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, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
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/module.h>
45 #include <linux/percpu.h>
46 #include <linux/notifier.h>
47 #include <linux/cpu.h>
48 #include <linux/mutex.h>
49 #include <linux/time.h>
50 #include <linux/kernel_stat.h>
51 #include <linux/wait.h>
52 #include <linux/kthread.h>
53 #include <linux/prefetch.h>
54 #include <linux/delay.h>
55 #include <linux/stop_machine.h>
56 #include <linux/random.h>
57 #include <linux/ftrace_event.h>
58 #include <linux/suspend.h>
63 MODULE_ALIAS("rcutree");
64 #ifdef MODULE_PARAM_PREFIX
65 #undef MODULE_PARAM_PREFIX
67 #define MODULE_PARAM_PREFIX "rcutree."
69 /* Data structures. */
71 static struct lock_class_key rcu_node_class
[RCU_NUM_LVLS
];
72 static struct lock_class_key rcu_fqs_class
[RCU_NUM_LVLS
];
75 * In order to export the rcu_state name to the tracing tools, it
76 * needs to be added in the __tracepoint_string section.
77 * This requires defining a separate variable tp_<sname>_varname
78 * that points to the string being used, and this will allow
79 * the tracing userspace tools to be able to decipher the string
80 * address to the matching string.
82 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
83 static char sname##_varname[] = #sname; \
84 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
85 struct rcu_state sname##_state = { \
86 .level = { &sname##_state.node[0] }, \
88 .fqs_state = RCU_GP_IDLE, \
89 .gpnum = 0UL - 300UL, \
90 .completed = 0UL - 300UL, \
91 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
92 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
93 .orphan_donetail = &sname##_state.orphan_donelist, \
94 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
95 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
96 .name = sname##_varname, \
99 DEFINE_PER_CPU(struct rcu_data, sname##_data)
101 RCU_STATE_INITIALIZER(rcu_sched
, 's', call_rcu_sched
);
102 RCU_STATE_INITIALIZER(rcu_bh
, 'b', call_rcu_bh
);
104 static struct rcu_state
*rcu_state
;
105 LIST_HEAD(rcu_struct_flavors
);
107 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
108 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
109 module_param(rcu_fanout_leaf
, int, 0444);
110 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
111 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
118 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
121 * The rcu_scheduler_active variable transitions from zero to one just
122 * before the first task is spawned. So when this variable is zero, RCU
123 * can assume that there is but one task, allowing RCU to (for example)
124 * optimize synchronize_sched() to a simple barrier(). When this variable
125 * is one, RCU must actually do all the hard work required to detect real
126 * grace periods. This variable is also used to suppress boot-time false
127 * positives from lockdep-RCU error checking.
129 int rcu_scheduler_active __read_mostly
;
130 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
133 * The rcu_scheduler_fully_active variable transitions from zero to one
134 * during the early_initcall() processing, which is after the scheduler
135 * is capable of creating new tasks. So RCU processing (for example,
136 * creating tasks for RCU priority boosting) must be delayed until after
137 * rcu_scheduler_fully_active transitions from zero to one. We also
138 * currently delay invocation of any RCU callbacks until after this point.
140 * It might later prove better for people registering RCU callbacks during
141 * early boot to take responsibility for these callbacks, but one step at
144 static int rcu_scheduler_fully_active __read_mostly
;
146 #ifdef CONFIG_RCU_BOOST
149 * Control variables for per-CPU and per-rcu_node kthreads. These
150 * handle all flavors of RCU.
152 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
153 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
154 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
155 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
157 #endif /* #ifdef CONFIG_RCU_BOOST */
159 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
160 static void invoke_rcu_core(void);
161 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
164 * Track the rcutorture test sequence number and the update version
165 * number within a given test. The rcutorture_testseq is incremented
166 * on every rcutorture module load and unload, so has an odd value
167 * when a test is running. The rcutorture_vernum is set to zero
168 * when rcutorture starts and is incremented on each rcutorture update.
169 * These variables enable correlating rcutorture output with the
170 * RCU tracing information.
172 unsigned long rcutorture_testseq
;
173 unsigned long rcutorture_vernum
;
176 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
177 * permit this function to be invoked without holding the root rcu_node
178 * structure's ->lock, but of course results can be subject to change.
180 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
182 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
186 * Note a quiescent state. Because we do not need to know
187 * how many quiescent states passed, just if there was at least
188 * one since the start of the grace period, this just sets a flag.
189 * The caller must have disabled preemption.
191 void rcu_sched_qs(int cpu
)
193 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
195 if (rdp
->passed_quiesce
== 0)
196 trace_rcu_grace_period(TPS("rcu_sched"), rdp
->gpnum
, TPS("cpuqs"));
197 rdp
->passed_quiesce
= 1;
200 void rcu_bh_qs(int cpu
)
202 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
204 if (rdp
->passed_quiesce
== 0)
205 trace_rcu_grace_period(TPS("rcu_bh"), rdp
->gpnum
, TPS("cpuqs"));
206 rdp
->passed_quiesce
= 1;
210 * Note a context switch. This is a quiescent state for RCU-sched,
211 * and requires special handling for preemptible RCU.
212 * The caller must have disabled preemption.
214 void rcu_note_context_switch(int cpu
)
216 trace_rcu_utilization(TPS("Start context switch"));
218 rcu_preempt_note_context_switch(cpu
);
219 trace_rcu_utilization(TPS("End context switch"));
221 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
223 static DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
224 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
225 .dynticks
= ATOMIC_INIT(1),
226 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
227 .dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
,
228 .dynticks_idle
= ATOMIC_INIT(1),
229 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
232 static long blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
233 static long qhimark
= 10000; /* If this many pending, ignore blimit. */
234 static long qlowmark
= 100; /* Once only this many pending, use blimit. */
236 module_param(blimit
, long, 0444);
237 module_param(qhimark
, long, 0444);
238 module_param(qlowmark
, long, 0444);
240 static ulong jiffies_till_first_fqs
= ULONG_MAX
;
241 static ulong jiffies_till_next_fqs
= ULONG_MAX
;
243 module_param(jiffies_till_first_fqs
, ulong
, 0644);
244 module_param(jiffies_till_next_fqs
, ulong
, 0644);
246 static bool rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
247 struct rcu_data
*rdp
);
248 static void force_qs_rnp(struct rcu_state
*rsp
,
249 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
250 unsigned long *maxj
),
251 bool *isidle
, unsigned long *maxj
);
252 static void force_quiescent_state(struct rcu_state
*rsp
);
253 static int rcu_pending(int cpu
);
256 * Return the number of RCU-sched batches processed thus far for debug & stats.
258 long rcu_batches_completed_sched(void)
260 return rcu_sched_state
.completed
;
262 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
265 * Return the number of RCU BH batches processed thus far for debug & stats.
267 long rcu_batches_completed_bh(void)
269 return rcu_bh_state
.completed
;
271 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
274 * Force a quiescent state for RCU BH.
276 void rcu_bh_force_quiescent_state(void)
278 force_quiescent_state(&rcu_bh_state
);
280 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
283 * Record the number of times rcutorture tests have been initiated and
284 * terminated. This information allows the debugfs tracing stats to be
285 * correlated to the rcutorture messages, even when the rcutorture module
286 * is being repeatedly loaded and unloaded. In other words, we cannot
287 * store this state in rcutorture itself.
289 void rcutorture_record_test_transition(void)
291 rcutorture_testseq
++;
292 rcutorture_vernum
= 0;
294 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
297 * Record the number of writer passes through the current rcutorture test.
298 * This is also used to correlate debugfs tracing stats with the rcutorture
301 void rcutorture_record_progress(unsigned long vernum
)
305 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
308 * Force a quiescent state for RCU-sched.
310 void rcu_sched_force_quiescent_state(void)
312 force_quiescent_state(&rcu_sched_state
);
314 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
317 * Does the CPU have callbacks ready to be invoked?
320 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
322 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
] &&
323 rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
;
327 * Return the root node of the specified rcu_state structure.
329 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
331 return &rsp
->node
[0];
335 * Is there any need for future grace periods?
336 * Interrupts must be disabled. If the caller does not hold the root
337 * rnp_node structure's ->lock, the results are advisory only.
339 static int rcu_future_needs_gp(struct rcu_state
*rsp
)
341 struct rcu_node
*rnp
= rcu_get_root(rsp
);
342 int idx
= (ACCESS_ONCE(rnp
->completed
) + 1) & 0x1;
343 int *fp
= &rnp
->need_future_gp
[idx
];
345 return ACCESS_ONCE(*fp
);
349 * Does the current CPU require a not-yet-started grace period?
350 * The caller must have disabled interrupts to prevent races with
351 * normal callback registry.
354 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
358 if (rcu_gp_in_progress(rsp
))
359 return 0; /* No, a grace period is already in progress. */
360 if (rcu_future_needs_gp(rsp
))
361 return 1; /* Yes, a no-CBs CPU needs one. */
362 if (!rdp
->nxttail
[RCU_NEXT_TAIL
])
363 return 0; /* No, this is a no-CBs (or offline) CPU. */
364 if (*rdp
->nxttail
[RCU_NEXT_READY_TAIL
])
365 return 1; /* Yes, this CPU has newly registered callbacks. */
366 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
367 if (rdp
->nxttail
[i
- 1] != rdp
->nxttail
[i
] &&
368 ULONG_CMP_LT(ACCESS_ONCE(rsp
->completed
),
369 rdp
->nxtcompleted
[i
]))
370 return 1; /* Yes, CBs for future grace period. */
371 return 0; /* No grace period needed. */
375 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
377 * If the new value of the ->dynticks_nesting counter now is zero,
378 * we really have entered idle, and must do the appropriate accounting.
379 * The caller must have disabled interrupts.
381 static void rcu_eqs_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
,
384 struct rcu_state
*rsp
;
385 struct rcu_data
*rdp
;
387 trace_rcu_dyntick(TPS("Start"), oldval
, rdtp
->dynticks_nesting
);
388 if (!user
&& !is_idle_task(current
)) {
389 struct task_struct
*idle __maybe_unused
=
390 idle_task(smp_processor_id());
392 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval
, 0);
393 ftrace_dump(DUMP_ORIG
);
394 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
395 current
->pid
, current
->comm
,
396 idle
->pid
, idle
->comm
); /* must be idle task! */
398 for_each_rcu_flavor(rsp
) {
399 rdp
= this_cpu_ptr(rsp
->rda
);
400 do_nocb_deferred_wakeup(rdp
);
402 rcu_prepare_for_idle(smp_processor_id());
403 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
404 smp_mb__before_atomic_inc(); /* See above. */
405 atomic_inc(&rdtp
->dynticks
);
406 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
407 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
410 * It is illegal to enter an extended quiescent state while
411 * in an RCU read-side critical section.
413 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
414 "Illegal idle entry in RCU read-side critical section.");
415 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
416 "Illegal idle entry in RCU-bh read-side critical section.");
417 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
418 "Illegal idle entry in RCU-sched read-side critical section.");
422 * Enter an RCU extended quiescent state, which can be either the
423 * idle loop or adaptive-tickless usermode execution.
425 static void rcu_eqs_enter(bool user
)
428 struct rcu_dynticks
*rdtp
;
430 rdtp
= this_cpu_ptr(&rcu_dynticks
);
431 oldval
= rdtp
->dynticks_nesting
;
432 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
433 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
) {
434 rdtp
->dynticks_nesting
= 0;
435 rcu_eqs_enter_common(rdtp
, oldval
, user
);
437 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
442 * rcu_idle_enter - inform RCU that current CPU is entering idle
444 * Enter idle mode, in other words, -leave- the mode in which RCU
445 * read-side critical sections can occur. (Though RCU read-side
446 * critical sections can occur in irq handlers in idle, a possibility
447 * handled by irq_enter() and irq_exit().)
449 * We crowbar the ->dynticks_nesting field to zero to allow for
450 * the possibility of usermode upcalls having messed up our count
451 * of interrupt nesting level during the prior busy period.
453 void rcu_idle_enter(void)
457 local_irq_save(flags
);
458 rcu_eqs_enter(false);
459 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks
), 0);
460 local_irq_restore(flags
);
462 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
464 #ifdef CONFIG_RCU_USER_QS
466 * rcu_user_enter - inform RCU that we are resuming userspace.
468 * Enter RCU idle mode right before resuming userspace. No use of RCU
469 * is permitted between this call and rcu_user_exit(). This way the
470 * CPU doesn't need to maintain the tick for RCU maintenance purposes
471 * when the CPU runs in userspace.
473 void rcu_user_enter(void)
477 #endif /* CONFIG_RCU_USER_QS */
480 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
482 * Exit from an interrupt handler, which might possibly result in entering
483 * idle mode, in other words, leaving the mode in which read-side critical
484 * sections can occur.
486 * This code assumes that the idle loop never does anything that might
487 * result in unbalanced calls to irq_enter() and irq_exit(). If your
488 * architecture violates this assumption, RCU will give you what you
489 * deserve, good and hard. But very infrequently and irreproducibly.
491 * Use things like work queues to work around this limitation.
493 * You have been warned.
495 void rcu_irq_exit(void)
499 struct rcu_dynticks
*rdtp
;
501 local_irq_save(flags
);
502 rdtp
= this_cpu_ptr(&rcu_dynticks
);
503 oldval
= rdtp
->dynticks_nesting
;
504 rdtp
->dynticks_nesting
--;
505 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
506 if (rdtp
->dynticks_nesting
)
507 trace_rcu_dyntick(TPS("--="), oldval
, rdtp
->dynticks_nesting
);
509 rcu_eqs_enter_common(rdtp
, oldval
, true);
510 rcu_sysidle_enter(rdtp
, 1);
511 local_irq_restore(flags
);
515 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
517 * If the new value of the ->dynticks_nesting counter was previously zero,
518 * we really have exited idle, and must do the appropriate accounting.
519 * The caller must have disabled interrupts.
521 static void rcu_eqs_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
,
524 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
525 atomic_inc(&rdtp
->dynticks
);
526 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
527 smp_mb__after_atomic_inc(); /* See above. */
528 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
529 rcu_cleanup_after_idle(smp_processor_id());
530 trace_rcu_dyntick(TPS("End"), oldval
, rdtp
->dynticks_nesting
);
531 if (!user
&& !is_idle_task(current
)) {
532 struct task_struct
*idle __maybe_unused
=
533 idle_task(smp_processor_id());
535 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
536 oldval
, rdtp
->dynticks_nesting
);
537 ftrace_dump(DUMP_ORIG
);
538 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
539 current
->pid
, current
->comm
,
540 idle
->pid
, idle
->comm
); /* must be idle task! */
545 * Exit an RCU extended quiescent state, which can be either the
546 * idle loop or adaptive-tickless usermode execution.
548 static void rcu_eqs_exit(bool user
)
550 struct rcu_dynticks
*rdtp
;
553 rdtp
= this_cpu_ptr(&rcu_dynticks
);
554 oldval
= rdtp
->dynticks_nesting
;
555 WARN_ON_ONCE(oldval
< 0);
556 if (oldval
& DYNTICK_TASK_NEST_MASK
) {
557 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
559 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
560 rcu_eqs_exit_common(rdtp
, oldval
, user
);
565 * rcu_idle_exit - inform RCU that current CPU is leaving idle
567 * Exit idle mode, in other words, -enter- the mode in which RCU
568 * read-side critical sections can occur.
570 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
571 * allow for the possibility of usermode upcalls messing up our count
572 * of interrupt nesting level during the busy period that is just
575 void rcu_idle_exit(void)
579 local_irq_save(flags
);
581 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks
), 0);
582 local_irq_restore(flags
);
584 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
586 #ifdef CONFIG_RCU_USER_QS
588 * rcu_user_exit - inform RCU that we are exiting userspace.
590 * Exit RCU idle mode while entering the kernel because it can
591 * run a RCU read side critical section anytime.
593 void rcu_user_exit(void)
597 #endif /* CONFIG_RCU_USER_QS */
600 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
602 * Enter an interrupt handler, which might possibly result in exiting
603 * idle mode, in other words, entering the mode in which read-side critical
604 * sections can occur.
606 * Note that the Linux kernel is fully capable of entering an interrupt
607 * handler that it never exits, for example when doing upcalls to
608 * user mode! This code assumes that the idle loop never does upcalls to
609 * user mode. If your architecture does do upcalls from the idle loop (or
610 * does anything else that results in unbalanced calls to the irq_enter()
611 * and irq_exit() functions), RCU will give you what you deserve, good
612 * and hard. But very infrequently and irreproducibly.
614 * Use things like work queues to work around this limitation.
616 * You have been warned.
618 void rcu_irq_enter(void)
621 struct rcu_dynticks
*rdtp
;
624 local_irq_save(flags
);
625 rdtp
= this_cpu_ptr(&rcu_dynticks
);
626 oldval
= rdtp
->dynticks_nesting
;
627 rdtp
->dynticks_nesting
++;
628 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
630 trace_rcu_dyntick(TPS("++="), oldval
, rdtp
->dynticks_nesting
);
632 rcu_eqs_exit_common(rdtp
, oldval
, true);
633 rcu_sysidle_exit(rdtp
, 1);
634 local_irq_restore(flags
);
638 * rcu_nmi_enter - inform RCU of entry to NMI context
640 * If the CPU was idle with dynamic ticks active, and there is no
641 * irq handler running, this updates rdtp->dynticks_nmi to let the
642 * RCU grace-period handling know that the CPU is active.
644 void rcu_nmi_enter(void)
646 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
648 if (rdtp
->dynticks_nmi_nesting
== 0 &&
649 (atomic_read(&rdtp
->dynticks
) & 0x1))
651 rdtp
->dynticks_nmi_nesting
++;
652 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
653 atomic_inc(&rdtp
->dynticks
);
654 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
655 smp_mb__after_atomic_inc(); /* See above. */
656 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
660 * rcu_nmi_exit - inform RCU of exit from NMI context
662 * If the CPU was idle with dynamic ticks active, and there is no
663 * irq handler running, this updates rdtp->dynticks_nmi to let the
664 * RCU grace-period handling know that the CPU is no longer active.
666 void rcu_nmi_exit(void)
668 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
670 if (rdtp
->dynticks_nmi_nesting
== 0 ||
671 --rdtp
->dynticks_nmi_nesting
!= 0)
673 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
674 smp_mb__before_atomic_inc(); /* See above. */
675 atomic_inc(&rdtp
->dynticks
);
676 smp_mb__after_atomic_inc(); /* Force delay to next write. */
677 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
681 * __rcu_is_watching - are RCU read-side critical sections safe?
683 * Return true if RCU is watching the running CPU, which means that
684 * this CPU can safely enter RCU read-side critical sections. Unlike
685 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
686 * least disabled preemption.
688 bool notrace
__rcu_is_watching(void)
690 return atomic_read(this_cpu_ptr(&rcu_dynticks
.dynticks
)) & 0x1;
694 * rcu_is_watching - see if RCU thinks that the current CPU is idle
696 * If the current CPU is in its idle loop and is neither in an interrupt
697 * or NMI handler, return true.
699 bool notrace
rcu_is_watching(void)
704 ret
= __rcu_is_watching();
708 EXPORT_SYMBOL_GPL(rcu_is_watching
);
710 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
713 * Is the current CPU online? Disable preemption to avoid false positives
714 * that could otherwise happen due to the current CPU number being sampled,
715 * this task being preempted, its old CPU being taken offline, resuming
716 * on some other CPU, then determining that its old CPU is now offline.
717 * It is OK to use RCU on an offline processor during initial boot, hence
718 * the check for rcu_scheduler_fully_active. Note also that it is OK
719 * for a CPU coming online to use RCU for one jiffy prior to marking itself
720 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
721 * offline to continue to use RCU for one jiffy after marking itself
722 * offline in the cpu_online_mask. This leniency is necessary given the
723 * non-atomic nature of the online and offline processing, for example,
724 * the fact that a CPU enters the scheduler after completing the CPU_DYING
727 * This is also why RCU internally marks CPUs online during the
728 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
730 * Disable checking if in an NMI handler because we cannot safely report
731 * errors from NMI handlers anyway.
733 bool rcu_lockdep_current_cpu_online(void)
735 struct rcu_data
*rdp
;
736 struct rcu_node
*rnp
;
742 rdp
= this_cpu_ptr(&rcu_sched_data
);
744 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
745 !rcu_scheduler_fully_active
;
749 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
751 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
754 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
756 * If the current CPU is idle or running at a first-level (not nested)
757 * interrupt from idle, return true. The caller must have at least
758 * disabled preemption.
760 static int rcu_is_cpu_rrupt_from_idle(void)
762 return __this_cpu_read(rcu_dynticks
.dynticks_nesting
) <= 1;
766 * Snapshot the specified CPU's dynticks counter so that we can later
767 * credit them with an implicit quiescent state. Return 1 if this CPU
768 * is in dynticks idle mode, which is an extended quiescent state.
770 static int dyntick_save_progress_counter(struct rcu_data
*rdp
,
771 bool *isidle
, unsigned long *maxj
)
773 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
774 rcu_sysidle_check_cpu(rdp
, isidle
, maxj
);
775 if ((rdp
->dynticks_snap
& 0x1) == 0) {
776 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("dti"));
784 * This function really isn't for public consumption, but RCU is special in
785 * that context switches can allow the state machine to make progress.
787 extern void resched_cpu(int cpu
);
790 * Return true if the specified CPU has passed through a quiescent
791 * state by virtue of being in or having passed through an dynticks
792 * idle state since the last call to dyntick_save_progress_counter()
793 * for this same CPU, or by virtue of having been offline.
795 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
,
796 bool *isidle
, unsigned long *maxj
)
801 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
802 snap
= (unsigned int)rdp
->dynticks_snap
;
805 * If the CPU passed through or entered a dynticks idle phase with
806 * no active irq/NMI handlers, then we can safely pretend that the CPU
807 * already acknowledged the request to pass through a quiescent
808 * state. Either way, that CPU cannot possibly be in an RCU
809 * read-side critical section that started before the beginning
810 * of the current RCU grace period.
812 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
813 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("dti"));
819 * Check for the CPU being offline, but only if the grace period
820 * is old enough. We don't need to worry about the CPU changing
821 * state: If we see it offline even once, it has been through a
824 * The reason for insisting that the grace period be at least
825 * one jiffy old is that CPUs that are not quite online and that
826 * have just gone offline can still execute RCU read-side critical
829 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
830 return 0; /* Grace period is not old enough. */
832 if (cpu_is_offline(rdp
->cpu
)) {
833 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("ofl"));
839 * There is a possibility that a CPU in adaptive-ticks state
840 * might run in the kernel with the scheduling-clock tick disabled
841 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
842 * force the CPU to restart the scheduling-clock tick in this
843 * CPU is in this state.
845 rcu_kick_nohz_cpu(rdp
->cpu
);
848 * Alternatively, the CPU might be running in the kernel
849 * for an extended period of time without a quiescent state.
850 * Attempt to force the CPU through the scheduler to gain the
851 * needed quiescent state, but only if the grace period has gone
852 * on for an uncommonly long time. If there are many stuck CPUs,
853 * we will beat on the first one until it gets unstuck, then move
854 * to the next. Only do this for the primary flavor of RCU.
856 if (rdp
->rsp
== rcu_state
&&
857 ULONG_CMP_GE(jiffies
, rdp
->rsp
->jiffies_resched
)) {
858 rdp
->rsp
->jiffies_resched
+= 5;
859 resched_cpu(rdp
->cpu
);
865 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
867 unsigned long j
= jiffies
;
871 smp_wmb(); /* Record start time before stall time. */
872 j1
= rcu_jiffies_till_stall_check();
873 ACCESS_ONCE(rsp
->jiffies_stall
) = j
+ j1
;
874 rsp
->jiffies_resched
= j
+ j1
/ 2;
878 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
879 * for architectures that do not implement trigger_all_cpu_backtrace().
880 * The NMI-triggered stack traces are more accurate because they are
881 * printed by the target CPU.
883 static void rcu_dump_cpu_stacks(struct rcu_state
*rsp
)
887 struct rcu_node
*rnp
;
889 rcu_for_each_leaf_node(rsp
, rnp
) {
890 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
891 if (rnp
->qsmask
!= 0) {
892 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
893 if (rnp
->qsmask
& (1UL << cpu
))
894 dump_cpu_task(rnp
->grplo
+ cpu
);
896 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
900 static void print_other_cpu_stall(struct rcu_state
*rsp
)
906 struct rcu_node
*rnp
= rcu_get_root(rsp
);
909 /* Only let one CPU complain about others per time interval. */
911 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
912 delta
= jiffies
- ACCESS_ONCE(rsp
->jiffies_stall
);
913 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
914 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
917 ACCESS_ONCE(rsp
->jiffies_stall
) = jiffies
+ 3 * rcu_jiffies_till_stall_check() + 3;
918 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
921 * OK, time to rat on our buddy...
922 * See Documentation/RCU/stallwarn.txt for info on how to debug
923 * RCU CPU stall warnings.
925 pr_err("INFO: %s detected stalls on CPUs/tasks:",
927 print_cpu_stall_info_begin();
928 rcu_for_each_leaf_node(rsp
, rnp
) {
929 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
930 ndetected
+= rcu_print_task_stall(rnp
);
931 if (rnp
->qsmask
!= 0) {
932 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
933 if (rnp
->qsmask
& (1UL << cpu
)) {
934 print_cpu_stall_info(rsp
,
939 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
943 * Now rat on any tasks that got kicked up to the root rcu_node
944 * due to CPU offlining.
946 rnp
= rcu_get_root(rsp
);
947 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
948 ndetected
+= rcu_print_task_stall(rnp
);
949 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
951 print_cpu_stall_info_end();
952 for_each_possible_cpu(cpu
)
953 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
954 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
955 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
),
956 (long)rsp
->gpnum
, (long)rsp
->completed
, totqlen
);
958 pr_err("INFO: Stall ended before state dump start\n");
959 else if (!trigger_all_cpu_backtrace())
960 rcu_dump_cpu_stacks(rsp
);
962 /* Complain about tasks blocking the grace period. */
964 rcu_print_detail_task_stall(rsp
);
966 force_quiescent_state(rsp
); /* Kick them all. */
970 * This function really isn't for public consumption, but RCU is special in
971 * that context switches can allow the state machine to make progress.
973 extern void resched_cpu(int cpu
);
975 static void print_cpu_stall(struct rcu_state
*rsp
)
979 struct rcu_node
*rnp
= rcu_get_root(rsp
);
983 * OK, time to rat on ourselves...
984 * See Documentation/RCU/stallwarn.txt for info on how to debug
985 * RCU CPU stall warnings.
987 pr_err("INFO: %s self-detected stall on CPU", rsp
->name
);
988 print_cpu_stall_info_begin();
989 print_cpu_stall_info(rsp
, smp_processor_id());
990 print_cpu_stall_info_end();
991 for_each_possible_cpu(cpu
)
992 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
993 pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
994 jiffies
- rsp
->gp_start
,
995 (long)rsp
->gpnum
, (long)rsp
->completed
, totqlen
);
996 if (!trigger_all_cpu_backtrace())
999 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1000 if (ULONG_CMP_GE(jiffies
, ACCESS_ONCE(rsp
->jiffies_stall
)))
1001 ACCESS_ONCE(rsp
->jiffies_stall
) = jiffies
+
1002 3 * rcu_jiffies_till_stall_check() + 3;
1003 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1006 * Attempt to revive the RCU machinery by forcing a context switch.
1008 * A context switch would normally allow the RCU state machine to make
1009 * progress and it could be we're stuck in kernel space without context
1010 * switches for an entirely unreasonable amount of time.
1012 resched_cpu(smp_processor_id());
1015 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1017 unsigned long completed
;
1018 unsigned long gpnum
;
1022 struct rcu_node
*rnp
;
1024 if (rcu_cpu_stall_suppress
|| !rcu_gp_in_progress(rsp
))
1029 * Lots of memory barriers to reject false positives.
1031 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1032 * then rsp->gp_start, and finally rsp->completed. These values
1033 * are updated in the opposite order with memory barriers (or
1034 * equivalent) during grace-period initialization and cleanup.
1035 * Now, a false positive can occur if we get an new value of
1036 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1037 * the memory barriers, the only way that this can happen is if one
1038 * grace period ends and another starts between these two fetches.
1039 * Detect this by comparing rsp->completed with the previous fetch
1042 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1043 * and rsp->gp_start suffice to forestall false positives.
1045 gpnum
= ACCESS_ONCE(rsp
->gpnum
);
1046 smp_rmb(); /* Pick up ->gpnum first... */
1047 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
1048 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1049 gps
= ACCESS_ONCE(rsp
->gp_start
);
1050 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1051 completed
= ACCESS_ONCE(rsp
->completed
);
1052 if (ULONG_CMP_GE(completed
, gpnum
) ||
1053 ULONG_CMP_LT(j
, js
) ||
1054 ULONG_CMP_GE(gps
, js
))
1055 return; /* No stall or GP completed since entering function. */
1057 if (rcu_gp_in_progress(rsp
) &&
1058 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
)) {
1060 /* We haven't checked in, so go dump stack. */
1061 print_cpu_stall(rsp
);
1063 } else if (rcu_gp_in_progress(rsp
) &&
1064 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
1066 /* They had a few time units to dump stack, so complain. */
1067 print_other_cpu_stall(rsp
);
1072 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1074 * Set the stall-warning timeout way off into the future, thus preventing
1075 * any RCU CPU stall-warning messages from appearing in the current set of
1076 * RCU grace periods.
1078 * The caller must disable hard irqs.
1080 void rcu_cpu_stall_reset(void)
1082 struct rcu_state
*rsp
;
1084 for_each_rcu_flavor(rsp
)
1085 ACCESS_ONCE(rsp
->jiffies_stall
) = jiffies
+ ULONG_MAX
/ 2;
1089 * Initialize the specified rcu_data structure's callback list to empty.
1091 static void init_callback_list(struct rcu_data
*rdp
)
1095 if (init_nocb_callback_list(rdp
))
1097 rdp
->nxtlist
= NULL
;
1098 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1099 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1103 * Determine the value that ->completed will have at the end of the
1104 * next subsequent grace period. This is used to tag callbacks so that
1105 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1106 * been dyntick-idle for an extended period with callbacks under the
1107 * influence of RCU_FAST_NO_HZ.
1109 * The caller must hold rnp->lock with interrupts disabled.
1111 static unsigned long rcu_cbs_completed(struct rcu_state
*rsp
,
1112 struct rcu_node
*rnp
)
1115 * If RCU is idle, we just wait for the next grace period.
1116 * But we can only be sure that RCU is idle if we are looking
1117 * at the root rcu_node structure -- otherwise, a new grace
1118 * period might have started, but just not yet gotten around
1119 * to initializing the current non-root rcu_node structure.
1121 if (rcu_get_root(rsp
) == rnp
&& rnp
->gpnum
== rnp
->completed
)
1122 return rnp
->completed
+ 1;
1125 * Otherwise, wait for a possible partial grace period and
1126 * then the subsequent full grace period.
1128 return rnp
->completed
+ 2;
1132 * Trace-event helper function for rcu_start_future_gp() and
1133 * rcu_nocb_wait_gp().
1135 static void trace_rcu_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
,
1136 unsigned long c
, const char *s
)
1138 trace_rcu_future_grace_period(rdp
->rsp
->name
, rnp
->gpnum
,
1139 rnp
->completed
, c
, rnp
->level
,
1140 rnp
->grplo
, rnp
->grphi
, s
);
1144 * Start some future grace period, as needed to handle newly arrived
1145 * callbacks. The required future grace periods are recorded in each
1146 * rcu_node structure's ->need_future_gp field. Returns true if there
1147 * is reason to awaken the grace-period kthread.
1149 * The caller must hold the specified rcu_node structure's ->lock.
1151 static bool __maybe_unused
1152 rcu_start_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
,
1153 unsigned long *c_out
)
1158 struct rcu_node
*rnp_root
= rcu_get_root(rdp
->rsp
);
1161 * Pick up grace-period number for new callbacks. If this
1162 * grace period is already marked as needed, return to the caller.
1164 c
= rcu_cbs_completed(rdp
->rsp
, rnp
);
1165 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startleaf"));
1166 if (rnp
->need_future_gp
[c
& 0x1]) {
1167 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartleaf"));
1172 * If either this rcu_node structure or the root rcu_node structure
1173 * believe that a grace period is in progress, then we must wait
1174 * for the one following, which is in "c". Because our request
1175 * will be noticed at the end of the current grace period, we don't
1176 * need to explicitly start one.
1178 if (rnp
->gpnum
!= rnp
->completed
||
1179 ACCESS_ONCE(rnp
->gpnum
) != ACCESS_ONCE(rnp
->completed
)) {
1180 rnp
->need_future_gp
[c
& 0x1]++;
1181 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleaf"));
1186 * There might be no grace period in progress. If we don't already
1187 * hold it, acquire the root rcu_node structure's lock in order to
1188 * start one (if needed).
1190 if (rnp
!= rnp_root
) {
1191 raw_spin_lock(&rnp_root
->lock
);
1192 smp_mb__after_unlock_lock();
1196 * Get a new grace-period number. If there really is no grace
1197 * period in progress, it will be smaller than the one we obtained
1198 * earlier. Adjust callbacks as needed. Note that even no-CBs
1199 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1201 c
= rcu_cbs_completed(rdp
->rsp
, rnp_root
);
1202 for (i
= RCU_DONE_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
1203 if (ULONG_CMP_LT(c
, rdp
->nxtcompleted
[i
]))
1204 rdp
->nxtcompleted
[i
] = c
;
1207 * If the needed for the required grace period is already
1208 * recorded, trace and leave.
1210 if (rnp_root
->need_future_gp
[c
& 0x1]) {
1211 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartedroot"));
1215 /* Record the need for the future grace period. */
1216 rnp_root
->need_future_gp
[c
& 0x1]++;
1218 /* If a grace period is not already in progress, start one. */
1219 if (rnp_root
->gpnum
!= rnp_root
->completed
) {
1220 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleafroot"));
1222 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedroot"));
1223 ret
= rcu_start_gp_advanced(rdp
->rsp
, rnp_root
, rdp
);
1226 if (rnp
!= rnp_root
)
1227 raw_spin_unlock(&rnp_root
->lock
);
1235 * Clean up any old requests for the just-ended grace period. Also return
1236 * whether any additional grace periods have been requested. Also invoke
1237 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1238 * waiting for this grace period to complete.
1240 static int rcu_future_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
1242 int c
= rnp
->completed
;
1244 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1246 rcu_nocb_gp_cleanup(rsp
, rnp
);
1247 rnp
->need_future_gp
[c
& 0x1] = 0;
1248 needmore
= rnp
->need_future_gp
[(c
+ 1) & 0x1];
1249 trace_rcu_future_gp(rnp
, rdp
, c
,
1250 needmore
? TPS("CleanupMore") : TPS("Cleanup"));
1255 * Awaken the grace-period kthread for the specified flavor of RCU.
1256 * Don't do a self-awaken, and don't bother awakening when there is
1257 * nothing for the grace-period kthread to do (as in several CPUs
1258 * raced to awaken, and we lost), and finally don't try to awaken
1259 * a kthread that has not yet been created.
1261 static void rcu_gp_kthread_wake(struct rcu_state
*rsp
)
1263 if (current
== rsp
->gp_kthread
||
1264 !ACCESS_ONCE(rsp
->gp_flags
) ||
1267 wake_up(&rsp
->gp_wq
);
1271 * If there is room, assign a ->completed number to any callbacks on
1272 * this CPU that have not already been assigned. Also accelerate any
1273 * callbacks that were previously assigned a ->completed number that has
1274 * since proven to be too conservative, which can happen if callbacks get
1275 * assigned a ->completed number while RCU is idle, but with reference to
1276 * a non-root rcu_node structure. This function is idempotent, so it does
1277 * not hurt to call it repeatedly. Returns an flag saying that we should
1278 * awaken the RCU grace-period kthread.
1280 * The caller must hold rnp->lock with interrupts disabled.
1282 static bool rcu_accelerate_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1283 struct rcu_data
*rdp
)
1289 /* If the CPU has no callbacks, nothing to do. */
1290 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1294 * Starting from the sublist containing the callbacks most
1295 * recently assigned a ->completed number and working down, find the
1296 * first sublist that is not assignable to an upcoming grace period.
1297 * Such a sublist has something in it (first two tests) and has
1298 * a ->completed number assigned that will complete sooner than
1299 * the ->completed number for newly arrived callbacks (last test).
1301 * The key point is that any later sublist can be assigned the
1302 * same ->completed number as the newly arrived callbacks, which
1303 * means that the callbacks in any of these later sublist can be
1304 * grouped into a single sublist, whether or not they have already
1305 * been assigned a ->completed number.
1307 c
= rcu_cbs_completed(rsp
, rnp
);
1308 for (i
= RCU_NEXT_TAIL
- 1; i
> RCU_DONE_TAIL
; i
--)
1309 if (rdp
->nxttail
[i
] != rdp
->nxttail
[i
- 1] &&
1310 !ULONG_CMP_GE(rdp
->nxtcompleted
[i
], c
))
1314 * If there are no sublist for unassigned callbacks, leave.
1315 * At the same time, advance "i" one sublist, so that "i" will
1316 * index into the sublist where all the remaining callbacks should
1319 if (++i
>= RCU_NEXT_TAIL
)
1323 * Assign all subsequent callbacks' ->completed number to the next
1324 * full grace period and group them all in the sublist initially
1327 for (; i
<= RCU_NEXT_TAIL
; i
++) {
1328 rdp
->nxttail
[i
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1329 rdp
->nxtcompleted
[i
] = c
;
1331 /* Record any needed additional grace periods. */
1332 ret
= rcu_start_future_gp(rnp
, rdp
, NULL
);
1334 /* Trace depending on how much we were able to accelerate. */
1335 if (!*rdp
->nxttail
[RCU_WAIT_TAIL
])
1336 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccWaitCB"));
1338 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccReadyCB"));
1343 * Move any callbacks whose grace period has completed to the
1344 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1345 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1346 * sublist. This function is idempotent, so it does not hurt to
1347 * invoke it repeatedly. As long as it is not invoked -too- often...
1348 * Returns true if the RCU grace-period kthread needs to be awakened.
1350 * The caller must hold rnp->lock with interrupts disabled.
1352 static bool rcu_advance_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1353 struct rcu_data
*rdp
)
1357 /* If the CPU has no callbacks, nothing to do. */
1358 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1362 * Find all callbacks whose ->completed numbers indicate that they
1363 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1365 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++) {
1366 if (ULONG_CMP_LT(rnp
->completed
, rdp
->nxtcompleted
[i
]))
1368 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[i
];
1370 /* Clean up any sublist tail pointers that were misordered above. */
1371 for (j
= RCU_WAIT_TAIL
; j
< i
; j
++)
1372 rdp
->nxttail
[j
] = rdp
->nxttail
[RCU_DONE_TAIL
];
1374 /* Copy down callbacks to fill in empty sublists. */
1375 for (j
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++, j
++) {
1376 if (rdp
->nxttail
[j
] == rdp
->nxttail
[RCU_NEXT_TAIL
])
1378 rdp
->nxttail
[j
] = rdp
->nxttail
[i
];
1379 rdp
->nxtcompleted
[j
] = rdp
->nxtcompleted
[i
];
1382 /* Classify any remaining callbacks. */
1383 return rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1387 * Update CPU-local rcu_data state to record the beginnings and ends of
1388 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1389 * structure corresponding to the current CPU, and must have irqs disabled.
1390 * Returns true if the grace-period kthread needs to be awakened.
1392 static bool __note_gp_changes(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1393 struct rcu_data
*rdp
)
1397 /* Handle the ends of any preceding grace periods first. */
1398 if (rdp
->completed
== rnp
->completed
) {
1400 /* No grace period end, so just accelerate recent callbacks. */
1401 ret
= rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1405 /* Advance callbacks. */
1406 ret
= rcu_advance_cbs(rsp
, rnp
, rdp
);
1408 /* Remember that we saw this grace-period completion. */
1409 rdp
->completed
= rnp
->completed
;
1410 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuend"));
1413 if (rdp
->gpnum
!= rnp
->gpnum
) {
1415 * If the current grace period is waiting for this CPU,
1416 * set up to detect a quiescent state, otherwise don't
1417 * go looking for one.
1419 rdp
->gpnum
= rnp
->gpnum
;
1420 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpustart"));
1421 rdp
->passed_quiesce
= 0;
1422 rdp
->qs_pending
= !!(rnp
->qsmask
& rdp
->grpmask
);
1423 zero_cpu_stall_ticks(rdp
);
1428 static void note_gp_changes(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1430 unsigned long flags
;
1432 struct rcu_node
*rnp
;
1434 local_irq_save(flags
);
1436 if ((rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) &&
1437 rdp
->completed
== ACCESS_ONCE(rnp
->completed
)) || /* w/out lock. */
1438 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1439 local_irq_restore(flags
);
1442 smp_mb__after_unlock_lock();
1443 needwake
= __note_gp_changes(rsp
, rnp
, rdp
);
1444 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1446 rcu_gp_kthread_wake(rsp
);
1450 * Initialize a new grace period. Return 0 if no grace period required.
1452 static int rcu_gp_init(struct rcu_state
*rsp
)
1454 struct rcu_data
*rdp
;
1455 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1457 rcu_bind_gp_kthread();
1458 raw_spin_lock_irq(&rnp
->lock
);
1459 smp_mb__after_unlock_lock();
1460 if (!ACCESS_ONCE(rsp
->gp_flags
)) {
1461 /* Spurious wakeup, tell caller to go back to sleep. */
1462 raw_spin_unlock_irq(&rnp
->lock
);
1465 ACCESS_ONCE(rsp
->gp_flags
) = 0; /* Clear all flags: New grace period. */
1467 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp
))) {
1469 * Grace period already in progress, don't start another.
1470 * Not supposed to be able to happen.
1472 raw_spin_unlock_irq(&rnp
->lock
);
1476 /* Advance to a new grace period and initialize state. */
1477 record_gp_stall_check_time(rsp
);
1478 /* Record GP times before starting GP, hence smp_store_release(). */
1479 smp_store_release(&rsp
->gpnum
, rsp
->gpnum
+ 1);
1480 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, TPS("start"));
1481 raw_spin_unlock_irq(&rnp
->lock
);
1483 /* Exclude any concurrent CPU-hotplug operations. */
1484 mutex_lock(&rsp
->onoff_mutex
);
1485 smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1488 * Set the quiescent-state-needed bits in all the rcu_node
1489 * structures for all currently online CPUs in breadth-first order,
1490 * starting from the root rcu_node structure, relying on the layout
1491 * of the tree within the rsp->node[] array. Note that other CPUs
1492 * will access only the leaves of the hierarchy, thus seeing that no
1493 * grace period is in progress, at least until the corresponding
1494 * leaf node has been initialized. In addition, we have excluded
1495 * CPU-hotplug operations.
1497 * The grace period cannot complete until the initialization
1498 * process finishes, because this kthread handles both.
1500 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1501 raw_spin_lock_irq(&rnp
->lock
);
1502 smp_mb__after_unlock_lock();
1503 rdp
= this_cpu_ptr(rsp
->rda
);
1504 rcu_preempt_check_blocked_tasks(rnp
);
1505 rnp
->qsmask
= rnp
->qsmaskinit
;
1506 ACCESS_ONCE(rnp
->gpnum
) = rsp
->gpnum
;
1507 WARN_ON_ONCE(rnp
->completed
!= rsp
->completed
);
1508 ACCESS_ONCE(rnp
->completed
) = rsp
->completed
;
1509 if (rnp
== rdp
->mynode
)
1510 (void)__note_gp_changes(rsp
, rnp
, rdp
);
1511 rcu_preempt_boost_start_gp(rnp
);
1512 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1513 rnp
->level
, rnp
->grplo
,
1514 rnp
->grphi
, rnp
->qsmask
);
1515 raw_spin_unlock_irq(&rnp
->lock
);
1516 #ifdef CONFIG_PROVE_RCU_DELAY
1517 if ((prandom_u32() % (rcu_num_nodes
+ 1)) == 0 &&
1518 system_state
== SYSTEM_RUNNING
)
1520 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1524 mutex_unlock(&rsp
->onoff_mutex
);
1529 * Do one round of quiescent-state forcing.
1531 static int rcu_gp_fqs(struct rcu_state
*rsp
, int fqs_state_in
)
1533 int fqs_state
= fqs_state_in
;
1534 bool isidle
= false;
1536 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1539 if (fqs_state
== RCU_SAVE_DYNTICK
) {
1540 /* Collect dyntick-idle snapshots. */
1541 if (is_sysidle_rcu_state(rsp
)) {
1543 maxj
= jiffies
- ULONG_MAX
/ 4;
1545 force_qs_rnp(rsp
, dyntick_save_progress_counter
,
1547 rcu_sysidle_report_gp(rsp
, isidle
, maxj
);
1548 fqs_state
= RCU_FORCE_QS
;
1550 /* Handle dyntick-idle and offline CPUs. */
1552 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
, &isidle
, &maxj
);
1554 /* Clear flag to prevent immediate re-entry. */
1555 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1556 raw_spin_lock_irq(&rnp
->lock
);
1557 smp_mb__after_unlock_lock();
1558 ACCESS_ONCE(rsp
->gp_flags
) &= ~RCU_GP_FLAG_FQS
;
1559 raw_spin_unlock_irq(&rnp
->lock
);
1565 * Clean up after the old grace period.
1567 static void rcu_gp_cleanup(struct rcu_state
*rsp
)
1569 unsigned long gp_duration
;
1570 bool needgp
= false;
1572 struct rcu_data
*rdp
;
1573 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1575 raw_spin_lock_irq(&rnp
->lock
);
1576 smp_mb__after_unlock_lock();
1577 gp_duration
= jiffies
- rsp
->gp_start
;
1578 if (gp_duration
> rsp
->gp_max
)
1579 rsp
->gp_max
= gp_duration
;
1582 * We know the grace period is complete, but to everyone else
1583 * it appears to still be ongoing. But it is also the case
1584 * that to everyone else it looks like there is nothing that
1585 * they can do to advance the grace period. It is therefore
1586 * safe for us to drop the lock in order to mark the grace
1587 * period as completed in all of the rcu_node structures.
1589 raw_spin_unlock_irq(&rnp
->lock
);
1592 * Propagate new ->completed value to rcu_node structures so
1593 * that other CPUs don't have to wait until the start of the next
1594 * grace period to process their callbacks. This also avoids
1595 * some nasty RCU grace-period initialization races by forcing
1596 * the end of the current grace period to be completely recorded in
1597 * all of the rcu_node structures before the beginning of the next
1598 * grace period is recorded in any of the rcu_node structures.
1600 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1601 raw_spin_lock_irq(&rnp
->lock
);
1602 smp_mb__after_unlock_lock();
1603 ACCESS_ONCE(rnp
->completed
) = rsp
->gpnum
;
1604 rdp
= this_cpu_ptr(rsp
->rda
);
1605 if (rnp
== rdp
->mynode
)
1606 needgp
= __note_gp_changes(rsp
, rnp
, rdp
) || needgp
;
1607 /* smp_mb() provided by prior unlock-lock pair. */
1608 nocb
+= rcu_future_gp_cleanup(rsp
, rnp
);
1609 raw_spin_unlock_irq(&rnp
->lock
);
1612 rnp
= rcu_get_root(rsp
);
1613 raw_spin_lock_irq(&rnp
->lock
);
1614 smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1615 rcu_nocb_gp_set(rnp
, nocb
);
1617 /* Declare grace period done. */
1618 ACCESS_ONCE(rsp
->completed
) = rsp
->gpnum
;
1619 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, TPS("end"));
1620 rsp
->fqs_state
= RCU_GP_IDLE
;
1621 rdp
= this_cpu_ptr(rsp
->rda
);
1622 /* Advance CBs to reduce false positives below. */
1623 needgp
= rcu_advance_cbs(rsp
, rnp
, rdp
) || needgp
;
1624 if (needgp
|| cpu_needs_another_gp(rsp
, rdp
)) {
1625 ACCESS_ONCE(rsp
->gp_flags
) = RCU_GP_FLAG_INIT
;
1626 trace_rcu_grace_period(rsp
->name
,
1627 ACCESS_ONCE(rsp
->gpnum
),
1630 raw_spin_unlock_irq(&rnp
->lock
);
1634 * Body of kthread that handles grace periods.
1636 static int __noreturn
rcu_gp_kthread(void *arg
)
1642 struct rcu_state
*rsp
= arg
;
1643 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1647 /* Handle grace-period start. */
1649 trace_rcu_grace_period(rsp
->name
,
1650 ACCESS_ONCE(rsp
->gpnum
),
1652 wait_event_interruptible(rsp
->gp_wq
,
1653 ACCESS_ONCE(rsp
->gp_flags
) &
1655 /* Locking provides needed memory barrier. */
1656 if (rcu_gp_init(rsp
))
1659 flush_signals(current
);
1660 trace_rcu_grace_period(rsp
->name
,
1661 ACCESS_ONCE(rsp
->gpnum
),
1665 /* Handle quiescent-state forcing. */
1666 fqs_state
= RCU_SAVE_DYNTICK
;
1667 j
= jiffies_till_first_fqs
;
1670 jiffies_till_first_fqs
= HZ
;
1675 rsp
->jiffies_force_qs
= jiffies
+ j
;
1676 trace_rcu_grace_period(rsp
->name
,
1677 ACCESS_ONCE(rsp
->gpnum
),
1679 ret
= wait_event_interruptible_timeout(rsp
->gp_wq
,
1680 ((gf
= ACCESS_ONCE(rsp
->gp_flags
)) &
1682 (!ACCESS_ONCE(rnp
->qsmask
) &&
1683 !rcu_preempt_blocked_readers_cgp(rnp
)),
1685 /* Locking provides needed memory barriers. */
1686 /* If grace period done, leave loop. */
1687 if (!ACCESS_ONCE(rnp
->qsmask
) &&
1688 !rcu_preempt_blocked_readers_cgp(rnp
))
1690 /* If time for quiescent-state forcing, do it. */
1691 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_force_qs
) ||
1692 (gf
& RCU_GP_FLAG_FQS
)) {
1693 trace_rcu_grace_period(rsp
->name
,
1694 ACCESS_ONCE(rsp
->gpnum
),
1696 fqs_state
= rcu_gp_fqs(rsp
, fqs_state
);
1697 trace_rcu_grace_period(rsp
->name
,
1698 ACCESS_ONCE(rsp
->gpnum
),
1702 /* Deal with stray signal. */
1704 flush_signals(current
);
1705 trace_rcu_grace_period(rsp
->name
,
1706 ACCESS_ONCE(rsp
->gpnum
),
1709 j
= jiffies_till_next_fqs
;
1712 jiffies_till_next_fqs
= HZ
;
1715 jiffies_till_next_fqs
= 1;
1719 /* Handle grace-period end. */
1720 rcu_gp_cleanup(rsp
);
1725 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1726 * in preparation for detecting the next grace period. The caller must hold
1727 * the root node's ->lock and hard irqs must be disabled.
1729 * Note that it is legal for a dying CPU (which is marked as offline) to
1730 * invoke this function. This can happen when the dying CPU reports its
1733 * Returns true if the grace-period kthread must be awakened.
1736 rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1737 struct rcu_data
*rdp
)
1739 if (!rsp
->gp_kthread
|| !cpu_needs_another_gp(rsp
, rdp
)) {
1741 * Either we have not yet spawned the grace-period
1742 * task, this CPU does not need another grace period,
1743 * or a grace period is already in progress.
1744 * Either way, don't start a new grace period.
1748 ACCESS_ONCE(rsp
->gp_flags
) = RCU_GP_FLAG_INIT
;
1749 trace_rcu_grace_period(rsp
->name
, ACCESS_ONCE(rsp
->gpnum
),
1753 * We can't do wakeups while holding the rnp->lock, as that
1754 * could cause possible deadlocks with the rq->lock. Defer
1755 * the wakeup to our caller.
1761 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1762 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1763 * is invoked indirectly from rcu_advance_cbs(), which would result in
1764 * endless recursion -- or would do so if it wasn't for the self-deadlock
1765 * that is encountered beforehand.
1767 * Returns true if the grace-period kthread needs to be awakened.
1769 static bool rcu_start_gp(struct rcu_state
*rsp
)
1771 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1772 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1776 * If there is no grace period in progress right now, any
1777 * callbacks we have up to this point will be satisfied by the
1778 * next grace period. Also, advancing the callbacks reduces the
1779 * probability of false positives from cpu_needs_another_gp()
1780 * resulting in pointless grace periods. So, advance callbacks
1781 * then start the grace period!
1783 ret
= rcu_advance_cbs(rsp
, rnp
, rdp
) || ret
;
1784 ret
= rcu_start_gp_advanced(rsp
, rnp
, rdp
) || ret
;
1789 * Report a full set of quiescent states to the specified rcu_state
1790 * data structure. This involves cleaning up after the prior grace
1791 * period and letting rcu_start_gp() start up the next grace period
1792 * if one is needed. Note that the caller must hold rnp->lock, which
1793 * is released before return.
1795 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1796 __releases(rcu_get_root(rsp
)->lock
)
1798 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1799 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
1800 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1804 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1805 * Allows quiescent states for a group of CPUs to be reported at one go
1806 * to the specified rcu_node structure, though all the CPUs in the group
1807 * must be represented by the same rcu_node structure (which need not be
1808 * a leaf rcu_node structure, though it often will be). That structure's
1809 * lock must be held upon entry, and it is released before return.
1812 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1813 struct rcu_node
*rnp
, unsigned long flags
)
1814 __releases(rnp
->lock
)
1816 struct rcu_node
*rnp_c
;
1818 /* Walk up the rcu_node hierarchy. */
1820 if (!(rnp
->qsmask
& mask
)) {
1822 /* Our bit has already been cleared, so done. */
1823 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1826 rnp
->qsmask
&= ~mask
;
1827 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1828 mask
, rnp
->qsmask
, rnp
->level
,
1829 rnp
->grplo
, rnp
->grphi
,
1831 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1833 /* Other bits still set at this level, so done. */
1834 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1837 mask
= rnp
->grpmask
;
1838 if (rnp
->parent
== NULL
) {
1840 /* No more levels. Exit loop holding root lock. */
1844 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1847 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1848 smp_mb__after_unlock_lock();
1849 WARN_ON_ONCE(rnp_c
->qsmask
);
1853 * Get here if we are the last CPU to pass through a quiescent
1854 * state for this grace period. Invoke rcu_report_qs_rsp()
1855 * to clean up and start the next grace period if one is needed.
1857 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1861 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1862 * structure. This must be either called from the specified CPU, or
1863 * called when the specified CPU is known to be offline (and when it is
1864 * also known that no other CPU is concurrently trying to help the offline
1865 * CPU). The lastcomp argument is used to make sure we are still in the
1866 * grace period of interest. We don't want to end the current grace period
1867 * based on quiescent states detected in an earlier grace period!
1870 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1872 unsigned long flags
;
1875 struct rcu_node
*rnp
;
1878 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1879 smp_mb__after_unlock_lock();
1880 if (rdp
->passed_quiesce
== 0 || rdp
->gpnum
!= rnp
->gpnum
||
1881 rnp
->completed
== rnp
->gpnum
) {
1884 * The grace period in which this quiescent state was
1885 * recorded has ended, so don't report it upwards.
1886 * We will instead need a new quiescent state that lies
1887 * within the current grace period.
1889 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1890 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1893 mask
= rdp
->grpmask
;
1894 if ((rnp
->qsmask
& mask
) == 0) {
1895 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1897 rdp
->qs_pending
= 0;
1900 * This GP can't end until cpu checks in, so all of our
1901 * callbacks can be processed during the next GP.
1903 needwake
= rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1905 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1907 rcu_gp_kthread_wake(rsp
);
1912 * Check to see if there is a new grace period of which this CPU
1913 * is not yet aware, and if so, set up local rcu_data state for it.
1914 * Otherwise, see if this CPU has just passed through its first
1915 * quiescent state for this grace period, and record that fact if so.
1918 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1920 /* Check for grace-period ends and beginnings. */
1921 note_gp_changes(rsp
, rdp
);
1924 * Does this CPU still need to do its part for current grace period?
1925 * If no, return and let the other CPUs do their part as well.
1927 if (!rdp
->qs_pending
)
1931 * Was there a quiescent state since the beginning of the grace
1932 * period? If no, then exit and wait for the next call.
1934 if (!rdp
->passed_quiesce
)
1938 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1941 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
);
1944 #ifdef CONFIG_HOTPLUG_CPU
1947 * Send the specified CPU's RCU callbacks to the orphanage. The
1948 * specified CPU must be offline, and the caller must hold the
1952 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1953 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1955 /* No-CBs CPUs do not have orphanable callbacks. */
1956 if (rcu_is_nocb_cpu(rdp
->cpu
))
1960 * Orphan the callbacks. First adjust the counts. This is safe
1961 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1962 * cannot be running now. Thus no memory barrier is required.
1964 if (rdp
->nxtlist
!= NULL
) {
1965 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1966 rsp
->qlen
+= rdp
->qlen
;
1967 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1969 ACCESS_ONCE(rdp
->qlen
) = 0;
1973 * Next, move those callbacks still needing a grace period to
1974 * the orphanage, where some other CPU will pick them up.
1975 * Some of the callbacks might have gone partway through a grace
1976 * period, but that is too bad. They get to start over because we
1977 * cannot assume that grace periods are synchronized across CPUs.
1978 * We don't bother updating the ->nxttail[] array yet, instead
1979 * we just reset the whole thing later on.
1981 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1982 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1983 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1984 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1988 * Then move the ready-to-invoke callbacks to the orphanage,
1989 * where some other CPU will pick them up. These will not be
1990 * required to pass though another grace period: They are done.
1992 if (rdp
->nxtlist
!= NULL
) {
1993 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1994 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1997 /* Finally, initialize the rcu_data structure's list to empty. */
1998 init_callback_list(rdp
);
2002 * Adopt the RCU callbacks from the specified rcu_state structure's
2003 * orphanage. The caller must hold the ->orphan_lock.
2005 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
, unsigned long flags
)
2008 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2010 /* No-CBs CPUs are handled specially. */
2011 if (rcu_nocb_adopt_orphan_cbs(rsp
, rdp
, flags
))
2014 /* Do the accounting first. */
2015 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
2016 rdp
->qlen
+= rsp
->qlen
;
2017 rdp
->n_cbs_adopted
+= rsp
->qlen
;
2018 if (rsp
->qlen_lazy
!= rsp
->qlen
)
2019 rcu_idle_count_callbacks_posted();
2024 * We do not need a memory barrier here because the only way we
2025 * can get here if there is an rcu_barrier() in flight is if
2026 * we are the task doing the rcu_barrier().
2029 /* First adopt the ready-to-invoke callbacks. */
2030 if (rsp
->orphan_donelist
!= NULL
) {
2031 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
2032 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
2033 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
2034 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
2035 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
2036 rsp
->orphan_donelist
= NULL
;
2037 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2040 /* And then adopt the callbacks that still need a grace period. */
2041 if (rsp
->orphan_nxtlist
!= NULL
) {
2042 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
2043 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
2044 rsp
->orphan_nxtlist
= NULL
;
2045 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2050 * Trace the fact that this CPU is going offline.
2052 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
2054 RCU_TRACE(unsigned long mask
);
2055 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
2056 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
2058 RCU_TRACE(mask
= rdp
->grpmask
);
2059 trace_rcu_grace_period(rsp
->name
,
2060 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
2065 * The CPU has been completely removed, and some other CPU is reporting
2066 * this fact from process context. Do the remainder of the cleanup,
2067 * including orphaning the outgoing CPU's RCU callbacks, and also
2068 * adopting them. There can only be one CPU hotplug operation at a time,
2069 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2071 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
2073 unsigned long flags
;
2075 int need_report
= 0;
2076 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2077 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
2079 /* Adjust any no-longer-needed kthreads. */
2080 rcu_boost_kthread_setaffinity(rnp
, -1);
2082 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2084 /* Exclude any attempts to start a new grace period. */
2085 mutex_lock(&rsp
->onoff_mutex
);
2086 raw_spin_lock_irqsave(&rsp
->orphan_lock
, flags
);
2088 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2089 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
2090 rcu_adopt_orphan_cbs(rsp
, flags
);
2092 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
2093 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
2095 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2096 smp_mb__after_unlock_lock();
2097 rnp
->qsmaskinit
&= ~mask
;
2098 if (rnp
->qsmaskinit
!= 0) {
2099 if (rnp
!= rdp
->mynode
)
2100 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2103 if (rnp
== rdp
->mynode
)
2104 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
2106 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2107 mask
= rnp
->grpmask
;
2109 } while (rnp
!= NULL
);
2112 * We still hold the leaf rcu_node structure lock here, and
2113 * irqs are still disabled. The reason for this subterfuge is
2114 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2115 * held leads to deadlock.
2117 raw_spin_unlock(&rsp
->orphan_lock
); /* irqs remain disabled. */
2119 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
2120 rcu_report_unblock_qs_rnp(rnp
, flags
);
2122 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2123 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
2124 rcu_report_exp_rnp(rsp
, rnp
, true);
2125 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
2126 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2127 cpu
, rdp
->qlen
, rdp
->nxtlist
);
2128 init_callback_list(rdp
);
2129 /* Disallow further callbacks on this CPU. */
2130 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2131 mutex_unlock(&rsp
->onoff_mutex
);
2134 #else /* #ifdef CONFIG_HOTPLUG_CPU */
2136 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
2140 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
2144 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2147 * Invoke any RCU callbacks that have made it to the end of their grace
2148 * period. Thottle as specified by rdp->blimit.
2150 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2152 unsigned long flags
;
2153 struct rcu_head
*next
, *list
, **tail
;
2154 long bl
, count
, count_lazy
;
2157 /* If no callbacks are ready, just return. */
2158 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
2159 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
2160 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
2161 need_resched(), is_idle_task(current
),
2162 rcu_is_callbacks_kthread());
2167 * Extract the list of ready callbacks, disabling to prevent
2168 * races with call_rcu() from interrupt handlers.
2170 local_irq_save(flags
);
2171 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2173 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
2174 list
= rdp
->nxtlist
;
2175 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
2176 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
2177 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
2178 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
2179 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
2180 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
2181 local_irq_restore(flags
);
2183 /* Invoke callbacks. */
2184 count
= count_lazy
= 0;
2188 debug_rcu_head_unqueue(list
);
2189 if (__rcu_reclaim(rsp
->name
, list
))
2192 /* Stop only if limit reached and CPU has something to do. */
2193 if (++count
>= bl
&&
2195 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
2199 local_irq_save(flags
);
2200 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
2201 is_idle_task(current
),
2202 rcu_is_callbacks_kthread());
2204 /* Update count, and requeue any remaining callbacks. */
2206 *tail
= rdp
->nxtlist
;
2207 rdp
->nxtlist
= list
;
2208 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
2209 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
2210 rdp
->nxttail
[i
] = tail
;
2214 smp_mb(); /* List handling before counting for rcu_barrier(). */
2215 rdp
->qlen_lazy
-= count_lazy
;
2216 ACCESS_ONCE(rdp
->qlen
) -= count
;
2217 rdp
->n_cbs_invoked
+= count
;
2219 /* Reinstate batch limit if we have worked down the excess. */
2220 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
2221 rdp
->blimit
= blimit
;
2223 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2224 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
2225 rdp
->qlen_last_fqs_check
= 0;
2226 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2227 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
2228 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2229 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
2231 local_irq_restore(flags
);
2233 /* Re-invoke RCU core processing if there are callbacks remaining. */
2234 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2239 * Check to see if this CPU is in a non-context-switch quiescent state
2240 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2241 * Also schedule RCU core processing.
2243 * This function must be called from hardirq context. It is normally
2244 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2245 * false, there is no point in invoking rcu_check_callbacks().
2247 void rcu_check_callbacks(int cpu
, int user
)
2249 trace_rcu_utilization(TPS("Start scheduler-tick"));
2250 increment_cpu_stall_ticks();
2251 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
2254 * Get here if this CPU took its interrupt from user
2255 * mode or from the idle loop, and if this is not a
2256 * nested interrupt. In this case, the CPU is in
2257 * a quiescent state, so note it.
2259 * No memory barrier is required here because both
2260 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2261 * variables that other CPUs neither access nor modify,
2262 * at least not while the corresponding CPU is online.
2268 } else if (!in_softirq()) {
2271 * Get here if this CPU did not take its interrupt from
2272 * softirq, in other words, if it is not interrupting
2273 * a rcu_bh read-side critical section. This is an _bh
2274 * critical section, so note it.
2279 rcu_preempt_check_callbacks(cpu
);
2280 if (rcu_pending(cpu
))
2282 trace_rcu_utilization(TPS("End scheduler-tick"));
2286 * Scan the leaf rcu_node structures, processing dyntick state for any that
2287 * have not yet encountered a quiescent state, using the function specified.
2288 * Also initiate boosting for any threads blocked on the root rcu_node.
2290 * The caller must have suppressed start of new grace periods.
2292 static void force_qs_rnp(struct rcu_state
*rsp
,
2293 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
2294 unsigned long *maxj
),
2295 bool *isidle
, unsigned long *maxj
)
2299 unsigned long flags
;
2301 struct rcu_node
*rnp
;
2303 rcu_for_each_leaf_node(rsp
, rnp
) {
2306 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2307 smp_mb__after_unlock_lock();
2308 if (!rcu_gp_in_progress(rsp
)) {
2309 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2312 if (rnp
->qsmask
== 0) {
2313 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
2318 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
2319 if ((rnp
->qsmask
& bit
) != 0) {
2320 if ((rnp
->qsmaskinit
& bit
) != 0)
2322 if (f(per_cpu_ptr(rsp
->rda
, cpu
), isidle
, maxj
))
2328 /* rcu_report_qs_rnp() releases rnp->lock. */
2329 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
2332 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2334 rnp
= rcu_get_root(rsp
);
2335 if (rnp
->qsmask
== 0) {
2336 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2337 smp_mb__after_unlock_lock();
2338 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
2343 * Force quiescent states on reluctant CPUs, and also detect which
2344 * CPUs are in dyntick-idle mode.
2346 static void force_quiescent_state(struct rcu_state
*rsp
)
2348 unsigned long flags
;
2350 struct rcu_node
*rnp
;
2351 struct rcu_node
*rnp_old
= NULL
;
2353 /* Funnel through hierarchy to reduce memory contention. */
2354 rnp
= per_cpu_ptr(rsp
->rda
, raw_smp_processor_id())->mynode
;
2355 for (; rnp
!= NULL
; rnp
= rnp
->parent
) {
2356 ret
= (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) ||
2357 !raw_spin_trylock(&rnp
->fqslock
);
2358 if (rnp_old
!= NULL
)
2359 raw_spin_unlock(&rnp_old
->fqslock
);
2361 ACCESS_ONCE(rsp
->n_force_qs_lh
)++;
2366 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2368 /* Reached the root of the rcu_node tree, acquire lock. */
2369 raw_spin_lock_irqsave(&rnp_old
->lock
, flags
);
2370 smp_mb__after_unlock_lock();
2371 raw_spin_unlock(&rnp_old
->fqslock
);
2372 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
2373 ACCESS_ONCE(rsp
->n_force_qs_lh
)++;
2374 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2375 return; /* Someone beat us to it. */
2377 ACCESS_ONCE(rsp
->gp_flags
) |= RCU_GP_FLAG_FQS
;
2378 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2379 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
2383 * This does the RCU core processing work for the specified rcu_state
2384 * and rcu_data structures. This may be called only from the CPU to
2385 * whom the rdp belongs.
2388 __rcu_process_callbacks(struct rcu_state
*rsp
)
2390 unsigned long flags
;
2392 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2394 WARN_ON_ONCE(rdp
->beenonline
== 0);
2396 /* Update RCU state based on any recent quiescent states. */
2397 rcu_check_quiescent_state(rsp
, rdp
);
2399 /* Does this CPU require a not-yet-started grace period? */
2400 local_irq_save(flags
);
2401 if (cpu_needs_another_gp(rsp
, rdp
)) {
2402 raw_spin_lock(&rcu_get_root(rsp
)->lock
); /* irqs disabled. */
2403 needwake
= rcu_start_gp(rsp
);
2404 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
2406 rcu_gp_kthread_wake(rsp
);
2408 local_irq_restore(flags
);
2411 /* If there are callbacks ready, invoke them. */
2412 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2413 invoke_rcu_callbacks(rsp
, rdp
);
2415 /* Do any needed deferred wakeups of rcuo kthreads. */
2416 do_nocb_deferred_wakeup(rdp
);
2420 * Do RCU core processing for the current CPU.
2422 static void rcu_process_callbacks(struct softirq_action
*unused
)
2424 struct rcu_state
*rsp
;
2426 if (cpu_is_offline(smp_processor_id()))
2428 trace_rcu_utilization(TPS("Start RCU core"));
2429 for_each_rcu_flavor(rsp
)
2430 __rcu_process_callbacks(rsp
);
2431 trace_rcu_utilization(TPS("End RCU core"));
2435 * Schedule RCU callback invocation. If the specified type of RCU
2436 * does not support RCU priority boosting, just do a direct call,
2437 * otherwise wake up the per-CPU kernel kthread. Note that because we
2438 * are running on the current CPU with interrupts disabled, the
2439 * rcu_cpu_kthread_task cannot disappear out from under us.
2441 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2443 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
2445 if (likely(!rsp
->boost
)) {
2446 rcu_do_batch(rsp
, rdp
);
2449 invoke_rcu_callbacks_kthread();
2452 static void invoke_rcu_core(void)
2454 if (cpu_online(smp_processor_id()))
2455 raise_softirq(RCU_SOFTIRQ
);
2459 * Handle any core-RCU processing required by a call_rcu() invocation.
2461 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
2462 struct rcu_head
*head
, unsigned long flags
)
2467 * If called from an extended quiescent state, invoke the RCU
2468 * core in order to force a re-evaluation of RCU's idleness.
2470 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2473 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2474 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
2478 * Force the grace period if too many callbacks or too long waiting.
2479 * Enforce hysteresis, and don't invoke force_quiescent_state()
2480 * if some other CPU has recently done so. Also, don't bother
2481 * invoking force_quiescent_state() if the newly enqueued callback
2482 * is the only one waiting for a grace period to complete.
2484 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
2486 /* Are we ignoring a completed grace period? */
2487 note_gp_changes(rsp
, rdp
);
2489 /* Start a new grace period if one not already started. */
2490 if (!rcu_gp_in_progress(rsp
)) {
2491 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
2493 raw_spin_lock(&rnp_root
->lock
);
2494 smp_mb__after_unlock_lock();
2495 needwake
= rcu_start_gp(rsp
);
2496 raw_spin_unlock(&rnp_root
->lock
);
2498 rcu_gp_kthread_wake(rsp
);
2500 /* Give the grace period a kick. */
2501 rdp
->blimit
= LONG_MAX
;
2502 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
2503 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
2504 force_quiescent_state(rsp
);
2505 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2506 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2512 * RCU callback function to leak a callback.
2514 static void rcu_leak_callback(struct rcu_head
*rhp
)
2519 * Helper function for call_rcu() and friends. The cpu argument will
2520 * normally be -1, indicating "currently running CPU". It may specify
2521 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2522 * is expected to specify a CPU.
2525 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
2526 struct rcu_state
*rsp
, int cpu
, bool lazy
)
2528 unsigned long flags
;
2529 struct rcu_data
*rdp
;
2531 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
2532 if (debug_rcu_head_queue(head
)) {
2533 /* Probable double call_rcu(), so leak the callback. */
2534 ACCESS_ONCE(head
->func
) = rcu_leak_callback
;
2535 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2542 * Opportunistically note grace-period endings and beginnings.
2543 * Note that we might see a beginning right after we see an
2544 * end, but never vice versa, since this CPU has to pass through
2545 * a quiescent state betweentimes.
2547 local_irq_save(flags
);
2548 rdp
= this_cpu_ptr(rsp
->rda
);
2550 /* Add the callback to our list. */
2551 if (unlikely(rdp
->nxttail
[RCU_NEXT_TAIL
] == NULL
) || cpu
!= -1) {
2555 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2556 offline
= !__call_rcu_nocb(rdp
, head
, lazy
, flags
);
2557 WARN_ON_ONCE(offline
);
2558 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2559 local_irq_restore(flags
);
2562 ACCESS_ONCE(rdp
->qlen
)++;
2566 rcu_idle_count_callbacks_posted();
2567 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2568 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
2569 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
2571 if (__is_kfree_rcu_offset((unsigned long)func
))
2572 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
2573 rdp
->qlen_lazy
, rdp
->qlen
);
2575 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
2577 /* Go handle any RCU core processing required. */
2578 __call_rcu_core(rsp
, rdp
, head
, flags
);
2579 local_irq_restore(flags
);
2583 * Queue an RCU-sched callback for invocation after a grace period.
2585 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2587 __call_rcu(head
, func
, &rcu_sched_state
, -1, 0);
2589 EXPORT_SYMBOL_GPL(call_rcu_sched
);
2592 * Queue an RCU callback for invocation after a quicker grace period.
2594 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2596 __call_rcu(head
, func
, &rcu_bh_state
, -1, 0);
2598 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2601 * Queue an RCU callback for lazy invocation after a grace period.
2602 * This will likely be later named something like "call_rcu_lazy()",
2603 * but this change will require some way of tagging the lazy RCU
2604 * callbacks in the list of pending callbacks. Until then, this
2605 * function may only be called from __kfree_rcu().
2607 void kfree_call_rcu(struct rcu_head
*head
,
2608 void (*func
)(struct rcu_head
*rcu
))
2610 __call_rcu(head
, func
, rcu_state
, -1, 1);
2612 EXPORT_SYMBOL_GPL(kfree_call_rcu
);
2615 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2616 * any blocking grace-period wait automatically implies a grace period
2617 * if there is only one CPU online at any point time during execution
2618 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2619 * occasionally incorrectly indicate that there are multiple CPUs online
2620 * when there was in fact only one the whole time, as this just adds
2621 * some overhead: RCU still operates correctly.
2623 static inline int rcu_blocking_is_gp(void)
2627 might_sleep(); /* Check for RCU read-side critical section. */
2629 ret
= num_online_cpus() <= 1;
2635 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2637 * Control will return to the caller some time after a full rcu-sched
2638 * grace period has elapsed, in other words after all currently executing
2639 * rcu-sched read-side critical sections have completed. These read-side
2640 * critical sections are delimited by rcu_read_lock_sched() and
2641 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2642 * local_irq_disable(), and so on may be used in place of
2643 * rcu_read_lock_sched().
2645 * This means that all preempt_disable code sequences, including NMI and
2646 * non-threaded hardware-interrupt handlers, in progress on entry will
2647 * have completed before this primitive returns. However, this does not
2648 * guarantee that softirq handlers will have completed, since in some
2649 * kernels, these handlers can run in process context, and can block.
2651 * Note that this guarantee implies further memory-ordering guarantees.
2652 * On systems with more than one CPU, when synchronize_sched() returns,
2653 * each CPU is guaranteed to have executed a full memory barrier since the
2654 * end of its last RCU-sched read-side critical section whose beginning
2655 * preceded the call to synchronize_sched(). In addition, each CPU having
2656 * an RCU read-side critical section that extends beyond the return from
2657 * synchronize_sched() is guaranteed to have executed a full memory barrier
2658 * after the beginning of synchronize_sched() and before the beginning of
2659 * that RCU read-side critical section. Note that these guarantees include
2660 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2661 * that are executing in the kernel.
2663 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2664 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2665 * to have executed a full memory barrier during the execution of
2666 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2667 * again only if the system has more than one CPU).
2669 * This primitive provides the guarantees made by the (now removed)
2670 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2671 * guarantees that rcu_read_lock() sections will have completed.
2672 * In "classic RCU", these two guarantees happen to be one and
2673 * the same, but can differ in realtime RCU implementations.
2675 void synchronize_sched(void)
2677 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2678 !lock_is_held(&rcu_lock_map
) &&
2679 !lock_is_held(&rcu_sched_lock_map
),
2680 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2681 if (rcu_blocking_is_gp())
2684 synchronize_sched_expedited();
2686 wait_rcu_gp(call_rcu_sched
);
2688 EXPORT_SYMBOL_GPL(synchronize_sched
);
2691 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2693 * Control will return to the caller some time after a full rcu_bh grace
2694 * period has elapsed, in other words after all currently executing rcu_bh
2695 * read-side critical sections have completed. RCU read-side critical
2696 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2697 * and may be nested.
2699 * See the description of synchronize_sched() for more detailed information
2700 * on memory ordering guarantees.
2702 void synchronize_rcu_bh(void)
2704 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2705 !lock_is_held(&rcu_lock_map
) &&
2706 !lock_is_held(&rcu_sched_lock_map
),
2707 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2708 if (rcu_blocking_is_gp())
2711 synchronize_rcu_bh_expedited();
2713 wait_rcu_gp(call_rcu_bh
);
2715 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2718 * get_state_synchronize_rcu - Snapshot current RCU state
2720 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2721 * to determine whether or not a full grace period has elapsed in the
2724 unsigned long get_state_synchronize_rcu(void)
2727 * Any prior manipulation of RCU-protected data must happen
2728 * before the load from ->gpnum.
2733 * Make sure this load happens before the purportedly
2734 * time-consuming work between get_state_synchronize_rcu()
2735 * and cond_synchronize_rcu().
2737 return smp_load_acquire(&rcu_state
->gpnum
);
2739 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu
);
2742 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2744 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2746 * If a full RCU grace period has elapsed since the earlier call to
2747 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2748 * synchronize_rcu() to wait for a full grace period.
2750 * Yes, this function does not take counter wrap into account. But
2751 * counter wrap is harmless. If the counter wraps, we have waited for
2752 * more than 2 billion grace periods (and way more on a 64-bit system!),
2753 * so waiting for one additional grace period should be just fine.
2755 void cond_synchronize_rcu(unsigned long oldstate
)
2757 unsigned long newstate
;
2760 * Ensure that this load happens before any RCU-destructive
2761 * actions the caller might carry out after we return.
2763 newstate
= smp_load_acquire(&rcu_state
->completed
);
2764 if (ULONG_CMP_GE(oldstate
, newstate
))
2767 EXPORT_SYMBOL_GPL(cond_synchronize_rcu
);
2769 static int synchronize_sched_expedited_cpu_stop(void *data
)
2772 * There must be a full memory barrier on each affected CPU
2773 * between the time that try_stop_cpus() is called and the
2774 * time that it returns.
2776 * In the current initial implementation of cpu_stop, the
2777 * above condition is already met when the control reaches
2778 * this point and the following smp_mb() is not strictly
2779 * necessary. Do smp_mb() anyway for documentation and
2780 * robustness against future implementation changes.
2782 smp_mb(); /* See above comment block. */
2787 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2789 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2790 * approach to force the grace period to end quickly. This consumes
2791 * significant time on all CPUs and is unfriendly to real-time workloads,
2792 * so is thus not recommended for any sort of common-case code. In fact,
2793 * if you are using synchronize_sched_expedited() in a loop, please
2794 * restructure your code to batch your updates, and then use a single
2795 * synchronize_sched() instead.
2797 * Note that it is illegal to call this function while holding any lock
2798 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2799 * to call this function from a CPU-hotplug notifier. Failing to observe
2800 * these restriction will result in deadlock.
2802 * This implementation can be thought of as an application of ticket
2803 * locking to RCU, with sync_sched_expedited_started and
2804 * sync_sched_expedited_done taking on the roles of the halves
2805 * of the ticket-lock word. Each task atomically increments
2806 * sync_sched_expedited_started upon entry, snapshotting the old value,
2807 * then attempts to stop all the CPUs. If this succeeds, then each
2808 * CPU will have executed a context switch, resulting in an RCU-sched
2809 * grace period. We are then done, so we use atomic_cmpxchg() to
2810 * update sync_sched_expedited_done to match our snapshot -- but
2811 * only if someone else has not already advanced past our snapshot.
2813 * On the other hand, if try_stop_cpus() fails, we check the value
2814 * of sync_sched_expedited_done. If it has advanced past our
2815 * initial snapshot, then someone else must have forced a grace period
2816 * some time after we took our snapshot. In this case, our work is
2817 * done for us, and we can simply return. Otherwise, we try again,
2818 * but keep our initial snapshot for purposes of checking for someone
2819 * doing our work for us.
2821 * If we fail too many times in a row, we fall back to synchronize_sched().
2823 void synchronize_sched_expedited(void)
2825 long firstsnap
, s
, snap
;
2827 struct rcu_state
*rsp
= &rcu_sched_state
;
2830 * If we are in danger of counter wrap, just do synchronize_sched().
2831 * By allowing sync_sched_expedited_started to advance no more than
2832 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2833 * that more than 3.5 billion CPUs would be required to force a
2834 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2835 * course be required on a 64-bit system.
2837 if (ULONG_CMP_GE((ulong
)atomic_long_read(&rsp
->expedited_start
),
2838 (ulong
)atomic_long_read(&rsp
->expedited_done
) +
2840 synchronize_sched();
2841 atomic_long_inc(&rsp
->expedited_wrap
);
2846 * Take a ticket. Note that atomic_inc_return() implies a
2847 * full memory barrier.
2849 snap
= atomic_long_inc_return(&rsp
->expedited_start
);
2852 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2855 * Each pass through the following loop attempts to force a
2856 * context switch on each CPU.
2858 while (try_stop_cpus(cpu_online_mask
,
2859 synchronize_sched_expedited_cpu_stop
,
2862 atomic_long_inc(&rsp
->expedited_tryfail
);
2864 /* Check to see if someone else did our work for us. */
2865 s
= atomic_long_read(&rsp
->expedited_done
);
2866 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2867 /* ensure test happens before caller kfree */
2868 smp_mb__before_atomic_inc(); /* ^^^ */
2869 atomic_long_inc(&rsp
->expedited_workdone1
);
2873 /* No joy, try again later. Or just synchronize_sched(). */
2874 if (trycount
++ < 10) {
2875 udelay(trycount
* num_online_cpus());
2877 wait_rcu_gp(call_rcu_sched
);
2878 atomic_long_inc(&rsp
->expedited_normal
);
2882 /* Recheck to see if someone else did our work for us. */
2883 s
= atomic_long_read(&rsp
->expedited_done
);
2884 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2885 /* ensure test happens before caller kfree */
2886 smp_mb__before_atomic_inc(); /* ^^^ */
2887 atomic_long_inc(&rsp
->expedited_workdone2
);
2892 * Refetching sync_sched_expedited_started allows later
2893 * callers to piggyback on our grace period. We retry
2894 * after they started, so our grace period works for them,
2895 * and they started after our first try, so their grace
2896 * period works for us.
2899 snap
= atomic_long_read(&rsp
->expedited_start
);
2900 smp_mb(); /* ensure read is before try_stop_cpus(). */
2902 atomic_long_inc(&rsp
->expedited_stoppedcpus
);
2905 * Everyone up to our most recent fetch is covered by our grace
2906 * period. Update the counter, but only if our work is still
2907 * relevant -- which it won't be if someone who started later
2908 * than we did already did their update.
2911 atomic_long_inc(&rsp
->expedited_done_tries
);
2912 s
= atomic_long_read(&rsp
->expedited_done
);
2913 if (ULONG_CMP_GE((ulong
)s
, (ulong
)snap
)) {
2914 /* ensure test happens before caller kfree */
2915 smp_mb__before_atomic_inc(); /* ^^^ */
2916 atomic_long_inc(&rsp
->expedited_done_lost
);
2919 } while (atomic_long_cmpxchg(&rsp
->expedited_done
, s
, snap
) != s
);
2920 atomic_long_inc(&rsp
->expedited_done_exit
);
2924 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2927 * Check to see if there is any immediate RCU-related work to be done
2928 * by the current CPU, for the specified type of RCU, returning 1 if so.
2929 * The checks are in order of increasing expense: checks that can be
2930 * carried out against CPU-local state are performed first. However,
2931 * we must check for CPU stalls first, else we might not get a chance.
2933 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2935 struct rcu_node
*rnp
= rdp
->mynode
;
2937 rdp
->n_rcu_pending
++;
2939 /* Check for CPU stalls, if enabled. */
2940 check_cpu_stall(rsp
, rdp
);
2942 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2943 if (rcu_nohz_full_cpu(rsp
))
2946 /* Is the RCU core waiting for a quiescent state from this CPU? */
2947 if (rcu_scheduler_fully_active
&&
2948 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2949 rdp
->n_rp_qs_pending
++;
2950 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2951 rdp
->n_rp_report_qs
++;
2955 /* Does this CPU have callbacks ready to invoke? */
2956 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2957 rdp
->n_rp_cb_ready
++;
2961 /* Has RCU gone idle with this CPU needing another grace period? */
2962 if (cpu_needs_another_gp(rsp
, rdp
)) {
2963 rdp
->n_rp_cpu_needs_gp
++;
2967 /* Has another RCU grace period completed? */
2968 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2969 rdp
->n_rp_gp_completed
++;
2973 /* Has a new RCU grace period started? */
2974 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2975 rdp
->n_rp_gp_started
++;
2979 /* Does this CPU need a deferred NOCB wakeup? */
2980 if (rcu_nocb_need_deferred_wakeup(rdp
)) {
2981 rdp
->n_rp_nocb_defer_wakeup
++;
2986 rdp
->n_rp_need_nothing
++;
2991 * Check to see if there is any immediate RCU-related work to be done
2992 * by the current CPU, returning 1 if so. This function is part of the
2993 * RCU implementation; it is -not- an exported member of the RCU API.
2995 static int rcu_pending(int cpu
)
2997 struct rcu_state
*rsp
;
2999 for_each_rcu_flavor(rsp
)
3000 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
3006 * Return true if the specified CPU has any callback. If all_lazy is
3007 * non-NULL, store an indication of whether all callbacks are lazy.
3008 * (If there are no callbacks, all of them are deemed to be lazy.)
3010 static int __maybe_unused
rcu_cpu_has_callbacks(int cpu
, bool *all_lazy
)
3014 struct rcu_data
*rdp
;
3015 struct rcu_state
*rsp
;
3017 for_each_rcu_flavor(rsp
) {
3018 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3022 if (rdp
->qlen
!= rdp
->qlen_lazy
|| !all_lazy
) {
3033 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3034 * the compiler is expected to optimize this away.
3036 static void _rcu_barrier_trace(struct rcu_state
*rsp
, const char *s
,
3037 int cpu
, unsigned long done
)
3039 trace_rcu_barrier(rsp
->name
, s
, cpu
,
3040 atomic_read(&rsp
->barrier_cpu_count
), done
);
3044 * RCU callback function for _rcu_barrier(). If we are last, wake
3045 * up the task executing _rcu_barrier().
3047 static void rcu_barrier_callback(struct rcu_head
*rhp
)
3049 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
3050 struct rcu_state
*rsp
= rdp
->rsp
;
3052 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
3053 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
3054 complete(&rsp
->barrier_completion
);
3056 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
3061 * Called with preemption disabled, and from cross-cpu IRQ context.
3063 static void rcu_barrier_func(void *type
)
3065 struct rcu_state
*rsp
= type
;
3066 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
3068 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
3069 atomic_inc(&rsp
->barrier_cpu_count
);
3070 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
3074 * Orchestrate the specified type of RCU barrier, waiting for all
3075 * RCU callbacks of the specified type to complete.
3077 static void _rcu_barrier(struct rcu_state
*rsp
)
3080 struct rcu_data
*rdp
;
3081 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
3082 unsigned long snap_done
;
3084 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
3086 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3087 mutex_lock(&rsp
->barrier_mutex
);
3090 * Ensure that all prior references, including to ->n_barrier_done,
3091 * are ordered before the _rcu_barrier() machinery.
3093 smp_mb(); /* See above block comment. */
3096 * Recheck ->n_barrier_done to see if others did our work for us.
3097 * This means checking ->n_barrier_done for an even-to-odd-to-even
3098 * transition. The "if" expression below therefore rounds the old
3099 * value up to the next even number and adds two before comparing.
3101 snap_done
= rsp
->n_barrier_done
;
3102 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
3105 * If the value in snap is odd, we needed to wait for the current
3106 * rcu_barrier() to complete, then wait for the next one, in other
3107 * words, we need the value of snap_done to be three larger than
3108 * the value of snap. On the other hand, if the value in snap is
3109 * even, we only had to wait for the next rcu_barrier() to complete,
3110 * in other words, we need the value of snap_done to be only two
3111 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
3112 * this for us (thank you, Linus!).
3114 if (ULONG_CMP_GE(snap_done
, (snap
+ 3) & ~0x1)) {
3115 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
3116 smp_mb(); /* caller's subsequent code after above check. */
3117 mutex_unlock(&rsp
->barrier_mutex
);
3122 * Increment ->n_barrier_done to avoid duplicate work. Use
3123 * ACCESS_ONCE() to prevent the compiler from speculating
3124 * the increment to precede the early-exit check.
3126 ACCESS_ONCE(rsp
->n_barrier_done
)++;
3127 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
3128 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
3129 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3132 * Initialize the count to one rather than to zero in order to
3133 * avoid a too-soon return to zero in case of a short grace period
3134 * (or preemption of this task). Exclude CPU-hotplug operations
3135 * to ensure that no offline CPU has callbacks queued.
3137 init_completion(&rsp
->barrier_completion
);
3138 atomic_set(&rsp
->barrier_cpu_count
, 1);
3142 * Force each CPU with callbacks to register a new callback.
3143 * When that callback is invoked, we will know that all of the
3144 * corresponding CPU's preceding callbacks have been invoked.
3146 for_each_possible_cpu(cpu
) {
3147 if (!cpu_online(cpu
) && !rcu_is_nocb_cpu(cpu
))
3149 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3150 if (rcu_is_nocb_cpu(cpu
)) {
3151 _rcu_barrier_trace(rsp
, "OnlineNoCB", cpu
,
3152 rsp
->n_barrier_done
);
3153 atomic_inc(&rsp
->barrier_cpu_count
);
3154 __call_rcu(&rdp
->barrier_head
, rcu_barrier_callback
,
3156 } else if (ACCESS_ONCE(rdp
->qlen
)) {
3157 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
3158 rsp
->n_barrier_done
);
3159 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
3161 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
3162 rsp
->n_barrier_done
);
3168 * Now that we have an rcu_barrier_callback() callback on each
3169 * CPU, and thus each counted, remove the initial count.
3171 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
3172 complete(&rsp
->barrier_completion
);
3174 /* Increment ->n_barrier_done to prevent duplicate work. */
3175 smp_mb(); /* Keep increment after above mechanism. */
3176 ACCESS_ONCE(rsp
->n_barrier_done
)++;
3177 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
3178 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
3179 smp_mb(); /* Keep increment before caller's subsequent code. */
3181 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3182 wait_for_completion(&rsp
->barrier_completion
);
3184 /* Other rcu_barrier() invocations can now safely proceed. */
3185 mutex_unlock(&rsp
->barrier_mutex
);
3189 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3191 void rcu_barrier_bh(void)
3193 _rcu_barrier(&rcu_bh_state
);
3195 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
3198 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3200 void rcu_barrier_sched(void)
3202 _rcu_barrier(&rcu_sched_state
);
3204 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
3207 * Do boot-time initialization of a CPU's per-CPU RCU data.
3210 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
3212 unsigned long flags
;
3213 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3214 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3216 /* Set up local state, ensuring consistent view of global state. */
3217 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3218 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
3219 init_callback_list(rdp
);
3221 ACCESS_ONCE(rdp
->qlen
) = 0;
3222 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
3223 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
3224 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
3227 rcu_boot_init_nocb_percpu_data(rdp
);
3228 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3232 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3233 * offline event can be happening at a given time. Note also that we
3234 * can accept some slop in the rsp->completed access due to the fact
3235 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3238 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
3240 unsigned long flags
;
3242 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3243 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3245 /* Exclude new grace periods. */
3246 mutex_lock(&rsp
->onoff_mutex
);
3248 /* Set up local state, ensuring consistent view of global state. */
3249 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3250 rdp
->beenonline
= 1; /* We have now been online. */
3251 rdp
->qlen_last_fqs_check
= 0;
3252 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
3253 rdp
->blimit
= blimit
;
3254 init_callback_list(rdp
); /* Re-enable callbacks on this CPU. */
3255 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
3256 rcu_sysidle_init_percpu_data(rdp
->dynticks
);
3257 atomic_set(&rdp
->dynticks
->dynticks
,
3258 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
3259 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
3261 /* Add CPU to rcu_node bitmasks. */
3263 mask
= rdp
->grpmask
;
3265 /* Exclude any attempts to start a new GP on small systems. */
3266 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
3267 rnp
->qsmaskinit
|= mask
;
3268 mask
= rnp
->grpmask
;
3269 if (rnp
== rdp
->mynode
) {
3271 * If there is a grace period in progress, we will
3272 * set up to wait for it next time we run the
3275 rdp
->gpnum
= rnp
->completed
;
3276 rdp
->completed
= rnp
->completed
;
3277 rdp
->passed_quiesce
= 0;
3278 rdp
->qs_pending
= 0;
3279 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuonl"));
3281 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
3283 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
3284 local_irq_restore(flags
);
3286 mutex_unlock(&rsp
->onoff_mutex
);
3289 static void rcu_prepare_cpu(int cpu
)
3291 struct rcu_state
*rsp
;
3293 for_each_rcu_flavor(rsp
)
3294 rcu_init_percpu_data(cpu
, rsp
);
3298 * Handle CPU online/offline notification events.
3300 static int rcu_cpu_notify(struct notifier_block
*self
,
3301 unsigned long action
, void *hcpu
)
3303 long cpu
= (long)hcpu
;
3304 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
3305 struct rcu_node
*rnp
= rdp
->mynode
;
3306 struct rcu_state
*rsp
;
3308 trace_rcu_utilization(TPS("Start CPU hotplug"));
3310 case CPU_UP_PREPARE
:
3311 case CPU_UP_PREPARE_FROZEN
:
3312 rcu_prepare_cpu(cpu
);
3313 rcu_prepare_kthreads(cpu
);
3316 case CPU_DOWN_FAILED
:
3317 rcu_boost_kthread_setaffinity(rnp
, -1);
3319 case CPU_DOWN_PREPARE
:
3320 rcu_boost_kthread_setaffinity(rnp
, cpu
);
3323 case CPU_DYING_FROZEN
:
3324 for_each_rcu_flavor(rsp
)
3325 rcu_cleanup_dying_cpu(rsp
);
3328 case CPU_DEAD_FROZEN
:
3329 case CPU_UP_CANCELED
:
3330 case CPU_UP_CANCELED_FROZEN
:
3331 for_each_rcu_flavor(rsp
)
3332 rcu_cleanup_dead_cpu(cpu
, rsp
);
3337 trace_rcu_utilization(TPS("End CPU hotplug"));
3341 static int rcu_pm_notify(struct notifier_block
*self
,
3342 unsigned long action
, void *hcpu
)
3345 case PM_HIBERNATION_PREPARE
:
3346 case PM_SUSPEND_PREPARE
:
3347 if (nr_cpu_ids
<= 256) /* Expediting bad for large systems. */
3350 case PM_POST_HIBERNATION
:
3351 case PM_POST_SUSPEND
:
3361 * Spawn the kthread that handles this RCU flavor's grace periods.
3363 static int __init
rcu_spawn_gp_kthread(void)
3365 unsigned long flags
;
3366 struct rcu_node
*rnp
;
3367 struct rcu_state
*rsp
;
3368 struct task_struct
*t
;
3370 for_each_rcu_flavor(rsp
) {
3371 t
= kthread_run(rcu_gp_kthread
, rsp
, "%s", rsp
->name
);
3373 rnp
= rcu_get_root(rsp
);
3374 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3375 rsp
->gp_kthread
= t
;
3376 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3377 rcu_spawn_nocb_kthreads(rsp
);
3381 early_initcall(rcu_spawn_gp_kthread
);
3384 * This function is invoked towards the end of the scheduler's initialization
3385 * process. Before this is called, the idle task might contain
3386 * RCU read-side critical sections (during which time, this idle
3387 * task is booting the system). After this function is called, the
3388 * idle tasks are prohibited from containing RCU read-side critical
3389 * sections. This function also enables RCU lockdep checking.
3391 void rcu_scheduler_starting(void)
3393 WARN_ON(num_online_cpus() != 1);
3394 WARN_ON(nr_context_switches() > 0);
3395 rcu_scheduler_active
= 1;
3399 * Compute the per-level fanout, either using the exact fanout specified
3400 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3402 #ifdef CONFIG_RCU_FANOUT_EXACT
3403 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3407 rsp
->levelspread
[rcu_num_lvls
- 1] = rcu_fanout_leaf
;
3408 for (i
= rcu_num_lvls
- 2; i
>= 0; i
--)
3409 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
3411 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3412 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3419 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3420 ccur
= rsp
->levelcnt
[i
];
3421 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
3425 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3428 * Helper function for rcu_init() that initializes one rcu_state structure.
3430 static void __init
rcu_init_one(struct rcu_state
*rsp
,
3431 struct rcu_data __percpu
*rda
)
3433 static char *buf
[] = { "rcu_node_0",
3436 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3437 static char *fqs
[] = { "rcu_node_fqs_0",
3440 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3444 struct rcu_node
*rnp
;
3446 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
3448 /* Silence gcc 4.8 warning about array index out of range. */
3449 if (rcu_num_lvls
> RCU_NUM_LVLS
)
3450 panic("rcu_init_one: rcu_num_lvls overflow");
3452 /* Initialize the level-tracking arrays. */
3454 for (i
= 0; i
< rcu_num_lvls
; i
++)
3455 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
3456 for (i
= 1; i
< rcu_num_lvls
; i
++)
3457 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
3458 rcu_init_levelspread(rsp
);
3460 /* Initialize the elements themselves, starting from the leaves. */
3462 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3463 cpustride
*= rsp
->levelspread
[i
];
3464 rnp
= rsp
->level
[i
];
3465 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
3466 raw_spin_lock_init(&rnp
->lock
);
3467 lockdep_set_class_and_name(&rnp
->lock
,
3468 &rcu_node_class
[i
], buf
[i
]);
3469 raw_spin_lock_init(&rnp
->fqslock
);
3470 lockdep_set_class_and_name(&rnp
->fqslock
,
3471 &rcu_fqs_class
[i
], fqs
[i
]);
3472 rnp
->gpnum
= rsp
->gpnum
;
3473 rnp
->completed
= rsp
->completed
;
3475 rnp
->qsmaskinit
= 0;
3476 rnp
->grplo
= j
* cpustride
;
3477 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
3478 if (rnp
->grphi
>= nr_cpu_ids
)
3479 rnp
->grphi
= nr_cpu_ids
- 1;
3485 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
3486 rnp
->grpmask
= 1UL << rnp
->grpnum
;
3487 rnp
->parent
= rsp
->level
[i
- 1] +
3488 j
/ rsp
->levelspread
[i
- 1];
3491 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
3492 rcu_init_one_nocb(rnp
);
3497 init_waitqueue_head(&rsp
->gp_wq
);
3498 rnp
= rsp
->level
[rcu_num_lvls
- 1];
3499 for_each_possible_cpu(i
) {
3500 while (i
> rnp
->grphi
)
3502 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
3503 rcu_boot_init_percpu_data(i
, rsp
);
3505 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
3509 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3510 * replace the definitions in tree.h because those are needed to size
3511 * the ->node array in the rcu_state structure.
3513 static void __init
rcu_init_geometry(void)
3519 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
3522 * Initialize any unspecified boot parameters.
3523 * The default values of jiffies_till_first_fqs and
3524 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3525 * value, which is a function of HZ, then adding one for each
3526 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3528 d
= RCU_JIFFIES_TILL_FORCE_QS
+ nr_cpu_ids
/ RCU_JIFFIES_FQS_DIV
;
3529 if (jiffies_till_first_fqs
== ULONG_MAX
)
3530 jiffies_till_first_fqs
= d
;
3531 if (jiffies_till_next_fqs
== ULONG_MAX
)
3532 jiffies_till_next_fqs
= d
;
3534 /* If the compile-time values are accurate, just leave. */
3535 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
&&
3536 nr_cpu_ids
== NR_CPUS
)
3538 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
3539 rcu_fanout_leaf
, nr_cpu_ids
);
3542 * Compute number of nodes that can be handled an rcu_node tree
3543 * with the given number of levels. Setting rcu_capacity[0] makes
3544 * some of the arithmetic easier.
3546 rcu_capacity
[0] = 1;
3547 rcu_capacity
[1] = rcu_fanout_leaf
;
3548 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
3549 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
3552 * The boot-time rcu_fanout_leaf parameter is only permitted
3553 * to increase the leaf-level fanout, not decrease it. Of course,
3554 * the leaf-level fanout cannot exceed the number of bits in
3555 * the rcu_node masks. Finally, the tree must be able to accommodate
3556 * the configured number of CPUs. Complain and fall back to the
3557 * compile-time values if these limits are exceeded.
3559 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
3560 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
3561 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
3566 /* Calculate the number of rcu_nodes at each level of the tree. */
3567 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
3568 if (n
<= rcu_capacity
[i
]) {
3569 for (j
= 0; j
<= i
; j
++)
3571 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
3573 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
3578 /* Calculate the total number of rcu_node structures. */
3580 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
3581 rcu_num_nodes
+= num_rcu_lvl
[i
];
3585 void __init
rcu_init(void)
3589 rcu_bootup_announce();
3590 rcu_init_geometry();
3591 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
3592 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
3593 __rcu_init_preempt();
3594 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
3597 * We don't need protection against CPU-hotplug here because
3598 * this is called early in boot, before either interrupts
3599 * or the scheduler are operational.
3601 cpu_notifier(rcu_cpu_notify
, 0);
3602 pm_notifier(rcu_pm_notify
, 0);
3603 for_each_online_cpu(cpu
)
3604 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
3607 #include "tree_plugin.h"