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(structname) { \
58 .level = { &structname.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 = __RAW_SPIN_LOCK_UNLOCKED(&structname.onofflock), \
70 .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
72 .n_force_qs_ngp = 0, \
73 .name = #structname, \
76 struct rcu_state rcu_sched_state
= RCU_STATE_INITIALIZER(rcu_sched_state
);
77 DEFINE_PER_CPU(struct rcu_data
, rcu_sched_data
);
79 struct rcu_state rcu_bh_state
= RCU_STATE_INITIALIZER(rcu_bh_state
);
80 DEFINE_PER_CPU(struct rcu_data
, rcu_bh_data
);
82 int rcu_scheduler_active __read_mostly
;
83 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
86 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
87 * permit this function to be invoked without holding the root rcu_node
88 * structure's ->lock, but of course results can be subject to change.
90 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
92 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
96 * Note a quiescent state. Because we do not need to know
97 * how many quiescent states passed, just if there was at least
98 * one since the start of the grace period, this just sets a flag.
100 void rcu_sched_qs(int cpu
)
102 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
104 rdp
->passed_quiesc_completed
= rdp
->gpnum
- 1;
106 rdp
->passed_quiesc
= 1;
109 void rcu_bh_qs(int cpu
)
111 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
113 rdp
->passed_quiesc_completed
= rdp
->gpnum
- 1;
115 rdp
->passed_quiesc
= 1;
119 * Note a context switch. This is a quiescent state for RCU-sched,
120 * and requires special handling for preemptible RCU.
122 void rcu_note_context_switch(int cpu
)
125 rcu_preempt_note_context_switch(cpu
);
129 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
130 .dynticks_nesting
= 1,
131 .dynticks
= ATOMIC_INIT(1),
133 #endif /* #ifdef CONFIG_NO_HZ */
135 static int blimit
= 10; /* Maximum callbacks per softirq. */
136 static int qhimark
= 10000; /* If this many pending, ignore blimit. */
137 static int qlowmark
= 100; /* Once only this many pending, use blimit. */
139 module_param(blimit
, int, 0);
140 module_param(qhimark
, int, 0);
141 module_param(qlowmark
, int, 0);
143 int rcu_cpu_stall_suppress __read_mostly
;
144 module_param(rcu_cpu_stall_suppress
, int, 0644);
146 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
);
147 static int rcu_pending(int cpu
);
150 * Return the number of RCU-sched batches processed thus far for debug & stats.
152 long rcu_batches_completed_sched(void)
154 return rcu_sched_state
.completed
;
156 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
159 * Return the number of RCU BH batches processed thus far for debug & stats.
161 long rcu_batches_completed_bh(void)
163 return rcu_bh_state
.completed
;
165 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
168 * Force a quiescent state for RCU BH.
170 void rcu_bh_force_quiescent_state(void)
172 force_quiescent_state(&rcu_bh_state
, 0);
174 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
177 * Force a quiescent state for RCU-sched.
179 void rcu_sched_force_quiescent_state(void)
181 force_quiescent_state(&rcu_sched_state
, 0);
183 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
186 * Does the CPU have callbacks ready to be invoked?
189 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
191 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
];
195 * Does the current CPU require a yet-as-unscheduled grace period?
198 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
200 return *rdp
->nxttail
[RCU_DONE_TAIL
] && !rcu_gp_in_progress(rsp
);
204 * Return the root node of the specified rcu_state structure.
206 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
208 return &rsp
->node
[0];
214 * If the specified CPU is offline, tell the caller that it is in
215 * a quiescent state. Otherwise, whack it with a reschedule IPI.
216 * Grace periods can end up waiting on an offline CPU when that
217 * CPU is in the process of coming online -- it will be added to the
218 * rcu_node bitmasks before it actually makes it online. The same thing
219 * can happen while a CPU is in the process of coming online. Because this
220 * race is quite rare, we check for it after detecting that the grace
221 * period has been delayed rather than checking each and every CPU
222 * each and every time we start a new grace period.
224 static int rcu_implicit_offline_qs(struct rcu_data
*rdp
)
227 * If the CPU is offline, it is in a quiescent state. We can
228 * trust its state not to change because interrupts are disabled.
230 if (cpu_is_offline(rdp
->cpu
)) {
235 /* If preemptable RCU, no point in sending reschedule IPI. */
236 if (rdp
->preemptable
)
239 /* The CPU is online, so send it a reschedule IPI. */
240 if (rdp
->cpu
!= smp_processor_id())
241 smp_send_reschedule(rdp
->cpu
);
248 #endif /* #ifdef CONFIG_SMP */
253 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
255 * Enter nohz mode, in other words, -leave- the mode in which RCU
256 * read-side critical sections can occur. (Though RCU read-side
257 * critical sections can occur in irq handlers in nohz mode, a possibility
258 * handled by rcu_irq_enter() and rcu_irq_exit()).
260 void rcu_enter_nohz(void)
263 struct rcu_dynticks
*rdtp
;
265 local_irq_save(flags
);
266 rdtp
= &__get_cpu_var(rcu_dynticks
);
267 if (--rdtp
->dynticks_nesting
) {
268 local_irq_restore(flags
);
271 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
272 smp_mb__before_atomic_inc(); /* See above. */
273 atomic_inc(&rdtp
->dynticks
);
274 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
275 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
276 local_irq_restore(flags
);
278 /* If the interrupt queued a callback, get out of dyntick mode. */
280 (__get_cpu_var(rcu_sched_data
).nxtlist
||
281 __get_cpu_var(rcu_bh_data
).nxtlist
||
282 rcu_preempt_needs_cpu(smp_processor_id())))
287 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
289 * Exit nohz mode, in other words, -enter- the mode in which RCU
290 * read-side critical sections normally occur.
292 void rcu_exit_nohz(void)
295 struct rcu_dynticks
*rdtp
;
297 local_irq_save(flags
);
298 rdtp
= &__get_cpu_var(rcu_dynticks
);
299 if (rdtp
->dynticks_nesting
++) {
300 local_irq_restore(flags
);
303 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
304 atomic_inc(&rdtp
->dynticks
);
305 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
306 smp_mb__after_atomic_inc(); /* See above. */
307 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
308 local_irq_restore(flags
);
312 * rcu_nmi_enter - inform RCU of entry to NMI context
314 * If the CPU was idle with dynamic ticks active, and there is no
315 * irq handler running, this updates rdtp->dynticks_nmi to let the
316 * RCU grace-period handling know that the CPU is active.
318 void rcu_nmi_enter(void)
320 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
322 if (rdtp
->dynticks_nmi_nesting
== 0 &&
323 (atomic_read(&rdtp
->dynticks
) & 0x1))
325 rdtp
->dynticks_nmi_nesting
++;
326 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
327 atomic_inc(&rdtp
->dynticks
);
328 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
329 smp_mb__after_atomic_inc(); /* See above. */
330 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
334 * rcu_nmi_exit - inform RCU of exit from NMI context
336 * If the CPU was idle with dynamic ticks active, and there is no
337 * irq handler running, this updates rdtp->dynticks_nmi to let the
338 * RCU grace-period handling know that the CPU is no longer active.
340 void rcu_nmi_exit(void)
342 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
344 if (rdtp
->dynticks_nmi_nesting
== 0 ||
345 --rdtp
->dynticks_nmi_nesting
!= 0)
347 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
348 smp_mb__before_atomic_inc(); /* See above. */
349 atomic_inc(&rdtp
->dynticks
);
350 smp_mb__after_atomic_inc(); /* Force delay to next write. */
351 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
355 * rcu_irq_enter - inform RCU of entry to hard irq context
357 * If the CPU was idle with dynamic ticks active, this updates the
358 * rdtp->dynticks to let the RCU handling know that the CPU is active.
360 void rcu_irq_enter(void)
366 * rcu_irq_exit - inform RCU of exit from hard irq context
368 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
369 * to put let the RCU handling be aware that the CPU is going back to idle
372 void rcu_irq_exit(void)
380 * Snapshot the specified CPU's dynticks counter so that we can later
381 * credit them with an implicit quiescent state. Return 1 if this CPU
382 * is in dynticks idle mode, which is an extended quiescent state.
384 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
386 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
391 * Return true if the specified CPU has passed through a quiescent
392 * state by virtue of being in or having passed through an dynticks
393 * idle state since the last call to dyntick_save_progress_counter()
396 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
401 curr
= (unsigned long)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
402 snap
= (unsigned long)rdp
->dynticks_snap
;
405 * If the CPU passed through or entered a dynticks idle phase with
406 * no active irq/NMI handlers, then we can safely pretend that the CPU
407 * already acknowledged the request to pass through a quiescent
408 * state. Either way, that CPU cannot possibly be in an RCU
409 * read-side critical section that started before the beginning
410 * of the current RCU grace period.
412 if ((curr
& 0x1) == 0 || ULONG_CMP_GE(curr
, snap
+ 2)) {
417 /* Go check for the CPU being offline. */
418 return rcu_implicit_offline_qs(rdp
);
421 #endif /* #ifdef CONFIG_SMP */
423 #else /* #ifdef CONFIG_NO_HZ */
427 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
432 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
434 return rcu_implicit_offline_qs(rdp
);
437 #endif /* #ifdef CONFIG_SMP */
439 #endif /* #else #ifdef CONFIG_NO_HZ */
441 int rcu_cpu_stall_suppress __read_mostly
;
443 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
445 rsp
->gp_start
= jiffies
;
446 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_CHECK
;
449 static void print_other_cpu_stall(struct rcu_state
*rsp
)
454 struct rcu_node
*rnp
= rcu_get_root(rsp
);
456 /* Only let one CPU complain about others per time interval. */
458 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
459 delta
= jiffies
- rsp
->jiffies_stall
;
460 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
461 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
464 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
467 * Now rat on any tasks that got kicked up to the root rcu_node
468 * due to CPU offlining.
470 rcu_print_task_stall(rnp
);
471 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
474 * OK, time to rat on our buddy...
475 * See Documentation/RCU/stallwarn.txt for info on how to debug
476 * RCU CPU stall warnings.
478 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks: {",
480 rcu_for_each_leaf_node(rsp
, rnp
) {
481 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
482 rcu_print_task_stall(rnp
);
483 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
484 if (rnp
->qsmask
== 0)
486 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
487 if (rnp
->qsmask
& (1UL << cpu
))
488 printk(" %d", rnp
->grplo
+ cpu
);
490 printk("} (detected by %d, t=%ld jiffies)\n",
491 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
));
492 trigger_all_cpu_backtrace();
494 /* If so configured, complain about tasks blocking the grace period. */
496 rcu_print_detail_task_stall(rsp
);
498 force_quiescent_state(rsp
, 0); /* Kick them all. */
501 static void print_cpu_stall(struct rcu_state
*rsp
)
504 struct rcu_node
*rnp
= rcu_get_root(rsp
);
507 * OK, time to rat on ourselves...
508 * See Documentation/RCU/stallwarn.txt for info on how to debug
509 * RCU CPU stall warnings.
511 printk(KERN_ERR
"INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
512 rsp
->name
, smp_processor_id(), jiffies
- rsp
->gp_start
);
513 trigger_all_cpu_backtrace();
515 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
516 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
518 jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
519 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
521 set_need_resched(); /* kick ourselves to get things going. */
524 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
527 struct rcu_node
*rnp
;
529 if (rcu_cpu_stall_suppress
)
531 delta
= jiffies
- ACCESS_ONCE(rsp
->jiffies_stall
);
533 if ((ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && delta
>= 0) {
535 /* We haven't checked in, so go dump stack. */
536 print_cpu_stall(rsp
);
538 } else if (rcu_gp_in_progress(rsp
) && delta
>= RCU_STALL_RAT_DELAY
) {
540 /* They had two time units to dump stack, so complain. */
541 print_other_cpu_stall(rsp
);
545 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
547 rcu_cpu_stall_suppress
= 1;
552 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
554 * Set the stall-warning timeout way off into the future, thus preventing
555 * any RCU CPU stall-warning messages from appearing in the current set of
558 * The caller must disable hard irqs.
560 void rcu_cpu_stall_reset(void)
562 rcu_sched_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
563 rcu_bh_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
564 rcu_preempt_stall_reset();
567 static struct notifier_block rcu_panic_block
= {
568 .notifier_call
= rcu_panic
,
571 static void __init
check_cpu_stall_init(void)
573 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
577 * Update CPU-local rcu_data state to record the newly noticed grace period.
578 * This is used both when we started the grace period and when we notice
579 * that someone else started the grace period. The caller must hold the
580 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
581 * and must have irqs disabled.
583 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
585 if (rdp
->gpnum
!= rnp
->gpnum
) {
587 * If the current grace period is waiting for this CPU,
588 * set up to detect a quiescent state, otherwise don't
589 * go looking for one.
591 rdp
->gpnum
= rnp
->gpnum
;
592 if (rnp
->qsmask
& rdp
->grpmask
) {
594 rdp
->passed_quiesc
= 0;
600 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
603 struct rcu_node
*rnp
;
605 local_irq_save(flags
);
607 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
608 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
609 local_irq_restore(flags
);
612 __note_new_gpnum(rsp
, rnp
, rdp
);
613 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
617 * Did someone else start a new RCU grace period start since we last
618 * checked? Update local state appropriately if so. Must be called
619 * on the CPU corresponding to rdp.
622 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
627 local_irq_save(flags
);
628 if (rdp
->gpnum
!= rsp
->gpnum
) {
629 note_new_gpnum(rsp
, rdp
);
632 local_irq_restore(flags
);
637 * Advance this CPU's callbacks, but only if the current grace period
638 * has ended. This may be called only from the CPU to whom the rdp
639 * belongs. In addition, the corresponding leaf rcu_node structure's
640 * ->lock must be held by the caller, with irqs disabled.
643 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
645 /* Did another grace period end? */
646 if (rdp
->completed
!= rnp
->completed
) {
648 /* Advance callbacks. No harm if list empty. */
649 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
650 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
651 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
653 /* Remember that we saw this grace-period completion. */
654 rdp
->completed
= rnp
->completed
;
657 * If we were in an extended quiescent state, we may have
658 * missed some grace periods that others CPUs handled on
659 * our behalf. Catch up with this state to avoid noting
660 * spurious new grace periods. If another grace period
661 * has started, then rnp->gpnum will have advanced, so
662 * we will detect this later on.
664 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
))
665 rdp
->gpnum
= rdp
->completed
;
668 * If RCU does not need a quiescent state from this CPU,
669 * then make sure that this CPU doesn't go looking for one.
671 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
677 * Advance this CPU's callbacks, but only if the current grace period
678 * has ended. This may be called only from the CPU to whom the rdp
682 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
685 struct rcu_node
*rnp
;
687 local_irq_save(flags
);
689 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
690 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
691 local_irq_restore(flags
);
694 __rcu_process_gp_end(rsp
, rnp
, rdp
);
695 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
699 * Do per-CPU grace-period initialization for running CPU. The caller
700 * must hold the lock of the leaf rcu_node structure corresponding to
704 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
706 /* Prior grace period ended, so advance callbacks for current CPU. */
707 __rcu_process_gp_end(rsp
, rnp
, rdp
);
710 * Because this CPU just now started the new grace period, we know
711 * that all of its callbacks will be covered by this upcoming grace
712 * period, even the ones that were registered arbitrarily recently.
713 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
715 * Other CPUs cannot be sure exactly when the grace period started.
716 * Therefore, their recently registered callbacks must pass through
717 * an additional RCU_NEXT_READY stage, so that they will be handled
718 * by the next RCU grace period.
720 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
721 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
723 /* Set state so that this CPU will detect the next quiescent state. */
724 __note_new_gpnum(rsp
, rnp
, rdp
);
728 * Start a new RCU grace period if warranted, re-initializing the hierarchy
729 * in preparation for detecting the next grace period. The caller must hold
730 * the root node's ->lock, which is released before return. Hard irqs must
734 rcu_start_gp(struct rcu_state
*rsp
, unsigned long flags
)
735 __releases(rcu_get_root(rsp
)->lock
)
737 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
738 struct rcu_node
*rnp
= rcu_get_root(rsp
);
740 if (!cpu_needs_another_gp(rsp
, rdp
) || rsp
->fqs_active
) {
741 if (cpu_needs_another_gp(rsp
, rdp
))
742 rsp
->fqs_need_gp
= 1;
743 if (rnp
->completed
== rsp
->completed
) {
744 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
747 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
750 * Propagate new ->completed value to rcu_node structures
751 * so that other CPUs don't have to wait until the start
752 * of the next grace period to process their callbacks.
754 rcu_for_each_node_breadth_first(rsp
, rnp
) {
755 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
756 rnp
->completed
= rsp
->completed
;
757 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
759 local_irq_restore(flags
);
763 /* Advance to a new grace period and initialize state. */
765 WARN_ON_ONCE(rsp
->signaled
== RCU_GP_INIT
);
766 rsp
->signaled
= RCU_GP_INIT
; /* Hold off force_quiescent_state. */
767 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
768 record_gp_stall_check_time(rsp
);
770 /* Special-case the common single-level case. */
771 if (NUM_RCU_NODES
== 1) {
772 rcu_preempt_check_blocked_tasks(rnp
);
773 rnp
->qsmask
= rnp
->qsmaskinit
;
774 rnp
->gpnum
= rsp
->gpnum
;
775 rnp
->completed
= rsp
->completed
;
776 rsp
->signaled
= RCU_SIGNAL_INIT
; /* force_quiescent_state OK. */
777 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
778 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
782 raw_spin_unlock(&rnp
->lock
); /* leave irqs disabled. */
785 /* Exclude any concurrent CPU-hotplug operations. */
786 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
789 * Set the quiescent-state-needed bits in all the rcu_node
790 * structures for all currently online CPUs in breadth-first
791 * order, starting from the root rcu_node structure. This
792 * operation relies on the layout of the hierarchy within the
793 * rsp->node[] array. Note that other CPUs will access only
794 * the leaves of the hierarchy, which still indicate that no
795 * grace period is in progress, at least until the corresponding
796 * leaf node has been initialized. In addition, we have excluded
797 * CPU-hotplug operations.
799 * Note that the grace period cannot complete until we finish
800 * the initialization process, as there will be at least one
801 * qsmask bit set in the root node until that time, namely the
802 * one corresponding to this CPU, due to the fact that we have
805 rcu_for_each_node_breadth_first(rsp
, rnp
) {
806 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
807 rcu_preempt_check_blocked_tasks(rnp
);
808 rnp
->qsmask
= rnp
->qsmaskinit
;
809 rnp
->gpnum
= rsp
->gpnum
;
810 rnp
->completed
= rsp
->completed
;
811 if (rnp
== rdp
->mynode
)
812 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
813 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
816 rnp
= rcu_get_root(rsp
);
817 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
818 rsp
->signaled
= RCU_SIGNAL_INIT
; /* force_quiescent_state now OK. */
819 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
820 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
824 * Report a full set of quiescent states to the specified rcu_state
825 * data structure. This involves cleaning up after the prior grace
826 * period and letting rcu_start_gp() start up the next grace period
827 * if one is needed. Note that the caller must hold rnp->lock, as
828 * required by rcu_start_gp(), which will release it.
830 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
831 __releases(rcu_get_root(rsp
)->lock
)
833 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
836 * Ensure that all grace-period and pre-grace-period activity
837 * is seen before the assignment to rsp->completed.
839 smp_mb(); /* See above block comment. */
840 rsp
->completed
= rsp
->gpnum
;
841 rsp
->signaled
= RCU_GP_IDLE
;
842 rcu_start_gp(rsp
, flags
); /* releases root node's rnp->lock. */
846 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
847 * Allows quiescent states for a group of CPUs to be reported at one go
848 * to the specified rcu_node structure, though all the CPUs in the group
849 * must be represented by the same rcu_node structure (which need not be
850 * a leaf rcu_node structure, though it often will be). That structure's
851 * lock must be held upon entry, and it is released before return.
854 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
855 struct rcu_node
*rnp
, unsigned long flags
)
856 __releases(rnp
->lock
)
858 struct rcu_node
*rnp_c
;
860 /* Walk up the rcu_node hierarchy. */
862 if (!(rnp
->qsmask
& mask
)) {
864 /* Our bit has already been cleared, so done. */
865 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
868 rnp
->qsmask
&= ~mask
;
869 if (rnp
->qsmask
!= 0 || rcu_preempted_readers(rnp
)) {
871 /* Other bits still set at this level, so done. */
872 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
876 if (rnp
->parent
== NULL
) {
878 /* No more levels. Exit loop holding root lock. */
882 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
885 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
886 WARN_ON_ONCE(rnp_c
->qsmask
);
890 * Get here if we are the last CPU to pass through a quiescent
891 * state for this grace period. Invoke rcu_report_qs_rsp()
892 * to clean up and start the next grace period if one is needed.
894 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
898 * Record a quiescent state for the specified CPU to that CPU's rcu_data
899 * structure. This must be either called from the specified CPU, or
900 * called when the specified CPU is known to be offline (and when it is
901 * also known that no other CPU is concurrently trying to help the offline
902 * CPU). The lastcomp argument is used to make sure we are still in the
903 * grace period of interest. We don't want to end the current grace period
904 * based on quiescent states detected in an earlier grace period!
907 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
, long lastcomp
)
911 struct rcu_node
*rnp
;
914 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
915 if (lastcomp
!= rnp
->completed
) {
918 * Someone beat us to it for this grace period, so leave.
919 * The race with GP start is resolved by the fact that we
920 * hold the leaf rcu_node lock, so that the per-CPU bits
921 * cannot yet be initialized -- so we would simply find our
922 * CPU's bit already cleared in rcu_report_qs_rnp() if this
925 rdp
->passed_quiesc
= 0; /* try again later! */
926 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
930 if ((rnp
->qsmask
& mask
) == 0) {
931 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
936 * This GP can't end until cpu checks in, so all of our
937 * callbacks can be processed during the next GP.
939 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
941 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
946 * Check to see if there is a new grace period of which this CPU
947 * is not yet aware, and if so, set up local rcu_data state for it.
948 * Otherwise, see if this CPU has just passed through its first
949 * quiescent state for this grace period, and record that fact if so.
952 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
954 /* If there is now a new grace period, record and return. */
955 if (check_for_new_grace_period(rsp
, rdp
))
959 * Does this CPU still need to do its part for current grace period?
960 * If no, return and let the other CPUs do their part as well.
962 if (!rdp
->qs_pending
)
966 * Was there a quiescent state since the beginning of the grace
967 * period? If no, then exit and wait for the next call.
969 if (!rdp
->passed_quiesc
)
973 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
976 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
, rdp
->passed_quiesc_completed
);
979 #ifdef CONFIG_HOTPLUG_CPU
982 * Move a dying CPU's RCU callbacks to online CPU's callback list.
983 * Synchronization is not required because this function executes
984 * in stop_machine() context.
986 static void rcu_send_cbs_to_online(struct rcu_state
*rsp
)
989 /* current DYING CPU is cleared in the cpu_online_mask */
990 int receive_cpu
= cpumask_any(cpu_online_mask
);
991 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
992 struct rcu_data
*receive_rdp
= per_cpu_ptr(rsp
->rda
, receive_cpu
);
994 if (rdp
->nxtlist
== NULL
)
995 return; /* irqs disabled, so comparison is stable. */
997 *receive_rdp
->nxttail
[RCU_NEXT_TAIL
] = rdp
->nxtlist
;
998 receive_rdp
->nxttail
[RCU_NEXT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
999 receive_rdp
->qlen
+= rdp
->qlen
;
1000 receive_rdp
->n_cbs_adopted
+= rdp
->qlen
;
1001 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1003 rdp
->nxtlist
= NULL
;
1004 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1005 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1010 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1011 * and move all callbacks from the outgoing CPU to the current one.
1013 static void __rcu_offline_cpu(int cpu
, struct rcu_state
*rsp
)
1015 unsigned long flags
;
1017 int need_report
= 0;
1018 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1019 struct rcu_node
*rnp
;
1021 /* Exclude any attempts to start a new grace period. */
1022 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
1024 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1025 rnp
= rdp
->mynode
; /* this is the outgoing CPU's rnp. */
1026 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1028 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1029 rnp
->qsmaskinit
&= ~mask
;
1030 if (rnp
->qsmaskinit
!= 0) {
1031 if (rnp
!= rdp
->mynode
)
1032 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1035 if (rnp
== rdp
->mynode
)
1036 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1038 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1039 mask
= rnp
->grpmask
;
1041 } while (rnp
!= NULL
);
1044 * We still hold the leaf rcu_node structure lock here, and
1045 * irqs are still disabled. The reason for this subterfuge is
1046 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1047 * held leads to deadlock.
1049 raw_spin_unlock(&rsp
->onofflock
); /* irqs remain disabled. */
1051 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1052 rcu_report_unblock_qs_rnp(rnp
, flags
);
1054 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1055 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1056 rcu_report_exp_rnp(rsp
, rnp
);
1060 * Remove the specified CPU from the RCU hierarchy and move any pending
1061 * callbacks that it might have to the current CPU. This code assumes
1062 * that at least one CPU in the system will remain running at all times.
1063 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1065 static void rcu_offline_cpu(int cpu
)
1067 __rcu_offline_cpu(cpu
, &rcu_sched_state
);
1068 __rcu_offline_cpu(cpu
, &rcu_bh_state
);
1069 rcu_preempt_offline_cpu(cpu
);
1072 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1074 static void rcu_send_cbs_to_online(struct rcu_state
*rsp
)
1078 static void rcu_offline_cpu(int cpu
)
1082 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1085 * Invoke any RCU callbacks that have made it to the end of their grace
1086 * period. Thottle as specified by rdp->blimit.
1088 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1090 unsigned long flags
;
1091 struct rcu_head
*next
, *list
, **tail
;
1094 /* If no callbacks are ready, just return.*/
1095 if (!cpu_has_callbacks_ready_to_invoke(rdp
))
1099 * Extract the list of ready callbacks, disabling to prevent
1100 * races with call_rcu() from interrupt handlers.
1102 local_irq_save(flags
);
1103 list
= rdp
->nxtlist
;
1104 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1105 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1106 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1107 for (count
= RCU_NEXT_SIZE
- 1; count
>= 0; count
--)
1108 if (rdp
->nxttail
[count
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1109 rdp
->nxttail
[count
] = &rdp
->nxtlist
;
1110 local_irq_restore(flags
);
1112 /* Invoke callbacks. */
1117 debug_rcu_head_unqueue(list
);
1120 if (++count
>= rdp
->blimit
)
1124 local_irq_save(flags
);
1126 /* Update count, and requeue any remaining callbacks. */
1128 rdp
->n_cbs_invoked
+= count
;
1130 *tail
= rdp
->nxtlist
;
1131 rdp
->nxtlist
= list
;
1132 for (count
= 0; count
< RCU_NEXT_SIZE
; count
++)
1133 if (&rdp
->nxtlist
== rdp
->nxttail
[count
])
1134 rdp
->nxttail
[count
] = tail
;
1139 /* Reinstate batch limit if we have worked down the excess. */
1140 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1141 rdp
->blimit
= blimit
;
1143 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1144 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1145 rdp
->qlen_last_fqs_check
= 0;
1146 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1147 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1148 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1150 local_irq_restore(flags
);
1152 /* Re-raise the RCU softirq if there are callbacks remaining. */
1153 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1154 raise_softirq(RCU_SOFTIRQ
);
1158 * Check to see if this CPU is in a non-context-switch quiescent state
1159 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1160 * Also schedule the RCU softirq handler.
1162 * This function must be called with hardirqs disabled. It is normally
1163 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1164 * false, there is no point in invoking rcu_check_callbacks().
1166 void rcu_check_callbacks(int cpu
, int user
)
1169 (idle_cpu(cpu
) && rcu_scheduler_active
&&
1170 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT
))) {
1173 * Get here if this CPU took its interrupt from user
1174 * mode or from the idle loop, and if this is not a
1175 * nested interrupt. In this case, the CPU is in
1176 * a quiescent state, so note it.
1178 * No memory barrier is required here because both
1179 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1180 * variables that other CPUs neither access nor modify,
1181 * at least not while the corresponding CPU is online.
1187 } else if (!in_softirq()) {
1190 * Get here if this CPU did not take its interrupt from
1191 * softirq, in other words, if it is not interrupting
1192 * a rcu_bh read-side critical section. This is an _bh
1193 * critical section, so note it.
1198 rcu_preempt_check_callbacks(cpu
);
1199 if (rcu_pending(cpu
))
1200 raise_softirq(RCU_SOFTIRQ
);
1206 * Scan the leaf rcu_node structures, processing dyntick state for any that
1207 * have not yet encountered a quiescent state, using the function specified.
1208 * The caller must have suppressed start of new grace periods.
1210 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1214 unsigned long flags
;
1216 struct rcu_node
*rnp
;
1218 rcu_for_each_leaf_node(rsp
, rnp
) {
1220 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1221 if (!rcu_gp_in_progress(rsp
)) {
1222 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1225 if (rnp
->qsmask
== 0) {
1226 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1231 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1232 if ((rnp
->qsmask
& bit
) != 0 &&
1233 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1238 /* rcu_report_qs_rnp() releases rnp->lock. */
1239 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1242 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1247 * Force quiescent states on reluctant CPUs, and also detect which
1248 * CPUs are in dyntick-idle mode.
1250 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1252 unsigned long flags
;
1253 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1255 if (!rcu_gp_in_progress(rsp
))
1256 return; /* No grace period in progress, nothing to force. */
1257 if (!raw_spin_trylock_irqsave(&rsp
->fqslock
, flags
)) {
1258 rsp
->n_force_qs_lh
++; /* Inexact, can lose counts. Tough! */
1259 return; /* Someone else is already on the job. */
1261 if (relaxed
&& ULONG_CMP_GE(rsp
->jiffies_force_qs
, jiffies
))
1262 goto unlock_fqs_ret
; /* no emergency and done recently. */
1264 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1265 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
1266 if(!rcu_gp_in_progress(rsp
)) {
1267 rsp
->n_force_qs_ngp
++;
1268 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1269 goto unlock_fqs_ret
; /* no GP in progress, time updated. */
1271 rsp
->fqs_active
= 1;
1272 switch (rsp
->signaled
) {
1276 break; /* grace period idle or initializing, ignore. */
1278 case RCU_SAVE_DYNTICK
:
1279 if (RCU_SIGNAL_INIT
!= RCU_SAVE_DYNTICK
)
1280 break; /* So gcc recognizes the dead code. */
1282 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1284 /* Record dyntick-idle state. */
1285 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1286 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1287 if (rcu_gp_in_progress(rsp
))
1288 rsp
->signaled
= RCU_FORCE_QS
;
1293 /* Check dyntick-idle state, send IPI to laggarts. */
1294 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1295 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1297 /* Leave state in case more forcing is required. */
1299 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1302 rsp
->fqs_active
= 0;
1303 if (rsp
->fqs_need_gp
) {
1304 raw_spin_unlock(&rsp
->fqslock
); /* irqs remain disabled */
1305 rsp
->fqs_need_gp
= 0;
1306 rcu_start_gp(rsp
, flags
); /* releases rnp->lock */
1309 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1311 raw_spin_unlock_irqrestore(&rsp
->fqslock
, flags
);
1314 #else /* #ifdef CONFIG_SMP */
1316 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1321 #endif /* #else #ifdef CONFIG_SMP */
1324 * This does the RCU processing work from softirq context for the
1325 * specified rcu_state and rcu_data structures. This may be called
1326 * only from the CPU to whom the rdp belongs.
1329 __rcu_process_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1331 unsigned long flags
;
1333 WARN_ON_ONCE(rdp
->beenonline
== 0);
1336 * If an RCU GP has gone long enough, go check for dyntick
1337 * idle CPUs and, if needed, send resched IPIs.
1339 if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1340 force_quiescent_state(rsp
, 1);
1343 * Advance callbacks in response to end of earlier grace
1344 * period that some other CPU ended.
1346 rcu_process_gp_end(rsp
, rdp
);
1348 /* Update RCU state based on any recent quiescent states. */
1349 rcu_check_quiescent_state(rsp
, rdp
);
1351 /* Does this CPU require a not-yet-started grace period? */
1352 if (cpu_needs_another_gp(rsp
, rdp
)) {
1353 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1354 rcu_start_gp(rsp
, flags
); /* releases above lock */
1357 /* If there are callbacks ready, invoke them. */
1358 rcu_do_batch(rsp
, rdp
);
1362 * Do softirq processing for the current CPU.
1364 static void rcu_process_callbacks(struct softirq_action
*unused
)
1366 __rcu_process_callbacks(&rcu_sched_state
,
1367 &__get_cpu_var(rcu_sched_data
));
1368 __rcu_process_callbacks(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1369 rcu_preempt_process_callbacks();
1371 /* If we are last CPU on way to dyntick-idle mode, accelerate it. */
1372 rcu_needs_cpu_flush();
1376 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1377 struct rcu_state
*rsp
)
1379 unsigned long flags
;
1380 struct rcu_data
*rdp
;
1382 debug_rcu_head_queue(head
);
1386 smp_mb(); /* Ensure RCU update seen before callback registry. */
1389 * Opportunistically note grace-period endings and beginnings.
1390 * Note that we might see a beginning right after we see an
1391 * end, but never vice versa, since this CPU has to pass through
1392 * a quiescent state betweentimes.
1394 local_irq_save(flags
);
1395 rdp
= this_cpu_ptr(rsp
->rda
);
1397 /* Add the callback to our list. */
1398 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1399 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1402 * Force the grace period if too many callbacks or too long waiting.
1403 * Enforce hysteresis, and don't invoke force_quiescent_state()
1404 * if some other CPU has recently done so. Also, don't bother
1405 * invoking force_quiescent_state() if the newly enqueued callback
1406 * is the only one waiting for a grace period to complete.
1408 if (unlikely(++rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1410 /* Are we ignoring a completed grace period? */
1411 rcu_process_gp_end(rsp
, rdp
);
1412 check_for_new_grace_period(rsp
, rdp
);
1414 /* Start a new grace period if one not already started. */
1415 if (!rcu_gp_in_progress(rsp
)) {
1416 unsigned long nestflag
;
1417 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1419 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1420 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
1422 /* Give the grace period a kick. */
1423 rdp
->blimit
= LONG_MAX
;
1424 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1425 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1426 force_quiescent_state(rsp
, 0);
1427 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1428 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1430 } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1431 force_quiescent_state(rsp
, 1);
1432 local_irq_restore(flags
);
1436 * Queue an RCU-sched callback for invocation after a grace period.
1438 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1440 __call_rcu(head
, func
, &rcu_sched_state
);
1442 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1445 * Queue an RCU for invocation after a quicker grace period.
1447 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1449 __call_rcu(head
, func
, &rcu_bh_state
);
1451 EXPORT_SYMBOL_GPL(call_rcu_bh
);
1454 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1456 * Control will return to the caller some time after a full rcu-sched
1457 * grace period has elapsed, in other words after all currently executing
1458 * rcu-sched read-side critical sections have completed. These read-side
1459 * critical sections are delimited by rcu_read_lock_sched() and
1460 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1461 * local_irq_disable(), and so on may be used in place of
1462 * rcu_read_lock_sched().
1464 * This means that all preempt_disable code sequences, including NMI and
1465 * hardware-interrupt handlers, in progress on entry will have completed
1466 * before this primitive returns. However, this does not guarantee that
1467 * softirq handlers will have completed, since in some kernels, these
1468 * handlers can run in process context, and can block.
1470 * This primitive provides the guarantees made by the (now removed)
1471 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1472 * guarantees that rcu_read_lock() sections will have completed.
1473 * In "classic RCU", these two guarantees happen to be one and
1474 * the same, but can differ in realtime RCU implementations.
1476 void synchronize_sched(void)
1478 struct rcu_synchronize rcu
;
1480 if (rcu_blocking_is_gp())
1483 init_rcu_head_on_stack(&rcu
.head
);
1484 init_completion(&rcu
.completion
);
1485 /* Will wake me after RCU finished. */
1486 call_rcu_sched(&rcu
.head
, wakeme_after_rcu
);
1488 wait_for_completion(&rcu
.completion
);
1489 destroy_rcu_head_on_stack(&rcu
.head
);
1491 EXPORT_SYMBOL_GPL(synchronize_sched
);
1494 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1496 * Control will return to the caller some time after a full rcu_bh grace
1497 * period has elapsed, in other words after all currently executing rcu_bh
1498 * read-side critical sections have completed. RCU read-side critical
1499 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1500 * and may be nested.
1502 void synchronize_rcu_bh(void)
1504 struct rcu_synchronize rcu
;
1506 if (rcu_blocking_is_gp())
1509 init_rcu_head_on_stack(&rcu
.head
);
1510 init_completion(&rcu
.completion
);
1511 /* Will wake me after RCU finished. */
1512 call_rcu_bh(&rcu
.head
, wakeme_after_rcu
);
1514 wait_for_completion(&rcu
.completion
);
1515 destroy_rcu_head_on_stack(&rcu
.head
);
1517 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
1520 * Check to see if there is any immediate RCU-related work to be done
1521 * by the current CPU, for the specified type of RCU, returning 1 if so.
1522 * The checks are in order of increasing expense: checks that can be
1523 * carried out against CPU-local state are performed first. However,
1524 * we must check for CPU stalls first, else we might not get a chance.
1526 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1528 struct rcu_node
*rnp
= rdp
->mynode
;
1530 rdp
->n_rcu_pending
++;
1532 /* Check for CPU stalls, if enabled. */
1533 check_cpu_stall(rsp
, rdp
);
1535 /* Is the RCU core waiting for a quiescent state from this CPU? */
1536 if (rdp
->qs_pending
&& !rdp
->passed_quiesc
) {
1539 * If force_quiescent_state() coming soon and this CPU
1540 * needs a quiescent state, and this is either RCU-sched
1541 * or RCU-bh, force a local reschedule.
1543 rdp
->n_rp_qs_pending
++;
1544 if (!rdp
->preemptable
&&
1545 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
) - 1,
1548 } else if (rdp
->qs_pending
&& rdp
->passed_quiesc
) {
1549 rdp
->n_rp_report_qs
++;
1553 /* Does this CPU have callbacks ready to invoke? */
1554 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
1555 rdp
->n_rp_cb_ready
++;
1559 /* Has RCU gone idle with this CPU needing another grace period? */
1560 if (cpu_needs_another_gp(rsp
, rdp
)) {
1561 rdp
->n_rp_cpu_needs_gp
++;
1565 /* Has another RCU grace period completed? */
1566 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
1567 rdp
->n_rp_gp_completed
++;
1571 /* Has a new RCU grace period started? */
1572 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
1573 rdp
->n_rp_gp_started
++;
1577 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1578 if (rcu_gp_in_progress(rsp
) &&
1579 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
)) {
1580 rdp
->n_rp_need_fqs
++;
1585 rdp
->n_rp_need_nothing
++;
1590 * Check to see if there is any immediate RCU-related work to be done
1591 * by the current CPU, returning 1 if so. This function is part of the
1592 * RCU implementation; it is -not- an exported member of the RCU API.
1594 static int rcu_pending(int cpu
)
1596 return __rcu_pending(&rcu_sched_state
, &per_cpu(rcu_sched_data
, cpu
)) ||
1597 __rcu_pending(&rcu_bh_state
, &per_cpu(rcu_bh_data
, cpu
)) ||
1598 rcu_preempt_pending(cpu
);
1602 * Check to see if any future RCU-related work will need to be done
1603 * by the current CPU, even if none need be done immediately, returning
1606 static int rcu_needs_cpu_quick_check(int cpu
)
1608 /* RCU callbacks either ready or pending? */
1609 return per_cpu(rcu_sched_data
, cpu
).nxtlist
||
1610 per_cpu(rcu_bh_data
, cpu
).nxtlist
||
1611 rcu_preempt_needs_cpu(cpu
);
1614 static DEFINE_PER_CPU(struct rcu_head
, rcu_barrier_head
) = {NULL
};
1615 static atomic_t rcu_barrier_cpu_count
;
1616 static DEFINE_MUTEX(rcu_barrier_mutex
);
1617 static struct completion rcu_barrier_completion
;
1619 static void rcu_barrier_callback(struct rcu_head
*notused
)
1621 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1622 complete(&rcu_barrier_completion
);
1626 * Called with preemption disabled, and from cross-cpu IRQ context.
1628 static void rcu_barrier_func(void *type
)
1630 int cpu
= smp_processor_id();
1631 struct rcu_head
*head
= &per_cpu(rcu_barrier_head
, cpu
);
1632 void (*call_rcu_func
)(struct rcu_head
*head
,
1633 void (*func
)(struct rcu_head
*head
));
1635 atomic_inc(&rcu_barrier_cpu_count
);
1636 call_rcu_func
= type
;
1637 call_rcu_func(head
, rcu_barrier_callback
);
1641 * Orchestrate the specified type of RCU barrier, waiting for all
1642 * RCU callbacks of the specified type to complete.
1644 static void _rcu_barrier(struct rcu_state
*rsp
,
1645 void (*call_rcu_func
)(struct rcu_head
*head
,
1646 void (*func
)(struct rcu_head
*head
)))
1648 BUG_ON(in_interrupt());
1649 /* Take mutex to serialize concurrent rcu_barrier() requests. */
1650 mutex_lock(&rcu_barrier_mutex
);
1651 init_completion(&rcu_barrier_completion
);
1653 * Initialize rcu_barrier_cpu_count to 1, then invoke
1654 * rcu_barrier_func() on each CPU, so that each CPU also has
1655 * incremented rcu_barrier_cpu_count. Only then is it safe to
1656 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1657 * might complete its grace period before all of the other CPUs
1658 * did their increment, causing this function to return too
1659 * early. Note that on_each_cpu() disables irqs, which prevents
1660 * any CPUs from coming online or going offline until each online
1661 * CPU has queued its RCU-barrier callback.
1663 atomic_set(&rcu_barrier_cpu_count
, 1);
1664 on_each_cpu(rcu_barrier_func
, (void *)call_rcu_func
, 1);
1665 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1666 complete(&rcu_barrier_completion
);
1667 wait_for_completion(&rcu_barrier_completion
);
1668 mutex_unlock(&rcu_barrier_mutex
);
1672 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1674 void rcu_barrier_bh(void)
1676 _rcu_barrier(&rcu_bh_state
, call_rcu_bh
);
1678 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
1681 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1683 void rcu_barrier_sched(void)
1685 _rcu_barrier(&rcu_sched_state
, call_rcu_sched
);
1687 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
1690 * Do boot-time initialization of a CPU's per-CPU RCU data.
1693 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
1695 unsigned long flags
;
1697 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1698 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1700 /* Set up local state, ensuring consistent view of global state. */
1701 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1702 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
1703 rdp
->nxtlist
= NULL
;
1704 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1705 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1708 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
1709 #endif /* #ifdef CONFIG_NO_HZ */
1711 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1715 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1716 * offline event can be happening at a given time. Note also that we
1717 * can accept some slop in the rsp->completed access due to the fact
1718 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1720 static void __cpuinit
1721 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptable
)
1723 unsigned long flags
;
1725 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1726 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1728 /* Set up local state, ensuring consistent view of global state. */
1729 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1730 rdp
->passed_quiesc
= 0; /* We could be racing with new GP, */
1731 rdp
->qs_pending
= 1; /* so set up to respond to current GP. */
1732 rdp
->beenonline
= 1; /* We have now been online. */
1733 rdp
->preemptable
= preemptable
;
1734 rdp
->qlen_last_fqs_check
= 0;
1735 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1736 rdp
->blimit
= blimit
;
1737 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1740 * A new grace period might start here. If so, we won't be part
1741 * of it, but that is OK, as we are currently in a quiescent state.
1744 /* Exclude any attempts to start a new GP on large systems. */
1745 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
1747 /* Add CPU to rcu_node bitmasks. */
1749 mask
= rdp
->grpmask
;
1751 /* Exclude any attempts to start a new GP on small systems. */
1752 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1753 rnp
->qsmaskinit
|= mask
;
1754 mask
= rnp
->grpmask
;
1755 if (rnp
== rdp
->mynode
) {
1756 rdp
->gpnum
= rnp
->completed
; /* if GP in progress... */
1757 rdp
->completed
= rnp
->completed
;
1758 rdp
->passed_quiesc_completed
= rnp
->completed
- 1;
1760 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
1762 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
1764 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
1767 static void __cpuinit
rcu_online_cpu(int cpu
)
1769 rcu_init_percpu_data(cpu
, &rcu_sched_state
, 0);
1770 rcu_init_percpu_data(cpu
, &rcu_bh_state
, 0);
1771 rcu_preempt_init_percpu_data(cpu
);
1775 * Handle CPU online/offline notification events.
1777 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
1778 unsigned long action
, void *hcpu
)
1780 long cpu
= (long)hcpu
;
1783 case CPU_UP_PREPARE
:
1784 case CPU_UP_PREPARE_FROZEN
:
1785 rcu_online_cpu(cpu
);
1788 case CPU_DYING_FROZEN
:
1790 * The whole machine is "stopped" except this CPU, so we can
1791 * touch any data without introducing corruption. We send the
1792 * dying CPU's callbacks to an arbitrarily chosen online CPU.
1794 rcu_send_cbs_to_online(&rcu_bh_state
);
1795 rcu_send_cbs_to_online(&rcu_sched_state
);
1796 rcu_preempt_send_cbs_to_online();
1799 case CPU_DEAD_FROZEN
:
1800 case CPU_UP_CANCELED
:
1801 case CPU_UP_CANCELED_FROZEN
:
1802 rcu_offline_cpu(cpu
);
1811 * This function is invoked towards the end of the scheduler's initialization
1812 * process. Before this is called, the idle task might contain
1813 * RCU read-side critical sections (during which time, this idle
1814 * task is booting the system). After this function is called, the
1815 * idle tasks are prohibited from containing RCU read-side critical
1816 * sections. This function also enables RCU lockdep checking.
1818 void rcu_scheduler_starting(void)
1820 WARN_ON(num_online_cpus() != 1);
1821 WARN_ON(nr_context_switches() > 0);
1822 rcu_scheduler_active
= 1;
1826 * Compute the per-level fanout, either using the exact fanout specified
1827 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1829 #ifdef CONFIG_RCU_FANOUT_EXACT
1830 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
1834 for (i
= NUM_RCU_LVLS
- 1; i
> 0; i
--)
1835 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
1836 rsp
->levelspread
[0] = RCU_FANOUT_LEAF
;
1838 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1839 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
1846 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
1847 ccur
= rsp
->levelcnt
[i
];
1848 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
1852 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1855 * Helper function for rcu_init() that initializes one rcu_state structure.
1857 static void __init
rcu_init_one(struct rcu_state
*rsp
,
1858 struct rcu_data __percpu
*rda
)
1860 static char *buf
[] = { "rcu_node_level_0",
1863 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
1867 struct rcu_node
*rnp
;
1869 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
1871 /* Initialize the level-tracking arrays. */
1873 for (i
= 1; i
< NUM_RCU_LVLS
; i
++)
1874 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
1875 rcu_init_levelspread(rsp
);
1877 /* Initialize the elements themselves, starting from the leaves. */
1879 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
1880 cpustride
*= rsp
->levelspread
[i
];
1881 rnp
= rsp
->level
[i
];
1882 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
1883 raw_spin_lock_init(&rnp
->lock
);
1884 lockdep_set_class_and_name(&rnp
->lock
,
1885 &rcu_node_class
[i
], buf
[i
]);
1888 rnp
->qsmaskinit
= 0;
1889 rnp
->grplo
= j
* cpustride
;
1890 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
1891 if (rnp
->grphi
>= NR_CPUS
)
1892 rnp
->grphi
= NR_CPUS
- 1;
1898 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
1899 rnp
->grpmask
= 1UL << rnp
->grpnum
;
1900 rnp
->parent
= rsp
->level
[i
- 1] +
1901 j
/ rsp
->levelspread
[i
- 1];
1904 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
1909 rnp
= rsp
->level
[NUM_RCU_LVLS
- 1];
1910 for_each_possible_cpu(i
) {
1911 while (i
> rnp
->grphi
)
1913 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
1914 rcu_boot_init_percpu_data(i
, rsp
);
1918 void __init
rcu_init(void)
1922 rcu_bootup_announce();
1923 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
1924 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
1925 __rcu_init_preempt();
1926 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
1929 * We don't need protection against CPU-hotplug here because
1930 * this is called early in boot, before either interrupts
1931 * or the scheduler are operational.
1933 cpu_notifier(rcu_cpu_notify
, 0);
1934 for_each_online_cpu(cpu
)
1935 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
1936 check_cpu_stall_init();
1939 #include "rcutree_plugin.h"