Input: implement input filters
[linux/fpc-iii.git] / kernel / rcutree.c
blob53ae9598f798c61398578b39f6d5f4969601961f
1 /*
2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2008
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
27 * For detailed explanation of Read-Copy Update mechanism see -
28 * Documentation/RCU
30 #include <linux/types.h>
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 #include <linux/smp.h>
35 #include <linux/rcupdate.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/nmi.h>
39 #include <asm/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/module.h>
42 #include <linux/completion.h>
43 #include <linux/moduleparam.h>
44 #include <linux/percpu.h>
45 #include <linux/notifier.h>
46 #include <linux/cpu.h>
47 #include <linux/mutex.h>
48 #include <linux/time.h>
49 #include <linux/kernel_stat.h>
51 #include "rcutree.h"
53 /* Data structures. */
55 static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
57 #define RCU_STATE_INITIALIZER(name) { \
58 .level = { &name.node[0] }, \
59 .levelcnt = { \
60 NUM_RCU_LVL_0, /* root of hierarchy. */ \
61 NUM_RCU_LVL_1, \
62 NUM_RCU_LVL_2, \
63 NUM_RCU_LVL_3, \
64 NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
65 }, \
66 .signaled = RCU_GP_IDLE, \
67 .gpnum = -300, \
68 .completed = -300, \
69 .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
70 .orphan_cbs_list = NULL, \
71 .orphan_cbs_tail = &name.orphan_cbs_list, \
72 .orphan_qlen = 0, \
73 .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
74 .n_force_qs = 0, \
75 .n_force_qs_ngp = 0, \
78 struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
79 DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
81 struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
82 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
84 static int rcu_scheduler_active __read_mostly;
88 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
89 * permit this function to be invoked without holding the root rcu_node
90 * structure's ->lock, but of course results can be subject to change.
92 static int rcu_gp_in_progress(struct rcu_state *rsp)
94 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
98 * Note a quiescent state. Because we do not need to know
99 * how many quiescent states passed, just if there was at least
100 * one since the start of the grace period, this just sets a flag.
102 void rcu_sched_qs(int cpu)
104 struct rcu_data *rdp;
106 rdp = &per_cpu(rcu_sched_data, cpu);
107 rdp->passed_quiesc_completed = rdp->gpnum - 1;
108 barrier();
109 rdp->passed_quiesc = 1;
110 rcu_preempt_note_context_switch(cpu);
113 void rcu_bh_qs(int cpu)
115 struct rcu_data *rdp;
117 rdp = &per_cpu(rcu_bh_data, cpu);
118 rdp->passed_quiesc_completed = rdp->gpnum - 1;
119 barrier();
120 rdp->passed_quiesc = 1;
123 #ifdef CONFIG_NO_HZ
124 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
125 .dynticks_nesting = 1,
126 .dynticks = 1,
128 #endif /* #ifdef CONFIG_NO_HZ */
130 static int blimit = 10; /* Maximum callbacks per softirq. */
131 static int qhimark = 10000; /* If this many pending, ignore blimit. */
132 static int qlowmark = 100; /* Once only this many pending, use blimit. */
134 module_param(blimit, int, 0);
135 module_param(qhimark, int, 0);
136 module_param(qlowmark, int, 0);
138 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
139 static int rcu_pending(int cpu);
142 * Return the number of RCU-sched batches processed thus far for debug & stats.
144 long rcu_batches_completed_sched(void)
146 return rcu_sched_state.completed;
148 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
151 * Return the number of RCU BH batches processed thus far for debug & stats.
153 long rcu_batches_completed_bh(void)
155 return rcu_bh_state.completed;
157 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
160 * Does the CPU have callbacks ready to be invoked?
162 static int
163 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
165 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
169 * Does the current CPU require a yet-as-unscheduled grace period?
171 static int
172 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
174 return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
178 * Return the root node of the specified rcu_state structure.
180 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
182 return &rsp->node[0];
185 #ifdef CONFIG_SMP
188 * If the specified CPU is offline, tell the caller that it is in
189 * a quiescent state. Otherwise, whack it with a reschedule IPI.
190 * Grace periods can end up waiting on an offline CPU when that
191 * CPU is in the process of coming online -- it will be added to the
192 * rcu_node bitmasks before it actually makes it online. The same thing
193 * can happen while a CPU is in the process of coming online. Because this
194 * race is quite rare, we check for it after detecting that the grace
195 * period has been delayed rather than checking each and every CPU
196 * each and every time we start a new grace period.
198 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
201 * If the CPU is offline, it is in a quiescent state. We can
202 * trust its state not to change because interrupts are disabled.
204 if (cpu_is_offline(rdp->cpu)) {
205 rdp->offline_fqs++;
206 return 1;
209 /* If preemptable RCU, no point in sending reschedule IPI. */
210 if (rdp->preemptable)
211 return 0;
213 /* The CPU is online, so send it a reschedule IPI. */
214 if (rdp->cpu != smp_processor_id())
215 smp_send_reschedule(rdp->cpu);
216 else
217 set_need_resched();
218 rdp->resched_ipi++;
219 return 0;
222 #endif /* #ifdef CONFIG_SMP */
224 #ifdef CONFIG_NO_HZ
227 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
229 * Enter nohz mode, in other words, -leave- the mode in which RCU
230 * read-side critical sections can occur. (Though RCU read-side
231 * critical sections can occur in irq handlers in nohz mode, a possibility
232 * handled by rcu_irq_enter() and rcu_irq_exit()).
234 void rcu_enter_nohz(void)
236 unsigned long flags;
237 struct rcu_dynticks *rdtp;
239 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
240 local_irq_save(flags);
241 rdtp = &__get_cpu_var(rcu_dynticks);
242 rdtp->dynticks++;
243 rdtp->dynticks_nesting--;
244 WARN_ON_ONCE(rdtp->dynticks & 0x1);
245 local_irq_restore(flags);
249 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
251 * Exit nohz mode, in other words, -enter- the mode in which RCU
252 * read-side critical sections normally occur.
254 void rcu_exit_nohz(void)
256 unsigned long flags;
257 struct rcu_dynticks *rdtp;
259 local_irq_save(flags);
260 rdtp = &__get_cpu_var(rcu_dynticks);
261 rdtp->dynticks++;
262 rdtp->dynticks_nesting++;
263 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
264 local_irq_restore(flags);
265 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
269 * rcu_nmi_enter - inform RCU of entry to NMI context
271 * If the CPU was idle with dynamic ticks active, and there is no
272 * irq handler running, this updates rdtp->dynticks_nmi to let the
273 * RCU grace-period handling know that the CPU is active.
275 void rcu_nmi_enter(void)
277 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
279 if (rdtp->dynticks & 0x1)
280 return;
281 rdtp->dynticks_nmi++;
282 WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
283 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
287 * rcu_nmi_exit - inform RCU of exit from NMI context
289 * If the CPU was idle with dynamic ticks active, and there is no
290 * irq handler running, this updates rdtp->dynticks_nmi to let the
291 * RCU grace-period handling know that the CPU is no longer active.
293 void rcu_nmi_exit(void)
295 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
297 if (rdtp->dynticks & 0x1)
298 return;
299 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
300 rdtp->dynticks_nmi++;
301 WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
305 * rcu_irq_enter - inform RCU of entry to hard irq context
307 * If the CPU was idle with dynamic ticks active, this updates the
308 * rdtp->dynticks to let the RCU handling know that the CPU is active.
310 void rcu_irq_enter(void)
312 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
314 if (rdtp->dynticks_nesting++)
315 return;
316 rdtp->dynticks++;
317 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
318 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
322 * rcu_irq_exit - inform RCU of exit from hard irq context
324 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
325 * to put let the RCU handling be aware that the CPU is going back to idle
326 * with no ticks.
328 void rcu_irq_exit(void)
330 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
332 if (--rdtp->dynticks_nesting)
333 return;
334 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
335 rdtp->dynticks++;
336 WARN_ON_ONCE(rdtp->dynticks & 0x1);
338 /* If the interrupt queued a callback, get out of dyntick mode. */
339 if (__get_cpu_var(rcu_sched_data).nxtlist ||
340 __get_cpu_var(rcu_bh_data).nxtlist)
341 set_need_resched();
344 #ifdef CONFIG_SMP
347 * Snapshot the specified CPU's dynticks counter so that we can later
348 * credit them with an implicit quiescent state. Return 1 if this CPU
349 * is in dynticks idle mode, which is an extended quiescent state.
351 static int dyntick_save_progress_counter(struct rcu_data *rdp)
353 int ret;
354 int snap;
355 int snap_nmi;
357 snap = rdp->dynticks->dynticks;
358 snap_nmi = rdp->dynticks->dynticks_nmi;
359 smp_mb(); /* Order sampling of snap with end of grace period. */
360 rdp->dynticks_snap = snap;
361 rdp->dynticks_nmi_snap = snap_nmi;
362 ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
363 if (ret)
364 rdp->dynticks_fqs++;
365 return ret;
369 * Return true if the specified CPU has passed through a quiescent
370 * state by virtue of being in or having passed through an dynticks
371 * idle state since the last call to dyntick_save_progress_counter()
372 * for this same CPU.
374 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
376 long curr;
377 long curr_nmi;
378 long snap;
379 long snap_nmi;
381 curr = rdp->dynticks->dynticks;
382 snap = rdp->dynticks_snap;
383 curr_nmi = rdp->dynticks->dynticks_nmi;
384 snap_nmi = rdp->dynticks_nmi_snap;
385 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
388 * If the CPU passed through or entered a dynticks idle phase with
389 * no active irq/NMI handlers, then we can safely pretend that the CPU
390 * already acknowledged the request to pass through a quiescent
391 * state. Either way, that CPU cannot possibly be in an RCU
392 * read-side critical section that started before the beginning
393 * of the current RCU grace period.
395 if ((curr != snap || (curr & 0x1) == 0) &&
396 (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
397 rdp->dynticks_fqs++;
398 return 1;
401 /* Go check for the CPU being offline. */
402 return rcu_implicit_offline_qs(rdp);
405 #endif /* #ifdef CONFIG_SMP */
407 #else /* #ifdef CONFIG_NO_HZ */
409 #ifdef CONFIG_SMP
411 static int dyntick_save_progress_counter(struct rcu_data *rdp)
413 return 0;
416 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
418 return rcu_implicit_offline_qs(rdp);
421 #endif /* #ifdef CONFIG_SMP */
423 #endif /* #else #ifdef CONFIG_NO_HZ */
425 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
427 static void record_gp_stall_check_time(struct rcu_state *rsp)
429 rsp->gp_start = jiffies;
430 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
433 static void print_other_cpu_stall(struct rcu_state *rsp)
435 int cpu;
436 long delta;
437 unsigned long flags;
438 struct rcu_node *rnp = rcu_get_root(rsp);
440 /* Only let one CPU complain about others per time interval. */
442 spin_lock_irqsave(&rnp->lock, flags);
443 delta = jiffies - rsp->jiffies_stall;
444 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
445 spin_unlock_irqrestore(&rnp->lock, flags);
446 return;
448 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
451 * Now rat on any tasks that got kicked up to the root rcu_node
452 * due to CPU offlining.
454 rcu_print_task_stall(rnp);
455 spin_unlock_irqrestore(&rnp->lock, flags);
457 /* OK, time to rat on our buddy... */
459 printk(KERN_ERR "INFO: RCU detected CPU stalls:");
460 rcu_for_each_leaf_node(rsp, rnp) {
461 rcu_print_task_stall(rnp);
462 if (rnp->qsmask == 0)
463 continue;
464 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
465 if (rnp->qsmask & (1UL << cpu))
466 printk(" %d", rnp->grplo + cpu);
468 printk(" (detected by %d, t=%ld jiffies)\n",
469 smp_processor_id(), (long)(jiffies - rsp->gp_start));
470 trigger_all_cpu_backtrace();
472 force_quiescent_state(rsp, 0); /* Kick them all. */
475 static void print_cpu_stall(struct rcu_state *rsp)
477 unsigned long flags;
478 struct rcu_node *rnp = rcu_get_root(rsp);
480 printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
481 smp_processor_id(), jiffies - rsp->gp_start);
482 trigger_all_cpu_backtrace();
484 spin_lock_irqsave(&rnp->lock, flags);
485 if ((long)(jiffies - rsp->jiffies_stall) >= 0)
486 rsp->jiffies_stall =
487 jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
488 spin_unlock_irqrestore(&rnp->lock, flags);
490 set_need_resched(); /* kick ourselves to get things going. */
493 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
495 long delta;
496 struct rcu_node *rnp;
498 delta = jiffies - rsp->jiffies_stall;
499 rnp = rdp->mynode;
500 if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
502 /* We haven't checked in, so go dump stack. */
503 print_cpu_stall(rsp);
505 } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
507 /* They had two time units to dump stack, so complain. */
508 print_other_cpu_stall(rsp);
512 #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
514 static void record_gp_stall_check_time(struct rcu_state *rsp)
518 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
522 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
525 * Update CPU-local rcu_data state to record the newly noticed grace period.
526 * This is used both when we started the grace period and when we notice
527 * that someone else started the grace period. The caller must hold the
528 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
529 * and must have irqs disabled.
531 static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
533 if (rdp->gpnum != rnp->gpnum) {
534 rdp->qs_pending = 1;
535 rdp->passed_quiesc = 0;
536 rdp->gpnum = rnp->gpnum;
540 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
542 unsigned long flags;
543 struct rcu_node *rnp;
545 local_irq_save(flags);
546 rnp = rdp->mynode;
547 if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
548 !spin_trylock(&rnp->lock)) { /* irqs already off, retry later. */
549 local_irq_restore(flags);
550 return;
552 __note_new_gpnum(rsp, rnp, rdp);
553 spin_unlock_irqrestore(&rnp->lock, flags);
557 * Did someone else start a new RCU grace period start since we last
558 * checked? Update local state appropriately if so. Must be called
559 * on the CPU corresponding to rdp.
561 static int
562 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
564 unsigned long flags;
565 int ret = 0;
567 local_irq_save(flags);
568 if (rdp->gpnum != rsp->gpnum) {
569 note_new_gpnum(rsp, rdp);
570 ret = 1;
572 local_irq_restore(flags);
573 return ret;
577 * Advance this CPU's callbacks, but only if the current grace period
578 * has ended. This may be called only from the CPU to whom the rdp
579 * belongs. In addition, the corresponding leaf rcu_node structure's
580 * ->lock must be held by the caller, with irqs disabled.
582 static void
583 __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
585 /* Did another grace period end? */
586 if (rdp->completed != rnp->completed) {
588 /* Advance callbacks. No harm if list empty. */
589 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
590 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
591 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
593 /* Remember that we saw this grace-period completion. */
594 rdp->completed = rnp->completed;
599 * Advance this CPU's callbacks, but only if the current grace period
600 * has ended. This may be called only from the CPU to whom the rdp
601 * belongs.
603 static void
604 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
606 unsigned long flags;
607 struct rcu_node *rnp;
609 local_irq_save(flags);
610 rnp = rdp->mynode;
611 if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
612 !spin_trylock(&rnp->lock)) { /* irqs already off, retry later. */
613 local_irq_restore(flags);
614 return;
616 __rcu_process_gp_end(rsp, rnp, rdp);
617 spin_unlock_irqrestore(&rnp->lock, flags);
621 * Do per-CPU grace-period initialization for running CPU. The caller
622 * must hold the lock of the leaf rcu_node structure corresponding to
623 * this CPU.
625 static void
626 rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
628 /* Prior grace period ended, so advance callbacks for current CPU. */
629 __rcu_process_gp_end(rsp, rnp, rdp);
632 * Because this CPU just now started the new grace period, we know
633 * that all of its callbacks will be covered by this upcoming grace
634 * period, even the ones that were registered arbitrarily recently.
635 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
637 * Other CPUs cannot be sure exactly when the grace period started.
638 * Therefore, their recently registered callbacks must pass through
639 * an additional RCU_NEXT_READY stage, so that they will be handled
640 * by the next RCU grace period.
642 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
643 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
645 /* Set state so that this CPU will detect the next quiescent state. */
646 __note_new_gpnum(rsp, rnp, rdp);
650 * Start a new RCU grace period if warranted, re-initializing the hierarchy
651 * in preparation for detecting the next grace period. The caller must hold
652 * the root node's ->lock, which is released before return. Hard irqs must
653 * be disabled.
655 static void
656 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
657 __releases(rcu_get_root(rsp)->lock)
659 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
660 struct rcu_node *rnp = rcu_get_root(rsp);
662 if (!cpu_needs_another_gp(rsp, rdp)) {
663 if (rnp->completed == rsp->completed) {
664 spin_unlock_irqrestore(&rnp->lock, flags);
665 return;
667 spin_unlock(&rnp->lock); /* irqs remain disabled. */
670 * Propagate new ->completed value to rcu_node structures
671 * so that other CPUs don't have to wait until the start
672 * of the next grace period to process their callbacks.
674 rcu_for_each_node_breadth_first(rsp, rnp) {
675 spin_lock(&rnp->lock); /* irqs already disabled. */
676 rnp->completed = rsp->completed;
677 spin_unlock(&rnp->lock); /* irqs remain disabled. */
679 local_irq_restore(flags);
680 return;
683 /* Advance to a new grace period and initialize state. */
684 rsp->gpnum++;
685 WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
686 rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
687 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
688 record_gp_stall_check_time(rsp);
690 /* Special-case the common single-level case. */
691 if (NUM_RCU_NODES == 1) {
692 rcu_preempt_check_blocked_tasks(rnp);
693 rnp->qsmask = rnp->qsmaskinit;
694 rnp->gpnum = rsp->gpnum;
695 rnp->completed = rsp->completed;
696 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
697 rcu_start_gp_per_cpu(rsp, rnp, rdp);
698 spin_unlock_irqrestore(&rnp->lock, flags);
699 return;
702 spin_unlock(&rnp->lock); /* leave irqs disabled. */
705 /* Exclude any concurrent CPU-hotplug operations. */
706 spin_lock(&rsp->onofflock); /* irqs already disabled. */
709 * Set the quiescent-state-needed bits in all the rcu_node
710 * structures for all currently online CPUs in breadth-first
711 * order, starting from the root rcu_node structure. This
712 * operation relies on the layout of the hierarchy within the
713 * rsp->node[] array. Note that other CPUs will access only
714 * the leaves of the hierarchy, which still indicate that no
715 * grace period is in progress, at least until the corresponding
716 * leaf node has been initialized. In addition, we have excluded
717 * CPU-hotplug operations.
719 * Note that the grace period cannot complete until we finish
720 * the initialization process, as there will be at least one
721 * qsmask bit set in the root node until that time, namely the
722 * one corresponding to this CPU, due to the fact that we have
723 * irqs disabled.
725 rcu_for_each_node_breadth_first(rsp, rnp) {
726 spin_lock(&rnp->lock); /* irqs already disabled. */
727 rcu_preempt_check_blocked_tasks(rnp);
728 rnp->qsmask = rnp->qsmaskinit;
729 rnp->gpnum = rsp->gpnum;
730 rnp->completed = rsp->completed;
731 if (rnp == rdp->mynode)
732 rcu_start_gp_per_cpu(rsp, rnp, rdp);
733 spin_unlock(&rnp->lock); /* irqs remain disabled. */
736 rnp = rcu_get_root(rsp);
737 spin_lock(&rnp->lock); /* irqs already disabled. */
738 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
739 spin_unlock(&rnp->lock); /* irqs remain disabled. */
740 spin_unlock_irqrestore(&rsp->onofflock, flags);
744 * Report a full set of quiescent states to the specified rcu_state
745 * data structure. This involves cleaning up after the prior grace
746 * period and letting rcu_start_gp() start up the next grace period
747 * if one is needed. Note that the caller must hold rnp->lock, as
748 * required by rcu_start_gp(), which will release it.
750 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
751 __releases(rcu_get_root(rsp)->lock)
753 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
754 rsp->completed = rsp->gpnum;
755 rsp->signaled = RCU_GP_IDLE;
756 rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
760 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
761 * Allows quiescent states for a group of CPUs to be reported at one go
762 * to the specified rcu_node structure, though all the CPUs in the group
763 * must be represented by the same rcu_node structure (which need not be
764 * a leaf rcu_node structure, though it often will be). That structure's
765 * lock must be held upon entry, and it is released before return.
767 static void
768 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
769 struct rcu_node *rnp, unsigned long flags)
770 __releases(rnp->lock)
772 struct rcu_node *rnp_c;
774 /* Walk up the rcu_node hierarchy. */
775 for (;;) {
776 if (!(rnp->qsmask & mask)) {
778 /* Our bit has already been cleared, so done. */
779 spin_unlock_irqrestore(&rnp->lock, flags);
780 return;
782 rnp->qsmask &= ~mask;
783 if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
785 /* Other bits still set at this level, so done. */
786 spin_unlock_irqrestore(&rnp->lock, flags);
787 return;
789 mask = rnp->grpmask;
790 if (rnp->parent == NULL) {
792 /* No more levels. Exit loop holding root lock. */
794 break;
796 spin_unlock_irqrestore(&rnp->lock, flags);
797 rnp_c = rnp;
798 rnp = rnp->parent;
799 spin_lock_irqsave(&rnp->lock, flags);
800 WARN_ON_ONCE(rnp_c->qsmask);
804 * Get here if we are the last CPU to pass through a quiescent
805 * state for this grace period. Invoke rcu_report_qs_rsp()
806 * to clean up and start the next grace period if one is needed.
808 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
812 * Record a quiescent state for the specified CPU to that CPU's rcu_data
813 * structure. This must be either called from the specified CPU, or
814 * called when the specified CPU is known to be offline (and when it is
815 * also known that no other CPU is concurrently trying to help the offline
816 * CPU). The lastcomp argument is used to make sure we are still in the
817 * grace period of interest. We don't want to end the current grace period
818 * based on quiescent states detected in an earlier grace period!
820 static void
821 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
823 unsigned long flags;
824 unsigned long mask;
825 struct rcu_node *rnp;
827 rnp = rdp->mynode;
828 spin_lock_irqsave(&rnp->lock, flags);
829 if (lastcomp != rnp->completed) {
832 * Someone beat us to it for this grace period, so leave.
833 * The race with GP start is resolved by the fact that we
834 * hold the leaf rcu_node lock, so that the per-CPU bits
835 * cannot yet be initialized -- so we would simply find our
836 * CPU's bit already cleared in rcu_report_qs_rnp() if this
837 * race occurred.
839 rdp->passed_quiesc = 0; /* try again later! */
840 spin_unlock_irqrestore(&rnp->lock, flags);
841 return;
843 mask = rdp->grpmask;
844 if ((rnp->qsmask & mask) == 0) {
845 spin_unlock_irqrestore(&rnp->lock, flags);
846 } else {
847 rdp->qs_pending = 0;
850 * This GP can't end until cpu checks in, so all of our
851 * callbacks can be processed during the next GP.
853 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
855 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
860 * Check to see if there is a new grace period of which this CPU
861 * is not yet aware, and if so, set up local rcu_data state for it.
862 * Otherwise, see if this CPU has just passed through its first
863 * quiescent state for this grace period, and record that fact if so.
865 static void
866 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
868 /* If there is now a new grace period, record and return. */
869 if (check_for_new_grace_period(rsp, rdp))
870 return;
873 * Does this CPU still need to do its part for current grace period?
874 * If no, return and let the other CPUs do their part as well.
876 if (!rdp->qs_pending)
877 return;
880 * Was there a quiescent state since the beginning of the grace
881 * period? If no, then exit and wait for the next call.
883 if (!rdp->passed_quiesc)
884 return;
887 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
888 * judge of that).
890 rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
893 #ifdef CONFIG_HOTPLUG_CPU
896 * Move a dying CPU's RCU callbacks to the ->orphan_cbs_list for the
897 * specified flavor of RCU. The callbacks will be adopted by the next
898 * _rcu_barrier() invocation or by the CPU_DEAD notifier, whichever
899 * comes first. Because this is invoked from the CPU_DYING notifier,
900 * irqs are already disabled.
902 static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
904 int i;
905 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
907 if (rdp->nxtlist == NULL)
908 return; /* irqs disabled, so comparison is stable. */
909 spin_lock(&rsp->onofflock); /* irqs already disabled. */
910 *rsp->orphan_cbs_tail = rdp->nxtlist;
911 rsp->orphan_cbs_tail = rdp->nxttail[RCU_NEXT_TAIL];
912 rdp->nxtlist = NULL;
913 for (i = 0; i < RCU_NEXT_SIZE; i++)
914 rdp->nxttail[i] = &rdp->nxtlist;
915 rsp->orphan_qlen += rdp->qlen;
916 rdp->qlen = 0;
917 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
921 * Adopt previously orphaned RCU callbacks.
923 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
925 unsigned long flags;
926 struct rcu_data *rdp;
928 spin_lock_irqsave(&rsp->onofflock, flags);
929 rdp = rsp->rda[smp_processor_id()];
930 if (rsp->orphan_cbs_list == NULL) {
931 spin_unlock_irqrestore(&rsp->onofflock, flags);
932 return;
934 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list;
935 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail;
936 rdp->qlen += rsp->orphan_qlen;
937 rsp->orphan_cbs_list = NULL;
938 rsp->orphan_cbs_tail = &rsp->orphan_cbs_list;
939 rsp->orphan_qlen = 0;
940 spin_unlock_irqrestore(&rsp->onofflock, flags);
944 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
945 * and move all callbacks from the outgoing CPU to the current one.
947 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
949 unsigned long flags;
950 unsigned long mask;
951 int need_report = 0;
952 struct rcu_data *rdp = rsp->rda[cpu];
953 struct rcu_node *rnp;
955 /* Exclude any attempts to start a new grace period. */
956 spin_lock_irqsave(&rsp->onofflock, flags);
958 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
959 rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
960 mask = rdp->grpmask; /* rnp->grplo is constant. */
961 do {
962 spin_lock(&rnp->lock); /* irqs already disabled. */
963 rnp->qsmaskinit &= ~mask;
964 if (rnp->qsmaskinit != 0) {
965 if (rnp != rdp->mynode)
966 spin_unlock(&rnp->lock); /* irqs remain disabled. */
967 break;
969 if (rnp == rdp->mynode)
970 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
971 else
972 spin_unlock(&rnp->lock); /* irqs remain disabled. */
973 mask = rnp->grpmask;
974 rnp = rnp->parent;
975 } while (rnp != NULL);
978 * We still hold the leaf rcu_node structure lock here, and
979 * irqs are still disabled. The reason for this subterfuge is
980 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
981 * held leads to deadlock.
983 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
984 rnp = rdp->mynode;
985 if (need_report & RCU_OFL_TASKS_NORM_GP)
986 rcu_report_unblock_qs_rnp(rnp, flags);
987 else
988 spin_unlock_irqrestore(&rnp->lock, flags);
989 if (need_report & RCU_OFL_TASKS_EXP_GP)
990 rcu_report_exp_rnp(rsp, rnp);
992 rcu_adopt_orphan_cbs(rsp);
996 * Remove the specified CPU from the RCU hierarchy and move any pending
997 * callbacks that it might have to the current CPU. This code assumes
998 * that at least one CPU in the system will remain running at all times.
999 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1001 static void rcu_offline_cpu(int cpu)
1003 __rcu_offline_cpu(cpu, &rcu_sched_state);
1004 __rcu_offline_cpu(cpu, &rcu_bh_state);
1005 rcu_preempt_offline_cpu(cpu);
1008 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1010 static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
1014 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
1018 static void rcu_offline_cpu(int cpu)
1022 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1025 * Invoke any RCU callbacks that have made it to the end of their grace
1026 * period. Thottle as specified by rdp->blimit.
1028 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1030 unsigned long flags;
1031 struct rcu_head *next, *list, **tail;
1032 int count;
1034 /* If no callbacks are ready, just return.*/
1035 if (!cpu_has_callbacks_ready_to_invoke(rdp))
1036 return;
1039 * Extract the list of ready callbacks, disabling to prevent
1040 * races with call_rcu() from interrupt handlers.
1042 local_irq_save(flags);
1043 list = rdp->nxtlist;
1044 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1045 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1046 tail = rdp->nxttail[RCU_DONE_TAIL];
1047 for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
1048 if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
1049 rdp->nxttail[count] = &rdp->nxtlist;
1050 local_irq_restore(flags);
1052 /* Invoke callbacks. */
1053 count = 0;
1054 while (list) {
1055 next = list->next;
1056 prefetch(next);
1057 list->func(list);
1058 list = next;
1059 if (++count >= rdp->blimit)
1060 break;
1063 local_irq_save(flags);
1065 /* Update count, and requeue any remaining callbacks. */
1066 rdp->qlen -= count;
1067 if (list != NULL) {
1068 *tail = rdp->nxtlist;
1069 rdp->nxtlist = list;
1070 for (count = 0; count < RCU_NEXT_SIZE; count++)
1071 if (&rdp->nxtlist == rdp->nxttail[count])
1072 rdp->nxttail[count] = tail;
1073 else
1074 break;
1077 /* Reinstate batch limit if we have worked down the excess. */
1078 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1079 rdp->blimit = blimit;
1081 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1082 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1083 rdp->qlen_last_fqs_check = 0;
1084 rdp->n_force_qs_snap = rsp->n_force_qs;
1085 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1086 rdp->qlen_last_fqs_check = rdp->qlen;
1088 local_irq_restore(flags);
1090 /* Re-raise the RCU softirq if there are callbacks remaining. */
1091 if (cpu_has_callbacks_ready_to_invoke(rdp))
1092 raise_softirq(RCU_SOFTIRQ);
1096 * Check to see if this CPU is in a non-context-switch quiescent state
1097 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1098 * Also schedule the RCU softirq handler.
1100 * This function must be called with hardirqs disabled. It is normally
1101 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1102 * false, there is no point in invoking rcu_check_callbacks().
1104 void rcu_check_callbacks(int cpu, int user)
1106 if (!rcu_pending(cpu))
1107 return; /* if nothing for RCU to do. */
1108 if (user ||
1109 (idle_cpu(cpu) && rcu_scheduler_active &&
1110 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1113 * Get here if this CPU took its interrupt from user
1114 * mode or from the idle loop, and if this is not a
1115 * nested interrupt. In this case, the CPU is in
1116 * a quiescent state, so note it.
1118 * No memory barrier is required here because both
1119 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1120 * variables that other CPUs neither access nor modify,
1121 * at least not while the corresponding CPU is online.
1124 rcu_sched_qs(cpu);
1125 rcu_bh_qs(cpu);
1127 } else if (!in_softirq()) {
1130 * Get here if this CPU did not take its interrupt from
1131 * softirq, in other words, if it is not interrupting
1132 * a rcu_bh read-side critical section. This is an _bh
1133 * critical section, so note it.
1136 rcu_bh_qs(cpu);
1138 rcu_preempt_check_callbacks(cpu);
1139 raise_softirq(RCU_SOFTIRQ);
1142 #ifdef CONFIG_SMP
1145 * Scan the leaf rcu_node structures, processing dyntick state for any that
1146 * have not yet encountered a quiescent state, using the function specified.
1147 * Returns 1 if the current grace period ends while scanning (possibly
1148 * because we made it end).
1150 static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
1151 int (*f)(struct rcu_data *))
1153 unsigned long bit;
1154 int cpu;
1155 unsigned long flags;
1156 unsigned long mask;
1157 struct rcu_node *rnp;
1159 rcu_for_each_leaf_node(rsp, rnp) {
1160 mask = 0;
1161 spin_lock_irqsave(&rnp->lock, flags);
1162 if (rnp->completed != lastcomp) {
1163 spin_unlock_irqrestore(&rnp->lock, flags);
1164 return 1;
1166 if (rnp->qsmask == 0) {
1167 spin_unlock_irqrestore(&rnp->lock, flags);
1168 continue;
1170 cpu = rnp->grplo;
1171 bit = 1;
1172 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1173 if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1174 mask |= bit;
1176 if (mask != 0 && rnp->completed == lastcomp) {
1178 /* rcu_report_qs_rnp() releases rnp->lock. */
1179 rcu_report_qs_rnp(mask, rsp, rnp, flags);
1180 continue;
1182 spin_unlock_irqrestore(&rnp->lock, flags);
1184 return 0;
1188 * Force quiescent states on reluctant CPUs, and also detect which
1189 * CPUs are in dyntick-idle mode.
1191 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1193 unsigned long flags;
1194 long lastcomp;
1195 struct rcu_node *rnp = rcu_get_root(rsp);
1196 u8 signaled;
1197 u8 forcenow;
1199 if (!rcu_gp_in_progress(rsp))
1200 return; /* No grace period in progress, nothing to force. */
1201 if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
1202 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1203 return; /* Someone else is already on the job. */
1205 if (relaxed &&
1206 (long)(rsp->jiffies_force_qs - jiffies) >= 0)
1207 goto unlock_ret; /* no emergency and done recently. */
1208 rsp->n_force_qs++;
1209 spin_lock(&rnp->lock);
1210 lastcomp = rsp->gpnum - 1;
1211 signaled = rsp->signaled;
1212 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1213 if(!rcu_gp_in_progress(rsp)) {
1214 rsp->n_force_qs_ngp++;
1215 spin_unlock(&rnp->lock);
1216 goto unlock_ret; /* no GP in progress, time updated. */
1218 spin_unlock(&rnp->lock);
1219 switch (signaled) {
1220 case RCU_GP_IDLE:
1221 case RCU_GP_INIT:
1223 break; /* grace period idle or initializing, ignore. */
1225 case RCU_SAVE_DYNTICK:
1227 if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1228 break; /* So gcc recognizes the dead code. */
1230 /* Record dyntick-idle state. */
1231 if (rcu_process_dyntick(rsp, lastcomp,
1232 dyntick_save_progress_counter))
1233 goto unlock_ret;
1234 /* fall into next case. */
1236 case RCU_SAVE_COMPLETED:
1238 /* Update state, record completion counter. */
1239 forcenow = 0;
1240 spin_lock(&rnp->lock);
1241 if (lastcomp + 1 == rsp->gpnum &&
1242 lastcomp == rsp->completed &&
1243 rsp->signaled == signaled) {
1244 rsp->signaled = RCU_FORCE_QS;
1245 rsp->completed_fqs = lastcomp;
1246 forcenow = signaled == RCU_SAVE_COMPLETED;
1248 spin_unlock(&rnp->lock);
1249 if (!forcenow)
1250 break;
1251 /* fall into next case. */
1253 case RCU_FORCE_QS:
1255 /* Check dyntick-idle state, send IPI to laggarts. */
1256 if (rcu_process_dyntick(rsp, rsp->completed_fqs,
1257 rcu_implicit_dynticks_qs))
1258 goto unlock_ret;
1260 /* Leave state in case more forcing is required. */
1262 break;
1264 unlock_ret:
1265 spin_unlock_irqrestore(&rsp->fqslock, flags);
1268 #else /* #ifdef CONFIG_SMP */
1270 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1272 set_need_resched();
1275 #endif /* #else #ifdef CONFIG_SMP */
1278 * This does the RCU processing work from softirq context for the
1279 * specified rcu_state and rcu_data structures. This may be called
1280 * only from the CPU to whom the rdp belongs.
1282 static void
1283 __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1285 unsigned long flags;
1287 WARN_ON_ONCE(rdp->beenonline == 0);
1290 * If an RCU GP has gone long enough, go check for dyntick
1291 * idle CPUs and, if needed, send resched IPIs.
1293 if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1294 force_quiescent_state(rsp, 1);
1297 * Advance callbacks in response to end of earlier grace
1298 * period that some other CPU ended.
1300 rcu_process_gp_end(rsp, rdp);
1302 /* Update RCU state based on any recent quiescent states. */
1303 rcu_check_quiescent_state(rsp, rdp);
1305 /* Does this CPU require a not-yet-started grace period? */
1306 if (cpu_needs_another_gp(rsp, rdp)) {
1307 spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1308 rcu_start_gp(rsp, flags); /* releases above lock */
1311 /* If there are callbacks ready, invoke them. */
1312 rcu_do_batch(rsp, rdp);
1316 * Do softirq processing for the current CPU.
1318 static void rcu_process_callbacks(struct softirq_action *unused)
1321 * Memory references from any prior RCU read-side critical sections
1322 * executed by the interrupted code must be seen before any RCU
1323 * grace-period manipulations below.
1325 smp_mb(); /* See above block comment. */
1327 __rcu_process_callbacks(&rcu_sched_state,
1328 &__get_cpu_var(rcu_sched_data));
1329 __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1330 rcu_preempt_process_callbacks();
1333 * Memory references from any later RCU read-side critical sections
1334 * executed by the interrupted code must be seen after any RCU
1335 * grace-period manipulations above.
1337 smp_mb(); /* See above block comment. */
1340 static void
1341 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1342 struct rcu_state *rsp)
1344 unsigned long flags;
1345 struct rcu_data *rdp;
1347 head->func = func;
1348 head->next = NULL;
1350 smp_mb(); /* Ensure RCU update seen before callback registry. */
1353 * Opportunistically note grace-period endings and beginnings.
1354 * Note that we might see a beginning right after we see an
1355 * end, but never vice versa, since this CPU has to pass through
1356 * a quiescent state betweentimes.
1358 local_irq_save(flags);
1359 rdp = rsp->rda[smp_processor_id()];
1360 rcu_process_gp_end(rsp, rdp);
1361 check_for_new_grace_period(rsp, rdp);
1363 /* Add the callback to our list. */
1364 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1365 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1367 /* Start a new grace period if one not already started. */
1368 if (!rcu_gp_in_progress(rsp)) {
1369 unsigned long nestflag;
1370 struct rcu_node *rnp_root = rcu_get_root(rsp);
1372 spin_lock_irqsave(&rnp_root->lock, nestflag);
1373 rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */
1377 * Force the grace period if too many callbacks or too long waiting.
1378 * Enforce hysteresis, and don't invoke force_quiescent_state()
1379 * if some other CPU has recently done so. Also, don't bother
1380 * invoking force_quiescent_state() if the newly enqueued callback
1381 * is the only one waiting for a grace period to complete.
1383 if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1384 rdp->blimit = LONG_MAX;
1385 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1386 *rdp->nxttail[RCU_DONE_TAIL] != head)
1387 force_quiescent_state(rsp, 0);
1388 rdp->n_force_qs_snap = rsp->n_force_qs;
1389 rdp->qlen_last_fqs_check = rdp->qlen;
1390 } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1391 force_quiescent_state(rsp, 1);
1392 local_irq_restore(flags);
1396 * Queue an RCU-sched callback for invocation after a grace period.
1398 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1400 __call_rcu(head, func, &rcu_sched_state);
1402 EXPORT_SYMBOL_GPL(call_rcu_sched);
1405 * Queue an RCU for invocation after a quicker grace period.
1407 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1409 __call_rcu(head, func, &rcu_bh_state);
1411 EXPORT_SYMBOL_GPL(call_rcu_bh);
1414 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1416 * Control will return to the caller some time after a full rcu-sched
1417 * grace period has elapsed, in other words after all currently executing
1418 * rcu-sched read-side critical sections have completed. These read-side
1419 * critical sections are delimited by rcu_read_lock_sched() and
1420 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1421 * local_irq_disable(), and so on may be used in place of
1422 * rcu_read_lock_sched().
1424 * This means that all preempt_disable code sequences, including NMI and
1425 * hardware-interrupt handlers, in progress on entry will have completed
1426 * before this primitive returns. However, this does not guarantee that
1427 * softirq handlers will have completed, since in some kernels, these
1428 * handlers can run in process context, and can block.
1430 * This primitive provides the guarantees made by the (now removed)
1431 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1432 * guarantees that rcu_read_lock() sections will have completed.
1433 * In "classic RCU", these two guarantees happen to be one and
1434 * the same, but can differ in realtime RCU implementations.
1436 void synchronize_sched(void)
1438 struct rcu_synchronize rcu;
1440 if (rcu_blocking_is_gp())
1441 return;
1443 init_completion(&rcu.completion);
1444 /* Will wake me after RCU finished. */
1445 call_rcu_sched(&rcu.head, wakeme_after_rcu);
1446 /* Wait for it. */
1447 wait_for_completion(&rcu.completion);
1449 EXPORT_SYMBOL_GPL(synchronize_sched);
1452 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1454 * Control will return to the caller some time after a full rcu_bh grace
1455 * period has elapsed, in other words after all currently executing rcu_bh
1456 * read-side critical sections have completed. RCU read-side critical
1457 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1458 * and may be nested.
1460 void synchronize_rcu_bh(void)
1462 struct rcu_synchronize rcu;
1464 if (rcu_blocking_is_gp())
1465 return;
1467 init_completion(&rcu.completion);
1468 /* Will wake me after RCU finished. */
1469 call_rcu_bh(&rcu.head, wakeme_after_rcu);
1470 /* Wait for it. */
1471 wait_for_completion(&rcu.completion);
1473 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
1476 * Check to see if there is any immediate RCU-related work to be done
1477 * by the current CPU, for the specified type of RCU, returning 1 if so.
1478 * The checks are in order of increasing expense: checks that can be
1479 * carried out against CPU-local state are performed first. However,
1480 * we must check for CPU stalls first, else we might not get a chance.
1482 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1484 struct rcu_node *rnp = rdp->mynode;
1486 rdp->n_rcu_pending++;
1488 /* Check for CPU stalls, if enabled. */
1489 check_cpu_stall(rsp, rdp);
1491 /* Is the RCU core waiting for a quiescent state from this CPU? */
1492 if (rdp->qs_pending) {
1493 rdp->n_rp_qs_pending++;
1494 return 1;
1497 /* Does this CPU have callbacks ready to invoke? */
1498 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1499 rdp->n_rp_cb_ready++;
1500 return 1;
1503 /* Has RCU gone idle with this CPU needing another grace period? */
1504 if (cpu_needs_another_gp(rsp, rdp)) {
1505 rdp->n_rp_cpu_needs_gp++;
1506 return 1;
1509 /* Has another RCU grace period completed? */
1510 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
1511 rdp->n_rp_gp_completed++;
1512 return 1;
1515 /* Has a new RCU grace period started? */
1516 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
1517 rdp->n_rp_gp_started++;
1518 return 1;
1521 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1522 if (rcu_gp_in_progress(rsp) &&
1523 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
1524 rdp->n_rp_need_fqs++;
1525 return 1;
1528 /* nothing to do */
1529 rdp->n_rp_need_nothing++;
1530 return 0;
1534 * Check to see if there is any immediate RCU-related work to be done
1535 * by the current CPU, returning 1 if so. This function is part of the
1536 * RCU implementation; it is -not- an exported member of the RCU API.
1538 static int rcu_pending(int cpu)
1540 return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1541 __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1542 rcu_preempt_pending(cpu);
1546 * Check to see if any future RCU-related work will need to be done
1547 * by the current CPU, even if none need be done immediately, returning
1548 * 1 if so. This function is part of the RCU implementation; it is -not-
1549 * an exported member of the RCU API.
1551 int rcu_needs_cpu(int cpu)
1553 /* RCU callbacks either ready or pending? */
1554 return per_cpu(rcu_sched_data, cpu).nxtlist ||
1555 per_cpu(rcu_bh_data, cpu).nxtlist ||
1556 rcu_preempt_needs_cpu(cpu);
1560 * This function is invoked towards the end of the scheduler's initialization
1561 * process. Before this is called, the idle task might contain
1562 * RCU read-side critical sections (during which time, this idle
1563 * task is booting the system). After this function is called, the
1564 * idle tasks are prohibited from containing RCU read-side critical
1565 * sections.
1567 void rcu_scheduler_starting(void)
1569 WARN_ON(num_online_cpus() != 1);
1570 WARN_ON(nr_context_switches() > 0);
1571 rcu_scheduler_active = 1;
1574 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1575 static atomic_t rcu_barrier_cpu_count;
1576 static DEFINE_MUTEX(rcu_barrier_mutex);
1577 static struct completion rcu_barrier_completion;
1579 static void rcu_barrier_callback(struct rcu_head *notused)
1581 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1582 complete(&rcu_barrier_completion);
1586 * Called with preemption disabled, and from cross-cpu IRQ context.
1588 static void rcu_barrier_func(void *type)
1590 int cpu = smp_processor_id();
1591 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1592 void (*call_rcu_func)(struct rcu_head *head,
1593 void (*func)(struct rcu_head *head));
1595 atomic_inc(&rcu_barrier_cpu_count);
1596 call_rcu_func = type;
1597 call_rcu_func(head, rcu_barrier_callback);
1601 * Orchestrate the specified type of RCU barrier, waiting for all
1602 * RCU callbacks of the specified type to complete.
1604 static void _rcu_barrier(struct rcu_state *rsp,
1605 void (*call_rcu_func)(struct rcu_head *head,
1606 void (*func)(struct rcu_head *head)))
1608 BUG_ON(in_interrupt());
1609 /* Take mutex to serialize concurrent rcu_barrier() requests. */
1610 mutex_lock(&rcu_barrier_mutex);
1611 init_completion(&rcu_barrier_completion);
1613 * Initialize rcu_barrier_cpu_count to 1, then invoke
1614 * rcu_barrier_func() on each CPU, so that each CPU also has
1615 * incremented rcu_barrier_cpu_count. Only then is it safe to
1616 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1617 * might complete its grace period before all of the other CPUs
1618 * did their increment, causing this function to return too
1619 * early.
1621 atomic_set(&rcu_barrier_cpu_count, 1);
1622 preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */
1623 rcu_adopt_orphan_cbs(rsp);
1624 on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1625 preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */
1626 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1627 complete(&rcu_barrier_completion);
1628 wait_for_completion(&rcu_barrier_completion);
1629 mutex_unlock(&rcu_barrier_mutex);
1633 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1635 void rcu_barrier_bh(void)
1637 _rcu_barrier(&rcu_bh_state, call_rcu_bh);
1639 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1642 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1644 void rcu_barrier_sched(void)
1646 _rcu_barrier(&rcu_sched_state, call_rcu_sched);
1648 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1651 * Do boot-time initialization of a CPU's per-CPU RCU data.
1653 static void __init
1654 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1656 unsigned long flags;
1657 int i;
1658 struct rcu_data *rdp = rsp->rda[cpu];
1659 struct rcu_node *rnp = rcu_get_root(rsp);
1661 /* Set up local state, ensuring consistent view of global state. */
1662 spin_lock_irqsave(&rnp->lock, flags);
1663 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1664 rdp->nxtlist = NULL;
1665 for (i = 0; i < RCU_NEXT_SIZE; i++)
1666 rdp->nxttail[i] = &rdp->nxtlist;
1667 rdp->qlen = 0;
1668 #ifdef CONFIG_NO_HZ
1669 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1670 #endif /* #ifdef CONFIG_NO_HZ */
1671 rdp->cpu = cpu;
1672 spin_unlock_irqrestore(&rnp->lock, flags);
1676 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1677 * offline event can be happening at a given time. Note also that we
1678 * can accept some slop in the rsp->completed access due to the fact
1679 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1681 static void __cpuinit
1682 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1684 unsigned long flags;
1685 unsigned long mask;
1686 struct rcu_data *rdp = rsp->rda[cpu];
1687 struct rcu_node *rnp = rcu_get_root(rsp);
1689 /* Set up local state, ensuring consistent view of global state. */
1690 spin_lock_irqsave(&rnp->lock, flags);
1691 rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1692 rdp->qs_pending = 1; /* so set up to respond to current GP. */
1693 rdp->beenonline = 1; /* We have now been online. */
1694 rdp->preemptable = preemptable;
1695 rdp->qlen_last_fqs_check = 0;
1696 rdp->n_force_qs_snap = rsp->n_force_qs;
1697 rdp->blimit = blimit;
1698 spin_unlock(&rnp->lock); /* irqs remain disabled. */
1701 * A new grace period might start here. If so, we won't be part
1702 * of it, but that is OK, as we are currently in a quiescent state.
1705 /* Exclude any attempts to start a new GP on large systems. */
1706 spin_lock(&rsp->onofflock); /* irqs already disabled. */
1708 /* Add CPU to rcu_node bitmasks. */
1709 rnp = rdp->mynode;
1710 mask = rdp->grpmask;
1711 do {
1712 /* Exclude any attempts to start a new GP on small systems. */
1713 spin_lock(&rnp->lock); /* irqs already disabled. */
1714 rnp->qsmaskinit |= mask;
1715 mask = rnp->grpmask;
1716 if (rnp == rdp->mynode) {
1717 rdp->gpnum = rnp->completed; /* if GP in progress... */
1718 rdp->completed = rnp->completed;
1719 rdp->passed_quiesc_completed = rnp->completed - 1;
1721 spin_unlock(&rnp->lock); /* irqs already disabled. */
1722 rnp = rnp->parent;
1723 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1725 spin_unlock_irqrestore(&rsp->onofflock, flags);
1728 static void __cpuinit rcu_online_cpu(int cpu)
1730 rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1731 rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1732 rcu_preempt_init_percpu_data(cpu);
1736 * Handle CPU online/offline notification events.
1738 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1739 unsigned long action, void *hcpu)
1741 long cpu = (long)hcpu;
1743 switch (action) {
1744 case CPU_UP_PREPARE:
1745 case CPU_UP_PREPARE_FROZEN:
1746 rcu_online_cpu(cpu);
1747 break;
1748 case CPU_DYING:
1749 case CPU_DYING_FROZEN:
1751 * preempt_disable() in _rcu_barrier() prevents stop_machine(),
1752 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
1753 * returns, all online cpus have queued rcu_barrier_func().
1754 * The dying CPU clears its cpu_online_mask bit and
1755 * moves all of its RCU callbacks to ->orphan_cbs_list
1756 * in the context of stop_machine(), so subsequent calls
1757 * to _rcu_barrier() will adopt these callbacks and only
1758 * then queue rcu_barrier_func() on all remaining CPUs.
1760 rcu_send_cbs_to_orphanage(&rcu_bh_state);
1761 rcu_send_cbs_to_orphanage(&rcu_sched_state);
1762 rcu_preempt_send_cbs_to_orphanage();
1763 break;
1764 case CPU_DEAD:
1765 case CPU_DEAD_FROZEN:
1766 case CPU_UP_CANCELED:
1767 case CPU_UP_CANCELED_FROZEN:
1768 rcu_offline_cpu(cpu);
1769 break;
1770 default:
1771 break;
1773 return NOTIFY_OK;
1777 * Compute the per-level fanout, either using the exact fanout specified
1778 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1780 #ifdef CONFIG_RCU_FANOUT_EXACT
1781 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1783 int i;
1785 for (i = NUM_RCU_LVLS - 1; i >= 0; i--)
1786 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1788 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1789 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1791 int ccur;
1792 int cprv;
1793 int i;
1795 cprv = NR_CPUS;
1796 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1797 ccur = rsp->levelcnt[i];
1798 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1799 cprv = ccur;
1802 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1805 * Helper function for rcu_init() that initializes one rcu_state structure.
1807 static void __init rcu_init_one(struct rcu_state *rsp)
1809 int cpustride = 1;
1810 int i;
1811 int j;
1812 struct rcu_node *rnp;
1814 /* Initialize the level-tracking arrays. */
1816 for (i = 1; i < NUM_RCU_LVLS; i++)
1817 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1818 rcu_init_levelspread(rsp);
1820 /* Initialize the elements themselves, starting from the leaves. */
1822 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1823 cpustride *= rsp->levelspread[i];
1824 rnp = rsp->level[i];
1825 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1826 spin_lock_init(&rnp->lock);
1827 lockdep_set_class(&rnp->lock, &rcu_node_class[i]);
1828 rnp->gpnum = 0;
1829 rnp->qsmask = 0;
1830 rnp->qsmaskinit = 0;
1831 rnp->grplo = j * cpustride;
1832 rnp->grphi = (j + 1) * cpustride - 1;
1833 if (rnp->grphi >= NR_CPUS)
1834 rnp->grphi = NR_CPUS - 1;
1835 if (i == 0) {
1836 rnp->grpnum = 0;
1837 rnp->grpmask = 0;
1838 rnp->parent = NULL;
1839 } else {
1840 rnp->grpnum = j % rsp->levelspread[i - 1];
1841 rnp->grpmask = 1UL << rnp->grpnum;
1842 rnp->parent = rsp->level[i - 1] +
1843 j / rsp->levelspread[i - 1];
1845 rnp->level = i;
1846 INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1847 INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1848 INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
1849 INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
1855 * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used
1856 * nowhere else! Assigns leaf node pointers into each CPU's rcu_data
1857 * structure.
1859 #define RCU_INIT_FLAVOR(rsp, rcu_data) \
1860 do { \
1861 int i; \
1862 int j; \
1863 struct rcu_node *rnp; \
1865 rcu_init_one(rsp); \
1866 rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
1867 j = 0; \
1868 for_each_possible_cpu(i) { \
1869 if (i > rnp[j].grphi) \
1870 j++; \
1871 per_cpu(rcu_data, i).mynode = &rnp[j]; \
1872 (rsp)->rda[i] = &per_cpu(rcu_data, i); \
1873 rcu_boot_init_percpu_data(i, rsp); \
1875 } while (0)
1877 void __init rcu_init(void)
1879 int i;
1881 rcu_bootup_announce();
1882 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
1883 printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
1884 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
1885 #if NUM_RCU_LVL_4 != 0
1886 printk(KERN_INFO "Experimental four-level hierarchy is enabled.\n");
1887 #endif /* #if NUM_RCU_LVL_4 != 0 */
1888 RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
1889 RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
1890 __rcu_init_preempt();
1891 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1894 * We don't need protection against CPU-hotplug here because
1895 * this is called early in boot, before either interrupts
1896 * or the scheduler are operational.
1898 cpu_notifier(rcu_cpu_notify, 0);
1899 for_each_online_cpu(i)
1900 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)i);
1903 #include "rcutree_plugin.h"