /* Check the current state. */
2801         switch (ACCESS_ONCE(full_sysidle_state)) {
2802         case RCU_SYSIDLE_NOT:
2803 
2804                 /* First time all are idle, so note a short idle period. */
2805                 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2806                 break;
2807 
2808         case RCU_SYSIDLE_SHORT:
2809 
2810                 /*
2811                  * Idle for a bit, time to advance to next state?
2812                  * cmpxchg failure means race with non-idle, let them win.
2813                  */
2814                 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2815                         (void)cmpxchg(&full_sysidle_state,
2816                                       RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2817                 break;
2818 
2819         case RCU_SYSIDLE_LONG:
2820 
2821                 /*
2822                  * Do an additional check pass before advancing to full.
2823                  * cmpxchg failure means race with non-idle, let them win.
2824                  */
2825                 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2826                         (void)cmpxchg(&full_sysidle_state,
2827                                       RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2828                 break;
2829 
2830         default:
2831                 break;
2832         }
2833 }
2834 
2835 /*
2836  * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2837  * back to the beginning.
2838  */
2839 static void rcu_sysidle_cancel(void)
2840 {
2841         smp_mb();
2842         if (full_sysidle_state > RCU_SYSIDLE_SHORT)
2843                 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2844 }
2845 
2846 /*
2847  * Update the sysidle state based on the results of a force-quiescent-state
2848  * scan of the CPUs' dyntick-idle state.
2849  */
2850 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2851                                unsigned long maxj, bool gpkt)
2852 {
2853         if (rsp != rcu_sysidle_state)
2854                 return;  /* Wrong flavor, ignore. */
2855         if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2856                 return;  /* Running state machine from timekeeping CPU. */
2857         if (isidle)
2858                 rcu_sysidle(maxj);    /* More idle! */
2859         else
2860                 rcu_sysidle_cancel(); /* Idle is over. */
2861 }
2862 
2863 /*
2864  * Wrapper for rcu_sysidle_report() when called from the grace-period
2865  * kthread's context.
2866  */
2867 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2868                                   unsigned long maxj)
2869 {
2870         rcu_sysidle_report(rsp, isidle, maxj, true);
2871 }
2872 
2873 /* Callback and function for forcing an RCU grace period. */
2874 struct rcu_sysidle_head {
2875         struct rcu_head rh;
2876         int inuse;
2877 };
2878 
2879 static void rcu_sysidle_cb(struct rcu_head *rhp)
2880 {
2881         struct rcu_sysidle_head *rshp;
2882 
2883         /*
2884          * The following memory barrier is needed to replace the
2885          * memory barriers that would normally be in the memory
2886          * allocator.
2887          */
2888         smp_mb();  /* grace period precedes setting inuse. */
2889 
2890         rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2891         ACCESS_ONCE(rshp->inuse) = 0;
2892 }
2893 
2894 /*
2895  * Check to see if the system is fully idle, other than the timekeeping CPU.
2896  * The caller must have disabled interrupts.
2897  */
2898 bool rcu_sys_is_idle(void)
2899 {
2900         static struct rcu_sysidle_head rsh;
2901         int rss = ACCESS_ONCE(full_sysidle_state);
2902 
2903         if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2904                 return false;
2905 
2906         /* Handle small-system case by doing a full scan of CPUs. */
2907         if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2908                 int oldrss = rss - 1;
2909 
2910                 /*
2911                  * One pass to advance to each state up to _FULL.
2912                  * Give up if any pass fails to advance the state.
2913                  */
2914                 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2915                         int cpu;
2916                         bool isidle = true;
2917                         unsigned long maxj = jiffies - ULONG_MAX / 4;
2918                         struct rcu_data *rdp;
2919 
2920                         /* Scan all the CPUs looking for nonidle CPUs. */
2921                         for_each_possible_cpu(cpu) {
2922                                 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2923                                 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2924                                 if (!isidle)
2925                                         break;
2926                         }
2927                         rcu_sysidle_report(rcu_sysidle_state,
2928                                            isidle, maxj, false);
2929                         oldrss = rss;
2930                         rss = ACCESS_ONCE(full_sysidle_state);
2931                 }
2932         }
2933 
2934         /* If this is the first observation of an idle period, record it. */
2935         if (rss == RCU_SYSIDLE_FULL) {
2936                 rss = cmpxchg(&full_sysidle_state,
2937                               RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2938                 return rss == RCU_SYSIDLE_FULL;
2939         }
2940 
2941         smp_mb(); /* ensure rss load happens before later caller actions. */
2942 
2943         /* If already fully idle, tell the caller (in case of races). */
2944         if (rss == RCU_SYSIDLE_FULL_NOTED)
2945                 return true;
2946 
2947         /*
2948          * If we aren't there yet, and a grace period is not in flight,
2949          * initiate a grace period.  Either way, tell the caller that
2950          * we are not there yet.  We use an xchg() rather than an assignment
2951          * to make up for the memory barriers that would otherwise be
2952          * provided by the memory allocator.
2953          */
2954         if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2955             !rcu_gp_in_progress(rcu_sysidle_state) &&
2956             !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2957                 call_rcu(&rsh.rh, rcu_sysidle_cb);
2958         return false;
2959 }
2960 
2961 /*
2962  * Initialize dynticks sysidle state for CPUs coming online.
2963  */
2964 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2965 {
2966         rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2967 }
2968 
2969 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2970 
2971 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2972 {
2973 }
2974 
2975 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2976 {
2977 }
2978 
2979 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2980                                   unsigned long *maxj)
2981 {
2982 }
2983 
2984 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2985 {
2986         return false;
2987 }
2988 
2989 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2990                                   unsigned long maxj)
2991 {
2992 }
2993 
2994 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2995 {
2996 }
2997 
2998 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2999 
3000 /*
3001  * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
3002  * grace-period kthread will do force_quiescent_state() processing?
3003  * The idea is to avoid waking up RCU core processing on such a
3004  * CPU unless the grace period has extended for too long.
3005  *
3006  * This code relies on the fact that all NO_HZ_FULL CPUs are also
3007  * CONFIG_RCU_NOCB_CPU CPUs.
3008  */
3009 static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
3010 {
3011 #ifdef CONFIG_NO_HZ_FULL
3012         if (tick_nohz_full_cpu(smp_processor_id()) &&
3013             (!rcu_gp_in_progress(rsp) ||
3014              ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
3015                 return 1;
3016 #endif /* #ifdef CONFIG_NO_HZ_FULL */
3017         return 0;
3018 }
3019 
3020 /*
3021  * Bind the grace-period kthread for the sysidle flavor of RCU to the
3022  * timekeeping CPU.
3023  */
3024 static void rcu_bind_gp_kthread(void)
3025 {
3026         int __maybe_unused cpu;
3027 
3028         if (!tick_nohz_full_enabled())
3029                 return;
3030 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
3031         cpu = tick_do_timer_cpu;
3032         if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
3033                 set_cpus_allowed_ptr(current, cpumask_of(cpu));
3034 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3035         if (!is_housekeeping_cpu(raw_smp_processor_id()))
3036                 housekeeping_affine(current);
3037 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3038 }
3039 

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