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 <linux/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/export.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>
50 #include <linux/wait.h>
51 #include <linux/kthread.h>
52 #include <linux/prefetch.h>
55 #include <trace/events/rcu.h>
59 /* Data structures. */
61 static struct lock_class_key rcu_node_class
[NUM_RCU_LVLS
];
63 #define RCU_STATE_INITIALIZER(structname) { \
64 .level = { &structname##_state.node[0] }, \
66 NUM_RCU_LVL_0, /* root of hierarchy. */ \
70 NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
72 .fqs_state = RCU_GP_IDLE, \
75 .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.onofflock), \
76 .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname##_state.fqslock), \
78 .n_force_qs_ngp = 0, \
79 .name = #structname, \
82 struct rcu_state rcu_sched_state
= RCU_STATE_INITIALIZER(rcu_sched
);
83 DEFINE_PER_CPU(struct rcu_data
, rcu_sched_data
);
85 struct rcu_state rcu_bh_state
= RCU_STATE_INITIALIZER(rcu_bh
);
86 DEFINE_PER_CPU(struct rcu_data
, rcu_bh_data
);
88 static struct rcu_state
*rcu_state
;
91 * The rcu_scheduler_active variable transitions from zero to one just
92 * before the first task is spawned. So when this variable is zero, RCU
93 * can assume that there is but one task, allowing RCU to (for example)
94 * optimized synchronize_sched() to a simple barrier(). When this variable
95 * is one, RCU must actually do all the hard work required to detect real
96 * grace periods. This variable is also used to suppress boot-time false
97 * positives from lockdep-RCU error checking.
99 int rcu_scheduler_active __read_mostly
;
100 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
103 * The rcu_scheduler_fully_active variable transitions from zero to one
104 * during the early_initcall() processing, which is after the scheduler
105 * is capable of creating new tasks. So RCU processing (for example,
106 * creating tasks for RCU priority boosting) must be delayed until after
107 * rcu_scheduler_fully_active transitions from zero to one. We also
108 * currently delay invocation of any RCU callbacks until after this point.
110 * It might later prove better for people registering RCU callbacks during
111 * early boot to take responsibility for these callbacks, but one step at
114 static int rcu_scheduler_fully_active __read_mostly
;
116 #ifdef CONFIG_RCU_BOOST
119 * Control variables for per-CPU and per-rcu_node kthreads. These
120 * handle all flavors of RCU.
122 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
123 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
124 DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu
);
125 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
126 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
128 #endif /* #ifdef CONFIG_RCU_BOOST */
130 static void rcu_node_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
131 static void invoke_rcu_core(void);
132 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
135 * Track the rcutorture test sequence number and the update version
136 * number within a given test. The rcutorture_testseq is incremented
137 * on every rcutorture module load and unload, so has an odd value
138 * when a test is running. The rcutorture_vernum is set to zero
139 * when rcutorture starts and is incremented on each rcutorture update.
140 * These variables enable correlating rcutorture output with the
141 * RCU tracing information.
143 unsigned long rcutorture_testseq
;
144 unsigned long rcutorture_vernum
;
147 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
148 * permit this function to be invoked without holding the root rcu_node
149 * structure's ->lock, but of course results can be subject to change.
151 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
153 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
157 * Note a quiescent state. Because we do not need to know
158 * how many quiescent states passed, just if there was at least
159 * one since the start of the grace period, this just sets a flag.
160 * The caller must have disabled preemption.
162 void rcu_sched_qs(int cpu
)
164 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
166 rdp
->passed_quiesce_gpnum
= rdp
->gpnum
;
168 if (rdp
->passed_quiesce
== 0)
169 trace_rcu_grace_period("rcu_sched", rdp
->gpnum
, "cpuqs");
170 rdp
->passed_quiesce
= 1;
173 void rcu_bh_qs(int cpu
)
175 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
177 rdp
->passed_quiesce_gpnum
= rdp
->gpnum
;
179 if (rdp
->passed_quiesce
== 0)
180 trace_rcu_grace_period("rcu_bh", rdp
->gpnum
, "cpuqs");
181 rdp
->passed_quiesce
= 1;
185 * Note a context switch. This is a quiescent state for RCU-sched,
186 * and requires special handling for preemptible RCU.
187 * The caller must have disabled preemption.
189 void rcu_note_context_switch(int cpu
)
191 trace_rcu_utilization("Start context switch");
193 rcu_preempt_note_context_switch(cpu
);
194 trace_rcu_utilization("End context switch");
196 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
198 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
199 .dynticks_nesting
= DYNTICK_TASK_NESTING
,
200 .dynticks
= ATOMIC_INIT(1),
203 static int blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
204 static int qhimark
= 10000; /* If this many pending, ignore blimit. */
205 static int qlowmark
= 100; /* Once only this many pending, use blimit. */
207 module_param(blimit
, int, 0);
208 module_param(qhimark
, int, 0);
209 module_param(qlowmark
, int, 0);
211 int rcu_cpu_stall_suppress __read_mostly
;
212 module_param(rcu_cpu_stall_suppress
, int, 0644);
214 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
);
215 static int rcu_pending(int cpu
);
218 * Return the number of RCU-sched batches processed thus far for debug & stats.
220 long rcu_batches_completed_sched(void)
222 return rcu_sched_state
.completed
;
224 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
227 * Return the number of RCU BH batches processed thus far for debug & stats.
229 long rcu_batches_completed_bh(void)
231 return rcu_bh_state
.completed
;
233 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
236 * Force a quiescent state for RCU BH.
238 void rcu_bh_force_quiescent_state(void)
240 force_quiescent_state(&rcu_bh_state
, 0);
242 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
245 * Record the number of times rcutorture tests have been initiated and
246 * terminated. This information allows the debugfs tracing stats to be
247 * correlated to the rcutorture messages, even when the rcutorture module
248 * is being repeatedly loaded and unloaded. In other words, we cannot
249 * store this state in rcutorture itself.
251 void rcutorture_record_test_transition(void)
253 rcutorture_testseq
++;
254 rcutorture_vernum
= 0;
256 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
259 * Record the number of writer passes through the current rcutorture test.
260 * This is also used to correlate debugfs tracing stats with the rcutorture
263 void rcutorture_record_progress(unsigned long vernum
)
267 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
270 * Force a quiescent state for RCU-sched.
272 void rcu_sched_force_quiescent_state(void)
274 force_quiescent_state(&rcu_sched_state
, 0);
276 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
279 * Does the CPU have callbacks ready to be invoked?
282 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
284 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
];
288 * Does the current CPU require a yet-as-unscheduled grace period?
291 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
293 return *rdp
->nxttail
[RCU_DONE_TAIL
] && !rcu_gp_in_progress(rsp
);
297 * Return the root node of the specified rcu_state structure.
299 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
301 return &rsp
->node
[0];
307 * If the specified CPU is offline, tell the caller that it is in
308 * a quiescent state. Otherwise, whack it with a reschedule IPI.
309 * Grace periods can end up waiting on an offline CPU when that
310 * CPU is in the process of coming online -- it will be added to the
311 * rcu_node bitmasks before it actually makes it online. The same thing
312 * can happen while a CPU is in the process of coming online. Because this
313 * race is quite rare, we check for it after detecting that the grace
314 * period has been delayed rather than checking each and every CPU
315 * each and every time we start a new grace period.
317 static int rcu_implicit_offline_qs(struct rcu_data
*rdp
)
320 * If the CPU is offline, it is in a quiescent state. We can
321 * trust its state not to change because interrupts are disabled.
323 if (cpu_is_offline(rdp
->cpu
)) {
324 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "ofl");
330 * The CPU is online, so send it a reschedule IPI. This forces
331 * it through the scheduler, and (inefficiently) also handles cases
332 * where idle loops fail to inform RCU about the CPU being idle.
334 if (rdp
->cpu
!= smp_processor_id())
335 smp_send_reschedule(rdp
->cpu
);
342 #endif /* #ifdef CONFIG_SMP */
345 * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
347 * If the new value of the ->dynticks_nesting counter now is zero,
348 * we really have entered idle, and must do the appropriate accounting.
349 * The caller must have disabled interrupts.
351 static void rcu_idle_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
)
353 if (rdtp
->dynticks_nesting
) {
354 trace_rcu_dyntick("--=", oldval
, rdtp
->dynticks_nesting
);
357 trace_rcu_dyntick("Start", oldval
, rdtp
->dynticks_nesting
);
358 if (!idle_cpu(smp_processor_id())) {
359 struct task_struct
*idle
= idle_task(smp_processor_id());
361 trace_rcu_dyntick("Error on entry: not idle task",
362 oldval
, rdtp
->dynticks_nesting
);
363 ftrace_dump(DUMP_ALL
);
364 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
365 current
->pid
, current
->comm
,
366 idle
->pid
, idle
->comm
); /* must be idle task! */
368 rcu_prepare_for_idle(smp_processor_id());
369 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
370 smp_mb__before_atomic_inc(); /* See above. */
371 atomic_inc(&rdtp
->dynticks
);
372 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
373 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
377 * rcu_idle_enter - inform RCU that current CPU is entering idle
379 * Enter idle mode, in other words, -leave- the mode in which RCU
380 * read-side critical sections can occur. (Though RCU read-side
381 * critical sections can occur in irq handlers in idle, a possibility
382 * handled by irq_enter() and irq_exit().)
384 * We crowbar the ->dynticks_nesting field to zero to allow for
385 * the possibility of usermode upcalls having messed up our count
386 * of interrupt nesting level during the prior busy period.
388 void rcu_idle_enter(void)
392 struct rcu_dynticks
*rdtp
;
394 local_irq_save(flags
);
395 rdtp
= &__get_cpu_var(rcu_dynticks
);
396 oldval
= rdtp
->dynticks_nesting
;
397 rdtp
->dynticks_nesting
= 0;
398 rcu_idle_enter_common(rdtp
, oldval
);
399 local_irq_restore(flags
);
403 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
405 * Exit from an interrupt handler, which might possibly result in entering
406 * idle mode, in other words, leaving the mode in which read-side critical
407 * sections can occur.
409 * This code assumes that the idle loop never does anything that might
410 * result in unbalanced calls to irq_enter() and irq_exit(). If your
411 * architecture violates this assumption, RCU will give you what you
412 * deserve, good and hard. But very infrequently and irreproducibly.
414 * Use things like work queues to work around this limitation.
416 * You have been warned.
418 void rcu_irq_exit(void)
422 struct rcu_dynticks
*rdtp
;
424 local_irq_save(flags
);
425 rdtp
= &__get_cpu_var(rcu_dynticks
);
426 oldval
= rdtp
->dynticks_nesting
;
427 rdtp
->dynticks_nesting
--;
428 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
429 rcu_idle_enter_common(rdtp
, oldval
);
430 local_irq_restore(flags
);
434 * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
436 * If the new value of the ->dynticks_nesting counter was previously zero,
437 * we really have exited idle, and must do the appropriate accounting.
438 * The caller must have disabled interrupts.
440 static void rcu_idle_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
)
443 trace_rcu_dyntick("++=", oldval
, rdtp
->dynticks_nesting
);
446 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
447 atomic_inc(&rdtp
->dynticks
);
448 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
449 smp_mb__after_atomic_inc(); /* See above. */
450 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
451 trace_rcu_dyntick("End", oldval
, rdtp
->dynticks_nesting
);
452 if (!idle_cpu(smp_processor_id())) {
453 struct task_struct
*idle
= idle_task(smp_processor_id());
455 trace_rcu_dyntick("Error on exit: not idle task",
456 oldval
, rdtp
->dynticks_nesting
);
457 ftrace_dump(DUMP_ALL
);
458 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
459 current
->pid
, current
->comm
,
460 idle
->pid
, idle
->comm
); /* must be idle task! */
465 * rcu_idle_exit - inform RCU that current CPU is leaving idle
467 * Exit idle mode, in other words, -enter- the mode in which RCU
468 * read-side critical sections can occur.
470 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
471 * allow for the possibility of usermode upcalls messing up our count
472 * of interrupt nesting level during the busy period that is just
475 void rcu_idle_exit(void)
478 struct rcu_dynticks
*rdtp
;
481 local_irq_save(flags
);
482 rdtp
= &__get_cpu_var(rcu_dynticks
);
483 oldval
= rdtp
->dynticks_nesting
;
484 WARN_ON_ONCE(oldval
!= 0);
485 rdtp
->dynticks_nesting
= DYNTICK_TASK_NESTING
;
486 rcu_idle_exit_common(rdtp
, oldval
);
487 local_irq_restore(flags
);
491 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
493 * Enter an interrupt handler, which might possibly result in exiting
494 * idle mode, in other words, entering the mode in which read-side critical
495 * sections can occur.
497 * Note that the Linux kernel is fully capable of entering an interrupt
498 * handler that it never exits, for example when doing upcalls to
499 * user mode! This code assumes that the idle loop never does upcalls to
500 * user mode. If your architecture does do upcalls from the idle loop (or
501 * does anything else that results in unbalanced calls to the irq_enter()
502 * and irq_exit() functions), RCU will give you what you deserve, good
503 * and hard. But very infrequently and irreproducibly.
505 * Use things like work queues to work around this limitation.
507 * You have been warned.
509 void rcu_irq_enter(void)
512 struct rcu_dynticks
*rdtp
;
515 local_irq_save(flags
);
516 rdtp
= &__get_cpu_var(rcu_dynticks
);
517 oldval
= rdtp
->dynticks_nesting
;
518 rdtp
->dynticks_nesting
++;
519 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
520 rcu_idle_exit_common(rdtp
, oldval
);
521 local_irq_restore(flags
);
525 * rcu_nmi_enter - inform RCU of entry to NMI context
527 * If the CPU was idle with dynamic ticks active, and there is no
528 * irq handler running, this updates rdtp->dynticks_nmi to let the
529 * RCU grace-period handling know that the CPU is active.
531 void rcu_nmi_enter(void)
533 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
535 if (rdtp
->dynticks_nmi_nesting
== 0 &&
536 (atomic_read(&rdtp
->dynticks
) & 0x1))
538 rdtp
->dynticks_nmi_nesting
++;
539 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
540 atomic_inc(&rdtp
->dynticks
);
541 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
542 smp_mb__after_atomic_inc(); /* See above. */
543 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
547 * rcu_nmi_exit - inform RCU of exit from NMI context
549 * If the CPU was idle with dynamic ticks active, and there is no
550 * irq handler running, this updates rdtp->dynticks_nmi to let the
551 * RCU grace-period handling know that the CPU is no longer active.
553 void rcu_nmi_exit(void)
555 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
557 if (rdtp
->dynticks_nmi_nesting
== 0 ||
558 --rdtp
->dynticks_nmi_nesting
!= 0)
560 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
561 smp_mb__before_atomic_inc(); /* See above. */
562 atomic_inc(&rdtp
->dynticks
);
563 smp_mb__after_atomic_inc(); /* Force delay to next write. */
564 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
567 #ifdef CONFIG_PROVE_RCU
570 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
572 * If the current CPU is in its idle loop and is neither in an interrupt
573 * or NMI handler, return true.
575 int rcu_is_cpu_idle(void)
580 ret
= (atomic_read(&__get_cpu_var(rcu_dynticks
).dynticks
) & 0x1) == 0;
584 EXPORT_SYMBOL(rcu_is_cpu_idle
);
586 #endif /* #ifdef CONFIG_PROVE_RCU */
589 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
591 * If the current CPU is idle or running at a first-level (not nested)
592 * interrupt from idle, return true. The caller must have at least
593 * disabled preemption.
595 int rcu_is_cpu_rrupt_from_idle(void)
597 return __get_cpu_var(rcu_dynticks
).dynticks_nesting
<= 1;
603 * Snapshot the specified CPU's dynticks counter so that we can later
604 * credit them with an implicit quiescent state. Return 1 if this CPU
605 * is in dynticks idle mode, which is an extended quiescent state.
607 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
609 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
614 * Return true if the specified CPU has passed through a quiescent
615 * state by virtue of being in or having passed through an dynticks
616 * idle state since the last call to dyntick_save_progress_counter()
619 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
624 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
625 snap
= (unsigned int)rdp
->dynticks_snap
;
628 * If the CPU passed through or entered a dynticks idle phase with
629 * no active irq/NMI handlers, then we can safely pretend that the CPU
630 * already acknowledged the request to pass through a quiescent
631 * state. Either way, that CPU cannot possibly be in an RCU
632 * read-side critical section that started before the beginning
633 * of the current RCU grace period.
635 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
636 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "dti");
641 /* Go check for the CPU being offline. */
642 return rcu_implicit_offline_qs(rdp
);
645 #endif /* #ifdef CONFIG_SMP */
647 int rcu_cpu_stall_suppress __read_mostly
;
649 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
651 rsp
->gp_start
= jiffies
;
652 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_CHECK
;
655 static void print_other_cpu_stall(struct rcu_state
*rsp
)
661 struct rcu_node
*rnp
= rcu_get_root(rsp
);
663 /* Only let one CPU complain about others per time interval. */
665 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
666 delta
= jiffies
- rsp
->jiffies_stall
;
667 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
668 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
671 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
674 * Now rat on any tasks that got kicked up to the root rcu_node
675 * due to CPU offlining.
677 ndetected
= rcu_print_task_stall(rnp
);
678 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
681 * OK, time to rat on our buddy...
682 * See Documentation/RCU/stallwarn.txt for info on how to debug
683 * RCU CPU stall warnings.
685 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks: {",
687 rcu_for_each_leaf_node(rsp
, rnp
) {
688 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
689 ndetected
+= rcu_print_task_stall(rnp
);
690 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
691 if (rnp
->qsmask
== 0)
693 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
694 if (rnp
->qsmask
& (1UL << cpu
)) {
695 printk(" %d", rnp
->grplo
+ cpu
);
699 printk("} (detected by %d, t=%ld jiffies)\n",
700 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
));
702 printk(KERN_ERR
"INFO: Stall ended before state dump start\n");
703 else if (!trigger_all_cpu_backtrace())
706 /* If so configured, complain about tasks blocking the grace period. */
708 rcu_print_detail_task_stall(rsp
);
710 force_quiescent_state(rsp
, 0); /* Kick them all. */
713 static void print_cpu_stall(struct rcu_state
*rsp
)
716 struct rcu_node
*rnp
= rcu_get_root(rsp
);
719 * OK, time to rat on ourselves...
720 * See Documentation/RCU/stallwarn.txt for info on how to debug
721 * RCU CPU stall warnings.
723 printk(KERN_ERR
"INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
724 rsp
->name
, smp_processor_id(), jiffies
- rsp
->gp_start
);
725 if (!trigger_all_cpu_backtrace())
728 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
729 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
731 jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
732 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
734 set_need_resched(); /* kick ourselves to get things going. */
737 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
741 struct rcu_node
*rnp
;
743 if (rcu_cpu_stall_suppress
)
745 j
= ACCESS_ONCE(jiffies
);
746 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
748 if ((ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && ULONG_CMP_GE(j
, js
)) {
750 /* We haven't checked in, so go dump stack. */
751 print_cpu_stall(rsp
);
753 } else if (rcu_gp_in_progress(rsp
) &&
754 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
756 /* They had a few time units to dump stack, so complain. */
757 print_other_cpu_stall(rsp
);
761 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
763 rcu_cpu_stall_suppress
= 1;
768 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
770 * Set the stall-warning timeout way off into the future, thus preventing
771 * any RCU CPU stall-warning messages from appearing in the current set of
774 * The caller must disable hard irqs.
776 void rcu_cpu_stall_reset(void)
778 rcu_sched_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
779 rcu_bh_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
780 rcu_preempt_stall_reset();
783 static struct notifier_block rcu_panic_block
= {
784 .notifier_call
= rcu_panic
,
787 static void __init
check_cpu_stall_init(void)
789 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
793 * Update CPU-local rcu_data state to record the newly noticed grace period.
794 * This is used both when we started the grace period and when we notice
795 * that someone else started the grace period. The caller must hold the
796 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
797 * and must have irqs disabled.
799 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
801 if (rdp
->gpnum
!= rnp
->gpnum
) {
803 * If the current grace period is waiting for this CPU,
804 * set up to detect a quiescent state, otherwise don't
805 * go looking for one.
807 rdp
->gpnum
= rnp
->gpnum
;
808 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpustart");
809 if (rnp
->qsmask
& rdp
->grpmask
) {
811 rdp
->passed_quiesce
= 0;
817 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
820 struct rcu_node
*rnp
;
822 local_irq_save(flags
);
824 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
825 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
826 local_irq_restore(flags
);
829 __note_new_gpnum(rsp
, rnp
, rdp
);
830 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
834 * Did someone else start a new RCU grace period start since we last
835 * checked? Update local state appropriately if so. Must be called
836 * on the CPU corresponding to rdp.
839 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
844 local_irq_save(flags
);
845 if (rdp
->gpnum
!= rsp
->gpnum
) {
846 note_new_gpnum(rsp
, rdp
);
849 local_irq_restore(flags
);
854 * Advance this CPU's callbacks, but only if the current grace period
855 * has ended. This may be called only from the CPU to whom the rdp
856 * belongs. In addition, the corresponding leaf rcu_node structure's
857 * ->lock must be held by the caller, with irqs disabled.
860 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
862 /* Did another grace period end? */
863 if (rdp
->completed
!= rnp
->completed
) {
865 /* Advance callbacks. No harm if list empty. */
866 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
867 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
868 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
870 /* Remember that we saw this grace-period completion. */
871 rdp
->completed
= rnp
->completed
;
872 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuend");
875 * If we were in an extended quiescent state, we may have
876 * missed some grace periods that others CPUs handled on
877 * our behalf. Catch up with this state to avoid noting
878 * spurious new grace periods. If another grace period
879 * has started, then rnp->gpnum will have advanced, so
880 * we will detect this later on.
882 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
))
883 rdp
->gpnum
= rdp
->completed
;
886 * If RCU does not need a quiescent state from this CPU,
887 * then make sure that this CPU doesn't go looking for one.
889 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
895 * Advance this CPU's callbacks, but only if the current grace period
896 * has ended. This may be called only from the CPU to whom the rdp
900 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
903 struct rcu_node
*rnp
;
905 local_irq_save(flags
);
907 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
908 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
909 local_irq_restore(flags
);
912 __rcu_process_gp_end(rsp
, rnp
, rdp
);
913 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
917 * Do per-CPU grace-period initialization for running CPU. The caller
918 * must hold the lock of the leaf rcu_node structure corresponding to
922 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
924 /* Prior grace period ended, so advance callbacks for current CPU. */
925 __rcu_process_gp_end(rsp
, rnp
, rdp
);
928 * Because this CPU just now started the new grace period, we know
929 * that all of its callbacks will be covered by this upcoming grace
930 * period, even the ones that were registered arbitrarily recently.
931 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
933 * Other CPUs cannot be sure exactly when the grace period started.
934 * Therefore, their recently registered callbacks must pass through
935 * an additional RCU_NEXT_READY stage, so that they will be handled
936 * by the next RCU grace period.
938 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
939 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
941 /* Set state so that this CPU will detect the next quiescent state. */
942 __note_new_gpnum(rsp
, rnp
, rdp
);
946 * Start a new RCU grace period if warranted, re-initializing the hierarchy
947 * in preparation for detecting the next grace period. The caller must hold
948 * the root node's ->lock, which is released before return. Hard irqs must
952 rcu_start_gp(struct rcu_state
*rsp
, unsigned long flags
)
953 __releases(rcu_get_root(rsp
)->lock
)
955 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
956 struct rcu_node
*rnp
= rcu_get_root(rsp
);
958 if (!rcu_scheduler_fully_active
||
959 !cpu_needs_another_gp(rsp
, rdp
)) {
961 * Either the scheduler hasn't yet spawned the first
962 * non-idle task or this CPU does not need another
963 * grace period. Either way, don't start a new grace
966 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
970 if (rsp
->fqs_active
) {
972 * This CPU needs a grace period, but force_quiescent_state()
973 * is running. Tell it to start one on this CPU's behalf.
975 rsp
->fqs_need_gp
= 1;
976 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
980 /* Advance to a new grace period and initialize state. */
982 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, "start");
983 WARN_ON_ONCE(rsp
->fqs_state
== RCU_GP_INIT
);
984 rsp
->fqs_state
= RCU_GP_INIT
; /* Hold off force_quiescent_state. */
985 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
986 record_gp_stall_check_time(rsp
);
988 /* Special-case the common single-level case. */
989 if (NUM_RCU_NODES
== 1) {
990 rcu_preempt_check_blocked_tasks(rnp
);
991 rnp
->qsmask
= rnp
->qsmaskinit
;
992 rnp
->gpnum
= rsp
->gpnum
;
993 rnp
->completed
= rsp
->completed
;
994 rsp
->fqs_state
= RCU_SIGNAL_INIT
; /* force_quiescent_state OK */
995 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
996 rcu_preempt_boost_start_gp(rnp
);
997 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
998 rnp
->level
, rnp
->grplo
,
999 rnp
->grphi
, rnp
->qsmask
);
1000 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1004 raw_spin_unlock(&rnp
->lock
); /* leave irqs disabled. */
1007 /* Exclude any concurrent CPU-hotplug operations. */
1008 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
1011 * Set the quiescent-state-needed bits in all the rcu_node
1012 * structures for all currently online CPUs in breadth-first
1013 * order, starting from the root rcu_node structure. This
1014 * operation relies on the layout of the hierarchy within the
1015 * rsp->node[] array. Note that other CPUs will access only
1016 * the leaves of the hierarchy, which still indicate that no
1017 * grace period is in progress, at least until the corresponding
1018 * leaf node has been initialized. In addition, we have excluded
1019 * CPU-hotplug operations.
1021 * Note that the grace period cannot complete until we finish
1022 * the initialization process, as there will be at least one
1023 * qsmask bit set in the root node until that time, namely the
1024 * one corresponding to this CPU, due to the fact that we have
1027 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1028 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1029 rcu_preempt_check_blocked_tasks(rnp
);
1030 rnp
->qsmask
= rnp
->qsmaskinit
;
1031 rnp
->gpnum
= rsp
->gpnum
;
1032 rnp
->completed
= rsp
->completed
;
1033 if (rnp
== rdp
->mynode
)
1034 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
1035 rcu_preempt_boost_start_gp(rnp
);
1036 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1037 rnp
->level
, rnp
->grplo
,
1038 rnp
->grphi
, rnp
->qsmask
);
1039 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1042 rnp
= rcu_get_root(rsp
);
1043 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1044 rsp
->fqs_state
= RCU_SIGNAL_INIT
; /* force_quiescent_state now OK. */
1045 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1046 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
1050 * Report a full set of quiescent states to the specified rcu_state
1051 * data structure. This involves cleaning up after the prior grace
1052 * period and letting rcu_start_gp() start up the next grace period
1053 * if one is needed. Note that the caller must hold rnp->lock, as
1054 * required by rcu_start_gp(), which will release it.
1056 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1057 __releases(rcu_get_root(rsp
)->lock
)
1059 unsigned long gp_duration
;
1060 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1061 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1063 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1066 * Ensure that all grace-period and pre-grace-period activity
1067 * is seen before the assignment to rsp->completed.
1069 smp_mb(); /* See above block comment. */
1070 gp_duration
= jiffies
- rsp
->gp_start
;
1071 if (gp_duration
> rsp
->gp_max
)
1072 rsp
->gp_max
= gp_duration
;
1075 * We know the grace period is complete, but to everyone else
1076 * it appears to still be ongoing. But it is also the case
1077 * that to everyone else it looks like there is nothing that
1078 * they can do to advance the grace period. It is therefore
1079 * safe for us to drop the lock in order to mark the grace
1080 * period as completed in all of the rcu_node structures.
1082 * But if this CPU needs another grace period, it will take
1083 * care of this while initializing the next grace period.
1084 * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
1085 * because the callbacks have not yet been advanced: Those
1086 * callbacks are waiting on the grace period that just now
1089 rcu_schedule_wake_gp_end();
1090 if (*rdp
->nxttail
[RCU_WAIT_TAIL
] == NULL
) {
1091 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1094 * Propagate new ->completed value to rcu_node structures
1095 * so that other CPUs don't have to wait until the start
1096 * of the next grace period to process their callbacks.
1098 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1099 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1100 rnp
->completed
= rsp
->gpnum
;
1101 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1103 rnp
= rcu_get_root(rsp
);
1104 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1107 rsp
->completed
= rsp
->gpnum
; /* Declare the grace period complete. */
1108 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, "end");
1109 rsp
->fqs_state
= RCU_GP_IDLE
;
1110 rcu_start_gp(rsp
, flags
); /* releases root node's rnp->lock. */
1114 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1115 * Allows quiescent states for a group of CPUs to be reported at one go
1116 * to the specified rcu_node structure, though all the CPUs in the group
1117 * must be represented by the same rcu_node structure (which need not be
1118 * a leaf rcu_node structure, though it often will be). That structure's
1119 * lock must be held upon entry, and it is released before return.
1122 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1123 struct rcu_node
*rnp
, unsigned long flags
)
1124 __releases(rnp
->lock
)
1126 struct rcu_node
*rnp_c
;
1128 /* Walk up the rcu_node hierarchy. */
1130 if (!(rnp
->qsmask
& mask
)) {
1132 /* Our bit has already been cleared, so done. */
1133 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1136 rnp
->qsmask
&= ~mask
;
1137 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1138 mask
, rnp
->qsmask
, rnp
->level
,
1139 rnp
->grplo
, rnp
->grphi
,
1141 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1143 /* Other bits still set at this level, so done. */
1144 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1147 mask
= rnp
->grpmask
;
1148 if (rnp
->parent
== NULL
) {
1150 /* No more levels. Exit loop holding root lock. */
1154 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1157 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1158 WARN_ON_ONCE(rnp_c
->qsmask
);
1162 * Get here if we are the last CPU to pass through a quiescent
1163 * state for this grace period. Invoke rcu_report_qs_rsp()
1164 * to clean up and start the next grace period if one is needed.
1166 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1170 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1171 * structure. This must be either called from the specified CPU, or
1172 * called when the specified CPU is known to be offline (and when it is
1173 * also known that no other CPU is concurrently trying to help the offline
1174 * CPU). The lastcomp argument is used to make sure we are still in the
1175 * grace period of interest. We don't want to end the current grace period
1176 * based on quiescent states detected in an earlier grace period!
1179 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
, long lastgp
)
1181 unsigned long flags
;
1183 struct rcu_node
*rnp
;
1186 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1187 if (lastgp
!= rnp
->gpnum
|| rnp
->completed
== rnp
->gpnum
) {
1190 * The grace period in which this quiescent state was
1191 * recorded has ended, so don't report it upwards.
1192 * We will instead need a new quiescent state that lies
1193 * within the current grace period.
1195 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1196 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1199 mask
= rdp
->grpmask
;
1200 if ((rnp
->qsmask
& mask
) == 0) {
1201 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1203 rdp
->qs_pending
= 0;
1206 * This GP can't end until cpu checks in, so all of our
1207 * callbacks can be processed during the next GP.
1209 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1211 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1216 * Check to see if there is a new grace period of which this CPU
1217 * is not yet aware, and if so, set up local rcu_data state for it.
1218 * Otherwise, see if this CPU has just passed through its first
1219 * quiescent state for this grace period, and record that fact if so.
1222 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1224 /* If there is now a new grace period, record and return. */
1225 if (check_for_new_grace_period(rsp
, rdp
))
1229 * Does this CPU still need to do its part for current grace period?
1230 * If no, return and let the other CPUs do their part as well.
1232 if (!rdp
->qs_pending
)
1236 * Was there a quiescent state since the beginning of the grace
1237 * period? If no, then exit and wait for the next call.
1239 if (!rdp
->passed_quiesce
)
1243 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1246 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
, rdp
->passed_quiesce_gpnum
);
1249 #ifdef CONFIG_HOTPLUG_CPU
1252 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1253 * Synchronization is not required because this function executes
1254 * in stop_machine() context.
1256 static void rcu_send_cbs_to_online(struct rcu_state
*rsp
)
1259 /* current DYING CPU is cleared in the cpu_online_mask */
1260 int receive_cpu
= cpumask_any(cpu_online_mask
);
1261 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1262 struct rcu_data
*receive_rdp
= per_cpu_ptr(rsp
->rda
, receive_cpu
);
1264 if (rdp
->nxtlist
== NULL
)
1265 return; /* irqs disabled, so comparison is stable. */
1267 *receive_rdp
->nxttail
[RCU_NEXT_TAIL
] = rdp
->nxtlist
;
1268 receive_rdp
->nxttail
[RCU_NEXT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1269 receive_rdp
->qlen
+= rdp
->qlen
;
1270 receive_rdp
->n_cbs_adopted
+= rdp
->qlen
;
1271 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1273 rdp
->nxtlist
= NULL
;
1274 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1275 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1280 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1281 * and move all callbacks from the outgoing CPU to the current one.
1282 * There can only be one CPU hotplug operation at a time, so no other
1283 * CPU can be attempting to update rcu_cpu_kthread_task.
1285 static void __rcu_offline_cpu(int cpu
, struct rcu_state
*rsp
)
1287 unsigned long flags
;
1289 int need_report
= 0;
1290 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1291 struct rcu_node
*rnp
;
1293 rcu_stop_cpu_kthread(cpu
);
1295 /* Exclude any attempts to start a new grace period. */
1296 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
1298 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1299 rnp
= rdp
->mynode
; /* this is the outgoing CPU's rnp. */
1300 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1302 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1303 rnp
->qsmaskinit
&= ~mask
;
1304 if (rnp
->qsmaskinit
!= 0) {
1305 if (rnp
!= rdp
->mynode
)
1306 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1308 trace_rcu_grace_period(rsp
->name
,
1310 !!(rnp
->qsmask
& mask
),
1314 if (rnp
== rdp
->mynode
) {
1315 trace_rcu_grace_period(rsp
->name
,
1317 !!(rnp
->qsmask
& mask
),
1319 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1321 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1322 mask
= rnp
->grpmask
;
1324 } while (rnp
!= NULL
);
1327 * We still hold the leaf rcu_node structure lock here, and
1328 * irqs are still disabled. The reason for this subterfuge is
1329 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1330 * held leads to deadlock.
1332 raw_spin_unlock(&rsp
->onofflock
); /* irqs remain disabled. */
1334 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1335 rcu_report_unblock_qs_rnp(rnp
, flags
);
1337 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1338 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1339 rcu_report_exp_rnp(rsp
, rnp
, true);
1340 rcu_node_kthread_setaffinity(rnp
, -1);
1344 * Remove the specified CPU from the RCU hierarchy and move any pending
1345 * callbacks that it might have to the current CPU. This code assumes
1346 * that at least one CPU in the system will remain running at all times.
1347 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1349 static void rcu_offline_cpu(int cpu
)
1351 __rcu_offline_cpu(cpu
, &rcu_sched_state
);
1352 __rcu_offline_cpu(cpu
, &rcu_bh_state
);
1353 rcu_preempt_offline_cpu(cpu
);
1356 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1358 static void rcu_send_cbs_to_online(struct rcu_state
*rsp
)
1362 static void rcu_offline_cpu(int cpu
)
1366 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1369 * Invoke any RCU callbacks that have made it to the end of their grace
1370 * period. Thottle as specified by rdp->blimit.
1372 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1374 unsigned long flags
;
1375 struct rcu_head
*next
, *list
, **tail
;
1378 /* If no callbacks are ready, just return.*/
1379 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
1380 trace_rcu_batch_start(rsp
->name
, 0, 0);
1381 trace_rcu_batch_end(rsp
->name
, 0);
1386 * Extract the list of ready callbacks, disabling to prevent
1387 * races with call_rcu() from interrupt handlers.
1389 local_irq_save(flags
);
1391 trace_rcu_batch_start(rsp
->name
, rdp
->qlen
, bl
);
1392 list
= rdp
->nxtlist
;
1393 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1394 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1395 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1396 for (count
= RCU_NEXT_SIZE
- 1; count
>= 0; count
--)
1397 if (rdp
->nxttail
[count
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1398 rdp
->nxttail
[count
] = &rdp
->nxtlist
;
1399 local_irq_restore(flags
);
1401 /* Invoke callbacks. */
1406 debug_rcu_head_unqueue(list
);
1407 __rcu_reclaim(rsp
->name
, list
);
1413 local_irq_save(flags
);
1414 trace_rcu_batch_end(rsp
->name
, count
);
1416 /* Update count, and requeue any remaining callbacks. */
1418 rdp
->n_cbs_invoked
+= count
;
1420 *tail
= rdp
->nxtlist
;
1421 rdp
->nxtlist
= list
;
1422 for (count
= 0; count
< RCU_NEXT_SIZE
; count
++)
1423 if (&rdp
->nxtlist
== rdp
->nxttail
[count
])
1424 rdp
->nxttail
[count
] = tail
;
1429 /* Reinstate batch limit if we have worked down the excess. */
1430 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1431 rdp
->blimit
= blimit
;
1433 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1434 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1435 rdp
->qlen_last_fqs_check
= 0;
1436 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1437 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1438 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1440 local_irq_restore(flags
);
1442 /* Re-invoke RCU core processing if there are callbacks remaining. */
1443 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1448 * Check to see if this CPU is in a non-context-switch quiescent state
1449 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1450 * Also schedule RCU core processing.
1452 * This function must be called from hardirq context. It is normally
1453 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1454 * false, there is no point in invoking rcu_check_callbacks().
1456 void rcu_check_callbacks(int cpu
, int user
)
1458 trace_rcu_utilization("Start scheduler-tick");
1459 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
1462 * Get here if this CPU took its interrupt from user
1463 * mode or from the idle loop, and if this is not a
1464 * nested interrupt. In this case, the CPU is in
1465 * a quiescent state, so note it.
1467 * No memory barrier is required here because both
1468 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1469 * variables that other CPUs neither access nor modify,
1470 * at least not while the corresponding CPU is online.
1476 } else if (!in_softirq()) {
1479 * Get here if this CPU did not take its interrupt from
1480 * softirq, in other words, if it is not interrupting
1481 * a rcu_bh read-side critical section. This is an _bh
1482 * critical section, so note it.
1487 rcu_preempt_check_callbacks(cpu
);
1488 if (rcu_pending(cpu
))
1490 trace_rcu_utilization("End scheduler-tick");
1496 * Scan the leaf rcu_node structures, processing dyntick state for any that
1497 * have not yet encountered a quiescent state, using the function specified.
1498 * Also initiate boosting for any threads blocked on the root rcu_node.
1500 * The caller must have suppressed start of new grace periods.
1502 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1506 unsigned long flags
;
1508 struct rcu_node
*rnp
;
1510 rcu_for_each_leaf_node(rsp
, rnp
) {
1512 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1513 if (!rcu_gp_in_progress(rsp
)) {
1514 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1517 if (rnp
->qsmask
== 0) {
1518 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1523 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1524 if ((rnp
->qsmask
& bit
) != 0 &&
1525 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1530 /* rcu_report_qs_rnp() releases rnp->lock. */
1531 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1534 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1536 rnp
= rcu_get_root(rsp
);
1537 if (rnp
->qsmask
== 0) {
1538 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1539 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1544 * Force quiescent states on reluctant CPUs, and also detect which
1545 * CPUs are in dyntick-idle mode.
1547 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1549 unsigned long flags
;
1550 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1552 trace_rcu_utilization("Start fqs");
1553 if (!rcu_gp_in_progress(rsp
)) {
1554 trace_rcu_utilization("End fqs");
1555 return; /* No grace period in progress, nothing to force. */
1557 if (!raw_spin_trylock_irqsave(&rsp
->fqslock
, flags
)) {
1558 rsp
->n_force_qs_lh
++; /* Inexact, can lose counts. Tough! */
1559 trace_rcu_utilization("End fqs");
1560 return; /* Someone else is already on the job. */
1562 if (relaxed
&& ULONG_CMP_GE(rsp
->jiffies_force_qs
, jiffies
))
1563 goto unlock_fqs_ret
; /* no emergency and done recently. */
1565 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1566 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
1567 if(!rcu_gp_in_progress(rsp
)) {
1568 rsp
->n_force_qs_ngp
++;
1569 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1570 goto unlock_fqs_ret
; /* no GP in progress, time updated. */
1572 rsp
->fqs_active
= 1;
1573 switch (rsp
->fqs_state
) {
1577 break; /* grace period idle or initializing, ignore. */
1579 case RCU_SAVE_DYNTICK
:
1580 if (RCU_SIGNAL_INIT
!= RCU_SAVE_DYNTICK
)
1581 break; /* So gcc recognizes the dead code. */
1583 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1585 /* Record dyntick-idle state. */
1586 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1587 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1588 if (rcu_gp_in_progress(rsp
))
1589 rsp
->fqs_state
= RCU_FORCE_QS
;
1594 /* Check dyntick-idle state, send IPI to laggarts. */
1595 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1596 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1598 /* Leave state in case more forcing is required. */
1600 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1603 rsp
->fqs_active
= 0;
1604 if (rsp
->fqs_need_gp
) {
1605 raw_spin_unlock(&rsp
->fqslock
); /* irqs remain disabled */
1606 rsp
->fqs_need_gp
= 0;
1607 rcu_start_gp(rsp
, flags
); /* releases rnp->lock */
1608 trace_rcu_utilization("End fqs");
1611 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1613 raw_spin_unlock_irqrestore(&rsp
->fqslock
, flags
);
1614 trace_rcu_utilization("End fqs");
1617 #else /* #ifdef CONFIG_SMP */
1619 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1624 #endif /* #else #ifdef CONFIG_SMP */
1627 * This does the RCU core processing work for the specified rcu_state
1628 * and rcu_data structures. This may be called only from the CPU to
1629 * whom the rdp belongs.
1632 __rcu_process_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1634 unsigned long flags
;
1636 WARN_ON_ONCE(rdp
->beenonline
== 0);
1639 * If an RCU GP has gone long enough, go check for dyntick
1640 * idle CPUs and, if needed, send resched IPIs.
1642 if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1643 force_quiescent_state(rsp
, 1);
1646 * Advance callbacks in response to end of earlier grace
1647 * period that some other CPU ended.
1649 rcu_process_gp_end(rsp
, rdp
);
1651 /* Update RCU state based on any recent quiescent states. */
1652 rcu_check_quiescent_state(rsp
, rdp
);
1654 /* Does this CPU require a not-yet-started grace period? */
1655 if (cpu_needs_another_gp(rsp
, rdp
)) {
1656 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1657 rcu_start_gp(rsp
, flags
); /* releases above lock */
1660 /* If there are callbacks ready, invoke them. */
1661 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1662 invoke_rcu_callbacks(rsp
, rdp
);
1666 * Do RCU core processing for the current CPU.
1668 static void rcu_process_callbacks(struct softirq_action
*unused
)
1670 trace_rcu_utilization("Start RCU core");
1671 __rcu_process_callbacks(&rcu_sched_state
,
1672 &__get_cpu_var(rcu_sched_data
));
1673 __rcu_process_callbacks(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1674 rcu_preempt_process_callbacks();
1675 rcu_wake_cpus_for_gp_end();
1676 trace_rcu_utilization("End RCU core");
1680 * Schedule RCU callback invocation. If the specified type of RCU
1681 * does not support RCU priority boosting, just do a direct call,
1682 * otherwise wake up the per-CPU kernel kthread. Note that because we
1683 * are running on the current CPU with interrupts disabled, the
1684 * rcu_cpu_kthread_task cannot disappear out from under us.
1686 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1688 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
1690 if (likely(!rsp
->boost
)) {
1691 rcu_do_batch(rsp
, rdp
);
1694 invoke_rcu_callbacks_kthread();
1697 static void invoke_rcu_core(void)
1699 raise_softirq(RCU_SOFTIRQ
);
1703 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1704 struct rcu_state
*rsp
)
1706 unsigned long flags
;
1707 struct rcu_data
*rdp
;
1709 debug_rcu_head_queue(head
);
1713 smp_mb(); /* Ensure RCU update seen before callback registry. */
1716 * Opportunistically note grace-period endings and beginnings.
1717 * Note that we might see a beginning right after we see an
1718 * end, but never vice versa, since this CPU has to pass through
1719 * a quiescent state betweentimes.
1721 local_irq_save(flags
);
1722 rdp
= this_cpu_ptr(rsp
->rda
);
1724 /* Add the callback to our list. */
1725 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1726 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1729 if (__is_kfree_rcu_offset((unsigned long)func
))
1730 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
1733 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen
);
1735 /* If interrupts were disabled, don't dive into RCU core. */
1736 if (irqs_disabled_flags(flags
)) {
1737 local_irq_restore(flags
);
1742 * Force the grace period if too many callbacks or too long waiting.
1743 * Enforce hysteresis, and don't invoke force_quiescent_state()
1744 * if some other CPU has recently done so. Also, don't bother
1745 * invoking force_quiescent_state() if the newly enqueued callback
1746 * is the only one waiting for a grace period to complete.
1748 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1750 /* Are we ignoring a completed grace period? */
1751 rcu_process_gp_end(rsp
, rdp
);
1752 check_for_new_grace_period(rsp
, rdp
);
1754 /* Start a new grace period if one not already started. */
1755 if (!rcu_gp_in_progress(rsp
)) {
1756 unsigned long nestflag
;
1757 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1759 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1760 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
1762 /* Give the grace period a kick. */
1763 rdp
->blimit
= LONG_MAX
;
1764 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1765 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1766 force_quiescent_state(rsp
, 0);
1767 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1768 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1770 } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1771 force_quiescent_state(rsp
, 1);
1772 local_irq_restore(flags
);
1776 * Queue an RCU-sched callback for invocation after a grace period.
1778 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1780 __call_rcu(head
, func
, &rcu_sched_state
);
1782 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1785 * Queue an RCU for invocation after a quicker grace period.
1787 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1789 __call_rcu(head
, func
, &rcu_bh_state
);
1791 EXPORT_SYMBOL_GPL(call_rcu_bh
);
1794 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1796 * Control will return to the caller some time after a full rcu-sched
1797 * grace period has elapsed, in other words after all currently executing
1798 * rcu-sched read-side critical sections have completed. These read-side
1799 * critical sections are delimited by rcu_read_lock_sched() and
1800 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1801 * local_irq_disable(), and so on may be used in place of
1802 * rcu_read_lock_sched().
1804 * This means that all preempt_disable code sequences, including NMI and
1805 * hardware-interrupt handlers, in progress on entry will have completed
1806 * before this primitive returns. However, this does not guarantee that
1807 * softirq handlers will have completed, since in some kernels, these
1808 * handlers can run in process context, and can block.
1810 * This primitive provides the guarantees made by the (now removed)
1811 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1812 * guarantees that rcu_read_lock() sections will have completed.
1813 * In "classic RCU", these two guarantees happen to be one and
1814 * the same, but can differ in realtime RCU implementations.
1816 void synchronize_sched(void)
1818 if (rcu_blocking_is_gp())
1820 wait_rcu_gp(call_rcu_sched
);
1822 EXPORT_SYMBOL_GPL(synchronize_sched
);
1825 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1827 * Control will return to the caller some time after a full rcu_bh grace
1828 * period has elapsed, in other words after all currently executing rcu_bh
1829 * read-side critical sections have completed. RCU read-side critical
1830 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1831 * and may be nested.
1833 void synchronize_rcu_bh(void)
1835 if (rcu_blocking_is_gp())
1837 wait_rcu_gp(call_rcu_bh
);
1839 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
1842 * Check to see if there is any immediate RCU-related work to be done
1843 * by the current CPU, for the specified type of RCU, returning 1 if so.
1844 * The checks are in order of increasing expense: checks that can be
1845 * carried out against CPU-local state are performed first. However,
1846 * we must check for CPU stalls first, else we might not get a chance.
1848 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1850 struct rcu_node
*rnp
= rdp
->mynode
;
1852 rdp
->n_rcu_pending
++;
1854 /* Check for CPU stalls, if enabled. */
1855 check_cpu_stall(rsp
, rdp
);
1857 /* Is the RCU core waiting for a quiescent state from this CPU? */
1858 if (rcu_scheduler_fully_active
&&
1859 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
1862 * If force_quiescent_state() coming soon and this CPU
1863 * needs a quiescent state, and this is either RCU-sched
1864 * or RCU-bh, force a local reschedule.
1866 rdp
->n_rp_qs_pending
++;
1867 if (!rdp
->preemptible
&&
1868 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
) - 1,
1871 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
1872 rdp
->n_rp_report_qs
++;
1876 /* Does this CPU have callbacks ready to invoke? */
1877 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
1878 rdp
->n_rp_cb_ready
++;
1882 /* Has RCU gone idle with this CPU needing another grace period? */
1883 if (cpu_needs_another_gp(rsp
, rdp
)) {
1884 rdp
->n_rp_cpu_needs_gp
++;
1888 /* Has another RCU grace period completed? */
1889 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
1890 rdp
->n_rp_gp_completed
++;
1894 /* Has a new RCU grace period started? */
1895 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
1896 rdp
->n_rp_gp_started
++;
1900 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1901 if (rcu_gp_in_progress(rsp
) &&
1902 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
)) {
1903 rdp
->n_rp_need_fqs
++;
1908 rdp
->n_rp_need_nothing
++;
1913 * Check to see if there is any immediate RCU-related work to be done
1914 * by the current CPU, returning 1 if so. This function is part of the
1915 * RCU implementation; it is -not- an exported member of the RCU API.
1917 static int rcu_pending(int cpu
)
1919 return __rcu_pending(&rcu_sched_state
, &per_cpu(rcu_sched_data
, cpu
)) ||
1920 __rcu_pending(&rcu_bh_state
, &per_cpu(rcu_bh_data
, cpu
)) ||
1921 rcu_preempt_pending(cpu
);
1925 * Check to see if any future RCU-related work will need to be done
1926 * by the current CPU, even if none need be done immediately, returning
1929 static int rcu_cpu_has_callbacks(int cpu
)
1931 /* RCU callbacks either ready or pending? */
1932 return per_cpu(rcu_sched_data
, cpu
).nxtlist
||
1933 per_cpu(rcu_bh_data
, cpu
).nxtlist
||
1934 rcu_preempt_needs_cpu(cpu
);
1937 static DEFINE_PER_CPU(struct rcu_head
, rcu_barrier_head
) = {NULL
};
1938 static atomic_t rcu_barrier_cpu_count
;
1939 static DEFINE_MUTEX(rcu_barrier_mutex
);
1940 static struct completion rcu_barrier_completion
;
1942 static void rcu_barrier_callback(struct rcu_head
*notused
)
1944 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1945 complete(&rcu_barrier_completion
);
1949 * Called with preemption disabled, and from cross-cpu IRQ context.
1951 static void rcu_barrier_func(void *type
)
1953 int cpu
= smp_processor_id();
1954 struct rcu_head
*head
= &per_cpu(rcu_barrier_head
, cpu
);
1955 void (*call_rcu_func
)(struct rcu_head
*head
,
1956 void (*func
)(struct rcu_head
*head
));
1958 atomic_inc(&rcu_barrier_cpu_count
);
1959 call_rcu_func
= type
;
1960 call_rcu_func(head
, rcu_barrier_callback
);
1964 * Orchestrate the specified type of RCU barrier, waiting for all
1965 * RCU callbacks of the specified type to complete.
1967 static void _rcu_barrier(struct rcu_state
*rsp
,
1968 void (*call_rcu_func
)(struct rcu_head
*head
,
1969 void (*func
)(struct rcu_head
*head
)))
1971 BUG_ON(in_interrupt());
1972 /* Take mutex to serialize concurrent rcu_barrier() requests. */
1973 mutex_lock(&rcu_barrier_mutex
);
1974 init_completion(&rcu_barrier_completion
);
1976 * Initialize rcu_barrier_cpu_count to 1, then invoke
1977 * rcu_barrier_func() on each CPU, so that each CPU also has
1978 * incremented rcu_barrier_cpu_count. Only then is it safe to
1979 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1980 * might complete its grace period before all of the other CPUs
1981 * did their increment, causing this function to return too
1982 * early. Note that on_each_cpu() disables irqs, which prevents
1983 * any CPUs from coming online or going offline until each online
1984 * CPU has queued its RCU-barrier callback.
1986 atomic_set(&rcu_barrier_cpu_count
, 1);
1987 on_each_cpu(rcu_barrier_func
, (void *)call_rcu_func
, 1);
1988 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1989 complete(&rcu_barrier_completion
);
1990 wait_for_completion(&rcu_barrier_completion
);
1991 mutex_unlock(&rcu_barrier_mutex
);
1995 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1997 void rcu_barrier_bh(void)
1999 _rcu_barrier(&rcu_bh_state
, call_rcu_bh
);
2001 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2004 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2006 void rcu_barrier_sched(void)
2008 _rcu_barrier(&rcu_sched_state
, call_rcu_sched
);
2010 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2013 * Do boot-time initialization of a CPU's per-CPU RCU data.
2016 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2018 unsigned long flags
;
2020 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2021 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2023 /* Set up local state, ensuring consistent view of global state. */
2024 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2025 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2026 rdp
->nxtlist
= NULL
;
2027 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
2028 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
2030 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2031 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_NESTING
);
2032 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2035 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2039 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2040 * offline event can be happening at a given time. Note also that we
2041 * can accept some slop in the rsp->completed access due to the fact
2042 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2044 static void __cpuinit
2045 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2047 unsigned long flags
;
2049 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2050 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2052 /* Set up local state, ensuring consistent view of global state. */
2053 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2054 rdp
->beenonline
= 1; /* We have now been online. */
2055 rdp
->preemptible
= preemptible
;
2056 rdp
->qlen_last_fqs_check
= 0;
2057 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2058 rdp
->blimit
= blimit
;
2059 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_NESTING
);
2060 WARN_ON_ONCE((atomic_read(&rdp
->dynticks
->dynticks
) & 0x1) != 1);
2061 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2064 * A new grace period might start here. If so, we won't be part
2065 * of it, but that is OK, as we are currently in a quiescent state.
2068 /* Exclude any attempts to start a new GP on large systems. */
2069 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
2071 /* Add CPU to rcu_node bitmasks. */
2073 mask
= rdp
->grpmask
;
2075 /* Exclude any attempts to start a new GP on small systems. */
2076 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2077 rnp
->qsmaskinit
|= mask
;
2078 mask
= rnp
->grpmask
;
2079 if (rnp
== rdp
->mynode
) {
2081 * If there is a grace period in progress, we will
2082 * set up to wait for it next time we run the
2085 rdp
->gpnum
= rnp
->completed
;
2086 rdp
->completed
= rnp
->completed
;
2087 rdp
->passed_quiesce
= 0;
2088 rdp
->qs_pending
= 0;
2089 rdp
->passed_quiesce_gpnum
= rnp
->gpnum
- 1;
2090 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2092 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2094 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2096 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2099 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2101 rcu_init_percpu_data(cpu
, &rcu_sched_state
, 0);
2102 rcu_init_percpu_data(cpu
, &rcu_bh_state
, 0);
2103 rcu_preempt_init_percpu_data(cpu
);
2107 * Handle CPU online/offline notification events.
2109 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2110 unsigned long action
, void *hcpu
)
2112 long cpu
= (long)hcpu
;
2113 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2114 struct rcu_node
*rnp
= rdp
->mynode
;
2116 trace_rcu_utilization("Start CPU hotplug");
2118 case CPU_UP_PREPARE
:
2119 case CPU_UP_PREPARE_FROZEN
:
2120 rcu_prepare_cpu(cpu
);
2121 rcu_prepare_kthreads(cpu
);
2124 case CPU_DOWN_FAILED
:
2125 rcu_node_kthread_setaffinity(rnp
, -1);
2126 rcu_cpu_kthread_setrt(cpu
, 1);
2128 case CPU_DOWN_PREPARE
:
2129 rcu_node_kthread_setaffinity(rnp
, cpu
);
2130 rcu_cpu_kthread_setrt(cpu
, 0);
2133 case CPU_DYING_FROZEN
:
2135 * The whole machine is "stopped" except this CPU, so we can
2136 * touch any data without introducing corruption. We send the
2137 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2139 rcu_send_cbs_to_online(&rcu_bh_state
);
2140 rcu_send_cbs_to_online(&rcu_sched_state
);
2141 rcu_preempt_send_cbs_to_online();
2144 case CPU_DEAD_FROZEN
:
2145 case CPU_UP_CANCELED
:
2146 case CPU_UP_CANCELED_FROZEN
:
2147 rcu_offline_cpu(cpu
);
2152 trace_rcu_utilization("End CPU hotplug");
2157 * This function is invoked towards the end of the scheduler's initialization
2158 * process. Before this is called, the idle task might contain
2159 * RCU read-side critical sections (during which time, this idle
2160 * task is booting the system). After this function is called, the
2161 * idle tasks are prohibited from containing RCU read-side critical
2162 * sections. This function also enables RCU lockdep checking.
2164 void rcu_scheduler_starting(void)
2166 WARN_ON(num_online_cpus() != 1);
2167 WARN_ON(nr_context_switches() > 0);
2168 rcu_scheduler_active
= 1;
2172 * Compute the per-level fanout, either using the exact fanout specified
2173 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2175 #ifdef CONFIG_RCU_FANOUT_EXACT
2176 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2180 for (i
= NUM_RCU_LVLS
- 1; i
> 0; i
--)
2181 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2182 rsp
->levelspread
[0] = RCU_FANOUT_LEAF
;
2184 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2185 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2192 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
2193 ccur
= rsp
->levelcnt
[i
];
2194 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2198 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2201 * Helper function for rcu_init() that initializes one rcu_state structure.
2203 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2204 struct rcu_data __percpu
*rda
)
2206 static char *buf
[] = { "rcu_node_level_0",
2209 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
2213 struct rcu_node
*rnp
;
2215 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2217 /* Initialize the level-tracking arrays. */
2219 for (i
= 1; i
< NUM_RCU_LVLS
; i
++)
2220 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2221 rcu_init_levelspread(rsp
);
2223 /* Initialize the elements themselves, starting from the leaves. */
2225 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
2226 cpustride
*= rsp
->levelspread
[i
];
2227 rnp
= rsp
->level
[i
];
2228 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2229 raw_spin_lock_init(&rnp
->lock
);
2230 lockdep_set_class_and_name(&rnp
->lock
,
2231 &rcu_node_class
[i
], buf
[i
]);
2234 rnp
->qsmaskinit
= 0;
2235 rnp
->grplo
= j
* cpustride
;
2236 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2237 if (rnp
->grphi
>= NR_CPUS
)
2238 rnp
->grphi
= NR_CPUS
- 1;
2244 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2245 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2246 rnp
->parent
= rsp
->level
[i
- 1] +
2247 j
/ rsp
->levelspread
[i
- 1];
2250 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2255 rnp
= rsp
->level
[NUM_RCU_LVLS
- 1];
2256 for_each_possible_cpu(i
) {
2257 while (i
> rnp
->grphi
)
2259 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2260 rcu_boot_init_percpu_data(i
, rsp
);
2264 void __init
rcu_init(void)
2268 rcu_bootup_announce();
2269 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
2270 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
2271 __rcu_init_preempt();
2272 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
2275 * We don't need protection against CPU-hotplug here because
2276 * this is called early in boot, before either interrupts
2277 * or the scheduler are operational.
2279 cpu_notifier(rcu_cpu_notify
, 0);
2280 for_each_online_cpu(cpu
)
2281 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
2282 check_cpu_stall_init();
2285 #include "rcutree_plugin.h"