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 trace_rcu_dyntick("Start", oldval
, 0);
354 if (!is_idle_task(current
)) {
355 struct task_struct
*idle
= idle_task(smp_processor_id());
357 trace_rcu_dyntick("Error on entry: not idle task", oldval
, 0);
358 ftrace_dump(DUMP_ALL
);
359 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
360 current
->pid
, current
->comm
,
361 idle
->pid
, idle
->comm
); /* must be idle task! */
363 rcu_prepare_for_idle(smp_processor_id());
364 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
365 smp_mb__before_atomic_inc(); /* See above. */
366 atomic_inc(&rdtp
->dynticks
);
367 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
368 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
372 * rcu_idle_enter - inform RCU that current CPU is entering idle
374 * Enter idle mode, in other words, -leave- the mode in which RCU
375 * read-side critical sections can occur. (Though RCU read-side
376 * critical sections can occur in irq handlers in idle, a possibility
377 * handled by irq_enter() and irq_exit().)
379 * We crowbar the ->dynticks_nesting field to zero to allow for
380 * the possibility of usermode upcalls having messed up our count
381 * of interrupt nesting level during the prior busy period.
383 void rcu_idle_enter(void)
387 struct rcu_dynticks
*rdtp
;
389 local_irq_save(flags
);
390 rdtp
= &__get_cpu_var(rcu_dynticks
);
391 oldval
= rdtp
->dynticks_nesting
;
392 rdtp
->dynticks_nesting
= 0;
393 rcu_idle_enter_common(rdtp
, oldval
);
394 local_irq_restore(flags
);
398 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
400 * Exit from an interrupt handler, which might possibly result in entering
401 * idle mode, in other words, leaving the mode in which read-side critical
402 * sections can occur.
404 * This code assumes that the idle loop never does anything that might
405 * result in unbalanced calls to irq_enter() and irq_exit(). If your
406 * architecture violates this assumption, RCU will give you what you
407 * deserve, good and hard. But very infrequently and irreproducibly.
409 * Use things like work queues to work around this limitation.
411 * You have been warned.
413 void rcu_irq_exit(void)
417 struct rcu_dynticks
*rdtp
;
419 local_irq_save(flags
);
420 rdtp
= &__get_cpu_var(rcu_dynticks
);
421 oldval
= rdtp
->dynticks_nesting
;
422 rdtp
->dynticks_nesting
--;
423 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
424 if (rdtp
->dynticks_nesting
)
425 trace_rcu_dyntick("--=", oldval
, rdtp
->dynticks_nesting
);
427 rcu_idle_enter_common(rdtp
, oldval
);
428 local_irq_restore(flags
);
432 * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
434 * If the new value of the ->dynticks_nesting counter was previously zero,
435 * we really have exited idle, and must do the appropriate accounting.
436 * The caller must have disabled interrupts.
438 static void rcu_idle_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
)
440 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
441 atomic_inc(&rdtp
->dynticks
);
442 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
443 smp_mb__after_atomic_inc(); /* See above. */
444 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
445 rcu_cleanup_after_idle(smp_processor_id());
446 trace_rcu_dyntick("End", oldval
, rdtp
->dynticks_nesting
);
447 if (!is_idle_task(current
)) {
448 struct task_struct
*idle
= idle_task(smp_processor_id());
450 trace_rcu_dyntick("Error on exit: not idle task",
451 oldval
, rdtp
->dynticks_nesting
);
452 ftrace_dump(DUMP_ALL
);
453 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
454 current
->pid
, current
->comm
,
455 idle
->pid
, idle
->comm
); /* must be idle task! */
460 * rcu_idle_exit - inform RCU that current CPU is leaving idle
462 * Exit idle mode, in other words, -enter- the mode in which RCU
463 * read-side critical sections can occur.
465 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
466 * allow for the possibility of usermode upcalls messing up our count
467 * of interrupt nesting level during the busy period that is just
470 void rcu_idle_exit(void)
473 struct rcu_dynticks
*rdtp
;
476 local_irq_save(flags
);
477 rdtp
= &__get_cpu_var(rcu_dynticks
);
478 oldval
= rdtp
->dynticks_nesting
;
479 WARN_ON_ONCE(oldval
!= 0);
480 rdtp
->dynticks_nesting
= DYNTICK_TASK_NESTING
;
481 rcu_idle_exit_common(rdtp
, oldval
);
482 local_irq_restore(flags
);
486 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
488 * Enter an interrupt handler, which might possibly result in exiting
489 * idle mode, in other words, entering the mode in which read-side critical
490 * sections can occur.
492 * Note that the Linux kernel is fully capable of entering an interrupt
493 * handler that it never exits, for example when doing upcalls to
494 * user mode! This code assumes that the idle loop never does upcalls to
495 * user mode. If your architecture does do upcalls from the idle loop (or
496 * does anything else that results in unbalanced calls to the irq_enter()
497 * and irq_exit() functions), RCU will give you what you deserve, good
498 * and hard. But very infrequently and irreproducibly.
500 * Use things like work queues to work around this limitation.
502 * You have been warned.
504 void rcu_irq_enter(void)
507 struct rcu_dynticks
*rdtp
;
510 local_irq_save(flags
);
511 rdtp
= &__get_cpu_var(rcu_dynticks
);
512 oldval
= rdtp
->dynticks_nesting
;
513 rdtp
->dynticks_nesting
++;
514 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
516 trace_rcu_dyntick("++=", oldval
, rdtp
->dynticks_nesting
);
518 rcu_idle_exit_common(rdtp
, oldval
);
519 local_irq_restore(flags
);
523 * rcu_nmi_enter - inform RCU of entry to NMI context
525 * If the CPU was idle with dynamic ticks active, and there is no
526 * irq handler running, this updates rdtp->dynticks_nmi to let the
527 * RCU grace-period handling know that the CPU is active.
529 void rcu_nmi_enter(void)
531 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
533 if (rdtp
->dynticks_nmi_nesting
== 0 &&
534 (atomic_read(&rdtp
->dynticks
) & 0x1))
536 rdtp
->dynticks_nmi_nesting
++;
537 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
538 atomic_inc(&rdtp
->dynticks
);
539 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
540 smp_mb__after_atomic_inc(); /* See above. */
541 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
545 * rcu_nmi_exit - inform RCU of exit from NMI context
547 * If the CPU was idle with dynamic ticks active, and there is no
548 * irq handler running, this updates rdtp->dynticks_nmi to let the
549 * RCU grace-period handling know that the CPU is no longer active.
551 void rcu_nmi_exit(void)
553 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
555 if (rdtp
->dynticks_nmi_nesting
== 0 ||
556 --rdtp
->dynticks_nmi_nesting
!= 0)
558 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
559 smp_mb__before_atomic_inc(); /* See above. */
560 atomic_inc(&rdtp
->dynticks
);
561 smp_mb__after_atomic_inc(); /* Force delay to next write. */
562 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
565 #ifdef CONFIG_PROVE_RCU
568 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
570 * If the current CPU is in its idle loop and is neither in an interrupt
571 * or NMI handler, return true.
573 int rcu_is_cpu_idle(void)
578 ret
= (atomic_read(&__get_cpu_var(rcu_dynticks
).dynticks
) & 0x1) == 0;
582 EXPORT_SYMBOL(rcu_is_cpu_idle
);
584 #endif /* #ifdef CONFIG_PROVE_RCU */
587 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
589 * If the current CPU is idle or running at a first-level (not nested)
590 * interrupt from idle, return true. The caller must have at least
591 * disabled preemption.
593 int rcu_is_cpu_rrupt_from_idle(void)
595 return __get_cpu_var(rcu_dynticks
).dynticks_nesting
<= 1;
601 * Snapshot the specified CPU's dynticks counter so that we can later
602 * credit them with an implicit quiescent state. Return 1 if this CPU
603 * is in dynticks idle mode, which is an extended quiescent state.
605 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
607 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
608 return (rdp
->dynticks_snap
& 0x1) == 0;
612 * Return true if the specified CPU has passed through a quiescent
613 * state by virtue of being in or having passed through an dynticks
614 * idle state since the last call to dyntick_save_progress_counter()
617 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
622 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
623 snap
= (unsigned int)rdp
->dynticks_snap
;
626 * If the CPU passed through or entered a dynticks idle phase with
627 * no active irq/NMI handlers, then we can safely pretend that the CPU
628 * already acknowledged the request to pass through a quiescent
629 * state. Either way, that CPU cannot possibly be in an RCU
630 * read-side critical section that started before the beginning
631 * of the current RCU grace period.
633 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
634 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "dti");
639 /* Go check for the CPU being offline. */
640 return rcu_implicit_offline_qs(rdp
);
643 #endif /* #ifdef CONFIG_SMP */
645 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
647 rsp
->gp_start
= jiffies
;
648 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_CHECK
;
651 static void print_other_cpu_stall(struct rcu_state
*rsp
)
657 struct rcu_node
*rnp
= rcu_get_root(rsp
);
659 /* Only let one CPU complain about others per time interval. */
661 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
662 delta
= jiffies
- rsp
->jiffies_stall
;
663 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
664 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
667 rsp
->jiffies_stall
= jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
670 * Now rat on any tasks that got kicked up to the root rcu_node
671 * due to CPU offlining.
673 ndetected
= rcu_print_task_stall(rnp
);
674 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
677 * OK, time to rat on our buddy...
678 * See Documentation/RCU/stallwarn.txt for info on how to debug
679 * RCU CPU stall warnings.
681 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks: {",
683 rcu_for_each_leaf_node(rsp
, rnp
) {
684 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
685 ndetected
+= rcu_print_task_stall(rnp
);
686 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
687 if (rnp
->qsmask
== 0)
689 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
690 if (rnp
->qsmask
& (1UL << cpu
)) {
691 printk(" %d", rnp
->grplo
+ cpu
);
695 printk("} (detected by %d, t=%ld jiffies)\n",
696 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
));
698 printk(KERN_ERR
"INFO: Stall ended before state dump start\n");
699 else if (!trigger_all_cpu_backtrace())
702 /* If so configured, complain about tasks blocking the grace period. */
704 rcu_print_detail_task_stall(rsp
);
706 force_quiescent_state(rsp
, 0); /* Kick them all. */
709 static void print_cpu_stall(struct rcu_state
*rsp
)
712 struct rcu_node
*rnp
= rcu_get_root(rsp
);
715 * OK, time to rat on ourselves...
716 * See Documentation/RCU/stallwarn.txt for info on how to debug
717 * RCU CPU stall warnings.
719 printk(KERN_ERR
"INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
720 rsp
->name
, smp_processor_id(), jiffies
- rsp
->gp_start
);
721 if (!trigger_all_cpu_backtrace())
724 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
725 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
727 jiffies
+ RCU_SECONDS_TILL_STALL_RECHECK
;
728 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
730 set_need_resched(); /* kick ourselves to get things going. */
733 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
737 struct rcu_node
*rnp
;
739 if (rcu_cpu_stall_suppress
)
741 j
= ACCESS_ONCE(jiffies
);
742 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
744 if ((ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && ULONG_CMP_GE(j
, js
)) {
746 /* We haven't checked in, so go dump stack. */
747 print_cpu_stall(rsp
);
749 } else if (rcu_gp_in_progress(rsp
) &&
750 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
752 /* They had a few time units to dump stack, so complain. */
753 print_other_cpu_stall(rsp
);
757 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
759 rcu_cpu_stall_suppress
= 1;
764 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
766 * Set the stall-warning timeout way off into the future, thus preventing
767 * any RCU CPU stall-warning messages from appearing in the current set of
770 * The caller must disable hard irqs.
772 void rcu_cpu_stall_reset(void)
774 rcu_sched_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
775 rcu_bh_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
776 rcu_preempt_stall_reset();
779 static struct notifier_block rcu_panic_block
= {
780 .notifier_call
= rcu_panic
,
783 static void __init
check_cpu_stall_init(void)
785 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
789 * Update CPU-local rcu_data state to record the newly noticed grace period.
790 * This is used both when we started the grace period and when we notice
791 * that someone else started the grace period. The caller must hold the
792 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
793 * and must have irqs disabled.
795 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
797 if (rdp
->gpnum
!= rnp
->gpnum
) {
799 * If the current grace period is waiting for this CPU,
800 * set up to detect a quiescent state, otherwise don't
801 * go looking for one.
803 rdp
->gpnum
= rnp
->gpnum
;
804 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpustart");
805 if (rnp
->qsmask
& rdp
->grpmask
) {
807 rdp
->passed_quiesce
= 0;
813 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
816 struct rcu_node
*rnp
;
818 local_irq_save(flags
);
820 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
821 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
822 local_irq_restore(flags
);
825 __note_new_gpnum(rsp
, rnp
, rdp
);
826 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
830 * Did someone else start a new RCU grace period start since we last
831 * checked? Update local state appropriately if so. Must be called
832 * on the CPU corresponding to rdp.
835 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
840 local_irq_save(flags
);
841 if (rdp
->gpnum
!= rsp
->gpnum
) {
842 note_new_gpnum(rsp
, rdp
);
845 local_irq_restore(flags
);
850 * Advance this CPU's callbacks, but only if the current grace period
851 * has ended. This may be called only from the CPU to whom the rdp
852 * belongs. In addition, the corresponding leaf rcu_node structure's
853 * ->lock must be held by the caller, with irqs disabled.
856 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
858 /* Did another grace period end? */
859 if (rdp
->completed
!= rnp
->completed
) {
861 /* Advance callbacks. No harm if list empty. */
862 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
863 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
864 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
866 /* Remember that we saw this grace-period completion. */
867 rdp
->completed
= rnp
->completed
;
868 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuend");
871 * If we were in an extended quiescent state, we may have
872 * missed some grace periods that others CPUs handled on
873 * our behalf. Catch up with this state to avoid noting
874 * spurious new grace periods. If another grace period
875 * has started, then rnp->gpnum will have advanced, so
876 * we will detect this later on.
878 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
))
879 rdp
->gpnum
= rdp
->completed
;
882 * If RCU does not need a quiescent state from this CPU,
883 * then make sure that this CPU doesn't go looking for one.
885 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
891 * Advance this CPU's callbacks, but only if the current grace period
892 * has ended. This may be called only from the CPU to whom the rdp
896 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
899 struct rcu_node
*rnp
;
901 local_irq_save(flags
);
903 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
904 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
905 local_irq_restore(flags
);
908 __rcu_process_gp_end(rsp
, rnp
, rdp
);
909 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
913 * Do per-CPU grace-period initialization for running CPU. The caller
914 * must hold the lock of the leaf rcu_node structure corresponding to
918 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
920 /* Prior grace period ended, so advance callbacks for current CPU. */
921 __rcu_process_gp_end(rsp
, rnp
, rdp
);
924 * Because this CPU just now started the new grace period, we know
925 * that all of its callbacks will be covered by this upcoming grace
926 * period, even the ones that were registered arbitrarily recently.
927 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
929 * Other CPUs cannot be sure exactly when the grace period started.
930 * Therefore, their recently registered callbacks must pass through
931 * an additional RCU_NEXT_READY stage, so that they will be handled
932 * by the next RCU grace period.
934 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
935 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
937 /* Set state so that this CPU will detect the next quiescent state. */
938 __note_new_gpnum(rsp
, rnp
, rdp
);
942 * Start a new RCU grace period if warranted, re-initializing the hierarchy
943 * in preparation for detecting the next grace period. The caller must hold
944 * the root node's ->lock, which is released before return. Hard irqs must
947 * Note that it is legal for a dying CPU (which is marked as offline) to
948 * invoke this function. This can happen when the dying CPU reports its
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 if (*rdp
->nxttail
[RCU_WAIT_TAIL
] == NULL
) {
1090 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1093 * Propagate new ->completed value to rcu_node structures
1094 * so that other CPUs don't have to wait until the start
1095 * of the next grace period to process their callbacks.
1097 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1098 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1099 rnp
->completed
= rsp
->gpnum
;
1100 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1102 rnp
= rcu_get_root(rsp
);
1103 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1106 rsp
->completed
= rsp
->gpnum
; /* Declare the grace period complete. */
1107 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, "end");
1108 rsp
->fqs_state
= RCU_GP_IDLE
;
1109 rcu_start_gp(rsp
, flags
); /* releases root node's rnp->lock. */
1113 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1114 * Allows quiescent states for a group of CPUs to be reported at one go
1115 * to the specified rcu_node structure, though all the CPUs in the group
1116 * must be represented by the same rcu_node structure (which need not be
1117 * a leaf rcu_node structure, though it often will be). That structure's
1118 * lock must be held upon entry, and it is released before return.
1121 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1122 struct rcu_node
*rnp
, unsigned long flags
)
1123 __releases(rnp
->lock
)
1125 struct rcu_node
*rnp_c
;
1127 /* Walk up the rcu_node hierarchy. */
1129 if (!(rnp
->qsmask
& mask
)) {
1131 /* Our bit has already been cleared, so done. */
1132 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1135 rnp
->qsmask
&= ~mask
;
1136 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1137 mask
, rnp
->qsmask
, rnp
->level
,
1138 rnp
->grplo
, rnp
->grphi
,
1140 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1142 /* Other bits still set at this level, so done. */
1143 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1146 mask
= rnp
->grpmask
;
1147 if (rnp
->parent
== NULL
) {
1149 /* No more levels. Exit loop holding root lock. */
1153 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1156 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1157 WARN_ON_ONCE(rnp_c
->qsmask
);
1161 * Get here if we are the last CPU to pass through a quiescent
1162 * state for this grace period. Invoke rcu_report_qs_rsp()
1163 * to clean up and start the next grace period if one is needed.
1165 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1169 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1170 * structure. This must be either called from the specified CPU, or
1171 * called when the specified CPU is known to be offline (and when it is
1172 * also known that no other CPU is concurrently trying to help the offline
1173 * CPU). The lastcomp argument is used to make sure we are still in the
1174 * grace period of interest. We don't want to end the current grace period
1175 * based on quiescent states detected in an earlier grace period!
1178 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
, long lastgp
)
1180 unsigned long flags
;
1182 struct rcu_node
*rnp
;
1185 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1186 if (lastgp
!= rnp
->gpnum
|| rnp
->completed
== rnp
->gpnum
) {
1189 * The grace period in which this quiescent state was
1190 * recorded has ended, so don't report it upwards.
1191 * We will instead need a new quiescent state that lies
1192 * within the current grace period.
1194 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1195 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1198 mask
= rdp
->grpmask
;
1199 if ((rnp
->qsmask
& mask
) == 0) {
1200 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1202 rdp
->qs_pending
= 0;
1205 * This GP can't end until cpu checks in, so all of our
1206 * callbacks can be processed during the next GP.
1208 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1210 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1215 * Check to see if there is a new grace period of which this CPU
1216 * is not yet aware, and if so, set up local rcu_data state for it.
1217 * Otherwise, see if this CPU has just passed through its first
1218 * quiescent state for this grace period, and record that fact if so.
1221 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1223 /* If there is now a new grace period, record and return. */
1224 if (check_for_new_grace_period(rsp
, rdp
))
1228 * Does this CPU still need to do its part for current grace period?
1229 * If no, return and let the other CPUs do their part as well.
1231 if (!rdp
->qs_pending
)
1235 * Was there a quiescent state since the beginning of the grace
1236 * period? If no, then exit and wait for the next call.
1238 if (!rdp
->passed_quiesce
)
1242 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1245 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
, rdp
->passed_quiesce_gpnum
);
1248 #ifdef CONFIG_HOTPLUG_CPU
1251 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1252 * Also record a quiescent state for this CPU for the current grace period.
1253 * Synchronization and interrupt disabling are not required because
1254 * this function executes in stop_machine() context. Therefore, cleanup
1255 * operations that might block must be done later from the CPU_DEAD
1258 * Note that the outgoing CPU's bit has already been cleared in the
1259 * cpu_online_mask. This allows us to randomly pick a callback
1260 * destination from the bits set in that mask.
1262 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1264 unsigned long flags
;
1268 int receive_cpu
= cpumask_any(cpu_online_mask
);
1269 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1270 struct rcu_data
*receive_rdp
= per_cpu_ptr(rsp
->rda
, receive_cpu
);
1271 struct rcu_node
*rnp
= rdp
->mynode
; /* For dying CPU. */
1273 /* First, adjust the counts. */
1274 if (rdp
->nxtlist
!= NULL
) {
1275 receive_rdp
->qlen_lazy
+= rdp
->qlen_lazy
;
1276 receive_rdp
->qlen
+= rdp
->qlen
;
1282 * Next, move ready-to-invoke callbacks to be invoked on some
1283 * other CPU. These will not be required to pass through another
1284 * grace period: They are done, regardless of CPU.
1286 if (rdp
->nxtlist
!= NULL
&&
1287 rdp
->nxttail
[RCU_DONE_TAIL
] != &rdp
->nxtlist
) {
1288 struct rcu_head
*oldhead
;
1289 struct rcu_head
**oldtail
;
1290 struct rcu_head
**newtail
;
1292 oldhead
= rdp
->nxtlist
;
1293 oldtail
= receive_rdp
->nxttail
[RCU_DONE_TAIL
];
1294 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1295 *rdp
->nxttail
[RCU_DONE_TAIL
] = *oldtail
;
1296 *receive_rdp
->nxttail
[RCU_DONE_TAIL
] = oldhead
;
1297 newtail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1298 for (i
= RCU_DONE_TAIL
; i
< RCU_NEXT_SIZE
; i
++) {
1299 if (receive_rdp
->nxttail
[i
] == oldtail
)
1300 receive_rdp
->nxttail
[i
] = newtail
;
1301 if (rdp
->nxttail
[i
] == newtail
)
1302 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1307 * Finally, put the rest of the callbacks at the end of the list.
1308 * The ones that made it partway through get to start over: We
1309 * cannot assume that grace periods are synchronized across CPUs.
1310 * (We could splice RCU_WAIT_TAIL into RCU_NEXT_READY_TAIL, but
1311 * this does not seem compelling. Not yet, anyway.)
1313 if (rdp
->nxtlist
!= NULL
) {
1314 *receive_rdp
->nxttail
[RCU_NEXT_TAIL
] = rdp
->nxtlist
;
1315 receive_rdp
->nxttail
[RCU_NEXT_TAIL
] =
1316 rdp
->nxttail
[RCU_NEXT_TAIL
];
1317 receive_rdp
->n_cbs_adopted
+= rdp
->qlen
;
1318 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1320 rdp
->nxtlist
= NULL
;
1321 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1322 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1326 * Record a quiescent state for the dying CPU. This is safe
1327 * only because we have already cleared out the callbacks.
1328 * (Otherwise, the RCU core might try to schedule the invocation
1329 * of callbacks on this now-offline CPU, which would be bad.)
1331 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1332 trace_rcu_grace_period(rsp
->name
,
1333 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
1335 rcu_report_qs_rdp(smp_processor_id(), rsp
, rdp
, rsp
->gpnum
);
1336 /* Note that rcu_report_qs_rdp() might call trace_rcu_grace_period(). */
1339 * Remove the dying CPU from the bitmasks in the rcu_node
1340 * hierarchy. Because we are in stop_machine() context, we
1341 * automatically exclude ->onofflock critical sections.
1344 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1345 rnp
->qsmaskinit
&= ~mask
;
1346 if (rnp
->qsmaskinit
!= 0) {
1347 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1350 if (rnp
== rdp
->mynode
) {
1351 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1352 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1353 rcu_report_unblock_qs_rnp(rnp
, flags
);
1355 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1356 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1357 rcu_report_exp_rnp(rsp
, rnp
, true);
1359 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1360 mask
= rnp
->grpmask
;
1362 } while (rnp
!= NULL
);
1366 * The CPU has been completely removed, and some other CPU is reporting
1367 * this fact from process context. Do the remainder of the cleanup.
1368 * There can only be one CPU hotplug operation at a time, so no other
1369 * CPU can be attempting to update rcu_cpu_kthread_task.
1371 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1373 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1374 struct rcu_node
*rnp
= rdp
->mynode
;
1376 rcu_stop_cpu_kthread(cpu
);
1377 rcu_node_kthread_setaffinity(rnp
, -1);
1380 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1382 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1386 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1390 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1393 * Invoke any RCU callbacks that have made it to the end of their grace
1394 * period. Thottle as specified by rdp->blimit.
1396 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1398 unsigned long flags
;
1399 struct rcu_head
*next
, *list
, **tail
;
1400 int bl
, count
, count_lazy
;
1402 /* If no callbacks are ready, just return.*/
1403 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
1404 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
1405 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
1406 need_resched(), is_idle_task(current
),
1407 rcu_is_callbacks_kthread());
1412 * Extract the list of ready callbacks, disabling to prevent
1413 * races with call_rcu() from interrupt handlers.
1415 local_irq_save(flags
);
1416 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1418 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
1419 list
= rdp
->nxtlist
;
1420 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1421 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1422 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1423 for (count
= RCU_NEXT_SIZE
- 1; count
>= 0; count
--)
1424 if (rdp
->nxttail
[count
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1425 rdp
->nxttail
[count
] = &rdp
->nxtlist
;
1426 local_irq_restore(flags
);
1428 /* Invoke callbacks. */
1429 count
= count_lazy
= 0;
1433 debug_rcu_head_unqueue(list
);
1434 if (__rcu_reclaim(rsp
->name
, list
))
1437 /* Stop only if limit reached and CPU has something to do. */
1438 if (++count
>= bl
&&
1440 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
1444 local_irq_save(flags
);
1445 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
1446 is_idle_task(current
),
1447 rcu_is_callbacks_kthread());
1449 /* Update count, and requeue any remaining callbacks. */
1450 rdp
->qlen_lazy
-= count_lazy
;
1452 rdp
->n_cbs_invoked
+= count
;
1454 *tail
= rdp
->nxtlist
;
1455 rdp
->nxtlist
= list
;
1456 for (count
= 0; count
< RCU_NEXT_SIZE
; count
++)
1457 if (&rdp
->nxtlist
== rdp
->nxttail
[count
])
1458 rdp
->nxttail
[count
] = tail
;
1463 /* Reinstate batch limit if we have worked down the excess. */
1464 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1465 rdp
->blimit
= blimit
;
1467 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1468 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1469 rdp
->qlen_last_fqs_check
= 0;
1470 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1471 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1472 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1474 local_irq_restore(flags
);
1476 /* Re-invoke RCU core processing if there are callbacks remaining. */
1477 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1482 * Check to see if this CPU is in a non-context-switch quiescent state
1483 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1484 * Also schedule RCU core processing.
1486 * This function must be called from hardirq context. It is normally
1487 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1488 * false, there is no point in invoking rcu_check_callbacks().
1490 void rcu_check_callbacks(int cpu
, int user
)
1492 trace_rcu_utilization("Start scheduler-tick");
1493 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
1496 * Get here if this CPU took its interrupt from user
1497 * mode or from the idle loop, and if this is not a
1498 * nested interrupt. In this case, the CPU is in
1499 * a quiescent state, so note it.
1501 * No memory barrier is required here because both
1502 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1503 * variables that other CPUs neither access nor modify,
1504 * at least not while the corresponding CPU is online.
1510 } else if (!in_softirq()) {
1513 * Get here if this CPU did not take its interrupt from
1514 * softirq, in other words, if it is not interrupting
1515 * a rcu_bh read-side critical section. This is an _bh
1516 * critical section, so note it.
1521 rcu_preempt_check_callbacks(cpu
);
1522 if (rcu_pending(cpu
))
1524 trace_rcu_utilization("End scheduler-tick");
1530 * Scan the leaf rcu_node structures, processing dyntick state for any that
1531 * have not yet encountered a quiescent state, using the function specified.
1532 * Also initiate boosting for any threads blocked on the root rcu_node.
1534 * The caller must have suppressed start of new grace periods.
1536 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1540 unsigned long flags
;
1542 struct rcu_node
*rnp
;
1544 rcu_for_each_leaf_node(rsp
, rnp
) {
1546 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1547 if (!rcu_gp_in_progress(rsp
)) {
1548 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1551 if (rnp
->qsmask
== 0) {
1552 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1557 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1558 if ((rnp
->qsmask
& bit
) != 0 &&
1559 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1564 /* rcu_report_qs_rnp() releases rnp->lock. */
1565 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1568 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1570 rnp
= rcu_get_root(rsp
);
1571 if (rnp
->qsmask
== 0) {
1572 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1573 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1578 * Force quiescent states on reluctant CPUs, and also detect which
1579 * CPUs are in dyntick-idle mode.
1581 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1583 unsigned long flags
;
1584 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1586 trace_rcu_utilization("Start fqs");
1587 if (!rcu_gp_in_progress(rsp
)) {
1588 trace_rcu_utilization("End fqs");
1589 return; /* No grace period in progress, nothing to force. */
1591 if (!raw_spin_trylock_irqsave(&rsp
->fqslock
, flags
)) {
1592 rsp
->n_force_qs_lh
++; /* Inexact, can lose counts. Tough! */
1593 trace_rcu_utilization("End fqs");
1594 return; /* Someone else is already on the job. */
1596 if (relaxed
&& ULONG_CMP_GE(rsp
->jiffies_force_qs
, jiffies
))
1597 goto unlock_fqs_ret
; /* no emergency and done recently. */
1599 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1600 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
1601 if(!rcu_gp_in_progress(rsp
)) {
1602 rsp
->n_force_qs_ngp
++;
1603 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1604 goto unlock_fqs_ret
; /* no GP in progress, time updated. */
1606 rsp
->fqs_active
= 1;
1607 switch (rsp
->fqs_state
) {
1611 break; /* grace period idle or initializing, ignore. */
1613 case RCU_SAVE_DYNTICK
:
1614 if (RCU_SIGNAL_INIT
!= RCU_SAVE_DYNTICK
)
1615 break; /* So gcc recognizes the dead code. */
1617 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1619 /* Record dyntick-idle state. */
1620 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1621 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1622 if (rcu_gp_in_progress(rsp
))
1623 rsp
->fqs_state
= RCU_FORCE_QS
;
1628 /* Check dyntick-idle state, send IPI to laggarts. */
1629 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1630 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1632 /* Leave state in case more forcing is required. */
1634 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1637 rsp
->fqs_active
= 0;
1638 if (rsp
->fqs_need_gp
) {
1639 raw_spin_unlock(&rsp
->fqslock
); /* irqs remain disabled */
1640 rsp
->fqs_need_gp
= 0;
1641 rcu_start_gp(rsp
, flags
); /* releases rnp->lock */
1642 trace_rcu_utilization("End fqs");
1645 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1647 raw_spin_unlock_irqrestore(&rsp
->fqslock
, flags
);
1648 trace_rcu_utilization("End fqs");
1651 #else /* #ifdef CONFIG_SMP */
1653 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1658 #endif /* #else #ifdef CONFIG_SMP */
1661 * This does the RCU core processing work for the specified rcu_state
1662 * and rcu_data structures. This may be called only from the CPU to
1663 * whom the rdp belongs.
1666 __rcu_process_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1668 unsigned long flags
;
1670 WARN_ON_ONCE(rdp
->beenonline
== 0);
1673 * If an RCU GP has gone long enough, go check for dyntick
1674 * idle CPUs and, if needed, send resched IPIs.
1676 if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1677 force_quiescent_state(rsp
, 1);
1680 * Advance callbacks in response to end of earlier grace
1681 * period that some other CPU ended.
1683 rcu_process_gp_end(rsp
, rdp
);
1685 /* Update RCU state based on any recent quiescent states. */
1686 rcu_check_quiescent_state(rsp
, rdp
);
1688 /* Does this CPU require a not-yet-started grace period? */
1689 if (cpu_needs_another_gp(rsp
, rdp
)) {
1690 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1691 rcu_start_gp(rsp
, flags
); /* releases above lock */
1694 /* If there are callbacks ready, invoke them. */
1695 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1696 invoke_rcu_callbacks(rsp
, rdp
);
1700 * Do RCU core processing for the current CPU.
1702 static void rcu_process_callbacks(struct softirq_action
*unused
)
1704 trace_rcu_utilization("Start RCU core");
1705 __rcu_process_callbacks(&rcu_sched_state
,
1706 &__get_cpu_var(rcu_sched_data
));
1707 __rcu_process_callbacks(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1708 rcu_preempt_process_callbacks();
1709 trace_rcu_utilization("End RCU core");
1713 * Schedule RCU callback invocation. If the specified type of RCU
1714 * does not support RCU priority boosting, just do a direct call,
1715 * otherwise wake up the per-CPU kernel kthread. Note that because we
1716 * are running on the current CPU with interrupts disabled, the
1717 * rcu_cpu_kthread_task cannot disappear out from under us.
1719 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1721 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
1723 if (likely(!rsp
->boost
)) {
1724 rcu_do_batch(rsp
, rdp
);
1727 invoke_rcu_callbacks_kthread();
1730 static void invoke_rcu_core(void)
1732 raise_softirq(RCU_SOFTIRQ
);
1736 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1737 struct rcu_state
*rsp
, bool lazy
)
1739 unsigned long flags
;
1740 struct rcu_data
*rdp
;
1742 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
1743 debug_rcu_head_queue(head
);
1747 smp_mb(); /* Ensure RCU update seen before callback registry. */
1750 * Opportunistically note grace-period endings and beginnings.
1751 * Note that we might see a beginning right after we see an
1752 * end, but never vice versa, since this CPU has to pass through
1753 * a quiescent state betweentimes.
1755 local_irq_save(flags
);
1756 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1757 rdp
= this_cpu_ptr(rsp
->rda
);
1759 /* Add the callback to our list. */
1760 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1761 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1766 if (__is_kfree_rcu_offset((unsigned long)func
))
1767 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
1768 rdp
->qlen_lazy
, rdp
->qlen
);
1770 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
1772 /* If interrupts were disabled, don't dive into RCU core. */
1773 if (irqs_disabled_flags(flags
)) {
1774 local_irq_restore(flags
);
1779 * Force the grace period if too many callbacks or too long waiting.
1780 * Enforce hysteresis, and don't invoke force_quiescent_state()
1781 * if some other CPU has recently done so. Also, don't bother
1782 * invoking force_quiescent_state() if the newly enqueued callback
1783 * is the only one waiting for a grace period to complete.
1785 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1787 /* Are we ignoring a completed grace period? */
1788 rcu_process_gp_end(rsp
, rdp
);
1789 check_for_new_grace_period(rsp
, rdp
);
1791 /* Start a new grace period if one not already started. */
1792 if (!rcu_gp_in_progress(rsp
)) {
1793 unsigned long nestflag
;
1794 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1796 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1797 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
1799 /* Give the grace period a kick. */
1800 rdp
->blimit
= LONG_MAX
;
1801 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1802 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1803 force_quiescent_state(rsp
, 0);
1804 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1805 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1807 } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1808 force_quiescent_state(rsp
, 1);
1809 local_irq_restore(flags
);
1813 * Queue an RCU-sched callback for invocation after a grace period.
1815 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1817 __call_rcu(head
, func
, &rcu_sched_state
, 0);
1819 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1822 * Queue an RCU callback for invocation after a quicker grace period.
1824 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1826 __call_rcu(head
, func
, &rcu_bh_state
, 0);
1828 EXPORT_SYMBOL_GPL(call_rcu_bh
);
1831 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1833 * Control will return to the caller some time after a full rcu-sched
1834 * grace period has elapsed, in other words after all currently executing
1835 * rcu-sched read-side critical sections have completed. These read-side
1836 * critical sections are delimited by rcu_read_lock_sched() and
1837 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1838 * local_irq_disable(), and so on may be used in place of
1839 * rcu_read_lock_sched().
1841 * This means that all preempt_disable code sequences, including NMI and
1842 * hardware-interrupt handlers, in progress on entry will have completed
1843 * before this primitive returns. However, this does not guarantee that
1844 * softirq handlers will have completed, since in some kernels, these
1845 * handlers can run in process context, and can block.
1847 * This primitive provides the guarantees made by the (now removed)
1848 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1849 * guarantees that rcu_read_lock() sections will have completed.
1850 * In "classic RCU", these two guarantees happen to be one and
1851 * the same, but can differ in realtime RCU implementations.
1853 void synchronize_sched(void)
1855 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
1856 !lock_is_held(&rcu_lock_map
) &&
1857 !lock_is_held(&rcu_sched_lock_map
),
1858 "Illegal synchronize_sched() in RCU-sched read-side critical section");
1859 if (rcu_blocking_is_gp())
1861 wait_rcu_gp(call_rcu_sched
);
1863 EXPORT_SYMBOL_GPL(synchronize_sched
);
1866 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1868 * Control will return to the caller some time after a full rcu_bh grace
1869 * period has elapsed, in other words after all currently executing rcu_bh
1870 * read-side critical sections have completed. RCU read-side critical
1871 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1872 * and may be nested.
1874 void synchronize_rcu_bh(void)
1876 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
1877 !lock_is_held(&rcu_lock_map
) &&
1878 !lock_is_held(&rcu_sched_lock_map
),
1879 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
1880 if (rcu_blocking_is_gp())
1882 wait_rcu_gp(call_rcu_bh
);
1884 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
1887 * Check to see if there is any immediate RCU-related work to be done
1888 * by the current CPU, for the specified type of RCU, returning 1 if so.
1889 * The checks are in order of increasing expense: checks that can be
1890 * carried out against CPU-local state are performed first. However,
1891 * we must check for CPU stalls first, else we might not get a chance.
1893 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1895 struct rcu_node
*rnp
= rdp
->mynode
;
1897 rdp
->n_rcu_pending
++;
1899 /* Check for CPU stalls, if enabled. */
1900 check_cpu_stall(rsp
, rdp
);
1902 /* Is the RCU core waiting for a quiescent state from this CPU? */
1903 if (rcu_scheduler_fully_active
&&
1904 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
1907 * If force_quiescent_state() coming soon and this CPU
1908 * needs a quiescent state, and this is either RCU-sched
1909 * or RCU-bh, force a local reschedule.
1911 rdp
->n_rp_qs_pending
++;
1912 if (!rdp
->preemptible
&&
1913 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
) - 1,
1916 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
1917 rdp
->n_rp_report_qs
++;
1921 /* Does this CPU have callbacks ready to invoke? */
1922 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
1923 rdp
->n_rp_cb_ready
++;
1927 /* Has RCU gone idle with this CPU needing another grace period? */
1928 if (cpu_needs_another_gp(rsp
, rdp
)) {
1929 rdp
->n_rp_cpu_needs_gp
++;
1933 /* Has another RCU grace period completed? */
1934 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
1935 rdp
->n_rp_gp_completed
++;
1939 /* Has a new RCU grace period started? */
1940 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
1941 rdp
->n_rp_gp_started
++;
1945 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1946 if (rcu_gp_in_progress(rsp
) &&
1947 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
)) {
1948 rdp
->n_rp_need_fqs
++;
1953 rdp
->n_rp_need_nothing
++;
1958 * Check to see if there is any immediate RCU-related work to be done
1959 * by the current CPU, returning 1 if so. This function is part of the
1960 * RCU implementation; it is -not- an exported member of the RCU API.
1962 static int rcu_pending(int cpu
)
1964 return __rcu_pending(&rcu_sched_state
, &per_cpu(rcu_sched_data
, cpu
)) ||
1965 __rcu_pending(&rcu_bh_state
, &per_cpu(rcu_bh_data
, cpu
)) ||
1966 rcu_preempt_pending(cpu
);
1970 * Check to see if any future RCU-related work will need to be done
1971 * by the current CPU, even if none need be done immediately, returning
1974 static int rcu_cpu_has_callbacks(int cpu
)
1976 /* RCU callbacks either ready or pending? */
1977 return per_cpu(rcu_sched_data
, cpu
).nxtlist
||
1978 per_cpu(rcu_bh_data
, cpu
).nxtlist
||
1979 rcu_preempt_needs_cpu(cpu
);
1982 static DEFINE_PER_CPU(struct rcu_head
, rcu_barrier_head
) = {NULL
};
1983 static atomic_t rcu_barrier_cpu_count
;
1984 static DEFINE_MUTEX(rcu_barrier_mutex
);
1985 static struct completion rcu_barrier_completion
;
1987 static void rcu_barrier_callback(struct rcu_head
*notused
)
1989 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
1990 complete(&rcu_barrier_completion
);
1994 * Called with preemption disabled, and from cross-cpu IRQ context.
1996 static void rcu_barrier_func(void *type
)
1998 int cpu
= smp_processor_id();
1999 struct rcu_head
*head
= &per_cpu(rcu_barrier_head
, cpu
);
2000 void (*call_rcu_func
)(struct rcu_head
*head
,
2001 void (*func
)(struct rcu_head
*head
));
2003 atomic_inc(&rcu_barrier_cpu_count
);
2004 call_rcu_func
= type
;
2005 call_rcu_func(head
, rcu_barrier_callback
);
2009 * Orchestrate the specified type of RCU barrier, waiting for all
2010 * RCU callbacks of the specified type to complete.
2012 static void _rcu_barrier(struct rcu_state
*rsp
,
2013 void (*call_rcu_func
)(struct rcu_head
*head
,
2014 void (*func
)(struct rcu_head
*head
)))
2016 BUG_ON(in_interrupt());
2017 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2018 mutex_lock(&rcu_barrier_mutex
);
2019 init_completion(&rcu_barrier_completion
);
2021 * Initialize rcu_barrier_cpu_count to 1, then invoke
2022 * rcu_barrier_func() on each CPU, so that each CPU also has
2023 * incremented rcu_barrier_cpu_count. Only then is it safe to
2024 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
2025 * might complete its grace period before all of the other CPUs
2026 * did their increment, causing this function to return too
2027 * early. Note that on_each_cpu() disables irqs, which prevents
2028 * any CPUs from coming online or going offline until each online
2029 * CPU has queued its RCU-barrier callback.
2031 atomic_set(&rcu_barrier_cpu_count
, 1);
2032 on_each_cpu(rcu_barrier_func
, (void *)call_rcu_func
, 1);
2033 if (atomic_dec_and_test(&rcu_barrier_cpu_count
))
2034 complete(&rcu_barrier_completion
);
2035 wait_for_completion(&rcu_barrier_completion
);
2036 mutex_unlock(&rcu_barrier_mutex
);
2040 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2042 void rcu_barrier_bh(void)
2044 _rcu_barrier(&rcu_bh_state
, call_rcu_bh
);
2046 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2049 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2051 void rcu_barrier_sched(void)
2053 _rcu_barrier(&rcu_sched_state
, call_rcu_sched
);
2055 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2058 * Do boot-time initialization of a CPU's per-CPU RCU data.
2061 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2063 unsigned long flags
;
2065 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2066 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2068 /* Set up local state, ensuring consistent view of global state. */
2069 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2070 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2071 rdp
->nxtlist
= NULL
;
2072 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
2073 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
2076 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2077 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_NESTING
);
2078 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2081 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2085 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2086 * offline event can be happening at a given time. Note also that we
2087 * can accept some slop in the rsp->completed access due to the fact
2088 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2090 static void __cpuinit
2091 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2093 unsigned long flags
;
2095 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2096 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2098 /* Set up local state, ensuring consistent view of global state. */
2099 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2100 rdp
->beenonline
= 1; /* We have now been online. */
2101 rdp
->preemptible
= preemptible
;
2102 rdp
->qlen_last_fqs_check
= 0;
2103 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2104 rdp
->blimit
= blimit
;
2105 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_NESTING
;
2106 atomic_set(&rdp
->dynticks
->dynticks
,
2107 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
2108 rcu_prepare_for_idle_init(cpu
);
2109 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2112 * A new grace period might start here. If so, we won't be part
2113 * of it, but that is OK, as we are currently in a quiescent state.
2116 /* Exclude any attempts to start a new GP on large systems. */
2117 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
2119 /* Add CPU to rcu_node bitmasks. */
2121 mask
= rdp
->grpmask
;
2123 /* Exclude any attempts to start a new GP on small systems. */
2124 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2125 rnp
->qsmaskinit
|= mask
;
2126 mask
= rnp
->grpmask
;
2127 if (rnp
== rdp
->mynode
) {
2129 * If there is a grace period in progress, we will
2130 * set up to wait for it next time we run the
2133 rdp
->gpnum
= rnp
->completed
;
2134 rdp
->completed
= rnp
->completed
;
2135 rdp
->passed_quiesce
= 0;
2136 rdp
->qs_pending
= 0;
2137 rdp
->passed_quiesce_gpnum
= rnp
->gpnum
- 1;
2138 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2140 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2142 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2144 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2147 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2149 rcu_init_percpu_data(cpu
, &rcu_sched_state
, 0);
2150 rcu_init_percpu_data(cpu
, &rcu_bh_state
, 0);
2151 rcu_preempt_init_percpu_data(cpu
);
2155 * Handle CPU online/offline notification events.
2157 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2158 unsigned long action
, void *hcpu
)
2160 long cpu
= (long)hcpu
;
2161 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2162 struct rcu_node
*rnp
= rdp
->mynode
;
2164 trace_rcu_utilization("Start CPU hotplug");
2166 case CPU_UP_PREPARE
:
2167 case CPU_UP_PREPARE_FROZEN
:
2168 rcu_prepare_cpu(cpu
);
2169 rcu_prepare_kthreads(cpu
);
2172 case CPU_DOWN_FAILED
:
2173 rcu_node_kthread_setaffinity(rnp
, -1);
2174 rcu_cpu_kthread_setrt(cpu
, 1);
2176 case CPU_DOWN_PREPARE
:
2177 rcu_node_kthread_setaffinity(rnp
, cpu
);
2178 rcu_cpu_kthread_setrt(cpu
, 0);
2181 case CPU_DYING_FROZEN
:
2183 * The whole machine is "stopped" except this CPU, so we can
2184 * touch any data without introducing corruption. We send the
2185 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2187 rcu_cleanup_dying_cpu(&rcu_bh_state
);
2188 rcu_cleanup_dying_cpu(&rcu_sched_state
);
2189 rcu_preempt_cleanup_dying_cpu();
2190 rcu_cleanup_after_idle(cpu
);
2193 case CPU_DEAD_FROZEN
:
2194 case CPU_UP_CANCELED
:
2195 case CPU_UP_CANCELED_FROZEN
:
2196 rcu_cleanup_dead_cpu(cpu
, &rcu_bh_state
);
2197 rcu_cleanup_dead_cpu(cpu
, &rcu_sched_state
);
2198 rcu_preempt_cleanup_dead_cpu(cpu
);
2203 trace_rcu_utilization("End CPU hotplug");
2208 * This function is invoked towards the end of the scheduler's initialization
2209 * process. Before this is called, the idle task might contain
2210 * RCU read-side critical sections (during which time, this idle
2211 * task is booting the system). After this function is called, the
2212 * idle tasks are prohibited from containing RCU read-side critical
2213 * sections. This function also enables RCU lockdep checking.
2215 void rcu_scheduler_starting(void)
2217 WARN_ON(num_online_cpus() != 1);
2218 WARN_ON(nr_context_switches() > 0);
2219 rcu_scheduler_active
= 1;
2223 * Compute the per-level fanout, either using the exact fanout specified
2224 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2226 #ifdef CONFIG_RCU_FANOUT_EXACT
2227 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2231 for (i
= NUM_RCU_LVLS
- 1; i
> 0; i
--)
2232 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2233 rsp
->levelspread
[0] = RCU_FANOUT_LEAF
;
2235 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2236 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2243 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
2244 ccur
= rsp
->levelcnt
[i
];
2245 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2249 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2252 * Helper function for rcu_init() that initializes one rcu_state structure.
2254 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2255 struct rcu_data __percpu
*rda
)
2257 static char *buf
[] = { "rcu_node_level_0",
2260 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
2264 struct rcu_node
*rnp
;
2266 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2268 /* Initialize the level-tracking arrays. */
2270 for (i
= 1; i
< NUM_RCU_LVLS
; i
++)
2271 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2272 rcu_init_levelspread(rsp
);
2274 /* Initialize the elements themselves, starting from the leaves. */
2276 for (i
= NUM_RCU_LVLS
- 1; i
>= 0; i
--) {
2277 cpustride
*= rsp
->levelspread
[i
];
2278 rnp
= rsp
->level
[i
];
2279 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2280 raw_spin_lock_init(&rnp
->lock
);
2281 lockdep_set_class_and_name(&rnp
->lock
,
2282 &rcu_node_class
[i
], buf
[i
]);
2285 rnp
->qsmaskinit
= 0;
2286 rnp
->grplo
= j
* cpustride
;
2287 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2288 if (rnp
->grphi
>= NR_CPUS
)
2289 rnp
->grphi
= NR_CPUS
- 1;
2295 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2296 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2297 rnp
->parent
= rsp
->level
[i
- 1] +
2298 j
/ rsp
->levelspread
[i
- 1];
2301 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2306 rnp
= rsp
->level
[NUM_RCU_LVLS
- 1];
2307 for_each_possible_cpu(i
) {
2308 while (i
> rnp
->grphi
)
2310 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2311 rcu_boot_init_percpu_data(i
, rsp
);
2315 void __init
rcu_init(void)
2319 rcu_bootup_announce();
2320 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
2321 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
2322 __rcu_init_preempt();
2323 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
2326 * We don't need protection against CPU-hotplug here because
2327 * this is called early in boot, before either interrupts
2328 * or the scheduler are operational.
2330 cpu_notifier(rcu_cpu_notify
, 0);
2331 for_each_online_cpu(cpu
)
2332 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
2333 check_cpu_stall_init();
2336 #include "rcutree_plugin.h"