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 -
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>
52 #ifdef CONFIG_DEBUG_LOCK_ALLOC
53 static struct lock_class_key rcu_lock_key;
54 struct lockdep_map rcu_lock_map =
55 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
56 EXPORT_SYMBOL_GPL(rcu_lock_map);
59 /* Data structures. */
61 #define RCU_STATE_INITIALIZER(name) { \
62 .level = { &name.node[0] }, \
64 NUM_RCU_LVL_0, /* root of hierarchy. */ \
67 NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
69 .signaled = RCU_SIGNAL_INIT, \
72 .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
73 .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
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 extern long rcu_batches_completed_sched(void);
85 static struct rcu_node *rcu_get_root(struct rcu_state *rsp);
86 static void cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp,
87 struct rcu_node *rnp, unsigned long flags);
88 static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags);
89 #ifdef CONFIG_HOTPLUG_CPU
90 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp);
91 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
92 static void __rcu_process_callbacks(struct rcu_state *rsp,
93 struct rcu_data *rdp);
94 static void __call_rcu(struct rcu_head *head,
95 void (*func)(struct rcu_head *rcu),
96 struct rcu_state *rsp);
97 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp);
98 static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_state *rsp,
101 #include "rcutree_plugin.h"
104 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
105 * permit this function to be invoked without holding the root rcu_node
106 * structure's ->lock, but of course results can be subject to change.
108 static int rcu_gp_in_progress(struct rcu_state *rsp)
110 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
114 * Note a quiescent state. Because we do not need to know
115 * how many quiescent states passed, just if there was at least
116 * one since the start of the grace period, this just sets a flag.
118 void rcu_sched_qs(int cpu)
120 struct rcu_data *rdp;
122 rdp = &per_cpu(rcu_sched_data, cpu);
123 rdp->passed_quiesc_completed = rdp->completed;
125 rdp->passed_quiesc = 1;
126 rcu_preempt_note_context_switch(cpu);
129 void rcu_bh_qs(int cpu)
131 struct rcu_data *rdp;
133 rdp = &per_cpu(rcu_bh_data, cpu);
134 rdp->passed_quiesc_completed = rdp->completed;
136 rdp->passed_quiesc = 1;
140 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
141 .dynticks_nesting = 1,
144 #endif /* #ifdef CONFIG_NO_HZ */
146 static int blimit = 10; /* Maximum callbacks per softirq. */
147 static int qhimark = 10000; /* If this many pending, ignore blimit. */
148 static int qlowmark = 100; /* Once only this many pending, use blimit. */
150 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
151 static int rcu_pending(int cpu);
154 * Return the number of RCU-sched batches processed thus far for debug & stats.
156 long rcu_batches_completed_sched(void)
158 return rcu_sched_state.completed;
160 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
163 * Return the number of RCU BH batches processed thus far for debug & stats.
165 long rcu_batches_completed_bh(void)
167 return rcu_bh_state.completed;
169 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
172 * Does the CPU have callbacks ready to be invoked?
175 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
177 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
181 * Does the current CPU require a yet-as-unscheduled grace period?
184 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
186 return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
190 * Return the root node of the specified rcu_state structure.
192 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
194 return &rsp->node[0];
200 * If the specified CPU is offline, tell the caller that it is in
201 * a quiescent state. Otherwise, whack it with a reschedule IPI.
202 * Grace periods can end up waiting on an offline CPU when that
203 * CPU is in the process of coming online -- it will be added to the
204 * rcu_node bitmasks before it actually makes it online. The same thing
205 * can happen while a CPU is in the process of coming online. Because this
206 * race is quite rare, we check for it after detecting that the grace
207 * period has been delayed rather than checking each and every CPU
208 * each and every time we start a new grace period.
210 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
213 * If the CPU is offline, it is in a quiescent state. We can
214 * trust its state not to change because interrupts are disabled.
216 if (cpu_is_offline(rdp->cpu)) {
221 /* If preemptable RCU, no point in sending reschedule IPI. */
222 if (rdp->preemptable)
225 /* The CPU is online, so send it a reschedule IPI. */
226 if (rdp->cpu != smp_processor_id())
227 smp_send_reschedule(rdp->cpu);
234 #endif /* #ifdef CONFIG_SMP */
239 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
241 * Enter nohz mode, in other words, -leave- the mode in which RCU
242 * read-side critical sections can occur. (Though RCU read-side
243 * critical sections can occur in irq handlers in nohz mode, a possibility
244 * handled by rcu_irq_enter() and rcu_irq_exit()).
246 void rcu_enter_nohz(void)
249 struct rcu_dynticks *rdtp;
251 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
252 local_irq_save(flags);
253 rdtp = &__get_cpu_var(rcu_dynticks);
255 rdtp->dynticks_nesting--;
256 WARN_ON_ONCE(rdtp->dynticks & 0x1);
257 local_irq_restore(flags);
261 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
263 * Exit nohz mode, in other words, -enter- the mode in which RCU
264 * read-side critical sections normally occur.
266 void rcu_exit_nohz(void)
269 struct rcu_dynticks *rdtp;
271 local_irq_save(flags);
272 rdtp = &__get_cpu_var(rcu_dynticks);
274 rdtp->dynticks_nesting++;
275 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
276 local_irq_restore(flags);
277 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
281 * rcu_nmi_enter - inform RCU of entry to NMI context
283 * If the CPU was idle with dynamic ticks active, and there is no
284 * irq handler running, this updates rdtp->dynticks_nmi to let the
285 * RCU grace-period handling know that the CPU is active.
287 void rcu_nmi_enter(void)
289 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
291 if (rdtp->dynticks & 0x1)
293 rdtp->dynticks_nmi++;
294 WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
295 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
299 * rcu_nmi_exit - inform RCU of exit from NMI context
301 * If the CPU was idle with dynamic ticks active, and there is no
302 * irq handler running, this updates rdtp->dynticks_nmi to let the
303 * RCU grace-period handling know that the CPU is no longer active.
305 void rcu_nmi_exit(void)
307 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
309 if (rdtp->dynticks & 0x1)
311 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
312 rdtp->dynticks_nmi++;
313 WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
317 * rcu_irq_enter - inform RCU of entry to hard irq context
319 * If the CPU was idle with dynamic ticks active, this updates the
320 * rdtp->dynticks to let the RCU handling know that the CPU is active.
322 void rcu_irq_enter(void)
324 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
326 if (rdtp->dynticks_nesting++)
329 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
330 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
334 * rcu_irq_exit - inform RCU of exit from hard irq context
336 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
337 * to put let the RCU handling be aware that the CPU is going back to idle
340 void rcu_irq_exit(void)
342 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
344 if (--rdtp->dynticks_nesting)
346 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
348 WARN_ON_ONCE(rdtp->dynticks & 0x1);
350 /* If the interrupt queued a callback, get out of dyntick mode. */
351 if (__get_cpu_var(rcu_sched_data).nxtlist ||
352 __get_cpu_var(rcu_bh_data).nxtlist)
357 * Record the specified "completed" value, which is later used to validate
358 * dynticks counter manipulations. Specify "rsp->completed - 1" to
359 * unconditionally invalidate any future dynticks manipulations (which is
360 * useful at the beginning of a grace period).
362 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
364 rsp->dynticks_completed = comp;
370 * Recall the previously recorded value of the completion for dynticks.
372 static long dyntick_recall_completed(struct rcu_state *rsp)
374 return rsp->dynticks_completed;
378 * Snapshot the specified CPU's dynticks counter so that we can later
379 * credit them with an implicit quiescent state. Return 1 if this CPU
380 * is already in a quiescent state courtesy of dynticks idle mode.
382 static int dyntick_save_progress_counter(struct rcu_data *rdp)
388 snap = rdp->dynticks->dynticks;
389 snap_nmi = rdp->dynticks->dynticks_nmi;
390 smp_mb(); /* Order sampling of snap with end of grace period. */
391 rdp->dynticks_snap = snap;
392 rdp->dynticks_nmi_snap = snap_nmi;
393 ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
400 * Return true if the specified CPU has passed through a quiescent
401 * state by virtue of being in or having passed through an dynticks
402 * idle state since the last call to dyntick_save_progress_counter()
405 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
412 curr = rdp->dynticks->dynticks;
413 snap = rdp->dynticks_snap;
414 curr_nmi = rdp->dynticks->dynticks_nmi;
415 snap_nmi = rdp->dynticks_nmi_snap;
416 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
419 * If the CPU passed through or entered a dynticks idle phase with
420 * no active irq/NMI handlers, then we can safely pretend that the CPU
421 * already acknowledged the request to pass through a quiescent
422 * state. Either way, that CPU cannot possibly be in an RCU
423 * read-side critical section that started before the beginning
424 * of the current RCU grace period.
426 if ((curr != snap || (curr & 0x1) == 0) &&
427 (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
432 /* Go check for the CPU being offline. */
433 return rcu_implicit_offline_qs(rdp);
436 #endif /* #ifdef CONFIG_SMP */
438 #else /* #ifdef CONFIG_NO_HZ */
440 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
447 * If there are no dynticks, then the only way that a CPU can passively
448 * be in a quiescent state is to be offline. Unlike dynticks idle, which
449 * is a point in time during the prior (already finished) grace period,
450 * an offline CPU is always in a quiescent state, and thus can be
451 * unconditionally applied. So just return the current value of completed.
453 static long dyntick_recall_completed(struct rcu_state *rsp)
455 return rsp->completed;
458 static int dyntick_save_progress_counter(struct rcu_data *rdp)
463 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
465 return rcu_implicit_offline_qs(rdp);
468 #endif /* #ifdef CONFIG_SMP */
470 #endif /* #else #ifdef CONFIG_NO_HZ */
472 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
474 static void record_gp_stall_check_time(struct rcu_state *rsp)
476 rsp->gp_start = jiffies;
477 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
480 static void print_other_cpu_stall(struct rcu_state *rsp)
485 struct rcu_node *rnp = rcu_get_root(rsp);
486 struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
487 struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
489 /* Only let one CPU complain about others per time interval. */
491 spin_lock_irqsave(&rnp->lock, flags);
492 delta = jiffies - rsp->jiffies_stall;
493 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
494 spin_unlock_irqrestore(&rnp->lock, flags);
497 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
498 spin_unlock_irqrestore(&rnp->lock, flags);
500 /* OK, time to rat on our buddy... */
502 printk(KERN_ERR "INFO: RCU detected CPU stalls:");
503 for (; rnp_cur < rnp_end; rnp_cur++) {
504 rcu_print_task_stall(rnp);
505 if (rnp_cur->qsmask == 0)
507 for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)
508 if (rnp_cur->qsmask & (1UL << cpu))
509 printk(" %d", rnp_cur->grplo + cpu);
511 printk(" (detected by %d, t=%ld jiffies)\n",
512 smp_processor_id(), (long)(jiffies - rsp->gp_start));
513 trigger_all_cpu_backtrace();
515 force_quiescent_state(rsp, 0); /* Kick them all. */
518 static void print_cpu_stall(struct rcu_state *rsp)
521 struct rcu_node *rnp = rcu_get_root(rsp);
523 printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
524 smp_processor_id(), jiffies - rsp->gp_start);
525 trigger_all_cpu_backtrace();
527 spin_lock_irqsave(&rnp->lock, flags);
528 if ((long)(jiffies - rsp->jiffies_stall) >= 0)
530 jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
531 spin_unlock_irqrestore(&rnp->lock, flags);
533 set_need_resched(); /* kick ourselves to get things going. */
536 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
539 struct rcu_node *rnp;
541 delta = jiffies - rsp->jiffies_stall;
543 if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
545 /* We haven't checked in, so go dump stack. */
546 print_cpu_stall(rsp);
548 } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
550 /* They had two time units to dump stack, so complain. */
551 print_other_cpu_stall(rsp);
555 #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
557 static void record_gp_stall_check_time(struct rcu_state *rsp)
561 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
565 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
568 * Update CPU-local rcu_data state to record the newly noticed grace period.
569 * This is used both when we started the grace period and when we notice
570 * that someone else started the grace period.
572 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
575 rdp->passed_quiesc = 0;
576 rdp->gpnum = rsp->gpnum;
580 * Did someone else start a new RCU grace period start since we last
581 * checked? Update local state appropriately if so. Must be called
582 * on the CPU corresponding to rdp.
585 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
590 local_irq_save(flags);
591 if (rdp->gpnum != rsp->gpnum) {
592 note_new_gpnum(rsp, rdp);
595 local_irq_restore(flags);
600 * Start a new RCU grace period if warranted, re-initializing the hierarchy
601 * in preparation for detecting the next grace period. The caller must hold
602 * the root node's ->lock, which is released before return. Hard irqs must
606 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
607 __releases(rcu_get_root(rsp)->lock)
609 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
610 struct rcu_node *rnp = rcu_get_root(rsp);
612 if (!cpu_needs_another_gp(rsp, rdp)) {
613 spin_unlock_irqrestore(&rnp->lock, flags);
617 /* Advance to a new grace period and initialize state. */
619 WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
620 rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
621 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
622 record_gp_stall_check_time(rsp);
623 dyntick_record_completed(rsp, rsp->completed - 1);
624 note_new_gpnum(rsp, rdp);
627 * Because we are first, we know that all our callbacks will
628 * be covered by this upcoming grace period, even the ones
629 * that were registered arbitrarily recently.
631 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
632 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
634 /* Special-case the common single-level case. */
635 if (NUM_RCU_NODES == 1) {
636 rcu_preempt_check_blocked_tasks(rnp);
637 rnp->qsmask = rnp->qsmaskinit;
638 rnp->gpnum = rsp->gpnum;
639 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
640 spin_unlock_irqrestore(&rnp->lock, flags);
644 spin_unlock(&rnp->lock); /* leave irqs disabled. */
647 /* Exclude any concurrent CPU-hotplug operations. */
648 spin_lock(&rsp->onofflock); /* irqs already disabled. */
651 * Set the quiescent-state-needed bits in all the rcu_node
652 * structures for all currently online CPUs in breadth-first
653 * order, starting from the root rcu_node structure. This
654 * operation relies on the layout of the hierarchy within the
655 * rsp->node[] array. Note that other CPUs will access only
656 * the leaves of the hierarchy, which still indicate that no
657 * grace period is in progress, at least until the corresponding
658 * leaf node has been initialized. In addition, we have excluded
659 * CPU-hotplug operations.
661 * Note that the grace period cannot complete until we finish
662 * the initialization process, as there will be at least one
663 * qsmask bit set in the root node until that time, namely the
664 * one corresponding to this CPU, due to the fact that we have
667 for (rnp = &rsp->node[0]; rnp < &rsp->node[NUM_RCU_NODES]; rnp++) {
668 spin_lock(&rnp->lock); /* irqs already disabled. */
669 rcu_preempt_check_blocked_tasks(rnp);
670 rnp->qsmask = rnp->qsmaskinit;
671 rnp->gpnum = rsp->gpnum;
672 spin_unlock(&rnp->lock); /* irqs already disabled. */
675 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
676 spin_unlock_irqrestore(&rsp->onofflock, flags);
680 * Advance this CPU's callbacks, but only if the current grace period
681 * has ended. This may be called only from the CPU to whom the rdp
685 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
690 local_irq_save(flags);
691 completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */
693 /* Did another grace period end? */
694 if (rdp->completed != completed_snap) {
696 /* Advance callbacks. No harm if list empty. */
697 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
698 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
699 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
701 /* Remember that we saw this grace-period completion. */
702 rdp->completed = completed_snap;
704 local_irq_restore(flags);
708 * Clean up after the prior grace period and let rcu_start_gp() start up
709 * the next grace period if one is needed. Note that the caller must
710 * hold rnp->lock, as required by rcu_start_gp(), which will release it.
712 static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags)
713 __releases(rcu_get_root(rsp)->lock)
715 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
716 rsp->completed = rsp->gpnum;
717 rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
718 rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
722 * Similar to cpu_quiet(), for which it is a helper function. Allows
723 * a group of CPUs to be quieted at one go, though all the CPUs in the
724 * group must be represented by the same leaf rcu_node structure.
725 * That structure's lock must be held upon entry, and it is released
729 cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp,
731 __releases(rnp->lock)
733 struct rcu_node *rnp_c;
735 /* Walk up the rcu_node hierarchy. */
737 if (!(rnp->qsmask & mask)) {
739 /* Our bit has already been cleared, so done. */
740 spin_unlock_irqrestore(&rnp->lock, flags);
743 rnp->qsmask &= ~mask;
744 if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
746 /* Other bits still set at this level, so done. */
747 spin_unlock_irqrestore(&rnp->lock, flags);
751 if (rnp->parent == NULL) {
753 /* No more levels. Exit loop holding root lock. */
757 spin_unlock_irqrestore(&rnp->lock, flags);
760 spin_lock_irqsave(&rnp->lock, flags);
761 WARN_ON_ONCE(rnp_c->qsmask);
765 * Get here if we are the last CPU to pass through a quiescent
766 * state for this grace period. Invoke cpu_quiet_msk_finish()
767 * to clean up and start the next grace period if one is needed.
769 cpu_quiet_msk_finish(rsp, flags); /* releases rnp->lock. */
773 * Record a quiescent state for the specified CPU, which must either be
774 * the current CPU. The lastcomp argument is used to make sure we are
775 * still in the grace period of interest. We don't want to end the current
776 * grace period based on quiescent states detected in an earlier grace
780 cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
784 struct rcu_node *rnp;
787 spin_lock_irqsave(&rnp->lock, flags);
788 if (lastcomp != ACCESS_ONCE(rsp->completed)) {
791 * Someone beat us to it for this grace period, so leave.
792 * The race with GP start is resolved by the fact that we
793 * hold the leaf rcu_node lock, so that the per-CPU bits
794 * cannot yet be initialized -- so we would simply find our
795 * CPU's bit already cleared in cpu_quiet_msk() if this race
798 rdp->passed_quiesc = 0; /* try again later! */
799 spin_unlock_irqrestore(&rnp->lock, flags);
803 if ((rnp->qsmask & mask) == 0) {
804 spin_unlock_irqrestore(&rnp->lock, flags);
809 * This GP can't end until cpu checks in, so all of our
810 * callbacks can be processed during the next GP.
812 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
814 cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */
819 * Check to see if there is a new grace period of which this CPU
820 * is not yet aware, and if so, set up local rcu_data state for it.
821 * Otherwise, see if this CPU has just passed through its first
822 * quiescent state for this grace period, and record that fact if so.
825 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
827 /* If there is now a new grace period, record and return. */
828 if (check_for_new_grace_period(rsp, rdp))
832 * Does this CPU still need to do its part for current grace period?
833 * If no, return and let the other CPUs do their part as well.
835 if (!rdp->qs_pending)
839 * Was there a quiescent state since the beginning of the grace
840 * period? If no, then exit and wait for the next call.
842 if (!rdp->passed_quiesc)
845 /* Tell RCU we are done (but cpu_quiet() will be the judge of that). */
846 cpu_quiet(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
849 #ifdef CONFIG_HOTPLUG_CPU
852 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
853 * and move all callbacks from the outgoing CPU to the current one.
855 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
861 struct rcu_data *rdp = rsp->rda[cpu];
862 struct rcu_data *rdp_me;
863 struct rcu_node *rnp;
865 /* Exclude any attempts to start a new grace period. */
866 spin_lock_irqsave(&rsp->onofflock, flags);
868 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
869 rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
870 mask = rdp->grpmask; /* rnp->grplo is constant. */
872 spin_lock(&rnp->lock); /* irqs already disabled. */
873 rnp->qsmaskinit &= ~mask;
874 if (rnp->qsmaskinit != 0) {
875 spin_unlock(&rnp->lock); /* irqs remain disabled. */
878 rcu_preempt_offline_tasks(rsp, rnp, rdp);
880 spin_unlock(&rnp->lock); /* irqs remain disabled. */
882 } while (rnp != NULL);
883 lastcomp = rsp->completed;
885 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
888 * Move callbacks from the outgoing CPU to the running CPU.
889 * Note that the outgoing CPU is now quiscent, so it is now
890 * (uncharacteristically) safe to access its rcu_data structure.
891 * Note also that we must carefully retain the order of the
892 * outgoing CPU's callbacks in order for rcu_barrier() to work
893 * correctly. Finally, note that we start all the callbacks
894 * afresh, even those that have passed through a grace period
895 * and are therefore ready to invoke. The theory is that hotplug
896 * events are rare, and that if they are frequent enough to
897 * indefinitely delay callbacks, you have far worse things to
900 rdp_me = rsp->rda[smp_processor_id()];
901 if (rdp->nxtlist != NULL) {
902 *rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
903 rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
905 for (i = 0; i < RCU_NEXT_SIZE; i++)
906 rdp->nxttail[i] = &rdp->nxtlist;
907 rdp_me->qlen += rdp->qlen;
910 local_irq_restore(flags);
914 * Remove the specified CPU from the RCU hierarchy and move any pending
915 * callbacks that it might have to the current CPU. This code assumes
916 * that at least one CPU in the system will remain running at all times.
917 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
919 static void rcu_offline_cpu(int cpu)
921 __rcu_offline_cpu(cpu, &rcu_sched_state);
922 __rcu_offline_cpu(cpu, &rcu_bh_state);
923 rcu_preempt_offline_cpu(cpu);
926 #else /* #ifdef CONFIG_HOTPLUG_CPU */
928 static void rcu_offline_cpu(int cpu)
932 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
935 * Invoke any RCU callbacks that have made it to the end of their grace
936 * period. Thottle as specified by rdp->blimit.
938 static void rcu_do_batch(struct rcu_data *rdp)
941 struct rcu_head *next, *list, **tail;
944 /* If no callbacks are ready, just return.*/
945 if (!cpu_has_callbacks_ready_to_invoke(rdp))
949 * Extract the list of ready callbacks, disabling to prevent
950 * races with call_rcu() from interrupt handlers.
952 local_irq_save(flags);
954 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
955 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
956 tail = rdp->nxttail[RCU_DONE_TAIL];
957 for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
958 if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
959 rdp->nxttail[count] = &rdp->nxtlist;
960 local_irq_restore(flags);
962 /* Invoke callbacks. */
969 if (++count >= rdp->blimit)
973 local_irq_save(flags);
975 /* Update count, and requeue any remaining callbacks. */
978 *tail = rdp->nxtlist;
980 for (count = 0; count < RCU_NEXT_SIZE; count++)
981 if (&rdp->nxtlist == rdp->nxttail[count])
982 rdp->nxttail[count] = tail;
987 /* Reinstate batch limit if we have worked down the excess. */
988 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
989 rdp->blimit = blimit;
991 local_irq_restore(flags);
993 /* Re-raise the RCU softirq if there are callbacks remaining. */
994 if (cpu_has_callbacks_ready_to_invoke(rdp))
995 raise_softirq(RCU_SOFTIRQ);
999 * Check to see if this CPU is in a non-context-switch quiescent state
1000 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1001 * Also schedule the RCU softirq handler.
1003 * This function must be called with hardirqs disabled. It is normally
1004 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1005 * false, there is no point in invoking rcu_check_callbacks().
1007 void rcu_check_callbacks(int cpu, int user)
1009 if (!rcu_pending(cpu))
1010 return; /* if nothing for RCU to do. */
1012 (idle_cpu(cpu) && rcu_scheduler_active &&
1013 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1016 * Get here if this CPU took its interrupt from user
1017 * mode or from the idle loop, and if this is not a
1018 * nested interrupt. In this case, the CPU is in
1019 * a quiescent state, so note it.
1021 * No memory barrier is required here because both
1022 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1023 * variables that other CPUs neither access nor modify,
1024 * at least not while the corresponding CPU is online.
1030 } else if (!in_softirq()) {
1033 * Get here if this CPU did not take its interrupt from
1034 * softirq, in other words, if it is not interrupting
1035 * a rcu_bh read-side critical section. This is an _bh
1036 * critical section, so note it.
1041 rcu_preempt_check_callbacks(cpu);
1042 raise_softirq(RCU_SOFTIRQ);
1048 * Scan the leaf rcu_node structures, processing dyntick state for any that
1049 * have not yet encountered a quiescent state, using the function specified.
1050 * Returns 1 if the current grace period ends while scanning (possibly
1051 * because we made it end).
1053 static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
1054 int (*f)(struct rcu_data *))
1058 unsigned long flags;
1060 struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
1061 struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
1063 for (; rnp_cur < rnp_end; rnp_cur++) {
1065 spin_lock_irqsave(&rnp_cur->lock, flags);
1066 if (rsp->completed != lastcomp) {
1067 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1070 if (rnp_cur->qsmask == 0) {
1071 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1074 cpu = rnp_cur->grplo;
1076 for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) {
1077 if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1080 if (mask != 0 && rsp->completed == lastcomp) {
1082 /* cpu_quiet_msk() releases rnp_cur->lock. */
1083 cpu_quiet_msk(mask, rsp, rnp_cur, flags);
1086 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1092 * Force quiescent states on reluctant CPUs, and also detect which
1093 * CPUs are in dyntick-idle mode.
1095 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1097 unsigned long flags;
1099 struct rcu_node *rnp = rcu_get_root(rsp);
1102 if (!rcu_gp_in_progress(rsp))
1103 return; /* No grace period in progress, nothing to force. */
1104 if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
1105 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1106 return; /* Someone else is already on the job. */
1109 (long)(rsp->jiffies_force_qs - jiffies) >= 0)
1110 goto unlock_ret; /* no emergency and done recently. */
1112 spin_lock(&rnp->lock);
1113 lastcomp = rsp->completed;
1114 signaled = rsp->signaled;
1115 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1116 if (lastcomp == rsp->gpnum) {
1117 rsp->n_force_qs_ngp++;
1118 spin_unlock(&rnp->lock);
1119 goto unlock_ret; /* no GP in progress, time updated. */
1121 spin_unlock(&rnp->lock);
1125 break; /* grace period still initializing, ignore. */
1127 case RCU_SAVE_DYNTICK:
1129 if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1130 break; /* So gcc recognizes the dead code. */
1132 /* Record dyntick-idle state. */
1133 if (rcu_process_dyntick(rsp, lastcomp,
1134 dyntick_save_progress_counter))
1137 /* Update state, record completion counter. */
1138 spin_lock(&rnp->lock);
1139 if (lastcomp == rsp->completed) {
1140 rsp->signaled = RCU_FORCE_QS;
1141 dyntick_record_completed(rsp, lastcomp);
1143 spin_unlock(&rnp->lock);
1148 /* Check dyntick-idle state, send IPI to laggarts. */
1149 if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp),
1150 rcu_implicit_dynticks_qs))
1153 /* Leave state in case more forcing is required. */
1158 spin_unlock_irqrestore(&rsp->fqslock, flags);
1161 #else /* #ifdef CONFIG_SMP */
1163 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1168 #endif /* #else #ifdef CONFIG_SMP */
1171 * This does the RCU processing work from softirq context for the
1172 * specified rcu_state and rcu_data structures. This may be called
1173 * only from the CPU to whom the rdp belongs.
1176 __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1178 unsigned long flags;
1180 WARN_ON_ONCE(rdp->beenonline == 0);
1183 * If an RCU GP has gone long enough, go check for dyntick
1184 * idle CPUs and, if needed, send resched IPIs.
1186 if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1187 force_quiescent_state(rsp, 1);
1190 * Advance callbacks in response to end of earlier grace
1191 * period that some other CPU ended.
1193 rcu_process_gp_end(rsp, rdp);
1195 /* Update RCU state based on any recent quiescent states. */
1196 rcu_check_quiescent_state(rsp, rdp);
1198 /* Does this CPU require a not-yet-started grace period? */
1199 if (cpu_needs_another_gp(rsp, rdp)) {
1200 spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1201 rcu_start_gp(rsp, flags); /* releases above lock */
1204 /* If there are callbacks ready, invoke them. */
1209 * Do softirq processing for the current CPU.
1211 static void rcu_process_callbacks(struct softirq_action *unused)
1214 * Memory references from any prior RCU read-side critical sections
1215 * executed by the interrupted code must be seen before any RCU
1216 * grace-period manipulations below.
1218 smp_mb(); /* See above block comment. */
1220 __rcu_process_callbacks(&rcu_sched_state,
1221 &__get_cpu_var(rcu_sched_data));
1222 __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1223 rcu_preempt_process_callbacks();
1226 * Memory references from any later RCU read-side critical sections
1227 * executed by the interrupted code must be seen after any RCU
1228 * grace-period manipulations above.
1230 smp_mb(); /* See above block comment. */
1234 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1235 struct rcu_state *rsp)
1237 unsigned long flags;
1238 struct rcu_data *rdp;
1243 smp_mb(); /* Ensure RCU update seen before callback registry. */
1246 * Opportunistically note grace-period endings and beginnings.
1247 * Note that we might see a beginning right after we see an
1248 * end, but never vice versa, since this CPU has to pass through
1249 * a quiescent state betweentimes.
1251 local_irq_save(flags);
1252 rdp = rsp->rda[smp_processor_id()];
1253 rcu_process_gp_end(rsp, rdp);
1254 check_for_new_grace_period(rsp, rdp);
1256 /* Add the callback to our list. */
1257 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1258 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1260 /* Start a new grace period if one not already started. */
1261 if (!rcu_gp_in_progress(rsp)) {
1262 unsigned long nestflag;
1263 struct rcu_node *rnp_root = rcu_get_root(rsp);
1265 spin_lock_irqsave(&rnp_root->lock, nestflag);
1266 rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */
1269 /* Force the grace period if too many callbacks or too long waiting. */
1270 if (unlikely(++rdp->qlen > qhimark)) {
1271 rdp->blimit = LONG_MAX;
1272 force_quiescent_state(rsp, 0);
1273 } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1274 force_quiescent_state(rsp, 1);
1275 local_irq_restore(flags);
1279 * Queue an RCU-sched callback for invocation after a grace period.
1281 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1283 __call_rcu(head, func, &rcu_sched_state);
1285 EXPORT_SYMBOL_GPL(call_rcu_sched);
1288 * Queue an RCU for invocation after a quicker grace period.
1290 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1292 __call_rcu(head, func, &rcu_bh_state);
1294 EXPORT_SYMBOL_GPL(call_rcu_bh);
1297 * Check to see if there is any immediate RCU-related work to be done
1298 * by the current CPU, for the specified type of RCU, returning 1 if so.
1299 * The checks are in order of increasing expense: checks that can be
1300 * carried out against CPU-local state are performed first. However,
1301 * we must check for CPU stalls first, else we might not get a chance.
1303 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1305 rdp->n_rcu_pending++;
1307 /* Check for CPU stalls, if enabled. */
1308 check_cpu_stall(rsp, rdp);
1310 /* Is the RCU core waiting for a quiescent state from this CPU? */
1311 if (rdp->qs_pending) {
1312 rdp->n_rp_qs_pending++;
1316 /* Does this CPU have callbacks ready to invoke? */
1317 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1318 rdp->n_rp_cb_ready++;
1322 /* Has RCU gone idle with this CPU needing another grace period? */
1323 if (cpu_needs_another_gp(rsp, rdp)) {
1324 rdp->n_rp_cpu_needs_gp++;
1328 /* Has another RCU grace period completed? */
1329 if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
1330 rdp->n_rp_gp_completed++;
1334 /* Has a new RCU grace period started? */
1335 if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
1336 rdp->n_rp_gp_started++;
1340 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1341 if (rcu_gp_in_progress(rsp) &&
1342 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
1343 rdp->n_rp_need_fqs++;
1348 rdp->n_rp_need_nothing++;
1353 * Check to see if there is any immediate RCU-related work to be done
1354 * by the current CPU, returning 1 if so. This function is part of the
1355 * RCU implementation; it is -not- an exported member of the RCU API.
1357 static int rcu_pending(int cpu)
1359 return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1360 __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1361 rcu_preempt_pending(cpu);
1365 * Check to see if any future RCU-related work will need to be done
1366 * by the current CPU, even if none need be done immediately, returning
1367 * 1 if so. This function is part of the RCU implementation; it is -not-
1368 * an exported member of the RCU API.
1370 int rcu_needs_cpu(int cpu)
1372 /* RCU callbacks either ready or pending? */
1373 return per_cpu(rcu_sched_data, cpu).nxtlist ||
1374 per_cpu(rcu_bh_data, cpu).nxtlist ||
1375 rcu_preempt_needs_cpu(cpu);
1379 * Do boot-time initialization of a CPU's per-CPU RCU data.
1382 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1384 unsigned long flags;
1386 struct rcu_data *rdp = rsp->rda[cpu];
1387 struct rcu_node *rnp = rcu_get_root(rsp);
1389 /* Set up local state, ensuring consistent view of global state. */
1390 spin_lock_irqsave(&rnp->lock, flags);
1391 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1392 rdp->nxtlist = NULL;
1393 for (i = 0; i < RCU_NEXT_SIZE; i++)
1394 rdp->nxttail[i] = &rdp->nxtlist;
1397 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1398 #endif /* #ifdef CONFIG_NO_HZ */
1400 spin_unlock_irqrestore(&rnp->lock, flags);
1404 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1405 * offline event can be happening at a given time. Note also that we
1406 * can accept some slop in the rsp->completed access due to the fact
1407 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1409 static void __cpuinit
1410 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1412 unsigned long flags;
1415 struct rcu_data *rdp = rsp->rda[cpu];
1416 struct rcu_node *rnp = rcu_get_root(rsp);
1418 /* Set up local state, ensuring consistent view of global state. */
1419 spin_lock_irqsave(&rnp->lock, flags);
1420 lastcomp = rsp->completed;
1421 rdp->completed = lastcomp;
1422 rdp->gpnum = lastcomp;
1423 rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1424 rdp->qs_pending = 1; /* so set up to respond to current GP. */
1425 rdp->beenonline = 1; /* We have now been online. */
1426 rdp->preemptable = preemptable;
1427 rdp->passed_quiesc_completed = lastcomp - 1;
1428 rdp->blimit = blimit;
1429 spin_unlock(&rnp->lock); /* irqs remain disabled. */
1432 * A new grace period might start here. If so, we won't be part
1433 * of it, but that is OK, as we are currently in a quiescent state.
1436 /* Exclude any attempts to start a new GP on large systems. */
1437 spin_lock(&rsp->onofflock); /* irqs already disabled. */
1439 /* Add CPU to rcu_node bitmasks. */
1441 mask = rdp->grpmask;
1443 /* Exclude any attempts to start a new GP on small systems. */
1444 spin_lock(&rnp->lock); /* irqs already disabled. */
1445 rnp->qsmaskinit |= mask;
1446 mask = rnp->grpmask;
1447 spin_unlock(&rnp->lock); /* irqs already disabled. */
1449 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1451 spin_unlock_irqrestore(&rsp->onofflock, flags);
1454 static void __cpuinit rcu_online_cpu(int cpu)
1456 rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1457 rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1458 rcu_preempt_init_percpu_data(cpu);
1462 * Handle CPU online/offline notification events.
1464 int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1465 unsigned long action, void *hcpu)
1467 long cpu = (long)hcpu;
1470 case CPU_UP_PREPARE:
1471 case CPU_UP_PREPARE_FROZEN:
1472 rcu_online_cpu(cpu);
1475 case CPU_DEAD_FROZEN:
1476 case CPU_UP_CANCELED:
1477 case CPU_UP_CANCELED_FROZEN:
1478 rcu_offline_cpu(cpu);
1487 * Compute the per-level fanout, either using the exact fanout specified
1488 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1490 #ifdef CONFIG_RCU_FANOUT_EXACT
1491 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1495 for (i = NUM_RCU_LVLS - 1; i >= 0; i--)
1496 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1498 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1499 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1506 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1507 ccur = rsp->levelcnt[i];
1508 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1512 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1515 * Helper function for rcu_init() that initializes one rcu_state structure.
1517 static void __init rcu_init_one(struct rcu_state *rsp)
1522 struct rcu_node *rnp;
1524 /* Initialize the level-tracking arrays. */
1526 for (i = 1; i < NUM_RCU_LVLS; i++)
1527 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1528 rcu_init_levelspread(rsp);
1530 /* Initialize the elements themselves, starting from the leaves. */
1532 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1533 cpustride *= rsp->levelspread[i];
1534 rnp = rsp->level[i];
1535 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1536 spin_lock_init(&rnp->lock);
1539 rnp->qsmaskinit = 0;
1540 rnp->grplo = j * cpustride;
1541 rnp->grphi = (j + 1) * cpustride - 1;
1542 if (rnp->grphi >= NR_CPUS)
1543 rnp->grphi = NR_CPUS - 1;
1549 rnp->grpnum = j % rsp->levelspread[i - 1];
1550 rnp->grpmask = 1UL << rnp->grpnum;
1551 rnp->parent = rsp->level[i - 1] +
1552 j / rsp->levelspread[i - 1];
1555 INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1556 INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1562 * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used
1563 * nowhere else! Assigns leaf node pointers into each CPU's rcu_data
1566 #define RCU_INIT_FLAVOR(rsp, rcu_data) \
1568 rcu_init_one(rsp); \
1569 rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
1571 for_each_possible_cpu(i) { \
1572 if (i > rnp[j].grphi) \
1574 per_cpu(rcu_data, i).mynode = &rnp[j]; \
1575 (rsp)->rda[i] = &per_cpu(rcu_data, i); \
1576 rcu_boot_init_percpu_data(i, rsp); \
1580 #ifdef CONFIG_TREE_PREEMPT_RCU
1582 void __init __rcu_init_preempt(void)
1584 int i; /* All used by RCU_INIT_FLAVOR(). */
1586 struct rcu_node *rnp;
1588 RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
1591 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
1593 void __init __rcu_init_preempt(void)
1597 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1599 void __init __rcu_init(void)
1601 int i; /* All used by RCU_INIT_FLAVOR(). */
1603 struct rcu_node *rnp;
1605 rcu_bootup_announce();
1606 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
1607 printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
1608 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
1609 RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
1610 RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
1611 __rcu_init_preempt();
1612 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1615 module_param(blimit, int, 0);
1616 module_param(qhimark, int, 0);
1617 module_param(qlowmark, int, 0);