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), \
80 struct rcu_state rcu_sched_state
=
81 RCU_STATE_INITIALIZER(rcu_sched
, call_rcu_sched
);
82 DEFINE_PER_CPU(struct rcu_data
, rcu_sched_data
);
84 struct rcu_state rcu_bh_state
= RCU_STATE_INITIALIZER(rcu_bh
, call_rcu_bh
);
85 DEFINE_PER_CPU(struct rcu_data
, rcu_bh_data
);
87 static struct rcu_state
*rcu_state
;
88 LIST_HEAD(rcu_struct_flavors
);
90 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
91 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
92 module_param(rcu_fanout_leaf
, int, 0444);
93 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
94 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
101 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
104 * The rcu_scheduler_active variable transitions from zero to one just
105 * before the first task is spawned. So when this variable is zero, RCU
106 * can assume that there is but one task, allowing RCU to (for example)
107 * optimized synchronize_sched() to a simple barrier(). When this variable
108 * is one, RCU must actually do all the hard work required to detect real
109 * grace periods. This variable is also used to suppress boot-time false
110 * positives from lockdep-RCU error checking.
112 int rcu_scheduler_active __read_mostly
;
113 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
116 * The rcu_scheduler_fully_active variable transitions from zero to one
117 * during the early_initcall() processing, which is after the scheduler
118 * is capable of creating new tasks. So RCU processing (for example,
119 * creating tasks for RCU priority boosting) must be delayed until after
120 * rcu_scheduler_fully_active transitions from zero to one. We also
121 * currently delay invocation of any RCU callbacks until after this point.
123 * It might later prove better for people registering RCU callbacks during
124 * early boot to take responsibility for these callbacks, but one step at
127 static int rcu_scheduler_fully_active __read_mostly
;
129 #ifdef CONFIG_RCU_BOOST
132 * Control variables for per-CPU and per-rcu_node kthreads. These
133 * handle all flavors of RCU.
135 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
136 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
137 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
138 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
140 #endif /* #ifdef CONFIG_RCU_BOOST */
142 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
143 static void invoke_rcu_core(void);
144 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
147 * Track the rcutorture test sequence number and the update version
148 * number within a given test. The rcutorture_testseq is incremented
149 * on every rcutorture module load and unload, so has an odd value
150 * when a test is running. The rcutorture_vernum is set to zero
151 * when rcutorture starts and is incremented on each rcutorture update.
152 * These variables enable correlating rcutorture output with the
153 * RCU tracing information.
155 unsigned long rcutorture_testseq
;
156 unsigned long rcutorture_vernum
;
159 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
160 * permit this function to be invoked without holding the root rcu_node
161 * structure's ->lock, but of course results can be subject to change.
163 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
165 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
169 * Note a quiescent state. Because we do not need to know
170 * how many quiescent states passed, just if there was at least
171 * one since the start of the grace period, this just sets a flag.
172 * The caller must have disabled preemption.
174 void rcu_sched_qs(int cpu
)
176 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
178 if (rdp
->passed_quiesce
== 0)
179 trace_rcu_grace_period("rcu_sched", rdp
->gpnum
, "cpuqs");
180 rdp
->passed_quiesce
= 1;
183 void rcu_bh_qs(int cpu
)
185 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
187 if (rdp
->passed_quiesce
== 0)
188 trace_rcu_grace_period("rcu_bh", rdp
->gpnum
, "cpuqs");
189 rdp
->passed_quiesce
= 1;
193 * Note a context switch. This is a quiescent state for RCU-sched,
194 * and requires special handling for preemptible RCU.
195 * The caller must have disabled preemption.
197 void rcu_note_context_switch(int cpu
)
199 trace_rcu_utilization("Start context switch");
201 rcu_preempt_note_context_switch(cpu
);
202 trace_rcu_utilization("End context switch");
204 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
206 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
207 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
208 .dynticks
= ATOMIC_INIT(1),
209 #if defined(CONFIG_RCU_USER_QS) && !defined(CONFIG_RCU_USER_QS_FORCE)
210 .ignore_user_qs
= true,
214 static int blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
215 static int qhimark
= 10000; /* If this many pending, ignore blimit. */
216 static int qlowmark
= 100; /* Once only this many pending, use blimit. */
218 module_param(blimit
, int, 0444);
219 module_param(qhimark
, int, 0444);
220 module_param(qlowmark
, int, 0444);
222 int rcu_cpu_stall_suppress __read_mostly
; /* 1 = suppress stall warnings. */
223 int rcu_cpu_stall_timeout __read_mostly
= CONFIG_RCU_CPU_STALL_TIMEOUT
;
225 module_param(rcu_cpu_stall_suppress
, int, 0644);
226 module_param(rcu_cpu_stall_timeout
, int, 0644);
228 static ulong jiffies_till_first_fqs
= RCU_JIFFIES_TILL_FORCE_QS
;
229 static ulong jiffies_till_next_fqs
= RCU_JIFFIES_TILL_FORCE_QS
;
231 module_param(jiffies_till_first_fqs
, ulong
, 0644);
232 module_param(jiffies_till_next_fqs
, ulong
, 0644);
234 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*));
235 static void force_quiescent_state(struct rcu_state
*rsp
);
236 static int rcu_pending(int cpu
);
239 * Return the number of RCU-sched batches processed thus far for debug & stats.
241 long rcu_batches_completed_sched(void)
243 return rcu_sched_state
.completed
;
245 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
248 * Return the number of RCU BH batches processed thus far for debug & stats.
250 long rcu_batches_completed_bh(void)
252 return rcu_bh_state
.completed
;
254 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
257 * Force a quiescent state for RCU BH.
259 void rcu_bh_force_quiescent_state(void)
261 force_quiescent_state(&rcu_bh_state
);
263 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
266 * Record the number of times rcutorture tests have been initiated and
267 * terminated. This information allows the debugfs tracing stats to be
268 * correlated to the rcutorture messages, even when the rcutorture module
269 * is being repeatedly loaded and unloaded. In other words, we cannot
270 * store this state in rcutorture itself.
272 void rcutorture_record_test_transition(void)
274 rcutorture_testseq
++;
275 rcutorture_vernum
= 0;
277 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
280 * Record the number of writer passes through the current rcutorture test.
281 * This is also used to correlate debugfs tracing stats with the rcutorture
284 void rcutorture_record_progress(unsigned long vernum
)
288 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
291 * Force a quiescent state for RCU-sched.
293 void rcu_sched_force_quiescent_state(void)
295 force_quiescent_state(&rcu_sched_state
);
297 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
300 * Does the CPU have callbacks ready to be invoked?
303 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
305 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
];
309 * Does the current CPU require a yet-as-unscheduled grace period?
312 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
314 return *rdp
->nxttail
[RCU_DONE_TAIL
+
315 ACCESS_ONCE(rsp
->completed
) != rdp
->completed
] &&
316 !rcu_gp_in_progress(rsp
);
320 * Return the root node of the specified rcu_state structure.
322 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
324 return &rsp
->node
[0];
328 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
330 * If the new value of the ->dynticks_nesting counter now is zero,
331 * we really have entered idle, and must do the appropriate accounting.
332 * The caller must have disabled interrupts.
334 static void rcu_eqs_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
,
337 trace_rcu_dyntick("Start", oldval
, 0);
338 if (!user
&& !is_idle_task(current
)) {
339 struct task_struct
*idle
= idle_task(smp_processor_id());
341 trace_rcu_dyntick("Error on entry: not idle task", oldval
, 0);
342 ftrace_dump(DUMP_ORIG
);
343 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
344 current
->pid
, current
->comm
,
345 idle
->pid
, idle
->comm
); /* must be idle task! */
347 rcu_prepare_for_idle(smp_processor_id());
348 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
349 smp_mb__before_atomic_inc(); /* See above. */
350 atomic_inc(&rdtp
->dynticks
);
351 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
352 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
355 * It is illegal to enter an extended quiescent state while
356 * in an RCU read-side critical section.
358 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
359 "Illegal idle entry in RCU read-side critical section.");
360 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
361 "Illegal idle entry in RCU-bh read-side critical section.");
362 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
363 "Illegal idle entry in RCU-sched read-side critical section.");
367 * Enter an RCU extended quiescent state, which can be either the
368 * idle loop or adaptive-tickless usermode execution.
370 static void rcu_eqs_enter(bool user
)
373 struct rcu_dynticks
*rdtp
;
375 rdtp
= &__get_cpu_var(rcu_dynticks
);
376 oldval
= rdtp
->dynticks_nesting
;
377 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
378 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
)
379 rdtp
->dynticks_nesting
= 0;
381 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
382 rcu_eqs_enter_common(rdtp
, oldval
, user
);
386 * rcu_idle_enter - inform RCU that current CPU is entering idle
388 * Enter idle mode, in other words, -leave- the mode in which RCU
389 * read-side critical sections can occur. (Though RCU read-side
390 * critical sections can occur in irq handlers in idle, a possibility
391 * handled by irq_enter() and irq_exit().)
393 * We crowbar the ->dynticks_nesting field to zero to allow for
394 * the possibility of usermode upcalls having messed up our count
395 * of interrupt nesting level during the prior busy period.
397 void rcu_idle_enter(void)
401 local_irq_save(flags
);
402 rcu_eqs_enter(false);
403 local_irq_restore(flags
);
405 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
407 #ifdef CONFIG_RCU_USER_QS
409 * rcu_user_enter - inform RCU that we are resuming userspace.
411 * Enter RCU idle mode right before resuming userspace. No use of RCU
412 * is permitted between this call and rcu_user_exit(). This way the
413 * CPU doesn't need to maintain the tick for RCU maintenance purposes
414 * when the CPU runs in userspace.
416 void rcu_user_enter(void)
419 struct rcu_dynticks
*rdtp
;
422 * Some contexts may involve an exception occuring in an irq,
423 * leading to that nesting:
424 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
425 * This would mess up the dyntick_nesting count though. And rcu_irq_*()
426 * helpers are enough to protect RCU uses inside the exception. So
427 * just return immediately if we detect we are in an IRQ.
432 WARN_ON_ONCE(!current
->mm
);
434 local_irq_save(flags
);
435 rdtp
= &__get_cpu_var(rcu_dynticks
);
436 if (!rdtp
->ignore_user_qs
&& !rdtp
->in_user
) {
437 rdtp
->in_user
= true;
440 local_irq_restore(flags
);
444 * rcu_user_enter_after_irq - inform RCU that we are going to resume userspace
445 * after the current irq returns.
447 * This is similar to rcu_user_enter() but in the context of a non-nesting
448 * irq. After this call, RCU enters into idle mode when the interrupt
451 void rcu_user_enter_after_irq(void)
454 struct rcu_dynticks
*rdtp
;
456 local_irq_save(flags
);
457 rdtp
= &__get_cpu_var(rcu_dynticks
);
458 /* Ensure this irq is interrupting a non-idle RCU state. */
459 WARN_ON_ONCE(!(rdtp
->dynticks_nesting
& DYNTICK_TASK_MASK
));
460 rdtp
->dynticks_nesting
= 1;
461 local_irq_restore(flags
);
463 #endif /* CONFIG_RCU_USER_QS */
466 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
468 * Exit from an interrupt handler, which might possibly result in entering
469 * idle mode, in other words, leaving the mode in which read-side critical
470 * sections can occur.
472 * This code assumes that the idle loop never does anything that might
473 * result in unbalanced calls to irq_enter() and irq_exit(). If your
474 * architecture violates this assumption, RCU will give you what you
475 * deserve, good and hard. But very infrequently and irreproducibly.
477 * Use things like work queues to work around this limitation.
479 * You have been warned.
481 void rcu_irq_exit(void)
485 struct rcu_dynticks
*rdtp
;
487 local_irq_save(flags
);
488 rdtp
= &__get_cpu_var(rcu_dynticks
);
489 oldval
= rdtp
->dynticks_nesting
;
490 rdtp
->dynticks_nesting
--;
491 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
492 if (rdtp
->dynticks_nesting
)
493 trace_rcu_dyntick("--=", oldval
, rdtp
->dynticks_nesting
);
495 rcu_eqs_enter_common(rdtp
, oldval
, true);
496 local_irq_restore(flags
);
500 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
502 * If the new value of the ->dynticks_nesting counter was previously zero,
503 * we really have exited idle, and must do the appropriate accounting.
504 * The caller must have disabled interrupts.
506 static void rcu_eqs_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
,
509 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
510 atomic_inc(&rdtp
->dynticks
);
511 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
512 smp_mb__after_atomic_inc(); /* See above. */
513 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
514 rcu_cleanup_after_idle(smp_processor_id());
515 trace_rcu_dyntick("End", oldval
, rdtp
->dynticks_nesting
);
516 if (!user
&& !is_idle_task(current
)) {
517 struct task_struct
*idle
= idle_task(smp_processor_id());
519 trace_rcu_dyntick("Error on exit: not idle task",
520 oldval
, rdtp
->dynticks_nesting
);
521 ftrace_dump(DUMP_ORIG
);
522 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
523 current
->pid
, current
->comm
,
524 idle
->pid
, idle
->comm
); /* must be idle task! */
529 * Exit an RCU extended quiescent state, which can be either the
530 * idle loop or adaptive-tickless usermode execution.
532 static void rcu_eqs_exit(bool user
)
534 struct rcu_dynticks
*rdtp
;
537 rdtp
= &__get_cpu_var(rcu_dynticks
);
538 oldval
= rdtp
->dynticks_nesting
;
539 WARN_ON_ONCE(oldval
< 0);
540 if (oldval
& DYNTICK_TASK_NEST_MASK
)
541 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
543 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
544 rcu_eqs_exit_common(rdtp
, oldval
, user
);
548 * rcu_idle_exit - inform RCU that current CPU is leaving idle
550 * Exit idle mode, in other words, -enter- the mode in which RCU
551 * read-side critical sections can occur.
553 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
554 * allow for the possibility of usermode upcalls messing up our count
555 * of interrupt nesting level during the busy period that is just
558 void rcu_idle_exit(void)
562 local_irq_save(flags
);
564 local_irq_restore(flags
);
566 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
568 #ifdef CONFIG_RCU_USER_QS
570 * rcu_user_exit - inform RCU that we are exiting userspace.
572 * Exit RCU idle mode while entering the kernel because it can
573 * run a RCU read side critical section anytime.
575 void rcu_user_exit(void)
578 struct rcu_dynticks
*rdtp
;
581 * Some contexts may involve an exception occuring in an irq,
582 * leading to that nesting:
583 * rcu_irq_enter() rcu_user_exit() rcu_user_exit() rcu_irq_exit()
584 * This would mess up the dyntick_nesting count though. And rcu_irq_*()
585 * helpers are enough to protect RCU uses inside the exception. So
586 * just return immediately if we detect we are in an IRQ.
591 local_irq_save(flags
);
592 rdtp
= &__get_cpu_var(rcu_dynticks
);
594 rdtp
->in_user
= false;
597 local_irq_restore(flags
);
601 * rcu_user_exit_after_irq - inform RCU that we won't resume to userspace
602 * idle mode after the current non-nesting irq returns.
604 * This is similar to rcu_user_exit() but in the context of an irq.
605 * This is called when the irq has interrupted a userspace RCU idle mode
606 * context. When the current non-nesting interrupt returns after this call,
607 * the CPU won't restore the RCU idle mode.
609 void rcu_user_exit_after_irq(void)
612 struct rcu_dynticks
*rdtp
;
614 local_irq_save(flags
);
615 rdtp
= &__get_cpu_var(rcu_dynticks
);
616 /* Ensure we are interrupting an RCU idle mode. */
617 WARN_ON_ONCE(rdtp
->dynticks_nesting
& DYNTICK_TASK_NEST_MASK
);
618 rdtp
->dynticks_nesting
+= DYNTICK_TASK_EXIT_IDLE
;
619 local_irq_restore(flags
);
621 #endif /* CONFIG_RCU_USER_QS */
624 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
626 * Enter an interrupt handler, which might possibly result in exiting
627 * idle mode, in other words, entering the mode in which read-side critical
628 * sections can occur.
630 * Note that the Linux kernel is fully capable of entering an interrupt
631 * handler that it never exits, for example when doing upcalls to
632 * user mode! This code assumes that the idle loop never does upcalls to
633 * user mode. If your architecture does do upcalls from the idle loop (or
634 * does anything else that results in unbalanced calls to the irq_enter()
635 * and irq_exit() functions), RCU will give you what you deserve, good
636 * and hard. But very infrequently and irreproducibly.
638 * Use things like work queues to work around this limitation.
640 * You have been warned.
642 void rcu_irq_enter(void)
645 struct rcu_dynticks
*rdtp
;
648 local_irq_save(flags
);
649 rdtp
= &__get_cpu_var(rcu_dynticks
);
650 oldval
= rdtp
->dynticks_nesting
;
651 rdtp
->dynticks_nesting
++;
652 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
654 trace_rcu_dyntick("++=", oldval
, rdtp
->dynticks_nesting
);
656 rcu_eqs_exit_common(rdtp
, oldval
, true);
657 local_irq_restore(flags
);
661 * rcu_nmi_enter - inform RCU of entry to NMI context
663 * If the CPU was idle with dynamic ticks active, and there is no
664 * irq handler running, this updates rdtp->dynticks_nmi to let the
665 * RCU grace-period handling know that the CPU is active.
667 void rcu_nmi_enter(void)
669 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
671 if (rdtp
->dynticks_nmi_nesting
== 0 &&
672 (atomic_read(&rdtp
->dynticks
) & 0x1))
674 rdtp
->dynticks_nmi_nesting
++;
675 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
676 atomic_inc(&rdtp
->dynticks
);
677 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
678 smp_mb__after_atomic_inc(); /* See above. */
679 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
683 * rcu_nmi_exit - inform RCU of exit from NMI context
685 * If the CPU was idle with dynamic ticks active, and there is no
686 * irq handler running, this updates rdtp->dynticks_nmi to let the
687 * RCU grace-period handling know that the CPU is no longer active.
689 void rcu_nmi_exit(void)
691 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
693 if (rdtp
->dynticks_nmi_nesting
== 0 ||
694 --rdtp
->dynticks_nmi_nesting
!= 0)
696 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
697 smp_mb__before_atomic_inc(); /* See above. */
698 atomic_inc(&rdtp
->dynticks
);
699 smp_mb__after_atomic_inc(); /* Force delay to next write. */
700 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
704 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
706 * If the current CPU is in its idle loop and is neither in an interrupt
707 * or NMI handler, return true.
709 int rcu_is_cpu_idle(void)
714 ret
= (atomic_read(&__get_cpu_var(rcu_dynticks
).dynticks
) & 0x1) == 0;
718 EXPORT_SYMBOL(rcu_is_cpu_idle
);
720 #ifdef CONFIG_RCU_USER_QS
721 void rcu_user_hooks_switch(struct task_struct
*prev
,
722 struct task_struct
*next
)
724 struct rcu_dynticks
*rdtp
;
726 /* Interrupts are disabled in context switch */
727 rdtp
= &__get_cpu_var(rcu_dynticks
);
728 if (!rdtp
->ignore_user_qs
) {
729 clear_tsk_thread_flag(prev
, TIF_NOHZ
);
730 set_tsk_thread_flag(next
, TIF_NOHZ
);
733 #endif /* #ifdef CONFIG_RCU_USER_QS */
735 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
738 * Is the current CPU online? Disable preemption to avoid false positives
739 * that could otherwise happen due to the current CPU number being sampled,
740 * this task being preempted, its old CPU being taken offline, resuming
741 * on some other CPU, then determining that its old CPU is now offline.
742 * It is OK to use RCU on an offline processor during initial boot, hence
743 * the check for rcu_scheduler_fully_active. Note also that it is OK
744 * for a CPU coming online to use RCU for one jiffy prior to marking itself
745 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
746 * offline to continue to use RCU for one jiffy after marking itself
747 * offline in the cpu_online_mask. This leniency is necessary given the
748 * non-atomic nature of the online and offline processing, for example,
749 * the fact that a CPU enters the scheduler after completing the CPU_DYING
752 * This is also why RCU internally marks CPUs online during the
753 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
755 * Disable checking if in an NMI handler because we cannot safely report
756 * errors from NMI handlers anyway.
758 bool rcu_lockdep_current_cpu_online(void)
760 struct rcu_data
*rdp
;
761 struct rcu_node
*rnp
;
767 rdp
= &__get_cpu_var(rcu_sched_data
);
769 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
770 !rcu_scheduler_fully_active
;
774 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
776 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
779 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
781 * If the current CPU is idle or running at a first-level (not nested)
782 * interrupt from idle, return true. The caller must have at least
783 * disabled preemption.
785 int rcu_is_cpu_rrupt_from_idle(void)
787 return __get_cpu_var(rcu_dynticks
).dynticks_nesting
<= 1;
791 * Snapshot the specified CPU's dynticks counter so that we can later
792 * credit them with an implicit quiescent state. Return 1 if this CPU
793 * is in dynticks idle mode, which is an extended quiescent state.
795 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
797 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
798 return (rdp
->dynticks_snap
& 0x1) == 0;
802 * Return true if the specified CPU has passed through a quiescent
803 * state by virtue of being in or having passed through an dynticks
804 * idle state since the last call to dyntick_save_progress_counter()
805 * for this same CPU, or by virtue of having been offline.
807 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
812 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
813 snap
= (unsigned int)rdp
->dynticks_snap
;
816 * If the CPU passed through or entered a dynticks idle phase with
817 * no active irq/NMI handlers, then we can safely pretend that the CPU
818 * already acknowledged the request to pass through a quiescent
819 * state. Either way, that CPU cannot possibly be in an RCU
820 * read-side critical section that started before the beginning
821 * of the current RCU grace period.
823 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
824 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "dti");
830 * Check for the CPU being offline, but only if the grace period
831 * is old enough. We don't need to worry about the CPU changing
832 * state: If we see it offline even once, it has been through a
835 * The reason for insisting that the grace period be at least
836 * one jiffy old is that CPUs that are not quite online and that
837 * have just gone offline can still execute RCU read-side critical
840 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
841 return 0; /* Grace period is not old enough. */
843 if (cpu_is_offline(rdp
->cpu
)) {
844 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "ofl");
851 static int jiffies_till_stall_check(void)
853 int till_stall_check
= ACCESS_ONCE(rcu_cpu_stall_timeout
);
856 * Limit check must be consistent with the Kconfig limits
857 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
859 if (till_stall_check
< 3) {
860 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 3;
861 till_stall_check
= 3;
862 } else if (till_stall_check
> 300) {
863 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 300;
864 till_stall_check
= 300;
866 return till_stall_check
* HZ
+ RCU_STALL_DELAY_DELTA
;
869 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
871 rsp
->gp_start
= jiffies
;
872 rsp
->jiffies_stall
= jiffies
+ jiffies_till_stall_check();
875 static void print_other_cpu_stall(struct rcu_state
*rsp
)
881 struct rcu_node
*rnp
= rcu_get_root(rsp
);
883 /* Only let one CPU complain about others per time interval. */
885 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
886 delta
= jiffies
- rsp
->jiffies_stall
;
887 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
888 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
891 rsp
->jiffies_stall
= jiffies
+ 3 * jiffies_till_stall_check() + 3;
892 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
895 * OK, time to rat on our buddy...
896 * See Documentation/RCU/stallwarn.txt for info on how to debug
897 * RCU CPU stall warnings.
899 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks:",
901 print_cpu_stall_info_begin();
902 rcu_for_each_leaf_node(rsp
, rnp
) {
903 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
904 ndetected
+= rcu_print_task_stall(rnp
);
905 if (rnp
->qsmask
!= 0) {
906 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
907 if (rnp
->qsmask
& (1UL << cpu
)) {
908 print_cpu_stall_info(rsp
,
913 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
917 * Now rat on any tasks that got kicked up to the root rcu_node
918 * due to CPU offlining.
920 rnp
= rcu_get_root(rsp
);
921 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
922 ndetected
+= rcu_print_task_stall(rnp
);
923 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
925 print_cpu_stall_info_end();
926 printk(KERN_CONT
"(detected by %d, t=%ld jiffies)\n",
927 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
));
929 printk(KERN_ERR
"INFO: Stall ended before state dump start\n");
930 else if (!trigger_all_cpu_backtrace())
933 /* Complain about tasks blocking the grace period. */
935 rcu_print_detail_task_stall(rsp
);
937 force_quiescent_state(rsp
); /* Kick them all. */
940 static void print_cpu_stall(struct rcu_state
*rsp
)
943 struct rcu_node
*rnp
= rcu_get_root(rsp
);
946 * OK, time to rat on ourselves...
947 * See Documentation/RCU/stallwarn.txt for info on how to debug
948 * RCU CPU stall warnings.
950 printk(KERN_ERR
"INFO: %s self-detected stall on CPU", rsp
->name
);
951 print_cpu_stall_info_begin();
952 print_cpu_stall_info(rsp
, smp_processor_id());
953 print_cpu_stall_info_end();
954 printk(KERN_CONT
" (t=%lu jiffies)\n", jiffies
- rsp
->gp_start
);
955 if (!trigger_all_cpu_backtrace())
958 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
959 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
960 rsp
->jiffies_stall
= jiffies
+
961 3 * jiffies_till_stall_check() + 3;
962 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
964 set_need_resched(); /* kick ourselves to get things going. */
967 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
971 struct rcu_node
*rnp
;
973 if (rcu_cpu_stall_suppress
)
975 j
= ACCESS_ONCE(jiffies
);
976 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
978 if (rcu_gp_in_progress(rsp
) &&
979 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && ULONG_CMP_GE(j
, js
)) {
981 /* We haven't checked in, so go dump stack. */
982 print_cpu_stall(rsp
);
984 } else if (rcu_gp_in_progress(rsp
) &&
985 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
987 /* They had a few time units to dump stack, so complain. */
988 print_other_cpu_stall(rsp
);
992 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
994 rcu_cpu_stall_suppress
= 1;
999 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1001 * Set the stall-warning timeout way off into the future, thus preventing
1002 * any RCU CPU stall-warning messages from appearing in the current set of
1003 * RCU grace periods.
1005 * The caller must disable hard irqs.
1007 void rcu_cpu_stall_reset(void)
1009 struct rcu_state
*rsp
;
1011 for_each_rcu_flavor(rsp
)
1012 rsp
->jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
1015 static struct notifier_block rcu_panic_block
= {
1016 .notifier_call
= rcu_panic
,
1019 static void __init
check_cpu_stall_init(void)
1021 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
1025 * Update CPU-local rcu_data state to record the newly noticed grace period.
1026 * This is used both when we started the grace period and when we notice
1027 * that someone else started the grace period. The caller must hold the
1028 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
1029 * and must have irqs disabled.
1031 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1033 if (rdp
->gpnum
!= rnp
->gpnum
) {
1035 * If the current grace period is waiting for this CPU,
1036 * set up to detect a quiescent state, otherwise don't
1037 * go looking for one.
1039 rdp
->gpnum
= rnp
->gpnum
;
1040 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpustart");
1041 rdp
->passed_quiesce
= 0;
1042 rdp
->qs_pending
= !!(rnp
->qsmask
& rdp
->grpmask
);
1043 zero_cpu_stall_ticks(rdp
);
1047 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1049 unsigned long flags
;
1050 struct rcu_node
*rnp
;
1052 local_irq_save(flags
);
1054 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
1055 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1056 local_irq_restore(flags
);
1059 __note_new_gpnum(rsp
, rnp
, rdp
);
1060 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1064 * Did someone else start a new RCU grace period start since we last
1065 * checked? Update local state appropriately if so. Must be called
1066 * on the CPU corresponding to rdp.
1069 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1071 unsigned long flags
;
1074 local_irq_save(flags
);
1075 if (rdp
->gpnum
!= rsp
->gpnum
) {
1076 note_new_gpnum(rsp
, rdp
);
1079 local_irq_restore(flags
);
1084 * Initialize the specified rcu_data structure's callback list to empty.
1086 static void init_callback_list(struct rcu_data
*rdp
)
1090 rdp
->nxtlist
= NULL
;
1091 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1092 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1096 * Advance this CPU's callbacks, but only if the current grace period
1097 * has ended. This may be called only from the CPU to whom the rdp
1098 * belongs. In addition, the corresponding leaf rcu_node structure's
1099 * ->lock must be held by the caller, with irqs disabled.
1102 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1104 /* Did another grace period end? */
1105 if (rdp
->completed
!= rnp
->completed
) {
1107 /* Advance callbacks. No harm if list empty. */
1108 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
1109 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
1110 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1112 /* Remember that we saw this grace-period completion. */
1113 rdp
->completed
= rnp
->completed
;
1114 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuend");
1117 * If we were in an extended quiescent state, we may have
1118 * missed some grace periods that others CPUs handled on
1119 * our behalf. Catch up with this state to avoid noting
1120 * spurious new grace periods. If another grace period
1121 * has started, then rnp->gpnum will have advanced, so
1122 * we will detect this later on. Of course, any quiescent
1123 * states we found for the old GP are now invalid.
1125 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
)) {
1126 rdp
->gpnum
= rdp
->completed
;
1127 rdp
->passed_quiesce
= 0;
1131 * If RCU does not need a quiescent state from this CPU,
1132 * then make sure that this CPU doesn't go looking for one.
1134 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
1135 rdp
->qs_pending
= 0;
1140 * Advance this CPU's callbacks, but only if the current grace period
1141 * has ended. This may be called only from the CPU to whom the rdp
1145 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1147 unsigned long flags
;
1148 struct rcu_node
*rnp
;
1150 local_irq_save(flags
);
1152 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
1153 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1154 local_irq_restore(flags
);
1157 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1158 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1162 * Do per-CPU grace-period initialization for running CPU. The caller
1163 * must hold the lock of the leaf rcu_node structure corresponding to
1167 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1169 /* Prior grace period ended, so advance callbacks for current CPU. */
1170 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1172 /* Set state so that this CPU will detect the next quiescent state. */
1173 __note_new_gpnum(rsp
, rnp
, rdp
);
1177 * Initialize a new grace period.
1179 static int rcu_gp_init(struct rcu_state
*rsp
)
1181 struct rcu_data
*rdp
;
1182 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1184 raw_spin_lock_irq(&rnp
->lock
);
1185 rsp
->gp_flags
= 0; /* Clear all flags: New grace period. */
1187 if (rcu_gp_in_progress(rsp
)) {
1188 /* Grace period already in progress, don't start another. */
1189 raw_spin_unlock_irq(&rnp
->lock
);
1193 /* Advance to a new grace period and initialize state. */
1195 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, "start");
1196 record_gp_stall_check_time(rsp
);
1197 raw_spin_unlock_irq(&rnp
->lock
);
1199 /* Exclude any concurrent CPU-hotplug operations. */
1203 * Set the quiescent-state-needed bits in all the rcu_node
1204 * structures for all currently online CPUs in breadth-first order,
1205 * starting from the root rcu_node structure, relying on the layout
1206 * of the tree within the rsp->node[] array. Note that other CPUs
1207 * will access only the leaves of the hierarchy, thus seeing that no
1208 * grace period is in progress, at least until the corresponding
1209 * leaf node has been initialized. In addition, we have excluded
1210 * CPU-hotplug operations.
1212 * The grace period cannot complete until the initialization
1213 * process finishes, because this kthread handles both.
1215 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1216 raw_spin_lock_irq(&rnp
->lock
);
1217 rdp
= this_cpu_ptr(rsp
->rda
);
1218 rcu_preempt_check_blocked_tasks(rnp
);
1219 rnp
->qsmask
= rnp
->qsmaskinit
;
1220 rnp
->gpnum
= rsp
->gpnum
;
1221 WARN_ON_ONCE(rnp
->completed
!= rsp
->completed
);
1222 rnp
->completed
= rsp
->completed
;
1223 if (rnp
== rdp
->mynode
)
1224 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
1225 rcu_preempt_boost_start_gp(rnp
);
1226 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1227 rnp
->level
, rnp
->grplo
,
1228 rnp
->grphi
, rnp
->qsmask
);
1229 raw_spin_unlock_irq(&rnp
->lock
);
1230 #ifdef CONFIG_PROVE_RCU_DELAY
1231 if ((random32() % (rcu_num_nodes
* 8)) == 0)
1232 schedule_timeout_uninterruptible(2);
1233 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1242 * Do one round of quiescent-state forcing.
1244 int rcu_gp_fqs(struct rcu_state
*rsp
, int fqs_state_in
)
1246 int fqs_state
= fqs_state_in
;
1247 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1250 if (fqs_state
== RCU_SAVE_DYNTICK
) {
1251 /* Collect dyntick-idle snapshots. */
1252 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1253 fqs_state
= RCU_FORCE_QS
;
1255 /* Handle dyntick-idle and offline CPUs. */
1256 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1258 /* Clear flag to prevent immediate re-entry. */
1259 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1260 raw_spin_lock_irq(&rnp
->lock
);
1261 rsp
->gp_flags
&= ~RCU_GP_FLAG_FQS
;
1262 raw_spin_unlock_irq(&rnp
->lock
);
1268 * Clean up after the old grace period.
1270 static void rcu_gp_cleanup(struct rcu_state
*rsp
)
1272 unsigned long gp_duration
;
1273 struct rcu_data
*rdp
;
1274 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1276 raw_spin_lock_irq(&rnp
->lock
);
1277 gp_duration
= jiffies
- rsp
->gp_start
;
1278 if (gp_duration
> rsp
->gp_max
)
1279 rsp
->gp_max
= gp_duration
;
1282 * We know the grace period is complete, but to everyone else
1283 * it appears to still be ongoing. But it is also the case
1284 * that to everyone else it looks like there is nothing that
1285 * they can do to advance the grace period. It is therefore
1286 * safe for us to drop the lock in order to mark the grace
1287 * period as completed in all of the rcu_node structures.
1289 raw_spin_unlock_irq(&rnp
->lock
);
1292 * Propagate new ->completed value to rcu_node structures so
1293 * that other CPUs don't have to wait until the start of the next
1294 * grace period to process their callbacks. This also avoids
1295 * some nasty RCU grace-period initialization races by forcing
1296 * the end of the current grace period to be completely recorded in
1297 * all of the rcu_node structures before the beginning of the next
1298 * grace period is recorded in any of the rcu_node structures.
1300 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1301 raw_spin_lock_irq(&rnp
->lock
);
1302 rnp
->completed
= rsp
->gpnum
;
1303 raw_spin_unlock_irq(&rnp
->lock
);
1306 rnp
= rcu_get_root(rsp
);
1307 raw_spin_lock_irq(&rnp
->lock
);
1309 rsp
->completed
= rsp
->gpnum
; /* Declare grace period done. */
1310 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, "end");
1311 rsp
->fqs_state
= RCU_GP_IDLE
;
1312 rdp
= this_cpu_ptr(rsp
->rda
);
1313 if (cpu_needs_another_gp(rsp
, rdp
))
1315 raw_spin_unlock_irq(&rnp
->lock
);
1319 * Body of kthread that handles grace periods.
1321 static int __noreturn
rcu_gp_kthread(void *arg
)
1326 struct rcu_state
*rsp
= arg
;
1327 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1331 /* Handle grace-period start. */
1333 wait_event_interruptible(rsp
->gp_wq
,
1336 if ((rsp
->gp_flags
& RCU_GP_FLAG_INIT
) &&
1340 flush_signals(current
);
1343 /* Handle quiescent-state forcing. */
1344 fqs_state
= RCU_SAVE_DYNTICK
;
1345 j
= jiffies_till_first_fqs
;
1348 jiffies_till_first_fqs
= HZ
;
1351 rsp
->jiffies_force_qs
= jiffies
+ j
;
1352 ret
= wait_event_interruptible_timeout(rsp
->gp_wq
,
1353 (rsp
->gp_flags
& RCU_GP_FLAG_FQS
) ||
1354 (!ACCESS_ONCE(rnp
->qsmask
) &&
1355 !rcu_preempt_blocked_readers_cgp(rnp
)),
1357 /* If grace period done, leave loop. */
1358 if (!ACCESS_ONCE(rnp
->qsmask
) &&
1359 !rcu_preempt_blocked_readers_cgp(rnp
))
1361 /* If time for quiescent-state forcing, do it. */
1362 if (ret
== 0 || (rsp
->gp_flags
& RCU_GP_FLAG_FQS
)) {
1363 fqs_state
= rcu_gp_fqs(rsp
, fqs_state
);
1366 /* Deal with stray signal. */
1368 flush_signals(current
);
1370 j
= jiffies_till_next_fqs
;
1373 jiffies_till_next_fqs
= HZ
;
1376 jiffies_till_next_fqs
= 1;
1380 /* Handle grace-period end. */
1381 rcu_gp_cleanup(rsp
);
1386 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1387 * in preparation for detecting the next grace period. The caller must hold
1388 * the root node's ->lock, which is released before return. Hard irqs must
1391 * Note that it is legal for a dying CPU (which is marked as offline) to
1392 * invoke this function. This can happen when the dying CPU reports its
1396 rcu_start_gp(struct rcu_state
*rsp
, unsigned long flags
)
1397 __releases(rcu_get_root(rsp
)->lock
)
1399 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1400 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1402 if (!rsp
->gp_kthread
||
1403 !cpu_needs_another_gp(rsp
, rdp
)) {
1405 * Either we have not yet spawned the grace-period
1406 * task or this CPU does not need another grace period.
1407 * Either way, don't start a new grace period.
1409 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1413 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1414 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1415 wake_up(&rsp
->gp_wq
);
1419 * Report a full set of quiescent states to the specified rcu_state
1420 * data structure. This involves cleaning up after the prior grace
1421 * period and letting rcu_start_gp() start up the next grace period
1422 * if one is needed. Note that the caller must hold rnp->lock, as
1423 * required by rcu_start_gp(), which will release it.
1425 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1426 __releases(rcu_get_root(rsp
)->lock
)
1428 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1429 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
1430 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1434 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1435 * Allows quiescent states for a group of CPUs to be reported at one go
1436 * to the specified rcu_node structure, though all the CPUs in the group
1437 * must be represented by the same rcu_node structure (which need not be
1438 * a leaf rcu_node structure, though it often will be). That structure's
1439 * lock must be held upon entry, and it is released before return.
1442 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1443 struct rcu_node
*rnp
, unsigned long flags
)
1444 __releases(rnp
->lock
)
1446 struct rcu_node
*rnp_c
;
1448 /* Walk up the rcu_node hierarchy. */
1450 if (!(rnp
->qsmask
& mask
)) {
1452 /* Our bit has already been cleared, so done. */
1453 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1456 rnp
->qsmask
&= ~mask
;
1457 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1458 mask
, rnp
->qsmask
, rnp
->level
,
1459 rnp
->grplo
, rnp
->grphi
,
1461 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1463 /* Other bits still set at this level, so done. */
1464 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1467 mask
= rnp
->grpmask
;
1468 if (rnp
->parent
== NULL
) {
1470 /* No more levels. Exit loop holding root lock. */
1474 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1477 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1478 WARN_ON_ONCE(rnp_c
->qsmask
);
1482 * Get here if we are the last CPU to pass through a quiescent
1483 * state for this grace period. Invoke rcu_report_qs_rsp()
1484 * to clean up and start the next grace period if one is needed.
1486 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1490 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1491 * structure. This must be either called from the specified CPU, or
1492 * called when the specified CPU is known to be offline (and when it is
1493 * also known that no other CPU is concurrently trying to help the offline
1494 * CPU). The lastcomp argument is used to make sure we are still in the
1495 * grace period of interest. We don't want to end the current grace period
1496 * based on quiescent states detected in an earlier grace period!
1499 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1501 unsigned long flags
;
1503 struct rcu_node
*rnp
;
1506 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1507 if (rdp
->passed_quiesce
== 0 || rdp
->gpnum
!= rnp
->gpnum
||
1508 rnp
->completed
== rnp
->gpnum
) {
1511 * The grace period in which this quiescent state was
1512 * recorded has ended, so don't report it upwards.
1513 * We will instead need a new quiescent state that lies
1514 * within the current grace period.
1516 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1517 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1520 mask
= rdp
->grpmask
;
1521 if ((rnp
->qsmask
& mask
) == 0) {
1522 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1524 rdp
->qs_pending
= 0;
1527 * This GP can't end until cpu checks in, so all of our
1528 * callbacks can be processed during the next GP.
1530 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1532 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1537 * Check to see if there is a new grace period of which this CPU
1538 * is not yet aware, and if so, set up local rcu_data state for it.
1539 * Otherwise, see if this CPU has just passed through its first
1540 * quiescent state for this grace period, and record that fact if so.
1543 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1545 /* If there is now a new grace period, record and return. */
1546 if (check_for_new_grace_period(rsp
, rdp
))
1550 * Does this CPU still need to do its part for current grace period?
1551 * If no, return and let the other CPUs do their part as well.
1553 if (!rdp
->qs_pending
)
1557 * Was there a quiescent state since the beginning of the grace
1558 * period? If no, then exit and wait for the next call.
1560 if (!rdp
->passed_quiesce
)
1564 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1567 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
);
1570 #ifdef CONFIG_HOTPLUG_CPU
1573 * Send the specified CPU's RCU callbacks to the orphanage. The
1574 * specified CPU must be offline, and the caller must hold the
1578 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1579 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1582 * Orphan the callbacks. First adjust the counts. This is safe
1583 * because ->onofflock excludes _rcu_barrier()'s adoption of
1584 * the callbacks, thus no memory barrier is required.
1586 if (rdp
->nxtlist
!= NULL
) {
1587 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1588 rsp
->qlen
+= rdp
->qlen
;
1589 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1591 ACCESS_ONCE(rdp
->qlen
) = 0;
1595 * Next, move those callbacks still needing a grace period to
1596 * the orphanage, where some other CPU will pick them up.
1597 * Some of the callbacks might have gone partway through a grace
1598 * period, but that is too bad. They get to start over because we
1599 * cannot assume that grace periods are synchronized across CPUs.
1600 * We don't bother updating the ->nxttail[] array yet, instead
1601 * we just reset the whole thing later on.
1603 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1604 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1605 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1606 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1610 * Then move the ready-to-invoke callbacks to the orphanage,
1611 * where some other CPU will pick them up. These will not be
1612 * required to pass though another grace period: They are done.
1614 if (rdp
->nxtlist
!= NULL
) {
1615 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1616 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1619 /* Finally, initialize the rcu_data structure's list to empty. */
1620 init_callback_list(rdp
);
1624 * Adopt the RCU callbacks from the specified rcu_state structure's
1625 * orphanage. The caller must hold the ->onofflock.
1627 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
)
1630 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1632 /* Do the accounting first. */
1633 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
1634 rdp
->qlen
+= rsp
->qlen
;
1635 rdp
->n_cbs_adopted
+= rsp
->qlen
;
1636 if (rsp
->qlen_lazy
!= rsp
->qlen
)
1637 rcu_idle_count_callbacks_posted();
1642 * We do not need a memory barrier here because the only way we
1643 * can get here if there is an rcu_barrier() in flight is if
1644 * we are the task doing the rcu_barrier().
1647 /* First adopt the ready-to-invoke callbacks. */
1648 if (rsp
->orphan_donelist
!= NULL
) {
1649 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1650 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
1651 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
1652 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1653 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
1654 rsp
->orphan_donelist
= NULL
;
1655 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
1658 /* And then adopt the callbacks that still need a grace period. */
1659 if (rsp
->orphan_nxtlist
!= NULL
) {
1660 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
1661 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
1662 rsp
->orphan_nxtlist
= NULL
;
1663 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
1668 * Trace the fact that this CPU is going offline.
1670 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1672 RCU_TRACE(unsigned long mask
);
1673 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
1674 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
1676 RCU_TRACE(mask
= rdp
->grpmask
);
1677 trace_rcu_grace_period(rsp
->name
,
1678 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
1683 * The CPU has been completely removed, and some other CPU is reporting
1684 * this fact from process context. Do the remainder of the cleanup,
1685 * including orphaning the outgoing CPU's RCU callbacks, and also
1686 * adopting them. There can only be one CPU hotplug operation at a time,
1687 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
1689 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1691 unsigned long flags
;
1693 int need_report
= 0;
1694 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1695 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
1697 /* Adjust any no-longer-needed kthreads. */
1698 rcu_boost_kthread_setaffinity(rnp
, -1);
1700 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
1702 /* Exclude any attempts to start a new grace period. */
1703 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
1705 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
1706 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
1707 rcu_adopt_orphan_cbs(rsp
);
1709 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1710 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1712 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1713 rnp
->qsmaskinit
&= ~mask
;
1714 if (rnp
->qsmaskinit
!= 0) {
1715 if (rnp
!= rdp
->mynode
)
1716 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1719 if (rnp
== rdp
->mynode
)
1720 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1722 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1723 mask
= rnp
->grpmask
;
1725 } while (rnp
!= NULL
);
1728 * We still hold the leaf rcu_node structure lock here, and
1729 * irqs are still disabled. The reason for this subterfuge is
1730 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1731 * held leads to deadlock.
1733 raw_spin_unlock(&rsp
->onofflock
); /* irqs remain disabled. */
1735 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1736 rcu_report_unblock_qs_rnp(rnp
, flags
);
1738 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1739 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1740 rcu_report_exp_rnp(rsp
, rnp
, true);
1741 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
1742 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
1743 cpu
, rdp
->qlen
, rdp
->nxtlist
);
1744 init_callback_list(rdp
);
1745 /* Disallow further callbacks on this CPU. */
1746 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
1749 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1751 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1755 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1759 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1762 * Invoke any RCU callbacks that have made it to the end of their grace
1763 * period. Thottle as specified by rdp->blimit.
1765 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1767 unsigned long flags
;
1768 struct rcu_head
*next
, *list
, **tail
;
1769 int bl
, count
, count_lazy
, i
;
1771 /* If no callbacks are ready, just return.*/
1772 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
1773 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
1774 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
1775 need_resched(), is_idle_task(current
),
1776 rcu_is_callbacks_kthread());
1781 * Extract the list of ready callbacks, disabling to prevent
1782 * races with call_rcu() from interrupt handlers.
1784 local_irq_save(flags
);
1785 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1787 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
1788 list
= rdp
->nxtlist
;
1789 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1790 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1791 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1792 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
1793 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1794 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1795 local_irq_restore(flags
);
1797 /* Invoke callbacks. */
1798 count
= count_lazy
= 0;
1802 debug_rcu_head_unqueue(list
);
1803 if (__rcu_reclaim(rsp
->name
, list
))
1806 /* Stop only if limit reached and CPU has something to do. */
1807 if (++count
>= bl
&&
1809 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
1813 local_irq_save(flags
);
1814 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
1815 is_idle_task(current
),
1816 rcu_is_callbacks_kthread());
1818 /* Update count, and requeue any remaining callbacks. */
1820 *tail
= rdp
->nxtlist
;
1821 rdp
->nxtlist
= list
;
1822 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1823 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
1824 rdp
->nxttail
[i
] = tail
;
1828 smp_mb(); /* List handling before counting for rcu_barrier(). */
1829 rdp
->qlen_lazy
-= count_lazy
;
1830 ACCESS_ONCE(rdp
->qlen
) -= count
;
1831 rdp
->n_cbs_invoked
+= count
;
1833 /* Reinstate batch limit if we have worked down the excess. */
1834 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1835 rdp
->blimit
= blimit
;
1837 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1838 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1839 rdp
->qlen_last_fqs_check
= 0;
1840 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1841 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1842 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1843 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
1845 local_irq_restore(flags
);
1847 /* Re-invoke RCU core processing if there are callbacks remaining. */
1848 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1853 * Check to see if this CPU is in a non-context-switch quiescent state
1854 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1855 * Also schedule RCU core processing.
1857 * This function must be called from hardirq context. It is normally
1858 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1859 * false, there is no point in invoking rcu_check_callbacks().
1861 void rcu_check_callbacks(int cpu
, int user
)
1863 trace_rcu_utilization("Start scheduler-tick");
1864 increment_cpu_stall_ticks();
1865 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
1868 * Get here if this CPU took its interrupt from user
1869 * mode or from the idle loop, and if this is not a
1870 * nested interrupt. In this case, the CPU is in
1871 * a quiescent state, so note it.
1873 * No memory barrier is required here because both
1874 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1875 * variables that other CPUs neither access nor modify,
1876 * at least not while the corresponding CPU is online.
1882 } else if (!in_softirq()) {
1885 * Get here if this CPU did not take its interrupt from
1886 * softirq, in other words, if it is not interrupting
1887 * a rcu_bh read-side critical section. This is an _bh
1888 * critical section, so note it.
1893 rcu_preempt_check_callbacks(cpu
);
1894 if (rcu_pending(cpu
))
1896 trace_rcu_utilization("End scheduler-tick");
1900 * Scan the leaf rcu_node structures, processing dyntick state for any that
1901 * have not yet encountered a quiescent state, using the function specified.
1902 * Also initiate boosting for any threads blocked on the root rcu_node.
1904 * The caller must have suppressed start of new grace periods.
1906 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1910 unsigned long flags
;
1912 struct rcu_node
*rnp
;
1914 rcu_for_each_leaf_node(rsp
, rnp
) {
1917 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1918 if (!rcu_gp_in_progress(rsp
)) {
1919 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1922 if (rnp
->qsmask
== 0) {
1923 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1928 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1929 if ((rnp
->qsmask
& bit
) != 0 &&
1930 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1935 /* rcu_report_qs_rnp() releases rnp->lock. */
1936 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1939 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1941 rnp
= rcu_get_root(rsp
);
1942 if (rnp
->qsmask
== 0) {
1943 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1944 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1949 * Force quiescent states on reluctant CPUs, and also detect which
1950 * CPUs are in dyntick-idle mode.
1952 static void force_quiescent_state(struct rcu_state
*rsp
)
1954 unsigned long flags
;
1956 struct rcu_node
*rnp
;
1957 struct rcu_node
*rnp_old
= NULL
;
1959 /* Funnel through hierarchy to reduce memory contention. */
1960 rnp
= per_cpu_ptr(rsp
->rda
, raw_smp_processor_id())->mynode
;
1961 for (; rnp
!= NULL
; rnp
= rnp
->parent
) {
1962 ret
= (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) ||
1963 !raw_spin_trylock(&rnp
->fqslock
);
1964 if (rnp_old
!= NULL
)
1965 raw_spin_unlock(&rnp_old
->fqslock
);
1967 rsp
->n_force_qs_lh
++;
1972 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
1974 /* Reached the root of the rcu_node tree, acquire lock. */
1975 raw_spin_lock_irqsave(&rnp_old
->lock
, flags
);
1976 raw_spin_unlock(&rnp_old
->fqslock
);
1977 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1978 rsp
->n_force_qs_lh
++;
1979 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
1980 return; /* Someone beat us to it. */
1982 rsp
->gp_flags
|= RCU_GP_FLAG_FQS
;
1983 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
1984 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1988 * This does the RCU core processing work for the specified rcu_state
1989 * and rcu_data structures. This may be called only from the CPU to
1990 * whom the rdp belongs.
1993 __rcu_process_callbacks(struct rcu_state
*rsp
)
1995 unsigned long flags
;
1996 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1998 WARN_ON_ONCE(rdp
->beenonline
== 0);
2001 * Advance callbacks in response to end of earlier grace
2002 * period that some other CPU ended.
2004 rcu_process_gp_end(rsp
, rdp
);
2006 /* Update RCU state based on any recent quiescent states. */
2007 rcu_check_quiescent_state(rsp
, rdp
);
2009 /* Does this CPU require a not-yet-started grace period? */
2010 if (cpu_needs_another_gp(rsp
, rdp
)) {
2011 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
2012 rcu_start_gp(rsp
, flags
); /* releases above lock */
2015 /* If there are callbacks ready, invoke them. */
2016 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2017 invoke_rcu_callbacks(rsp
, rdp
);
2021 * Do RCU core processing for the current CPU.
2023 static void rcu_process_callbacks(struct softirq_action
*unused
)
2025 struct rcu_state
*rsp
;
2027 if (cpu_is_offline(smp_processor_id()))
2029 trace_rcu_utilization("Start RCU core");
2030 for_each_rcu_flavor(rsp
)
2031 __rcu_process_callbacks(rsp
);
2032 trace_rcu_utilization("End RCU core");
2036 * Schedule RCU callback invocation. If the specified type of RCU
2037 * does not support RCU priority boosting, just do a direct call,
2038 * otherwise wake up the per-CPU kernel kthread. Note that because we
2039 * are running on the current CPU with interrupts disabled, the
2040 * rcu_cpu_kthread_task cannot disappear out from under us.
2042 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2044 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
2046 if (likely(!rsp
->boost
)) {
2047 rcu_do_batch(rsp
, rdp
);
2050 invoke_rcu_callbacks_kthread();
2053 static void invoke_rcu_core(void)
2055 raise_softirq(RCU_SOFTIRQ
);
2059 * Handle any core-RCU processing required by a call_rcu() invocation.
2061 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
2062 struct rcu_head
*head
, unsigned long flags
)
2065 * If called from an extended quiescent state, invoke the RCU
2066 * core in order to force a re-evaluation of RCU's idleness.
2068 if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
2071 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2072 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
2076 * Force the grace period if too many callbacks or too long waiting.
2077 * Enforce hysteresis, and don't invoke force_quiescent_state()
2078 * if some other CPU has recently done so. Also, don't bother
2079 * invoking force_quiescent_state() if the newly enqueued callback
2080 * is the only one waiting for a grace period to complete.
2082 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
2084 /* Are we ignoring a completed grace period? */
2085 rcu_process_gp_end(rsp
, rdp
);
2086 check_for_new_grace_period(rsp
, rdp
);
2088 /* Start a new grace period if one not already started. */
2089 if (!rcu_gp_in_progress(rsp
)) {
2090 unsigned long nestflag
;
2091 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
2093 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
2094 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
2096 /* Give the grace period a kick. */
2097 rdp
->blimit
= LONG_MAX
;
2098 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
2099 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
2100 force_quiescent_state(rsp
);
2101 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2102 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2108 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
2109 struct rcu_state
*rsp
, bool lazy
)
2111 unsigned long flags
;
2112 struct rcu_data
*rdp
;
2114 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
2115 debug_rcu_head_queue(head
);
2120 * Opportunistically note grace-period endings and beginnings.
2121 * Note that we might see a beginning right after we see an
2122 * end, but never vice versa, since this CPU has to pass through
2123 * a quiescent state betweentimes.
2125 local_irq_save(flags
);
2126 rdp
= this_cpu_ptr(rsp
->rda
);
2128 /* Add the callback to our list. */
2129 if (unlikely(rdp
->nxttail
[RCU_NEXT_TAIL
] == NULL
)) {
2130 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2132 local_irq_restore(flags
);
2135 ACCESS_ONCE(rdp
->qlen
)++;
2139 rcu_idle_count_callbacks_posted();
2140 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2141 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
2142 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
2144 if (__is_kfree_rcu_offset((unsigned long)func
))
2145 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
2146 rdp
->qlen_lazy
, rdp
->qlen
);
2148 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
2150 /* Go handle any RCU core processing required. */
2151 __call_rcu_core(rsp
, rdp
, head
, flags
);
2152 local_irq_restore(flags
);
2156 * Queue an RCU-sched callback for invocation after a grace period.
2158 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2160 __call_rcu(head
, func
, &rcu_sched_state
, 0);
2162 EXPORT_SYMBOL_GPL(call_rcu_sched
);
2165 * Queue an RCU callback for invocation after a quicker grace period.
2167 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2169 __call_rcu(head
, func
, &rcu_bh_state
, 0);
2171 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2174 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2175 * any blocking grace-period wait automatically implies a grace period
2176 * if there is only one CPU online at any point time during execution
2177 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2178 * occasionally incorrectly indicate that there are multiple CPUs online
2179 * when there was in fact only one the whole time, as this just adds
2180 * some overhead: RCU still operates correctly.
2182 static inline int rcu_blocking_is_gp(void)
2186 might_sleep(); /* Check for RCU read-side critical section. */
2188 ret
= num_online_cpus() <= 1;
2194 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2196 * Control will return to the caller some time after a full rcu-sched
2197 * grace period has elapsed, in other words after all currently executing
2198 * rcu-sched read-side critical sections have completed. These read-side
2199 * critical sections are delimited by rcu_read_lock_sched() and
2200 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2201 * local_irq_disable(), and so on may be used in place of
2202 * rcu_read_lock_sched().
2204 * This means that all preempt_disable code sequences, including NMI and
2205 * hardware-interrupt handlers, in progress on entry will have completed
2206 * before this primitive returns. However, this does not guarantee that
2207 * softirq handlers will have completed, since in some kernels, these
2208 * handlers can run in process context, and can block.
2210 * This primitive provides the guarantees made by the (now removed)
2211 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2212 * guarantees that rcu_read_lock() sections will have completed.
2213 * In "classic RCU", these two guarantees happen to be one and
2214 * the same, but can differ in realtime RCU implementations.
2216 void synchronize_sched(void)
2218 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2219 !lock_is_held(&rcu_lock_map
) &&
2220 !lock_is_held(&rcu_sched_lock_map
),
2221 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2222 if (rcu_blocking_is_gp())
2224 wait_rcu_gp(call_rcu_sched
);
2226 EXPORT_SYMBOL_GPL(synchronize_sched
);
2229 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2231 * Control will return to the caller some time after a full rcu_bh grace
2232 * period has elapsed, in other words after all currently executing rcu_bh
2233 * read-side critical sections have completed. RCU read-side critical
2234 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2235 * and may be nested.
2237 void synchronize_rcu_bh(void)
2239 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2240 !lock_is_held(&rcu_lock_map
) &&
2241 !lock_is_held(&rcu_sched_lock_map
),
2242 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2243 if (rcu_blocking_is_gp())
2245 wait_rcu_gp(call_rcu_bh
);
2247 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2249 static atomic_t sync_sched_expedited_started
= ATOMIC_INIT(0);
2250 static atomic_t sync_sched_expedited_done
= ATOMIC_INIT(0);
2252 static int synchronize_sched_expedited_cpu_stop(void *data
)
2255 * There must be a full memory barrier on each affected CPU
2256 * between the time that try_stop_cpus() is called and the
2257 * time that it returns.
2259 * In the current initial implementation of cpu_stop, the
2260 * above condition is already met when the control reaches
2261 * this point and the following smp_mb() is not strictly
2262 * necessary. Do smp_mb() anyway for documentation and
2263 * robustness against future implementation changes.
2265 smp_mb(); /* See above comment block. */
2270 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2272 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2273 * approach to force the grace period to end quickly. This consumes
2274 * significant time on all CPUs and is unfriendly to real-time workloads,
2275 * so is thus not recommended for any sort of common-case code. In fact,
2276 * if you are using synchronize_sched_expedited() in a loop, please
2277 * restructure your code to batch your updates, and then use a single
2278 * synchronize_sched() instead.
2280 * Note that it is illegal to call this function while holding any lock
2281 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2282 * to call this function from a CPU-hotplug notifier. Failing to observe
2283 * these restriction will result in deadlock.
2285 * This implementation can be thought of as an application of ticket
2286 * locking to RCU, with sync_sched_expedited_started and
2287 * sync_sched_expedited_done taking on the roles of the halves
2288 * of the ticket-lock word. Each task atomically increments
2289 * sync_sched_expedited_started upon entry, snapshotting the old value,
2290 * then attempts to stop all the CPUs. If this succeeds, then each
2291 * CPU will have executed a context switch, resulting in an RCU-sched
2292 * grace period. We are then done, so we use atomic_cmpxchg() to
2293 * update sync_sched_expedited_done to match our snapshot -- but
2294 * only if someone else has not already advanced past our snapshot.
2296 * On the other hand, if try_stop_cpus() fails, we check the value
2297 * of sync_sched_expedited_done. If it has advanced past our
2298 * initial snapshot, then someone else must have forced a grace period
2299 * some time after we took our snapshot. In this case, our work is
2300 * done for us, and we can simply return. Otherwise, we try again,
2301 * but keep our initial snapshot for purposes of checking for someone
2302 * doing our work for us.
2304 * If we fail too many times in a row, we fall back to synchronize_sched().
2306 void synchronize_sched_expedited(void)
2308 int firstsnap
, s
, snap
, trycount
= 0;
2310 /* Note that atomic_inc_return() implies full memory barrier. */
2311 firstsnap
= snap
= atomic_inc_return(&sync_sched_expedited_started
);
2313 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2316 * Each pass through the following loop attempts to force a
2317 * context switch on each CPU.
2319 while (try_stop_cpus(cpu_online_mask
,
2320 synchronize_sched_expedited_cpu_stop
,
2324 /* No joy, try again later. Or just synchronize_sched(). */
2325 if (trycount
++ < 10) {
2326 udelay(trycount
* num_online_cpus());
2328 synchronize_sched();
2332 /* Check to see if someone else did our work for us. */
2333 s
= atomic_read(&sync_sched_expedited_done
);
2334 if (UINT_CMP_GE((unsigned)s
, (unsigned)firstsnap
)) {
2335 smp_mb(); /* ensure test happens before caller kfree */
2340 * Refetching sync_sched_expedited_started allows later
2341 * callers to piggyback on our grace period. We subtract
2342 * 1 to get the same token that the last incrementer got.
2343 * We retry after they started, so our grace period works
2344 * for them, and they started after our first try, so their
2345 * grace period works for us.
2348 snap
= atomic_read(&sync_sched_expedited_started
);
2349 smp_mb(); /* ensure read is before try_stop_cpus(). */
2353 * Everyone up to our most recent fetch is covered by our grace
2354 * period. Update the counter, but only if our work is still
2355 * relevant -- which it won't be if someone who started later
2356 * than we did beat us to the punch.
2359 s
= atomic_read(&sync_sched_expedited_done
);
2360 if (UINT_CMP_GE((unsigned)s
, (unsigned)snap
)) {
2361 smp_mb(); /* ensure test happens before caller kfree */
2364 } while (atomic_cmpxchg(&sync_sched_expedited_done
, s
, snap
) != s
);
2368 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2371 * Check to see if there is any immediate RCU-related work to be done
2372 * by the current CPU, for the specified type of RCU, returning 1 if so.
2373 * The checks are in order of increasing expense: checks that can be
2374 * carried out against CPU-local state are performed first. However,
2375 * we must check for CPU stalls first, else we might not get a chance.
2377 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2379 struct rcu_node
*rnp
= rdp
->mynode
;
2381 rdp
->n_rcu_pending
++;
2383 /* Check for CPU stalls, if enabled. */
2384 check_cpu_stall(rsp
, rdp
);
2386 /* Is the RCU core waiting for a quiescent state from this CPU? */
2387 if (rcu_scheduler_fully_active
&&
2388 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2389 rdp
->n_rp_qs_pending
++;
2390 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2391 rdp
->n_rp_report_qs
++;
2395 /* Does this CPU have callbacks ready to invoke? */
2396 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2397 rdp
->n_rp_cb_ready
++;
2401 /* Has RCU gone idle with this CPU needing another grace period? */
2402 if (cpu_needs_another_gp(rsp
, rdp
)) {
2403 rdp
->n_rp_cpu_needs_gp
++;
2407 /* Has another RCU grace period completed? */
2408 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2409 rdp
->n_rp_gp_completed
++;
2413 /* Has a new RCU grace period started? */
2414 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2415 rdp
->n_rp_gp_started
++;
2420 rdp
->n_rp_need_nothing
++;
2425 * Check to see if there is any immediate RCU-related work to be done
2426 * by the current CPU, returning 1 if so. This function is part of the
2427 * RCU implementation; it is -not- an exported member of the RCU API.
2429 static int rcu_pending(int cpu
)
2431 struct rcu_state
*rsp
;
2433 for_each_rcu_flavor(rsp
)
2434 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2440 * Check to see if any future RCU-related work will need to be done
2441 * by the current CPU, even if none need be done immediately, returning
2444 static int rcu_cpu_has_callbacks(int cpu
)
2446 struct rcu_state
*rsp
;
2448 /* RCU callbacks either ready or pending? */
2449 for_each_rcu_flavor(rsp
)
2450 if (per_cpu_ptr(rsp
->rda
, cpu
)->nxtlist
)
2456 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2457 * the compiler is expected to optimize this away.
2459 static void _rcu_barrier_trace(struct rcu_state
*rsp
, char *s
,
2460 int cpu
, unsigned long done
)
2462 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2463 atomic_read(&rsp
->barrier_cpu_count
), done
);
2467 * RCU callback function for _rcu_barrier(). If we are last, wake
2468 * up the task executing _rcu_barrier().
2470 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2472 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2473 struct rcu_state
*rsp
= rdp
->rsp
;
2475 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2476 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2477 complete(&rsp
->barrier_completion
);
2479 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2484 * Called with preemption disabled, and from cross-cpu IRQ context.
2486 static void rcu_barrier_func(void *type
)
2488 struct rcu_state
*rsp
= type
;
2489 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2491 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2492 atomic_inc(&rsp
->barrier_cpu_count
);
2493 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2497 * Orchestrate the specified type of RCU barrier, waiting for all
2498 * RCU callbacks of the specified type to complete.
2500 static void _rcu_barrier(struct rcu_state
*rsp
)
2503 struct rcu_data
*rdp
;
2504 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
2505 unsigned long snap_done
;
2507 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
2509 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2510 mutex_lock(&rsp
->barrier_mutex
);
2513 * Ensure that all prior references, including to ->n_barrier_done,
2514 * are ordered before the _rcu_barrier() machinery.
2516 smp_mb(); /* See above block comment. */
2519 * Recheck ->n_barrier_done to see if others did our work for us.
2520 * This means checking ->n_barrier_done for an even-to-odd-to-even
2521 * transition. The "if" expression below therefore rounds the old
2522 * value up to the next even number and adds two before comparing.
2524 snap_done
= ACCESS_ONCE(rsp
->n_barrier_done
);
2525 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
2526 if (ULONG_CMP_GE(snap_done
, ((snap
+ 1) & ~0x1) + 2)) {
2527 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
2528 smp_mb(); /* caller's subsequent code after above check. */
2529 mutex_unlock(&rsp
->barrier_mutex
);
2534 * Increment ->n_barrier_done to avoid duplicate work. Use
2535 * ACCESS_ONCE() to prevent the compiler from speculating
2536 * the increment to precede the early-exit check.
2538 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2539 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
2540 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
2541 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2544 * Initialize the count to one rather than to zero in order to
2545 * avoid a too-soon return to zero in case of a short grace period
2546 * (or preemption of this task). Exclude CPU-hotplug operations
2547 * to ensure that no offline CPU has callbacks queued.
2549 init_completion(&rsp
->barrier_completion
);
2550 atomic_set(&rsp
->barrier_cpu_count
, 1);
2554 * Force each CPU with callbacks to register a new callback.
2555 * When that callback is invoked, we will know that all of the
2556 * corresponding CPU's preceding callbacks have been invoked.
2558 for_each_online_cpu(cpu
) {
2559 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2560 if (ACCESS_ONCE(rdp
->qlen
)) {
2561 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
2562 rsp
->n_barrier_done
);
2563 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
2565 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
2566 rsp
->n_barrier_done
);
2572 * Now that we have an rcu_barrier_callback() callback on each
2573 * CPU, and thus each counted, remove the initial count.
2575 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
2576 complete(&rsp
->barrier_completion
);
2578 /* Increment ->n_barrier_done to prevent duplicate work. */
2579 smp_mb(); /* Keep increment after above mechanism. */
2580 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2581 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
2582 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
2583 smp_mb(); /* Keep increment before caller's subsequent code. */
2585 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2586 wait_for_completion(&rsp
->barrier_completion
);
2588 /* Other rcu_barrier() invocations can now safely proceed. */
2589 mutex_unlock(&rsp
->barrier_mutex
);
2593 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2595 void rcu_barrier_bh(void)
2597 _rcu_barrier(&rcu_bh_state
);
2599 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2602 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2604 void rcu_barrier_sched(void)
2606 _rcu_barrier(&rcu_sched_state
);
2608 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2611 * Do boot-time initialization of a CPU's per-CPU RCU data.
2614 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2616 unsigned long flags
;
2617 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2618 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2620 /* Set up local state, ensuring consistent view of global state. */
2621 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2622 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2623 init_callback_list(rdp
);
2625 ACCESS_ONCE(rdp
->qlen
) = 0;
2626 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2627 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
2628 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2629 #ifdef CONFIG_RCU_USER_QS
2630 WARN_ON_ONCE(rdp
->dynticks
->in_user
);
2634 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2638 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2639 * offline event can be happening at a given time. Note also that we
2640 * can accept some slop in the rsp->completed access due to the fact
2641 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2643 static void __cpuinit
2644 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2646 unsigned long flags
;
2648 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2649 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2651 /* Set up local state, ensuring consistent view of global state. */
2652 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2653 rdp
->beenonline
= 1; /* We have now been online. */
2654 rdp
->preemptible
= preemptible
;
2655 rdp
->qlen_last_fqs_check
= 0;
2656 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2657 rdp
->blimit
= blimit
;
2658 init_callback_list(rdp
); /* Re-enable callbacks on this CPU. */
2659 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2660 atomic_set(&rdp
->dynticks
->dynticks
,
2661 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
2662 rcu_prepare_for_idle_init(cpu
);
2663 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2666 * A new grace period might start here. If so, we won't be part
2667 * of it, but that is OK, as we are currently in a quiescent state.
2670 /* Exclude any attempts to start a new GP on large systems. */
2671 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
2673 /* Add CPU to rcu_node bitmasks. */
2675 mask
= rdp
->grpmask
;
2677 /* Exclude any attempts to start a new GP on small systems. */
2678 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2679 rnp
->qsmaskinit
|= mask
;
2680 mask
= rnp
->grpmask
;
2681 if (rnp
== rdp
->mynode
) {
2683 * If there is a grace period in progress, we will
2684 * set up to wait for it next time we run the
2687 rdp
->gpnum
= rnp
->completed
;
2688 rdp
->completed
= rnp
->completed
;
2689 rdp
->passed_quiesce
= 0;
2690 rdp
->qs_pending
= 0;
2691 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2693 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2695 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2697 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2700 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2702 struct rcu_state
*rsp
;
2704 for_each_rcu_flavor(rsp
)
2705 rcu_init_percpu_data(cpu
, rsp
,
2706 strcmp(rsp
->name
, "rcu_preempt") == 0);
2710 * Handle CPU online/offline notification events.
2712 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2713 unsigned long action
, void *hcpu
)
2715 long cpu
= (long)hcpu
;
2716 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2717 struct rcu_node
*rnp
= rdp
->mynode
;
2718 struct rcu_state
*rsp
;
2720 trace_rcu_utilization("Start CPU hotplug");
2722 case CPU_UP_PREPARE
:
2723 case CPU_UP_PREPARE_FROZEN
:
2724 rcu_prepare_cpu(cpu
);
2725 rcu_prepare_kthreads(cpu
);
2728 case CPU_DOWN_FAILED
:
2729 rcu_boost_kthread_setaffinity(rnp
, -1);
2731 case CPU_DOWN_PREPARE
:
2732 rcu_boost_kthread_setaffinity(rnp
, cpu
);
2735 case CPU_DYING_FROZEN
:
2737 * The whole machine is "stopped" except this CPU, so we can
2738 * touch any data without introducing corruption. We send the
2739 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2741 for_each_rcu_flavor(rsp
)
2742 rcu_cleanup_dying_cpu(rsp
);
2743 rcu_cleanup_after_idle(cpu
);
2746 case CPU_DEAD_FROZEN
:
2747 case CPU_UP_CANCELED
:
2748 case CPU_UP_CANCELED_FROZEN
:
2749 for_each_rcu_flavor(rsp
)
2750 rcu_cleanup_dead_cpu(cpu
, rsp
);
2755 trace_rcu_utilization("End CPU hotplug");
2760 * Spawn the kthread that handles this RCU flavor's grace periods.
2762 static int __init
rcu_spawn_gp_kthread(void)
2764 unsigned long flags
;
2765 struct rcu_node
*rnp
;
2766 struct rcu_state
*rsp
;
2767 struct task_struct
*t
;
2769 for_each_rcu_flavor(rsp
) {
2770 t
= kthread_run(rcu_gp_kthread
, rsp
, rsp
->name
);
2772 rnp
= rcu_get_root(rsp
);
2773 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2774 rsp
->gp_kthread
= t
;
2775 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2779 early_initcall(rcu_spawn_gp_kthread
);
2782 * This function is invoked towards the end of the scheduler's initialization
2783 * process. Before this is called, the idle task might contain
2784 * RCU read-side critical sections (during which time, this idle
2785 * task is booting the system). After this function is called, the
2786 * idle tasks are prohibited from containing RCU read-side critical
2787 * sections. This function also enables RCU lockdep checking.
2789 void rcu_scheduler_starting(void)
2791 WARN_ON(num_online_cpus() != 1);
2792 WARN_ON(nr_context_switches() > 0);
2793 rcu_scheduler_active
= 1;
2797 * Compute the per-level fanout, either using the exact fanout specified
2798 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2800 #ifdef CONFIG_RCU_FANOUT_EXACT
2801 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2805 for (i
= rcu_num_lvls
- 1; i
> 0; i
--)
2806 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2807 rsp
->levelspread
[0] = rcu_fanout_leaf
;
2809 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2810 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2817 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2818 ccur
= rsp
->levelcnt
[i
];
2819 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2823 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2826 * Helper function for rcu_init() that initializes one rcu_state structure.
2828 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2829 struct rcu_data __percpu
*rda
)
2831 static char *buf
[] = { "rcu_node_0",
2834 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
2835 static char *fqs
[] = { "rcu_node_fqs_0",
2838 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
2842 struct rcu_node
*rnp
;
2844 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2846 /* Initialize the level-tracking arrays. */
2848 for (i
= 0; i
< rcu_num_lvls
; i
++)
2849 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
2850 for (i
= 1; i
< rcu_num_lvls
; i
++)
2851 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2852 rcu_init_levelspread(rsp
);
2854 /* Initialize the elements themselves, starting from the leaves. */
2856 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2857 cpustride
*= rsp
->levelspread
[i
];
2858 rnp
= rsp
->level
[i
];
2859 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2860 raw_spin_lock_init(&rnp
->lock
);
2861 lockdep_set_class_and_name(&rnp
->lock
,
2862 &rcu_node_class
[i
], buf
[i
]);
2863 raw_spin_lock_init(&rnp
->fqslock
);
2864 lockdep_set_class_and_name(&rnp
->fqslock
,
2865 &rcu_fqs_class
[i
], fqs
[i
]);
2866 rnp
->gpnum
= rsp
->gpnum
;
2867 rnp
->completed
= rsp
->completed
;
2869 rnp
->qsmaskinit
= 0;
2870 rnp
->grplo
= j
* cpustride
;
2871 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2872 if (rnp
->grphi
>= NR_CPUS
)
2873 rnp
->grphi
= NR_CPUS
- 1;
2879 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2880 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2881 rnp
->parent
= rsp
->level
[i
- 1] +
2882 j
/ rsp
->levelspread
[i
- 1];
2885 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2890 init_waitqueue_head(&rsp
->gp_wq
);
2891 rnp
= rsp
->level
[rcu_num_lvls
- 1];
2892 for_each_possible_cpu(i
) {
2893 while (i
> rnp
->grphi
)
2895 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2896 rcu_boot_init_percpu_data(i
, rsp
);
2898 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
2902 * Compute the rcu_node tree geometry from kernel parameters. This cannot
2903 * replace the definitions in rcutree.h because those are needed to size
2904 * the ->node array in the rcu_state structure.
2906 static void __init
rcu_init_geometry(void)
2911 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
2913 /* If the compile-time values are accurate, just leave. */
2914 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
&&
2915 nr_cpu_ids
== NR_CPUS
)
2919 * Compute number of nodes that can be handled an rcu_node tree
2920 * with the given number of levels. Setting rcu_capacity[0] makes
2921 * some of the arithmetic easier.
2923 rcu_capacity
[0] = 1;
2924 rcu_capacity
[1] = rcu_fanout_leaf
;
2925 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
2926 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
2929 * The boot-time rcu_fanout_leaf parameter is only permitted
2930 * to increase the leaf-level fanout, not decrease it. Of course,
2931 * the leaf-level fanout cannot exceed the number of bits in
2932 * the rcu_node masks. Finally, the tree must be able to accommodate
2933 * the configured number of CPUs. Complain and fall back to the
2934 * compile-time values if these limits are exceeded.
2936 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
2937 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
2938 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
2943 /* Calculate the number of rcu_nodes at each level of the tree. */
2944 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
2945 if (n
<= rcu_capacity
[i
]) {
2946 for (j
= 0; j
<= i
; j
++)
2948 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
2950 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
2955 /* Calculate the total number of rcu_node structures. */
2957 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
2958 rcu_num_nodes
+= num_rcu_lvl
[i
];
2962 void __init
rcu_init(void)
2966 rcu_bootup_announce();
2967 rcu_init_geometry();
2968 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
2969 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
2970 __rcu_init_preempt();
2971 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
2974 * We don't need protection against CPU-hotplug here because
2975 * this is called early in boot, before either interrupts
2976 * or the scheduler are operational.
2978 cpu_notifier(rcu_cpu_notify
, 0);
2979 for_each_online_cpu(cpu
)
2980 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
2981 check_cpu_stall_init();
2984 #include "rcutree_plugin.h"