2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2008
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
27 * For detailed explanation of Read-Copy Update mechanism see -
30 #include <linux/types.h>
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 #include <linux/smp.h>
35 #include <linux/rcupdate.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/nmi.h>
39 #include <linux/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/export.h>
42 #include <linux/completion.h>
43 #include <linux/moduleparam.h>
44 #include <linux/percpu.h>
45 #include <linux/notifier.h>
46 #include <linux/cpu.h>
47 #include <linux/mutex.h>
48 #include <linux/time.h>
49 #include <linux/kernel_stat.h>
50 #include <linux/wait.h>
51 #include <linux/kthread.h>
52 #include <linux/prefetch.h>
53 #include <linux/delay.h>
54 #include <linux/stop_machine.h>
55 #include <linux/random.h>
56 #include <linux/ftrace_event.h>
57 #include <linux/suspend.h>
60 #include <trace/events/rcu.h>
64 /* Data structures. */
66 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
67 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
70 * In order to export the rcu_state name to the tracing tools, it
71 * needs to be added in the __tracepoint_string section.
72 * This requires defining a separate variable tp_<sname>_varname
73 * that points to the string being used, and this will allow
74 * the tracing userspace tools to be able to decipher the string
75 * address to the matching string.
77 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
78 static char sname##_varname[] = #sname; \
79 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
80 struct rcu_state sname##_state = { \
81 .level = { &sname##_state.node[0] }, \
83 .fqs_state = RCU_GP_IDLE, \
84 .gpnum = 0UL - 300UL, \
85 .completed = 0UL - 300UL, \
86 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
87 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
88 .orphan_donetail = &sname##_state.orphan_donelist, \
89 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
90 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
91 .name = sname##_varname, \
94 DEFINE_PER_CPU(struct rcu_data, sname##_data)
96 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
97 RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
99 static struct rcu_state *rcu_state;
100 LIST_HEAD(rcu_struct_flavors);
102 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
103 static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
104 module_param(rcu_fanout_leaf, int, 0444);
105 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
106 static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */
113 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
116 * The rcu_scheduler_active variable transitions from zero to one just
117 * before the first task is spawned. So when this variable is zero, RCU
118 * can assume that there is but one task, allowing RCU to (for example)
119 * optimize synchronize_sched() to a simple barrier(). When this variable
120 * is one, RCU must actually do all the hard work required to detect real
121 * grace periods. This variable is also used to suppress boot-time false
122 * positives from lockdep-RCU error checking.
124 int rcu_scheduler_active __read_mostly;
125 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
128 * The rcu_scheduler_fully_active variable transitions from zero to one
129 * during the early_initcall() processing, which is after the scheduler
130 * is capable of creating new tasks. So RCU processing (for example,
131 * creating tasks for RCU priority boosting) must be delayed until after
132 * rcu_scheduler_fully_active transitions from zero to one. We also
133 * currently delay invocation of any RCU callbacks until after this point.
135 * It might later prove better for people registering RCU callbacks during
136 * early boot to take responsibility for these callbacks, but one step at
139 static int rcu_scheduler_fully_active __read_mostly;
141 #ifdef CONFIG_RCU_BOOST
144 * Control variables for per-CPU and per-rcu_node kthreads. These
145 * handle all flavors of RCU.
147 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
148 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
149 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
150 DEFINE_PER_CPU(char, rcu_cpu_has_work);
152 #endif /* #ifdef CONFIG_RCU_BOOST */
154 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
155 static void invoke_rcu_core(void);
156 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
159 * Track the rcutorture test sequence number and the update version
160 * number within a given test. The rcutorture_testseq is incremented
161 * on every rcutorture module load and unload, so has an odd value
162 * when a test is running. The rcutorture_vernum is set to zero
163 * when rcutorture starts and is incremented on each rcutorture update.
164 * These variables enable correlating rcutorture output with the
165 * RCU tracing information.
167 unsigned long rcutorture_testseq;
168 unsigned long rcutorture_vernum;
171 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
172 * permit this function to be invoked without holding the root rcu_node
173 * structure's ->lock, but of course results can be subject to change.
175 static int rcu_gp_in_progress(struct rcu_state *rsp)
177 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
181 * Note a quiescent state. Because we do not need to know
182 * how many quiescent states passed, just if there was at least
183 * one since the start of the grace period, this just sets a flag.
184 * The caller must have disabled preemption.
186 void rcu_sched_qs(int cpu)
188 struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
190 if (rdp->passed_quiesce == 0)
191 trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
192 rdp->passed_quiesce = 1;
195 void rcu_bh_qs(int cpu)
197 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
199 if (rdp->passed_quiesce == 0)
200 trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
201 rdp->passed_quiesce = 1;
205 * Note a context switch. This is a quiescent state for RCU-sched,
206 * and requires special handling for preemptible RCU.
207 * The caller must have disabled preemption.
209 void rcu_note_context_switch(int cpu)
211 trace_rcu_utilization(TPS("Start context switch"));
213 rcu_preempt_note_context_switch(cpu);
214 trace_rcu_utilization(TPS("End context switch"));
216 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
218 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
219 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
220 .dynticks = ATOMIC_INIT(1),
221 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
222 .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
223 .dynticks_idle = ATOMIC_INIT(1),
224 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
227 static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
228 static long qhimark = 10000; /* If this many pending, ignore blimit. */
229 static long qlowmark = 100; /* Once only this many pending, use blimit. */
231 module_param(blimit, long, 0444);
232 module_param(qhimark, long, 0444);
233 module_param(qlowmark, long, 0444);
235 static ulong jiffies_till_first_fqs = ULONG_MAX;
236 static ulong jiffies_till_next_fqs = ULONG_MAX;
238 module_param(jiffies_till_first_fqs, ulong, 0644);
239 module_param(jiffies_till_next_fqs, ulong, 0644);
241 static void rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
242 struct rcu_data *rdp);
243 static void force_qs_rnp(struct rcu_state *rsp,
244 int (*f)(struct rcu_data *rsp, bool *isidle,
245 unsigned long *maxj),
246 bool *isidle, unsigned long *maxj);
247 static void force_quiescent_state(struct rcu_state *rsp);
248 static int rcu_pending(int cpu);
251 * Return the number of RCU-sched batches processed thus far for debug & stats.
253 long rcu_batches_completed_sched(void)
255 return rcu_sched_state.completed;
257 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
260 * Return the number of RCU BH batches processed thus far for debug & stats.
262 long rcu_batches_completed_bh(void)
264 return rcu_bh_state.completed;
266 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
269 * Force a quiescent state for RCU BH.
271 void rcu_bh_force_quiescent_state(void)
273 force_quiescent_state(&rcu_bh_state);
275 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
278 * Record the number of times rcutorture tests have been initiated and
279 * terminated. This information allows the debugfs tracing stats to be
280 * correlated to the rcutorture messages, even when the rcutorture module
281 * is being repeatedly loaded and unloaded. In other words, we cannot
282 * store this state in rcutorture itself.
284 void rcutorture_record_test_transition(void)
286 rcutorture_testseq++;
287 rcutorture_vernum = 0;
289 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
292 * Record the number of writer passes through the current rcutorture test.
293 * This is also used to correlate debugfs tracing stats with the rcutorture
296 void rcutorture_record_progress(unsigned long vernum)
300 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
303 * Force a quiescent state for RCU-sched.
305 void rcu_sched_force_quiescent_state(void)
307 force_quiescent_state(&rcu_sched_state);
309 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
312 * Does the CPU have callbacks ready to be invoked?
315 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
317 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
318 rdp->nxttail[RCU_DONE_TAIL] != NULL;
322 * Does the current CPU require a not-yet-started grace period?
323 * The caller must have disabled interrupts to prevent races with
324 * normal callback registry.
327 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
331 if (rcu_gp_in_progress(rsp))
332 return 0; /* No, a grace period is already in progress. */
333 if (rcu_nocb_needs_gp(rsp))
334 return 1; /* Yes, a no-CBs CPU needs one. */
335 if (!rdp->nxttail[RCU_NEXT_TAIL])
336 return 0; /* No, this is a no-CBs (or offline) CPU. */
337 if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
338 return 1; /* Yes, this CPU has newly registered callbacks. */
339 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
340 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
341 ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
342 rdp->nxtcompleted[i]))
343 return 1; /* Yes, CBs for future grace period. */
344 return 0; /* No grace period needed. */
348 * Return the root node of the specified rcu_state structure.
350 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
352 return &rsp->node[0];
356 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
358 * If the new value of the ->dynticks_nesting counter now is zero,
359 * we really have entered idle, and must do the appropriate accounting.
360 * The caller must have disabled interrupts.
362 static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
365 trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
366 if (!user && !is_idle_task(current)) {
367 struct task_struct *idle __maybe_unused =
368 idle_task(smp_processor_id());
370 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
371 ftrace_dump(DUMP_ORIG);
372 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
373 current->pid, current->comm,
374 idle->pid, idle->comm); /* must be idle task! */
376 rcu_prepare_for_idle(smp_processor_id());
377 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
378 smp_mb__before_atomic_inc(); /* See above. */
379 atomic_inc(&rdtp->dynticks);
380 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
381 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
384 * It is illegal to enter an extended quiescent state while
385 * in an RCU read-side critical section.
387 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
388 "Illegal idle entry in RCU read-side critical section.");
389 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
390 "Illegal idle entry in RCU-bh read-side critical section.");
391 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
392 "Illegal idle entry in RCU-sched read-side critical section.");
396 * Enter an RCU extended quiescent state, which can be either the
397 * idle loop or adaptive-tickless usermode execution.
399 static void rcu_eqs_enter(bool user)
402 struct rcu_dynticks *rdtp;
404 rdtp = this_cpu_ptr(&rcu_dynticks);
405 oldval = rdtp->dynticks_nesting;
406 WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
407 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
408 rdtp->dynticks_nesting = 0;
410 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
411 rcu_eqs_enter_common(rdtp, oldval, user);
415 * rcu_idle_enter - inform RCU that current CPU is entering idle
417 * Enter idle mode, in other words, -leave- the mode in which RCU
418 * read-side critical sections can occur. (Though RCU read-side
419 * critical sections can occur in irq handlers in idle, a possibility
420 * handled by irq_enter() and irq_exit().)
422 * We crowbar the ->dynticks_nesting field to zero to allow for
423 * the possibility of usermode upcalls having messed up our count
424 * of interrupt nesting level during the prior busy period.
426 void rcu_idle_enter(void)
430 local_irq_save(flags);
431 rcu_eqs_enter(false);
432 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
433 local_irq_restore(flags);
435 EXPORT_SYMBOL_GPL(rcu_idle_enter);
437 #ifdef CONFIG_RCU_USER_QS
439 * rcu_user_enter - inform RCU that we are resuming userspace.
441 * Enter RCU idle mode right before resuming userspace. No use of RCU
442 * is permitted between this call and rcu_user_exit(). This way the
443 * CPU doesn't need to maintain the tick for RCU maintenance purposes
444 * when the CPU runs in userspace.
446 void rcu_user_enter(void)
450 #endif /* CONFIG_RCU_USER_QS */
453 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
455 * Exit from an interrupt handler, which might possibly result in entering
456 * idle mode, in other words, leaving the mode in which read-side critical
457 * sections can occur.
459 * This code assumes that the idle loop never does anything that might
460 * result in unbalanced calls to irq_enter() and irq_exit(). If your
461 * architecture violates this assumption, RCU will give you what you
462 * deserve, good and hard. But very infrequently and irreproducibly.
464 * Use things like work queues to work around this limitation.
466 * You have been warned.
468 void rcu_irq_exit(void)
472 struct rcu_dynticks *rdtp;
474 local_irq_save(flags);
475 rdtp = this_cpu_ptr(&rcu_dynticks);
476 oldval = rdtp->dynticks_nesting;
477 rdtp->dynticks_nesting--;
478 WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
479 if (rdtp->dynticks_nesting)
480 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
482 rcu_eqs_enter_common(rdtp, oldval, true);
483 rcu_sysidle_enter(rdtp, 1);
484 local_irq_restore(flags);
488 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
490 * If the new value of the ->dynticks_nesting counter was previously zero,
491 * we really have exited idle, and must do the appropriate accounting.
492 * The caller must have disabled interrupts.
494 static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
497 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
498 atomic_inc(&rdtp->dynticks);
499 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
500 smp_mb__after_atomic_inc(); /* See above. */
501 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
502 rcu_cleanup_after_idle(smp_processor_id());
503 trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
504 if (!user && !is_idle_task(current)) {
505 struct task_struct *idle __maybe_unused =
506 idle_task(smp_processor_id());
508 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
509 oldval, rdtp->dynticks_nesting);
510 ftrace_dump(DUMP_ORIG);
511 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
512 current->pid, current->comm,
513 idle->pid, idle->comm); /* must be idle task! */
518 * Exit an RCU extended quiescent state, which can be either the
519 * idle loop or adaptive-tickless usermode execution.
521 static void rcu_eqs_exit(bool user)
523 struct rcu_dynticks *rdtp;
526 rdtp = this_cpu_ptr(&rcu_dynticks);
527 oldval = rdtp->dynticks_nesting;
528 WARN_ON_ONCE(oldval < 0);
529 if (oldval & DYNTICK_TASK_NEST_MASK)
530 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
532 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
533 rcu_eqs_exit_common(rdtp, oldval, user);
537 * rcu_idle_exit - inform RCU that current CPU is leaving idle
539 * Exit idle mode, in other words, -enter- the mode in which RCU
540 * read-side critical sections can occur.
542 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
543 * allow for the possibility of usermode upcalls messing up our count
544 * of interrupt nesting level during the busy period that is just
547 void rcu_idle_exit(void)
551 local_irq_save(flags);
553 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
554 local_irq_restore(flags);
556 EXPORT_SYMBOL_GPL(rcu_idle_exit);
558 #ifdef CONFIG_RCU_USER_QS
560 * rcu_user_exit - inform RCU that we are exiting userspace.
562 * Exit RCU idle mode while entering the kernel because it can
563 * run a RCU read side critical section anytime.
565 void rcu_user_exit(void)
569 #endif /* CONFIG_RCU_USER_QS */
572 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
574 * Enter an interrupt handler, which might possibly result in exiting
575 * idle mode, in other words, entering the mode in which read-side critical
576 * sections can occur.
578 * Note that the Linux kernel is fully capable of entering an interrupt
579 * handler that it never exits, for example when doing upcalls to
580 * user mode! This code assumes that the idle loop never does upcalls to
581 * user mode. If your architecture does do upcalls from the idle loop (or
582 * does anything else that results in unbalanced calls to the irq_enter()
583 * and irq_exit() functions), RCU will give you what you deserve, good
584 * and hard. But very infrequently and irreproducibly.
586 * Use things like work queues to work around this limitation.
588 * You have been warned.
590 void rcu_irq_enter(void)
593 struct rcu_dynticks *rdtp;
596 local_irq_save(flags);
597 rdtp = this_cpu_ptr(&rcu_dynticks);
598 oldval = rdtp->dynticks_nesting;
599 rdtp->dynticks_nesting++;
600 WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
602 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
604 rcu_eqs_exit_common(rdtp, oldval, true);
605 rcu_sysidle_exit(rdtp, 1);
606 local_irq_restore(flags);
610 * rcu_nmi_enter - inform RCU of entry to NMI context
612 * If the CPU was idle with dynamic ticks active, and there is no
613 * irq handler running, this updates rdtp->dynticks_nmi to let the
614 * RCU grace-period handling know that the CPU is active.
616 void rcu_nmi_enter(void)
618 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
620 if (rdtp->dynticks_nmi_nesting == 0 &&
621 (atomic_read(&rdtp->dynticks) & 0x1))
623 rdtp->dynticks_nmi_nesting++;
624 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
625 atomic_inc(&rdtp->dynticks);
626 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
627 smp_mb__after_atomic_inc(); /* See above. */
628 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
632 * rcu_nmi_exit - inform RCU of exit from NMI context
634 * If the CPU was idle with dynamic ticks active, and there is no
635 * irq handler running, this updates rdtp->dynticks_nmi to let the
636 * RCU grace-period handling know that the CPU is no longer active.
638 void rcu_nmi_exit(void)
640 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
642 if (rdtp->dynticks_nmi_nesting == 0 ||
643 --rdtp->dynticks_nmi_nesting != 0)
645 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
646 smp_mb__before_atomic_inc(); /* See above. */
647 atomic_inc(&rdtp->dynticks);
648 smp_mb__after_atomic_inc(); /* Force delay to next write. */
649 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
653 * __rcu_is_watching - are RCU read-side critical sections safe?
655 * Return true if RCU is watching the running CPU, which means that
656 * this CPU can safely enter RCU read-side critical sections. Unlike
657 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
658 * least disabled preemption.
660 bool __rcu_is_watching(void)
662 return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
666 * rcu_is_watching - see if RCU thinks that the current CPU is idle
668 * If the current CPU is in its idle loop and is neither in an interrupt
669 * or NMI handler, return true.
671 bool rcu_is_watching(void)
676 ret = __rcu_is_watching();
680 EXPORT_SYMBOL_GPL(rcu_is_watching);
682 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
685 * Is the current CPU online? Disable preemption to avoid false positives
686 * that could otherwise happen due to the current CPU number being sampled,
687 * this task being preempted, its old CPU being taken offline, resuming
688 * on some other CPU, then determining that its old CPU is now offline.
689 * It is OK to use RCU on an offline processor during initial boot, hence
690 * the check for rcu_scheduler_fully_active. Note also that it is OK
691 * for a CPU coming online to use RCU for one jiffy prior to marking itself
692 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
693 * offline to continue to use RCU for one jiffy after marking itself
694 * offline in the cpu_online_mask. This leniency is necessary given the
695 * non-atomic nature of the online and offline processing, for example,
696 * the fact that a CPU enters the scheduler after completing the CPU_DYING
699 * This is also why RCU internally marks CPUs online during the
700 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
702 * Disable checking if in an NMI handler because we cannot safely report
703 * errors from NMI handlers anyway.
705 bool rcu_lockdep_current_cpu_online(void)
707 struct rcu_data *rdp;
708 struct rcu_node *rnp;
714 rdp = this_cpu_ptr(&rcu_sched_data);
716 ret = (rdp->grpmask & rnp->qsmaskinit) ||
717 !rcu_scheduler_fully_active;
721 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
723 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
726 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
728 * If the current CPU is idle or running at a first-level (not nested)
729 * interrupt from idle, return true. The caller must have at least
730 * disabled preemption.
732 static int rcu_is_cpu_rrupt_from_idle(void)
734 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
738 * Snapshot the specified CPU's dynticks counter so that we can later
739 * credit them with an implicit quiescent state. Return 1 if this CPU
740 * is in dynticks idle mode, which is an extended quiescent state.
742 static int dyntick_save_progress_counter(struct rcu_data *rdp,
743 bool *isidle, unsigned long *maxj)
745 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
746 rcu_sysidle_check_cpu(rdp, isidle, maxj);
747 return (rdp->dynticks_snap & 0x1) == 0;
751 * Return true if the specified CPU has passed through a quiescent
752 * state by virtue of being in or having passed through an dynticks
753 * idle state since the last call to dyntick_save_progress_counter()
754 * for this same CPU, or by virtue of having been offline.
756 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
757 bool *isidle, unsigned long *maxj)
762 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
763 snap = (unsigned int)rdp->dynticks_snap;
766 * If the CPU passed through or entered a dynticks idle phase with
767 * no active irq/NMI handlers, then we can safely pretend that the CPU
768 * already acknowledged the request to pass through a quiescent
769 * state. Either way, that CPU cannot possibly be in an RCU
770 * read-side critical section that started before the beginning
771 * of the current RCU grace period.
773 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
774 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
780 * Check for the CPU being offline, but only if the grace period
781 * is old enough. We don't need to worry about the CPU changing
782 * state: If we see it offline even once, it has been through a
785 * The reason for insisting that the grace period be at least
786 * one jiffy old is that CPUs that are not quite online and that
787 * have just gone offline can still execute RCU read-side critical
790 if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
791 return 0; /* Grace period is not old enough. */
793 if (cpu_is_offline(rdp->cpu)) {
794 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
800 * There is a possibility that a CPU in adaptive-ticks state
801 * might run in the kernel with the scheduling-clock tick disabled
802 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
803 * force the CPU to restart the scheduling-clock tick in this
804 * CPU is in this state.
806 rcu_kick_nohz_cpu(rdp->cpu);
811 static void record_gp_stall_check_time(struct rcu_state *rsp)
813 unsigned long j = ACCESS_ONCE(jiffies);
816 smp_wmb(); /* Record start time before stall time. */
817 rsp->jiffies_stall = j + rcu_jiffies_till_stall_check();
821 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
822 * for architectures that do not implement trigger_all_cpu_backtrace().
823 * The NMI-triggered stack traces are more accurate because they are
824 * printed by the target CPU.
826 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
830 struct rcu_node *rnp;
832 rcu_for_each_leaf_node(rsp, rnp) {
833 raw_spin_lock_irqsave(&rnp->lock, flags);
834 if (rnp->qsmask != 0) {
835 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
836 if (rnp->qsmask & (1UL << cpu))
837 dump_cpu_task(rnp->grplo + cpu);
839 raw_spin_unlock_irqrestore(&rnp->lock, flags);
843 static void print_other_cpu_stall(struct rcu_state *rsp)
849 struct rcu_node *rnp = rcu_get_root(rsp);
852 /* Only let one CPU complain about others per time interval. */
854 raw_spin_lock_irqsave(&rnp->lock, flags);
855 delta = jiffies - rsp->jiffies_stall;
856 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
857 raw_spin_unlock_irqrestore(&rnp->lock, flags);
860 rsp->jiffies_stall = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
861 raw_spin_unlock_irqrestore(&rnp->lock, flags);
864 * OK, time to rat on our buddy...
865 * See Documentation/RCU/stallwarn.txt for info on how to debug
866 * RCU CPU stall warnings.
868 pr_err("INFO: %s detected stalls on CPUs/tasks:",
870 print_cpu_stall_info_begin();
871 rcu_for_each_leaf_node(rsp, rnp) {
872 raw_spin_lock_irqsave(&rnp->lock, flags);
873 ndetected += rcu_print_task_stall(rnp);
874 if (rnp->qsmask != 0) {
875 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
876 if (rnp->qsmask & (1UL << cpu)) {
877 print_cpu_stall_info(rsp,
882 raw_spin_unlock_irqrestore(&rnp->lock, flags);
886 * Now rat on any tasks that got kicked up to the root rcu_node
887 * due to CPU offlining.
889 rnp = rcu_get_root(rsp);
890 raw_spin_lock_irqsave(&rnp->lock, flags);
891 ndetected += rcu_print_task_stall(rnp);
892 raw_spin_unlock_irqrestore(&rnp->lock, flags);
894 print_cpu_stall_info_end();
895 for_each_possible_cpu(cpu)
896 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
897 pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
898 smp_processor_id(), (long)(jiffies - rsp->gp_start),
899 rsp->gpnum, rsp->completed, totqlen);
901 pr_err("INFO: Stall ended before state dump start\n");
902 else if (!trigger_all_cpu_backtrace())
903 rcu_dump_cpu_stacks(rsp);
905 /* Complain about tasks blocking the grace period. */
907 rcu_print_detail_task_stall(rsp);
909 force_quiescent_state(rsp); /* Kick them all. */
912 static void print_cpu_stall(struct rcu_state *rsp)
916 struct rcu_node *rnp = rcu_get_root(rsp);
920 * OK, time to rat on ourselves...
921 * See Documentation/RCU/stallwarn.txt for info on how to debug
922 * RCU CPU stall warnings.
924 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
925 print_cpu_stall_info_begin();
926 print_cpu_stall_info(rsp, smp_processor_id());
927 print_cpu_stall_info_end();
928 for_each_possible_cpu(cpu)
929 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
930 pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
931 jiffies - rsp->gp_start, rsp->gpnum, rsp->completed, totqlen);
932 if (!trigger_all_cpu_backtrace())
935 raw_spin_lock_irqsave(&rnp->lock, flags);
936 if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
937 rsp->jiffies_stall = jiffies +
938 3 * rcu_jiffies_till_stall_check() + 3;
939 raw_spin_unlock_irqrestore(&rnp->lock, flags);
941 set_need_resched(); /* kick ourselves to get things going. */
944 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
946 unsigned long completed;
951 struct rcu_node *rnp;
953 if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
955 j = ACCESS_ONCE(jiffies);
958 * Lots of memory barriers to reject false positives.
960 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
961 * then rsp->gp_start, and finally rsp->completed. These values
962 * are updated in the opposite order with memory barriers (or
963 * equivalent) during grace-period initialization and cleanup.
964 * Now, a false positive can occur if we get an new value of
965 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
966 * the memory barriers, the only way that this can happen is if one
967 * grace period ends and another starts between these two fetches.
968 * Detect this by comparing rsp->completed with the previous fetch
971 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
972 * and rsp->gp_start suffice to forestall false positives.
974 gpnum = ACCESS_ONCE(rsp->gpnum);
975 smp_rmb(); /* Pick up ->gpnum first... */
976 js = ACCESS_ONCE(rsp->jiffies_stall);
977 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
978 gps = ACCESS_ONCE(rsp->gp_start);
979 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
980 completed = ACCESS_ONCE(rsp->completed);
981 if (ULONG_CMP_GE(completed, gpnum) ||
982 ULONG_CMP_LT(j, js) ||
983 ULONG_CMP_GE(gps, js))
984 return; /* No stall or GP completed since entering function. */
986 if (rcu_gp_in_progress(rsp) &&
987 (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
989 /* We haven't checked in, so go dump stack. */
990 print_cpu_stall(rsp);
992 } else if (rcu_gp_in_progress(rsp) &&
993 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
995 /* They had a few time units to dump stack, so complain. */
996 print_other_cpu_stall(rsp);
1001 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1003 * Set the stall-warning timeout way off into the future, thus preventing
1004 * any RCU CPU stall-warning messages from appearing in the current set of
1005 * RCU grace periods.
1007 * The caller must disable hard irqs.
1009 void rcu_cpu_stall_reset(void)
1011 struct rcu_state *rsp;
1013 for_each_rcu_flavor(rsp)
1014 rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
1018 * Initialize the specified rcu_data structure's callback list to empty.
1020 static void init_callback_list(struct rcu_data *rdp)
1024 if (init_nocb_callback_list(rdp))
1026 rdp->nxtlist = NULL;
1027 for (i = 0; i < RCU_NEXT_SIZE; i++)
1028 rdp->nxttail[i] = &rdp->nxtlist;
1032 * Determine the value that ->completed will have at the end of the
1033 * next subsequent grace period. This is used to tag callbacks so that
1034 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1035 * been dyntick-idle for an extended period with callbacks under the
1036 * influence of RCU_FAST_NO_HZ.
1038 * The caller must hold rnp->lock with interrupts disabled.
1040 static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1041 struct rcu_node *rnp)
1044 * If RCU is idle, we just wait for the next grace period.
1045 * But we can only be sure that RCU is idle if we are looking
1046 * at the root rcu_node structure -- otherwise, a new grace
1047 * period might have started, but just not yet gotten around
1048 * to initializing the current non-root rcu_node structure.
1050 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1051 return rnp->completed + 1;
1054 * Otherwise, wait for a possible partial grace period and
1055 * then the subsequent full grace period.
1057 return rnp->completed + 2;
1061 * Trace-event helper function for rcu_start_future_gp() and
1062 * rcu_nocb_wait_gp().
1064 static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1065 unsigned long c, const char *s)
1067 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1068 rnp->completed, c, rnp->level,
1069 rnp->grplo, rnp->grphi, s);
1073 * Start some future grace period, as needed to handle newly arrived
1074 * callbacks. The required future grace periods are recorded in each
1075 * rcu_node structure's ->need_future_gp field.
1077 * The caller must hold the specified rcu_node structure's ->lock.
1079 static unsigned long __maybe_unused
1080 rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp)
1084 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1087 * Pick up grace-period number for new callbacks. If this
1088 * grace period is already marked as needed, return to the caller.
1090 c = rcu_cbs_completed(rdp->rsp, rnp);
1091 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1092 if (rnp->need_future_gp[c & 0x1]) {
1093 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1098 * If either this rcu_node structure or the root rcu_node structure
1099 * believe that a grace period is in progress, then we must wait
1100 * for the one following, which is in "c". Because our request
1101 * will be noticed at the end of the current grace period, we don't
1102 * need to explicitly start one.
1104 if (rnp->gpnum != rnp->completed ||
1105 ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
1106 rnp->need_future_gp[c & 0x1]++;
1107 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1112 * There might be no grace period in progress. If we don't already
1113 * hold it, acquire the root rcu_node structure's lock in order to
1114 * start one (if needed).
1116 if (rnp != rnp_root)
1117 raw_spin_lock(&rnp_root->lock);
1120 * Get a new grace-period number. If there really is no grace
1121 * period in progress, it will be smaller than the one we obtained
1122 * earlier. Adjust callbacks as needed. Note that even no-CBs
1123 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1125 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1126 for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1127 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1128 rdp->nxtcompleted[i] = c;
1131 * If the needed for the required grace period is already
1132 * recorded, trace and leave.
1134 if (rnp_root->need_future_gp[c & 0x1]) {
1135 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1139 /* Record the need for the future grace period. */
1140 rnp_root->need_future_gp[c & 0x1]++;
1142 /* If a grace period is not already in progress, start one. */
1143 if (rnp_root->gpnum != rnp_root->completed) {
1144 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1146 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1147 rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1150 if (rnp != rnp_root)
1151 raw_spin_unlock(&rnp_root->lock);
1156 * Clean up any old requests for the just-ended grace period. Also return
1157 * whether any additional grace periods have been requested. Also invoke
1158 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1159 * waiting for this grace period to complete.
1161 static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1163 int c = rnp->completed;
1165 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1167 rcu_nocb_gp_cleanup(rsp, rnp);
1168 rnp->need_future_gp[c & 0x1] = 0;
1169 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1170 trace_rcu_future_gp(rnp, rdp, c,
1171 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1176 * If there is room, assign a ->completed number to any callbacks on
1177 * this CPU that have not already been assigned. Also accelerate any
1178 * callbacks that were previously assigned a ->completed number that has
1179 * since proven to be too conservative, which can happen if callbacks get
1180 * assigned a ->completed number while RCU is idle, but with reference to
1181 * a non-root rcu_node structure. This function is idempotent, so it does
1182 * not hurt to call it repeatedly.
1184 * The caller must hold rnp->lock with interrupts disabled.
1186 static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1187 struct rcu_data *rdp)
1192 /* If the CPU has no callbacks, nothing to do. */
1193 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1197 * Starting from the sublist containing the callbacks most
1198 * recently assigned a ->completed number and working down, find the
1199 * first sublist that is not assignable to an upcoming grace period.
1200 * Such a sublist has something in it (first two tests) and has
1201 * a ->completed number assigned that will complete sooner than
1202 * the ->completed number for newly arrived callbacks (last test).
1204 * The key point is that any later sublist can be assigned the
1205 * same ->completed number as the newly arrived callbacks, which
1206 * means that the callbacks in any of these later sublist can be
1207 * grouped into a single sublist, whether or not they have already
1208 * been assigned a ->completed number.
1210 c = rcu_cbs_completed(rsp, rnp);
1211 for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1212 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1213 !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1217 * If there are no sublist for unassigned callbacks, leave.
1218 * At the same time, advance "i" one sublist, so that "i" will
1219 * index into the sublist where all the remaining callbacks should
1222 if (++i >= RCU_NEXT_TAIL)
1226 * Assign all subsequent callbacks' ->completed number to the next
1227 * full grace period and group them all in the sublist initially
1230 for (; i <= RCU_NEXT_TAIL; i++) {
1231 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1232 rdp->nxtcompleted[i] = c;
1234 /* Record any needed additional grace periods. */
1235 rcu_start_future_gp(rnp, rdp);
1237 /* Trace depending on how much we were able to accelerate. */
1238 if (!*rdp->nxttail[RCU_WAIT_TAIL])
1239 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1241 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1245 * Move any callbacks whose grace period has completed to the
1246 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1247 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1248 * sublist. This function is idempotent, so it does not hurt to
1249 * invoke it repeatedly. As long as it is not invoked -too- often...
1251 * The caller must hold rnp->lock with interrupts disabled.
1253 static void rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1254 struct rcu_data *rdp)
1258 /* If the CPU has no callbacks, nothing to do. */
1259 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1263 * Find all callbacks whose ->completed numbers indicate that they
1264 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1266 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1267 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1269 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1271 /* Clean up any sublist tail pointers that were misordered above. */
1272 for (j = RCU_WAIT_TAIL; j < i; j++)
1273 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1275 /* Copy down callbacks to fill in empty sublists. */
1276 for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1277 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1279 rdp->nxttail[j] = rdp->nxttail[i];
1280 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1283 /* Classify any remaining callbacks. */
1284 rcu_accelerate_cbs(rsp, rnp, rdp);
1288 * Update CPU-local rcu_data state to record the beginnings and ends of
1289 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1290 * structure corresponding to the current CPU, and must have irqs disabled.
1292 static void __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
1294 /* Handle the ends of any preceding grace periods first. */
1295 if (rdp->completed == rnp->completed) {
1297 /* No grace period end, so just accelerate recent callbacks. */
1298 rcu_accelerate_cbs(rsp, rnp, rdp);
1302 /* Advance callbacks. */
1303 rcu_advance_cbs(rsp, rnp, rdp);
1305 /* Remember that we saw this grace-period completion. */
1306 rdp->completed = rnp->completed;
1307 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1310 if (rdp->gpnum != rnp->gpnum) {
1312 * If the current grace period is waiting for this CPU,
1313 * set up to detect a quiescent state, otherwise don't
1314 * go looking for one.
1316 rdp->gpnum = rnp->gpnum;
1317 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1318 rdp->passed_quiesce = 0;
1319 rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
1320 zero_cpu_stall_ticks(rdp);
1324 static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1326 unsigned long flags;
1327 struct rcu_node *rnp;
1329 local_irq_save(flags);
1331 if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
1332 rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
1333 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
1334 local_irq_restore(flags);
1337 __note_gp_changes(rsp, rnp, rdp);
1338 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1342 * Initialize a new grace period. Return 0 if no grace period required.
1344 static int rcu_gp_init(struct rcu_state *rsp)
1346 struct rcu_data *rdp;
1347 struct rcu_node *rnp = rcu_get_root(rsp);
1349 rcu_bind_gp_kthread();
1350 raw_spin_lock_irq(&rnp->lock);
1351 if (rsp->gp_flags == 0) {
1352 /* Spurious wakeup, tell caller to go back to sleep. */
1353 raw_spin_unlock_irq(&rnp->lock);
1356 rsp->gp_flags = 0; /* Clear all flags: New grace period. */
1358 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1360 * Grace period already in progress, don't start another.
1361 * Not supposed to be able to happen.
1363 raw_spin_unlock_irq(&rnp->lock);
1367 /* Advance to a new grace period and initialize state. */
1368 record_gp_stall_check_time(rsp);
1369 smp_wmb(); /* Record GP times before starting GP. */
1371 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1372 raw_spin_unlock_irq(&rnp->lock);
1374 /* Exclude any concurrent CPU-hotplug operations. */
1375 mutex_lock(&rsp->onoff_mutex);
1378 * Set the quiescent-state-needed bits in all the rcu_node
1379 * structures for all currently online CPUs in breadth-first order,
1380 * starting from the root rcu_node structure, relying on the layout
1381 * of the tree within the rsp->node[] array. Note that other CPUs
1382 * will access only the leaves of the hierarchy, thus seeing that no
1383 * grace period is in progress, at least until the corresponding
1384 * leaf node has been initialized. In addition, we have excluded
1385 * CPU-hotplug operations.
1387 * The grace period cannot complete until the initialization
1388 * process finishes, because this kthread handles both.
1390 rcu_for_each_node_breadth_first(rsp, rnp) {
1391 raw_spin_lock_irq(&rnp->lock);
1392 rdp = this_cpu_ptr(rsp->rda);
1393 rcu_preempt_check_blocked_tasks(rnp);
1394 rnp->qsmask = rnp->qsmaskinit;
1395 ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1396 WARN_ON_ONCE(rnp->completed != rsp->completed);
1397 ACCESS_ONCE(rnp->completed) = rsp->completed;
1398 if (rnp == rdp->mynode)
1399 __note_gp_changes(rsp, rnp, rdp);
1400 rcu_preempt_boost_start_gp(rnp);
1401 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1402 rnp->level, rnp->grplo,
1403 rnp->grphi, rnp->qsmask);
1404 raw_spin_unlock_irq(&rnp->lock);
1405 #ifdef CONFIG_PROVE_RCU_DELAY
1406 if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&
1407 system_state == SYSTEM_RUNNING)
1409 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1413 mutex_unlock(&rsp->onoff_mutex);
1418 * Do one round of quiescent-state forcing.
1420 static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1422 int fqs_state = fqs_state_in;
1423 bool isidle = false;
1425 struct rcu_node *rnp = rcu_get_root(rsp);
1428 if (fqs_state == RCU_SAVE_DYNTICK) {
1429 /* Collect dyntick-idle snapshots. */
1430 if (is_sysidle_rcu_state(rsp)) {
1432 maxj = jiffies - ULONG_MAX / 4;
1434 force_qs_rnp(rsp, dyntick_save_progress_counter,
1436 rcu_sysidle_report_gp(rsp, isidle, maxj);
1437 fqs_state = RCU_FORCE_QS;
1439 /* Handle dyntick-idle and offline CPUs. */
1441 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1443 /* Clear flag to prevent immediate re-entry. */
1444 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1445 raw_spin_lock_irq(&rnp->lock);
1446 rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
1447 raw_spin_unlock_irq(&rnp->lock);
1453 * Clean up after the old grace period.
1455 static void rcu_gp_cleanup(struct rcu_state *rsp)
1457 unsigned long gp_duration;
1459 struct rcu_data *rdp;
1460 struct rcu_node *rnp = rcu_get_root(rsp);
1462 raw_spin_lock_irq(&rnp->lock);
1463 gp_duration = jiffies - rsp->gp_start;
1464 if (gp_duration > rsp->gp_max)
1465 rsp->gp_max = gp_duration;
1468 * We know the grace period is complete, but to everyone else
1469 * it appears to still be ongoing. But it is also the case
1470 * that to everyone else it looks like there is nothing that
1471 * they can do to advance the grace period. It is therefore
1472 * safe for us to drop the lock in order to mark the grace
1473 * period as completed in all of the rcu_node structures.
1475 raw_spin_unlock_irq(&rnp->lock);
1478 * Propagate new ->completed value to rcu_node structures so
1479 * that other CPUs don't have to wait until the start of the next
1480 * grace period to process their callbacks. This also avoids
1481 * some nasty RCU grace-period initialization races by forcing
1482 * the end of the current grace period to be completely recorded in
1483 * all of the rcu_node structures before the beginning of the next
1484 * grace period is recorded in any of the rcu_node structures.
1486 rcu_for_each_node_breadth_first(rsp, rnp) {
1487 raw_spin_lock_irq(&rnp->lock);
1488 ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1489 rdp = this_cpu_ptr(rsp->rda);
1490 if (rnp == rdp->mynode)
1491 __note_gp_changes(rsp, rnp, rdp);
1492 nocb += rcu_future_gp_cleanup(rsp, rnp);
1493 raw_spin_unlock_irq(&rnp->lock);
1496 rnp = rcu_get_root(rsp);
1497 raw_spin_lock_irq(&rnp->lock);
1498 rcu_nocb_gp_set(rnp, nocb);
1500 rsp->completed = rsp->gpnum; /* Declare grace period done. */
1501 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1502 rsp->fqs_state = RCU_GP_IDLE;
1503 rdp = this_cpu_ptr(rsp->rda);
1504 rcu_advance_cbs(rsp, rnp, rdp); /* Reduce false positives below. */
1505 if (cpu_needs_another_gp(rsp, rdp)) {
1506 rsp->gp_flags = RCU_GP_FLAG_INIT;
1507 trace_rcu_grace_period(rsp->name,
1508 ACCESS_ONCE(rsp->gpnum),
1511 raw_spin_unlock_irq(&rnp->lock);
1515 * Body of kthread that handles grace periods.
1517 static int __noreturn rcu_gp_kthread(void *arg)
1523 struct rcu_state *rsp = arg;
1524 struct rcu_node *rnp = rcu_get_root(rsp);
1528 /* Handle grace-period start. */
1530 trace_rcu_grace_period(rsp->name,
1531 ACCESS_ONCE(rsp->gpnum),
1533 wait_event_interruptible(rsp->gp_wq,
1534 ACCESS_ONCE(rsp->gp_flags) &
1536 if (rcu_gp_init(rsp))
1539 flush_signals(current);
1540 trace_rcu_grace_period(rsp->name,
1541 ACCESS_ONCE(rsp->gpnum),
1545 /* Handle quiescent-state forcing. */
1546 fqs_state = RCU_SAVE_DYNTICK;
1547 j = jiffies_till_first_fqs;
1550 jiffies_till_first_fqs = HZ;
1555 rsp->jiffies_force_qs = jiffies + j;
1556 trace_rcu_grace_period(rsp->name,
1557 ACCESS_ONCE(rsp->gpnum),
1559 ret = wait_event_interruptible_timeout(rsp->gp_wq,
1560 ((gf = ACCESS_ONCE(rsp->gp_flags)) &
1562 (!ACCESS_ONCE(rnp->qsmask) &&
1563 !rcu_preempt_blocked_readers_cgp(rnp)),
1565 /* If grace period done, leave loop. */
1566 if (!ACCESS_ONCE(rnp->qsmask) &&
1567 !rcu_preempt_blocked_readers_cgp(rnp))
1569 /* If time for quiescent-state forcing, do it. */
1570 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
1571 (gf & RCU_GP_FLAG_FQS)) {
1572 trace_rcu_grace_period(rsp->name,
1573 ACCESS_ONCE(rsp->gpnum),
1575 fqs_state = rcu_gp_fqs(rsp, fqs_state);
1576 trace_rcu_grace_period(rsp->name,
1577 ACCESS_ONCE(rsp->gpnum),
1581 /* Deal with stray signal. */
1583 flush_signals(current);
1584 trace_rcu_grace_period(rsp->name,
1585 ACCESS_ONCE(rsp->gpnum),
1588 j = jiffies_till_next_fqs;
1591 jiffies_till_next_fqs = HZ;
1594 jiffies_till_next_fqs = 1;
1598 /* Handle grace-period end. */
1599 rcu_gp_cleanup(rsp);
1603 static void rsp_wakeup(struct irq_work *work)
1605 struct rcu_state *rsp = container_of(work, struct rcu_state, wakeup_work);
1607 /* Wake up rcu_gp_kthread() to start the grace period. */
1608 wake_up(&rsp->gp_wq);
1612 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1613 * in preparation for detecting the next grace period. The caller must hold
1614 * the root node's ->lock and hard irqs must be disabled.
1616 * Note that it is legal for a dying CPU (which is marked as offline) to
1617 * invoke this function. This can happen when the dying CPU reports its
1621 rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
1622 struct rcu_data *rdp)
1624 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
1626 * Either we have not yet spawned the grace-period
1627 * task, this CPU does not need another grace period,
1628 * or a grace period is already in progress.
1629 * Either way, don't start a new grace period.
1633 rsp->gp_flags = RCU_GP_FLAG_INIT;
1634 trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
1638 * We can't do wakeups while holding the rnp->lock, as that
1639 * could cause possible deadlocks with the rq->lock. Defer
1640 * the wakeup to interrupt context. And don't bother waking
1641 * up the running kthread.
1643 if (current != rsp->gp_kthread)
1644 irq_work_queue(&rsp->wakeup_work);
1648 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1649 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1650 * is invoked indirectly from rcu_advance_cbs(), which would result in
1651 * endless recursion -- or would do so if it wasn't for the self-deadlock
1652 * that is encountered beforehand.
1655 rcu_start_gp(struct rcu_state *rsp)
1657 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1658 struct rcu_node *rnp = rcu_get_root(rsp);
1661 * If there is no grace period in progress right now, any
1662 * callbacks we have up to this point will be satisfied by the
1663 * next grace period. Also, advancing the callbacks reduces the
1664 * probability of false positives from cpu_needs_another_gp()
1665 * resulting in pointless grace periods. So, advance callbacks
1666 * then start the grace period!
1668 rcu_advance_cbs(rsp, rnp, rdp);
1669 rcu_start_gp_advanced(rsp, rnp, rdp);
1673 * Report a full set of quiescent states to the specified rcu_state
1674 * data structure. This involves cleaning up after the prior grace
1675 * period and letting rcu_start_gp() start up the next grace period
1676 * if one is needed. Note that the caller must hold rnp->lock, which
1677 * is released before return.
1679 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1680 __releases(rcu_get_root(rsp)->lock)
1682 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1683 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
1684 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
1688 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1689 * Allows quiescent states for a group of CPUs to be reported at one go
1690 * to the specified rcu_node structure, though all the CPUs in the group
1691 * must be represented by the same rcu_node structure (which need not be
1692 * a leaf rcu_node structure, though it often will be). That structure's
1693 * lock must be held upon entry, and it is released before return.
1696 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
1697 struct rcu_node *rnp, unsigned long flags)
1698 __releases(rnp->lock)
1700 struct rcu_node *rnp_c;
1702 /* Walk up the rcu_node hierarchy. */
1704 if (!(rnp->qsmask & mask)) {
1706 /* Our bit has already been cleared, so done. */
1707 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1710 rnp->qsmask &= ~mask;
1711 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
1712 mask, rnp->qsmask, rnp->level,
1713 rnp->grplo, rnp->grphi,
1715 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1717 /* Other bits still set at this level, so done. */
1718 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1721 mask = rnp->grpmask;
1722 if (rnp->parent == NULL) {
1724 /* No more levels. Exit loop holding root lock. */
1728 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1731 raw_spin_lock_irqsave(&rnp->lock, flags);
1732 WARN_ON_ONCE(rnp_c->qsmask);
1736 * Get here if we are the last CPU to pass through a quiescent
1737 * state for this grace period. Invoke rcu_report_qs_rsp()
1738 * to clean up and start the next grace period if one is needed.
1740 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1744 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1745 * structure. This must be either called from the specified CPU, or
1746 * called when the specified CPU is known to be offline (and when it is
1747 * also known that no other CPU is concurrently trying to help the offline
1748 * CPU). The lastcomp argument is used to make sure we are still in the
1749 * grace period of interest. We don't want to end the current grace period
1750 * based on quiescent states detected in an earlier grace period!
1753 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
1755 unsigned long flags;
1757 struct rcu_node *rnp;
1760 raw_spin_lock_irqsave(&rnp->lock, flags);
1761 if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
1762 rnp->completed == rnp->gpnum) {
1765 * The grace period in which this quiescent state was
1766 * recorded has ended, so don't report it upwards.
1767 * We will instead need a new quiescent state that lies
1768 * within the current grace period.
1770 rdp->passed_quiesce = 0; /* need qs for new gp. */
1771 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1774 mask = rdp->grpmask;
1775 if ((rnp->qsmask & mask) == 0) {
1776 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1778 rdp->qs_pending = 0;
1781 * This GP can't end until cpu checks in, so all of our
1782 * callbacks can be processed during the next GP.
1784 rcu_accelerate_cbs(rsp, rnp, rdp);
1786 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1791 * Check to see if there is a new grace period of which this CPU
1792 * is not yet aware, and if so, set up local rcu_data state for it.
1793 * Otherwise, see if this CPU has just passed through its first
1794 * quiescent state for this grace period, and record that fact if so.
1797 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
1799 /* Check for grace-period ends and beginnings. */
1800 note_gp_changes(rsp, rdp);
1803 * Does this CPU still need to do its part for current grace period?
1804 * If no, return and let the other CPUs do their part as well.
1806 if (!rdp->qs_pending)
1810 * Was there a quiescent state since the beginning of the grace
1811 * period? If no, then exit and wait for the next call.
1813 if (!rdp->passed_quiesce)
1817 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1820 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
1823 #ifdef CONFIG_HOTPLUG_CPU
1826 * Send the specified CPU's RCU callbacks to the orphanage. The
1827 * specified CPU must be offline, and the caller must hold the
1831 rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
1832 struct rcu_node *rnp, struct rcu_data *rdp)
1834 /* No-CBs CPUs do not have orphanable callbacks. */
1835 if (rcu_is_nocb_cpu(rdp->cpu))
1839 * Orphan the callbacks. First adjust the counts. This is safe
1840 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1841 * cannot be running now. Thus no memory barrier is required.
1843 if (rdp->nxtlist != NULL) {
1844 rsp->qlen_lazy += rdp->qlen_lazy;
1845 rsp->qlen += rdp->qlen;
1846 rdp->n_cbs_orphaned += rdp->qlen;
1848 ACCESS_ONCE(rdp->qlen) = 0;
1852 * Next, move those callbacks still needing a grace period to
1853 * the orphanage, where some other CPU will pick them up.
1854 * Some of the callbacks might have gone partway through a grace
1855 * period, but that is too bad. They get to start over because we
1856 * cannot assume that grace periods are synchronized across CPUs.
1857 * We don't bother updating the ->nxttail[] array yet, instead
1858 * we just reset the whole thing later on.
1860 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
1861 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
1862 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
1863 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1867 * Then move the ready-to-invoke callbacks to the orphanage,
1868 * where some other CPU will pick them up. These will not be
1869 * required to pass though another grace period: They are done.
1871 if (rdp->nxtlist != NULL) {
1872 *rsp->orphan_donetail = rdp->nxtlist;
1873 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
1876 /* Finally, initialize the rcu_data structure's list to empty. */
1877 init_callback_list(rdp);
1881 * Adopt the RCU callbacks from the specified rcu_state structure's
1882 * orphanage. The caller must hold the ->orphan_lock.
1884 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
1887 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
1889 /* No-CBs CPUs are handled specially. */
1890 if (rcu_nocb_adopt_orphan_cbs(rsp, rdp))
1893 /* Do the accounting first. */
1894 rdp->qlen_lazy += rsp->qlen_lazy;
1895 rdp->qlen += rsp->qlen;
1896 rdp->n_cbs_adopted += rsp->qlen;
1897 if (rsp->qlen_lazy != rsp->qlen)
1898 rcu_idle_count_callbacks_posted();
1903 * We do not need a memory barrier here because the only way we
1904 * can get here if there is an rcu_barrier() in flight is if
1905 * we are the task doing the rcu_barrier().
1908 /* First adopt the ready-to-invoke callbacks. */
1909 if (rsp->orphan_donelist != NULL) {
1910 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
1911 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
1912 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
1913 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
1914 rdp->nxttail[i] = rsp->orphan_donetail;
1915 rsp->orphan_donelist = NULL;
1916 rsp->orphan_donetail = &rsp->orphan_donelist;
1919 /* And then adopt the callbacks that still need a grace period. */
1920 if (rsp->orphan_nxtlist != NULL) {
1921 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
1922 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
1923 rsp->orphan_nxtlist = NULL;
1924 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
1929 * Trace the fact that this CPU is going offline.
1931 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1933 RCU_TRACE(unsigned long mask);
1934 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
1935 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
1937 RCU_TRACE(mask = rdp->grpmask);
1938 trace_rcu_grace_period(rsp->name,
1939 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
1944 * The CPU has been completely removed, and some other CPU is reporting
1945 * this fact from process context. Do the remainder of the cleanup,
1946 * including orphaning the outgoing CPU's RCU callbacks, and also
1947 * adopting them. There can only be one CPU hotplug operation at a time,
1948 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
1950 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
1952 unsigned long flags;
1954 int need_report = 0;
1955 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1956 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
1958 /* Adjust any no-longer-needed kthreads. */
1959 rcu_boost_kthread_setaffinity(rnp, -1);
1961 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
1963 /* Exclude any attempts to start a new grace period. */
1964 mutex_lock(&rsp->onoff_mutex);
1965 raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
1967 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
1968 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
1969 rcu_adopt_orphan_cbs(rsp);
1971 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1972 mask = rdp->grpmask; /* rnp->grplo is constant. */
1974 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1975 rnp->qsmaskinit &= ~mask;
1976 if (rnp->qsmaskinit != 0) {
1977 if (rnp != rdp->mynode)
1978 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1981 if (rnp == rdp->mynode)
1982 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1984 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1985 mask = rnp->grpmask;
1987 } while (rnp != NULL);
1990 * We still hold the leaf rcu_node structure lock here, and
1991 * irqs are still disabled. The reason for this subterfuge is
1992 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
1993 * held leads to deadlock.
1995 raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
1997 if (need_report & RCU_OFL_TASKS_NORM_GP)
1998 rcu_report_unblock_qs_rnp(rnp, flags);
2000 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2001 if (need_report & RCU_OFL_TASKS_EXP_GP)
2002 rcu_report_exp_rnp(rsp, rnp, true);
2003 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2004 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2005 cpu, rdp->qlen, rdp->nxtlist);
2006 init_callback_list(rdp);
2007 /* Disallow further callbacks on this CPU. */
2008 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2009 mutex_unlock(&rsp->onoff_mutex);
2012 #else /* #ifdef CONFIG_HOTPLUG_CPU */
2014 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2018 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2022 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2025 * Invoke any RCU callbacks that have made it to the end of their grace
2026 * period. Thottle as specified by rdp->blimit.
2028 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2030 unsigned long flags;
2031 struct rcu_head *next, *list, **tail;
2032 long bl, count, count_lazy;
2035 /* If no callbacks are ready, just return. */
2036 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2037 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2038 trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
2039 need_resched(), is_idle_task(current),
2040 rcu_is_callbacks_kthread());
2045 * Extract the list of ready callbacks, disabling to prevent
2046 * races with call_rcu() from interrupt handlers.
2048 local_irq_save(flags);
2049 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2051 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2052 list = rdp->nxtlist;
2053 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2054 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2055 tail = rdp->nxttail[RCU_DONE_TAIL];
2056 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2057 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2058 rdp->nxttail[i] = &rdp->nxtlist;
2059 local_irq_restore(flags);
2061 /* Invoke callbacks. */
2062 count = count_lazy = 0;
2066 debug_rcu_head_unqueue(list);
2067 if (__rcu_reclaim(rsp->name, list))
2070 /* Stop only if limit reached and CPU has something to do. */
2071 if (++count >= bl &&
2073 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2077 local_irq_save(flags);
2078 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2079 is_idle_task(current),
2080 rcu_is_callbacks_kthread());
2082 /* Update count, and requeue any remaining callbacks. */
2084 *tail = rdp->nxtlist;
2085 rdp->nxtlist = list;
2086 for (i = 0; i < RCU_NEXT_SIZE; i++)
2087 if (&rdp->nxtlist == rdp->nxttail[i])
2088 rdp->nxttail[i] = tail;
2092 smp_mb(); /* List handling before counting for rcu_barrier(). */
2093 rdp->qlen_lazy -= count_lazy;
2094 ACCESS_ONCE(rdp->qlen) -= count;
2095 rdp->n_cbs_invoked += count;
2097 /* Reinstate batch limit if we have worked down the excess. */
2098 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2099 rdp->blimit = blimit;
2101 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2102 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2103 rdp->qlen_last_fqs_check = 0;
2104 rdp->n_force_qs_snap = rsp->n_force_qs;
2105 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2106 rdp->qlen_last_fqs_check = rdp->qlen;
2107 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2109 local_irq_restore(flags);
2111 /* Re-invoke RCU core processing if there are callbacks remaining. */
2112 if (cpu_has_callbacks_ready_to_invoke(rdp))
2117 * Check to see if this CPU is in a non-context-switch quiescent state
2118 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2119 * Also schedule RCU core processing.
2121 * This function must be called from hardirq context. It is normally
2122 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2123 * false, there is no point in invoking rcu_check_callbacks().
2125 void rcu_check_callbacks(int cpu, int user)
2127 trace_rcu_utilization(TPS("Start scheduler-tick"));
2128 increment_cpu_stall_ticks();
2129 if (user || rcu_is_cpu_rrupt_from_idle()) {
2132 * Get here if this CPU took its interrupt from user
2133 * mode or from the idle loop, and if this is not a
2134 * nested interrupt. In this case, the CPU is in
2135 * a quiescent state, so note it.
2137 * No memory barrier is required here because both
2138 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2139 * variables that other CPUs neither access nor modify,
2140 * at least not while the corresponding CPU is online.
2146 } else if (!in_softirq()) {
2149 * Get here if this CPU did not take its interrupt from
2150 * softirq, in other words, if it is not interrupting
2151 * a rcu_bh read-side critical section. This is an _bh
2152 * critical section, so note it.
2157 rcu_preempt_check_callbacks(cpu);
2158 if (rcu_pending(cpu))
2160 trace_rcu_utilization(TPS("End scheduler-tick"));
2164 * Scan the leaf rcu_node structures, processing dyntick state for any that
2165 * have not yet encountered a quiescent state, using the function specified.
2166 * Also initiate boosting for any threads blocked on the root rcu_node.
2168 * The caller must have suppressed start of new grace periods.
2170 static void force_qs_rnp(struct rcu_state *rsp,
2171 int (*f)(struct rcu_data *rsp, bool *isidle,
2172 unsigned long *maxj),
2173 bool *isidle, unsigned long *maxj)
2177 unsigned long flags;
2179 struct rcu_node *rnp;
2181 rcu_for_each_leaf_node(rsp, rnp) {
2184 raw_spin_lock_irqsave(&rnp->lock, flags);
2185 if (!rcu_gp_in_progress(rsp)) {
2186 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2189 if (rnp->qsmask == 0) {
2190 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2195 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2196 if ((rnp->qsmask & bit) != 0) {
2197 if ((rnp->qsmaskinit & bit) != 0)
2199 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2205 /* rcu_report_qs_rnp() releases rnp->lock. */
2206 rcu_report_qs_rnp(mask, rsp, rnp, flags);
2209 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2211 rnp = rcu_get_root(rsp);
2212 if (rnp->qsmask == 0) {
2213 raw_spin_lock_irqsave(&rnp->lock, flags);
2214 rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
2219 * Force quiescent states on reluctant CPUs, and also detect which
2220 * CPUs are in dyntick-idle mode.
2222 static void force_quiescent_state(struct rcu_state *rsp)
2224 unsigned long flags;
2226 struct rcu_node *rnp;
2227 struct rcu_node *rnp_old = NULL;
2229 /* Funnel through hierarchy to reduce memory contention. */
2230 rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
2231 for (; rnp != NULL; rnp = rnp->parent) {
2232 ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2233 !raw_spin_trylock(&rnp->fqslock);
2234 if (rnp_old != NULL)
2235 raw_spin_unlock(&rnp_old->fqslock);
2237 rsp->n_force_qs_lh++;
2242 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2244 /* Reached the root of the rcu_node tree, acquire lock. */
2245 raw_spin_lock_irqsave(&rnp_old->lock, flags);
2246 raw_spin_unlock(&rnp_old->fqslock);
2247 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2248 rsp->n_force_qs_lh++;
2249 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2250 return; /* Someone beat us to it. */
2252 rsp->gp_flags |= RCU_GP_FLAG_FQS;
2253 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2254 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
2258 * This does the RCU core processing work for the specified rcu_state
2259 * and rcu_data structures. This may be called only from the CPU to
2260 * whom the rdp belongs.
2263 __rcu_process_callbacks(struct rcu_state *rsp)
2265 unsigned long flags;
2266 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2268 WARN_ON_ONCE(rdp->beenonline == 0);
2270 /* Update RCU state based on any recent quiescent states. */
2271 rcu_check_quiescent_state(rsp, rdp);
2273 /* Does this CPU require a not-yet-started grace period? */
2274 local_irq_save(flags);
2275 if (cpu_needs_another_gp(rsp, rdp)) {
2276 raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2278 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2280 local_irq_restore(flags);
2283 /* If there are callbacks ready, invoke them. */
2284 if (cpu_has_callbacks_ready_to_invoke(rdp))
2285 invoke_rcu_callbacks(rsp, rdp);
2289 * Do RCU core processing for the current CPU.
2291 static void rcu_process_callbacks(struct softirq_action *unused)
2293 struct rcu_state *rsp;
2295 if (cpu_is_offline(smp_processor_id()))
2297 trace_rcu_utilization(TPS("Start RCU core"));
2298 for_each_rcu_flavor(rsp)
2299 __rcu_process_callbacks(rsp);
2300 trace_rcu_utilization(TPS("End RCU core"));
2304 * Schedule RCU callback invocation. If the specified type of RCU
2305 * does not support RCU priority boosting, just do a direct call,
2306 * otherwise wake up the per-CPU kernel kthread. Note that because we
2307 * are running on the current CPU with interrupts disabled, the
2308 * rcu_cpu_kthread_task cannot disappear out from under us.
2310 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2312 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
2314 if (likely(!rsp->boost)) {
2315 rcu_do_batch(rsp, rdp);
2318 invoke_rcu_callbacks_kthread();
2321 static void invoke_rcu_core(void)
2323 if (cpu_online(smp_processor_id()))
2324 raise_softirq(RCU_SOFTIRQ);
2328 * Handle any core-RCU processing required by a call_rcu() invocation.
2330 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2331 struct rcu_head *head, unsigned long flags)
2334 * If called from an extended quiescent state, invoke the RCU
2335 * core in order to force a re-evaluation of RCU's idleness.
2337 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2340 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2341 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2345 * Force the grace period if too many callbacks or too long waiting.
2346 * Enforce hysteresis, and don't invoke force_quiescent_state()
2347 * if some other CPU has recently done so. Also, don't bother
2348 * invoking force_quiescent_state() if the newly enqueued callback
2349 * is the only one waiting for a grace period to complete.
2351 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2353 /* Are we ignoring a completed grace period? */
2354 note_gp_changes(rsp, rdp);
2356 /* Start a new grace period if one not already started. */
2357 if (!rcu_gp_in_progress(rsp)) {
2358 struct rcu_node *rnp_root = rcu_get_root(rsp);
2360 raw_spin_lock(&rnp_root->lock);
2362 raw_spin_unlock(&rnp_root->lock);
2364 /* Give the grace period a kick. */
2365 rdp->blimit = LONG_MAX;
2366 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2367 *rdp->nxttail[RCU_DONE_TAIL] != head)
2368 force_quiescent_state(rsp);
2369 rdp->n_force_qs_snap = rsp->n_force_qs;
2370 rdp->qlen_last_fqs_check = rdp->qlen;
2376 * RCU callback function to leak a callback.
2378 static void rcu_leak_callback(struct rcu_head *rhp)
2383 * Helper function for call_rcu() and friends. The cpu argument will
2384 * normally be -1, indicating "currently running CPU". It may specify
2385 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2386 * is expected to specify a CPU.
2389 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
2390 struct rcu_state *rsp, int cpu, bool lazy)
2392 unsigned long flags;
2393 struct rcu_data *rdp;
2395 WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
2396 if (debug_rcu_head_queue(head)) {
2397 /* Probable double call_rcu(), so leak the callback. */
2398 ACCESS_ONCE(head->func) = rcu_leak_callback;
2399 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2406 * Opportunistically note grace-period endings and beginnings.
2407 * Note that we might see a beginning right after we see an
2408 * end, but never vice versa, since this CPU has to pass through
2409 * a quiescent state betweentimes.
2411 local_irq_save(flags);
2412 rdp = this_cpu_ptr(rsp->rda);
2414 /* Add the callback to our list. */
2415 if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
2419 rdp = per_cpu_ptr(rsp->rda, cpu);
2420 offline = !__call_rcu_nocb(rdp, head, lazy);
2421 WARN_ON_ONCE(offline);
2422 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2423 local_irq_restore(flags);
2426 ACCESS_ONCE(rdp->qlen)++;
2430 rcu_idle_count_callbacks_posted();
2431 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2432 *rdp->nxttail[RCU_NEXT_TAIL] = head;
2433 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2435 if (__is_kfree_rcu_offset((unsigned long)func))
2436 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2437 rdp->qlen_lazy, rdp->qlen);
2439 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2441 /* Go handle any RCU core processing required. */
2442 __call_rcu_core(rsp, rdp, head, flags);
2443 local_irq_restore(flags);
2447 * Queue an RCU-sched callback for invocation after a grace period.
2449 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2451 __call_rcu(head, func, &rcu_sched_state, -1, 0);
2453 EXPORT_SYMBOL_GPL(call_rcu_sched);
2456 * Queue an RCU callback for invocation after a quicker grace period.
2458 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2460 __call_rcu(head, func, &rcu_bh_state, -1, 0);
2462 EXPORT_SYMBOL_GPL(call_rcu_bh);
2465 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2466 * any blocking grace-period wait automatically implies a grace period
2467 * if there is only one CPU online at any point time during execution
2468 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2469 * occasionally incorrectly indicate that there are multiple CPUs online
2470 * when there was in fact only one the whole time, as this just adds
2471 * some overhead: RCU still operates correctly.
2473 static inline int rcu_blocking_is_gp(void)
2477 might_sleep(); /* Check for RCU read-side critical section. */
2479 ret = num_online_cpus() <= 1;
2485 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2487 * Control will return to the caller some time after a full rcu-sched
2488 * grace period has elapsed, in other words after all currently executing
2489 * rcu-sched read-side critical sections have completed. These read-side
2490 * critical sections are delimited by rcu_read_lock_sched() and
2491 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2492 * local_irq_disable(), and so on may be used in place of
2493 * rcu_read_lock_sched().
2495 * This means that all preempt_disable code sequences, including NMI and
2496 * non-threaded hardware-interrupt handlers, in progress on entry will
2497 * have completed before this primitive returns. However, this does not
2498 * guarantee that softirq handlers will have completed, since in some
2499 * kernels, these handlers can run in process context, and can block.
2501 * Note that this guarantee implies further memory-ordering guarantees.
2502 * On systems with more than one CPU, when synchronize_sched() returns,
2503 * each CPU is guaranteed to have executed a full memory barrier since the
2504 * end of its last RCU-sched read-side critical section whose beginning
2505 * preceded the call to synchronize_sched(). In addition, each CPU having
2506 * an RCU read-side critical section that extends beyond the return from
2507 * synchronize_sched() is guaranteed to have executed a full memory barrier
2508 * after the beginning of synchronize_sched() and before the beginning of
2509 * that RCU read-side critical section. Note that these guarantees include
2510 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2511 * that are executing in the kernel.
2513 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2514 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2515 * to have executed a full memory barrier during the execution of
2516 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2517 * again only if the system has more than one CPU).
2519 * This primitive provides the guarantees made by the (now removed)
2520 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2521 * guarantees that rcu_read_lock() sections will have completed.
2522 * In "classic RCU", these two guarantees happen to be one and
2523 * the same, but can differ in realtime RCU implementations.
2525 void synchronize_sched(void)
2527 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2528 !lock_is_held(&rcu_lock_map) &&
2529 !lock_is_held(&rcu_sched_lock_map),
2530 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2531 if (rcu_blocking_is_gp())
2534 synchronize_sched_expedited();
2536 wait_rcu_gp(call_rcu_sched);
2538 EXPORT_SYMBOL_GPL(synchronize_sched);
2541 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2543 * Control will return to the caller some time after a full rcu_bh grace
2544 * period has elapsed, in other words after all currently executing rcu_bh
2545 * read-side critical sections have completed. RCU read-side critical
2546 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2547 * and may be nested.
2549 * See the description of synchronize_sched() for more detailed information
2550 * on memory ordering guarantees.
2552 void synchronize_rcu_bh(void)
2554 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2555 !lock_is_held(&rcu_lock_map) &&
2556 !lock_is_held(&rcu_sched_lock_map),
2557 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2558 if (rcu_blocking_is_gp())
2561 synchronize_rcu_bh_expedited();
2563 wait_rcu_gp(call_rcu_bh);
2565 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
2567 static int synchronize_sched_expedited_cpu_stop(void *data)
2570 * There must be a full memory barrier on each affected CPU
2571 * between the time that try_stop_cpus() is called and the
2572 * time that it returns.
2574 * In the current initial implementation of cpu_stop, the
2575 * above condition is already met when the control reaches
2576 * this point and the following smp_mb() is not strictly
2577 * necessary. Do smp_mb() anyway for documentation and
2578 * robustness against future implementation changes.
2580 smp_mb(); /* See above comment block. */
2585 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2587 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2588 * approach to force the grace period to end quickly. This consumes
2589 * significant time on all CPUs and is unfriendly to real-time workloads,
2590 * so is thus not recommended for any sort of common-case code. In fact,
2591 * if you are using synchronize_sched_expedited() in a loop, please
2592 * restructure your code to batch your updates, and then use a single
2593 * synchronize_sched() instead.
2595 * Note that it is illegal to call this function while holding any lock
2596 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2597 * to call this function from a CPU-hotplug notifier. Failing to observe
2598 * these restriction will result in deadlock.
2600 * This implementation can be thought of as an application of ticket
2601 * locking to RCU, with sync_sched_expedited_started and
2602 * sync_sched_expedited_done taking on the roles of the halves
2603 * of the ticket-lock word. Each task atomically increments
2604 * sync_sched_expedited_started upon entry, snapshotting the old value,
2605 * then attempts to stop all the CPUs. If this succeeds, then each
2606 * CPU will have executed a context switch, resulting in an RCU-sched
2607 * grace period. We are then done, so we use atomic_cmpxchg() to
2608 * update sync_sched_expedited_done to match our snapshot -- but
2609 * only if someone else has not already advanced past our snapshot.
2611 * On the other hand, if try_stop_cpus() fails, we check the value
2612 * of sync_sched_expedited_done. If it has advanced past our
2613 * initial snapshot, then someone else must have forced a grace period
2614 * some time after we took our snapshot. In this case, our work is
2615 * done for us, and we can simply return. Otherwise, we try again,
2616 * but keep our initial snapshot for purposes of checking for someone
2617 * doing our work for us.
2619 * If we fail too many times in a row, we fall back to synchronize_sched().
2621 void synchronize_sched_expedited(void)
2623 long firstsnap, s, snap;
2625 struct rcu_state *rsp = &rcu_sched_state;
2628 * If we are in danger of counter wrap, just do synchronize_sched().
2629 * By allowing sync_sched_expedited_started to advance no more than
2630 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2631 * that more than 3.5 billion CPUs would be required to force a
2632 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2633 * course be required on a 64-bit system.
2635 if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
2636 (ulong)atomic_long_read(&rsp->expedited_done) +
2638 synchronize_sched();
2639 atomic_long_inc(&rsp->expedited_wrap);
2644 * Take a ticket. Note that atomic_inc_return() implies a
2645 * full memory barrier.
2647 snap = atomic_long_inc_return(&rsp->expedited_start);
2650 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2653 * Each pass through the following loop attempts to force a
2654 * context switch on each CPU.
2656 while (try_stop_cpus(cpu_online_mask,
2657 synchronize_sched_expedited_cpu_stop,
2660 atomic_long_inc(&rsp->expedited_tryfail);
2662 /* Check to see if someone else did our work for us. */
2663 s = atomic_long_read(&rsp->expedited_done);
2664 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2665 /* ensure test happens before caller kfree */
2666 smp_mb__before_atomic_inc(); /* ^^^ */
2667 atomic_long_inc(&rsp->expedited_workdone1);
2671 /* No joy, try again later. Or just synchronize_sched(). */
2672 if (trycount++ < 10) {
2673 udelay(trycount * num_online_cpus());
2675 wait_rcu_gp(call_rcu_sched);
2676 atomic_long_inc(&rsp->expedited_normal);
2680 /* Recheck to see if someone else did our work for us. */
2681 s = atomic_long_read(&rsp->expedited_done);
2682 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2683 /* ensure test happens before caller kfree */
2684 smp_mb__before_atomic_inc(); /* ^^^ */
2685 atomic_long_inc(&rsp->expedited_workdone2);
2690 * Refetching sync_sched_expedited_started allows later
2691 * callers to piggyback on our grace period. We retry
2692 * after they started, so our grace period works for them,
2693 * and they started after our first try, so their grace
2694 * period works for us.
2697 snap = atomic_long_read(&rsp->expedited_start);
2698 smp_mb(); /* ensure read is before try_stop_cpus(). */
2700 atomic_long_inc(&rsp->expedited_stoppedcpus);
2703 * Everyone up to our most recent fetch is covered by our grace
2704 * period. Update the counter, but only if our work is still
2705 * relevant -- which it won't be if someone who started later
2706 * than we did already did their update.
2709 atomic_long_inc(&rsp->expedited_done_tries);
2710 s = atomic_long_read(&rsp->expedited_done);
2711 if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
2712 /* ensure test happens before caller kfree */
2713 smp_mb__before_atomic_inc(); /* ^^^ */
2714 atomic_long_inc(&rsp->expedited_done_lost);
2717 } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
2718 atomic_long_inc(&rsp->expedited_done_exit);
2722 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
2725 * Check to see if there is any immediate RCU-related work to be done
2726 * by the current CPU, for the specified type of RCU, returning 1 if so.
2727 * The checks are in order of increasing expense: checks that can be
2728 * carried out against CPU-local state are performed first. However,
2729 * we must check for CPU stalls first, else we might not get a chance.
2731 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
2733 struct rcu_node *rnp = rdp->mynode;
2735 rdp->n_rcu_pending++;
2737 /* Check for CPU stalls, if enabled. */
2738 check_cpu_stall(rsp, rdp);
2740 /* Is the RCU core waiting for a quiescent state from this CPU? */
2741 if (rcu_scheduler_fully_active &&
2742 rdp->qs_pending && !rdp->passed_quiesce) {
2743 rdp->n_rp_qs_pending++;
2744 } else if (rdp->qs_pending && rdp->passed_quiesce) {
2745 rdp->n_rp_report_qs++;
2749 /* Does this CPU have callbacks ready to invoke? */
2750 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
2751 rdp->n_rp_cb_ready++;
2755 /* Has RCU gone idle with this CPU needing another grace period? */
2756 if (cpu_needs_another_gp(rsp, rdp)) {
2757 rdp->n_rp_cpu_needs_gp++;
2761 /* Has another RCU grace period completed? */
2762 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2763 rdp->n_rp_gp_completed++;
2767 /* Has a new RCU grace period started? */
2768 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2769 rdp->n_rp_gp_started++;
2774 rdp->n_rp_need_nothing++;
2779 * Check to see if there is any immediate RCU-related work to be done
2780 * by the current CPU, returning 1 if so. This function is part of the
2781 * RCU implementation; it is -not- an exported member of the RCU API.
2783 static int rcu_pending(int cpu)
2785 struct rcu_state *rsp;
2787 for_each_rcu_flavor(rsp)
2788 if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
2794 * Return true if the specified CPU has any callback. If all_lazy is
2795 * non-NULL, store an indication of whether all callbacks are lazy.
2796 * (If there are no callbacks, all of them are deemed to be lazy.)
2798 static int rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
2802 struct rcu_data *rdp;
2803 struct rcu_state *rsp;
2805 for_each_rcu_flavor(rsp) {
2806 rdp = per_cpu_ptr(rsp->rda, cpu);
2810 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
2821 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2822 * the compiler is expected to optimize this away.
2824 static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
2825 int cpu, unsigned long done)
2827 trace_rcu_barrier(rsp->name, s, cpu,
2828 atomic_read(&rsp->barrier_cpu_count), done);
2832 * RCU callback function for _rcu_barrier(). If we are last, wake
2833 * up the task executing _rcu_barrier().
2835 static void rcu_barrier_callback(struct rcu_head *rhp)
2837 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
2838 struct rcu_state *rsp = rdp->rsp;
2840 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
2841 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
2842 complete(&rsp->barrier_completion);
2844 _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
2849 * Called with preemption disabled, and from cross-cpu IRQ context.
2851 static void rcu_barrier_func(void *type)
2853 struct rcu_state *rsp = type;
2854 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2856 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
2857 atomic_inc(&rsp->barrier_cpu_count);
2858 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
2862 * Orchestrate the specified type of RCU barrier, waiting for all
2863 * RCU callbacks of the specified type to complete.
2865 static void _rcu_barrier(struct rcu_state *rsp)
2868 struct rcu_data *rdp;
2869 unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
2870 unsigned long snap_done;
2872 _rcu_barrier_trace(rsp, "Begin", -1, snap);
2874 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2875 mutex_lock(&rsp->barrier_mutex);
2878 * Ensure that all prior references, including to ->n_barrier_done,
2879 * are ordered before the _rcu_barrier() machinery.
2881 smp_mb(); /* See above block comment. */
2884 * Recheck ->n_barrier_done to see if others did our work for us.
2885 * This means checking ->n_barrier_done for an even-to-odd-to-even
2886 * transition. The "if" expression below therefore rounds the old
2887 * value up to the next even number and adds two before comparing.
2889 snap_done = rsp->n_barrier_done;
2890 _rcu_barrier_trace(rsp, "Check", -1, snap_done);
2893 * If the value in snap is odd, we needed to wait for the current
2894 * rcu_barrier() to complete, then wait for the next one, in other
2895 * words, we need the value of snap_done to be three larger than
2896 * the value of snap. On the other hand, if the value in snap is
2897 * even, we only had to wait for the next rcu_barrier() to complete,
2898 * in other words, we need the value of snap_done to be only two
2899 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
2900 * this for us (thank you, Linus!).
2902 if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
2903 _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
2904 smp_mb(); /* caller's subsequent code after above check. */
2905 mutex_unlock(&rsp->barrier_mutex);
2910 * Increment ->n_barrier_done to avoid duplicate work. Use
2911 * ACCESS_ONCE() to prevent the compiler from speculating
2912 * the increment to precede the early-exit check.
2914 ACCESS_ONCE(rsp->n_barrier_done)++;
2915 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
2916 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
2917 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2920 * Initialize the count to one rather than to zero in order to
2921 * avoid a too-soon return to zero in case of a short grace period
2922 * (or preemption of this task). Exclude CPU-hotplug operations
2923 * to ensure that no offline CPU has callbacks queued.
2925 init_completion(&rsp->barrier_completion);
2926 atomic_set(&rsp->barrier_cpu_count, 1);
2930 * Force each CPU with callbacks to register a new callback.
2931 * When that callback is invoked, we will know that all of the
2932 * corresponding CPU's preceding callbacks have been invoked.
2934 for_each_possible_cpu(cpu) {
2935 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
2937 rdp = per_cpu_ptr(rsp->rda, cpu);
2938 if (rcu_is_nocb_cpu(cpu)) {
2939 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
2940 rsp->n_barrier_done);
2941 atomic_inc(&rsp->barrier_cpu_count);
2942 __call_rcu(&rdp->barrier_head, rcu_barrier_callback,
2944 } else if (ACCESS_ONCE(rdp->qlen)) {
2945 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
2946 rsp->n_barrier_done);
2947 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
2949 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
2950 rsp->n_barrier_done);
2956 * Now that we have an rcu_barrier_callback() callback on each
2957 * CPU, and thus each counted, remove the initial count.
2959 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
2960 complete(&rsp->barrier_completion);
2962 /* Increment ->n_barrier_done to prevent duplicate work. */
2963 smp_mb(); /* Keep increment after above mechanism. */
2964 ACCESS_ONCE(rsp->n_barrier_done)++;
2965 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
2966 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
2967 smp_mb(); /* Keep increment before caller's subsequent code. */
2969 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2970 wait_for_completion(&rsp->barrier_completion);
2972 /* Other rcu_barrier() invocations can now safely proceed. */
2973 mutex_unlock(&rsp->barrier_mutex);
2977 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2979 void rcu_barrier_bh(void)
2981 _rcu_barrier(&rcu_bh_state);
2983 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
2986 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2988 void rcu_barrier_sched(void)
2990 _rcu_barrier(&rcu_sched_state);
2992 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
2995 * Do boot-time initialization of a CPU's per-CPU RCU data.
2998 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3000 unsigned long flags;
3001 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3002 struct rcu_node *rnp = rcu_get_root(rsp);
3004 /* Set up local state, ensuring consistent view of global state. */
3005 raw_spin_lock_irqsave(&rnp->lock, flags);
3006 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3007 init_callback_list(rdp);
3009 ACCESS_ONCE(rdp->qlen) = 0;
3010 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3011 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3012 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3015 rcu_boot_init_nocb_percpu_data(rdp);
3016 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3020 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3021 * offline event can be happening at a given time. Note also that we
3022 * can accept some slop in the rsp->completed access due to the fact
3023 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3026 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
3028 unsigned long flags;
3030 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3031 struct rcu_node *rnp = rcu_get_root(rsp);
3033 /* Exclude new grace periods. */
3034 mutex_lock(&rsp->onoff_mutex);
3036 /* Set up local state, ensuring consistent view of global state. */
3037 raw_spin_lock_irqsave(&rnp->lock, flags);
3038 rdp->beenonline = 1; /* We have now been online. */
3039 rdp->preemptible = preemptible;
3040 rdp->qlen_last_fqs_check = 0;
3041 rdp->n_force_qs_snap = rsp->n_force_qs;
3042 rdp->blimit = blimit;
3043 init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
3044 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3045 rcu_sysidle_init_percpu_data(rdp->dynticks);
3046 atomic_set(&rdp->dynticks->dynticks,
3047 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
3048 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
3050 /* Add CPU to rcu_node bitmasks. */
3052 mask = rdp->grpmask;
3054 /* Exclude any attempts to start a new GP on small systems. */
3055 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
3056 rnp->qsmaskinit |= mask;
3057 mask = rnp->grpmask;
3058 if (rnp == rdp->mynode) {
3060 * If there is a grace period in progress, we will
3061 * set up to wait for it next time we run the
3064 rdp->gpnum = rnp->completed;
3065 rdp->completed = rnp->completed;
3066 rdp->passed_quiesce = 0;
3067 rdp->qs_pending = 0;
3068 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3070 raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3072 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
3073 local_irq_restore(flags);
3075 mutex_unlock(&rsp->onoff_mutex);
3078 static void rcu_prepare_cpu(int cpu)
3080 struct rcu_state *rsp;
3082 for_each_rcu_flavor(rsp)
3083 rcu_init_percpu_data(cpu, rsp,
3084 strcmp(rsp->name, "rcu_preempt") == 0);
3088 * Handle CPU online/offline notification events.
3090 static int rcu_cpu_notify(struct notifier_block *self,
3091 unsigned long action, void *hcpu)
3093 long cpu = (long)hcpu;
3094 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
3095 struct rcu_node *rnp = rdp->mynode;
3096 struct rcu_state *rsp;
3098 trace_rcu_utilization(TPS("Start CPU hotplug"));
3100 case CPU_UP_PREPARE:
3101 case CPU_UP_PREPARE_FROZEN:
3102 rcu_prepare_cpu(cpu);
3103 rcu_prepare_kthreads(cpu);
3106 case CPU_DOWN_FAILED:
3107 rcu_boost_kthread_setaffinity(rnp, -1);
3109 case CPU_DOWN_PREPARE:
3110 rcu_boost_kthread_setaffinity(rnp, cpu);
3113 case CPU_DYING_FROZEN:
3114 for_each_rcu_flavor(rsp)
3115 rcu_cleanup_dying_cpu(rsp);
3118 case CPU_DEAD_FROZEN:
3119 case CPU_UP_CANCELED:
3120 case CPU_UP_CANCELED_FROZEN:
3121 for_each_rcu_flavor(rsp)
3122 rcu_cleanup_dead_cpu(cpu, rsp);
3127 trace_rcu_utilization(TPS("End CPU hotplug"));
3131 static int rcu_pm_notify(struct notifier_block *self,
3132 unsigned long action, void *hcpu)
3135 case PM_HIBERNATION_PREPARE:
3136 case PM_SUSPEND_PREPARE:
3137 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3140 case PM_POST_HIBERNATION:
3141 case PM_POST_SUSPEND:
3151 * Spawn the kthread that handles this RCU flavor's grace periods.
3153 static int __init rcu_spawn_gp_kthread(void)
3155 unsigned long flags;
3156 struct rcu_node *rnp;
3157 struct rcu_state *rsp;
3158 struct task_struct *t;
3160 for_each_rcu_flavor(rsp) {
3161 t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
3163 rnp = rcu_get_root(rsp);
3164 raw_spin_lock_irqsave(&rnp->lock, flags);
3165 rsp->gp_kthread = t;
3166 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3167 rcu_spawn_nocb_kthreads(rsp);
3171 early_initcall(rcu_spawn_gp_kthread);
3174 * This function is invoked towards the end of the scheduler's initialization
3175 * process. Before this is called, the idle task might contain
3176 * RCU read-side critical sections (during which time, this idle
3177 * task is booting the system). After this function is called, the
3178 * idle tasks are prohibited from containing RCU read-side critical
3179 * sections. This function also enables RCU lockdep checking.
3181 void rcu_scheduler_starting(void)
3183 WARN_ON(num_online_cpus() != 1);
3184 WARN_ON(nr_context_switches() > 0);
3185 rcu_scheduler_active = 1;
3189 * Compute the per-level fanout, either using the exact fanout specified
3190 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3192 #ifdef CONFIG_RCU_FANOUT_EXACT
3193 static void __init rcu_init_levelspread(struct rcu_state *rsp)
3197 for (i = rcu_num_lvls - 1; i > 0; i--)
3198 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
3199 rsp->levelspread[0] = rcu_fanout_leaf;
3201 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3202 static void __init rcu_init_levelspread(struct rcu_state *rsp)
3209 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3210 ccur = rsp->levelcnt[i];
3211 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
3215 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3218 * Helper function for rcu_init() that initializes one rcu_state structure.
3220 static void __init rcu_init_one(struct rcu_state *rsp,
3221 struct rcu_data __percpu *rda)
3223 static char *buf[] = { "rcu_node_0",
3226 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3227 static char *fqs[] = { "rcu_node_fqs_0",
3230 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3234 struct rcu_node *rnp;
3236 BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3238 /* Silence gcc 4.8 warning about array index out of range. */
3239 if (rcu_num_lvls > RCU_NUM_LVLS)
3240 panic("rcu_init_one: rcu_num_lvls overflow");
3242 /* Initialize the level-tracking arrays. */
3244 for (i = 0; i < rcu_num_lvls; i++)
3245 rsp->levelcnt[i] = num_rcu_lvl[i];
3246 for (i = 1; i < rcu_num_lvls; i++)
3247 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
3248 rcu_init_levelspread(rsp);
3250 /* Initialize the elements themselves, starting from the leaves. */
3252 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3253 cpustride *= rsp->levelspread[i];
3254 rnp = rsp->level[i];
3255 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
3256 raw_spin_lock_init(&rnp->lock);
3257 lockdep_set_class_and_name(&rnp->lock,
3258 &rcu_node_class[i], buf[i]);
3259 raw_spin_lock_init(&rnp->fqslock);
3260 lockdep_set_class_and_name(&rnp->fqslock,
3261 &rcu_fqs_class[i], fqs[i]);
3262 rnp->gpnum = rsp->gpnum;
3263 rnp->completed = rsp->completed;
3265 rnp->qsmaskinit = 0;
3266 rnp->grplo = j * cpustride;
3267 rnp->grphi = (j + 1) * cpustride - 1;
3268 if (rnp->grphi >= NR_CPUS)
3269 rnp->grphi = NR_CPUS - 1;
3275 rnp->grpnum = j % rsp->levelspread[i - 1];
3276 rnp->grpmask = 1UL << rnp->grpnum;
3277 rnp->parent = rsp->level[i - 1] +
3278 j / rsp->levelspread[i - 1];
3281 INIT_LIST_HEAD(&rnp->blkd_tasks);
3282 rcu_init_one_nocb(rnp);
3287 init_waitqueue_head(&rsp->gp_wq);
3288 init_irq_work(&rsp->wakeup_work, rsp_wakeup);
3289 rnp = rsp->level[rcu_num_lvls - 1];
3290 for_each_possible_cpu(i) {
3291 while (i > rnp->grphi)
3293 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3294 rcu_boot_init_percpu_data(i, rsp);
3296 list_add(&rsp->flavors, &rcu_struct_flavors);
3300 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3301 * replace the definitions in rcutree.h because those are needed to size
3302 * the ->node array in the rcu_state structure.
3304 static void __init rcu_init_geometry(void)
3310 int rcu_capacity[MAX_RCU_LVLS + 1];
3313 * Initialize any unspecified boot parameters.
3314 * The default values of jiffies_till_first_fqs and
3315 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3316 * value, which is a function of HZ, then adding one for each
3317 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3319 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3320 if (jiffies_till_first_fqs == ULONG_MAX)
3321 jiffies_till_first_fqs = d;
3322 if (jiffies_till_next_fqs == ULONG_MAX)
3323 jiffies_till_next_fqs = d;
3325 /* If the compile-time values are accurate, just leave. */
3326 if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
3327 nr_cpu_ids == NR_CPUS)
3331 * Compute number of nodes that can be handled an rcu_node tree
3332 * with the given number of levels. Setting rcu_capacity[0] makes
3333 * some of the arithmetic easier.
3335 rcu_capacity[0] = 1;
3336 rcu_capacity[1] = rcu_fanout_leaf;
3337 for (i = 2; i <= MAX_RCU_LVLS; i++)
3338 rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
3341 * The boot-time rcu_fanout_leaf parameter is only permitted
3342 * to increase the leaf-level fanout, not decrease it. Of course,
3343 * the leaf-level fanout cannot exceed the number of bits in
3344 * the rcu_node masks. Finally, the tree must be able to accommodate
3345 * the configured number of CPUs. Complain and fall back to the
3346 * compile-time values if these limits are exceeded.
3348 if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
3349 rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
3350 n > rcu_capacity[MAX_RCU_LVLS]) {
3355 /* Calculate the number of rcu_nodes at each level of the tree. */
3356 for (i = 1; i <= MAX_RCU_LVLS; i++)
3357 if (n <= rcu_capacity[i]) {
3358 for (j = 0; j <= i; j++)
3360 DIV_ROUND_UP(n, rcu_capacity[i - j]);
3362 for (j = i + 1; j <= MAX_RCU_LVLS; j++)
3367 /* Calculate the total number of rcu_node structures. */
3369 for (i = 0; i <= MAX_RCU_LVLS; i++)
3370 rcu_num_nodes += num_rcu_lvl[i];
3374 void __init rcu_init(void)
3378 rcu_bootup_announce();
3379 rcu_init_geometry();
3380 rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3381 rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3382 __rcu_init_preempt();
3383 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3386 * We don't need protection against CPU-hotplug here because
3387 * this is called early in boot, before either interrupts
3388 * or the scheduler are operational.
3390 cpu_notifier(rcu_cpu_notify, 0);
3391 pm_notifier(rcu_pm_notify, 0);
3392 for_each_online_cpu(cpu)
3393 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3396 #include "rcutree_plugin.h"