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>
53 #include <linux/delay.h>
54 #include <linux/stop_machine.h>
55 #include <linux/random.h>
58 #include <trace/events/rcu.h>
62 /* Data structures. */
64 static struct lock_class_key rcu_node_class
[RCU_NUM_LVLS
];
65 static struct lock_class_key rcu_fqs_class
[RCU_NUM_LVLS
];
67 #define RCU_STATE_INITIALIZER(sname, cr) { \
68 .level = { &sname##_state.node[0] }, \
70 .fqs_state = RCU_GP_IDLE, \
73 .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \
74 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
75 .orphan_donetail = &sname##_state.orphan_donelist, \
76 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
77 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
81 struct rcu_state rcu_sched_state
=
82 RCU_STATE_INITIALIZER(rcu_sched
, call_rcu_sched
);
83 DEFINE_PER_CPU(struct rcu_data
, rcu_sched_data
);
85 struct rcu_state rcu_bh_state
= RCU_STATE_INITIALIZER(rcu_bh
, call_rcu_bh
);
86 DEFINE_PER_CPU(struct rcu_data
, rcu_bh_data
);
88 static struct rcu_state
*rcu_state
;
89 LIST_HEAD(rcu_struct_flavors
);
91 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
92 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
93 module_param(rcu_fanout_leaf
, int, 0444);
94 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
95 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
102 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
105 * The rcu_scheduler_active variable transitions from zero to one just
106 * before the first task is spawned. So when this variable is zero, RCU
107 * can assume that there is but one task, allowing RCU to (for example)
108 * optimized synchronize_sched() to a simple barrier(). When this variable
109 * is one, RCU must actually do all the hard work required to detect real
110 * grace periods. This variable is also used to suppress boot-time false
111 * positives from lockdep-RCU error checking.
113 int rcu_scheduler_active __read_mostly
;
114 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
117 * The rcu_scheduler_fully_active variable transitions from zero to one
118 * during the early_initcall() processing, which is after the scheduler
119 * is capable of creating new tasks. So RCU processing (for example,
120 * creating tasks for RCU priority boosting) must be delayed until after
121 * rcu_scheduler_fully_active transitions from zero to one. We also
122 * currently delay invocation of any RCU callbacks until after this point.
124 * It might later prove better for people registering RCU callbacks during
125 * early boot to take responsibility for these callbacks, but one step at
128 static int rcu_scheduler_fully_active __read_mostly
;
130 #ifdef CONFIG_RCU_BOOST
133 * Control variables for per-CPU and per-rcu_node kthreads. These
134 * handle all flavors of RCU.
136 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
137 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
138 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
139 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
141 #endif /* #ifdef CONFIG_RCU_BOOST */
143 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
144 static void invoke_rcu_core(void);
145 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
148 * Track the rcutorture test sequence number and the update version
149 * number within a given test. The rcutorture_testseq is incremented
150 * on every rcutorture module load and unload, so has an odd value
151 * when a test is running. The rcutorture_vernum is set to zero
152 * when rcutorture starts and is incremented on each rcutorture update.
153 * These variables enable correlating rcutorture output with the
154 * RCU tracing information.
156 unsigned long rcutorture_testseq
;
157 unsigned long rcutorture_vernum
;
160 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
161 * permit this function to be invoked without holding the root rcu_node
162 * structure's ->lock, but of course results can be subject to change.
164 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
166 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
170 * Note a quiescent state. Because we do not need to know
171 * how many quiescent states passed, just if there was at least
172 * one since the start of the grace period, this just sets a flag.
173 * The caller must have disabled preemption.
175 void rcu_sched_qs(int cpu
)
177 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
179 if (rdp
->passed_quiesce
== 0)
180 trace_rcu_grace_period("rcu_sched", rdp
->gpnum
, "cpuqs");
181 rdp
->passed_quiesce
= 1;
184 void rcu_bh_qs(int cpu
)
186 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
188 if (rdp
->passed_quiesce
== 0)
189 trace_rcu_grace_period("rcu_bh", rdp
->gpnum
, "cpuqs");
190 rdp
->passed_quiesce
= 1;
194 * Note a context switch. This is a quiescent state for RCU-sched,
195 * and requires special handling for preemptible RCU.
196 * The caller must have disabled preemption.
198 void rcu_note_context_switch(int cpu
)
200 trace_rcu_utilization("Start context switch");
202 rcu_preempt_note_context_switch(cpu
);
203 trace_rcu_utilization("End context switch");
205 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
207 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
208 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
209 .dynticks
= ATOMIC_INIT(1),
210 #if defined(CONFIG_RCU_USER_QS) && !defined(CONFIG_RCU_USER_QS_FORCE)
211 .ignore_user_qs
= true,
215 static int blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
216 static int qhimark
= 10000; /* If this many pending, ignore blimit. */
217 static int qlowmark
= 100; /* Once only this many pending, use blimit. */
219 module_param(blimit
, int, 0444);
220 module_param(qhimark
, int, 0444);
221 module_param(qlowmark
, int, 0444);
223 int rcu_cpu_stall_suppress __read_mostly
; /* 1 = suppress stall warnings. */
224 int rcu_cpu_stall_timeout __read_mostly
= CONFIG_RCU_CPU_STALL_TIMEOUT
;
226 module_param(rcu_cpu_stall_suppress
, int, 0644);
227 module_param(rcu_cpu_stall_timeout
, int, 0644);
229 static ulong jiffies_till_first_fqs
= RCU_JIFFIES_TILL_FORCE_QS
;
230 static ulong jiffies_till_next_fqs
= RCU_JIFFIES_TILL_FORCE_QS
;
232 module_param(jiffies_till_first_fqs
, ulong
, 0644);
233 module_param(jiffies_till_next_fqs
, ulong
, 0644);
235 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*));
236 static void force_quiescent_state(struct rcu_state
*rsp
);
237 static int rcu_pending(int cpu
);
240 * Return the number of RCU-sched batches processed thus far for debug & stats.
242 long rcu_batches_completed_sched(void)
244 return rcu_sched_state
.completed
;
246 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
249 * Return the number of RCU BH batches processed thus far for debug & stats.
251 long rcu_batches_completed_bh(void)
253 return rcu_bh_state
.completed
;
255 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
258 * Force a quiescent state for RCU BH.
260 void rcu_bh_force_quiescent_state(void)
262 force_quiescent_state(&rcu_bh_state
);
264 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
267 * Record the number of times rcutorture tests have been initiated and
268 * terminated. This information allows the debugfs tracing stats to be
269 * correlated to the rcutorture messages, even when the rcutorture module
270 * is being repeatedly loaded and unloaded. In other words, we cannot
271 * store this state in rcutorture itself.
273 void rcutorture_record_test_transition(void)
275 rcutorture_testseq
++;
276 rcutorture_vernum
= 0;
278 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
281 * Record the number of writer passes through the current rcutorture test.
282 * This is also used to correlate debugfs tracing stats with the rcutorture
285 void rcutorture_record_progress(unsigned long vernum
)
289 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
292 * Force a quiescent state for RCU-sched.
294 void rcu_sched_force_quiescent_state(void)
296 force_quiescent_state(&rcu_sched_state
);
298 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
301 * Does the CPU have callbacks ready to be invoked?
304 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
306 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
];
310 * Does the current CPU require a yet-as-unscheduled grace period?
313 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
315 return *rdp
->nxttail
[RCU_DONE_TAIL
+
316 ACCESS_ONCE(rsp
->completed
) != rdp
->completed
] &&
317 !rcu_gp_in_progress(rsp
);
321 * Return the root node of the specified rcu_state structure.
323 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
325 return &rsp
->node
[0];
329 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
331 * If the new value of the ->dynticks_nesting counter now is zero,
332 * we really have entered idle, and must do the appropriate accounting.
333 * The caller must have disabled interrupts.
335 static void rcu_eqs_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
,
338 trace_rcu_dyntick("Start", oldval
, 0);
339 if (!user
&& !is_idle_task(current
)) {
340 struct task_struct
*idle
= idle_task(smp_processor_id());
342 trace_rcu_dyntick("Error on entry: not idle task", oldval
, 0);
343 ftrace_dump(DUMP_ORIG
);
344 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
345 current
->pid
, current
->comm
,
346 idle
->pid
, idle
->comm
); /* must be idle task! */
348 rcu_prepare_for_idle(smp_processor_id());
349 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
350 smp_mb__before_atomic_inc(); /* See above. */
351 atomic_inc(&rdtp
->dynticks
);
352 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
353 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
356 * It is illegal to enter an extended quiescent state while
357 * in an RCU read-side critical section.
359 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
360 "Illegal idle entry in RCU read-side critical section.");
361 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
362 "Illegal idle entry in RCU-bh read-side critical section.");
363 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
364 "Illegal idle entry in RCU-sched read-side critical section.");
368 * Enter an RCU extended quiescent state, which can be either the
369 * idle loop or adaptive-tickless usermode execution.
371 static void rcu_eqs_enter(bool user
)
374 struct rcu_dynticks
*rdtp
;
376 rdtp
= &__get_cpu_var(rcu_dynticks
);
377 oldval
= rdtp
->dynticks_nesting
;
378 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
379 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
)
380 rdtp
->dynticks_nesting
= 0;
382 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
383 rcu_eqs_enter_common(rdtp
, oldval
, user
);
387 * rcu_idle_enter - inform RCU that current CPU is entering idle
389 * Enter idle mode, in other words, -leave- the mode in which RCU
390 * read-side critical sections can occur. (Though RCU read-side
391 * critical sections can occur in irq handlers in idle, a possibility
392 * handled by irq_enter() and irq_exit().)
394 * We crowbar the ->dynticks_nesting field to zero to allow for
395 * the possibility of usermode upcalls having messed up our count
396 * of interrupt nesting level during the prior busy period.
398 void rcu_idle_enter(void)
402 local_irq_save(flags
);
403 rcu_eqs_enter(false);
404 local_irq_restore(flags
);
406 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
408 #ifdef CONFIG_RCU_USER_QS
410 * rcu_user_enter - inform RCU that we are resuming userspace.
412 * Enter RCU idle mode right before resuming userspace. No use of RCU
413 * is permitted between this call and rcu_user_exit(). This way the
414 * CPU doesn't need to maintain the tick for RCU maintenance purposes
415 * when the CPU runs in userspace.
417 void rcu_user_enter(void)
420 struct rcu_dynticks
*rdtp
;
423 * Some contexts may involve an exception occuring in an irq,
424 * leading to that nesting:
425 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
426 * This would mess up the dyntick_nesting count though. And rcu_irq_*()
427 * helpers are enough to protect RCU uses inside the exception. So
428 * just return immediately if we detect we are in an IRQ.
433 WARN_ON_ONCE(!current
->mm
);
435 local_irq_save(flags
);
436 rdtp
= &__get_cpu_var(rcu_dynticks
);
437 if (!rdtp
->ignore_user_qs
&& !rdtp
->in_user
) {
438 rdtp
->in_user
= true;
441 local_irq_restore(flags
);
445 * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
446 * after the current irq returns.
448 * This is similar to rcu_user_enter() but in the context of a non-nesting
449 * irq. After this call, RCU enters into idle mode when the interrupt
452 void rcu_user_enter_after_irq(void)
455 struct rcu_dynticks
*rdtp
;
457 local_irq_save(flags
);
458 rdtp
= &__get_cpu_var(rcu_dynticks
);
459 /* Ensure this irq is interrupting a non-idle RCU state. */
460 WARN_ON_ONCE(!(rdtp
->dynticks_nesting
& DYNTICK_TASK_MASK
));
461 rdtp
->dynticks_nesting
= 1;
462 local_irq_restore(flags
);
464 #endif /* CONFIG_RCU_USER_QS */
467 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
469 * Exit from an interrupt handler, which might possibly result in entering
470 * idle mode, in other words, leaving the mode in which read-side critical
471 * sections can occur.
473 * This code assumes that the idle loop never does anything that might
474 * result in unbalanced calls to irq_enter() and irq_exit(). If your
475 * architecture violates this assumption, RCU will give you what you
476 * deserve, good and hard. But very infrequently and irreproducibly.
478 * Use things like work queues to work around this limitation.
480 * You have been warned.
482 void rcu_irq_exit(void)
486 struct rcu_dynticks
*rdtp
;
488 local_irq_save(flags
);
489 rdtp
= &__get_cpu_var(rcu_dynticks
);
490 oldval
= rdtp
->dynticks_nesting
;
491 rdtp
->dynticks_nesting
--;
492 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
493 if (rdtp
->dynticks_nesting
)
494 trace_rcu_dyntick("--=", oldval
, rdtp
->dynticks_nesting
);
496 rcu_eqs_enter_common(rdtp
, oldval
, true);
497 local_irq_restore(flags
);
501 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
503 * If the new value of the ->dynticks_nesting counter was previously zero,
504 * we really have exited idle, and must do the appropriate accounting.
505 * The caller must have disabled interrupts.
507 static void rcu_eqs_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
,
510 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
511 atomic_inc(&rdtp
->dynticks
);
512 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
513 smp_mb__after_atomic_inc(); /* See above. */
514 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
515 rcu_cleanup_after_idle(smp_processor_id());
516 trace_rcu_dyntick("End", oldval
, rdtp
->dynticks_nesting
);
517 if (!user
&& !is_idle_task(current
)) {
518 struct task_struct
*idle
= idle_task(smp_processor_id());
520 trace_rcu_dyntick("Error on exit: not idle task",
521 oldval
, rdtp
->dynticks_nesting
);
522 ftrace_dump(DUMP_ORIG
);
523 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
524 current
->pid
, current
->comm
,
525 idle
->pid
, idle
->comm
); /* must be idle task! */
530 * Exit an RCU extended quiescent state, which can be either the
531 * idle loop or adaptive-tickless usermode execution.
533 static void rcu_eqs_exit(bool user
)
535 struct rcu_dynticks
*rdtp
;
538 rdtp
= &__get_cpu_var(rcu_dynticks
);
539 oldval
= rdtp
->dynticks_nesting
;
540 WARN_ON_ONCE(oldval
< 0);
541 if (oldval
& DYNTICK_TASK_NEST_MASK
)
542 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
544 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
545 rcu_eqs_exit_common(rdtp
, oldval
, user
);
549 * rcu_idle_exit - inform RCU that current CPU is leaving idle
551 * Exit idle mode, in other words, -enter- the mode in which RCU
552 * read-side critical sections can occur.
554 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
555 * allow for the possibility of usermode upcalls messing up our count
556 * of interrupt nesting level during the busy period that is just
559 void rcu_idle_exit(void)
563 local_irq_save(flags
);
565 local_irq_restore(flags
);
567 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
569 #ifdef CONFIG_RCU_USER_QS
571 * rcu_user_exit - inform RCU that we are exiting userspace.
573 * Exit RCU idle mode while entering the kernel because it can
574 * run a RCU read side critical section anytime.
576 void rcu_user_exit(void)
579 struct rcu_dynticks
*rdtp
;
582 * Some contexts may involve an exception occuring in an irq,
583 * leading to that nesting:
584 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
585 * This would mess up the dyntick_nesting count though. And rcu_irq_*()
586 * helpers are enough to protect RCU uses inside the exception. So
587 * just return immediately if we detect we are in an IRQ.
592 local_irq_save(flags
);
593 rdtp
= &__get_cpu_var(rcu_dynticks
);
595 rdtp
->in_user
= false;
598 local_irq_restore(flags
);
602 * rcu_user_exit_after_irq - inform RCU that we won't resume to userspace
603 * idle mode after the current non-nesting irq returns.
605 * This is similar to rcu_user_exit() but in the context of an irq.
606 * This is called when the irq has interrupted a userspace RCU idle mode
607 * context. When the current non-nesting interrupt returns after this call,
608 * the CPU won't restore the RCU idle mode.
610 void rcu_user_exit_after_irq(void)
613 struct rcu_dynticks
*rdtp
;
615 local_irq_save(flags
);
616 rdtp
= &__get_cpu_var(rcu_dynticks
);
617 /* Ensure we are interrupting an RCU idle mode. */
618 WARN_ON_ONCE(rdtp
->dynticks_nesting
& DYNTICK_TASK_NEST_MASK
);
619 rdtp
->dynticks_nesting
+= DYNTICK_TASK_EXIT_IDLE
;
620 local_irq_restore(flags
);
622 #endif /* CONFIG_RCU_USER_QS */
625 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
627 * Enter an interrupt handler, which might possibly result in exiting
628 * idle mode, in other words, entering the mode in which read-side critical
629 * sections can occur.
631 * Note that the Linux kernel is fully capable of entering an interrupt
632 * handler that it never exits, for example when doing upcalls to
633 * user mode! This code assumes that the idle loop never does upcalls to
634 * user mode. If your architecture does do upcalls from the idle loop (or
635 * does anything else that results in unbalanced calls to the irq_enter()
636 * and irq_exit() functions), RCU will give you what you deserve, good
637 * and hard. But very infrequently and irreproducibly.
639 * Use things like work queues to work around this limitation.
641 * You have been warned.
643 void rcu_irq_enter(void)
646 struct rcu_dynticks
*rdtp
;
649 local_irq_save(flags
);
650 rdtp
= &__get_cpu_var(rcu_dynticks
);
651 oldval
= rdtp
->dynticks_nesting
;
652 rdtp
->dynticks_nesting
++;
653 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
655 trace_rcu_dyntick("++=", oldval
, rdtp
->dynticks_nesting
);
657 rcu_eqs_exit_common(rdtp
, oldval
, true);
658 local_irq_restore(flags
);
662 * rcu_nmi_enter - inform RCU of entry to NMI context
664 * If the CPU was idle with dynamic ticks active, and there is no
665 * irq handler running, this updates rdtp->dynticks_nmi to let the
666 * RCU grace-period handling know that the CPU is active.
668 void rcu_nmi_enter(void)
670 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
672 if (rdtp
->dynticks_nmi_nesting
== 0 &&
673 (atomic_read(&rdtp
->dynticks
) & 0x1))
675 rdtp
->dynticks_nmi_nesting
++;
676 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
677 atomic_inc(&rdtp
->dynticks
);
678 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
679 smp_mb__after_atomic_inc(); /* See above. */
680 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
684 * rcu_nmi_exit - inform RCU of exit from NMI context
686 * If the CPU was idle with dynamic ticks active, and there is no
687 * irq handler running, this updates rdtp->dynticks_nmi to let the
688 * RCU grace-period handling know that the CPU is no longer active.
690 void rcu_nmi_exit(void)
692 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
694 if (rdtp
->dynticks_nmi_nesting
== 0 ||
695 --rdtp
->dynticks_nmi_nesting
!= 0)
697 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
698 smp_mb__before_atomic_inc(); /* See above. */
699 atomic_inc(&rdtp
->dynticks
);
700 smp_mb__after_atomic_inc(); /* Force delay to next write. */
701 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
705 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
707 * If the current CPU is in its idle loop and is neither in an interrupt
708 * or NMI handler, return true.
710 int rcu_is_cpu_idle(void)
715 ret
= (atomic_read(&__get_cpu_var(rcu_dynticks
).dynticks
) & 0x1) == 0;
719 EXPORT_SYMBOL(rcu_is_cpu_idle
);
721 #ifdef CONFIG_RCU_USER_QS
722 void rcu_user_hooks_switch(struct task_struct
*prev
,
723 struct task_struct
*next
)
725 struct rcu_dynticks
*rdtp
;
727 /* Interrupts are disabled in context switch */
728 rdtp
= &__get_cpu_var(rcu_dynticks
);
729 if (!rdtp
->ignore_user_qs
) {
730 clear_tsk_thread_flag(prev
, TIF_NOHZ
);
731 set_tsk_thread_flag(next
, TIF_NOHZ
);
734 #endif /* #ifdef CONFIG_RCU_USER_QS */
736 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
739 * Is the current CPU online? Disable preemption to avoid false positives
740 * that could otherwise happen due to the current CPU number being sampled,
741 * this task being preempted, its old CPU being taken offline, resuming
742 * on some other CPU, then determining that its old CPU is now offline.
743 * It is OK to use RCU on an offline processor during initial boot, hence
744 * the check for rcu_scheduler_fully_active. Note also that it is OK
745 * for a CPU coming online to use RCU for one jiffy prior to marking itself
746 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
747 * offline to continue to use RCU for one jiffy after marking itself
748 * offline in the cpu_online_mask. This leniency is necessary given the
749 * non-atomic nature of the online and offline processing, for example,
750 * the fact that a CPU enters the scheduler after completing the CPU_DYING
753 * This is also why RCU internally marks CPUs online during the
754 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
756 * Disable checking if in an NMI handler because we cannot safely report
757 * errors from NMI handlers anyway.
759 bool rcu_lockdep_current_cpu_online(void)
761 struct rcu_data
*rdp
;
762 struct rcu_node
*rnp
;
768 rdp
= &__get_cpu_var(rcu_sched_data
);
770 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
771 !rcu_scheduler_fully_active
;
775 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
777 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
780 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
782 * If the current CPU is idle or running at a first-level (not nested)
783 * interrupt from idle, return true. The caller must have at least
784 * disabled preemption.
786 int rcu_is_cpu_rrupt_from_idle(void)
788 return __get_cpu_var(rcu_dynticks
).dynticks_nesting
<= 1;
792 * Snapshot the specified CPU's dynticks counter so that we can later
793 * credit them with an implicit quiescent state. Return 1 if this CPU
794 * is in dynticks idle mode, which is an extended quiescent state.
796 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
798 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
799 return (rdp
->dynticks_snap
& 0x1) == 0;
803 * Return true if the specified CPU has passed through a quiescent
804 * state by virtue of being in or having passed through an dynticks
805 * idle state since the last call to dyntick_save_progress_counter()
806 * for this same CPU, or by virtue of having been offline.
808 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
813 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
814 snap
= (unsigned int)rdp
->dynticks_snap
;
817 * If the CPU passed through or entered a dynticks idle phase with
818 * no active irq/NMI handlers, then we can safely pretend that the CPU
819 * already acknowledged the request to pass through a quiescent
820 * state. Either way, that CPU cannot possibly be in an RCU
821 * read-side critical section that started before the beginning
822 * of the current RCU grace period.
824 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
825 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "dti");
831 * Check for the CPU being offline, but only if the grace period
832 * is old enough. We don't need to worry about the CPU changing
833 * state: If we see it offline even once, it has been through a
836 * The reason for insisting that the grace period be at least
837 * one jiffy old is that CPUs that are not quite online and that
838 * have just gone offline can still execute RCU read-side critical
841 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
842 return 0; /* Grace period is not old enough. */
844 if (cpu_is_offline(rdp
->cpu
)) {
845 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "ofl");
852 static int jiffies_till_stall_check(void)
854 int till_stall_check
= ACCESS_ONCE(rcu_cpu_stall_timeout
);
857 * Limit check must be consistent with the Kconfig limits
858 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
860 if (till_stall_check
< 3) {
861 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 3;
862 till_stall_check
= 3;
863 } else if (till_stall_check
> 300) {
864 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 300;
865 till_stall_check
= 300;
867 return till_stall_check
* HZ
+ RCU_STALL_DELAY_DELTA
;
870 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
872 rsp
->gp_start
= jiffies
;
873 rsp
->jiffies_stall
= jiffies
+ jiffies_till_stall_check();
877 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
878 * for architectures that do not implement trigger_all_cpu_backtrace().
879 * The NMI-triggered stack traces are more accurate because they are
880 * printed by the target CPU.
882 static void rcu_dump_cpu_stacks(struct rcu_state
*rsp
)
886 struct rcu_node
*rnp
;
888 rcu_for_each_leaf_node(rsp
, rnp
) {
889 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
890 if (rnp
->qsmask
!= 0) {
891 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
892 if (rnp
->qsmask
& (1UL << cpu
))
893 dump_cpu_task(rnp
->grplo
+ cpu
);
895 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
899 static void print_other_cpu_stall(struct rcu_state
*rsp
)
905 struct rcu_node
*rnp
= rcu_get_root(rsp
);
908 /* Only let one CPU complain about others per time interval. */
910 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
911 delta
= jiffies
- rsp
->jiffies_stall
;
912 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
913 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
916 rsp
->jiffies_stall
= jiffies
+ 3 * jiffies_till_stall_check() + 3;
917 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
920 * OK, time to rat on our buddy...
921 * See Documentation/RCU/stallwarn.txt for info on how to debug
922 * RCU CPU stall warnings.
924 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks:",
926 print_cpu_stall_info_begin();
927 rcu_for_each_leaf_node(rsp
, rnp
) {
928 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
929 ndetected
+= rcu_print_task_stall(rnp
);
930 if (rnp
->qsmask
!= 0) {
931 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
932 if (rnp
->qsmask
& (1UL << cpu
)) {
933 print_cpu_stall_info(rsp
,
938 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
942 * Now rat on any tasks that got kicked up to the root rcu_node
943 * due to CPU offlining.
945 rnp
= rcu_get_root(rsp
);
946 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
947 ndetected
+= rcu_print_task_stall(rnp
);
948 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
950 print_cpu_stall_info_end();
951 for_each_possible_cpu(cpu
)
952 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
953 pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
954 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
),
955 rsp
->gpnum
, rsp
->completed
, totqlen
);
957 printk(KERN_ERR
"INFO: Stall ended before state dump start\n");
958 else if (!trigger_all_cpu_backtrace())
959 rcu_dump_cpu_stacks(rsp
);
961 /* Complain about tasks blocking the grace period. */
963 rcu_print_detail_task_stall(rsp
);
965 force_quiescent_state(rsp
); /* Kick them all. */
968 static void print_cpu_stall(struct rcu_state
*rsp
)
972 struct rcu_node
*rnp
= rcu_get_root(rsp
);
976 * OK, time to rat on ourselves...
977 * See Documentation/RCU/stallwarn.txt for info on how to debug
978 * RCU CPU stall warnings.
980 printk(KERN_ERR
"INFO: %s self-detected stall on CPU", rsp
->name
);
981 print_cpu_stall_info_begin();
982 print_cpu_stall_info(rsp
, smp_processor_id());
983 print_cpu_stall_info_end();
984 for_each_possible_cpu(cpu
)
985 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
986 pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
987 jiffies
- rsp
->gp_start
, rsp
->gpnum
, rsp
->completed
, totqlen
);
988 if (!trigger_all_cpu_backtrace())
991 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
992 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
993 rsp
->jiffies_stall
= jiffies
+
994 3 * jiffies_till_stall_check() + 3;
995 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
997 set_need_resched(); /* kick ourselves to get things going. */
1000 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1004 struct rcu_node
*rnp
;
1006 if (rcu_cpu_stall_suppress
)
1008 j
= ACCESS_ONCE(jiffies
);
1009 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
1011 if (rcu_gp_in_progress(rsp
) &&
1012 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && ULONG_CMP_GE(j
, js
)) {
1014 /* We haven't checked in, so go dump stack. */
1015 print_cpu_stall(rsp
);
1017 } else if (rcu_gp_in_progress(rsp
) &&
1018 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
1020 /* They had a few time units to dump stack, so complain. */
1021 print_other_cpu_stall(rsp
);
1025 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
1027 rcu_cpu_stall_suppress
= 1;
1032 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1034 * Set the stall-warning timeout way off into the future, thus preventing
1035 * any RCU CPU stall-warning messages from appearing in the current set of
1036 * RCU grace periods.
1038 * The caller must disable hard irqs.
1040 void rcu_cpu_stall_reset(void)
1042 struct rcu_state
*rsp
;
1044 for_each_rcu_flavor(rsp
)
1045 rsp
->jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
1048 static struct notifier_block rcu_panic_block
= {
1049 .notifier_call
= rcu_panic
,
1052 static void __init
check_cpu_stall_init(void)
1054 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
1058 * Update CPU-local rcu_data state to record the newly noticed grace period.
1059 * This is used both when we started the grace period and when we notice
1060 * that someone else started the grace period. The caller must hold the
1061 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
1062 * and must have irqs disabled.
1064 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1066 if (rdp
->gpnum
!= rnp
->gpnum
) {
1068 * If the current grace period is waiting for this CPU,
1069 * set up to detect a quiescent state, otherwise don't
1070 * go looking for one.
1072 rdp
->gpnum
= rnp
->gpnum
;
1073 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpustart");
1074 rdp
->passed_quiesce
= 0;
1075 rdp
->qs_pending
= !!(rnp
->qsmask
& rdp
->grpmask
);
1076 zero_cpu_stall_ticks(rdp
);
1080 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1082 unsigned long flags
;
1083 struct rcu_node
*rnp
;
1085 local_irq_save(flags
);
1087 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
1088 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1089 local_irq_restore(flags
);
1092 __note_new_gpnum(rsp
, rnp
, rdp
);
1093 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1097 * Did someone else start a new RCU grace period start since we last
1098 * checked? Update local state appropriately if so. Must be called
1099 * on the CPU corresponding to rdp.
1102 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1104 unsigned long flags
;
1107 local_irq_save(flags
);
1108 if (rdp
->gpnum
!= rsp
->gpnum
) {
1109 note_new_gpnum(rsp
, rdp
);
1112 local_irq_restore(flags
);
1117 * Initialize the specified rcu_data structure's callback list to empty.
1119 static void init_callback_list(struct rcu_data
*rdp
)
1123 rdp
->nxtlist
= NULL
;
1124 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1125 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1129 * Advance this CPU's callbacks, but only if the current grace period
1130 * has ended. This may be called only from the CPU to whom the rdp
1131 * belongs. In addition, the corresponding leaf rcu_node structure's
1132 * ->lock must be held by the caller, with irqs disabled.
1135 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1137 /* Did another grace period end? */
1138 if (rdp
->completed
!= rnp
->completed
) {
1140 /* Advance callbacks. No harm if list empty. */
1141 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
1142 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
1143 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1145 /* Remember that we saw this grace-period completion. */
1146 rdp
->completed
= rnp
->completed
;
1147 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuend");
1150 * If we were in an extended quiescent state, we may have
1151 * missed some grace periods that others CPUs handled on
1152 * our behalf. Catch up with this state to avoid noting
1153 * spurious new grace periods. If another grace period
1154 * has started, then rnp->gpnum will have advanced, so
1155 * we will detect this later on. Of course, any quiescent
1156 * states we found for the old GP are now invalid.
1158 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
)) {
1159 rdp
->gpnum
= rdp
->completed
;
1160 rdp
->passed_quiesce
= 0;
1164 * If RCU does not need a quiescent state from this CPU,
1165 * then make sure that this CPU doesn't go looking for one.
1167 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
1168 rdp
->qs_pending
= 0;
1173 * Advance this CPU's callbacks, but only if the current grace period
1174 * has ended. This may be called only from the CPU to whom the rdp
1178 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1180 unsigned long flags
;
1181 struct rcu_node
*rnp
;
1183 local_irq_save(flags
);
1185 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
1186 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1187 local_irq_restore(flags
);
1190 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1191 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1195 * Do per-CPU grace-period initialization for running CPU. The caller
1196 * must hold the lock of the leaf rcu_node structure corresponding to
1200 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1202 /* Prior grace period ended, so advance callbacks for current CPU. */
1203 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1205 /* Set state so that this CPU will detect the next quiescent state. */
1206 __note_new_gpnum(rsp
, rnp
, rdp
);
1210 * Initialize a new grace period.
1212 static int rcu_gp_init(struct rcu_state
*rsp
)
1214 struct rcu_data
*rdp
;
1215 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1217 raw_spin_lock_irq(&rnp
->lock
);
1218 rsp
->gp_flags
= 0; /* Clear all flags: New grace period. */
1220 if (rcu_gp_in_progress(rsp
)) {
1221 /* Grace period already in progress, don't start another. */
1222 raw_spin_unlock_irq(&rnp
->lock
);
1226 /* Advance to a new grace period and initialize state. */
1228 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, "start");
1229 record_gp_stall_check_time(rsp
);
1230 raw_spin_unlock_irq(&rnp
->lock
);
1232 /* Exclude any concurrent CPU-hotplug operations. */
1233 mutex_lock(&rsp
->onoff_mutex
);
1236 * Set the quiescent-state-needed bits in all the rcu_node
1237 * structures for all currently online CPUs in breadth-first order,
1238 * starting from the root rcu_node structure, relying on the layout
1239 * of the tree within the rsp->node[] array. Note that other CPUs
1240 * will access only the leaves of the hierarchy, thus seeing that no
1241 * grace period is in progress, at least until the corresponding
1242 * leaf node has been initialized. In addition, we have excluded
1243 * CPU-hotplug operations.
1245 * The grace period cannot complete until the initialization
1246 * process finishes, because this kthread handles both.
1248 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1249 raw_spin_lock_irq(&rnp
->lock
);
1250 rdp
= this_cpu_ptr(rsp
->rda
);
1251 rcu_preempt_check_blocked_tasks(rnp
);
1252 rnp
->qsmask
= rnp
->qsmaskinit
;
1253 rnp
->gpnum
= rsp
->gpnum
;
1254 WARN_ON_ONCE(rnp
->completed
!= rsp
->completed
);
1255 rnp
->completed
= rsp
->completed
;
1256 if (rnp
== rdp
->mynode
)
1257 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
1258 rcu_preempt_boost_start_gp(rnp
);
1259 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1260 rnp
->level
, rnp
->grplo
,
1261 rnp
->grphi
, rnp
->qsmask
);
1262 raw_spin_unlock_irq(&rnp
->lock
);
1263 #ifdef CONFIG_PROVE_RCU_DELAY
1264 if ((random32() % (rcu_num_nodes
* 8)) == 0)
1265 schedule_timeout_uninterruptible(2);
1266 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1270 mutex_unlock(&rsp
->onoff_mutex
);
1275 * Do one round of quiescent-state forcing.
1277 int rcu_gp_fqs(struct rcu_state
*rsp
, int fqs_state_in
)
1279 int fqs_state
= fqs_state_in
;
1280 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1283 if (fqs_state
== RCU_SAVE_DYNTICK
) {
1284 /* Collect dyntick-idle snapshots. */
1285 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1286 fqs_state
= RCU_FORCE_QS
;
1288 /* Handle dyntick-idle and offline CPUs. */
1289 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1291 /* Clear flag to prevent immediate re-entry. */
1292 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1293 raw_spin_lock_irq(&rnp
->lock
);
1294 rsp
->gp_flags
&= ~RCU_GP_FLAG_FQS
;
1295 raw_spin_unlock_irq(&rnp
->lock
);
1301 * Clean up after the old grace period.
1303 static void rcu_gp_cleanup(struct rcu_state
*rsp
)
1305 unsigned long gp_duration
;
1306 struct rcu_data
*rdp
;
1307 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1309 raw_spin_lock_irq(&rnp
->lock
);
1310 gp_duration
= jiffies
- rsp
->gp_start
;
1311 if (gp_duration
> rsp
->gp_max
)
1312 rsp
->gp_max
= gp_duration
;
1315 * We know the grace period is complete, but to everyone else
1316 * it appears to still be ongoing. But it is also the case
1317 * that to everyone else it looks like there is nothing that
1318 * they can do to advance the grace period. It is therefore
1319 * safe for us to drop the lock in order to mark the grace
1320 * period as completed in all of the rcu_node structures.
1322 raw_spin_unlock_irq(&rnp
->lock
);
1325 * Propagate new ->completed value to rcu_node structures so
1326 * that other CPUs don't have to wait until the start of the next
1327 * grace period to process their callbacks. This also avoids
1328 * some nasty RCU grace-period initialization races by forcing
1329 * the end of the current grace period to be completely recorded in
1330 * all of the rcu_node structures before the beginning of the next
1331 * grace period is recorded in any of the rcu_node structures.
1333 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1334 raw_spin_lock_irq(&rnp
->lock
);
1335 rnp
->completed
= rsp
->gpnum
;
1336 raw_spin_unlock_irq(&rnp
->lock
);
1339 rnp
= rcu_get_root(rsp
);
1340 raw_spin_lock_irq(&rnp
->lock
);
1342 rsp
->completed
= rsp
->gpnum
; /* Declare grace period done. */
1343 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, "end");
1344 rsp
->fqs_state
= RCU_GP_IDLE
;
1345 rdp
= this_cpu_ptr(rsp
->rda
);
1346 if (cpu_needs_another_gp(rsp
, rdp
))
1348 raw_spin_unlock_irq(&rnp
->lock
);
1352 * Body of kthread that handles grace periods.
1354 static int __noreturn
rcu_gp_kthread(void *arg
)
1359 struct rcu_state
*rsp
= arg
;
1360 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1364 /* Handle grace-period start. */
1366 wait_event_interruptible(rsp
->gp_wq
,
1369 if ((rsp
->gp_flags
& RCU_GP_FLAG_INIT
) &&
1373 flush_signals(current
);
1376 /* Handle quiescent-state forcing. */
1377 fqs_state
= RCU_SAVE_DYNTICK
;
1378 j
= jiffies_till_first_fqs
;
1381 jiffies_till_first_fqs
= HZ
;
1384 rsp
->jiffies_force_qs
= jiffies
+ j
;
1385 ret
= wait_event_interruptible_timeout(rsp
->gp_wq
,
1386 (rsp
->gp_flags
& RCU_GP_FLAG_FQS
) ||
1387 (!ACCESS_ONCE(rnp
->qsmask
) &&
1388 !rcu_preempt_blocked_readers_cgp(rnp
)),
1390 /* If grace period done, leave loop. */
1391 if (!ACCESS_ONCE(rnp
->qsmask
) &&
1392 !rcu_preempt_blocked_readers_cgp(rnp
))
1394 /* If time for quiescent-state forcing, do it. */
1395 if (ret
== 0 || (rsp
->gp_flags
& RCU_GP_FLAG_FQS
)) {
1396 fqs_state
= rcu_gp_fqs(rsp
, fqs_state
);
1399 /* Deal with stray signal. */
1401 flush_signals(current
);
1403 j
= jiffies_till_next_fqs
;
1406 jiffies_till_next_fqs
= HZ
;
1409 jiffies_till_next_fqs
= 1;
1413 /* Handle grace-period end. */
1414 rcu_gp_cleanup(rsp
);
1419 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1420 * in preparation for detecting the next grace period. The caller must hold
1421 * the root node's ->lock, which is released before return. Hard irqs must
1424 * Note that it is legal for a dying CPU (which is marked as offline) to
1425 * invoke this function. This can happen when the dying CPU reports its
1429 rcu_start_gp(struct rcu_state
*rsp
, unsigned long flags
)
1430 __releases(rcu_get_root(rsp
)->lock
)
1432 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1433 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1435 if (!rsp
->gp_kthread
||
1436 !cpu_needs_another_gp(rsp
, rdp
)) {
1438 * Either we have not yet spawned the grace-period
1439 * task or this CPU does not need another grace period.
1440 * Either way, don't start a new grace period.
1442 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1446 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1447 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1448 wake_up(&rsp
->gp_wq
);
1452 * Report a full set of quiescent states to the specified rcu_state
1453 * data structure. This involves cleaning up after the prior grace
1454 * period and letting rcu_start_gp() start up the next grace period
1455 * if one is needed. Note that the caller must hold rnp->lock, as
1456 * required by rcu_start_gp(), which will release it.
1458 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1459 __releases(rcu_get_root(rsp
)->lock
)
1461 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1462 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
1463 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1467 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1468 * Allows quiescent states for a group of CPUs to be reported at one go
1469 * to the specified rcu_node structure, though all the CPUs in the group
1470 * must be represented by the same rcu_node structure (which need not be
1471 * a leaf rcu_node structure, though it often will be). That structure's
1472 * lock must be held upon entry, and it is released before return.
1475 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1476 struct rcu_node
*rnp
, unsigned long flags
)
1477 __releases(rnp
->lock
)
1479 struct rcu_node
*rnp_c
;
1481 /* Walk up the rcu_node hierarchy. */
1483 if (!(rnp
->qsmask
& mask
)) {
1485 /* Our bit has already been cleared, so done. */
1486 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1489 rnp
->qsmask
&= ~mask
;
1490 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1491 mask
, rnp
->qsmask
, rnp
->level
,
1492 rnp
->grplo
, rnp
->grphi
,
1494 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1496 /* Other bits still set at this level, so done. */
1497 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1500 mask
= rnp
->grpmask
;
1501 if (rnp
->parent
== NULL
) {
1503 /* No more levels. Exit loop holding root lock. */
1507 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1510 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1511 WARN_ON_ONCE(rnp_c
->qsmask
);
1515 * Get here if we are the last CPU to pass through a quiescent
1516 * state for this grace period. Invoke rcu_report_qs_rsp()
1517 * to clean up and start the next grace period if one is needed.
1519 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1523 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1524 * structure. This must be either called from the specified CPU, or
1525 * called when the specified CPU is known to be offline (and when it is
1526 * also known that no other CPU is concurrently trying to help the offline
1527 * CPU). The lastcomp argument is used to make sure we are still in the
1528 * grace period of interest. We don't want to end the current grace period
1529 * based on quiescent states detected in an earlier grace period!
1532 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1534 unsigned long flags
;
1536 struct rcu_node
*rnp
;
1539 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1540 if (rdp
->passed_quiesce
== 0 || rdp
->gpnum
!= rnp
->gpnum
||
1541 rnp
->completed
== rnp
->gpnum
) {
1544 * The grace period in which this quiescent state was
1545 * recorded has ended, so don't report it upwards.
1546 * We will instead need a new quiescent state that lies
1547 * within the current grace period.
1549 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1550 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1553 mask
= rdp
->grpmask
;
1554 if ((rnp
->qsmask
& mask
) == 0) {
1555 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1557 rdp
->qs_pending
= 0;
1560 * This GP can't end until cpu checks in, so all of our
1561 * callbacks can be processed during the next GP.
1563 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1565 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1570 * Check to see if there is a new grace period of which this CPU
1571 * is not yet aware, and if so, set up local rcu_data state for it.
1572 * Otherwise, see if this CPU has just passed through its first
1573 * quiescent state for this grace period, and record that fact if so.
1576 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1578 /* If there is now a new grace period, record and return. */
1579 if (check_for_new_grace_period(rsp
, rdp
))
1583 * Does this CPU still need to do its part for current grace period?
1584 * If no, return and let the other CPUs do their part as well.
1586 if (!rdp
->qs_pending
)
1590 * Was there a quiescent state since the beginning of the grace
1591 * period? If no, then exit and wait for the next call.
1593 if (!rdp
->passed_quiesce
)
1597 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1600 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
);
1603 #ifdef CONFIG_HOTPLUG_CPU
1606 * Send the specified CPU's RCU callbacks to the orphanage. The
1607 * specified CPU must be offline, and the caller must hold the
1611 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1612 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1615 * Orphan the callbacks. First adjust the counts. This is safe
1616 * because ->onofflock excludes _rcu_barrier()'s adoption of
1617 * the callbacks, thus no memory barrier is required.
1619 if (rdp
->nxtlist
!= NULL
) {
1620 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1621 rsp
->qlen
+= rdp
->qlen
;
1622 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1624 ACCESS_ONCE(rdp
->qlen
) = 0;
1628 * Next, move those callbacks still needing a grace period to
1629 * the orphanage, where some other CPU will pick them up.
1630 * Some of the callbacks might have gone partway through a grace
1631 * period, but that is too bad. They get to start over because we
1632 * cannot assume that grace periods are synchronized across CPUs.
1633 * We don't bother updating the ->nxttail[] array yet, instead
1634 * we just reset the whole thing later on.
1636 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1637 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1638 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1639 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1643 * Then move the ready-to-invoke callbacks to the orphanage,
1644 * where some other CPU will pick them up. These will not be
1645 * required to pass though another grace period: They are done.
1647 if (rdp
->nxtlist
!= NULL
) {
1648 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1649 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1652 /* Finally, initialize the rcu_data structure's list to empty. */
1653 init_callback_list(rdp
);
1657 * Adopt the RCU callbacks from the specified rcu_state structure's
1658 * orphanage. The caller must hold the ->onofflock.
1660 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
)
1663 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1665 /* Do the accounting first. */
1666 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
1667 rdp
->qlen
+= rsp
->qlen
;
1668 rdp
->n_cbs_adopted
+= rsp
->qlen
;
1669 if (rsp
->qlen_lazy
!= rsp
->qlen
)
1670 rcu_idle_count_callbacks_posted();
1675 * We do not need a memory barrier here because the only way we
1676 * can get here if there is an rcu_barrier() in flight is if
1677 * we are the task doing the rcu_barrier().
1680 /* First adopt the ready-to-invoke callbacks. */
1681 if (rsp
->orphan_donelist
!= NULL
) {
1682 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1683 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
1684 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
1685 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1686 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
1687 rsp
->orphan_donelist
= NULL
;
1688 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
1691 /* And then adopt the callbacks that still need a grace period. */
1692 if (rsp
->orphan_nxtlist
!= NULL
) {
1693 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
1694 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
1695 rsp
->orphan_nxtlist
= NULL
;
1696 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
1701 * Trace the fact that this CPU is going offline.
1703 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1705 RCU_TRACE(unsigned long mask
);
1706 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
1707 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
1709 RCU_TRACE(mask
= rdp
->grpmask
);
1710 trace_rcu_grace_period(rsp
->name
,
1711 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
1716 * The CPU has been completely removed, and some other CPU is reporting
1717 * this fact from process context. Do the remainder of the cleanup,
1718 * including orphaning the outgoing CPU's RCU callbacks, and also
1719 * adopting them. There can only be one CPU hotplug operation at a time,
1720 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
1722 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1724 unsigned long flags
;
1726 int need_report
= 0;
1727 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1728 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
1730 /* Adjust any no-longer-needed kthreads. */
1731 rcu_boost_kthread_setaffinity(rnp
, -1);
1733 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
1735 /* Exclude any attempts to start a new grace period. */
1736 mutex_lock(&rsp
->onoff_mutex
);
1737 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
1739 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
1740 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
1741 rcu_adopt_orphan_cbs(rsp
);
1743 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1744 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1746 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1747 rnp
->qsmaskinit
&= ~mask
;
1748 if (rnp
->qsmaskinit
!= 0) {
1749 if (rnp
!= rdp
->mynode
)
1750 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1753 if (rnp
== rdp
->mynode
)
1754 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1756 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1757 mask
= rnp
->grpmask
;
1759 } while (rnp
!= NULL
);
1762 * We still hold the leaf rcu_node structure lock here, and
1763 * irqs are still disabled. The reason for this subterfuge is
1764 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1765 * held leads to deadlock.
1767 raw_spin_unlock(&rsp
->onofflock
); /* irqs remain disabled. */
1769 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1770 rcu_report_unblock_qs_rnp(rnp
, flags
);
1772 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1773 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1774 rcu_report_exp_rnp(rsp
, rnp
, true);
1775 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
1776 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
1777 cpu
, rdp
->qlen
, rdp
->nxtlist
);
1778 init_callback_list(rdp
);
1779 /* Disallow further callbacks on this CPU. */
1780 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
1781 mutex_unlock(&rsp
->onoff_mutex
);
1784 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1786 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1790 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1794 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1797 * Invoke any RCU callbacks that have made it to the end of their grace
1798 * period. Thottle as specified by rdp->blimit.
1800 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1802 unsigned long flags
;
1803 struct rcu_head
*next
, *list
, **tail
;
1804 int bl
, count
, count_lazy
, i
;
1806 /* If no callbacks are ready, just return.*/
1807 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
1808 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
1809 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
1810 need_resched(), is_idle_task(current
),
1811 rcu_is_callbacks_kthread());
1816 * Extract the list of ready callbacks, disabling to prevent
1817 * races with call_rcu() from interrupt handlers.
1819 local_irq_save(flags
);
1820 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1822 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
1823 list
= rdp
->nxtlist
;
1824 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1825 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1826 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1827 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
1828 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1829 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1830 local_irq_restore(flags
);
1832 /* Invoke callbacks. */
1833 count
= count_lazy
= 0;
1837 debug_rcu_head_unqueue(list
);
1838 if (__rcu_reclaim(rsp
->name
, list
))
1841 /* Stop only if limit reached and CPU has something to do. */
1842 if (++count
>= bl
&&
1844 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
1848 local_irq_save(flags
);
1849 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
1850 is_idle_task(current
),
1851 rcu_is_callbacks_kthread());
1853 /* Update count, and requeue any remaining callbacks. */
1855 *tail
= rdp
->nxtlist
;
1856 rdp
->nxtlist
= list
;
1857 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1858 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
1859 rdp
->nxttail
[i
] = tail
;
1863 smp_mb(); /* List handling before counting for rcu_barrier(). */
1864 rdp
->qlen_lazy
-= count_lazy
;
1865 ACCESS_ONCE(rdp
->qlen
) -= count
;
1866 rdp
->n_cbs_invoked
+= count
;
1868 /* Reinstate batch limit if we have worked down the excess. */
1869 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1870 rdp
->blimit
= blimit
;
1872 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1873 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1874 rdp
->qlen_last_fqs_check
= 0;
1875 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1876 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1877 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1878 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
1880 local_irq_restore(flags
);
1882 /* Re-invoke RCU core processing if there are callbacks remaining. */
1883 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1888 * Check to see if this CPU is in a non-context-switch quiescent state
1889 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1890 * Also schedule RCU core processing.
1892 * This function must be called from hardirq context. It is normally
1893 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1894 * false, there is no point in invoking rcu_check_callbacks().
1896 void rcu_check_callbacks(int cpu
, int user
)
1898 trace_rcu_utilization("Start scheduler-tick");
1899 increment_cpu_stall_ticks();
1900 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
1903 * Get here if this CPU took its interrupt from user
1904 * mode or from the idle loop, and if this is not a
1905 * nested interrupt. In this case, the CPU is in
1906 * a quiescent state, so note it.
1908 * No memory barrier is required here because both
1909 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1910 * variables that other CPUs neither access nor modify,
1911 * at least not while the corresponding CPU is online.
1917 } else if (!in_softirq()) {
1920 * Get here if this CPU did not take its interrupt from
1921 * softirq, in other words, if it is not interrupting
1922 * a rcu_bh read-side critical section. This is an _bh
1923 * critical section, so note it.
1928 rcu_preempt_check_callbacks(cpu
);
1929 if (rcu_pending(cpu
))
1931 trace_rcu_utilization("End scheduler-tick");
1935 * Scan the leaf rcu_node structures, processing dyntick state for any that
1936 * have not yet encountered a quiescent state, using the function specified.
1937 * Also initiate boosting for any threads blocked on the root rcu_node.
1939 * The caller must have suppressed start of new grace periods.
1941 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1945 unsigned long flags
;
1947 struct rcu_node
*rnp
;
1949 rcu_for_each_leaf_node(rsp
, rnp
) {
1952 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1953 if (!rcu_gp_in_progress(rsp
)) {
1954 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1957 if (rnp
->qsmask
== 0) {
1958 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1963 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1964 if ((rnp
->qsmask
& bit
) != 0 &&
1965 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1970 /* rcu_report_qs_rnp() releases rnp->lock. */
1971 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1974 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1976 rnp
= rcu_get_root(rsp
);
1977 if (rnp
->qsmask
== 0) {
1978 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1979 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1984 * Force quiescent states on reluctant CPUs, and also detect which
1985 * CPUs are in dyntick-idle mode.
1987 static void force_quiescent_state(struct rcu_state
*rsp
)
1989 unsigned long flags
;
1991 struct rcu_node
*rnp
;
1992 struct rcu_node
*rnp_old
= NULL
;
1994 /* Funnel through hierarchy to reduce memory contention. */
1995 rnp
= per_cpu_ptr(rsp
->rda
, raw_smp_processor_id())->mynode
;
1996 for (; rnp
!= NULL
; rnp
= rnp
->parent
) {
1997 ret
= (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) ||
1998 !raw_spin_trylock(&rnp
->fqslock
);
1999 if (rnp_old
!= NULL
)
2000 raw_spin_unlock(&rnp_old
->fqslock
);
2002 rsp
->n_force_qs_lh
++;
2007 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2009 /* Reached the root of the rcu_node tree, acquire lock. */
2010 raw_spin_lock_irqsave(&rnp_old
->lock
, flags
);
2011 raw_spin_unlock(&rnp_old
->fqslock
);
2012 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
2013 rsp
->n_force_qs_lh
++;
2014 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2015 return; /* Someone beat us to it. */
2017 rsp
->gp_flags
|= RCU_GP_FLAG_FQS
;
2018 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2019 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
2023 * This does the RCU core processing work for the specified rcu_state
2024 * and rcu_data structures. This may be called only from the CPU to
2025 * whom the rdp belongs.
2028 __rcu_process_callbacks(struct rcu_state
*rsp
)
2030 unsigned long flags
;
2031 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2033 WARN_ON_ONCE(rdp
->beenonline
== 0);
2036 * Advance callbacks in response to end of earlier grace
2037 * period that some other CPU ended.
2039 rcu_process_gp_end(rsp
, rdp
);
2041 /* Update RCU state based on any recent quiescent states. */
2042 rcu_check_quiescent_state(rsp
, rdp
);
2044 /* Does this CPU require a not-yet-started grace period? */
2045 if (cpu_needs_another_gp(rsp
, rdp
)) {
2046 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
2047 rcu_start_gp(rsp
, flags
); /* releases above lock */
2050 /* If there are callbacks ready, invoke them. */
2051 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2052 invoke_rcu_callbacks(rsp
, rdp
);
2056 * Do RCU core processing for the current CPU.
2058 static void rcu_process_callbacks(struct softirq_action
*unused
)
2060 struct rcu_state
*rsp
;
2062 if (cpu_is_offline(smp_processor_id()))
2064 trace_rcu_utilization("Start RCU core");
2065 for_each_rcu_flavor(rsp
)
2066 __rcu_process_callbacks(rsp
);
2067 trace_rcu_utilization("End RCU core");
2071 * Schedule RCU callback invocation. If the specified type of RCU
2072 * does not support RCU priority boosting, just do a direct call,
2073 * otherwise wake up the per-CPU kernel kthread. Note that because we
2074 * are running on the current CPU with interrupts disabled, the
2075 * rcu_cpu_kthread_task cannot disappear out from under us.
2077 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2079 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
2081 if (likely(!rsp
->boost
)) {
2082 rcu_do_batch(rsp
, rdp
);
2085 invoke_rcu_callbacks_kthread();
2088 static void invoke_rcu_core(void)
2090 raise_softirq(RCU_SOFTIRQ
);
2094 * Handle any core-RCU processing required by a call_rcu() invocation.
2096 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
2097 struct rcu_head
*head
, unsigned long flags
)
2100 * If called from an extended quiescent state, invoke the RCU
2101 * core in order to force a re-evaluation of RCU's idleness.
2103 if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
2106 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2107 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
2111 * Force the grace period if too many callbacks or too long waiting.
2112 * Enforce hysteresis, and don't invoke force_quiescent_state()
2113 * if some other CPU has recently done so. Also, don't bother
2114 * invoking force_quiescent_state() if the newly enqueued callback
2115 * is the only one waiting for a grace period to complete.
2117 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
2119 /* Are we ignoring a completed grace period? */
2120 rcu_process_gp_end(rsp
, rdp
);
2121 check_for_new_grace_period(rsp
, rdp
);
2123 /* Start a new grace period if one not already started. */
2124 if (!rcu_gp_in_progress(rsp
)) {
2125 unsigned long nestflag
;
2126 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
2128 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
2129 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
2131 /* Give the grace period a kick. */
2132 rdp
->blimit
= LONG_MAX
;
2133 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
2134 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
2135 force_quiescent_state(rsp
);
2136 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2137 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2143 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
2144 struct rcu_state
*rsp
, bool lazy
)
2146 unsigned long flags
;
2147 struct rcu_data
*rdp
;
2149 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
2150 debug_rcu_head_queue(head
);
2155 * Opportunistically note grace-period endings and beginnings.
2156 * Note that we might see a beginning right after we see an
2157 * end, but never vice versa, since this CPU has to pass through
2158 * a quiescent state betweentimes.
2160 local_irq_save(flags
);
2161 rdp
= this_cpu_ptr(rsp
->rda
);
2163 /* Add the callback to our list. */
2164 if (unlikely(rdp
->nxttail
[RCU_NEXT_TAIL
] == NULL
)) {
2165 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2167 local_irq_restore(flags
);
2170 ACCESS_ONCE(rdp
->qlen
)++;
2174 rcu_idle_count_callbacks_posted();
2175 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2176 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
2177 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
2179 if (__is_kfree_rcu_offset((unsigned long)func
))
2180 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
2181 rdp
->qlen_lazy
, rdp
->qlen
);
2183 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
2185 /* Go handle any RCU core processing required. */
2186 __call_rcu_core(rsp
, rdp
, head
, flags
);
2187 local_irq_restore(flags
);
2191 * Queue an RCU-sched callback for invocation after a grace period.
2193 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2195 __call_rcu(head
, func
, &rcu_sched_state
, 0);
2197 EXPORT_SYMBOL_GPL(call_rcu_sched
);
2200 * Queue an RCU callback for invocation after a quicker grace period.
2202 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2204 __call_rcu(head
, func
, &rcu_bh_state
, 0);
2206 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2209 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2210 * any blocking grace-period wait automatically implies a grace period
2211 * if there is only one CPU online at any point time during execution
2212 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2213 * occasionally incorrectly indicate that there are multiple CPUs online
2214 * when there was in fact only one the whole time, as this just adds
2215 * some overhead: RCU still operates correctly.
2217 static inline int rcu_blocking_is_gp(void)
2221 might_sleep(); /* Check for RCU read-side critical section. */
2223 ret
= num_online_cpus() <= 1;
2229 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2231 * Control will return to the caller some time after a full rcu-sched
2232 * grace period has elapsed, in other words after all currently executing
2233 * rcu-sched read-side critical sections have completed. These read-side
2234 * critical sections are delimited by rcu_read_lock_sched() and
2235 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2236 * local_irq_disable(), and so on may be used in place of
2237 * rcu_read_lock_sched().
2239 * This means that all preempt_disable code sequences, including NMI and
2240 * hardware-interrupt handlers, in progress on entry will have completed
2241 * before this primitive returns. However, this does not guarantee that
2242 * softirq handlers will have completed, since in some kernels, these
2243 * handlers can run in process context, and can block.
2245 * This primitive provides the guarantees made by the (now removed)
2246 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2247 * guarantees that rcu_read_lock() sections will have completed.
2248 * In "classic RCU", these two guarantees happen to be one and
2249 * the same, but can differ in realtime RCU implementations.
2251 void synchronize_sched(void)
2253 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2254 !lock_is_held(&rcu_lock_map
) &&
2255 !lock_is_held(&rcu_sched_lock_map
),
2256 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2257 if (rcu_blocking_is_gp())
2259 wait_rcu_gp(call_rcu_sched
);
2261 EXPORT_SYMBOL_GPL(synchronize_sched
);
2264 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2266 * Control will return to the caller some time after a full rcu_bh grace
2267 * period has elapsed, in other words after all currently executing rcu_bh
2268 * read-side critical sections have completed. RCU read-side critical
2269 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2270 * and may be nested.
2272 void synchronize_rcu_bh(void)
2274 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2275 !lock_is_held(&rcu_lock_map
) &&
2276 !lock_is_held(&rcu_sched_lock_map
),
2277 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2278 if (rcu_blocking_is_gp())
2280 wait_rcu_gp(call_rcu_bh
);
2282 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2284 static atomic_t sync_sched_expedited_started
= ATOMIC_INIT(0);
2285 static atomic_t sync_sched_expedited_done
= ATOMIC_INIT(0);
2287 static int synchronize_sched_expedited_cpu_stop(void *data
)
2290 * There must be a full memory barrier on each affected CPU
2291 * between the time that try_stop_cpus() is called and the
2292 * time that it returns.
2294 * In the current initial implementation of cpu_stop, the
2295 * above condition is already met when the control reaches
2296 * this point and the following smp_mb() is not strictly
2297 * necessary. Do smp_mb() anyway for documentation and
2298 * robustness against future implementation changes.
2300 smp_mb(); /* See above comment block. */
2305 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2307 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2308 * approach to force the grace period to end quickly. This consumes
2309 * significant time on all CPUs and is unfriendly to real-time workloads,
2310 * so is thus not recommended for any sort of common-case code. In fact,
2311 * if you are using synchronize_sched_expedited() in a loop, please
2312 * restructure your code to batch your updates, and then use a single
2313 * synchronize_sched() instead.
2315 * Note that it is illegal to call this function while holding any lock
2316 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2317 * to call this function from a CPU-hotplug notifier. Failing to observe
2318 * these restriction will result in deadlock.
2320 * This implementation can be thought of as an application of ticket
2321 * locking to RCU, with sync_sched_expedited_started and
2322 * sync_sched_expedited_done taking on the roles of the halves
2323 * of the ticket-lock word. Each task atomically increments
2324 * sync_sched_expedited_started upon entry, snapshotting the old value,
2325 * then attempts to stop all the CPUs. If this succeeds, then each
2326 * CPU will have executed a context switch, resulting in an RCU-sched
2327 * grace period. We are then done, so we use atomic_cmpxchg() to
2328 * update sync_sched_expedited_done to match our snapshot -- but
2329 * only if someone else has not already advanced past our snapshot.
2331 * On the other hand, if try_stop_cpus() fails, we check the value
2332 * of sync_sched_expedited_done. If it has advanced past our
2333 * initial snapshot, then someone else must have forced a grace period
2334 * some time after we took our snapshot. In this case, our work is
2335 * done for us, and we can simply return. Otherwise, we try again,
2336 * but keep our initial snapshot for purposes of checking for someone
2337 * doing our work for us.
2339 * If we fail too many times in a row, we fall back to synchronize_sched().
2341 void synchronize_sched_expedited(void)
2343 int firstsnap
, s
, snap
, trycount
= 0;
2345 /* Note that atomic_inc_return() implies full memory barrier. */
2346 firstsnap
= snap
= atomic_inc_return(&sync_sched_expedited_started
);
2348 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2351 * Each pass through the following loop attempts to force a
2352 * context switch on each CPU.
2354 while (try_stop_cpus(cpu_online_mask
,
2355 synchronize_sched_expedited_cpu_stop
,
2359 /* No joy, try again later. Or just synchronize_sched(). */
2360 if (trycount
++ < 10) {
2361 udelay(trycount
* num_online_cpus());
2363 synchronize_sched();
2367 /* Check to see if someone else did our work for us. */
2368 s
= atomic_read(&sync_sched_expedited_done
);
2369 if (UINT_CMP_GE((unsigned)s
, (unsigned)firstsnap
)) {
2370 smp_mb(); /* ensure test happens before caller kfree */
2375 * Refetching sync_sched_expedited_started allows later
2376 * callers to piggyback on our grace period. We subtract
2377 * 1 to get the same token that the last incrementer got.
2378 * We retry after they started, so our grace period works
2379 * for them, and they started after our first try, so their
2380 * grace period works for us.
2383 snap
= atomic_read(&sync_sched_expedited_started
);
2384 smp_mb(); /* ensure read is before try_stop_cpus(). */
2388 * Everyone up to our most recent fetch is covered by our grace
2389 * period. Update the counter, but only if our work is still
2390 * relevant -- which it won't be if someone who started later
2391 * than we did beat us to the punch.
2394 s
= atomic_read(&sync_sched_expedited_done
);
2395 if (UINT_CMP_GE((unsigned)s
, (unsigned)snap
)) {
2396 smp_mb(); /* ensure test happens before caller kfree */
2399 } while (atomic_cmpxchg(&sync_sched_expedited_done
, s
, snap
) != s
);
2403 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2406 * Check to see if there is any immediate RCU-related work to be done
2407 * by the current CPU, for the specified type of RCU, returning 1 if so.
2408 * The checks are in order of increasing expense: checks that can be
2409 * carried out against CPU-local state are performed first. However,
2410 * we must check for CPU stalls first, else we might not get a chance.
2412 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2414 struct rcu_node
*rnp
= rdp
->mynode
;
2416 rdp
->n_rcu_pending
++;
2418 /* Check for CPU stalls, if enabled. */
2419 check_cpu_stall(rsp
, rdp
);
2421 /* Is the RCU core waiting for a quiescent state from this CPU? */
2422 if (rcu_scheduler_fully_active
&&
2423 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2424 rdp
->n_rp_qs_pending
++;
2425 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2426 rdp
->n_rp_report_qs
++;
2430 /* Does this CPU have callbacks ready to invoke? */
2431 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2432 rdp
->n_rp_cb_ready
++;
2436 /* Has RCU gone idle with this CPU needing another grace period? */
2437 if (cpu_needs_another_gp(rsp
, rdp
)) {
2438 rdp
->n_rp_cpu_needs_gp
++;
2442 /* Has another RCU grace period completed? */
2443 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2444 rdp
->n_rp_gp_completed
++;
2448 /* Has a new RCU grace period started? */
2449 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2450 rdp
->n_rp_gp_started
++;
2455 rdp
->n_rp_need_nothing
++;
2460 * Check to see if there is any immediate RCU-related work to be done
2461 * by the current CPU, returning 1 if so. This function is part of the
2462 * RCU implementation; it is -not- an exported member of the RCU API.
2464 static int rcu_pending(int cpu
)
2466 struct rcu_state
*rsp
;
2468 for_each_rcu_flavor(rsp
)
2469 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2475 * Check to see if any future RCU-related work will need to be done
2476 * by the current CPU, even if none need be done immediately, returning
2479 static int rcu_cpu_has_callbacks(int cpu
)
2481 struct rcu_state
*rsp
;
2483 /* RCU callbacks either ready or pending? */
2484 for_each_rcu_flavor(rsp
)
2485 if (per_cpu_ptr(rsp
->rda
, cpu
)->nxtlist
)
2491 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2492 * the compiler is expected to optimize this away.
2494 static void _rcu_barrier_trace(struct rcu_state
*rsp
, char *s
,
2495 int cpu
, unsigned long done
)
2497 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2498 atomic_read(&rsp
->barrier_cpu_count
), done
);
2502 * RCU callback function for _rcu_barrier(). If we are last, wake
2503 * up the task executing _rcu_barrier().
2505 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2507 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2508 struct rcu_state
*rsp
= rdp
->rsp
;
2510 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2511 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2512 complete(&rsp
->barrier_completion
);
2514 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2519 * Called with preemption disabled, and from cross-cpu IRQ context.
2521 static void rcu_barrier_func(void *type
)
2523 struct rcu_state
*rsp
= type
;
2524 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2526 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2527 atomic_inc(&rsp
->barrier_cpu_count
);
2528 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2532 * Orchestrate the specified type of RCU barrier, waiting for all
2533 * RCU callbacks of the specified type to complete.
2535 static void _rcu_barrier(struct rcu_state
*rsp
)
2538 struct rcu_data
*rdp
;
2539 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
2540 unsigned long snap_done
;
2542 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
2544 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2545 mutex_lock(&rsp
->barrier_mutex
);
2548 * Ensure that all prior references, including to ->n_barrier_done,
2549 * are ordered before the _rcu_barrier() machinery.
2551 smp_mb(); /* See above block comment. */
2554 * Recheck ->n_barrier_done to see if others did our work for us.
2555 * This means checking ->n_barrier_done for an even-to-odd-to-even
2556 * transition. The "if" expression below therefore rounds the old
2557 * value up to the next even number and adds two before comparing.
2559 snap_done
= ACCESS_ONCE(rsp
->n_barrier_done
);
2560 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
2561 if (ULONG_CMP_GE(snap_done
, ((snap
+ 1) & ~0x1) + 2)) {
2562 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
2563 smp_mb(); /* caller's subsequent code after above check. */
2564 mutex_unlock(&rsp
->barrier_mutex
);
2569 * Increment ->n_barrier_done to avoid duplicate work. Use
2570 * ACCESS_ONCE() to prevent the compiler from speculating
2571 * the increment to precede the early-exit check.
2573 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2574 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
2575 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
2576 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2579 * Initialize the count to one rather than to zero in order to
2580 * avoid a too-soon return to zero in case of a short grace period
2581 * (or preemption of this task). Exclude CPU-hotplug operations
2582 * to ensure that no offline CPU has callbacks queued.
2584 init_completion(&rsp
->barrier_completion
);
2585 atomic_set(&rsp
->barrier_cpu_count
, 1);
2589 * Force each CPU with callbacks to register a new callback.
2590 * When that callback is invoked, we will know that all of the
2591 * corresponding CPU's preceding callbacks have been invoked.
2593 for_each_online_cpu(cpu
) {
2594 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2595 if (ACCESS_ONCE(rdp
->qlen
)) {
2596 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
2597 rsp
->n_barrier_done
);
2598 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
2600 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
2601 rsp
->n_barrier_done
);
2607 * Now that we have an rcu_barrier_callback() callback on each
2608 * CPU, and thus each counted, remove the initial count.
2610 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
2611 complete(&rsp
->barrier_completion
);
2613 /* Increment ->n_barrier_done to prevent duplicate work. */
2614 smp_mb(); /* Keep increment after above mechanism. */
2615 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2616 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
2617 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
2618 smp_mb(); /* Keep increment before caller's subsequent code. */
2620 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2621 wait_for_completion(&rsp
->barrier_completion
);
2623 /* Other rcu_barrier() invocations can now safely proceed. */
2624 mutex_unlock(&rsp
->barrier_mutex
);
2628 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2630 void rcu_barrier_bh(void)
2632 _rcu_barrier(&rcu_bh_state
);
2634 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2637 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2639 void rcu_barrier_sched(void)
2641 _rcu_barrier(&rcu_sched_state
);
2643 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2646 * Do boot-time initialization of a CPU's per-CPU RCU data.
2649 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2651 unsigned long flags
;
2652 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2653 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2655 /* Set up local state, ensuring consistent view of global state. */
2656 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2657 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2658 init_callback_list(rdp
);
2660 ACCESS_ONCE(rdp
->qlen
) = 0;
2661 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2662 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
2663 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2664 #ifdef CONFIG_RCU_USER_QS
2665 WARN_ON_ONCE(rdp
->dynticks
->in_user
);
2669 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2673 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2674 * offline event can be happening at a given time. Note also that we
2675 * can accept some slop in the rsp->completed access due to the fact
2676 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2678 static void __cpuinit
2679 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2681 unsigned long flags
;
2683 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2684 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2686 /* Exclude new grace periods. */
2687 mutex_lock(&rsp
->onoff_mutex
);
2689 /* Set up local state, ensuring consistent view of global state. */
2690 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2691 rdp
->beenonline
= 1; /* We have now been online. */
2692 rdp
->preemptible
= preemptible
;
2693 rdp
->qlen_last_fqs_check
= 0;
2694 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2695 rdp
->blimit
= blimit
;
2696 init_callback_list(rdp
); /* Re-enable callbacks on this CPU. */
2697 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2698 atomic_set(&rdp
->dynticks
->dynticks
,
2699 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
2700 rcu_prepare_for_idle_init(cpu
);
2701 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2703 /* Add CPU to rcu_node bitmasks. */
2705 mask
= rdp
->grpmask
;
2707 /* Exclude any attempts to start a new GP on small systems. */
2708 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2709 rnp
->qsmaskinit
|= mask
;
2710 mask
= rnp
->grpmask
;
2711 if (rnp
== rdp
->mynode
) {
2713 * If there is a grace period in progress, we will
2714 * set up to wait for it next time we run the
2717 rdp
->gpnum
= rnp
->completed
;
2718 rdp
->completed
= rnp
->completed
;
2719 rdp
->passed_quiesce
= 0;
2720 rdp
->qs_pending
= 0;
2721 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2723 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2725 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2726 local_irq_restore(flags
);
2728 mutex_unlock(&rsp
->onoff_mutex
);
2731 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2733 struct rcu_state
*rsp
;
2735 for_each_rcu_flavor(rsp
)
2736 rcu_init_percpu_data(cpu
, rsp
,
2737 strcmp(rsp
->name
, "rcu_preempt") == 0);
2741 * Handle CPU online/offline notification events.
2743 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2744 unsigned long action
, void *hcpu
)
2746 long cpu
= (long)hcpu
;
2747 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2748 struct rcu_node
*rnp
= rdp
->mynode
;
2749 struct rcu_state
*rsp
;
2751 trace_rcu_utilization("Start CPU hotplug");
2753 case CPU_UP_PREPARE
:
2754 case CPU_UP_PREPARE_FROZEN
:
2755 rcu_prepare_cpu(cpu
);
2756 rcu_prepare_kthreads(cpu
);
2759 case CPU_DOWN_FAILED
:
2760 rcu_boost_kthread_setaffinity(rnp
, -1);
2762 case CPU_DOWN_PREPARE
:
2763 rcu_boost_kthread_setaffinity(rnp
, cpu
);
2766 case CPU_DYING_FROZEN
:
2768 * The whole machine is "stopped" except this CPU, so we can
2769 * touch any data without introducing corruption. We send the
2770 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2772 for_each_rcu_flavor(rsp
)
2773 rcu_cleanup_dying_cpu(rsp
);
2774 rcu_cleanup_after_idle(cpu
);
2777 case CPU_DEAD_FROZEN
:
2778 case CPU_UP_CANCELED
:
2779 case CPU_UP_CANCELED_FROZEN
:
2780 for_each_rcu_flavor(rsp
)
2781 rcu_cleanup_dead_cpu(cpu
, rsp
);
2786 trace_rcu_utilization("End CPU hotplug");
2791 * Spawn the kthread that handles this RCU flavor's grace periods.
2793 static int __init
rcu_spawn_gp_kthread(void)
2795 unsigned long flags
;
2796 struct rcu_node
*rnp
;
2797 struct rcu_state
*rsp
;
2798 struct task_struct
*t
;
2800 for_each_rcu_flavor(rsp
) {
2801 t
= kthread_run(rcu_gp_kthread
, rsp
, rsp
->name
);
2803 rnp
= rcu_get_root(rsp
);
2804 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2805 rsp
->gp_kthread
= t
;
2806 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2810 early_initcall(rcu_spawn_gp_kthread
);
2813 * This function is invoked towards the end of the scheduler's initialization
2814 * process. Before this is called, the idle task might contain
2815 * RCU read-side critical sections (during which time, this idle
2816 * task is booting the system). After this function is called, the
2817 * idle tasks are prohibited from containing RCU read-side critical
2818 * sections. This function also enables RCU lockdep checking.
2820 void rcu_scheduler_starting(void)
2822 WARN_ON(num_online_cpus() != 1);
2823 WARN_ON(nr_context_switches() > 0);
2824 rcu_scheduler_active
= 1;
2828 * Compute the per-level fanout, either using the exact fanout specified
2829 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2831 #ifdef CONFIG_RCU_FANOUT_EXACT
2832 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2836 for (i
= rcu_num_lvls
- 1; i
> 0; i
--)
2837 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2838 rsp
->levelspread
[0] = rcu_fanout_leaf
;
2840 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2841 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2848 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2849 ccur
= rsp
->levelcnt
[i
];
2850 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2854 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2857 * Helper function for rcu_init() that initializes one rcu_state structure.
2859 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2860 struct rcu_data __percpu
*rda
)
2862 static char *buf
[] = { "rcu_node_0",
2865 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
2866 static char *fqs
[] = { "rcu_node_fqs_0",
2869 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
2873 struct rcu_node
*rnp
;
2875 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2877 /* Initialize the level-tracking arrays. */
2879 for (i
= 0; i
< rcu_num_lvls
; i
++)
2880 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
2881 for (i
= 1; i
< rcu_num_lvls
; i
++)
2882 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2883 rcu_init_levelspread(rsp
);
2885 /* Initialize the elements themselves, starting from the leaves. */
2887 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2888 cpustride
*= rsp
->levelspread
[i
];
2889 rnp
= rsp
->level
[i
];
2890 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2891 raw_spin_lock_init(&rnp
->lock
);
2892 lockdep_set_class_and_name(&rnp
->lock
,
2893 &rcu_node_class
[i
], buf
[i
]);
2894 raw_spin_lock_init(&rnp
->fqslock
);
2895 lockdep_set_class_and_name(&rnp
->fqslock
,
2896 &rcu_fqs_class
[i
], fqs
[i
]);
2897 rnp
->gpnum
= rsp
->gpnum
;
2898 rnp
->completed
= rsp
->completed
;
2900 rnp
->qsmaskinit
= 0;
2901 rnp
->grplo
= j
* cpustride
;
2902 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2903 if (rnp
->grphi
>= NR_CPUS
)
2904 rnp
->grphi
= NR_CPUS
- 1;
2910 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2911 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2912 rnp
->parent
= rsp
->level
[i
- 1] +
2913 j
/ rsp
->levelspread
[i
- 1];
2916 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2921 init_waitqueue_head(&rsp
->gp_wq
);
2922 rnp
= rsp
->level
[rcu_num_lvls
- 1];
2923 for_each_possible_cpu(i
) {
2924 while (i
> rnp
->grphi
)
2926 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2927 rcu_boot_init_percpu_data(i
, rsp
);
2929 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
2933 * Compute the rcu_node tree geometry from kernel parameters. This cannot
2934 * replace the definitions in rcutree.h because those are needed to size
2935 * the ->node array in the rcu_state structure.
2937 static void __init
rcu_init_geometry(void)
2942 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
2944 /* If the compile-time values are accurate, just leave. */
2945 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
&&
2946 nr_cpu_ids
== NR_CPUS
)
2950 * Compute number of nodes that can be handled an rcu_node tree
2951 * with the given number of levels. Setting rcu_capacity[0] makes
2952 * some of the arithmetic easier.
2954 rcu_capacity
[0] = 1;
2955 rcu_capacity
[1] = rcu_fanout_leaf
;
2956 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
2957 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
2960 * The boot-time rcu_fanout_leaf parameter is only permitted
2961 * to increase the leaf-level fanout, not decrease it. Of course,
2962 * the leaf-level fanout cannot exceed the number of bits in
2963 * the rcu_node masks. Finally, the tree must be able to accommodate
2964 * the configured number of CPUs. Complain and fall back to the
2965 * compile-time values if these limits are exceeded.
2967 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
2968 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
2969 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
2974 /* Calculate the number of rcu_nodes at each level of the tree. */
2975 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
2976 if (n
<= rcu_capacity
[i
]) {
2977 for (j
= 0; j
<= i
; j
++)
2979 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
2981 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
2986 /* Calculate the total number of rcu_node structures. */
2988 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
2989 rcu_num_nodes
+= num_rcu_lvl
[i
];
2993 void __init
rcu_init(void)
2997 rcu_bootup_announce();
2998 rcu_init_geometry();
2999 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
3000 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
3001 __rcu_init_preempt();
3002 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
3005 * We don't need protection against CPU-hotplug here because
3006 * this is called early in boot, before either interrupts
3007 * or the scheduler are operational.
3009 cpu_notifier(rcu_cpu_notify
, 0);
3010 for_each_online_cpu(cpu
)
3011 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
3012 check_cpu_stall_init();
3015 #include "rcutree_plugin.h"