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>
49 #include <linux/kernel_stat.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] }, \
60 NUM_RCU_LVL_0, /* root of hierarchy. */ \
64 NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
66 .signaled = RCU_GP_IDLE, \
69 .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
70 .orphan_cbs_list = NULL, \
71 .orphan_cbs_tail = &name.orphan_cbs_list, \
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 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;
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;
120 rdp
->passed_quiesc
= 1;
124 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
125 .dynticks_nesting
= 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?
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?
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];
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
)) {
209 /* If preemptable RCU, no point in sending reschedule IPI. */
210 if (rdp
->preemptable
)
213 /* The CPU is online, so send it a reschedule IPI. */
214 if (rdp
->cpu
!= smp_processor_id())
215 smp_send_reschedule(rdp
->cpu
);
222 #endif /* #ifdef CONFIG_SMP */
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)
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
);
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)
257 struct rcu_dynticks
*rdtp
;
259 local_irq_save(flags
);
260 rdtp
= &__get_cpu_var(rcu_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)
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)
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
++)
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
328 void rcu_irq_exit(void)
330 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
332 if (--rdtp
->dynticks_nesting
)
334 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
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
)
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
)
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);
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()
374 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
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)) {
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 */
411 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
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
)
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
);
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)
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
)
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)
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
)
496 struct rcu_node
*rnp
;
498 delta
= jiffies
- rsp
->jiffies_stall
;
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
) {
535 rdp
->passed_quiesc
= 0;
536 rdp
->gpnum
= rnp
->gpnum
;
540 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
543 struct rcu_node
*rnp
;
545 local_irq_save(flags
);
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
);
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.
562 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
567 local_irq_save(flags
);
568 if (rdp
->gpnum
!= rsp
->gpnum
) {
569 note_new_gpnum(rsp
, rdp
);
572 local_irq_restore(flags
);
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.
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
604 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
607 struct rcu_node
*rnp
;
609 local_irq_save(flags
);
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
);
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
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
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
);
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
);
683 /* Advance to a new grace period and initialize state. */
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
);
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
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.
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. */
776 if (!(rnp
->qsmask
& mask
)) {
778 /* Our bit has already been cleared, so done. */
779 spin_unlock_irqrestore(&rnp
->lock
, flags
);
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
);
790 if (rnp
->parent
== NULL
) {
792 /* No more levels. Exit loop holding root lock. */
796 spin_unlock_irqrestore(&rnp
->lock
, flags
);
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!
821 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
, long lastcomp
)
825 struct rcu_node
*rnp
;
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
839 rdp
->passed_quiesc
= 0; /* try again later! */
840 spin_unlock_irqrestore(&rnp
->lock
, flags
);
844 if ((rnp
->qsmask
& mask
) == 0) {
845 spin_unlock_irqrestore(&rnp
->lock
, flags
);
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.
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
))
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
)
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
)
887 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
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
)
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
];
913 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
914 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
915 rsp
->orphan_qlen
+= rdp
->qlen
;
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
)
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
);
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
)
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. */
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. */
969 if (rnp
== rdp
->mynode
)
970 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
972 spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
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. */
985 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
986 rcu_report_unblock_qs_rnp(rnp
, flags
);
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
;
1034 /* If no callbacks are ready, just return.*/
1035 if (!cpu_has_callbacks_ready_to_invoke(rdp
))
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. */
1059 if (++count
>= rdp
->blimit
)
1063 local_irq_save(flags
);
1065 /* Update count, and requeue any remaining callbacks. */
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
;
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. */
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.
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.
1138 rcu_preempt_check_callbacks(cpu
);
1139 raise_softirq(RCU_SOFTIRQ
);
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
*))
1155 unsigned long flags
;
1157 struct rcu_node
*rnp
;
1159 rcu_for_each_leaf_node(rsp
, rnp
) {
1161 spin_lock_irqsave(&rnp
->lock
, flags
);
1162 if (rnp
->completed
!= lastcomp
) {
1163 spin_unlock_irqrestore(&rnp
->lock
, flags
);
1166 if (rnp
->qsmask
== 0) {
1167 spin_unlock_irqrestore(&rnp
->lock
, flags
);
1172 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1173 if ((rnp
->qsmask
& bit
) != 0 && f(rsp
->rda
[cpu
]))
1176 if (mask
!= 0 && rnp
->completed
== lastcomp
) {
1178 /* rcu_report_qs_rnp() releases rnp->lock. */
1179 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1182 spin_unlock_irqrestore(&rnp
->lock
, flags
);
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
;
1195 struct rcu_node
*rnp
= rcu_get_root(rsp
);
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. */
1206 (long)(rsp
->jiffies_force_qs
- jiffies
) >= 0)
1207 goto unlock_fqs_ret
; /* no emergency and done recently. */
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_fqs_ret
; /* no GP in progress, time updated. */
1222 spin_unlock(&rnp
->lock
);
1223 break; /* grace period idle or initializing, ignore. */
1225 case RCU_SAVE_DYNTICK
:
1227 spin_unlock(&rnp
->lock
);
1228 if (RCU_SIGNAL_INIT
!= RCU_SAVE_DYNTICK
)
1229 break; /* So gcc recognizes the dead code. */
1231 /* Record dyntick-idle state. */
1232 if (rcu_process_dyntick(rsp
, lastcomp
,
1233 dyntick_save_progress_counter
))
1234 goto unlock_fqs_ret
;
1235 spin_lock(&rnp
->lock
);
1236 /* fall into next case. */
1238 case RCU_SAVE_COMPLETED
:
1240 /* Update state, record completion counter. */
1242 if (lastcomp
+ 1 == rsp
->gpnum
&&
1243 lastcomp
== rsp
->completed
&&
1244 rsp
->signaled
== signaled
) {
1245 rsp
->signaled
= RCU_FORCE_QS
;
1246 rsp
->completed_fqs
= lastcomp
;
1247 forcenow
= signaled
== RCU_SAVE_COMPLETED
;
1250 spin_unlock(&rnp
->lock
);
1253 /* fall into next case. */
1257 /* Check dyntick-idle state, send IPI to laggarts. */
1258 spin_unlock(&rnp
->lock
);
1259 if (rcu_process_dyntick(rsp
, rsp
->completed_fqs
,
1260 rcu_implicit_dynticks_qs
))
1261 goto unlock_fqs_ret
;
1263 /* Leave state in case more forcing is required. */
1269 spin_unlock(&rnp
->lock
);
1274 spin_unlock_irqrestore(&rsp
->fqslock
, flags
);
1277 #else /* #ifdef CONFIG_SMP */
1279 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1284 #endif /* #else #ifdef CONFIG_SMP */
1287 * This does the RCU processing work from softirq context for the
1288 * specified rcu_state and rcu_data structures. This may be called
1289 * only from the CPU to whom the rdp belongs.
1292 __rcu_process_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1294 unsigned long flags
;
1296 WARN_ON_ONCE(rdp
->beenonline
== 0);
1299 * If an RCU GP has gone long enough, go check for dyntick
1300 * idle CPUs and, if needed, send resched IPIs.
1302 if ((long)(ACCESS_ONCE(rsp
->jiffies_force_qs
) - jiffies
) < 0)
1303 force_quiescent_state(rsp
, 1);
1306 * Advance callbacks in response to end of earlier grace
1307 * period that some other CPU ended.
1309 rcu_process_gp_end(rsp
, rdp
);
1311 /* Update RCU state based on any recent quiescent states. */
1312 rcu_check_quiescent_state(rsp
, rdp
);
1314 /* Does this CPU require a not-yet-started grace period? */
1315 if (cpu_needs_another_gp(rsp
, rdp
)) {
1316 spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1317 rcu_start_gp(rsp
, flags
); /* releases above lock */
1320 /* If there are callbacks ready, invoke them. */
1321 rcu_do_batch(rsp
, rdp
);
1325 * Do softirq processing for the current CPU.
1327 static void rcu_process_callbacks(struct softirq_action
*unused
)
1330 * Memory references from any prior RCU read-side critical sections
1331 * executed by the interrupted code must be seen before any RCU
1332 * grace-period manipulations below.
1334 smp_mb(); /* See above block comment. */
1336 __rcu_process_callbacks(&rcu_sched_state
,
1337 &__get_cpu_var(rcu_sched_data
));
1338 __rcu_process_callbacks(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1339 rcu_preempt_process_callbacks();
1342 * Memory references from any later RCU read-side critical sections
1343 * executed by the interrupted code must be seen after any RCU
1344 * grace-period manipulations above.
1346 smp_mb(); /* See above block comment. */
1350 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1351 struct rcu_state
*rsp
)
1353 unsigned long flags
;
1354 struct rcu_data
*rdp
;
1359 smp_mb(); /* Ensure RCU update seen before callback registry. */
1362 * Opportunistically note grace-period endings and beginnings.
1363 * Note that we might see a beginning right after we see an
1364 * end, but never vice versa, since this CPU has to pass through
1365 * a quiescent state betweentimes.
1367 local_irq_save(flags
);
1368 rdp
= rsp
->rda
[smp_processor_id()];
1369 rcu_process_gp_end(rsp
, rdp
);
1370 check_for_new_grace_period(rsp
, rdp
);
1372 /* Add the callback to our list. */
1373 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1374 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1376 /* Start a new grace period if one not already started. */
1377 if (!rcu_gp_in_progress(rsp
)) {
1378 unsigned long nestflag
;
1379 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1381 spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1382 rcu_start_gp(rsp
, nestflag
); /* releases rnp_root->lock. */
1386 * Force the grace period if too many callbacks or too long waiting.
1387 * Enforce hysteresis, and don't invoke force_quiescent_state()
1388 * if some other CPU has recently done so. Also, don't bother
1389 * invoking force_quiescent_state() if the newly enqueued callback
1390 * is the only one waiting for a grace period to complete.
1392 if (unlikely(++rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1393 rdp
->blimit
= LONG_MAX
;
1394 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1395 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1396 force_quiescent_state(rsp
, 0);
1397 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1398 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1399 } else if ((long)(ACCESS_ONCE(rsp
->jiffies_force_qs
) - jiffies
) < 0)
1400 force_quiescent_state(rsp
, 1);
1401 local_irq_restore(flags
);
1405 * Queue an RCU-sched callback for invocation after a grace period.
1407 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1409 __call_rcu(head
, func
, &rcu_sched_state
);
1411 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1414 * Queue an RCU for invocation after a quicker grace period.
1416 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1418 __call_rcu(head
, func
, &rcu_bh_state
);
1420 EXPORT_SYMBOL_GPL(call_rcu_bh
);
1423 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1425 * Control will return to the caller some time after a full rcu-sched
1426 * grace period has elapsed, in other words after all currently executing
1427 * rcu-sched read-side critical sections have completed. These read-side
1428 * critical sections are delimited by rcu_read_lock_sched() and
1429 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1430 * local_irq_disable(), and so on may be used in place of
1431 * rcu_read_lock_sched().
1433 * This means that all preempt_disable code sequences, including NMI and
1434 * hardware-interrupt handlers, in progress on entry will have completed
1435 * before this primitive returns. However, this does not guarantee that
1436 * softirq handlers will have completed, since in some kernels, these
1437 * handlers can run in process context, and can block.
1439 * This primitive provides the guarantees made by the (now removed)
1440 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1441 * guarantees that rcu_read_lock() sections will have completed.
1442 * In "classic RCU", these two guarantees happen to be one and
1443 * the same, but can differ in realtime RCU implementations.
1445 void synchronize_sched(void)
1447 struct rcu_synchronize rcu
;
1449 if (rcu_blocking_is_gp())
1452 init_completion(&rcu
.completion
);
1453 /* Will wake me after RCU finished. */
1454 call_rcu_sched(&rcu
.head
, wakeme_after_rcu
);
1456 wait_for_completion(&rcu
.completion
);
1458 EXPORT_SYMBOL_GPL(synchronize_sched
);
1461 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1463 * Control will return to the caller some time after a full rcu_bh grace
1464 * period has elapsed, in other words after all currently executing rcu_bh
1465 * read-side critical sections have completed. RCU read-side critical
1466 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1467 * and may be nested.
1469 void synchronize_rcu_bh(void)
1471 struct rcu_synchronize rcu
;
1473 if (rcu_blocking_is_gp())
1476 init_completion(&rcu
.completion
);
1477 /* Will wake me after RCU finished. */
1478 call_rcu_bh(&rcu
.head
, wakeme_after_rcu
);
1480 wait_for_completion(&rcu
.completion
);
1482 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
1485 * Check to see if there is any immediate RCU-related work to be done
1486 * by the current CPU, for the specified type of RCU, returning 1 if so.
1487 * The checks are in order of increasing expense: checks that can be
1488 * carried out against CPU-local state are performed first. However,
1489 * we must check for CPU stalls first, else we might not get a chance.
1491 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1493 struct rcu_node
*rnp
= rdp
->mynode
;
1495 rdp
->n_rcu_pending
++;
1497 /* Check for CPU stalls, if enabled. */
1498 check_cpu_stall(rsp
, rdp
);
1500 /* Is the RCU core waiting for a quiescent state from this CPU? */
1501 if (rdp
->qs_pending
) {
1502 rdp
->n_rp_qs_pending
++;
1506 /* Does this CPU have callbacks ready to invoke? */
1507 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
1508 rdp
->n_rp_cb_ready
++;
1512 /* Has RCU gone idle with this CPU needing another grace period? */
1513 if (cpu_needs_another_gp(rsp
, rdp
)) {
1514 rdp
->n_rp_cpu_needs_gp
++;
1518 /* Has another RCU grace period completed? */
1519 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
1520 rdp
->n_rp_gp_completed
++;
1524 /* Has a new RCU grace period started? */
1525 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
1526 rdp
->n_rp_gp_started
++;
1530 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1531 if (rcu_gp_in_progress(rsp
) &&
1532 ((long)(ACCESS_ONCE(rsp
->jiffies_force_qs
) - jiffies
) < 0)) {
1533 rdp
->n_rp_need_fqs
++;
1538 rdp
->n_rp_need_nothing
++;
1543 * Check to see if there is any immediate RCU-related work to be done
1544 * by the current CPU, returning 1 if so. This function is part of the
1545 * RCU implementation; it is -not- an exported member of the RCU API.
1547 static int rcu_pending(int cpu
)
1549 return __rcu_pending(&rcu_sched_state
, &per_cpu(rcu_sched_data
, cpu
)) ||
1550 __rcu_pending(&rcu_bh_state
, &per_cpu(rcu_bh_data
, cpu
)) ||
1551 rcu_preempt_pending(cpu
);
1555 * Check to see if any future RCU-related work will need to be done
1556 * by the current CPU, even if none need be done immediately, returning
1557 * 1 if so. This function is part of the RCU implementation; it is -not-
1558 * an exported member of the RCU API.
1560 int rcu_needs_cpu(int cpu
)
1562 /* RCU callbacks either ready or pending? */
1563 return per_cpu(rcu_sched_data
, cpu
).nxtlist
||
1564 per_cpu(rcu_bh_data
, cpu
).nxtlist
||
1565 rcu_preempt_needs_cpu(cpu
);
1569 * This function is invoked towards the end of the scheduler's initialization
1570 * process. Before this is called, the idle task might contain
1571 * RCU read-side critical sections (during which time, this idle
1572 * task is booting the system). After this function is called, the
1573 * idle tasks are prohibited from containing RCU read-side critical
1576 void rcu_scheduler_starting(void)
1578 WARN_ON(num_online_cpus() != 1);
1579 WARN_ON(nr_context_switches() > 0);
1580 rcu_scheduler_active
= 1;
1583 static DEFINE_PER_CPU(struct rcu_head
, rcu_barrier_head
) = {NULL
};
1584 static atomic_t rcu_barrier_cpu_count
;
1585 static DEFINE_MUTEX(rcu_barrier_mutex
);
1586 static struct completion rcu_barrier_completion
;
1588 static void rcu_barrier_callback(struct rcu_head
*notused
)
1590 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1591 complete(&rcu_barrier_completion
);
1595 * Called with preemption disabled, and from cross-cpu IRQ context.
1597 static void rcu_barrier_func(void *type
)
1599 int cpu
= smp_processor_id();
1600 struct rcu_head
*head
= &per_cpu(rcu_barrier_head
, cpu
);
1601 void (*call_rcu_func
)(struct rcu_head
*head
,
1602 void (*func
)(struct rcu_head
*head
));
1604 atomic_inc(&rcu_barrier_cpu_count
);
1605 call_rcu_func
= type
;
1606 call_rcu_func(head
, rcu_barrier_callback
);
1610 * Orchestrate the specified type of RCU barrier, waiting for all
1611 * RCU callbacks of the specified type to complete.
1613 static void _rcu_barrier(struct rcu_state
*rsp
,
1614 void (*call_rcu_func
)(struct rcu_head
*head
,
1615 void (*func
)(struct rcu_head
*head
)))
1617 BUG_ON(in_interrupt());
1618 /* Take mutex to serialize concurrent rcu_barrier() requests. */
1619 mutex_lock(&rcu_barrier_mutex
);
1620 init_completion(&rcu_barrier_completion
);
1622 * Initialize rcu_barrier_cpu_count to 1, then invoke
1623 * rcu_barrier_func() on each CPU, so that each CPU also has
1624 * incremented rcu_barrier_cpu_count. Only then is it safe to
1625 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1626 * might complete its grace period before all of the other CPUs
1627 * did their increment, causing this function to return too
1630 atomic_set(&rcu_barrier_cpu_count
, 1);
1631 preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */
1632 rcu_adopt_orphan_cbs(rsp
);
1633 on_each_cpu(rcu_barrier_func
, (void *)call_rcu_func
, 1);
1634 preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */
1635 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1636 complete(&rcu_barrier_completion
);
1637 wait_for_completion(&rcu_barrier_completion
);
1638 mutex_unlock(&rcu_barrier_mutex
);
1642 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1644 void rcu_barrier_bh(void)
1646 _rcu_barrier(&rcu_bh_state
, call_rcu_bh
);
1648 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
1651 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1653 void rcu_barrier_sched(void)
1655 _rcu_barrier(&rcu_sched_state
, call_rcu_sched
);
1657 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
1660 * Do boot-time initialization of a CPU's per-CPU RCU data.
1663 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
1665 unsigned long flags
;
1667 struct rcu_data
*rdp
= rsp
->rda
[cpu
];
1668 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1670 /* Set up local state, ensuring consistent view of global state. */
1671 spin_lock_irqsave(&rnp
->lock
, flags
);
1672 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
1673 rdp
->nxtlist
= NULL
;
1674 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1675 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1678 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
1679 #endif /* #ifdef CONFIG_NO_HZ */
1681 spin_unlock_irqrestore(&rnp
->lock
, flags
);
1685 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1686 * offline event can be happening at a given time. Note also that we
1687 * can accept some slop in the rsp->completed access due to the fact
1688 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1690 static void __cpuinit
1691 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptable
)
1693 unsigned long flags
;
1695 struct rcu_data
*rdp
= rsp
->rda
[cpu
];
1696 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1698 /* Set up local state, ensuring consistent view of global state. */
1699 spin_lock_irqsave(&rnp
->lock
, flags
);
1700 rdp
->passed_quiesc
= 0; /* We could be racing with new GP, */
1701 rdp
->qs_pending
= 1; /* so set up to respond to current GP. */
1702 rdp
->beenonline
= 1; /* We have now been online. */
1703 rdp
->preemptable
= preemptable
;
1704 rdp
->qlen_last_fqs_check
= 0;
1705 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1706 rdp
->blimit
= blimit
;
1707 spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1710 * A new grace period might start here. If so, we won't be part
1711 * of it, but that is OK, as we are currently in a quiescent state.
1714 /* Exclude any attempts to start a new GP on large systems. */
1715 spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
1717 /* Add CPU to rcu_node bitmasks. */
1719 mask
= rdp
->grpmask
;
1721 /* Exclude any attempts to start a new GP on small systems. */
1722 spin_lock(&rnp
->lock
); /* irqs already disabled. */
1723 rnp
->qsmaskinit
|= mask
;
1724 mask
= rnp
->grpmask
;
1725 if (rnp
== rdp
->mynode
) {
1726 rdp
->gpnum
= rnp
->completed
; /* if GP in progress... */
1727 rdp
->completed
= rnp
->completed
;
1728 rdp
->passed_quiesc_completed
= rnp
->completed
- 1;
1730 spin_unlock(&rnp
->lock
); /* irqs already disabled. */
1732 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
1734 spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
1737 static void __cpuinit
rcu_online_cpu(int cpu
)
1739 rcu_init_percpu_data(cpu
, &rcu_sched_state
, 0);
1740 rcu_init_percpu_data(cpu
, &rcu_bh_state
, 0);
1741 rcu_preempt_init_percpu_data(cpu
);
1745 * Handle CPU online/offline notification events.
1747 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
1748 unsigned long action
, void *hcpu
)
1750 long cpu
= (long)hcpu
;
1753 case CPU_UP_PREPARE
:
1754 case CPU_UP_PREPARE_FROZEN
:
1755 rcu_online_cpu(cpu
);
1758 case CPU_DYING_FROZEN
:
1760 * preempt_disable() in _rcu_barrier() prevents stop_machine(),
1761 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
1762 * returns, all online cpus have queued rcu_barrier_func().
1763 * The dying CPU clears its cpu_online_mask bit and
1764 * moves all of its RCU callbacks to ->orphan_cbs_list
1765 * in the context of stop_machine(), so subsequent calls
1766 * to _rcu_barrier() will adopt these callbacks and only
1767 * then queue rcu_barrier_func() on all remaining CPUs.
1769 rcu_send_cbs_to_orphanage(&rcu_bh_state
);
1770 rcu_send_cbs_to_orphanage(&rcu_sched_state
);
1771 rcu_preempt_send_cbs_to_orphanage();
1774 case CPU_DEAD_FROZEN
:
1775 case CPU_UP_CANCELED
:
1776 case CPU_UP_CANCELED_FROZEN
:
1777 rcu_offline_cpu(cpu
);
1786 * Compute the per-level fanout, either using the exact fanout specified
1787 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1789 #ifdef CONFIG_RCU_FANOUT_EXACT
1790 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
1794 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--)
1795 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
1797 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1798 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
1805 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
1806 ccur
= rsp
->levelcnt
[i
];
1807 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
1811 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1814 * Helper function for rcu_init() that initializes one rcu_state structure.
1816 static void __init
rcu_init_one(struct rcu_state
*rsp
)
1821 struct rcu_node
*rnp
;
1823 /* Initialize the level-tracking arrays. */
1825 for (i
= 1; i
< NUM_RCU_LVLS
; i
++)
1826 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
1827 rcu_init_levelspread(rsp
);
1829 /* Initialize the elements themselves, starting from the leaves. */
1831 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
1832 cpustride
*= rsp
->levelspread
[i
];
1833 rnp
= rsp
->level
[i
];
1834 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
1835 spin_lock_init(&rnp
->lock
);
1836 lockdep_set_class(&rnp
->lock
, &rcu_node_class
[i
]);
1839 rnp
->qsmaskinit
= 0;
1840 rnp
->grplo
= j
* cpustride
;
1841 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
1842 if (rnp
->grphi
>= NR_CPUS
)
1843 rnp
->grphi
= NR_CPUS
- 1;
1849 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
1850 rnp
->grpmask
= 1UL << rnp
->grpnum
;
1851 rnp
->parent
= rsp
->level
[i
- 1] +
1852 j
/ rsp
->levelspread
[i
- 1];
1855 INIT_LIST_HEAD(&rnp
->blocked_tasks
[0]);
1856 INIT_LIST_HEAD(&rnp
->blocked_tasks
[1]);
1857 INIT_LIST_HEAD(&rnp
->blocked_tasks
[2]);
1858 INIT_LIST_HEAD(&rnp
->blocked_tasks
[3]);
1864 * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used
1865 * nowhere else! Assigns leaf node pointers into each CPU's rcu_data
1868 #define RCU_INIT_FLAVOR(rsp, rcu_data) \
1872 struct rcu_node *rnp; \
1874 rcu_init_one(rsp); \
1875 rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
1877 for_each_possible_cpu(i) { \
1878 if (i > rnp[j].grphi) \
1880 per_cpu(rcu_data, i).mynode = &rnp[j]; \
1881 (rsp)->rda[i] = &per_cpu(rcu_data, i); \
1882 rcu_boot_init_percpu_data(i, rsp); \
1886 void __init
rcu_init(void)
1890 rcu_bootup_announce();
1891 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
1892 printk(KERN_INFO
"RCU-based detection of stalled CPUs is enabled.\n");
1893 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
1894 #if NUM_RCU_LVL_4 != 0
1895 printk(KERN_INFO
"Experimental four-level hierarchy is enabled.\n");
1896 #endif /* #if NUM_RCU_LVL_4 != 0 */
1897 RCU_INIT_FLAVOR(&rcu_sched_state
, rcu_sched_data
);
1898 RCU_INIT_FLAVOR(&rcu_bh_state
, rcu_bh_data
);
1899 __rcu_init_preempt();
1900 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
1903 * We don't need protection against CPU-hotplug here because
1904 * this is called early in boot, before either interrupts
1905 * or the scheduler are operational.
1907 cpu_notifier(rcu_cpu_notify
, 0);
1908 for_each_online_cpu(i
)
1909 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)i
);
1912 #include "rcutree_plugin.h"