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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion
4 *
5 * Copyright IBM Corporation, 2008
6 *
7 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
8 * Manfred Spraul <manfred@colorfullife.com>
9 * Paul E. McKenney <paulmck@linux.ibm.com> Hierarchical version
10 *
11 * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
12 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
13 *
14 * For detailed explanation of Read-Copy Update mechanism see -
15 * Documentation/RCU
16 */
17
18#define pr_fmt(fmt) "rcu: " fmt
19
20#include <linux/types.h>
21#include <linux/kernel.h>
22#include <linux/init.h>
23#include <linux/spinlock.h>
24#include <linux/smp.h>
25#include <linux/rcupdate_wait.h>
26#include <linux/interrupt.h>
27#include <linux/sched.h>
28#include <linux/sched/debug.h>
29#include <linux/nmi.h>
30#include <linux/atomic.h>
31#include <linux/bitops.h>
32#include <linux/export.h>
33#include <linux/completion.h>
34#include <linux/moduleparam.h>
35#include <linux/percpu.h>
36#include <linux/notifier.h>
37#include <linux/cpu.h>
38#include <linux/mutex.h>
39#include <linux/time.h>
40#include <linux/kernel_stat.h>
41#include <linux/wait.h>
42#include <linux/kthread.h>
43#include <uapi/linux/sched/types.h>
44#include <linux/prefetch.h>
45#include <linux/delay.h>
46#include <linux/stop_machine.h>
47#include <linux/random.h>
48#include <linux/trace_events.h>
49#include <linux/suspend.h>
50#include <linux/ftrace.h>
51#include <linux/tick.h>
52#include <linux/sysrq.h>
53#include <linux/kprobes.h>
54#include <linux/gfp.h>
55#include <linux/oom.h>
56#include <linux/smpboot.h>
57#include <linux/jiffies.h>
58#include <linux/sched/isolation.h>
59#include <linux/sched/clock.h>
60#include "../time/tick-internal.h"
61
62#include "tree.h"
63#include "rcu.h"
64
65#ifdef MODULE_PARAM_PREFIX
66#undef MODULE_PARAM_PREFIX
67#endif
68#define MODULE_PARAM_PREFIX "rcutree."
69
70/* Data structures. */
71
72/*
73 * Steal a bit from the bottom of ->dynticks for idle entry/exit
74 * control. Initially this is for TLB flushing.
75 */
76#define RCU_DYNTICK_CTRL_MASK 0x1
77#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
78#ifndef rcu_eqs_special_exit
79#define rcu_eqs_special_exit() do { } while (0)
80#endif
81
82static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
83 .dynticks_nesting = 1,
84 .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
85 .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
86};
87struct rcu_state rcu_state = {
88 .level = { &rcu_state.node[0] },
89 .gp_state = RCU_GP_IDLE,
90 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
91 .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
92 .name = RCU_NAME,
93 .abbr = RCU_ABBR,
94 .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
95 .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
96 .ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
97};
98
99/* Dump rcu_node combining tree at boot to verify correct setup. */
100static bool dump_tree;
101module_param(dump_tree, bool, 0444);
102/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
103static bool use_softirq = 1;
104module_param(use_softirq, bool, 0444);
105/* Control rcu_node-tree auto-balancing at boot time. */
106static bool rcu_fanout_exact;
107module_param(rcu_fanout_exact, bool, 0444);
108/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
109static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
110module_param(rcu_fanout_leaf, int, 0444);
111int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
112/* Number of rcu_nodes at specified level. */
113int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
114int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
115
116/*
117 * The rcu_scheduler_active variable is initialized to the value
118 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
119 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
120 * RCU can assume that there is but one task, allowing RCU to (for example)
121 * optimize synchronize_rcu() to a simple barrier(). When this variable
122 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
123 * to detect real grace periods. This variable is also used to suppress
124 * boot-time false positives from lockdep-RCU error checking. Finally, it
125 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
126 * is fully initialized, including all of its kthreads having been spawned.
127 */
128int rcu_scheduler_active __read_mostly;
129EXPORT_SYMBOL_GPL(rcu_scheduler_active);
130
131/*
132 * The rcu_scheduler_fully_active variable transitions from zero to one
133 * during the early_initcall() processing, which is after the scheduler
134 * is capable of creating new tasks. So RCU processing (for example,
135 * creating tasks for RCU priority boosting) must be delayed until after
136 * rcu_scheduler_fully_active transitions from zero to one. We also
137 * currently delay invocation of any RCU callbacks until after this point.
138 *
139 * It might later prove better for people registering RCU callbacks during
140 * early boot to take responsibility for these callbacks, but one step at
141 * a time.
142 */
143static int rcu_scheduler_fully_active __read_mostly;
144
145static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
146 unsigned long gps, unsigned long flags);
147static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
148static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
149static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
150static void invoke_rcu_core(void);
151static void rcu_report_exp_rdp(struct rcu_data *rdp);
152static void sync_sched_exp_online_cleanup(int cpu);
153
154/* rcuc/rcub kthread realtime priority */
155static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
156module_param(kthread_prio, int, 0444);
157
158/* Delay in jiffies for grace-period initialization delays, debug only. */
159
160static int gp_preinit_delay;
161module_param(gp_preinit_delay, int, 0444);
162static int gp_init_delay;
163module_param(gp_init_delay, int, 0444);
164static int gp_cleanup_delay;
165module_param(gp_cleanup_delay, int, 0444);
166
167/* Retrieve RCU kthreads priority for rcutorture */
168int rcu_get_gp_kthreads_prio(void)
169{
170 return kthread_prio;
171}
172EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
173
174/*
175 * Number of grace periods between delays, normalized by the duration of
176 * the delay. The longer the delay, the more the grace periods between
177 * each delay. The reason for this normalization is that it means that,
178 * for non-zero delays, the overall slowdown of grace periods is constant
179 * regardless of the duration of the delay. This arrangement balances
180 * the need for long delays to increase some race probabilities with the
181 * need for fast grace periods to increase other race probabilities.
182 */
183#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
184
185/*
186 * Compute the mask of online CPUs for the specified rcu_node structure.
187 * This will not be stable unless the rcu_node structure's ->lock is
188 * held, but the bit corresponding to the current CPU will be stable
189 * in most contexts.
190 */
191unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
192{
193 return READ_ONCE(rnp->qsmaskinitnext);
194}
195
196/*
197 * Return true if an RCU grace period is in progress. The READ_ONCE()s
198 * permit this function to be invoked without holding the root rcu_node
199 * structure's ->lock, but of course results can be subject to change.
200 */
201static int rcu_gp_in_progress(void)
202{
203 return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
204}
205
206/*
207 * Return the number of callbacks queued on the specified CPU.
208 * Handles both the nocbs and normal cases.
209 */
210static long rcu_get_n_cbs_cpu(int cpu)
211{
212 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
213
214 if (rcu_segcblist_is_enabled(&rdp->cblist))
215 return rcu_segcblist_n_cbs(&rdp->cblist);
216 return 0;
217}
218
219void rcu_softirq_qs(void)
220{
221 rcu_qs();
222 rcu_preempt_deferred_qs(current);
223}
224
225/*
226 * Record entry into an extended quiescent state. This is only to be
227 * called when not already in an extended quiescent state.
228 */
229static void rcu_dynticks_eqs_enter(void)
230{
231 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
232 int seq;
233
234 /*
235 * CPUs seeing atomic_add_return() must see prior RCU read-side
236 * critical sections, and we also must force ordering with the
237 * next idle sojourn.
238 */
239 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
240 /* Better be in an extended quiescent state! */
241 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
242 (seq & RCU_DYNTICK_CTRL_CTR));
243 /* Better not have special action (TLB flush) pending! */
244 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
245 (seq & RCU_DYNTICK_CTRL_MASK));
246}
247
248/*
249 * Record exit from an extended quiescent state. This is only to be
250 * called from an extended quiescent state.
251 */
252static void rcu_dynticks_eqs_exit(void)
253{
254 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
255 int seq;
256
257 /*
258 * CPUs seeing atomic_add_return() must see prior idle sojourns,
259 * and we also must force ordering with the next RCU read-side
260 * critical section.
261 */
262 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
263 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
264 !(seq & RCU_DYNTICK_CTRL_CTR));
265 if (seq & RCU_DYNTICK_CTRL_MASK) {
266 atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
267 smp_mb__after_atomic(); /* _exit after clearing mask. */
268 /* Prefer duplicate flushes to losing a flush. */
269 rcu_eqs_special_exit();
270 }
271}
272
273/*
274 * Reset the current CPU's ->dynticks counter to indicate that the
275 * newly onlined CPU is no longer in an extended quiescent state.
276 * This will either leave the counter unchanged, or increment it
277 * to the next non-quiescent value.
278 *
279 * The non-atomic test/increment sequence works because the upper bits
280 * of the ->dynticks counter are manipulated only by the corresponding CPU,
281 * or when the corresponding CPU is offline.
282 */
283static void rcu_dynticks_eqs_online(void)
284{
285 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
286
287 if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR)
288 return;
289 atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
290}
291
292/*
293 * Is the current CPU in an extended quiescent state?
294 *
295 * No ordering, as we are sampling CPU-local information.
296 */
297bool rcu_dynticks_curr_cpu_in_eqs(void)
298{
299 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
300
301 return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
302}
303
304/*
305 * Snapshot the ->dynticks counter with full ordering so as to allow
306 * stable comparison of this counter with past and future snapshots.
307 */
308int rcu_dynticks_snap(struct rcu_data *rdp)
309{
310 int snap = atomic_add_return(0, &rdp->dynticks);
311
312 return snap & ~RCU_DYNTICK_CTRL_MASK;
313}
314
315/*
316 * Return true if the snapshot returned from rcu_dynticks_snap()
317 * indicates that RCU is in an extended quiescent state.
318 */
319static bool rcu_dynticks_in_eqs(int snap)
320{
321 return !(snap & RCU_DYNTICK_CTRL_CTR);
322}
323
324/*
325 * Return true if the CPU corresponding to the specified rcu_data
326 * structure has spent some time in an extended quiescent state since
327 * rcu_dynticks_snap() returned the specified snapshot.
328 */
329static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
330{
331 return snap != rcu_dynticks_snap(rdp);
332}
333
334/*
335 * Set the special (bottom) bit of the specified CPU so that it
336 * will take special action (such as flushing its TLB) on the
337 * next exit from an extended quiescent state. Returns true if
338 * the bit was successfully set, or false if the CPU was not in
339 * an extended quiescent state.
340 */
341bool rcu_eqs_special_set(int cpu)
342{
343 int old;
344 int new;
345 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
346
347 do {
348 old = atomic_read(&rdp->dynticks);
349 if (old & RCU_DYNTICK_CTRL_CTR)
350 return false;
351 new = old | RCU_DYNTICK_CTRL_MASK;
352 } while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
353 return true;
354}
355
356/*
357 * Let the RCU core know that this CPU has gone through the scheduler,
358 * which is a quiescent state. This is called when the need for a
359 * quiescent state is urgent, so we burn an atomic operation and full
360 * memory barriers to let the RCU core know about it, regardless of what
361 * this CPU might (or might not) do in the near future.
362 *
363 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
364 *
365 * The caller must have disabled interrupts and must not be idle.
366 */
367static void __maybe_unused rcu_momentary_dyntick_idle(void)
368{
369 int special;
370
371 raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
372 special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
373 &this_cpu_ptr(&rcu_data)->dynticks);
374 /* It is illegal to call this from idle state. */
375 WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
376 rcu_preempt_deferred_qs(current);
377}
378
379/**
380 * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle
381 *
382 * If the current CPU is idle and running at a first-level (not nested)
383 * interrupt from idle, return true. The caller must have at least
384 * disabled preemption.
385 */
386static int rcu_is_cpu_rrupt_from_idle(void)
387{
388 /* Called only from within the scheduling-clock interrupt */
389 lockdep_assert_in_irq();
390
391 /* Check for counter underflows */
392 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
393 "RCU dynticks_nesting counter underflow!");
394 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0,
395 "RCU dynticks_nmi_nesting counter underflow/zero!");
396
397 /* Are we at first interrupt nesting level? */
398 if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1)
399 return false;
400
401 /* Does CPU appear to be idle from an RCU standpoint? */
402 return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
403}
404
405#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch ... */
406#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */
407static long blimit = DEFAULT_RCU_BLIMIT;
408#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
409static long qhimark = DEFAULT_RCU_QHIMARK;
410#define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
411static long qlowmark = DEFAULT_RCU_QLOMARK;
412
413module_param(blimit, long, 0444);
414module_param(qhimark, long, 0444);
415module_param(qlowmark, long, 0444);
416
417static ulong jiffies_till_first_fqs = ULONG_MAX;
418static ulong jiffies_till_next_fqs = ULONG_MAX;
419static bool rcu_kick_kthreads;
420static int rcu_divisor = 7;
421module_param(rcu_divisor, int, 0644);
422
423/* Force an exit from rcu_do_batch() after 3 milliseconds. */
424static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
425module_param(rcu_resched_ns, long, 0644);
426
427/*
428 * How long the grace period must be before we start recruiting
429 * quiescent-state help from rcu_note_context_switch().
430 */
431static ulong jiffies_till_sched_qs = ULONG_MAX;
432module_param(jiffies_till_sched_qs, ulong, 0444);
433static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
434module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
435
436/*
437 * Make sure that we give the grace-period kthread time to detect any
438 * idle CPUs before taking active measures to force quiescent states.
439 * However, don't go below 100 milliseconds, adjusted upwards for really
440 * large systems.
441 */
442static void adjust_jiffies_till_sched_qs(void)
443{
444 unsigned long j;
445
446 /* If jiffies_till_sched_qs was specified, respect the request. */
447 if (jiffies_till_sched_qs != ULONG_MAX) {
448 WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
449 return;
450 }
451 /* Otherwise, set to third fqs scan, but bound below on large system. */
452 j = READ_ONCE(jiffies_till_first_fqs) +
453 2 * READ_ONCE(jiffies_till_next_fqs);
454 if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
455 j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
456 pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
457 WRITE_ONCE(jiffies_to_sched_qs, j);
458}
459
460static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
461{
462 ulong j;
463 int ret = kstrtoul(val, 0, &j);
464
465 if (!ret) {
466 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
467 adjust_jiffies_till_sched_qs();
468 }
469 return ret;
470}
471
472static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
473{
474 ulong j;
475 int ret = kstrtoul(val, 0, &j);
476
477 if (!ret) {
478 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
479 adjust_jiffies_till_sched_qs();
480 }
481 return ret;
482}
483
484static struct kernel_param_ops first_fqs_jiffies_ops = {
485 .set = param_set_first_fqs_jiffies,
486 .get = param_get_ulong,
487};
488
489static struct kernel_param_ops next_fqs_jiffies_ops = {
490 .set = param_set_next_fqs_jiffies,
491 .get = param_get_ulong,
492};
493
494module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
495module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
496module_param(rcu_kick_kthreads, bool, 0644);
497
498static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
499static int rcu_pending(void);
500
501/*
502 * Return the number of RCU GPs completed thus far for debug & stats.
503 */
504unsigned long rcu_get_gp_seq(void)
505{
506 return READ_ONCE(rcu_state.gp_seq);
507}
508EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
509
510/*
511 * Return the number of RCU expedited batches completed thus far for
512 * debug & stats. Odd numbers mean that a batch is in progress, even
513 * numbers mean idle. The value returned will thus be roughly double
514 * the cumulative batches since boot.
515 */
516unsigned long rcu_exp_batches_completed(void)
517{
518 return rcu_state.expedited_sequence;
519}
520EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
521
522/*
523 * Return the root node of the rcu_state structure.
524 */
525static struct rcu_node *rcu_get_root(void)
526{
527 return &rcu_state.node[0];
528}
529
530/*
531 * Convert a ->gp_state value to a character string.
532 */
533static const char *gp_state_getname(short gs)
534{
535 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
536 return "???";
537 return gp_state_names[gs];
538}
539
540/*
541 * Send along grace-period-related data for rcutorture diagnostics.
542 */
543void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
544 unsigned long *gp_seq)
545{
546 switch (test_type) {
547 case RCU_FLAVOR:
548 *flags = READ_ONCE(rcu_state.gp_flags);
549 *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
550 break;
551 default:
552 break;
553 }
554}
555EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
556
557/*
558 * Enter an RCU extended quiescent state, which can be either the
559 * idle loop or adaptive-tickless usermode execution.
560 *
561 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
562 * the possibility of usermode upcalls having messed up our count
563 * of interrupt nesting level during the prior busy period.
564 */
565static void rcu_eqs_enter(bool user)
566{
567 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
568
569 WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
570 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
571 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
572 rdp->dynticks_nesting == 0);
573 if (rdp->dynticks_nesting != 1) {
574 rdp->dynticks_nesting--;
575 return;
576 }
577
578 lockdep_assert_irqs_disabled();
579 trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
580 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
581 rdp = this_cpu_ptr(&rcu_data);
582 do_nocb_deferred_wakeup(rdp);
583 rcu_prepare_for_idle();
584 rcu_preempt_deferred_qs(current);
585 WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
586 rcu_dynticks_eqs_enter();
587 rcu_dynticks_task_enter();
588}
589
590/**
591 * rcu_idle_enter - inform RCU that current CPU is entering idle
592 *
593 * Enter idle mode, in other words, -leave- the mode in which RCU
594 * read-side critical sections can occur. (Though RCU read-side
595 * critical sections can occur in irq handlers in idle, a possibility
596 * handled by irq_enter() and irq_exit().)
597 *
598 * If you add or remove a call to rcu_idle_enter(), be sure to test with
599 * CONFIG_RCU_EQS_DEBUG=y.
600 */
601void rcu_idle_enter(void)
602{
603 lockdep_assert_irqs_disabled();
604 rcu_eqs_enter(false);
605}
606
607#ifdef CONFIG_NO_HZ_FULL
608/**
609 * rcu_user_enter - inform RCU that we are resuming userspace.
610 *
611 * Enter RCU idle mode right before resuming userspace. No use of RCU
612 * is permitted between this call and rcu_user_exit(). This way the
613 * CPU doesn't need to maintain the tick for RCU maintenance purposes
614 * when the CPU runs in userspace.
615 *
616 * If you add or remove a call to rcu_user_enter(), be sure to test with
617 * CONFIG_RCU_EQS_DEBUG=y.
618 */
619void rcu_user_enter(void)
620{
621 lockdep_assert_irqs_disabled();
622 rcu_eqs_enter(true);
623}
624#endif /* CONFIG_NO_HZ_FULL */
625
626/*
627 * If we are returning from the outermost NMI handler that interrupted an
628 * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
629 * to let the RCU grace-period handling know that the CPU is back to
630 * being RCU-idle.
631 *
632 * If you add or remove a call to rcu_nmi_exit_common(), be sure to test
633 * with CONFIG_RCU_EQS_DEBUG=y.
634 */
635static __always_inline void rcu_nmi_exit_common(bool irq)
636{
637 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
638
639 /*
640 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
641 * (We are exiting an NMI handler, so RCU better be paying attention
642 * to us!)
643 */
644 WARN_ON_ONCE(rdp->dynticks_nmi_nesting <= 0);
645 WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
646
647 /*
648 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
649 * leave it in non-RCU-idle state.
650 */
651 if (rdp->dynticks_nmi_nesting != 1) {
652 trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
653 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
654 rdp->dynticks_nmi_nesting - 2);
655 return;
656 }
657
658 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
659 trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks);
660 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
661
662 if (irq)
663 rcu_prepare_for_idle();
664
665 rcu_dynticks_eqs_enter();
666
667 if (irq)
668 rcu_dynticks_task_enter();
669}
670
671/**
672 * rcu_nmi_exit - inform RCU of exit from NMI context
673 *
674 * If you add or remove a call to rcu_nmi_exit(), be sure to test
675 * with CONFIG_RCU_EQS_DEBUG=y.
676 */
677void rcu_nmi_exit(void)
678{
679 rcu_nmi_exit_common(false);
680}
681
682/**
683 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
684 *
685 * Exit from an interrupt handler, which might possibly result in entering
686 * idle mode, in other words, leaving the mode in which read-side critical
687 * sections can occur. The caller must have disabled interrupts.
688 *
689 * This code assumes that the idle loop never does anything that might
690 * result in unbalanced calls to irq_enter() and irq_exit(). If your
691 * architecture's idle loop violates this assumption, RCU will give you what
692 * you deserve, good and hard. But very infrequently and irreproducibly.
693 *
694 * Use things like work queues to work around this limitation.
695 *
696 * You have been warned.
697 *
698 * If you add or remove a call to rcu_irq_exit(), be sure to test with
699 * CONFIG_RCU_EQS_DEBUG=y.
700 */
701void rcu_irq_exit(void)
702{
703 lockdep_assert_irqs_disabled();
704 rcu_nmi_exit_common(true);
705}
706
707/*
708 * Wrapper for rcu_irq_exit() where interrupts are enabled.
709 *
710 * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
711 * with CONFIG_RCU_EQS_DEBUG=y.
712 */
713void rcu_irq_exit_irqson(void)
714{
715 unsigned long flags;
716
717 local_irq_save(flags);
718 rcu_irq_exit();
719 local_irq_restore(flags);
720}
721
722/*
723 * Exit an RCU extended quiescent state, which can be either the
724 * idle loop or adaptive-tickless usermode execution.
725 *
726 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
727 * allow for the possibility of usermode upcalls messing up our count of
728 * interrupt nesting level during the busy period that is just now starting.
729 */
730static void rcu_eqs_exit(bool user)
731{
732 struct rcu_data *rdp;
733 long oldval;
734
735 lockdep_assert_irqs_disabled();
736 rdp = this_cpu_ptr(&rcu_data);
737 oldval = rdp->dynticks_nesting;
738 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
739 if (oldval) {
740 rdp->dynticks_nesting++;
741 return;
742 }
743 rcu_dynticks_task_exit();
744 rcu_dynticks_eqs_exit();
745 rcu_cleanup_after_idle();
746 trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
747 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
748 WRITE_ONCE(rdp->dynticks_nesting, 1);
749 WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
750 WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
751}
752
753/**
754 * rcu_idle_exit - inform RCU that current CPU is leaving idle
755 *
756 * Exit idle mode, in other words, -enter- the mode in which RCU
757 * read-side critical sections can occur.
758 *
759 * If you add or remove a call to rcu_idle_exit(), be sure to test with
760 * CONFIG_RCU_EQS_DEBUG=y.
761 */
762void rcu_idle_exit(void)
763{
764 unsigned long flags;
765
766 local_irq_save(flags);
767 rcu_eqs_exit(false);
768 local_irq_restore(flags);
769}
770
771#ifdef CONFIG_NO_HZ_FULL
772/**
773 * rcu_user_exit - inform RCU that we are exiting userspace.
774 *
775 * Exit RCU idle mode while entering the kernel because it can
776 * run a RCU read side critical section anytime.
777 *
778 * If you add or remove a call to rcu_user_exit(), be sure to test with
779 * CONFIG_RCU_EQS_DEBUG=y.
780 */
781void rcu_user_exit(void)
782{
783 rcu_eqs_exit(1);
784}
785#endif /* CONFIG_NO_HZ_FULL */
786
787/**
788 * rcu_nmi_enter_common - inform RCU of entry to NMI context
789 * @irq: Is this call from rcu_irq_enter?
790 *
791 * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
792 * rdp->dynticks_nmi_nesting to let the RCU grace-period handling know
793 * that the CPU is active. This implementation permits nested NMIs, as
794 * long as the nesting level does not overflow an int. (You will probably
795 * run out of stack space first.)
796 *
797 * If you add or remove a call to rcu_nmi_enter_common(), be sure to test
798 * with CONFIG_RCU_EQS_DEBUG=y.
799 */
800static __always_inline void rcu_nmi_enter_common(bool irq)
801{
802 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
803 long incby = 2;
804
805 /* Complain about underflow. */
806 WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
807
808 /*
809 * If idle from RCU viewpoint, atomically increment ->dynticks
810 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
811 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
812 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
813 * to be in the outermost NMI handler that interrupted an RCU-idle
814 * period (observation due to Andy Lutomirski).
815 */
816 if (rcu_dynticks_curr_cpu_in_eqs()) {
817
818 if (irq)
819 rcu_dynticks_task_exit();
820
821 rcu_dynticks_eqs_exit();
822
823 if (irq)
824 rcu_cleanup_after_idle();
825
826 incby = 1;
827 }
828 trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
829 rdp->dynticks_nmi_nesting,
830 rdp->dynticks_nmi_nesting + incby, rdp->dynticks);
831 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
832 rdp->dynticks_nmi_nesting + incby);
833 barrier();
834}
835
836/**
837 * rcu_nmi_enter - inform RCU of entry to NMI context
838 */
839void rcu_nmi_enter(void)
840{
841 rcu_nmi_enter_common(false);
842}
843NOKPROBE_SYMBOL(rcu_nmi_enter);
844
845/**
846 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
847 *
848 * Enter an interrupt handler, which might possibly result in exiting
849 * idle mode, in other words, entering the mode in which read-side critical
850 * sections can occur. The caller must have disabled interrupts.
851 *
852 * Note that the Linux kernel is fully capable of entering an interrupt
853 * handler that it never exits, for example when doing upcalls to user mode!
854 * This code assumes that the idle loop never does upcalls to user mode.
855 * If your architecture's idle loop does do upcalls to user mode (or does
856 * anything else that results in unbalanced calls to the irq_enter() and
857 * irq_exit() functions), RCU will give you what you deserve, good and hard.
858 * But very infrequently and irreproducibly.
859 *
860 * Use things like work queues to work around this limitation.
861 *
862 * You have been warned.
863 *
864 * If you add or remove a call to rcu_irq_enter(), be sure to test with
865 * CONFIG_RCU_EQS_DEBUG=y.
866 */
867void rcu_irq_enter(void)
868{
869 lockdep_assert_irqs_disabled();
870 rcu_nmi_enter_common(true);
871}
872
873/*
874 * Wrapper for rcu_irq_enter() where interrupts are enabled.
875 *
876 * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
877 * with CONFIG_RCU_EQS_DEBUG=y.
878 */
879void rcu_irq_enter_irqson(void)
880{
881 unsigned long flags;
882
883 local_irq_save(flags);
884 rcu_irq_enter();
885 local_irq_restore(flags);
886}
887
888/**
889 * rcu_is_watching - see if RCU thinks that the current CPU is not idle
890 *
891 * Return true if RCU is watching the running CPU, which means that this
892 * CPU can safely enter RCU read-side critical sections. In other words,
893 * if the current CPU is not in its idle loop or is in an interrupt or
894 * NMI handler, return true.
895 */
896bool notrace rcu_is_watching(void)
897{
898 bool ret;
899
900 preempt_disable_notrace();
901 ret = !rcu_dynticks_curr_cpu_in_eqs();
902 preempt_enable_notrace();
903 return ret;
904}
905EXPORT_SYMBOL_GPL(rcu_is_watching);
906
907/*
908 * If a holdout task is actually running, request an urgent quiescent
909 * state from its CPU. This is unsynchronized, so migrations can cause
910 * the request to go to the wrong CPU. Which is OK, all that will happen
911 * is that the CPU's next context switch will be a bit slower and next
912 * time around this task will generate another request.
913 */
914void rcu_request_urgent_qs_task(struct task_struct *t)
915{
916 int cpu;
917
918 barrier();
919 cpu = task_cpu(t);
920 if (!task_curr(t))
921 return; /* This task is not running on that CPU. */
922 smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
923}
924
925#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
926
927/*
928 * Is the current CPU online as far as RCU is concerned?
929 *
930 * Disable preemption to avoid false positives that could otherwise
931 * happen due to the current CPU number being sampled, this task being
932 * preempted, its old CPU being taken offline, resuming on some other CPU,
933 * then determining that its old CPU is now offline.
934 *
935 * Disable checking if in an NMI handler because we cannot safely
936 * report errors from NMI handlers anyway. In addition, it is OK to use
937 * RCU on an offline processor during initial boot, hence the check for
938 * rcu_scheduler_fully_active.
939 */
940bool rcu_lockdep_current_cpu_online(void)
941{
942 struct rcu_data *rdp;
943 struct rcu_node *rnp;
944 bool ret = false;
945
946 if (in_nmi() || !rcu_scheduler_fully_active)
947 return true;
948 preempt_disable();
949 rdp = this_cpu_ptr(&rcu_data);
950 rnp = rdp->mynode;
951 if (rdp->grpmask & rcu_rnp_online_cpus(rnp))
952 ret = true;
953 preempt_enable();
954 return ret;
955}
956EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
957
958#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
959
960/*
961 * We are reporting a quiescent state on behalf of some other CPU, so
962 * it is our responsibility to check for and handle potential overflow
963 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
964 * After all, the CPU might be in deep idle state, and thus executing no
965 * code whatsoever.
966 */
967static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
968{
969 raw_lockdep_assert_held_rcu_node(rnp);
970 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
971 rnp->gp_seq))
972 WRITE_ONCE(rdp->gpwrap, true);
973 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
974 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
975}
976
977/*
978 * Snapshot the specified CPU's dynticks counter so that we can later
979 * credit them with an implicit quiescent state. Return 1 if this CPU
980 * is in dynticks idle mode, which is an extended quiescent state.
981 */
982static int dyntick_save_progress_counter(struct rcu_data *rdp)
983{
984 rdp->dynticks_snap = rcu_dynticks_snap(rdp);
985 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
986 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
987 rcu_gpnum_ovf(rdp->mynode, rdp);
988 return 1;
989 }
990 return 0;
991}
992
993/*
994 * Return true if the specified CPU has passed through a quiescent
995 * state by virtue of being in or having passed through an dynticks
996 * idle state since the last call to dyntick_save_progress_counter()
997 * for this same CPU, or by virtue of having been offline.
998 */
999static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1000{
1001 unsigned long jtsq;
1002 bool *rnhqp;
1003 bool *ruqp;
1004 struct rcu_node *rnp = rdp->mynode;
1005
1006 /*
1007 * If the CPU passed through or entered a dynticks idle phase with
1008 * no active irq/NMI handlers, then we can safely pretend that the CPU
1009 * already acknowledged the request to pass through a quiescent
1010 * state. Either way, that CPU cannot possibly be in an RCU
1011 * read-side critical section that started before the beginning
1012 * of the current RCU grace period.
1013 */
1014 if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
1015 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1016 rcu_gpnum_ovf(rnp, rdp);
1017 return 1;
1018 }
1019
1020 /* If waiting too long on an offline CPU, complain. */
1021 if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) &&
1022 time_after(jiffies, rcu_state.gp_start + HZ)) {
1023 bool onl;
1024 struct rcu_node *rnp1;
1025
1026 WARN_ON(1); /* Offline CPUs are supposed to report QS! */
1027 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
1028 __func__, rnp->grplo, rnp->grphi, rnp->level,
1029 (long)rnp->gp_seq, (long)rnp->completedqs);
1030 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
1031 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
1032 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
1033 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
1034 pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
1035 __func__, rdp->cpu, ".o"[onl],
1036 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
1037 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
1038 return 1; /* Break things loose after complaining. */
1039 }
1040
1041 /*
1042 * A CPU running for an extended time within the kernel can
1043 * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
1044 * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
1045 * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
1046 * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
1047 * variable are safe because the assignments are repeated if this
1048 * CPU failed to pass through a quiescent state. This code
1049 * also checks .jiffies_resched in case jiffies_to_sched_qs
1050 * is set way high.
1051 */
1052 jtsq = READ_ONCE(jiffies_to_sched_qs);
1053 ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu);
1054 rnhqp = &per_cpu(rcu_data.rcu_need_heavy_qs, rdp->cpu);
1055 if (!READ_ONCE(*rnhqp) &&
1056 (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
1057 time_after(jiffies, rcu_state.jiffies_resched))) {
1058 WRITE_ONCE(*rnhqp, true);
1059 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1060 smp_store_release(ruqp, true);
1061 } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
1062 WRITE_ONCE(*ruqp, true);
1063 }
1064
1065 /*
1066 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
1067 * The above code handles this, but only for straight cond_resched().
1068 * And some in-kernel loops check need_resched() before calling
1069 * cond_resched(), which defeats the above code for CPUs that are
1070 * running in-kernel with scheduling-clock interrupts disabled.
1071 * So hit them over the head with the resched_cpu() hammer!
1072 */
1073 if (tick_nohz_full_cpu(rdp->cpu) &&
1074 time_after(jiffies,
1075 READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
1076 resched_cpu(rdp->cpu);
1077 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1078 }
1079
1080 /*
1081 * If more than halfway to RCU CPU stall-warning time, invoke
1082 * resched_cpu() more frequently to try to loosen things up a bit.
1083 * Also check to see if the CPU is getting hammered with interrupts,
1084 * but only once per grace period, just to keep the IPIs down to
1085 * a dull roar.
1086 */
1087 if (time_after(jiffies, rcu_state.jiffies_resched)) {
1088 if (time_after(jiffies,
1089 READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
1090 resched_cpu(rdp->cpu);
1091 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1092 }
1093 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1094 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
1095 (rnp->ffmask & rdp->grpmask)) {
1096 init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
1097 rdp->rcu_iw_pending = true;
1098 rdp->rcu_iw_gp_seq = rnp->gp_seq;
1099 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1100 }
1101 }
1102
1103 return 0;
1104}
1105
1106/* Trace-event wrapper function for trace_rcu_future_grace_period. */
1107static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1108 unsigned long gp_seq_req, const char *s)
1109{
1110 trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req,
1111 rnp->level, rnp->grplo, rnp->grphi, s);
1112}
1113
1114/*
1115 * rcu_start_this_gp - Request the start of a particular grace period
1116 * @rnp_start: The leaf node of the CPU from which to start.
1117 * @rdp: The rcu_data corresponding to the CPU from which to start.
1118 * @gp_seq_req: The gp_seq of the grace period to start.
1119 *
1120 * Start the specified grace period, as needed to handle newly arrived
1121 * callbacks. The required future grace periods are recorded in each
1122 * rcu_node structure's ->gp_seq_needed field. Returns true if there
1123 * is reason to awaken the grace-period kthread.
1124 *
1125 * The caller must hold the specified rcu_node structure's ->lock, which
1126 * is why the caller is responsible for waking the grace-period kthread.
1127 *
1128 * Returns true if the GP thread needs to be awakened else false.
1129 */
1130static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
1131 unsigned long gp_seq_req)
1132{
1133 bool ret = false;
1134 struct rcu_node *rnp;
1135
1136 /*
1137 * Use funnel locking to either acquire the root rcu_node
1138 * structure's lock or bail out if the need for this grace period
1139 * has already been recorded -- or if that grace period has in
1140 * fact already started. If there is already a grace period in
1141 * progress in a non-leaf node, no recording is needed because the
1142 * end of the grace period will scan the leaf rcu_node structures.
1143 * Note that rnp_start->lock must not be released.
1144 */
1145 raw_lockdep_assert_held_rcu_node(rnp_start);
1146 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
1147 for (rnp = rnp_start; 1; rnp = rnp->parent) {
1148 if (rnp != rnp_start)
1149 raw_spin_lock_rcu_node(rnp);
1150 if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
1151 rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
1152 (rnp != rnp_start &&
1153 rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
1154 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
1155 TPS("Prestarted"));
1156 goto unlock_out;
1157 }
1158 rnp->gp_seq_needed = gp_seq_req;
1159 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
1160 /*
1161 * We just marked the leaf or internal node, and a
1162 * grace period is in progress, which means that
1163 * rcu_gp_cleanup() will see the marking. Bail to
1164 * reduce contention.
1165 */
1166 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
1167 TPS("Startedleaf"));
1168 goto unlock_out;
1169 }
1170 if (rnp != rnp_start && rnp->parent != NULL)
1171 raw_spin_unlock_rcu_node(rnp);
1172 if (!rnp->parent)
1173 break; /* At root, and perhaps also leaf. */
1174 }
1175
1176 /* If GP already in progress, just leave, otherwise start one. */
1177 if (rcu_gp_in_progress()) {
1178 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
1179 goto unlock_out;
1180 }
1181 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
1182 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
1183 rcu_state.gp_req_activity = jiffies;
1184 if (!rcu_state.gp_kthread) {
1185 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
1186 goto unlock_out;
1187 }
1188 trace_rcu_grace_period(rcu_state.name, READ_ONCE(rcu_state.gp_seq), TPS("newreq"));
1189 ret = true; /* Caller must wake GP kthread. */
1190unlock_out:
1191 /* Push furthest requested GP to leaf node and rcu_data structure. */
1192 if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
1193 rnp_start->gp_seq_needed = rnp->gp_seq_needed;
1194 rdp->gp_seq_needed = rnp->gp_seq_needed;
1195 }
1196 if (rnp != rnp_start)
1197 raw_spin_unlock_rcu_node(rnp);
1198 return ret;
1199}
1200
1201/*
1202 * Clean up any old requests for the just-ended grace period. Also return
1203 * whether any additional grace periods have been requested.
1204 */
1205static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
1206{
1207 bool needmore;
1208 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1209
1210 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1211 if (!needmore)
1212 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1213 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1214 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1215 return needmore;
1216}
1217
1218/*
1219 * Awaken the grace-period kthread. Don't do a self-awaken (unless in
1220 * an interrupt or softirq handler), and don't bother awakening when there
1221 * is nothing for the grace-period kthread to do (as in several CPUs raced
1222 * to awaken, and we lost), and finally don't try to awaken a kthread that
1223 * has not yet been created. If all those checks are passed, track some
1224 * debug information and awaken.
1225 *
1226 * So why do the self-wakeup when in an interrupt or softirq handler
1227 * in the grace-period kthread's context? Because the kthread might have
1228 * been interrupted just as it was going to sleep, and just after the final
1229 * pre-sleep check of the awaken condition. In this case, a wakeup really
1230 * is required, and is therefore supplied.
1231 */
1232static void rcu_gp_kthread_wake(void)
1233{
1234 if ((current == rcu_state.gp_kthread &&
1235 !in_irq() && !in_serving_softirq()) ||
1236 !READ_ONCE(rcu_state.gp_flags) ||
1237 !rcu_state.gp_kthread)
1238 return;
1239 WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
1240 WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
1241 swake_up_one(&rcu_state.gp_wq);
1242}
1243
1244/*
1245 * If there is room, assign a ->gp_seq number to any callbacks on this
1246 * CPU that have not already been assigned. Also accelerate any callbacks
1247 * that were previously assigned a ->gp_seq number that has since proven
1248 * to be too conservative, which can happen if callbacks get assigned a
1249 * ->gp_seq number while RCU is idle, but with reference to a non-root
1250 * rcu_node structure. This function is idempotent, so it does not hurt
1251 * to call it repeatedly. Returns an flag saying that we should awaken
1252 * the RCU grace-period kthread.
1253 *
1254 * The caller must hold rnp->lock with interrupts disabled.
1255 */
1256static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1257{
1258 unsigned long gp_seq_req;
1259 bool ret = false;
1260
1261 rcu_lockdep_assert_cblist_protected(rdp);
1262 raw_lockdep_assert_held_rcu_node(rnp);
1263
1264 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1265 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1266 return false;
1267
1268 /*
1269 * Callbacks are often registered with incomplete grace-period
1270 * information. Something about the fact that getting exact
1271 * information requires acquiring a global lock... RCU therefore
1272 * makes a conservative estimate of the grace period number at which
1273 * a given callback will become ready to invoke. The following
1274 * code checks this estimate and improves it when possible, thus
1275 * accelerating callback invocation to an earlier grace-period
1276 * number.
1277 */
1278 gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
1279 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1280 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1281
1282 /* Trace depending on how much we were able to accelerate. */
1283 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1284 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccWaitCB"));
1285 else
1286 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccReadyCB"));
1287 return ret;
1288}
1289
1290/*
1291 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1292 * rcu_node structure's ->lock be held. It consults the cached value
1293 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1294 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1295 * while holding the leaf rcu_node structure's ->lock.
1296 */
1297static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
1298 struct rcu_data *rdp)
1299{
1300 unsigned long c;
1301 bool needwake;
1302
1303 rcu_lockdep_assert_cblist_protected(rdp);
1304 c = rcu_seq_snap(&rcu_state.gp_seq);
1305 if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1306 /* Old request still live, so mark recent callbacks. */
1307 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1308 return;
1309 }
1310 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1311 needwake = rcu_accelerate_cbs(rnp, rdp);
1312 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1313 if (needwake)
1314 rcu_gp_kthread_wake();
1315}
1316
1317/*
1318 * Move any callbacks whose grace period has completed to the
1319 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1320 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1321 * sublist. This function is idempotent, so it does not hurt to
1322 * invoke it repeatedly. As long as it is not invoked -too- often...
1323 * Returns true if the RCU grace-period kthread needs to be awakened.
1324 *
1325 * The caller must hold rnp->lock with interrupts disabled.
1326 */
1327static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1328{
1329 rcu_lockdep_assert_cblist_protected(rdp);
1330 raw_lockdep_assert_held_rcu_node(rnp);
1331
1332 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1333 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1334 return false;
1335
1336 /*
1337 * Find all callbacks whose ->gp_seq numbers indicate that they
1338 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1339 */
1340 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1341
1342 /* Classify any remaining callbacks. */
1343 return rcu_accelerate_cbs(rnp, rdp);
1344}
1345
1346/*
1347 * Move and classify callbacks, but only if doing so won't require
1348 * that the RCU grace-period kthread be awakened.
1349 */
1350static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
1351 struct rcu_data *rdp)
1352{
1353 rcu_lockdep_assert_cblist_protected(rdp);
1354 if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
1355 !raw_spin_trylock_rcu_node(rnp))
1356 return;
1357 WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
1358 raw_spin_unlock_rcu_node(rnp);
1359}
1360
1361/*
1362 * Update CPU-local rcu_data state to record the beginnings and ends of
1363 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1364 * structure corresponding to the current CPU, and must have irqs disabled.
1365 * Returns true if the grace-period kthread needs to be awakened.
1366 */
1367static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
1368{
1369 bool ret = false;
1370 bool need_gp;
1371 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1372 rcu_segcblist_is_offloaded(&rdp->cblist);
1373
1374 raw_lockdep_assert_held_rcu_node(rnp);
1375
1376 if (rdp->gp_seq == rnp->gp_seq)
1377 return false; /* Nothing to do. */
1378
1379 /* Handle the ends of any preceding grace periods first. */
1380 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1381 unlikely(READ_ONCE(rdp->gpwrap))) {
1382 if (!offloaded)
1383 ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
1384 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
1385 } else {
1386 if (!offloaded)
1387 ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
1388 }
1389
1390 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1391 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1392 unlikely(READ_ONCE(rdp->gpwrap))) {
1393 /*
1394 * If the current grace period is waiting for this CPU,
1395 * set up to detect a quiescent state, otherwise don't
1396 * go looking for one.
1397 */
1398 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
1399 need_gp = !!(rnp->qsmask & rdp->grpmask);
1400 rdp->cpu_no_qs.b.norm = need_gp;
1401 rdp->core_needs_qs = need_gp;
1402 zero_cpu_stall_ticks(rdp);
1403 }
1404 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1405 if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
1406 rdp->gp_seq_needed = rnp->gp_seq_needed;
1407 WRITE_ONCE(rdp->gpwrap, false);
1408 rcu_gpnum_ovf(rnp, rdp);
1409 return ret;
1410}
1411
1412static void note_gp_changes(struct rcu_data *rdp)
1413{
1414 unsigned long flags;
1415 bool needwake;
1416 struct rcu_node *rnp;
1417
1418 local_irq_save(flags);
1419 rnp = rdp->mynode;
1420 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1421 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1422 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1423 local_irq_restore(flags);
1424 return;
1425 }
1426 needwake = __note_gp_changes(rnp, rdp);
1427 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1428 if (needwake)
1429 rcu_gp_kthread_wake();
1430}
1431
1432static void rcu_gp_slow(int delay)
1433{
1434 if (delay > 0 &&
1435 !(rcu_seq_ctr(rcu_state.gp_seq) %
1436 (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1437 schedule_timeout_uninterruptible(delay);
1438}
1439
1440/*
1441 * Initialize a new grace period. Return false if no grace period required.
1442 */
1443static bool rcu_gp_init(void)
1444{
1445 unsigned long flags;
1446 unsigned long oldmask;
1447 unsigned long mask;
1448 struct rcu_data *rdp;
1449 struct rcu_node *rnp = rcu_get_root();
1450
1451 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1452 raw_spin_lock_irq_rcu_node(rnp);
1453 if (!READ_ONCE(rcu_state.gp_flags)) {
1454 /* Spurious wakeup, tell caller to go back to sleep. */
1455 raw_spin_unlock_irq_rcu_node(rnp);
1456 return false;
1457 }
1458 WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
1459
1460 if (WARN_ON_ONCE(rcu_gp_in_progress())) {
1461 /*
1462 * Grace period already in progress, don't start another.
1463 * Not supposed to be able to happen.
1464 */
1465 raw_spin_unlock_irq_rcu_node(rnp);
1466 return false;
1467 }
1468
1469 /* Advance to a new grace period and initialize state. */
1470 record_gp_stall_check_time();
1471 /* Record GP times before starting GP, hence rcu_seq_start(). */
1472 rcu_seq_start(&rcu_state.gp_seq);
1473 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
1474 raw_spin_unlock_irq_rcu_node(rnp);
1475
1476 /*
1477 * Apply per-leaf buffered online and offline operations to the
1478 * rcu_node tree. Note that this new grace period need not wait
1479 * for subsequent online CPUs, and that quiescent-state forcing
1480 * will handle subsequent offline CPUs.
1481 */
1482 rcu_state.gp_state = RCU_GP_ONOFF;
1483 rcu_for_each_leaf_node(rnp) {
1484 raw_spin_lock(&rcu_state.ofl_lock);
1485 raw_spin_lock_irq_rcu_node(rnp);
1486 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1487 !rnp->wait_blkd_tasks) {
1488 /* Nothing to do on this leaf rcu_node structure. */
1489 raw_spin_unlock_irq_rcu_node(rnp);
1490 raw_spin_unlock(&rcu_state.ofl_lock);
1491 continue;
1492 }
1493
1494 /* Record old state, apply changes to ->qsmaskinit field. */
1495 oldmask = rnp->qsmaskinit;
1496 rnp->qsmaskinit = rnp->qsmaskinitnext;
1497
1498 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1499 if (!oldmask != !rnp->qsmaskinit) {
1500 if (!oldmask) { /* First online CPU for rcu_node. */
1501 if (!rnp->wait_blkd_tasks) /* Ever offline? */
1502 rcu_init_new_rnp(rnp);
1503 } else if (rcu_preempt_has_tasks(rnp)) {
1504 rnp->wait_blkd_tasks = true; /* blocked tasks */
1505 } else { /* Last offline CPU and can propagate. */
1506 rcu_cleanup_dead_rnp(rnp);
1507 }
1508 }
1509
1510 /*
1511 * If all waited-on tasks from prior grace period are
1512 * done, and if all this rcu_node structure's CPUs are
1513 * still offline, propagate up the rcu_node tree and
1514 * clear ->wait_blkd_tasks. Otherwise, if one of this
1515 * rcu_node structure's CPUs has since come back online,
1516 * simply clear ->wait_blkd_tasks.
1517 */
1518 if (rnp->wait_blkd_tasks &&
1519 (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
1520 rnp->wait_blkd_tasks = false;
1521 if (!rnp->qsmaskinit)
1522 rcu_cleanup_dead_rnp(rnp);
1523 }
1524
1525 raw_spin_unlock_irq_rcu_node(rnp);
1526 raw_spin_unlock(&rcu_state.ofl_lock);
1527 }
1528 rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
1529
1530 /*
1531 * Set the quiescent-state-needed bits in all the rcu_node
1532 * structures for all currently online CPUs in breadth-first
1533 * order, starting from the root rcu_node structure, relying on the
1534 * layout of the tree within the rcu_state.node[] array. Note that
1535 * other CPUs will access only the leaves of the hierarchy, thus
1536 * seeing that no grace period is in progress, at least until the
1537 * corresponding leaf node has been initialized.
1538 *
1539 * The grace period cannot complete until the initialization
1540 * process finishes, because this kthread handles both.
1541 */
1542 rcu_state.gp_state = RCU_GP_INIT;
1543 rcu_for_each_node_breadth_first(rnp) {
1544 rcu_gp_slow(gp_init_delay);
1545 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1546 rdp = this_cpu_ptr(&rcu_data);
1547 rcu_preempt_check_blocked_tasks(rnp);
1548 rnp->qsmask = rnp->qsmaskinit;
1549 WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
1550 if (rnp == rdp->mynode)
1551 (void)__note_gp_changes(rnp, rdp);
1552 rcu_preempt_boost_start_gp(rnp);
1553 trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
1554 rnp->level, rnp->grplo,
1555 rnp->grphi, rnp->qsmask);
1556 /* Quiescent states for tasks on any now-offline CPUs. */
1557 mask = rnp->qsmask & ~rnp->qsmaskinitnext;
1558 rnp->rcu_gp_init_mask = mask;
1559 if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
1560 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1561 else
1562 raw_spin_unlock_irq_rcu_node(rnp);
1563 cond_resched_tasks_rcu_qs();
1564 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1565 }
1566
1567 return true;
1568}
1569
1570/*
1571 * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
1572 * time.
1573 */
1574static bool rcu_gp_fqs_check_wake(int *gfp)
1575{
1576 struct rcu_node *rnp = rcu_get_root();
1577
1578 /* Someone like call_rcu() requested a force-quiescent-state scan. */
1579 *gfp = READ_ONCE(rcu_state.gp_flags);
1580 if (*gfp & RCU_GP_FLAG_FQS)
1581 return true;
1582
1583 /* The current grace period has completed. */
1584 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1585 return true;
1586
1587 return false;
1588}
1589
1590/*
1591 * Do one round of quiescent-state forcing.
1592 */
1593static void rcu_gp_fqs(bool first_time)
1594{
1595 struct rcu_node *rnp = rcu_get_root();
1596
1597 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1598 rcu_state.n_force_qs++;
1599 if (first_time) {
1600 /* Collect dyntick-idle snapshots. */
1601 force_qs_rnp(dyntick_save_progress_counter);
1602 } else {
1603 /* Handle dyntick-idle and offline CPUs. */
1604 force_qs_rnp(rcu_implicit_dynticks_qs);
1605 }
1606 /* Clear flag to prevent immediate re-entry. */
1607 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
1608 raw_spin_lock_irq_rcu_node(rnp);
1609 WRITE_ONCE(rcu_state.gp_flags,
1610 READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
1611 raw_spin_unlock_irq_rcu_node(rnp);
1612 }
1613}
1614
1615/*
1616 * Loop doing repeated quiescent-state forcing until the grace period ends.
1617 */
1618static void rcu_gp_fqs_loop(void)
1619{
1620 bool first_gp_fqs;
1621 int gf;
1622 unsigned long j;
1623 int ret;
1624 struct rcu_node *rnp = rcu_get_root();
1625
1626 first_gp_fqs = true;
1627 j = READ_ONCE(jiffies_till_first_fqs);
1628 ret = 0;
1629 for (;;) {
1630 if (!ret) {
1631 rcu_state.jiffies_force_qs = jiffies + j;
1632 WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
1633 jiffies + (j ? 3 * j : 2));
1634 }
1635 trace_rcu_grace_period(rcu_state.name,
1636 READ_ONCE(rcu_state.gp_seq),
1637 TPS("fqswait"));
1638 rcu_state.gp_state = RCU_GP_WAIT_FQS;
1639 ret = swait_event_idle_timeout_exclusive(
1640 rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
1641 rcu_state.gp_state = RCU_GP_DOING_FQS;
1642 /* Locking provides needed memory barriers. */
1643 /* If grace period done, leave loop. */
1644 if (!READ_ONCE(rnp->qsmask) &&
1645 !rcu_preempt_blocked_readers_cgp(rnp))
1646 break;
1647 /* If time for quiescent-state forcing, do it. */
1648 if (ULONG_CMP_GE(jiffies, rcu_state.jiffies_force_qs) ||
1649 (gf & RCU_GP_FLAG_FQS)) {
1650 trace_rcu_grace_period(rcu_state.name,
1651 READ_ONCE(rcu_state.gp_seq),
1652 TPS("fqsstart"));
1653 rcu_gp_fqs(first_gp_fqs);
1654 first_gp_fqs = false;
1655 trace_rcu_grace_period(rcu_state.name,
1656 READ_ONCE(rcu_state.gp_seq),
1657 TPS("fqsend"));
1658 cond_resched_tasks_rcu_qs();
1659 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1660 ret = 0; /* Force full wait till next FQS. */
1661 j = READ_ONCE(jiffies_till_next_fqs);
1662 } else {
1663 /* Deal with stray signal. */
1664 cond_resched_tasks_rcu_qs();
1665 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1666 WARN_ON(signal_pending(current));
1667 trace_rcu_grace_period(rcu_state.name,
1668 READ_ONCE(rcu_state.gp_seq),
1669 TPS("fqswaitsig"));
1670 ret = 1; /* Keep old FQS timing. */
1671 j = jiffies;
1672 if (time_after(jiffies, rcu_state.jiffies_force_qs))
1673 j = 1;
1674 else
1675 j = rcu_state.jiffies_force_qs - j;
1676 }
1677 }
1678}
1679
1680/*
1681 * Clean up after the old grace period.
1682 */
1683static void rcu_gp_cleanup(void)
1684{
1685 unsigned long gp_duration;
1686 bool needgp = false;
1687 unsigned long new_gp_seq;
1688 bool offloaded;
1689 struct rcu_data *rdp;
1690 struct rcu_node *rnp = rcu_get_root();
1691 struct swait_queue_head *sq;
1692
1693 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1694 raw_spin_lock_irq_rcu_node(rnp);
1695 rcu_state.gp_end = jiffies;
1696 gp_duration = rcu_state.gp_end - rcu_state.gp_start;
1697 if (gp_duration > rcu_state.gp_max)
1698 rcu_state.gp_max = gp_duration;
1699
1700 /*
1701 * We know the grace period is complete, but to everyone else
1702 * it appears to still be ongoing. But it is also the case
1703 * that to everyone else it looks like there is nothing that
1704 * they can do to advance the grace period. It is therefore
1705 * safe for us to drop the lock in order to mark the grace
1706 * period as completed in all of the rcu_node structures.
1707 */
1708 raw_spin_unlock_irq_rcu_node(rnp);
1709
1710 /*
1711 * Propagate new ->gp_seq value to rcu_node structures so that
1712 * other CPUs don't have to wait until the start of the next grace
1713 * period to process their callbacks. This also avoids some nasty
1714 * RCU grace-period initialization races by forcing the end of
1715 * the current grace period to be completely recorded in all of
1716 * the rcu_node structures before the beginning of the next grace
1717 * period is recorded in any of the rcu_node structures.
1718 */
1719 new_gp_seq = rcu_state.gp_seq;
1720 rcu_seq_end(&new_gp_seq);
1721 rcu_for_each_node_breadth_first(rnp) {
1722 raw_spin_lock_irq_rcu_node(rnp);
1723 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
1724 dump_blkd_tasks(rnp, 10);
1725 WARN_ON_ONCE(rnp->qsmask);
1726 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
1727 rdp = this_cpu_ptr(&rcu_data);
1728 if (rnp == rdp->mynode)
1729 needgp = __note_gp_changes(rnp, rdp) || needgp;
1730 /* smp_mb() provided by prior unlock-lock pair. */
1731 needgp = rcu_future_gp_cleanup(rnp) || needgp;
1732 sq = rcu_nocb_gp_get(rnp);
1733 raw_spin_unlock_irq_rcu_node(rnp);
1734 rcu_nocb_gp_cleanup(sq);
1735 cond_resched_tasks_rcu_qs();
1736 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1737 rcu_gp_slow(gp_cleanup_delay);
1738 }
1739 rnp = rcu_get_root();
1740 raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
1741
1742 /* Declare grace period done, trace first to use old GP number. */
1743 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
1744 rcu_seq_end(&rcu_state.gp_seq);
1745 rcu_state.gp_state = RCU_GP_IDLE;
1746 /* Check for GP requests since above loop. */
1747 rdp = this_cpu_ptr(&rcu_data);
1748 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
1749 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
1750 TPS("CleanupMore"));
1751 needgp = true;
1752 }
1753 /* Advance CBs to reduce false positives below. */
1754 offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1755 rcu_segcblist_is_offloaded(&rdp->cblist);
1756 if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
1757 WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
1758 rcu_state.gp_req_activity = jiffies;
1759 trace_rcu_grace_period(rcu_state.name,
1760 READ_ONCE(rcu_state.gp_seq),
1761 TPS("newreq"));
1762 } else {
1763 WRITE_ONCE(rcu_state.gp_flags,
1764 rcu_state.gp_flags & RCU_GP_FLAG_INIT);
1765 }
1766 raw_spin_unlock_irq_rcu_node(rnp);
1767}
1768
1769/*
1770 * Body of kthread that handles grace periods.
1771 */
1772static int __noreturn rcu_gp_kthread(void *unused)
1773{
1774 rcu_bind_gp_kthread();
1775 for (;;) {
1776
1777 /* Handle grace-period start. */
1778 for (;;) {
1779 trace_rcu_grace_period(rcu_state.name,
1780 READ_ONCE(rcu_state.gp_seq),
1781 TPS("reqwait"));
1782 rcu_state.gp_state = RCU_GP_WAIT_GPS;
1783 swait_event_idle_exclusive(rcu_state.gp_wq,
1784 READ_ONCE(rcu_state.gp_flags) &
1785 RCU_GP_FLAG_INIT);
1786 rcu_state.gp_state = RCU_GP_DONE_GPS;
1787 /* Locking provides needed memory barrier. */
1788 if (rcu_gp_init())
1789 break;
1790 cond_resched_tasks_rcu_qs();
1791 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1792 WARN_ON(signal_pending(current));
1793 trace_rcu_grace_period(rcu_state.name,
1794 READ_ONCE(rcu_state.gp_seq),
1795 TPS("reqwaitsig"));
1796 }
1797
1798 /* Handle quiescent-state forcing. */
1799 rcu_gp_fqs_loop();
1800
1801 /* Handle grace-period end. */
1802 rcu_state.gp_state = RCU_GP_CLEANUP;
1803 rcu_gp_cleanup();
1804 rcu_state.gp_state = RCU_GP_CLEANED;
1805 }
1806}
1807
1808/*
1809 * Report a full set of quiescent states to the rcu_state data structure.
1810 * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
1811 * another grace period is required. Whether we wake the grace-period
1812 * kthread or it awakens itself for the next round of quiescent-state
1813 * forcing, that kthread will clean up after the just-completed grace
1814 * period. Note that the caller must hold rnp->lock, which is released
1815 * before return.
1816 */
1817static void rcu_report_qs_rsp(unsigned long flags)
1818 __releases(rcu_get_root()->lock)
1819{
1820 raw_lockdep_assert_held_rcu_node(rcu_get_root());
1821 WARN_ON_ONCE(!rcu_gp_in_progress());
1822 WRITE_ONCE(rcu_state.gp_flags,
1823 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
1824 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
1825 rcu_gp_kthread_wake();
1826}
1827
1828/*
1829 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1830 * Allows quiescent states for a group of CPUs to be reported at one go
1831 * to the specified rcu_node structure, though all the CPUs in the group
1832 * must be represented by the same rcu_node structure (which need not be a
1833 * leaf rcu_node structure, though it often will be). The gps parameter
1834 * is the grace-period snapshot, which means that the quiescent states
1835 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
1836 * must be held upon entry, and it is released before return.
1837 *
1838 * As a special case, if mask is zero, the bit-already-cleared check is
1839 * disabled. This allows propagating quiescent state due to resumed tasks
1840 * during grace-period initialization.
1841 */
1842static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
1843 unsigned long gps, unsigned long flags)
1844 __releases(rnp->lock)
1845{
1846 unsigned long oldmask = 0;
1847 struct rcu_node *rnp_c;
1848
1849 raw_lockdep_assert_held_rcu_node(rnp);
1850
1851 /* Walk up the rcu_node hierarchy. */
1852 for (;;) {
1853 if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
1854
1855 /*
1856 * Our bit has already been cleared, or the
1857 * relevant grace period is already over, so done.
1858 */
1859 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1860 return;
1861 }
1862 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
1863 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
1864 rcu_preempt_blocked_readers_cgp(rnp));
1865 rnp->qsmask &= ~mask;
1866 trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
1867 mask, rnp->qsmask, rnp->level,
1868 rnp->grplo, rnp->grphi,
1869 !!rnp->gp_tasks);
1870 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1871
1872 /* Other bits still set at this level, so done. */
1873 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1874 return;
1875 }
1876 rnp->completedqs = rnp->gp_seq;
1877 mask = rnp->grpmask;
1878 if (rnp->parent == NULL) {
1879
1880 /* No more levels. Exit loop holding root lock. */
1881
1882 break;
1883 }
1884 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1885 rnp_c = rnp;
1886 rnp = rnp->parent;
1887 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1888 oldmask = rnp_c->qsmask;
1889 }
1890
1891 /*
1892 * Get here if we are the last CPU to pass through a quiescent
1893 * state for this grace period. Invoke rcu_report_qs_rsp()
1894 * to clean up and start the next grace period if one is needed.
1895 */
1896 rcu_report_qs_rsp(flags); /* releases rnp->lock. */
1897}
1898
1899/*
1900 * Record a quiescent state for all tasks that were previously queued
1901 * on the specified rcu_node structure and that were blocking the current
1902 * RCU grace period. The caller must hold the corresponding rnp->lock with
1903 * irqs disabled, and this lock is released upon return, but irqs remain
1904 * disabled.
1905 */
1906static void __maybe_unused
1907rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1908 __releases(rnp->lock)
1909{
1910 unsigned long gps;
1911 unsigned long mask;
1912 struct rcu_node *rnp_p;
1913
1914 raw_lockdep_assert_held_rcu_node(rnp);
1915 if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPTION)) ||
1916 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
1917 rnp->qsmask != 0) {
1918 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1919 return; /* Still need more quiescent states! */
1920 }
1921
1922 rnp->completedqs = rnp->gp_seq;
1923 rnp_p = rnp->parent;
1924 if (rnp_p == NULL) {
1925 /*
1926 * Only one rcu_node structure in the tree, so don't
1927 * try to report up to its nonexistent parent!
1928 */
1929 rcu_report_qs_rsp(flags);
1930 return;
1931 }
1932
1933 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
1934 gps = rnp->gp_seq;
1935 mask = rnp->grpmask;
1936 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1937 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
1938 rcu_report_qs_rnp(mask, rnp_p, gps, flags);
1939}
1940
1941/*
1942 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1943 * structure. This must be called from the specified CPU.
1944 */
1945static void
1946rcu_report_qs_rdp(int cpu, struct rcu_data *rdp)
1947{
1948 unsigned long flags;
1949 unsigned long mask;
1950 bool needwake = false;
1951 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1952 rcu_segcblist_is_offloaded(&rdp->cblist);
1953 struct rcu_node *rnp;
1954
1955 rnp = rdp->mynode;
1956 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1957 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
1958 rdp->gpwrap) {
1959
1960 /*
1961 * The grace period in which this quiescent state was
1962 * recorded has ended, so don't report it upwards.
1963 * We will instead need a new quiescent state that lies
1964 * within the current grace period.
1965 */
1966 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
1967 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1968 return;
1969 }
1970 mask = rdp->grpmask;
1971 rdp->core_needs_qs = false;
1972 if ((rnp->qsmask & mask) == 0) {
1973 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1974 } else {
1975 /*
1976 * This GP can't end until cpu checks in, so all of our
1977 * callbacks can be processed during the next GP.
1978 */
1979 if (!offloaded)
1980 needwake = rcu_accelerate_cbs(rnp, rdp);
1981
1982 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1983 /* ^^^ Released rnp->lock */
1984 if (needwake)
1985 rcu_gp_kthread_wake();
1986 }
1987}
1988
1989/*
1990 * Check to see if there is a new grace period of which this CPU
1991 * is not yet aware, and if so, set up local rcu_data state for it.
1992 * Otherwise, see if this CPU has just passed through its first
1993 * quiescent state for this grace period, and record that fact if so.
1994 */
1995static void
1996rcu_check_quiescent_state(struct rcu_data *rdp)
1997{
1998 /* Check for grace-period ends and beginnings. */
1999 note_gp_changes(rdp);
2000
2001 /*
2002 * Does this CPU still need to do its part for current grace period?
2003 * If no, return and let the other CPUs do their part as well.
2004 */
2005 if (!rdp->core_needs_qs)
2006 return;
2007
2008 /*
2009 * Was there a quiescent state since the beginning of the grace
2010 * period? If no, then exit and wait for the next call.
2011 */
2012 if (rdp->cpu_no_qs.b.norm)
2013 return;
2014
2015 /*
2016 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2017 * judge of that).
2018 */
2019 rcu_report_qs_rdp(rdp->cpu, rdp);
2020}
2021
2022/*
2023 * Near the end of the offline process. Trace the fact that this CPU
2024 * is going offline.
2025 */
2026int rcutree_dying_cpu(unsigned int cpu)
2027{
2028 bool blkd;
2029 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
2030 struct rcu_node *rnp = rdp->mynode;
2031
2032 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2033 return 0;
2034
2035 blkd = !!(rnp->qsmask & rdp->grpmask);
2036 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq,
2037 blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
2038 return 0;
2039}
2040
2041/*
2042 * All CPUs for the specified rcu_node structure have gone offline,
2043 * and all tasks that were preempted within an RCU read-side critical
2044 * section while running on one of those CPUs have since exited their RCU
2045 * read-side critical section. Some other CPU is reporting this fact with
2046 * the specified rcu_node structure's ->lock held and interrupts disabled.
2047 * This function therefore goes up the tree of rcu_node structures,
2048 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2049 * the leaf rcu_node structure's ->qsmaskinit field has already been
2050 * updated.
2051 *
2052 * This function does check that the specified rcu_node structure has
2053 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2054 * prematurely. That said, invoking it after the fact will cost you
2055 * a needless lock acquisition. So once it has done its work, don't
2056 * invoke it again.
2057 */
2058static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2059{
2060 long mask;
2061 struct rcu_node *rnp = rnp_leaf;
2062
2063 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2064 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2065 WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
2066 WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
2067 return;
2068 for (;;) {
2069 mask = rnp->grpmask;
2070 rnp = rnp->parent;
2071 if (!rnp)
2072 break;
2073 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2074 rnp->qsmaskinit &= ~mask;
2075 /* Between grace periods, so better already be zero! */
2076 WARN_ON_ONCE(rnp->qsmask);
2077 if (rnp->qsmaskinit) {
2078 raw_spin_unlock_rcu_node(rnp);
2079 /* irqs remain disabled. */
2080 return;
2081 }
2082 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2083 }
2084}
2085
2086/*
2087 * The CPU has been completely removed, and some other CPU is reporting
2088 * this fact from process context. Do the remainder of the cleanup.
2089 * There can only be one CPU hotplug operation at a time, so no need for
2090 * explicit locking.
2091 */
2092int rcutree_dead_cpu(unsigned int cpu)
2093{
2094 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2095 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2096
2097 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2098 return 0;
2099
2100 /* Adjust any no-longer-needed kthreads. */
2101 rcu_boost_kthread_setaffinity(rnp, -1);
2102 /* Do any needed no-CB deferred wakeups from this CPU. */
2103 do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
2104 return 0;
2105}
2106
2107/*
2108 * Invoke any RCU callbacks that have made it to the end of their grace
2109 * period. Thottle as specified by rdp->blimit.
2110 */
2111static void rcu_do_batch(struct rcu_data *rdp)
2112{
2113 unsigned long flags;
2114 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2115 rcu_segcblist_is_offloaded(&rdp->cblist);
2116 struct rcu_head *rhp;
2117 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2118 long bl, count;
2119 long pending, tlimit = 0;
2120
2121 /* If no callbacks are ready, just return. */
2122 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2123 trace_rcu_batch_start(rcu_state.name,
2124 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2125 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2126 trace_rcu_batch_end(rcu_state.name, 0,
2127 !rcu_segcblist_empty(&rdp->cblist),
2128 need_resched(), is_idle_task(current),
2129 rcu_is_callbacks_kthread());
2130 return;
2131 }
2132
2133 /*
2134 * Extract the list of ready callbacks, disabling to prevent
2135 * races with call_rcu() from interrupt handlers. Leave the
2136 * callback counts, as rcu_barrier() needs to be conservative.
2137 */
2138 local_irq_save(flags);
2139 rcu_nocb_lock(rdp);
2140 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2141 pending = rcu_segcblist_n_cbs(&rdp->cblist);
2142 bl = max(rdp->blimit, pending >> rcu_divisor);
2143 if (unlikely(bl > 100))
2144 tlimit = local_clock() + rcu_resched_ns;
2145 trace_rcu_batch_start(rcu_state.name,
2146 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2147 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2148 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2149 if (offloaded)
2150 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2151 rcu_nocb_unlock_irqrestore(rdp, flags);
2152
2153 /* Invoke callbacks. */
2154 rhp = rcu_cblist_dequeue(&rcl);
2155 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2156 debug_rcu_head_unqueue(rhp);
2157 if (__rcu_reclaim(rcu_state.name, rhp))
2158 rcu_cblist_dequeued_lazy(&rcl);
2159 /*
2160 * Stop only if limit reached and CPU has something to do.
2161 * Note: The rcl structure counts down from zero.
2162 */
2163 if (-rcl.len >= bl && !offloaded &&
2164 (need_resched() ||
2165 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2166 break;
2167 if (unlikely(tlimit)) {
2168 /* only call local_clock() every 32 callbacks */
2169 if (likely((-rcl.len & 31) || local_clock() < tlimit))
2170 continue;
2171 /* Exceeded the time limit, so leave. */
2172 break;
2173 }
2174 if (offloaded) {
2175 WARN_ON_ONCE(in_serving_softirq());
2176 local_bh_enable();
2177 lockdep_assert_irqs_enabled();
2178 cond_resched_tasks_rcu_qs();
2179 lockdep_assert_irqs_enabled();
2180 local_bh_disable();
2181 }
2182 }
2183
2184 local_irq_save(flags);
2185 rcu_nocb_lock(rdp);
2186 count = -rcl.len;
2187 trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
2188 is_idle_task(current), rcu_is_callbacks_kthread());
2189
2190 /* Update counts and requeue any remaining callbacks. */
2191 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2192 smp_mb(); /* List handling before counting for rcu_barrier(). */
2193 rcu_segcblist_insert_count(&rdp->cblist, &rcl);
2194
2195 /* Reinstate batch limit if we have worked down the excess. */
2196 count = rcu_segcblist_n_cbs(&rdp->cblist);
2197 if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
2198 rdp->blimit = blimit;
2199
2200 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2201 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2202 rdp->qlen_last_fqs_check = 0;
2203 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2204 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2205 rdp->qlen_last_fqs_check = count;
2206
2207 /*
2208 * The following usually indicates a double call_rcu(). To track
2209 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2210 */
2211 WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist));
2212 WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2213 count != 0 && rcu_segcblist_empty(&rdp->cblist));
2214
2215 rcu_nocb_unlock_irqrestore(rdp, flags);
2216
2217 /* Re-invoke RCU core processing if there are callbacks remaining. */
2218 if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
2219 invoke_rcu_core();
2220}
2221
2222/*
2223 * This function is invoked from each scheduling-clock interrupt,
2224 * and checks to see if this CPU is in a non-context-switch quiescent
2225 * state, for example, user mode or idle loop. It also schedules RCU
2226 * core processing. If the current grace period has gone on too long,
2227 * it will ask the scheduler to manufacture a context switch for the sole
2228 * purpose of providing a providing the needed quiescent state.
2229 */
2230void rcu_sched_clock_irq(int user)
2231{
2232 trace_rcu_utilization(TPS("Start scheduler-tick"));
2233 raw_cpu_inc(rcu_data.ticks_this_gp);
2234 /* The load-acquire pairs with the store-release setting to true. */
2235 if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
2236 /* Idle and userspace execution already are quiescent states. */
2237 if (!rcu_is_cpu_rrupt_from_idle() && !user) {
2238 set_tsk_need_resched(current);
2239 set_preempt_need_resched();
2240 }
2241 __this_cpu_write(rcu_data.rcu_urgent_qs, false);
2242 }
2243 rcu_flavor_sched_clock_irq(user);
2244 if (rcu_pending())
2245 invoke_rcu_core();
2246
2247 trace_rcu_utilization(TPS("End scheduler-tick"));
2248}
2249
2250/*
2251 * Scan the leaf rcu_node structures. For each structure on which all
2252 * CPUs have reported a quiescent state and on which there are tasks
2253 * blocking the current grace period, initiate RCU priority boosting.
2254 * Otherwise, invoke the specified function to check dyntick state for
2255 * each CPU that has not yet reported a quiescent state.
2256 */
2257static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
2258{
2259 int cpu;
2260 unsigned long flags;
2261 unsigned long mask;
2262 struct rcu_node *rnp;
2263
2264 rcu_for_each_leaf_node(rnp) {
2265 cond_resched_tasks_rcu_qs();
2266 mask = 0;
2267 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2268 if (rnp->qsmask == 0) {
2269 if (!IS_ENABLED(CONFIG_PREEMPTION) ||
2270 rcu_preempt_blocked_readers_cgp(rnp)) {
2271 /*
2272 * No point in scanning bits because they
2273 * are all zero. But we might need to
2274 * priority-boost blocked readers.
2275 */
2276 rcu_initiate_boost(rnp, flags);
2277 /* rcu_initiate_boost() releases rnp->lock */
2278 continue;
2279 }
2280 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2281 continue;
2282 }
2283 for_each_leaf_node_possible_cpu(rnp, cpu) {
2284 unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
2285 if ((rnp->qsmask & bit) != 0) {
2286 if (f(per_cpu_ptr(&rcu_data, cpu)))
2287 mask |= bit;
2288 }
2289 }
2290 if (mask != 0) {
2291 /* Idle/offline CPUs, report (releases rnp->lock). */
2292 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2293 } else {
2294 /* Nothing to do here, so just drop the lock. */
2295 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2296 }
2297 }
2298}
2299
2300/*
2301 * Force quiescent states on reluctant CPUs, and also detect which
2302 * CPUs are in dyntick-idle mode.
2303 */
2304void rcu_force_quiescent_state(void)
2305{
2306 unsigned long flags;
2307 bool ret;
2308 struct rcu_node *rnp;
2309 struct rcu_node *rnp_old = NULL;
2310
2311 /* Funnel through hierarchy to reduce memory contention. */
2312 rnp = __this_cpu_read(rcu_data.mynode);
2313 for (; rnp != NULL; rnp = rnp->parent) {
2314 ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
2315 !raw_spin_trylock(&rnp->fqslock);
2316 if (rnp_old != NULL)
2317 raw_spin_unlock(&rnp_old->fqslock);
2318 if (ret)
2319 return;
2320 rnp_old = rnp;
2321 }
2322 /* rnp_old == rcu_get_root(), rnp == NULL. */
2323
2324 /* Reached the root of the rcu_node tree, acquire lock. */
2325 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2326 raw_spin_unlock(&rnp_old->fqslock);
2327 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
2328 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2329 return; /* Someone beat us to it. */
2330 }
2331 WRITE_ONCE(rcu_state.gp_flags,
2332 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2333 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2334 rcu_gp_kthread_wake();
2335}
2336EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
2337
2338/* Perform RCU core processing work for the current CPU. */
2339static __latent_entropy void rcu_core(void)
2340{
2341 unsigned long flags;
2342 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2343 struct rcu_node *rnp = rdp->mynode;
2344 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2345 rcu_segcblist_is_offloaded(&rdp->cblist);
2346
2347 if (cpu_is_offline(smp_processor_id()))
2348 return;
2349 trace_rcu_utilization(TPS("Start RCU core"));
2350 WARN_ON_ONCE(!rdp->beenonline);
2351
2352 /* Report any deferred quiescent states if preemption enabled. */
2353 if (!(preempt_count() & PREEMPT_MASK)) {
2354 rcu_preempt_deferred_qs(current);
2355 } else if (rcu_preempt_need_deferred_qs(current)) {
2356 set_tsk_need_resched(current);
2357 set_preempt_need_resched();
2358 }
2359
2360 /* Update RCU state based on any recent quiescent states. */
2361 rcu_check_quiescent_state(rdp);
2362
2363 /* No grace period and unregistered callbacks? */
2364 if (!rcu_gp_in_progress() &&
2365 rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
2366 local_irq_save(flags);
2367 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2368 rcu_accelerate_cbs_unlocked(rnp, rdp);
2369 local_irq_restore(flags);
2370 }
2371
2372 rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
2373
2374 /* If there are callbacks ready, invoke them. */
2375 if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) &&
2376 likely(READ_ONCE(rcu_scheduler_fully_active)))
2377 rcu_do_batch(rdp);
2378
2379 /* Do any needed deferred wakeups of rcuo kthreads. */
2380 do_nocb_deferred_wakeup(rdp);
2381 trace_rcu_utilization(TPS("End RCU core"));
2382}
2383
2384static void rcu_core_si(struct softirq_action *h)
2385{
2386 rcu_core();
2387}
2388
2389static void rcu_wake_cond(struct task_struct *t, int status)
2390{
2391 /*
2392 * If the thread is yielding, only wake it when this
2393 * is invoked from idle
2394 */
2395 if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
2396 wake_up_process(t);
2397}
2398
2399static void invoke_rcu_core_kthread(void)
2400{
2401 struct task_struct *t;
2402 unsigned long flags;
2403
2404 local_irq_save(flags);
2405 __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
2406 t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
2407 if (t != NULL && t != current)
2408 rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
2409 local_irq_restore(flags);
2410}
2411
2412/*
2413 * Wake up this CPU's rcuc kthread to do RCU core processing.
2414 */
2415static void invoke_rcu_core(void)
2416{
2417 if (!cpu_online(smp_processor_id()))
2418 return;
2419 if (use_softirq)
2420 raise_softirq(RCU_SOFTIRQ);
2421 else
2422 invoke_rcu_core_kthread();
2423}
2424
2425static void rcu_cpu_kthread_park(unsigned int cpu)
2426{
2427 per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
2428}
2429
2430static int rcu_cpu_kthread_should_run(unsigned int cpu)
2431{
2432 return __this_cpu_read(rcu_data.rcu_cpu_has_work);
2433}
2434
2435/*
2436 * Per-CPU kernel thread that invokes RCU callbacks. This replaces
2437 * the RCU softirq used in configurations of RCU that do not support RCU
2438 * priority boosting.
2439 */
2440static void rcu_cpu_kthread(unsigned int cpu)
2441{
2442 unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
2443 char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
2444 int spincnt;
2445
2446 for (spincnt = 0; spincnt < 10; spincnt++) {
2447 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
2448 local_bh_disable();
2449 *statusp = RCU_KTHREAD_RUNNING;
2450 local_irq_disable();
2451 work = *workp;
2452 *workp = 0;
2453 local_irq_enable();
2454 if (work)
2455 rcu_core();
2456 local_bh_enable();
2457 if (*workp == 0) {
2458 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
2459 *statusp = RCU_KTHREAD_WAITING;
2460 return;
2461 }
2462 }
2463 *statusp = RCU_KTHREAD_YIELDING;
2464 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
2465 schedule_timeout_interruptible(2);
2466 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
2467 *statusp = RCU_KTHREAD_WAITING;
2468}
2469
2470static struct smp_hotplug_thread rcu_cpu_thread_spec = {
2471 .store = &rcu_data.rcu_cpu_kthread_task,
2472 .thread_should_run = rcu_cpu_kthread_should_run,
2473 .thread_fn = rcu_cpu_kthread,
2474 .thread_comm = "rcuc/%u",
2475 .setup = rcu_cpu_kthread_setup,
2476 .park = rcu_cpu_kthread_park,
2477};
2478
2479/*
2480 * Spawn per-CPU RCU core processing kthreads.
2481 */
2482static int __init rcu_spawn_core_kthreads(void)
2483{
2484 int cpu;
2485
2486 for_each_possible_cpu(cpu)
2487 per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
2488 if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq)
2489 return 0;
2490 WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
2491 "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
2492 return 0;
2493}
2494early_initcall(rcu_spawn_core_kthreads);
2495
2496/*
2497 * Handle any core-RCU processing required by a call_rcu() invocation.
2498 */
2499static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
2500 unsigned long flags)
2501{
2502 /*
2503 * If called from an extended quiescent state, invoke the RCU
2504 * core in order to force a re-evaluation of RCU's idleness.
2505 */
2506 if (!rcu_is_watching())
2507 invoke_rcu_core();
2508
2509 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2510 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2511 return;
2512
2513 /*
2514 * Force the grace period if too many callbacks or too long waiting.
2515 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
2516 * if some other CPU has recently done so. Also, don't bother
2517 * invoking rcu_force_quiescent_state() if the newly enqueued callback
2518 * is the only one waiting for a grace period to complete.
2519 */
2520 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2521 rdp->qlen_last_fqs_check + qhimark)) {
2522
2523 /* Are we ignoring a completed grace period? */
2524 note_gp_changes(rdp);
2525
2526 /* Start a new grace period if one not already started. */
2527 if (!rcu_gp_in_progress()) {
2528 rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
2529 } else {
2530 /* Give the grace period a kick. */
2531 rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
2532 if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
2533 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2534 rcu_force_quiescent_state();
2535 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2536 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2537 }
2538 }
2539}
2540
2541/*
2542 * RCU callback function to leak a callback.
2543 */
2544static void rcu_leak_callback(struct rcu_head *rhp)
2545{
2546}
2547
2548/*
2549 * Helper function for call_rcu() and friends. The cpu argument will
2550 * normally be -1, indicating "currently running CPU". It may specify
2551 * a CPU only if that CPU is a no-CBs CPU. Currently, only rcu_barrier()
2552 * is expected to specify a CPU.
2553 */
2554static void
2555__call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
2556{
2557 unsigned long flags;
2558 struct rcu_data *rdp;
2559 bool was_alldone;
2560
2561 /* Misaligned rcu_head! */
2562 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
2563
2564 if (debug_rcu_head_queue(head)) {
2565 /*
2566 * Probable double call_rcu(), so leak the callback.
2567 * Use rcu:rcu_callback trace event to find the previous
2568 * time callback was passed to __call_rcu().
2569 */
2570 WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n",
2571 head, head->func);
2572 WRITE_ONCE(head->func, rcu_leak_callback);
2573 return;
2574 }
2575 head->func = func;
2576 head->next = NULL;
2577 local_irq_save(flags);
2578 rdp = this_cpu_ptr(&rcu_data);
2579
2580 /* Add the callback to our list. */
2581 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
2582 // This can trigger due to call_rcu() from offline CPU:
2583 WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
2584 WARN_ON_ONCE(!rcu_is_watching());
2585 // Very early boot, before rcu_init(). Initialize if needed
2586 // and then drop through to queue the callback.
2587 if (rcu_segcblist_empty(&rdp->cblist))
2588 rcu_segcblist_init(&rdp->cblist);
2589 }
2590 if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
2591 return; // Enqueued onto ->nocb_bypass, so just leave.
2592 /* If we get here, rcu_nocb_try_bypass() acquired ->nocb_lock. */
2593 rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
2594 if (__is_kfree_rcu_offset((unsigned long)func))
2595 trace_rcu_kfree_callback(rcu_state.name, head,
2596 (unsigned long)func,
2597 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2598 rcu_segcblist_n_cbs(&rdp->cblist));
2599 else
2600 trace_rcu_callback(rcu_state.name, head,
2601 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2602 rcu_segcblist_n_cbs(&rdp->cblist));
2603
2604 /* Go handle any RCU core processing required. */
2605 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2606 unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
2607 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
2608 } else {
2609 __call_rcu_core(rdp, head, flags);
2610 local_irq_restore(flags);
2611 }
2612}
2613
2614/**
2615 * call_rcu() - Queue an RCU callback for invocation after a grace period.
2616 * @head: structure to be used for queueing the RCU updates.
2617 * @func: actual callback function to be invoked after the grace period
2618 *
2619 * The callback function will be invoked some time after a full grace
2620 * period elapses, in other words after all pre-existing RCU read-side
2621 * critical sections have completed. However, the callback function
2622 * might well execute concurrently with RCU read-side critical sections
2623 * that started after call_rcu() was invoked. RCU read-side critical
2624 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), and
2625 * may be nested. In addition, regions of code across which interrupts,
2626 * preemption, or softirqs have been disabled also serve as RCU read-side
2627 * critical sections. This includes hardware interrupt handlers, softirq
2628 * handlers, and NMI handlers.
2629 *
2630 * Note that all CPUs must agree that the grace period extended beyond
2631 * all pre-existing RCU read-side critical section. On systems with more
2632 * than one CPU, this means that when "func()" is invoked, each CPU is
2633 * guaranteed to have executed a full memory barrier since the end of its
2634 * last RCU read-side critical section whose beginning preceded the call
2635 * to call_rcu(). It also means that each CPU executing an RCU read-side
2636 * critical section that continues beyond the start of "func()" must have
2637 * executed a memory barrier after the call_rcu() but before the beginning
2638 * of that RCU read-side critical section. Note that these guarantees
2639 * include CPUs that are offline, idle, or executing in user mode, as
2640 * well as CPUs that are executing in the kernel.
2641 *
2642 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
2643 * resulting RCU callback function "func()", then both CPU A and CPU B are
2644 * guaranteed to execute a full memory barrier during the time interval
2645 * between the call to call_rcu() and the invocation of "func()" -- even
2646 * if CPU A and CPU B are the same CPU (but again only if the system has
2647 * more than one CPU).
2648 */
2649void call_rcu(struct rcu_head *head, rcu_callback_t func)
2650{
2651 __call_rcu(head, func, 0);
2652}
2653EXPORT_SYMBOL_GPL(call_rcu);
2654
2655/*
2656 * Queue an RCU callback for lazy invocation after a grace period.
2657 * This will likely be later named something like "call_rcu_lazy()",
2658 * but this change will require some way of tagging the lazy RCU
2659 * callbacks in the list of pending callbacks. Until then, this
2660 * function may only be called from __kfree_rcu().
2661 */
2662void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
2663{
2664 __call_rcu(head, func, 1);
2665}
2666EXPORT_SYMBOL_GPL(kfree_call_rcu);
2667
2668/*
2669 * During early boot, any blocking grace-period wait automatically
2670 * implies a grace period. Later on, this is never the case for PREEMPT.
2671 *
2672 * Howevr, because a context switch is a grace period for !PREEMPT, any
2673 * blocking grace-period wait automatically implies a grace period if
2674 * there is only one CPU online at any point time during execution of
2675 * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to
2676 * occasionally incorrectly indicate that there are multiple CPUs online
2677 * when there was in fact only one the whole time, as this just adds some
2678 * overhead: RCU still operates correctly.
2679 */
2680static int rcu_blocking_is_gp(void)
2681{
2682 int ret;
2683
2684 if (IS_ENABLED(CONFIG_PREEMPTION))
2685 return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
2686 might_sleep(); /* Check for RCU read-side critical section. */
2687 preempt_disable();
2688 ret = num_online_cpus() <= 1;
2689 preempt_enable();
2690 return ret;
2691}
2692
2693/**
2694 * synchronize_rcu - wait until a grace period has elapsed.
2695 *
2696 * Control will return to the caller some time after a full grace
2697 * period has elapsed, in other words after all currently executing RCU
2698 * read-side critical sections have completed. Note, however, that
2699 * upon return from synchronize_rcu(), the caller might well be executing
2700 * concurrently with new RCU read-side critical sections that began while
2701 * synchronize_rcu() was waiting. RCU read-side critical sections are
2702 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
2703 * In addition, regions of code across which interrupts, preemption, or
2704 * softirqs have been disabled also serve as RCU read-side critical
2705 * sections. This includes hardware interrupt handlers, softirq handlers,
2706 * and NMI handlers.
2707 *
2708 * Note that this guarantee implies further memory-ordering guarantees.
2709 * On systems with more than one CPU, when synchronize_rcu() returns,
2710 * each CPU is guaranteed to have executed a full memory barrier since
2711 * the end of its last RCU read-side critical section whose beginning
2712 * preceded the call to synchronize_rcu(). In addition, each CPU having
2713 * an RCU read-side critical section that extends beyond the return from
2714 * synchronize_rcu() is guaranteed to have executed a full memory barrier
2715 * after the beginning of synchronize_rcu() and before the beginning of
2716 * that RCU read-side critical section. Note that these guarantees include
2717 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2718 * that are executing in the kernel.
2719 *
2720 * Furthermore, if CPU A invoked synchronize_rcu(), which returned
2721 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2722 * to have executed a full memory barrier during the execution of
2723 * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
2724 * again only if the system has more than one CPU).
2725 */
2726void synchronize_rcu(void)
2727{
2728 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
2729 lock_is_held(&rcu_lock_map) ||
2730 lock_is_held(&rcu_sched_lock_map),
2731 "Illegal synchronize_rcu() in RCU read-side critical section");
2732 if (rcu_blocking_is_gp())
2733 return;
2734 if (rcu_gp_is_expedited())
2735 synchronize_rcu_expedited();
2736 else
2737 wait_rcu_gp(call_rcu);
2738}
2739EXPORT_SYMBOL_GPL(synchronize_rcu);
2740
2741/**
2742 * get_state_synchronize_rcu - Snapshot current RCU state
2743 *
2744 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2745 * to determine whether or not a full grace period has elapsed in the
2746 * meantime.
2747 */
2748unsigned long get_state_synchronize_rcu(void)
2749{
2750 /*
2751 * Any prior manipulation of RCU-protected data must happen
2752 * before the load from ->gp_seq.
2753 */
2754 smp_mb(); /* ^^^ */
2755 return rcu_seq_snap(&rcu_state.gp_seq);
2756}
2757EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
2758
2759/**
2760 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2761 *
2762 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2763 *
2764 * If a full RCU grace period has elapsed since the earlier call to
2765 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2766 * synchronize_rcu() to wait for a full grace period.
2767 *
2768 * Yes, this function does not take counter wrap into account. But
2769 * counter wrap is harmless. If the counter wraps, we have waited for
2770 * more than 2 billion grace periods (and way more on a 64-bit system!),
2771 * so waiting for one additional grace period should be just fine.
2772 */
2773void cond_synchronize_rcu(unsigned long oldstate)
2774{
2775 if (!rcu_seq_done(&rcu_state.gp_seq, oldstate))
2776 synchronize_rcu();
2777 else
2778 smp_mb(); /* Ensure GP ends before subsequent accesses. */
2779}
2780EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
2781
2782/*
2783 * Check to see if there is any immediate RCU-related work to be done by
2784 * the current CPU, returning 1 if so and zero otherwise. The checks are
2785 * in order of increasing expense: checks that can be carried out against
2786 * CPU-local state are performed first. However, we must check for CPU
2787 * stalls first, else we might not get a chance.
2788 */
2789static int rcu_pending(void)
2790{
2791 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
2792 struct rcu_node *rnp = rdp->mynode;
2793
2794 /* Check for CPU stalls, if enabled. */
2795 check_cpu_stall(rdp);
2796
2797 /* Does this CPU need a deferred NOCB wakeup? */
2798 if (rcu_nocb_need_deferred_wakeup(rdp))
2799 return 1;
2800
2801 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2802 if (rcu_nohz_full_cpu())
2803 return 0;
2804
2805 /* Is the RCU core waiting for a quiescent state from this CPU? */
2806 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
2807 return 1;
2808
2809 /* Does this CPU have callbacks ready to invoke? */
2810 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2811 return 1;
2812
2813 /* Has RCU gone idle with this CPU needing another grace period? */
2814 if (!rcu_gp_in_progress() &&
2815 rcu_segcblist_is_enabled(&rdp->cblist) &&
2816 (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) ||
2817 !rcu_segcblist_is_offloaded(&rdp->cblist)) &&
2818 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2819 return 1;
2820
2821 /* Have RCU grace period completed or started? */
2822 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
2823 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
2824 return 1;
2825
2826 /* nothing to do */
2827 return 0;
2828}
2829
2830/*
2831 * Helper function for rcu_barrier() tracing. If tracing is disabled,
2832 * the compiler is expected to optimize this away.
2833 */
2834static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
2835{
2836 trace_rcu_barrier(rcu_state.name, s, cpu,
2837 atomic_read(&rcu_state.barrier_cpu_count), done);
2838}
2839
2840/*
2841 * RCU callback function for rcu_barrier(). If we are last, wake
2842 * up the task executing rcu_barrier().
2843 */
2844static void rcu_barrier_callback(struct rcu_head *rhp)
2845{
2846 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
2847 rcu_barrier_trace(TPS("LastCB"), -1,
2848 rcu_state.barrier_sequence);
2849 complete(&rcu_state.barrier_completion);
2850 } else {
2851 rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
2852 }
2853}
2854
2855/*
2856 * Called with preemption disabled, and from cross-cpu IRQ context.
2857 */
2858static void rcu_barrier_func(void *unused)
2859{
2860 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2861
2862 rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
2863 rdp->barrier_head.func = rcu_barrier_callback;
2864 debug_rcu_head_queue(&rdp->barrier_head);
2865 rcu_nocb_lock(rdp);
2866 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
2867 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
2868 atomic_inc(&rcu_state.barrier_cpu_count);
2869 } else {
2870 debug_rcu_head_unqueue(&rdp->barrier_head);
2871 rcu_barrier_trace(TPS("IRQNQ"), -1,
2872 rcu_state.barrier_sequence);
2873 }
2874 rcu_nocb_unlock(rdp);
2875}
2876
2877/**
2878 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
2879 *
2880 * Note that this primitive does not necessarily wait for an RCU grace period
2881 * to complete. For example, if there are no RCU callbacks queued anywhere
2882 * in the system, then rcu_barrier() is within its rights to return
2883 * immediately, without waiting for anything, much less an RCU grace period.
2884 */
2885void rcu_barrier(void)
2886{
2887 int cpu;
2888 struct rcu_data *rdp;
2889 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
2890
2891 rcu_barrier_trace(TPS("Begin"), -1, s);
2892
2893 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2894 mutex_lock(&rcu_state.barrier_mutex);
2895
2896 /* Did someone else do our work for us? */
2897 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
2898 rcu_barrier_trace(TPS("EarlyExit"), -1,
2899 rcu_state.barrier_sequence);
2900 smp_mb(); /* caller's subsequent code after above check. */
2901 mutex_unlock(&rcu_state.barrier_mutex);
2902 return;
2903 }
2904
2905 /* Mark the start of the barrier operation. */
2906 rcu_seq_start(&rcu_state.barrier_sequence);
2907 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
2908
2909 /*
2910 * Initialize the count to one rather than to zero in order to
2911 * avoid a too-soon return to zero in case of a short grace period
2912 * (or preemption of this task). Exclude CPU-hotplug operations
2913 * to ensure that no offline CPU has callbacks queued.
2914 */
2915 init_completion(&rcu_state.barrier_completion);
2916 atomic_set(&rcu_state.barrier_cpu_count, 1);
2917 get_online_cpus();
2918
2919 /*
2920 * Force each CPU with callbacks to register a new callback.
2921 * When that callback is invoked, we will know that all of the
2922 * corresponding CPU's preceding callbacks have been invoked.
2923 */
2924 for_each_possible_cpu(cpu) {
2925 rdp = per_cpu_ptr(&rcu_data, cpu);
2926 if (!cpu_online(cpu) &&
2927 !rcu_segcblist_is_offloaded(&rdp->cblist))
2928 continue;
2929 if (rcu_segcblist_n_cbs(&rdp->cblist)) {
2930 rcu_barrier_trace(TPS("OnlineQ"), cpu,
2931 rcu_state.barrier_sequence);
2932 smp_call_function_single(cpu, rcu_barrier_func, NULL, 1);
2933 } else {
2934 rcu_barrier_trace(TPS("OnlineNQ"), cpu,
2935 rcu_state.barrier_sequence);
2936 }
2937 }
2938 put_online_cpus();
2939
2940 /*
2941 * Now that we have an rcu_barrier_callback() callback on each
2942 * CPU, and thus each counted, remove the initial count.
2943 */
2944 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count))
2945 complete(&rcu_state.barrier_completion);
2946
2947 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2948 wait_for_completion(&rcu_state.barrier_completion);
2949
2950 /* Mark the end of the barrier operation. */
2951 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
2952 rcu_seq_end(&rcu_state.barrier_sequence);
2953
2954 /* Other rcu_barrier() invocations can now safely proceed. */
2955 mutex_unlock(&rcu_state.barrier_mutex);
2956}
2957EXPORT_SYMBOL_GPL(rcu_barrier);
2958
2959/*
2960 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
2961 * first CPU in a given leaf rcu_node structure coming online. The caller
2962 * must hold the corresponding leaf rcu_node ->lock with interrrupts
2963 * disabled.
2964 */
2965static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
2966{
2967 long mask;
2968 long oldmask;
2969 struct rcu_node *rnp = rnp_leaf;
2970
2971 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2972 WARN_ON_ONCE(rnp->wait_blkd_tasks);
2973 for (;;) {
2974 mask = rnp->grpmask;
2975 rnp = rnp->parent;
2976 if (rnp == NULL)
2977 return;
2978 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
2979 oldmask = rnp->qsmaskinit;
2980 rnp->qsmaskinit |= mask;
2981 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
2982 if (oldmask)
2983 return;
2984 }
2985}
2986
2987/*
2988 * Do boot-time initialization of a CPU's per-CPU RCU data.
2989 */
2990static void __init
2991rcu_boot_init_percpu_data(int cpu)
2992{
2993 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2994
2995 /* Set up local state, ensuring consistent view of global state. */
2996 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
2997 WARN_ON_ONCE(rdp->dynticks_nesting != 1);
2998 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
2999 rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
3000 rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
3001 rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
3002 rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
3003 rdp->cpu = cpu;
3004 rcu_boot_init_nocb_percpu_data(rdp);
3005}
3006
3007/*
3008 * Invoked early in the CPU-online process, when pretty much all services
3009 * are available. The incoming CPU is not present.
3010 *
3011 * Initializes a CPU's per-CPU RCU data. Note that only one online or
3012 * offline event can be happening at a given time. Note also that we can
3013 * accept some slop in the rsp->gp_seq access due to the fact that this
3014 * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
3015 * And any offloaded callbacks are being numbered elsewhere.
3016 */
3017int rcutree_prepare_cpu(unsigned int cpu)
3018{
3019 unsigned long flags;
3020 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3021 struct rcu_node *rnp = rcu_get_root();
3022
3023 /* Set up local state, ensuring consistent view of global state. */
3024 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3025 rdp->qlen_last_fqs_check = 0;
3026 rdp->n_force_qs_snap = rcu_state.n_force_qs;
3027 rdp->blimit = blimit;
3028 if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
3029 !rcu_segcblist_is_offloaded(&rdp->cblist))
3030 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
3031 rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
3032 rcu_dynticks_eqs_online();
3033 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
3034
3035 /*
3036 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
3037 * propagation up the rcu_node tree will happen at the beginning
3038 * of the next grace period.
3039 */
3040 rnp = rdp->mynode;
3041 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
3042 rdp->beenonline = true; /* We have now been online. */
3043 rdp->gp_seq = rnp->gp_seq;
3044 rdp->gp_seq_needed = rnp->gp_seq;
3045 rdp->cpu_no_qs.b.norm = true;
3046 rdp->core_needs_qs = false;
3047 rdp->rcu_iw_pending = false;
3048 rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;
3049 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
3050 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3051 rcu_prepare_kthreads(cpu);
3052 rcu_spawn_cpu_nocb_kthread(cpu);
3053
3054 return 0;
3055}
3056
3057/*
3058 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
3059 */
3060static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
3061{
3062 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3063
3064 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
3065}
3066
3067/*
3068 * Near the end of the CPU-online process. Pretty much all services
3069 * enabled, and the CPU is now very much alive.
3070 */
3071int rcutree_online_cpu(unsigned int cpu)
3072{
3073 unsigned long flags;
3074 struct rcu_data *rdp;
3075 struct rcu_node *rnp;
3076
3077 rdp = per_cpu_ptr(&rcu_data, cpu);
3078 rnp = rdp->mynode;
3079 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3080 rnp->ffmask |= rdp->grpmask;
3081 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3082 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
3083 return 0; /* Too early in boot for scheduler work. */
3084 sync_sched_exp_online_cleanup(cpu);
3085 rcutree_affinity_setting(cpu, -1);
3086 return 0;
3087}
3088
3089/*
3090 * Near the beginning of the process. The CPU is still very much alive
3091 * with pretty much all services enabled.
3092 */
3093int rcutree_offline_cpu(unsigned int cpu)
3094{
3095 unsigned long flags;
3096 struct rcu_data *rdp;
3097 struct rcu_node *rnp;
3098
3099 rdp = per_cpu_ptr(&rcu_data, cpu);
3100 rnp = rdp->mynode;
3101 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3102 rnp->ffmask &= ~rdp->grpmask;
3103 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3104
3105 rcutree_affinity_setting(cpu, cpu);
3106 return 0;
3107}
3108
3109static DEFINE_PER_CPU(int, rcu_cpu_started);
3110
3111/*
3112 * Mark the specified CPU as being online so that subsequent grace periods
3113 * (both expedited and normal) will wait on it. Note that this means that
3114 * incoming CPUs are not allowed to use RCU read-side critical sections
3115 * until this function is called. Failing to observe this restriction
3116 * will result in lockdep splats.
3117 *
3118 * Note that this function is special in that it is invoked directly
3119 * from the incoming CPU rather than from the cpuhp_step mechanism.
3120 * This is because this function must be invoked at a precise location.
3121 */
3122void rcu_cpu_starting(unsigned int cpu)
3123{
3124 unsigned long flags;
3125 unsigned long mask;
3126 int nbits;
3127 unsigned long oldmask;
3128 struct rcu_data *rdp;
3129 struct rcu_node *rnp;
3130
3131 if (per_cpu(rcu_cpu_started, cpu))
3132 return;
3133
3134 per_cpu(rcu_cpu_started, cpu) = 1;
3135
3136 rdp = per_cpu_ptr(&rcu_data, cpu);
3137 rnp = rdp->mynode;
3138 mask = rdp->grpmask;
3139 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3140 rnp->qsmaskinitnext |= mask;
3141 oldmask = rnp->expmaskinitnext;
3142 rnp->expmaskinitnext |= mask;
3143 oldmask ^= rnp->expmaskinitnext;
3144 nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
3145 /* Allow lockless access for expedited grace periods. */
3146 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
3147 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
3148 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
3149 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
3150 if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
3151 /* Report QS -after- changing ->qsmaskinitnext! */
3152 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
3153 } else {
3154 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3155 }
3156 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
3157}
3158
3159#ifdef CONFIG_HOTPLUG_CPU
3160/*
3161 * The outgoing function has no further need of RCU, so remove it from
3162 * the rcu_node tree's ->qsmaskinitnext bit masks.
3163 *
3164 * Note that this function is special in that it is invoked directly
3165 * from the outgoing CPU rather than from the cpuhp_step mechanism.
3166 * This is because this function must be invoked at a precise location.
3167 */
3168void rcu_report_dead(unsigned int cpu)
3169{
3170 unsigned long flags;
3171 unsigned long mask;
3172 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3173 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
3174
3175 /* QS for any half-done expedited grace period. */
3176 preempt_disable();
3177 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
3178 preempt_enable();
3179 rcu_preempt_deferred_qs(current);
3180
3181 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
3182 mask = rdp->grpmask;
3183 raw_spin_lock(&rcu_state.ofl_lock);
3184 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
3185 rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
3186 rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
3187 if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
3188 /* Report quiescent state -before- changing ->qsmaskinitnext! */
3189 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
3190 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3191 }
3192 rnp->qsmaskinitnext &= ~mask;
3193 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3194 raw_spin_unlock(&rcu_state.ofl_lock);
3195
3196 per_cpu(rcu_cpu_started, cpu) = 0;
3197}
3198
3199/*
3200 * The outgoing CPU has just passed through the dying-idle state, and we
3201 * are being invoked from the CPU that was IPIed to continue the offline
3202 * operation. Migrate the outgoing CPU's callbacks to the current CPU.
3203 */
3204void rcutree_migrate_callbacks(int cpu)
3205{
3206 unsigned long flags;
3207 struct rcu_data *my_rdp;
3208 struct rcu_node *my_rnp;
3209 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3210 bool needwake;
3211
3212 if (rcu_segcblist_is_offloaded(&rdp->cblist) ||
3213 rcu_segcblist_empty(&rdp->cblist))
3214 return; /* No callbacks to migrate. */
3215
3216 local_irq_save(flags);
3217 my_rdp = this_cpu_ptr(&rcu_data);
3218 my_rnp = my_rdp->mynode;
3219 rcu_nocb_lock(my_rdp); /* irqs already disabled. */
3220 WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
3221 raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
3222 /* Leverage recent GPs and set GP for new callbacks. */
3223 needwake = rcu_advance_cbs(my_rnp, rdp) ||
3224 rcu_advance_cbs(my_rnp, my_rdp);
3225 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
3226 needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
3227 rcu_segcblist_disable(&rdp->cblist);
3228 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
3229 !rcu_segcblist_n_cbs(&my_rdp->cblist));
3230 if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) {
3231 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
3232 __call_rcu_nocb_wake(my_rdp, true, flags);
3233 } else {
3234 rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
3235 raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
3236 }
3237 if (needwake)
3238 rcu_gp_kthread_wake();
3239 lockdep_assert_irqs_enabled();
3240 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
3241 !rcu_segcblist_empty(&rdp->cblist),
3242 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
3243 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
3244 rcu_segcblist_first_cb(&rdp->cblist));
3245}
3246#endif
3247
3248/*
3249 * On non-huge systems, use expedited RCU grace periods to make suspend
3250 * and hibernation run faster.
3251 */
3252static int rcu_pm_notify(struct notifier_block *self,
3253 unsigned long action, void *hcpu)
3254{
3255 switch (action) {
3256 case PM_HIBERNATION_PREPARE:
3257 case PM_SUSPEND_PREPARE:
3258 rcu_expedite_gp();
3259 break;
3260 case PM_POST_HIBERNATION:
3261 case PM_POST_SUSPEND:
3262 rcu_unexpedite_gp();
3263 break;
3264 default:
3265 break;
3266 }
3267 return NOTIFY_OK;
3268}
3269
3270/*
3271 * Spawn the kthreads that handle RCU's grace periods.
3272 */
3273static int __init rcu_spawn_gp_kthread(void)
3274{
3275 unsigned long flags;
3276 int kthread_prio_in = kthread_prio;
3277 struct rcu_node *rnp;
3278 struct sched_param sp;
3279 struct task_struct *t;
3280
3281 /* Force priority into range. */
3282 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
3283 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
3284 kthread_prio = 2;
3285 else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
3286 kthread_prio = 1;
3287 else if (kthread_prio < 0)
3288 kthread_prio = 0;
3289 else if (kthread_prio > 99)
3290 kthread_prio = 99;
3291
3292 if (kthread_prio != kthread_prio_in)
3293 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
3294 kthread_prio, kthread_prio_in);
3295
3296 rcu_scheduler_fully_active = 1;
3297 t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
3298 if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
3299 return 0;
3300 if (kthread_prio) {
3301 sp.sched_priority = kthread_prio;
3302 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
3303 }
3304 rnp = rcu_get_root();
3305 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3306 rcu_state.gp_kthread = t;
3307 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3308 wake_up_process(t);
3309 rcu_spawn_nocb_kthreads();
3310 rcu_spawn_boost_kthreads();
3311 return 0;
3312}
3313early_initcall(rcu_spawn_gp_kthread);
3314
3315/*
3316 * This function is invoked towards the end of the scheduler's
3317 * initialization process. Before this is called, the idle task might
3318 * contain synchronous grace-period primitives (during which time, this idle
3319 * task is booting the system, and such primitives are no-ops). After this
3320 * function is called, any synchronous grace-period primitives are run as
3321 * expedited, with the requesting task driving the grace period forward.
3322 * A later core_initcall() rcu_set_runtime_mode() will switch to full
3323 * runtime RCU functionality.
3324 */
3325void rcu_scheduler_starting(void)
3326{
3327 WARN_ON(num_online_cpus() != 1);
3328 WARN_ON(nr_context_switches() > 0);
3329 rcu_test_sync_prims();
3330 rcu_scheduler_active = RCU_SCHEDULER_INIT;
3331 rcu_test_sync_prims();
3332}
3333
3334/*
3335 * Helper function for rcu_init() that initializes the rcu_state structure.
3336 */
3337static void __init rcu_init_one(void)
3338{
3339 static const char * const buf[] = RCU_NODE_NAME_INIT;
3340 static const char * const fqs[] = RCU_FQS_NAME_INIT;
3341 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
3342 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
3343
3344 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
3345 int cpustride = 1;
3346 int i;
3347 int j;
3348 struct rcu_node *rnp;
3349
3350 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3351
3352 /* Silence gcc 4.8 false positive about array index out of range. */
3353 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
3354 panic("rcu_init_one: rcu_num_lvls out of range");
3355
3356 /* Initialize the level-tracking arrays. */
3357
3358 for (i = 1; i < rcu_num_lvls; i++)
3359 rcu_state.level[i] =
3360 rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
3361 rcu_init_levelspread(levelspread, num_rcu_lvl);
3362
3363 /* Initialize the elements themselves, starting from the leaves. */
3364
3365 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3366 cpustride *= levelspread[i];
3367 rnp = rcu_state.level[i];
3368 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
3369 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
3370 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
3371 &rcu_node_class[i], buf[i]);
3372 raw_spin_lock_init(&rnp->fqslock);
3373 lockdep_set_class_and_name(&rnp->fqslock,
3374 &rcu_fqs_class[i], fqs[i]);
3375 rnp->gp_seq = rcu_state.gp_seq;
3376 rnp->gp_seq_needed = rcu_state.gp_seq;
3377 rnp->completedqs = rcu_state.gp_seq;
3378 rnp->qsmask = 0;
3379 rnp->qsmaskinit = 0;
3380 rnp->grplo = j * cpustride;
3381 rnp->grphi = (j + 1) * cpustride - 1;
3382 if (rnp->grphi >= nr_cpu_ids)
3383 rnp->grphi = nr_cpu_ids - 1;
3384 if (i == 0) {
3385 rnp->grpnum = 0;
3386 rnp->grpmask = 0;
3387 rnp->parent = NULL;
3388 } else {
3389 rnp->grpnum = j % levelspread[i - 1];
3390 rnp->grpmask = BIT(rnp->grpnum);
3391 rnp->parent = rcu_state.level[i - 1] +
3392 j / levelspread[i - 1];
3393 }
3394 rnp->level = i;
3395 INIT_LIST_HEAD(&rnp->blkd_tasks);
3396 rcu_init_one_nocb(rnp);
3397 init_waitqueue_head(&rnp->exp_wq[0]);
3398 init_waitqueue_head(&rnp->exp_wq[1]);
3399 init_waitqueue_head(&rnp->exp_wq[2]);
3400 init_waitqueue_head(&rnp->exp_wq[3]);
3401 spin_lock_init(&rnp->exp_lock);
3402 }
3403 }
3404
3405 init_swait_queue_head(&rcu_state.gp_wq);
3406 init_swait_queue_head(&rcu_state.expedited_wq);
3407 rnp = rcu_first_leaf_node();
3408 for_each_possible_cpu(i) {
3409 while (i > rnp->grphi)
3410 rnp++;
3411 per_cpu_ptr(&rcu_data, i)->mynode = rnp;
3412 rcu_boot_init_percpu_data(i);
3413 }
3414}
3415
3416/*
3417 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3418 * replace the definitions in tree.h because those are needed to size
3419 * the ->node array in the rcu_state structure.
3420 */
3421static void __init rcu_init_geometry(void)
3422{
3423 ulong d;
3424 int i;
3425 int rcu_capacity[RCU_NUM_LVLS];
3426
3427 /*
3428 * Initialize any unspecified boot parameters.
3429 * The default values of jiffies_till_first_fqs and
3430 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3431 * value, which is a function of HZ, then adding one for each
3432 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3433 */
3434 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3435 if (jiffies_till_first_fqs == ULONG_MAX)
3436 jiffies_till_first_fqs = d;
3437 if (jiffies_till_next_fqs == ULONG_MAX)
3438 jiffies_till_next_fqs = d;
3439 adjust_jiffies_till_sched_qs();
3440
3441 /* If the compile-time values are accurate, just leave. */
3442 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
3443 nr_cpu_ids == NR_CPUS)
3444 return;
3445 pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
3446 rcu_fanout_leaf, nr_cpu_ids);
3447
3448 /*
3449 * The boot-time rcu_fanout_leaf parameter must be at least two
3450 * and cannot exceed the number of bits in the rcu_node masks.
3451 * Complain and fall back to the compile-time values if this
3452 * limit is exceeded.
3453 */
3454 if (rcu_fanout_leaf < 2 ||
3455 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
3456 rcu_fanout_leaf = RCU_FANOUT_LEAF;
3457 WARN_ON(1);
3458 return;
3459 }
3460
3461 /*
3462 * Compute number of nodes that can be handled an rcu_node tree
3463 * with the given number of levels.
3464 */
3465 rcu_capacity[0] = rcu_fanout_leaf;
3466 for (i = 1; i < RCU_NUM_LVLS; i++)
3467 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
3468
3469 /*
3470 * The tree must be able to accommodate the configured number of CPUs.
3471 * If this limit is exceeded, fall back to the compile-time values.
3472 */
3473 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
3474 rcu_fanout_leaf = RCU_FANOUT_LEAF;
3475 WARN_ON(1);
3476 return;
3477 }
3478
3479 /* Calculate the number of levels in the tree. */
3480 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
3481 }
3482 rcu_num_lvls = i + 1;
3483
3484 /* Calculate the number of rcu_nodes at each level of the tree. */
3485 for (i = 0; i < rcu_num_lvls; i++) {
3486 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
3487 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
3488 }
3489
3490 /* Calculate the total number of rcu_node structures. */
3491 rcu_num_nodes = 0;
3492 for (i = 0; i < rcu_num_lvls; i++)
3493 rcu_num_nodes += num_rcu_lvl[i];
3494}
3495
3496/*
3497 * Dump out the structure of the rcu_node combining tree associated
3498 * with the rcu_state structure.
3499 */
3500static void __init rcu_dump_rcu_node_tree(void)
3501{
3502 int level = 0;
3503 struct rcu_node *rnp;
3504
3505 pr_info("rcu_node tree layout dump\n");
3506 pr_info(" ");
3507 rcu_for_each_node_breadth_first(rnp) {
3508 if (rnp->level != level) {
3509 pr_cont("\n");
3510 pr_info(" ");
3511 level = rnp->level;
3512 }
3513 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
3514 }
3515 pr_cont("\n");
3516}
3517
3518struct workqueue_struct *rcu_gp_wq;
3519struct workqueue_struct *rcu_par_gp_wq;
3520
3521void __init rcu_init(void)
3522{
3523 int cpu;
3524
3525 rcu_early_boot_tests();
3526
3527 rcu_bootup_announce();
3528 rcu_init_geometry();
3529 rcu_init_one();
3530 if (dump_tree)
3531 rcu_dump_rcu_node_tree();
3532 if (use_softirq)
3533 open_softirq(RCU_SOFTIRQ, rcu_core_si);
3534
3535 /*
3536 * We don't need protection against CPU-hotplug here because
3537 * this is called early in boot, before either interrupts
3538 * or the scheduler are operational.
3539 */
3540 pm_notifier(rcu_pm_notify, 0);
3541 for_each_online_cpu(cpu) {
3542 rcutree_prepare_cpu(cpu);
3543 rcu_cpu_starting(cpu);
3544 rcutree_online_cpu(cpu);
3545 }
3546
3547 /* Create workqueue for expedited GPs and for Tree SRCU. */
3548 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
3549 WARN_ON(!rcu_gp_wq);
3550 rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
3551 WARN_ON(!rcu_par_gp_wq);
3552 srcu_init();
3553}
3554
3555#include "tree_stall.h"
3556#include "tree_exp.h"
3557#include "tree_plugin.h"
1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
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.
8 *
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.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2008
19 *
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
23 *
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 *
27 * For detailed explanation of Read-Copy Update mechanism see -
28 * Documentation/RCU
29 */
30#include <linux/types.h>
31#include <linux/kernel.h>
32#include <linux/init.h>
33#include <linux/spinlock.h>
34#include <linux/smp.h>
35#include <linux/rcupdate.h>
36#include <linux/interrupt.h>
37#include <linux/sched.h>
38#include <linux/nmi.h>
39#include <linux/atomic.h>
40#include <linux/bitops.h>
41#include <linux/export.h>
42#include <linux/completion.h>
43#include <linux/moduleparam.h>
44#include <linux/module.h>
45#include <linux/percpu.h>
46#include <linux/notifier.h>
47#include <linux/cpu.h>
48#include <linux/mutex.h>
49#include <linux/time.h>
50#include <linux/kernel_stat.h>
51#include <linux/wait.h>
52#include <linux/kthread.h>
53#include <linux/prefetch.h>
54#include <linux/delay.h>
55#include <linux/stop_machine.h>
56#include <linux/random.h>
57#include <linux/trace_events.h>
58#include <linux/suspend.h>
59
60#include "tree.h"
61#include "rcu.h"
62
63MODULE_ALIAS("rcutree");
64#ifdef MODULE_PARAM_PREFIX
65#undef MODULE_PARAM_PREFIX
66#endif
67#define MODULE_PARAM_PREFIX "rcutree."
68
69/* Data structures. */
70
71/*
72 * In order to export the rcu_state name to the tracing tools, it
73 * needs to be added in the __tracepoint_string section.
74 * This requires defining a separate variable tp_<sname>_varname
75 * that points to the string being used, and this will allow
76 * the tracing userspace tools to be able to decipher the string
77 * address to the matching string.
78 */
79#ifdef CONFIG_TRACING
80# define DEFINE_RCU_TPS(sname) \
81static char sname##_varname[] = #sname; \
82static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
83# define RCU_STATE_NAME(sname) sname##_varname
84#else
85# define DEFINE_RCU_TPS(sname)
86# define RCU_STATE_NAME(sname) __stringify(sname)
87#endif
88
89#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
90DEFINE_RCU_TPS(sname) \
91static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
92struct rcu_state sname##_state = { \
93 .level = { &sname##_state.node[0] }, \
94 .rda = &sname##_data, \
95 .call = cr, \
96 .gp_state = RCU_GP_IDLE, \
97 .gpnum = 0UL - 300UL, \
98 .completed = 0UL - 300UL, \
99 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
100 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
101 .orphan_donetail = &sname##_state.orphan_donelist, \
102 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
103 .name = RCU_STATE_NAME(sname), \
104 .abbr = sabbr, \
105}
106
107RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
108RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
109
110static struct rcu_state *const rcu_state_p;
111LIST_HEAD(rcu_struct_flavors);
112
113/* Dump rcu_node combining tree at boot to verify correct setup. */
114static bool dump_tree;
115module_param(dump_tree, bool, 0444);
116/* Control rcu_node-tree auto-balancing at boot time. */
117static bool rcu_fanout_exact;
118module_param(rcu_fanout_exact, bool, 0444);
119/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
120static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
121module_param(rcu_fanout_leaf, int, 0444);
122int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
123/* Number of rcu_nodes at specified level. */
124static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
125int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
126
127/*
128 * The rcu_scheduler_active variable transitions from zero to one just
129 * before the first task is spawned. So when this variable is zero, RCU
130 * can assume that there is but one task, allowing RCU to (for example)
131 * optimize synchronize_sched() to a simple barrier(). When this variable
132 * is one, RCU must actually do all the hard work required to detect real
133 * grace periods. This variable is also used to suppress boot-time false
134 * positives from lockdep-RCU error checking.
135 */
136int rcu_scheduler_active __read_mostly;
137EXPORT_SYMBOL_GPL(rcu_scheduler_active);
138
139/*
140 * The rcu_scheduler_fully_active variable transitions from zero to one
141 * during the early_initcall() processing, which is after the scheduler
142 * is capable of creating new tasks. So RCU processing (for example,
143 * creating tasks for RCU priority boosting) must be delayed until after
144 * rcu_scheduler_fully_active transitions from zero to one. We also
145 * currently delay invocation of any RCU callbacks until after this point.
146 *
147 * It might later prove better for people registering RCU callbacks during
148 * early boot to take responsibility for these callbacks, but one step at
149 * a time.
150 */
151static int rcu_scheduler_fully_active __read_mostly;
152
153static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
154static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
155static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
156static void invoke_rcu_core(void);
157static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
158static void rcu_report_exp_rdp(struct rcu_state *rsp,
159 struct rcu_data *rdp, bool wake);
160
161/* rcuc/rcub kthread realtime priority */
162#ifdef CONFIG_RCU_KTHREAD_PRIO
163static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
164#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
165static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
166#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
167module_param(kthread_prio, int, 0644);
168
169/* Delay in jiffies for grace-period initialization delays, debug only. */
170
171#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT
172static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY;
173module_param(gp_preinit_delay, int, 0644);
174#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
175static const int gp_preinit_delay;
176#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
177
178#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
179static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
180module_param(gp_init_delay, int, 0644);
181#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
182static const int gp_init_delay;
183#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
184
185#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP
186static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY;
187module_param(gp_cleanup_delay, int, 0644);
188#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
189static const int gp_cleanup_delay;
190#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
191
192/*
193 * Number of grace periods between delays, normalized by the duration of
194 * the delay. The longer the the delay, the more the grace periods between
195 * each delay. The reason for this normalization is that it means that,
196 * for non-zero delays, the overall slowdown of grace periods is constant
197 * regardless of the duration of the delay. This arrangement balances
198 * the need for long delays to increase some race probabilities with the
199 * need for fast grace periods to increase other race probabilities.
200 */
201#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
202
203/*
204 * Track the rcutorture test sequence number and the update version
205 * number within a given test. The rcutorture_testseq is incremented
206 * on every rcutorture module load and unload, so has an odd value
207 * when a test is running. The rcutorture_vernum is set to zero
208 * when rcutorture starts and is incremented on each rcutorture update.
209 * These variables enable correlating rcutorture output with the
210 * RCU tracing information.
211 */
212unsigned long rcutorture_testseq;
213unsigned long rcutorture_vernum;
214
215/*
216 * Compute the mask of online CPUs for the specified rcu_node structure.
217 * This will not be stable unless the rcu_node structure's ->lock is
218 * held, but the bit corresponding to the current CPU will be stable
219 * in most contexts.
220 */
221unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
222{
223 return READ_ONCE(rnp->qsmaskinitnext);
224}
225
226/*
227 * Return true if an RCU grace period is in progress. The READ_ONCE()s
228 * permit this function to be invoked without holding the root rcu_node
229 * structure's ->lock, but of course results can be subject to change.
230 */
231static int rcu_gp_in_progress(struct rcu_state *rsp)
232{
233 return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
234}
235
236/*
237 * Note a quiescent state. Because we do not need to know
238 * how many quiescent states passed, just if there was at least
239 * one since the start of the grace period, this just sets a flag.
240 * The caller must have disabled preemption.
241 */
242void rcu_sched_qs(void)
243{
244 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
245 return;
246 trace_rcu_grace_period(TPS("rcu_sched"),
247 __this_cpu_read(rcu_sched_data.gpnum),
248 TPS("cpuqs"));
249 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
250 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
251 return;
252 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
253 rcu_report_exp_rdp(&rcu_sched_state,
254 this_cpu_ptr(&rcu_sched_data), true);
255}
256
257void rcu_bh_qs(void)
258{
259 if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
260 trace_rcu_grace_period(TPS("rcu_bh"),
261 __this_cpu_read(rcu_bh_data.gpnum),
262 TPS("cpuqs"));
263 __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
264 }
265}
266
267static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
268
269static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
270 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
271 .dynticks = ATOMIC_INIT(1),
272#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
273 .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
274 .dynticks_idle = ATOMIC_INIT(1),
275#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
276};
277
278DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr);
279EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr);
280
281/*
282 * Let the RCU core know that this CPU has gone through the scheduler,
283 * which is a quiescent state. This is called when the need for a
284 * quiescent state is urgent, so we burn an atomic operation and full
285 * memory barriers to let the RCU core know about it, regardless of what
286 * this CPU might (or might not) do in the near future.
287 *
288 * We inform the RCU core by emulating a zero-duration dyntick-idle
289 * period, which we in turn do by incrementing the ->dynticks counter
290 * by two.
291 *
292 * The caller must have disabled interrupts.
293 */
294static void rcu_momentary_dyntick_idle(void)
295{
296 struct rcu_data *rdp;
297 struct rcu_dynticks *rdtp;
298 int resched_mask;
299 struct rcu_state *rsp;
300
301 /*
302 * Yes, we can lose flag-setting operations. This is OK, because
303 * the flag will be set again after some delay.
304 */
305 resched_mask = raw_cpu_read(rcu_sched_qs_mask);
306 raw_cpu_write(rcu_sched_qs_mask, 0);
307
308 /* Find the flavor that needs a quiescent state. */
309 for_each_rcu_flavor(rsp) {
310 rdp = raw_cpu_ptr(rsp->rda);
311 if (!(resched_mask & rsp->flavor_mask))
312 continue;
313 smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */
314 if (READ_ONCE(rdp->mynode->completed) !=
315 READ_ONCE(rdp->cond_resched_completed))
316 continue;
317
318 /*
319 * Pretend to be momentarily idle for the quiescent state.
320 * This allows the grace-period kthread to record the
321 * quiescent state, with no need for this CPU to do anything
322 * further.
323 */
324 rdtp = this_cpu_ptr(&rcu_dynticks);
325 smp_mb__before_atomic(); /* Earlier stuff before QS. */
326 atomic_add(2, &rdtp->dynticks); /* QS. */
327 smp_mb__after_atomic(); /* Later stuff after QS. */
328 break;
329 }
330}
331
332/*
333 * Note a context switch. This is a quiescent state for RCU-sched,
334 * and requires special handling for preemptible RCU.
335 * The caller must have disabled interrupts.
336 */
337void rcu_note_context_switch(void)
338{
339 barrier(); /* Avoid RCU read-side critical sections leaking down. */
340 trace_rcu_utilization(TPS("Start context switch"));
341 rcu_sched_qs();
342 rcu_preempt_note_context_switch();
343 if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
344 rcu_momentary_dyntick_idle();
345 trace_rcu_utilization(TPS("End context switch"));
346 barrier(); /* Avoid RCU read-side critical sections leaking up. */
347}
348EXPORT_SYMBOL_GPL(rcu_note_context_switch);
349
350/*
351 * Register a quiescent state for all RCU flavors. If there is an
352 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
353 * dyntick-idle quiescent state visible to other CPUs (but only for those
354 * RCU flavors in desperate need of a quiescent state, which will normally
355 * be none of them). Either way, do a lightweight quiescent state for
356 * all RCU flavors.
357 *
358 * The barrier() calls are redundant in the common case when this is
359 * called externally, but just in case this is called from within this
360 * file.
361 *
362 */
363void rcu_all_qs(void)
364{
365 unsigned long flags;
366
367 barrier(); /* Avoid RCU read-side critical sections leaking down. */
368 if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
369 local_irq_save(flags);
370 rcu_momentary_dyntick_idle();
371 local_irq_restore(flags);
372 }
373 this_cpu_inc(rcu_qs_ctr);
374 barrier(); /* Avoid RCU read-side critical sections leaking up. */
375}
376EXPORT_SYMBOL_GPL(rcu_all_qs);
377
378static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
379static long qhimark = 10000; /* If this many pending, ignore blimit. */
380static long qlowmark = 100; /* Once only this many pending, use blimit. */
381
382module_param(blimit, long, 0444);
383module_param(qhimark, long, 0444);
384module_param(qlowmark, long, 0444);
385
386static ulong jiffies_till_first_fqs = ULONG_MAX;
387static ulong jiffies_till_next_fqs = ULONG_MAX;
388
389module_param(jiffies_till_first_fqs, ulong, 0644);
390module_param(jiffies_till_next_fqs, ulong, 0644);
391
392/*
393 * How long the grace period must be before we start recruiting
394 * quiescent-state help from rcu_note_context_switch().
395 */
396static ulong jiffies_till_sched_qs = HZ / 20;
397module_param(jiffies_till_sched_qs, ulong, 0644);
398
399static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
400 struct rcu_data *rdp);
401static void force_qs_rnp(struct rcu_state *rsp,
402 int (*f)(struct rcu_data *rsp, bool *isidle,
403 unsigned long *maxj),
404 bool *isidle, unsigned long *maxj);
405static void force_quiescent_state(struct rcu_state *rsp);
406static int rcu_pending(void);
407
408/*
409 * Return the number of RCU batches started thus far for debug & stats.
410 */
411unsigned long rcu_batches_started(void)
412{
413 return rcu_state_p->gpnum;
414}
415EXPORT_SYMBOL_GPL(rcu_batches_started);
416
417/*
418 * Return the number of RCU-sched batches started thus far for debug & stats.
419 */
420unsigned long rcu_batches_started_sched(void)
421{
422 return rcu_sched_state.gpnum;
423}
424EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
425
426/*
427 * Return the number of RCU BH batches started thus far for debug & stats.
428 */
429unsigned long rcu_batches_started_bh(void)
430{
431 return rcu_bh_state.gpnum;
432}
433EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
434
435/*
436 * Return the number of RCU batches completed thus far for debug & stats.
437 */
438unsigned long rcu_batches_completed(void)
439{
440 return rcu_state_p->completed;
441}
442EXPORT_SYMBOL_GPL(rcu_batches_completed);
443
444/*
445 * Return the number of RCU-sched batches completed thus far for debug & stats.
446 */
447unsigned long rcu_batches_completed_sched(void)
448{
449 return rcu_sched_state.completed;
450}
451EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
452
453/*
454 * Return the number of RCU BH batches completed thus far for debug & stats.
455 */
456unsigned long rcu_batches_completed_bh(void)
457{
458 return rcu_bh_state.completed;
459}
460EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
461
462/*
463 * Force a quiescent state.
464 */
465void rcu_force_quiescent_state(void)
466{
467 force_quiescent_state(rcu_state_p);
468}
469EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
470
471/*
472 * Force a quiescent state for RCU BH.
473 */
474void rcu_bh_force_quiescent_state(void)
475{
476 force_quiescent_state(&rcu_bh_state);
477}
478EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
479
480/*
481 * Force a quiescent state for RCU-sched.
482 */
483void rcu_sched_force_quiescent_state(void)
484{
485 force_quiescent_state(&rcu_sched_state);
486}
487EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
488
489/*
490 * Show the state of the grace-period kthreads.
491 */
492void show_rcu_gp_kthreads(void)
493{
494 struct rcu_state *rsp;
495
496 for_each_rcu_flavor(rsp) {
497 pr_info("%s: wait state: %d ->state: %#lx\n",
498 rsp->name, rsp->gp_state, rsp->gp_kthread->state);
499 /* sched_show_task(rsp->gp_kthread); */
500 }
501}
502EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
503
504/*
505 * Record the number of times rcutorture tests have been initiated and
506 * terminated. This information allows the debugfs tracing stats to be
507 * correlated to the rcutorture messages, even when the rcutorture module
508 * is being repeatedly loaded and unloaded. In other words, we cannot
509 * store this state in rcutorture itself.
510 */
511void rcutorture_record_test_transition(void)
512{
513 rcutorture_testseq++;
514 rcutorture_vernum = 0;
515}
516EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
517
518/*
519 * Send along grace-period-related data for rcutorture diagnostics.
520 */
521void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
522 unsigned long *gpnum, unsigned long *completed)
523{
524 struct rcu_state *rsp = NULL;
525
526 switch (test_type) {
527 case RCU_FLAVOR:
528 rsp = rcu_state_p;
529 break;
530 case RCU_BH_FLAVOR:
531 rsp = &rcu_bh_state;
532 break;
533 case RCU_SCHED_FLAVOR:
534 rsp = &rcu_sched_state;
535 break;
536 default:
537 break;
538 }
539 if (rsp != NULL) {
540 *flags = READ_ONCE(rsp->gp_flags);
541 *gpnum = READ_ONCE(rsp->gpnum);
542 *completed = READ_ONCE(rsp->completed);
543 return;
544 }
545 *flags = 0;
546 *gpnum = 0;
547 *completed = 0;
548}
549EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
550
551/*
552 * Record the number of writer passes through the current rcutorture test.
553 * This is also used to correlate debugfs tracing stats with the rcutorture
554 * messages.
555 */
556void rcutorture_record_progress(unsigned long vernum)
557{
558 rcutorture_vernum++;
559}
560EXPORT_SYMBOL_GPL(rcutorture_record_progress);
561
562/*
563 * Does the CPU have callbacks ready to be invoked?
564 */
565static int
566cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
567{
568 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
569 rdp->nxttail[RCU_DONE_TAIL] != NULL;
570}
571
572/*
573 * Return the root node of the specified rcu_state structure.
574 */
575static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
576{
577 return &rsp->node[0];
578}
579
580/*
581 * Is there any need for future grace periods?
582 * Interrupts must be disabled. If the caller does not hold the root
583 * rnp_node structure's ->lock, the results are advisory only.
584 */
585static int rcu_future_needs_gp(struct rcu_state *rsp)
586{
587 struct rcu_node *rnp = rcu_get_root(rsp);
588 int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
589 int *fp = &rnp->need_future_gp[idx];
590
591 return READ_ONCE(*fp);
592}
593
594/*
595 * Does the current CPU require a not-yet-started grace period?
596 * The caller must have disabled interrupts to prevent races with
597 * normal callback registry.
598 */
599static bool
600cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
601{
602 int i;
603
604 if (rcu_gp_in_progress(rsp))
605 return false; /* No, a grace period is already in progress. */
606 if (rcu_future_needs_gp(rsp))
607 return true; /* Yes, a no-CBs CPU needs one. */
608 if (!rdp->nxttail[RCU_NEXT_TAIL])
609 return false; /* No, this is a no-CBs (or offline) CPU. */
610 if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
611 return true; /* Yes, CPU has newly registered callbacks. */
612 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
613 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
614 ULONG_CMP_LT(READ_ONCE(rsp->completed),
615 rdp->nxtcompleted[i]))
616 return true; /* Yes, CBs for future grace period. */
617 return false; /* No grace period needed. */
618}
619
620/*
621 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
622 *
623 * If the new value of the ->dynticks_nesting counter now is zero,
624 * we really have entered idle, and must do the appropriate accounting.
625 * The caller must have disabled interrupts.
626 */
627static void rcu_eqs_enter_common(long long oldval, bool user)
628{
629 struct rcu_state *rsp;
630 struct rcu_data *rdp;
631 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
632
633 trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
634 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
635 !user && !is_idle_task(current)) {
636 struct task_struct *idle __maybe_unused =
637 idle_task(smp_processor_id());
638
639 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
640 ftrace_dump(DUMP_ORIG);
641 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
642 current->pid, current->comm,
643 idle->pid, idle->comm); /* must be idle task! */
644 }
645 for_each_rcu_flavor(rsp) {
646 rdp = this_cpu_ptr(rsp->rda);
647 do_nocb_deferred_wakeup(rdp);
648 }
649 rcu_prepare_for_idle();
650 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
651 smp_mb__before_atomic(); /* See above. */
652 atomic_inc(&rdtp->dynticks);
653 smp_mb__after_atomic(); /* Force ordering with next sojourn. */
654 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
655 atomic_read(&rdtp->dynticks) & 0x1);
656 rcu_dynticks_task_enter();
657
658 /*
659 * It is illegal to enter an extended quiescent state while
660 * in an RCU read-side critical section.
661 */
662 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
663 "Illegal idle entry in RCU read-side critical section.");
664 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
665 "Illegal idle entry in RCU-bh read-side critical section.");
666 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
667 "Illegal idle entry in RCU-sched read-side critical section.");
668}
669
670/*
671 * Enter an RCU extended quiescent state, which can be either the
672 * idle loop or adaptive-tickless usermode execution.
673 */
674static void rcu_eqs_enter(bool user)
675{
676 long long oldval;
677 struct rcu_dynticks *rdtp;
678
679 rdtp = this_cpu_ptr(&rcu_dynticks);
680 oldval = rdtp->dynticks_nesting;
681 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
682 (oldval & DYNTICK_TASK_NEST_MASK) == 0);
683 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
684 rdtp->dynticks_nesting = 0;
685 rcu_eqs_enter_common(oldval, user);
686 } else {
687 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
688 }
689}
690
691/**
692 * rcu_idle_enter - inform RCU that current CPU is entering idle
693 *
694 * Enter idle mode, in other words, -leave- the mode in which RCU
695 * read-side critical sections can occur. (Though RCU read-side
696 * critical sections can occur in irq handlers in idle, a possibility
697 * handled by irq_enter() and irq_exit().)
698 *
699 * We crowbar the ->dynticks_nesting field to zero to allow for
700 * the possibility of usermode upcalls having messed up our count
701 * of interrupt nesting level during the prior busy period.
702 */
703void rcu_idle_enter(void)
704{
705 unsigned long flags;
706
707 local_irq_save(flags);
708 rcu_eqs_enter(false);
709 rcu_sysidle_enter(0);
710 local_irq_restore(flags);
711}
712EXPORT_SYMBOL_GPL(rcu_idle_enter);
713
714#ifdef CONFIG_NO_HZ_FULL
715/**
716 * rcu_user_enter - inform RCU that we are resuming userspace.
717 *
718 * Enter RCU idle mode right before resuming userspace. No use of RCU
719 * is permitted between this call and rcu_user_exit(). This way the
720 * CPU doesn't need to maintain the tick for RCU maintenance purposes
721 * when the CPU runs in userspace.
722 */
723void rcu_user_enter(void)
724{
725 rcu_eqs_enter(1);
726}
727#endif /* CONFIG_NO_HZ_FULL */
728
729/**
730 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
731 *
732 * Exit from an interrupt handler, which might possibly result in entering
733 * idle mode, in other words, leaving the mode in which read-side critical
734 * sections can occur. The caller must have disabled interrupts.
735 *
736 * This code assumes that the idle loop never does anything that might
737 * result in unbalanced calls to irq_enter() and irq_exit(). If your
738 * architecture violates this assumption, RCU will give you what you
739 * deserve, good and hard. But very infrequently and irreproducibly.
740 *
741 * Use things like work queues to work around this limitation.
742 *
743 * You have been warned.
744 */
745void rcu_irq_exit(void)
746{
747 long long oldval;
748 struct rcu_dynticks *rdtp;
749
750 RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!");
751 rdtp = this_cpu_ptr(&rcu_dynticks);
752 oldval = rdtp->dynticks_nesting;
753 rdtp->dynticks_nesting--;
754 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
755 rdtp->dynticks_nesting < 0);
756 if (rdtp->dynticks_nesting)
757 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
758 else
759 rcu_eqs_enter_common(oldval, true);
760 rcu_sysidle_enter(1);
761}
762
763/*
764 * Wrapper for rcu_irq_exit() where interrupts are enabled.
765 */
766void rcu_irq_exit_irqson(void)
767{
768 unsigned long flags;
769
770 local_irq_save(flags);
771 rcu_irq_exit();
772 local_irq_restore(flags);
773}
774
775/*
776 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
777 *
778 * If the new value of the ->dynticks_nesting counter was previously zero,
779 * we really have exited idle, and must do the appropriate accounting.
780 * The caller must have disabled interrupts.
781 */
782static void rcu_eqs_exit_common(long long oldval, int user)
783{
784 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
785
786 rcu_dynticks_task_exit();
787 smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
788 atomic_inc(&rdtp->dynticks);
789 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
790 smp_mb__after_atomic(); /* See above. */
791 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
792 !(atomic_read(&rdtp->dynticks) & 0x1));
793 rcu_cleanup_after_idle();
794 trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
795 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
796 !user && !is_idle_task(current)) {
797 struct task_struct *idle __maybe_unused =
798 idle_task(smp_processor_id());
799
800 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
801 oldval, rdtp->dynticks_nesting);
802 ftrace_dump(DUMP_ORIG);
803 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
804 current->pid, current->comm,
805 idle->pid, idle->comm); /* must be idle task! */
806 }
807}
808
809/*
810 * Exit an RCU extended quiescent state, which can be either the
811 * idle loop or adaptive-tickless usermode execution.
812 */
813static void rcu_eqs_exit(bool user)
814{
815 struct rcu_dynticks *rdtp;
816 long long oldval;
817
818 rdtp = this_cpu_ptr(&rcu_dynticks);
819 oldval = rdtp->dynticks_nesting;
820 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
821 if (oldval & DYNTICK_TASK_NEST_MASK) {
822 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
823 } else {
824 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
825 rcu_eqs_exit_common(oldval, user);
826 }
827}
828
829/**
830 * rcu_idle_exit - inform RCU that current CPU is leaving idle
831 *
832 * Exit idle mode, in other words, -enter- the mode in which RCU
833 * read-side critical sections can occur.
834 *
835 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
836 * allow for the possibility of usermode upcalls messing up our count
837 * of interrupt nesting level during the busy period that is just
838 * now starting.
839 */
840void rcu_idle_exit(void)
841{
842 unsigned long flags;
843
844 local_irq_save(flags);
845 rcu_eqs_exit(false);
846 rcu_sysidle_exit(0);
847 local_irq_restore(flags);
848}
849EXPORT_SYMBOL_GPL(rcu_idle_exit);
850
851#ifdef CONFIG_NO_HZ_FULL
852/**
853 * rcu_user_exit - inform RCU that we are exiting userspace.
854 *
855 * Exit RCU idle mode while entering the kernel because it can
856 * run a RCU read side critical section anytime.
857 */
858void rcu_user_exit(void)
859{
860 rcu_eqs_exit(1);
861}
862#endif /* CONFIG_NO_HZ_FULL */
863
864/**
865 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
866 *
867 * Enter an interrupt handler, which might possibly result in exiting
868 * idle mode, in other words, entering the mode in which read-side critical
869 * sections can occur. The caller must have disabled interrupts.
870 *
871 * Note that the Linux kernel is fully capable of entering an interrupt
872 * handler that it never exits, for example when doing upcalls to
873 * user mode! This code assumes that the idle loop never does upcalls to
874 * user mode. If your architecture does do upcalls from the idle loop (or
875 * does anything else that results in unbalanced calls to the irq_enter()
876 * and irq_exit() functions), RCU will give you what you deserve, good
877 * and hard. But very infrequently and irreproducibly.
878 *
879 * Use things like work queues to work around this limitation.
880 *
881 * You have been warned.
882 */
883void rcu_irq_enter(void)
884{
885 struct rcu_dynticks *rdtp;
886 long long oldval;
887
888 RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!");
889 rdtp = this_cpu_ptr(&rcu_dynticks);
890 oldval = rdtp->dynticks_nesting;
891 rdtp->dynticks_nesting++;
892 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
893 rdtp->dynticks_nesting == 0);
894 if (oldval)
895 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
896 else
897 rcu_eqs_exit_common(oldval, true);
898 rcu_sysidle_exit(1);
899}
900
901/*
902 * Wrapper for rcu_irq_enter() where interrupts are enabled.
903 */
904void rcu_irq_enter_irqson(void)
905{
906 unsigned long flags;
907
908 local_irq_save(flags);
909 rcu_irq_enter();
910 local_irq_restore(flags);
911}
912
913/**
914 * rcu_nmi_enter - inform RCU of entry to NMI context
915 *
916 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
917 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
918 * that the CPU is active. This implementation permits nested NMIs, as
919 * long as the nesting level does not overflow an int. (You will probably
920 * run out of stack space first.)
921 */
922void rcu_nmi_enter(void)
923{
924 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
925 int incby = 2;
926
927 /* Complain about underflow. */
928 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
929
930 /*
931 * If idle from RCU viewpoint, atomically increment ->dynticks
932 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
933 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
934 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
935 * to be in the outermost NMI handler that interrupted an RCU-idle
936 * period (observation due to Andy Lutomirski).
937 */
938 if (!(atomic_read(&rdtp->dynticks) & 0x1)) {
939 smp_mb__before_atomic(); /* Force delay from prior write. */
940 atomic_inc(&rdtp->dynticks);
941 /* atomic_inc() before later RCU read-side crit sects */
942 smp_mb__after_atomic(); /* See above. */
943 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
944 incby = 1;
945 }
946 rdtp->dynticks_nmi_nesting += incby;
947 barrier();
948}
949
950/**
951 * rcu_nmi_exit - inform RCU of exit from NMI context
952 *
953 * If we are returning from the outermost NMI handler that interrupted an
954 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
955 * to let the RCU grace-period handling know that the CPU is back to
956 * being RCU-idle.
957 */
958void rcu_nmi_exit(void)
959{
960 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
961
962 /*
963 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
964 * (We are exiting an NMI handler, so RCU better be paying attention
965 * to us!)
966 */
967 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
968 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
969
970 /*
971 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
972 * leave it in non-RCU-idle state.
973 */
974 if (rdtp->dynticks_nmi_nesting != 1) {
975 rdtp->dynticks_nmi_nesting -= 2;
976 return;
977 }
978
979 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
980 rdtp->dynticks_nmi_nesting = 0;
981 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
982 smp_mb__before_atomic(); /* See above. */
983 atomic_inc(&rdtp->dynticks);
984 smp_mb__after_atomic(); /* Force delay to next write. */
985 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
986}
987
988/**
989 * __rcu_is_watching - are RCU read-side critical sections safe?
990 *
991 * Return true if RCU is watching the running CPU, which means that
992 * this CPU can safely enter RCU read-side critical sections. Unlike
993 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
994 * least disabled preemption.
995 */
996bool notrace __rcu_is_watching(void)
997{
998 return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
999}
1000
1001/**
1002 * rcu_is_watching - see if RCU thinks that the current CPU is idle
1003 *
1004 * If the current CPU is in its idle loop and is neither in an interrupt
1005 * or NMI handler, return true.
1006 */
1007bool notrace rcu_is_watching(void)
1008{
1009 bool ret;
1010
1011 preempt_disable_notrace();
1012 ret = __rcu_is_watching();
1013 preempt_enable_notrace();
1014 return ret;
1015}
1016EXPORT_SYMBOL_GPL(rcu_is_watching);
1017
1018#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1019
1020/*
1021 * Is the current CPU online? Disable preemption to avoid false positives
1022 * that could otherwise happen due to the current CPU number being sampled,
1023 * this task being preempted, its old CPU being taken offline, resuming
1024 * on some other CPU, then determining that its old CPU is now offline.
1025 * It is OK to use RCU on an offline processor during initial boot, hence
1026 * the check for rcu_scheduler_fully_active. Note also that it is OK
1027 * for a CPU coming online to use RCU for one jiffy prior to marking itself
1028 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
1029 * offline to continue to use RCU for one jiffy after marking itself
1030 * offline in the cpu_online_mask. This leniency is necessary given the
1031 * non-atomic nature of the online and offline processing, for example,
1032 * the fact that a CPU enters the scheduler after completing the CPU_DYING
1033 * notifiers.
1034 *
1035 * This is also why RCU internally marks CPUs online during the
1036 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
1037 *
1038 * Disable checking if in an NMI handler because we cannot safely report
1039 * errors from NMI handlers anyway.
1040 */
1041bool rcu_lockdep_current_cpu_online(void)
1042{
1043 struct rcu_data *rdp;
1044 struct rcu_node *rnp;
1045 bool ret;
1046
1047 if (in_nmi())
1048 return true;
1049 preempt_disable();
1050 rdp = this_cpu_ptr(&rcu_sched_data);
1051 rnp = rdp->mynode;
1052 ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1053 !rcu_scheduler_fully_active;
1054 preempt_enable();
1055 return ret;
1056}
1057EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1058
1059#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1060
1061/**
1062 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1063 *
1064 * If the current CPU is idle or running at a first-level (not nested)
1065 * interrupt from idle, return true. The caller must have at least
1066 * disabled preemption.
1067 */
1068static int rcu_is_cpu_rrupt_from_idle(void)
1069{
1070 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
1071}
1072
1073/*
1074 * Snapshot the specified CPU's dynticks counter so that we can later
1075 * credit them with an implicit quiescent state. Return 1 if this CPU
1076 * is in dynticks idle mode, which is an extended quiescent state.
1077 */
1078static int dyntick_save_progress_counter(struct rcu_data *rdp,
1079 bool *isidle, unsigned long *maxj)
1080{
1081 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
1082 rcu_sysidle_check_cpu(rdp, isidle, maxj);
1083 if ((rdp->dynticks_snap & 0x1) == 0) {
1084 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1085 if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
1086 rdp->mynode->gpnum))
1087 WRITE_ONCE(rdp->gpwrap, true);
1088 return 1;
1089 }
1090 return 0;
1091}
1092
1093/*
1094 * Return true if the specified CPU has passed through a quiescent
1095 * state by virtue of being in or having passed through an dynticks
1096 * idle state since the last call to dyntick_save_progress_counter()
1097 * for this same CPU, or by virtue of having been offline.
1098 */
1099static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
1100 bool *isidle, unsigned long *maxj)
1101{
1102 unsigned int curr;
1103 int *rcrmp;
1104 unsigned int snap;
1105
1106 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
1107 snap = (unsigned int)rdp->dynticks_snap;
1108
1109 /*
1110 * If the CPU passed through or entered a dynticks idle phase with
1111 * no active irq/NMI handlers, then we can safely pretend that the CPU
1112 * already acknowledged the request to pass through a quiescent
1113 * state. Either way, that CPU cannot possibly be in an RCU
1114 * read-side critical section that started before the beginning
1115 * of the current RCU grace period.
1116 */
1117 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
1118 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1119 rdp->dynticks_fqs++;
1120 return 1;
1121 }
1122
1123 /*
1124 * Check for the CPU being offline, but only if the grace period
1125 * is old enough. We don't need to worry about the CPU changing
1126 * state: If we see it offline even once, it has been through a
1127 * quiescent state.
1128 *
1129 * The reason for insisting that the grace period be at least
1130 * one jiffy old is that CPUs that are not quite online and that
1131 * have just gone offline can still execute RCU read-side critical
1132 * sections.
1133 */
1134 if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
1135 return 0; /* Grace period is not old enough. */
1136 barrier();
1137 if (cpu_is_offline(rdp->cpu)) {
1138 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1139 rdp->offline_fqs++;
1140 return 1;
1141 }
1142
1143 /*
1144 * A CPU running for an extended time within the kernel can
1145 * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
1146 * even context-switching back and forth between a pair of
1147 * in-kernel CPU-bound tasks cannot advance grace periods.
1148 * So if the grace period is old enough, make the CPU pay attention.
1149 * Note that the unsynchronized assignments to the per-CPU
1150 * rcu_sched_qs_mask variable are safe. Yes, setting of
1151 * bits can be lost, but they will be set again on the next
1152 * force-quiescent-state pass. So lost bit sets do not result
1153 * in incorrect behavior, merely in a grace period lasting
1154 * a few jiffies longer than it might otherwise. Because
1155 * there are at most four threads involved, and because the
1156 * updates are only once every few jiffies, the probability of
1157 * lossage (and thus of slight grace-period extension) is
1158 * quite low.
1159 *
1160 * Note that if the jiffies_till_sched_qs boot/sysfs parameter
1161 * is set too high, we override with half of the RCU CPU stall
1162 * warning delay.
1163 */
1164 rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
1165 if (ULONG_CMP_GE(jiffies,
1166 rdp->rsp->gp_start + jiffies_till_sched_qs) ||
1167 ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
1168 if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
1169 WRITE_ONCE(rdp->cond_resched_completed,
1170 READ_ONCE(rdp->mynode->completed));
1171 smp_mb(); /* ->cond_resched_completed before *rcrmp. */
1172 WRITE_ONCE(*rcrmp,
1173 READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
1174 }
1175 rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
1176 }
1177
1178 /* And if it has been a really long time, kick the CPU as well. */
1179 if (ULONG_CMP_GE(jiffies,
1180 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
1181 ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
1182 resched_cpu(rdp->cpu); /* Force CPU into scheduler. */
1183
1184 return 0;
1185}
1186
1187static void record_gp_stall_check_time(struct rcu_state *rsp)
1188{
1189 unsigned long j = jiffies;
1190 unsigned long j1;
1191
1192 rsp->gp_start = j;
1193 smp_wmb(); /* Record start time before stall time. */
1194 j1 = rcu_jiffies_till_stall_check();
1195 WRITE_ONCE(rsp->jiffies_stall, j + j1);
1196 rsp->jiffies_resched = j + j1 / 2;
1197 rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1198}
1199
1200/*
1201 * Convert a ->gp_state value to a character string.
1202 */
1203static const char *gp_state_getname(short gs)
1204{
1205 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
1206 return "???";
1207 return gp_state_names[gs];
1208}
1209
1210/*
1211 * Complain about starvation of grace-period kthread.
1212 */
1213static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1214{
1215 unsigned long gpa;
1216 unsigned long j;
1217
1218 j = jiffies;
1219 gpa = READ_ONCE(rsp->gp_activity);
1220 if (j - gpa > 2 * HZ) {
1221 pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx\n",
1222 rsp->name, j - gpa,
1223 rsp->gpnum, rsp->completed,
1224 rsp->gp_flags,
1225 gp_state_getname(rsp->gp_state), rsp->gp_state,
1226 rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
1227 if (rsp->gp_kthread)
1228 sched_show_task(rsp->gp_kthread);
1229 }
1230}
1231
1232/*
1233 * Dump stacks of all tasks running on stalled CPUs.
1234 */
1235static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1236{
1237 int cpu;
1238 unsigned long flags;
1239 struct rcu_node *rnp;
1240
1241 rcu_for_each_leaf_node(rsp, rnp) {
1242 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1243 if (rnp->qsmask != 0) {
1244 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1245 if (rnp->qsmask & (1UL << cpu))
1246 dump_cpu_task(rnp->grplo + cpu);
1247 }
1248 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1249 }
1250}
1251
1252static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1253{
1254 int cpu;
1255 long delta;
1256 unsigned long flags;
1257 unsigned long gpa;
1258 unsigned long j;
1259 int ndetected = 0;
1260 struct rcu_node *rnp = rcu_get_root(rsp);
1261 long totqlen = 0;
1262
1263 /* Only let one CPU complain about others per time interval. */
1264
1265 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1266 delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1267 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
1268 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1269 return;
1270 }
1271 WRITE_ONCE(rsp->jiffies_stall,
1272 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1273 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1274
1275 /*
1276 * OK, time to rat on our buddy...
1277 * See Documentation/RCU/stallwarn.txt for info on how to debug
1278 * RCU CPU stall warnings.
1279 */
1280 pr_err("INFO: %s detected stalls on CPUs/tasks:",
1281 rsp->name);
1282 print_cpu_stall_info_begin();
1283 rcu_for_each_leaf_node(rsp, rnp) {
1284 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1285 ndetected += rcu_print_task_stall(rnp);
1286 if (rnp->qsmask != 0) {
1287 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
1288 if (rnp->qsmask & (1UL << cpu)) {
1289 print_cpu_stall_info(rsp,
1290 rnp->grplo + cpu);
1291 ndetected++;
1292 }
1293 }
1294 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1295 }
1296
1297 print_cpu_stall_info_end();
1298 for_each_possible_cpu(cpu)
1299 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1300 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1301 smp_processor_id(), (long)(jiffies - rsp->gp_start),
1302 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1303 if (ndetected) {
1304 rcu_dump_cpu_stacks(rsp);
1305 } else {
1306 if (READ_ONCE(rsp->gpnum) != gpnum ||
1307 READ_ONCE(rsp->completed) == gpnum) {
1308 pr_err("INFO: Stall ended before state dump start\n");
1309 } else {
1310 j = jiffies;
1311 gpa = READ_ONCE(rsp->gp_activity);
1312 pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1313 rsp->name, j - gpa, j, gpa,
1314 jiffies_till_next_fqs,
1315 rcu_get_root(rsp)->qsmask);
1316 /* In this case, the current CPU might be at fault. */
1317 sched_show_task(current);
1318 }
1319 }
1320
1321 /* Complain about tasks blocking the grace period. */
1322 rcu_print_detail_task_stall(rsp);
1323
1324 rcu_check_gp_kthread_starvation(rsp);
1325
1326 force_quiescent_state(rsp); /* Kick them all. */
1327}
1328
1329static void print_cpu_stall(struct rcu_state *rsp)
1330{
1331 int cpu;
1332 unsigned long flags;
1333 struct rcu_node *rnp = rcu_get_root(rsp);
1334 long totqlen = 0;
1335
1336 /*
1337 * OK, time to rat on ourselves...
1338 * See Documentation/RCU/stallwarn.txt for info on how to debug
1339 * RCU CPU stall warnings.
1340 */
1341 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1342 print_cpu_stall_info_begin();
1343 print_cpu_stall_info(rsp, smp_processor_id());
1344 print_cpu_stall_info_end();
1345 for_each_possible_cpu(cpu)
1346 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
1347 pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
1348 jiffies - rsp->gp_start,
1349 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1350
1351 rcu_check_gp_kthread_starvation(rsp);
1352
1353 rcu_dump_cpu_stacks(rsp);
1354
1355 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1356 if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1357 WRITE_ONCE(rsp->jiffies_stall,
1358 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1359 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1360
1361 /*
1362 * Attempt to revive the RCU machinery by forcing a context switch.
1363 *
1364 * A context switch would normally allow the RCU state machine to make
1365 * progress and it could be we're stuck in kernel space without context
1366 * switches for an entirely unreasonable amount of time.
1367 */
1368 resched_cpu(smp_processor_id());
1369}
1370
1371static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1372{
1373 unsigned long completed;
1374 unsigned long gpnum;
1375 unsigned long gps;
1376 unsigned long j;
1377 unsigned long js;
1378 struct rcu_node *rnp;
1379
1380 if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1381 return;
1382 j = jiffies;
1383
1384 /*
1385 * Lots of memory barriers to reject false positives.
1386 *
1387 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1388 * then rsp->gp_start, and finally rsp->completed. These values
1389 * are updated in the opposite order with memory barriers (or
1390 * equivalent) during grace-period initialization and cleanup.
1391 * Now, a false positive can occur if we get an new value of
1392 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1393 * the memory barriers, the only way that this can happen is if one
1394 * grace period ends and another starts between these two fetches.
1395 * Detect this by comparing rsp->completed with the previous fetch
1396 * from rsp->gpnum.
1397 *
1398 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1399 * and rsp->gp_start suffice to forestall false positives.
1400 */
1401 gpnum = READ_ONCE(rsp->gpnum);
1402 smp_rmb(); /* Pick up ->gpnum first... */
1403 js = READ_ONCE(rsp->jiffies_stall);
1404 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1405 gps = READ_ONCE(rsp->gp_start);
1406 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1407 completed = READ_ONCE(rsp->completed);
1408 if (ULONG_CMP_GE(completed, gpnum) ||
1409 ULONG_CMP_LT(j, js) ||
1410 ULONG_CMP_GE(gps, js))
1411 return; /* No stall or GP completed since entering function. */
1412 rnp = rdp->mynode;
1413 if (rcu_gp_in_progress(rsp) &&
1414 (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1415
1416 /* We haven't checked in, so go dump stack. */
1417 print_cpu_stall(rsp);
1418
1419 } else if (rcu_gp_in_progress(rsp) &&
1420 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1421
1422 /* They had a few time units to dump stack, so complain. */
1423 print_other_cpu_stall(rsp, gpnum);
1424 }
1425}
1426
1427/**
1428 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1429 *
1430 * Set the stall-warning timeout way off into the future, thus preventing
1431 * any RCU CPU stall-warning messages from appearing in the current set of
1432 * RCU grace periods.
1433 *
1434 * The caller must disable hard irqs.
1435 */
1436void rcu_cpu_stall_reset(void)
1437{
1438 struct rcu_state *rsp;
1439
1440 for_each_rcu_flavor(rsp)
1441 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1442}
1443
1444/*
1445 * Initialize the specified rcu_data structure's default callback list
1446 * to empty. The default callback list is the one that is not used by
1447 * no-callbacks CPUs.
1448 */
1449static void init_default_callback_list(struct rcu_data *rdp)
1450{
1451 int i;
1452
1453 rdp->nxtlist = NULL;
1454 for (i = 0; i < RCU_NEXT_SIZE; i++)
1455 rdp->nxttail[i] = &rdp->nxtlist;
1456}
1457
1458/*
1459 * Initialize the specified rcu_data structure's callback list to empty.
1460 */
1461static void init_callback_list(struct rcu_data *rdp)
1462{
1463 if (init_nocb_callback_list(rdp))
1464 return;
1465 init_default_callback_list(rdp);
1466}
1467
1468/*
1469 * Determine the value that ->completed will have at the end of the
1470 * next subsequent grace period. This is used to tag callbacks so that
1471 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1472 * been dyntick-idle for an extended period with callbacks under the
1473 * influence of RCU_FAST_NO_HZ.
1474 *
1475 * The caller must hold rnp->lock with interrupts disabled.
1476 */
1477static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1478 struct rcu_node *rnp)
1479{
1480 /*
1481 * If RCU is idle, we just wait for the next grace period.
1482 * But we can only be sure that RCU is idle if we are looking
1483 * at the root rcu_node structure -- otherwise, a new grace
1484 * period might have started, but just not yet gotten around
1485 * to initializing the current non-root rcu_node structure.
1486 */
1487 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1488 return rnp->completed + 1;
1489
1490 /*
1491 * Otherwise, wait for a possible partial grace period and
1492 * then the subsequent full grace period.
1493 */
1494 return rnp->completed + 2;
1495}
1496
1497/*
1498 * Trace-event helper function for rcu_start_future_gp() and
1499 * rcu_nocb_wait_gp().
1500 */
1501static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1502 unsigned long c, const char *s)
1503{
1504 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1505 rnp->completed, c, rnp->level,
1506 rnp->grplo, rnp->grphi, s);
1507}
1508
1509/*
1510 * Start some future grace period, as needed to handle newly arrived
1511 * callbacks. The required future grace periods are recorded in each
1512 * rcu_node structure's ->need_future_gp field. Returns true if there
1513 * is reason to awaken the grace-period kthread.
1514 *
1515 * The caller must hold the specified rcu_node structure's ->lock.
1516 */
1517static bool __maybe_unused
1518rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1519 unsigned long *c_out)
1520{
1521 unsigned long c;
1522 int i;
1523 bool ret = false;
1524 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1525
1526 /*
1527 * Pick up grace-period number for new callbacks. If this
1528 * grace period is already marked as needed, return to the caller.
1529 */
1530 c = rcu_cbs_completed(rdp->rsp, rnp);
1531 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1532 if (rnp->need_future_gp[c & 0x1]) {
1533 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1534 goto out;
1535 }
1536
1537 /*
1538 * If either this rcu_node structure or the root rcu_node structure
1539 * believe that a grace period is in progress, then we must wait
1540 * for the one following, which is in "c". Because our request
1541 * will be noticed at the end of the current grace period, we don't
1542 * need to explicitly start one. We only do the lockless check
1543 * of rnp_root's fields if the current rcu_node structure thinks
1544 * there is no grace period in flight, and because we hold rnp->lock,
1545 * the only possible change is when rnp_root's two fields are
1546 * equal, in which case rnp_root->gpnum might be concurrently
1547 * incremented. But that is OK, as it will just result in our
1548 * doing some extra useless work.
1549 */
1550 if (rnp->gpnum != rnp->completed ||
1551 READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1552 rnp->need_future_gp[c & 0x1]++;
1553 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1554 goto out;
1555 }
1556
1557 /*
1558 * There might be no grace period in progress. If we don't already
1559 * hold it, acquire the root rcu_node structure's lock in order to
1560 * start one (if needed).
1561 */
1562 if (rnp != rnp_root)
1563 raw_spin_lock_rcu_node(rnp_root);
1564
1565 /*
1566 * Get a new grace-period number. If there really is no grace
1567 * period in progress, it will be smaller than the one we obtained
1568 * earlier. Adjust callbacks as needed. Note that even no-CBs
1569 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1570 */
1571 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1572 for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1573 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1574 rdp->nxtcompleted[i] = c;
1575
1576 /*
1577 * If the needed for the required grace period is already
1578 * recorded, trace and leave.
1579 */
1580 if (rnp_root->need_future_gp[c & 0x1]) {
1581 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1582 goto unlock_out;
1583 }
1584
1585 /* Record the need for the future grace period. */
1586 rnp_root->need_future_gp[c & 0x1]++;
1587
1588 /* If a grace period is not already in progress, start one. */
1589 if (rnp_root->gpnum != rnp_root->completed) {
1590 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1591 } else {
1592 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1593 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1594 }
1595unlock_out:
1596 if (rnp != rnp_root)
1597 raw_spin_unlock_rcu_node(rnp_root);
1598out:
1599 if (c_out != NULL)
1600 *c_out = c;
1601 return ret;
1602}
1603
1604/*
1605 * Clean up any old requests for the just-ended grace period. Also return
1606 * whether any additional grace periods have been requested. Also invoke
1607 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1608 * waiting for this grace period to complete.
1609 */
1610static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1611{
1612 int c = rnp->completed;
1613 int needmore;
1614 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1615
1616 rnp->need_future_gp[c & 0x1] = 0;
1617 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1618 trace_rcu_future_gp(rnp, rdp, c,
1619 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1620 return needmore;
1621}
1622
1623/*
1624 * Awaken the grace-period kthread for the specified flavor of RCU.
1625 * Don't do a self-awaken, and don't bother awakening when there is
1626 * nothing for the grace-period kthread to do (as in several CPUs
1627 * raced to awaken, and we lost), and finally don't try to awaken
1628 * a kthread that has not yet been created.
1629 */
1630static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1631{
1632 if (current == rsp->gp_kthread ||
1633 !READ_ONCE(rsp->gp_flags) ||
1634 !rsp->gp_kthread)
1635 return;
1636 swake_up(&rsp->gp_wq);
1637}
1638
1639/*
1640 * If there is room, assign a ->completed number to any callbacks on
1641 * this CPU that have not already been assigned. Also accelerate any
1642 * callbacks that were previously assigned a ->completed number that has
1643 * since proven to be too conservative, which can happen if callbacks get
1644 * assigned a ->completed number while RCU is idle, but with reference to
1645 * a non-root rcu_node structure. This function is idempotent, so it does
1646 * not hurt to call it repeatedly. Returns an flag saying that we should
1647 * awaken the RCU grace-period kthread.
1648 *
1649 * The caller must hold rnp->lock with interrupts disabled.
1650 */
1651static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1652 struct rcu_data *rdp)
1653{
1654 unsigned long c;
1655 int i;
1656 bool ret;
1657
1658 /* If the CPU has no callbacks, nothing to do. */
1659 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1660 return false;
1661
1662 /*
1663 * Starting from the sublist containing the callbacks most
1664 * recently assigned a ->completed number and working down, find the
1665 * first sublist that is not assignable to an upcoming grace period.
1666 * Such a sublist has something in it (first two tests) and has
1667 * a ->completed number assigned that will complete sooner than
1668 * the ->completed number for newly arrived callbacks (last test).
1669 *
1670 * The key point is that any later sublist can be assigned the
1671 * same ->completed number as the newly arrived callbacks, which
1672 * means that the callbacks in any of these later sublist can be
1673 * grouped into a single sublist, whether or not they have already
1674 * been assigned a ->completed number.
1675 */
1676 c = rcu_cbs_completed(rsp, rnp);
1677 for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1678 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1679 !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1680 break;
1681
1682 /*
1683 * If there are no sublist for unassigned callbacks, leave.
1684 * At the same time, advance "i" one sublist, so that "i" will
1685 * index into the sublist where all the remaining callbacks should
1686 * be grouped into.
1687 */
1688 if (++i >= RCU_NEXT_TAIL)
1689 return false;
1690
1691 /*
1692 * Assign all subsequent callbacks' ->completed number to the next
1693 * full grace period and group them all in the sublist initially
1694 * indexed by "i".
1695 */
1696 for (; i <= RCU_NEXT_TAIL; i++) {
1697 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1698 rdp->nxtcompleted[i] = c;
1699 }
1700 /* Record any needed additional grace periods. */
1701 ret = rcu_start_future_gp(rnp, rdp, NULL);
1702
1703 /* Trace depending on how much we were able to accelerate. */
1704 if (!*rdp->nxttail[RCU_WAIT_TAIL])
1705 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1706 else
1707 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1708 return ret;
1709}
1710
1711/*
1712 * Move any callbacks whose grace period has completed to the
1713 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1714 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1715 * sublist. This function is idempotent, so it does not hurt to
1716 * invoke it repeatedly. As long as it is not invoked -too- often...
1717 * Returns true if the RCU grace-period kthread needs to be awakened.
1718 *
1719 * The caller must hold rnp->lock with interrupts disabled.
1720 */
1721static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1722 struct rcu_data *rdp)
1723{
1724 int i, j;
1725
1726 /* If the CPU has no callbacks, nothing to do. */
1727 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1728 return false;
1729
1730 /*
1731 * Find all callbacks whose ->completed numbers indicate that they
1732 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1733 */
1734 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1735 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1736 break;
1737 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1738 }
1739 /* Clean up any sublist tail pointers that were misordered above. */
1740 for (j = RCU_WAIT_TAIL; j < i; j++)
1741 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1742
1743 /* Copy down callbacks to fill in empty sublists. */
1744 for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1745 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1746 break;
1747 rdp->nxttail[j] = rdp->nxttail[i];
1748 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1749 }
1750
1751 /* Classify any remaining callbacks. */
1752 return rcu_accelerate_cbs(rsp, rnp, rdp);
1753}
1754
1755/*
1756 * Update CPU-local rcu_data state to record the beginnings and ends of
1757 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1758 * structure corresponding to the current CPU, and must have irqs disabled.
1759 * Returns true if the grace-period kthread needs to be awakened.
1760 */
1761static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1762 struct rcu_data *rdp)
1763{
1764 bool ret;
1765
1766 /* Handle the ends of any preceding grace periods first. */
1767 if (rdp->completed == rnp->completed &&
1768 !unlikely(READ_ONCE(rdp->gpwrap))) {
1769
1770 /* No grace period end, so just accelerate recent callbacks. */
1771 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1772
1773 } else {
1774
1775 /* Advance callbacks. */
1776 ret = rcu_advance_cbs(rsp, rnp, rdp);
1777
1778 /* Remember that we saw this grace-period completion. */
1779 rdp->completed = rnp->completed;
1780 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1781 }
1782
1783 if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1784 /*
1785 * If the current grace period is waiting for this CPU,
1786 * set up to detect a quiescent state, otherwise don't
1787 * go looking for one.
1788 */
1789 rdp->gpnum = rnp->gpnum;
1790 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1791 rdp->cpu_no_qs.b.norm = true;
1792 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
1793 rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
1794 zero_cpu_stall_ticks(rdp);
1795 WRITE_ONCE(rdp->gpwrap, false);
1796 }
1797 return ret;
1798}
1799
1800static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1801{
1802 unsigned long flags;
1803 bool needwake;
1804 struct rcu_node *rnp;
1805
1806 local_irq_save(flags);
1807 rnp = rdp->mynode;
1808 if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
1809 rdp->completed == READ_ONCE(rnp->completed) &&
1810 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1811 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1812 local_irq_restore(flags);
1813 return;
1814 }
1815 needwake = __note_gp_changes(rsp, rnp, rdp);
1816 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1817 if (needwake)
1818 rcu_gp_kthread_wake(rsp);
1819}
1820
1821static void rcu_gp_slow(struct rcu_state *rsp, int delay)
1822{
1823 if (delay > 0 &&
1824 !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1825 schedule_timeout_uninterruptible(delay);
1826}
1827
1828/*
1829 * Initialize a new grace period. Return false if no grace period required.
1830 */
1831static bool rcu_gp_init(struct rcu_state *rsp)
1832{
1833 unsigned long oldmask;
1834 struct rcu_data *rdp;
1835 struct rcu_node *rnp = rcu_get_root(rsp);
1836
1837 WRITE_ONCE(rsp->gp_activity, jiffies);
1838 raw_spin_lock_irq_rcu_node(rnp);
1839 if (!READ_ONCE(rsp->gp_flags)) {
1840 /* Spurious wakeup, tell caller to go back to sleep. */
1841 raw_spin_unlock_irq_rcu_node(rnp);
1842 return false;
1843 }
1844 WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1845
1846 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1847 /*
1848 * Grace period already in progress, don't start another.
1849 * Not supposed to be able to happen.
1850 */
1851 raw_spin_unlock_irq_rcu_node(rnp);
1852 return false;
1853 }
1854
1855 /* Advance to a new grace period and initialize state. */
1856 record_gp_stall_check_time(rsp);
1857 /* Record GP times before starting GP, hence smp_store_release(). */
1858 smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1859 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1860 raw_spin_unlock_irq_rcu_node(rnp);
1861
1862 /*
1863 * Apply per-leaf buffered online and offline operations to the
1864 * rcu_node tree. Note that this new grace period need not wait
1865 * for subsequent online CPUs, and that quiescent-state forcing
1866 * will handle subsequent offline CPUs.
1867 */
1868 rcu_for_each_leaf_node(rsp, rnp) {
1869 rcu_gp_slow(rsp, gp_preinit_delay);
1870 raw_spin_lock_irq_rcu_node(rnp);
1871 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1872 !rnp->wait_blkd_tasks) {
1873 /* Nothing to do on this leaf rcu_node structure. */
1874 raw_spin_unlock_irq_rcu_node(rnp);
1875 continue;
1876 }
1877
1878 /* Record old state, apply changes to ->qsmaskinit field. */
1879 oldmask = rnp->qsmaskinit;
1880 rnp->qsmaskinit = rnp->qsmaskinitnext;
1881
1882 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1883 if (!oldmask != !rnp->qsmaskinit) {
1884 if (!oldmask) /* First online CPU for this rcu_node. */
1885 rcu_init_new_rnp(rnp);
1886 else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
1887 rnp->wait_blkd_tasks = true;
1888 else /* Last offline CPU and can propagate. */
1889 rcu_cleanup_dead_rnp(rnp);
1890 }
1891
1892 /*
1893 * If all waited-on tasks from prior grace period are
1894 * done, and if all this rcu_node structure's CPUs are
1895 * still offline, propagate up the rcu_node tree and
1896 * clear ->wait_blkd_tasks. Otherwise, if one of this
1897 * rcu_node structure's CPUs has since come back online,
1898 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
1899 * checks for this, so just call it unconditionally).
1900 */
1901 if (rnp->wait_blkd_tasks &&
1902 (!rcu_preempt_has_tasks(rnp) ||
1903 rnp->qsmaskinit)) {
1904 rnp->wait_blkd_tasks = false;
1905 rcu_cleanup_dead_rnp(rnp);
1906 }
1907
1908 raw_spin_unlock_irq_rcu_node(rnp);
1909 }
1910
1911 /*
1912 * Set the quiescent-state-needed bits in all the rcu_node
1913 * structures for all currently online CPUs in breadth-first order,
1914 * starting from the root rcu_node structure, relying on the layout
1915 * of the tree within the rsp->node[] array. Note that other CPUs
1916 * will access only the leaves of the hierarchy, thus seeing that no
1917 * grace period is in progress, at least until the corresponding
1918 * leaf node has been initialized. In addition, we have excluded
1919 * CPU-hotplug operations.
1920 *
1921 * The grace period cannot complete until the initialization
1922 * process finishes, because this kthread handles both.
1923 */
1924 rcu_for_each_node_breadth_first(rsp, rnp) {
1925 rcu_gp_slow(rsp, gp_init_delay);
1926 raw_spin_lock_irq_rcu_node(rnp);
1927 rdp = this_cpu_ptr(rsp->rda);
1928 rcu_preempt_check_blocked_tasks(rnp);
1929 rnp->qsmask = rnp->qsmaskinit;
1930 WRITE_ONCE(rnp->gpnum, rsp->gpnum);
1931 if (WARN_ON_ONCE(rnp->completed != rsp->completed))
1932 WRITE_ONCE(rnp->completed, rsp->completed);
1933 if (rnp == rdp->mynode)
1934 (void)__note_gp_changes(rsp, rnp, rdp);
1935 rcu_preempt_boost_start_gp(rnp);
1936 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1937 rnp->level, rnp->grplo,
1938 rnp->grphi, rnp->qsmask);
1939 raw_spin_unlock_irq_rcu_node(rnp);
1940 cond_resched_rcu_qs();
1941 WRITE_ONCE(rsp->gp_activity, jiffies);
1942 }
1943
1944 return true;
1945}
1946
1947/*
1948 * Helper function for wait_event_interruptible_timeout() wakeup
1949 * at force-quiescent-state time.
1950 */
1951static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
1952{
1953 struct rcu_node *rnp = rcu_get_root(rsp);
1954
1955 /* Someone like call_rcu() requested a force-quiescent-state scan. */
1956 *gfp = READ_ONCE(rsp->gp_flags);
1957 if (*gfp & RCU_GP_FLAG_FQS)
1958 return true;
1959
1960 /* The current grace period has completed. */
1961 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1962 return true;
1963
1964 return false;
1965}
1966
1967/*
1968 * Do one round of quiescent-state forcing.
1969 */
1970static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
1971{
1972 bool isidle = false;
1973 unsigned long maxj;
1974 struct rcu_node *rnp = rcu_get_root(rsp);
1975
1976 WRITE_ONCE(rsp->gp_activity, jiffies);
1977 rsp->n_force_qs++;
1978 if (first_time) {
1979 /* Collect dyntick-idle snapshots. */
1980 if (is_sysidle_rcu_state(rsp)) {
1981 isidle = true;
1982 maxj = jiffies - ULONG_MAX / 4;
1983 }
1984 force_qs_rnp(rsp, dyntick_save_progress_counter,
1985 &isidle, &maxj);
1986 rcu_sysidle_report_gp(rsp, isidle, maxj);
1987 } else {
1988 /* Handle dyntick-idle and offline CPUs. */
1989 isidle = true;
1990 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1991 }
1992 /* Clear flag to prevent immediate re-entry. */
1993 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1994 raw_spin_lock_irq_rcu_node(rnp);
1995 WRITE_ONCE(rsp->gp_flags,
1996 READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
1997 raw_spin_unlock_irq_rcu_node(rnp);
1998 }
1999}
2000
2001/*
2002 * Clean up after the old grace period.
2003 */
2004static void rcu_gp_cleanup(struct rcu_state *rsp)
2005{
2006 unsigned long gp_duration;
2007 bool needgp = false;
2008 int nocb = 0;
2009 struct rcu_data *rdp;
2010 struct rcu_node *rnp = rcu_get_root(rsp);
2011 struct swait_queue_head *sq;
2012
2013 WRITE_ONCE(rsp->gp_activity, jiffies);
2014 raw_spin_lock_irq_rcu_node(rnp);
2015 gp_duration = jiffies - rsp->gp_start;
2016 if (gp_duration > rsp->gp_max)
2017 rsp->gp_max = gp_duration;
2018
2019 /*
2020 * We know the grace period is complete, but to everyone else
2021 * it appears to still be ongoing. But it is also the case
2022 * that to everyone else it looks like there is nothing that
2023 * they can do to advance the grace period. It is therefore
2024 * safe for us to drop the lock in order to mark the grace
2025 * period as completed in all of the rcu_node structures.
2026 */
2027 raw_spin_unlock_irq_rcu_node(rnp);
2028
2029 /*
2030 * Propagate new ->completed value to rcu_node structures so
2031 * that other CPUs don't have to wait until the start of the next
2032 * grace period to process their callbacks. This also avoids
2033 * some nasty RCU grace-period initialization races by forcing
2034 * the end of the current grace period to be completely recorded in
2035 * all of the rcu_node structures before the beginning of the next
2036 * grace period is recorded in any of the rcu_node structures.
2037 */
2038 rcu_for_each_node_breadth_first(rsp, rnp) {
2039 raw_spin_lock_irq_rcu_node(rnp);
2040 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
2041 WARN_ON_ONCE(rnp->qsmask);
2042 WRITE_ONCE(rnp->completed, rsp->gpnum);
2043 rdp = this_cpu_ptr(rsp->rda);
2044 if (rnp == rdp->mynode)
2045 needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
2046 /* smp_mb() provided by prior unlock-lock pair. */
2047 nocb += rcu_future_gp_cleanup(rsp, rnp);
2048 sq = rcu_nocb_gp_get(rnp);
2049 raw_spin_unlock_irq_rcu_node(rnp);
2050 rcu_nocb_gp_cleanup(sq);
2051 cond_resched_rcu_qs();
2052 WRITE_ONCE(rsp->gp_activity, jiffies);
2053 rcu_gp_slow(rsp, gp_cleanup_delay);
2054 }
2055 rnp = rcu_get_root(rsp);
2056 raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
2057 rcu_nocb_gp_set(rnp, nocb);
2058
2059 /* Declare grace period done. */
2060 WRITE_ONCE(rsp->completed, rsp->gpnum);
2061 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
2062 rsp->gp_state = RCU_GP_IDLE;
2063 rdp = this_cpu_ptr(rsp->rda);
2064 /* Advance CBs to reduce false positives below. */
2065 needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
2066 if (needgp || cpu_needs_another_gp(rsp, rdp)) {
2067 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2068 trace_rcu_grace_period(rsp->name,
2069 READ_ONCE(rsp->gpnum),
2070 TPS("newreq"));
2071 }
2072 raw_spin_unlock_irq_rcu_node(rnp);
2073}
2074
2075/*
2076 * Body of kthread that handles grace periods.
2077 */
2078static int __noreturn rcu_gp_kthread(void *arg)
2079{
2080 bool first_gp_fqs;
2081 int gf;
2082 unsigned long j;
2083 int ret;
2084 struct rcu_state *rsp = arg;
2085 struct rcu_node *rnp = rcu_get_root(rsp);
2086
2087 rcu_bind_gp_kthread();
2088 for (;;) {
2089
2090 /* Handle grace-period start. */
2091 for (;;) {
2092 trace_rcu_grace_period(rsp->name,
2093 READ_ONCE(rsp->gpnum),
2094 TPS("reqwait"));
2095 rsp->gp_state = RCU_GP_WAIT_GPS;
2096 swait_event_interruptible(rsp->gp_wq,
2097 READ_ONCE(rsp->gp_flags) &
2098 RCU_GP_FLAG_INIT);
2099 rsp->gp_state = RCU_GP_DONE_GPS;
2100 /* Locking provides needed memory barrier. */
2101 if (rcu_gp_init(rsp))
2102 break;
2103 cond_resched_rcu_qs();
2104 WRITE_ONCE(rsp->gp_activity, jiffies);
2105 WARN_ON(signal_pending(current));
2106 trace_rcu_grace_period(rsp->name,
2107 READ_ONCE(rsp->gpnum),
2108 TPS("reqwaitsig"));
2109 }
2110
2111 /* Handle quiescent-state forcing. */
2112 first_gp_fqs = true;
2113 j = jiffies_till_first_fqs;
2114 if (j > HZ) {
2115 j = HZ;
2116 jiffies_till_first_fqs = HZ;
2117 }
2118 ret = 0;
2119 for (;;) {
2120 if (!ret)
2121 rsp->jiffies_force_qs = jiffies + j;
2122 trace_rcu_grace_period(rsp->name,
2123 READ_ONCE(rsp->gpnum),
2124 TPS("fqswait"));
2125 rsp->gp_state = RCU_GP_WAIT_FQS;
2126 ret = swait_event_interruptible_timeout(rsp->gp_wq,
2127 rcu_gp_fqs_check_wake(rsp, &gf), j);
2128 rsp->gp_state = RCU_GP_DOING_FQS;
2129 /* Locking provides needed memory barriers. */
2130 /* If grace period done, leave loop. */
2131 if (!READ_ONCE(rnp->qsmask) &&
2132 !rcu_preempt_blocked_readers_cgp(rnp))
2133 break;
2134 /* If time for quiescent-state forcing, do it. */
2135 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2136 (gf & RCU_GP_FLAG_FQS)) {
2137 trace_rcu_grace_period(rsp->name,
2138 READ_ONCE(rsp->gpnum),
2139 TPS("fqsstart"));
2140 rcu_gp_fqs(rsp, first_gp_fqs);
2141 first_gp_fqs = false;
2142 trace_rcu_grace_period(rsp->name,
2143 READ_ONCE(rsp->gpnum),
2144 TPS("fqsend"));
2145 cond_resched_rcu_qs();
2146 WRITE_ONCE(rsp->gp_activity, jiffies);
2147 } else {
2148 /* Deal with stray signal. */
2149 cond_resched_rcu_qs();
2150 WRITE_ONCE(rsp->gp_activity, jiffies);
2151 WARN_ON(signal_pending(current));
2152 trace_rcu_grace_period(rsp->name,
2153 READ_ONCE(rsp->gpnum),
2154 TPS("fqswaitsig"));
2155 }
2156 j = jiffies_till_next_fqs;
2157 if (j > HZ) {
2158 j = HZ;
2159 jiffies_till_next_fqs = HZ;
2160 } else if (j < 1) {
2161 j = 1;
2162 jiffies_till_next_fqs = 1;
2163 }
2164 }
2165
2166 /* Handle grace-period end. */
2167 rsp->gp_state = RCU_GP_CLEANUP;
2168 rcu_gp_cleanup(rsp);
2169 rsp->gp_state = RCU_GP_CLEANED;
2170 }
2171}
2172
2173/*
2174 * Start a new RCU grace period if warranted, re-initializing the hierarchy
2175 * in preparation for detecting the next grace period. The caller must hold
2176 * the root node's ->lock and hard irqs must be disabled.
2177 *
2178 * Note that it is legal for a dying CPU (which is marked as offline) to
2179 * invoke this function. This can happen when the dying CPU reports its
2180 * quiescent state.
2181 *
2182 * Returns true if the grace-period kthread must be awakened.
2183 */
2184static bool
2185rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
2186 struct rcu_data *rdp)
2187{
2188 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2189 /*
2190 * Either we have not yet spawned the grace-period
2191 * task, this CPU does not need another grace period,
2192 * or a grace period is already in progress.
2193 * Either way, don't start a new grace period.
2194 */
2195 return false;
2196 }
2197 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2198 trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2199 TPS("newreq"));
2200
2201 /*
2202 * We can't do wakeups while holding the rnp->lock, as that
2203 * could cause possible deadlocks with the rq->lock. Defer
2204 * the wakeup to our caller.
2205 */
2206 return true;
2207}
2208
2209/*
2210 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
2211 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
2212 * is invoked indirectly from rcu_advance_cbs(), which would result in
2213 * endless recursion -- or would do so if it wasn't for the self-deadlock
2214 * that is encountered beforehand.
2215 *
2216 * Returns true if the grace-period kthread needs to be awakened.
2217 */
2218static bool rcu_start_gp(struct rcu_state *rsp)
2219{
2220 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
2221 struct rcu_node *rnp = rcu_get_root(rsp);
2222 bool ret = false;
2223
2224 /*
2225 * If there is no grace period in progress right now, any
2226 * callbacks we have up to this point will be satisfied by the
2227 * next grace period. Also, advancing the callbacks reduces the
2228 * probability of false positives from cpu_needs_another_gp()
2229 * resulting in pointless grace periods. So, advance callbacks
2230 * then start the grace period!
2231 */
2232 ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
2233 ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
2234 return ret;
2235}
2236
2237/*
2238 * Report a full set of quiescent states to the specified rcu_state data
2239 * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
2240 * kthread if another grace period is required. Whether we wake
2241 * the grace-period kthread or it awakens itself for the next round
2242 * of quiescent-state forcing, that kthread will clean up after the
2243 * just-completed grace period. Note that the caller must hold rnp->lock,
2244 * which is released before return.
2245 */
2246static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2247 __releases(rcu_get_root(rsp)->lock)
2248{
2249 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2250 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2251 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2252 swake_up(&rsp->gp_wq); /* Memory barrier implied by swake_up() path. */
2253}
2254
2255/*
2256 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2257 * Allows quiescent states for a group of CPUs to be reported at one go
2258 * to the specified rcu_node structure, though all the CPUs in the group
2259 * must be represented by the same rcu_node structure (which need not be a
2260 * leaf rcu_node structure, though it often will be). The gps parameter
2261 * is the grace-period snapshot, which means that the quiescent states
2262 * are valid only if rnp->gpnum is equal to gps. That structure's lock
2263 * must be held upon entry, and it is released before return.
2264 */
2265static void
2266rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2267 struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2268 __releases(rnp->lock)
2269{
2270 unsigned long oldmask = 0;
2271 struct rcu_node *rnp_c;
2272
2273 /* Walk up the rcu_node hierarchy. */
2274 for (;;) {
2275 if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2276
2277 /*
2278 * Our bit has already been cleared, or the
2279 * relevant grace period is already over, so done.
2280 */
2281 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2282 return;
2283 }
2284 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2285 rnp->qsmask &= ~mask;
2286 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
2287 mask, rnp->qsmask, rnp->level,
2288 rnp->grplo, rnp->grphi,
2289 !!rnp->gp_tasks);
2290 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2291
2292 /* Other bits still set at this level, so done. */
2293 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2294 return;
2295 }
2296 mask = rnp->grpmask;
2297 if (rnp->parent == NULL) {
2298
2299 /* No more levels. Exit loop holding root lock. */
2300
2301 break;
2302 }
2303 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2304 rnp_c = rnp;
2305 rnp = rnp->parent;
2306 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2307 oldmask = rnp_c->qsmask;
2308 }
2309
2310 /*
2311 * Get here if we are the last CPU to pass through a quiescent
2312 * state for this grace period. Invoke rcu_report_qs_rsp()
2313 * to clean up and start the next grace period if one is needed.
2314 */
2315 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2316}
2317
2318/*
2319 * Record a quiescent state for all tasks that were previously queued
2320 * on the specified rcu_node structure and that were blocking the current
2321 * RCU grace period. The caller must hold the specified rnp->lock with
2322 * irqs disabled, and this lock is released upon return, but irqs remain
2323 * disabled.
2324 */
2325static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2326 struct rcu_node *rnp, unsigned long flags)
2327 __releases(rnp->lock)
2328{
2329 unsigned long gps;
2330 unsigned long mask;
2331 struct rcu_node *rnp_p;
2332
2333 if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2334 rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2335 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2336 return; /* Still need more quiescent states! */
2337 }
2338
2339 rnp_p = rnp->parent;
2340 if (rnp_p == NULL) {
2341 /*
2342 * Only one rcu_node structure in the tree, so don't
2343 * try to report up to its nonexistent parent!
2344 */
2345 rcu_report_qs_rsp(rsp, flags);
2346 return;
2347 }
2348
2349 /* Report up the rest of the hierarchy, tracking current ->gpnum. */
2350 gps = rnp->gpnum;
2351 mask = rnp->grpmask;
2352 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2353 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2354 rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2355}
2356
2357/*
2358 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2359 * structure. This must be called from the specified CPU.
2360 */
2361static void
2362rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2363{
2364 unsigned long flags;
2365 unsigned long mask;
2366 bool needwake;
2367 struct rcu_node *rnp;
2368
2369 rnp = rdp->mynode;
2370 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2371 if ((rdp->cpu_no_qs.b.norm &&
2372 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) ||
2373 rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum ||
2374 rdp->gpwrap) {
2375
2376 /*
2377 * The grace period in which this quiescent state was
2378 * recorded has ended, so don't report it upwards.
2379 * We will instead need a new quiescent state that lies
2380 * within the current grace period.
2381 */
2382 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2383 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr);
2384 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2385 return;
2386 }
2387 mask = rdp->grpmask;
2388 if ((rnp->qsmask & mask) == 0) {
2389 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2390 } else {
2391 rdp->core_needs_qs = false;
2392
2393 /*
2394 * This GP can't end until cpu checks in, so all of our
2395 * callbacks can be processed during the next GP.
2396 */
2397 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2398
2399 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2400 /* ^^^ Released rnp->lock */
2401 if (needwake)
2402 rcu_gp_kthread_wake(rsp);
2403 }
2404}
2405
2406/*
2407 * Check to see if there is a new grace period of which this CPU
2408 * is not yet aware, and if so, set up local rcu_data state for it.
2409 * Otherwise, see if this CPU has just passed through its first
2410 * quiescent state for this grace period, and record that fact if so.
2411 */
2412static void
2413rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2414{
2415 /* Check for grace-period ends and beginnings. */
2416 note_gp_changes(rsp, rdp);
2417
2418 /*
2419 * Does this CPU still need to do its part for current grace period?
2420 * If no, return and let the other CPUs do their part as well.
2421 */
2422 if (!rdp->core_needs_qs)
2423 return;
2424
2425 /*
2426 * Was there a quiescent state since the beginning of the grace
2427 * period? If no, then exit and wait for the next call.
2428 */
2429 if (rdp->cpu_no_qs.b.norm &&
2430 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr))
2431 return;
2432
2433 /*
2434 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2435 * judge of that).
2436 */
2437 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2438}
2439
2440/*
2441 * Send the specified CPU's RCU callbacks to the orphanage. The
2442 * specified CPU must be offline, and the caller must hold the
2443 * ->orphan_lock.
2444 */
2445static void
2446rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
2447 struct rcu_node *rnp, struct rcu_data *rdp)
2448{
2449 /* No-CBs CPUs do not have orphanable callbacks. */
2450 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
2451 return;
2452
2453 /*
2454 * Orphan the callbacks. First adjust the counts. This is safe
2455 * because _rcu_barrier() excludes CPU-hotplug operations, so it
2456 * cannot be running now. Thus no memory barrier is required.
2457 */
2458 if (rdp->nxtlist != NULL) {
2459 rsp->qlen_lazy += rdp->qlen_lazy;
2460 rsp->qlen += rdp->qlen;
2461 rdp->n_cbs_orphaned += rdp->qlen;
2462 rdp->qlen_lazy = 0;
2463 WRITE_ONCE(rdp->qlen, 0);
2464 }
2465
2466 /*
2467 * Next, move those callbacks still needing a grace period to
2468 * the orphanage, where some other CPU will pick them up.
2469 * Some of the callbacks might have gone partway through a grace
2470 * period, but that is too bad. They get to start over because we
2471 * cannot assume that grace periods are synchronized across CPUs.
2472 * We don't bother updating the ->nxttail[] array yet, instead
2473 * we just reset the whole thing later on.
2474 */
2475 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
2476 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
2477 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
2478 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2479 }
2480
2481 /*
2482 * Then move the ready-to-invoke callbacks to the orphanage,
2483 * where some other CPU will pick them up. These will not be
2484 * required to pass though another grace period: They are done.
2485 */
2486 if (rdp->nxtlist != NULL) {
2487 *rsp->orphan_donetail = rdp->nxtlist;
2488 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
2489 }
2490
2491 /*
2492 * Finally, initialize the rcu_data structure's list to empty and
2493 * disallow further callbacks on this CPU.
2494 */
2495 init_callback_list(rdp);
2496 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2497}
2498
2499/*
2500 * Adopt the RCU callbacks from the specified rcu_state structure's
2501 * orphanage. The caller must hold the ->orphan_lock.
2502 */
2503static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2504{
2505 int i;
2506 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2507
2508 /* No-CBs CPUs are handled specially. */
2509 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2510 rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
2511 return;
2512
2513 /* Do the accounting first. */
2514 rdp->qlen_lazy += rsp->qlen_lazy;
2515 rdp->qlen += rsp->qlen;
2516 rdp->n_cbs_adopted += rsp->qlen;
2517 if (rsp->qlen_lazy != rsp->qlen)
2518 rcu_idle_count_callbacks_posted();
2519 rsp->qlen_lazy = 0;
2520 rsp->qlen = 0;
2521
2522 /*
2523 * We do not need a memory barrier here because the only way we
2524 * can get here if there is an rcu_barrier() in flight is if
2525 * we are the task doing the rcu_barrier().
2526 */
2527
2528 /* First adopt the ready-to-invoke callbacks. */
2529 if (rsp->orphan_donelist != NULL) {
2530 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
2531 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
2532 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
2533 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2534 rdp->nxttail[i] = rsp->orphan_donetail;
2535 rsp->orphan_donelist = NULL;
2536 rsp->orphan_donetail = &rsp->orphan_donelist;
2537 }
2538
2539 /* And then adopt the callbacks that still need a grace period. */
2540 if (rsp->orphan_nxtlist != NULL) {
2541 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
2542 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
2543 rsp->orphan_nxtlist = NULL;
2544 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2545 }
2546}
2547
2548/*
2549 * Trace the fact that this CPU is going offline.
2550 */
2551static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2552{
2553 RCU_TRACE(unsigned long mask);
2554 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
2555 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
2556
2557 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2558 return;
2559
2560 RCU_TRACE(mask = rdp->grpmask);
2561 trace_rcu_grace_period(rsp->name,
2562 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2563 TPS("cpuofl"));
2564}
2565
2566/*
2567 * All CPUs for the specified rcu_node structure have gone offline,
2568 * and all tasks that were preempted within an RCU read-side critical
2569 * section while running on one of those CPUs have since exited their RCU
2570 * read-side critical section. Some other CPU is reporting this fact with
2571 * the specified rcu_node structure's ->lock held and interrupts disabled.
2572 * This function therefore goes up the tree of rcu_node structures,
2573 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2574 * the leaf rcu_node structure's ->qsmaskinit field has already been
2575 * updated
2576 *
2577 * This function does check that the specified rcu_node structure has
2578 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2579 * prematurely. That said, invoking it after the fact will cost you
2580 * a needless lock acquisition. So once it has done its work, don't
2581 * invoke it again.
2582 */
2583static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2584{
2585 long mask;
2586 struct rcu_node *rnp = rnp_leaf;
2587
2588 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2589 rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2590 return;
2591 for (;;) {
2592 mask = rnp->grpmask;
2593 rnp = rnp->parent;
2594 if (!rnp)
2595 break;
2596 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2597 rnp->qsmaskinit &= ~mask;
2598 rnp->qsmask &= ~mask;
2599 if (rnp->qsmaskinit) {
2600 raw_spin_unlock_rcu_node(rnp);
2601 /* irqs remain disabled. */
2602 return;
2603 }
2604 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2605 }
2606}
2607
2608/*
2609 * The CPU has been completely removed, and some other CPU is reporting
2610 * this fact from process context. Do the remainder of the cleanup,
2611 * including orphaning the outgoing CPU's RCU callbacks, and also
2612 * adopting them. There can only be one CPU hotplug operation at a time,
2613 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2614 */
2615static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2616{
2617 unsigned long flags;
2618 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2619 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2620
2621 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2622 return;
2623
2624 /* Adjust any no-longer-needed kthreads. */
2625 rcu_boost_kthread_setaffinity(rnp, -1);
2626
2627 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2628 raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2629 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2630 rcu_adopt_orphan_cbs(rsp, flags);
2631 raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
2632
2633 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2634 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2635 cpu, rdp->qlen, rdp->nxtlist);
2636}
2637
2638/*
2639 * Invoke any RCU callbacks that have made it to the end of their grace
2640 * period. Thottle as specified by rdp->blimit.
2641 */
2642static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2643{
2644 unsigned long flags;
2645 struct rcu_head *next, *list, **tail;
2646 long bl, count, count_lazy;
2647 int i;
2648
2649 /* If no callbacks are ready, just return. */
2650 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2651 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2652 trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist),
2653 need_resched(), is_idle_task(current),
2654 rcu_is_callbacks_kthread());
2655 return;
2656 }
2657
2658 /*
2659 * Extract the list of ready callbacks, disabling to prevent
2660 * races with call_rcu() from interrupt handlers.
2661 */
2662 local_irq_save(flags);
2663 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2664 bl = rdp->blimit;
2665 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2666 list = rdp->nxtlist;
2667 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2668 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2669 tail = rdp->nxttail[RCU_DONE_TAIL];
2670 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2671 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2672 rdp->nxttail[i] = &rdp->nxtlist;
2673 local_irq_restore(flags);
2674
2675 /* Invoke callbacks. */
2676 count = count_lazy = 0;
2677 while (list) {
2678 next = list->next;
2679 prefetch(next);
2680 debug_rcu_head_unqueue(list);
2681 if (__rcu_reclaim(rsp->name, list))
2682 count_lazy++;
2683 list = next;
2684 /* Stop only if limit reached and CPU has something to do. */
2685 if (++count >= bl &&
2686 (need_resched() ||
2687 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2688 break;
2689 }
2690
2691 local_irq_save(flags);
2692 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2693 is_idle_task(current),
2694 rcu_is_callbacks_kthread());
2695
2696 /* Update count, and requeue any remaining callbacks. */
2697 if (list != NULL) {
2698 *tail = rdp->nxtlist;
2699 rdp->nxtlist = list;
2700 for (i = 0; i < RCU_NEXT_SIZE; i++)
2701 if (&rdp->nxtlist == rdp->nxttail[i])
2702 rdp->nxttail[i] = tail;
2703 else
2704 break;
2705 }
2706 smp_mb(); /* List handling before counting for rcu_barrier(). */
2707 rdp->qlen_lazy -= count_lazy;
2708 WRITE_ONCE(rdp->qlen, rdp->qlen - count);
2709 rdp->n_cbs_invoked += count;
2710
2711 /* Reinstate batch limit if we have worked down the excess. */
2712 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2713 rdp->blimit = blimit;
2714
2715 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2716 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2717 rdp->qlen_last_fqs_check = 0;
2718 rdp->n_force_qs_snap = rsp->n_force_qs;
2719 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2720 rdp->qlen_last_fqs_check = rdp->qlen;
2721 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2722
2723 local_irq_restore(flags);
2724
2725 /* Re-invoke RCU core processing if there are callbacks remaining. */
2726 if (cpu_has_callbacks_ready_to_invoke(rdp))
2727 invoke_rcu_core();
2728}
2729
2730/*
2731 * Check to see if this CPU is in a non-context-switch quiescent state
2732 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2733 * Also schedule RCU core processing.
2734 *
2735 * This function must be called from hardirq context. It is normally
2736 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2737 * false, there is no point in invoking rcu_check_callbacks().
2738 */
2739void rcu_check_callbacks(int user)
2740{
2741 trace_rcu_utilization(TPS("Start scheduler-tick"));
2742 increment_cpu_stall_ticks();
2743 if (user || rcu_is_cpu_rrupt_from_idle()) {
2744
2745 /*
2746 * Get here if this CPU took its interrupt from user
2747 * mode or from the idle loop, and if this is not a
2748 * nested interrupt. In this case, the CPU is in
2749 * a quiescent state, so note it.
2750 *
2751 * No memory barrier is required here because both
2752 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2753 * variables that other CPUs neither access nor modify,
2754 * at least not while the corresponding CPU is online.
2755 */
2756
2757 rcu_sched_qs();
2758 rcu_bh_qs();
2759
2760 } else if (!in_softirq()) {
2761
2762 /*
2763 * Get here if this CPU did not take its interrupt from
2764 * softirq, in other words, if it is not interrupting
2765 * a rcu_bh read-side critical section. This is an _bh
2766 * critical section, so note it.
2767 */
2768
2769 rcu_bh_qs();
2770 }
2771 rcu_preempt_check_callbacks();
2772 if (rcu_pending())
2773 invoke_rcu_core();
2774 if (user)
2775 rcu_note_voluntary_context_switch(current);
2776 trace_rcu_utilization(TPS("End scheduler-tick"));
2777}
2778
2779/*
2780 * Scan the leaf rcu_node structures, processing dyntick state for any that
2781 * have not yet encountered a quiescent state, using the function specified.
2782 * Also initiate boosting for any threads blocked on the root rcu_node.
2783 *
2784 * The caller must have suppressed start of new grace periods.
2785 */
2786static void force_qs_rnp(struct rcu_state *rsp,
2787 int (*f)(struct rcu_data *rsp, bool *isidle,
2788 unsigned long *maxj),
2789 bool *isidle, unsigned long *maxj)
2790{
2791 unsigned long bit;
2792 int cpu;
2793 unsigned long flags;
2794 unsigned long mask;
2795 struct rcu_node *rnp;
2796
2797 rcu_for_each_leaf_node(rsp, rnp) {
2798 cond_resched_rcu_qs();
2799 mask = 0;
2800 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2801 if (rnp->qsmask == 0) {
2802 if (rcu_state_p == &rcu_sched_state ||
2803 rsp != rcu_state_p ||
2804 rcu_preempt_blocked_readers_cgp(rnp)) {
2805 /*
2806 * No point in scanning bits because they
2807 * are all zero. But we might need to
2808 * priority-boost blocked readers.
2809 */
2810 rcu_initiate_boost(rnp, flags);
2811 /* rcu_initiate_boost() releases rnp->lock */
2812 continue;
2813 }
2814 if (rnp->parent &&
2815 (rnp->parent->qsmask & rnp->grpmask)) {
2816 /*
2817 * Race between grace-period
2818 * initialization and task exiting RCU
2819 * read-side critical section: Report.
2820 */
2821 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2822 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2823 continue;
2824 }
2825 }
2826 cpu = rnp->grplo;
2827 bit = 1;
2828 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2829 if ((rnp->qsmask & bit) != 0) {
2830 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2831 mask |= bit;
2832 }
2833 }
2834 if (mask != 0) {
2835 /* Idle/offline CPUs, report (releases rnp->lock. */
2836 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2837 } else {
2838 /* Nothing to do here, so just drop the lock. */
2839 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2840 }
2841 }
2842}
2843
2844/*
2845 * Force quiescent states on reluctant CPUs, and also detect which
2846 * CPUs are in dyntick-idle mode.
2847 */
2848static void force_quiescent_state(struct rcu_state *rsp)
2849{
2850 unsigned long flags;
2851 bool ret;
2852 struct rcu_node *rnp;
2853 struct rcu_node *rnp_old = NULL;
2854
2855 /* Funnel through hierarchy to reduce memory contention. */
2856 rnp = __this_cpu_read(rsp->rda->mynode);
2857 for (; rnp != NULL; rnp = rnp->parent) {
2858 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2859 !raw_spin_trylock(&rnp->fqslock);
2860 if (rnp_old != NULL)
2861 raw_spin_unlock(&rnp_old->fqslock);
2862 if (ret) {
2863 rsp->n_force_qs_lh++;
2864 return;
2865 }
2866 rnp_old = rnp;
2867 }
2868 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2869
2870 /* Reached the root of the rcu_node tree, acquire lock. */
2871 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2872 raw_spin_unlock(&rnp_old->fqslock);
2873 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2874 rsp->n_force_qs_lh++;
2875 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2876 return; /* Someone beat us to it. */
2877 }
2878 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2879 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2880 swake_up(&rsp->gp_wq); /* Memory barrier implied by swake_up() path. */
2881}
2882
2883/*
2884 * This does the RCU core processing work for the specified rcu_state
2885 * and rcu_data structures. This may be called only from the CPU to
2886 * whom the rdp belongs.
2887 */
2888static void
2889__rcu_process_callbacks(struct rcu_state *rsp)
2890{
2891 unsigned long flags;
2892 bool needwake;
2893 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2894
2895 WARN_ON_ONCE(rdp->beenonline == 0);
2896
2897 /* Update RCU state based on any recent quiescent states. */
2898 rcu_check_quiescent_state(rsp, rdp);
2899
2900 /* Does this CPU require a not-yet-started grace period? */
2901 local_irq_save(flags);
2902 if (cpu_needs_another_gp(rsp, rdp)) {
2903 raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
2904 needwake = rcu_start_gp(rsp);
2905 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2906 if (needwake)
2907 rcu_gp_kthread_wake(rsp);
2908 } else {
2909 local_irq_restore(flags);
2910 }
2911
2912 /* If there are callbacks ready, invoke them. */
2913 if (cpu_has_callbacks_ready_to_invoke(rdp))
2914 invoke_rcu_callbacks(rsp, rdp);
2915
2916 /* Do any needed deferred wakeups of rcuo kthreads. */
2917 do_nocb_deferred_wakeup(rdp);
2918}
2919
2920/*
2921 * Do RCU core processing for the current CPU.
2922 */
2923static void rcu_process_callbacks(struct softirq_action *unused)
2924{
2925 struct rcu_state *rsp;
2926
2927 if (cpu_is_offline(smp_processor_id()))
2928 return;
2929 trace_rcu_utilization(TPS("Start RCU core"));
2930 for_each_rcu_flavor(rsp)
2931 __rcu_process_callbacks(rsp);
2932 trace_rcu_utilization(TPS("End RCU core"));
2933}
2934
2935/*
2936 * Schedule RCU callback invocation. If the specified type of RCU
2937 * does not support RCU priority boosting, just do a direct call,
2938 * otherwise wake up the per-CPU kernel kthread. Note that because we
2939 * are running on the current CPU with softirqs disabled, the
2940 * rcu_cpu_kthread_task cannot disappear out from under us.
2941 */
2942static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2943{
2944 if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2945 return;
2946 if (likely(!rsp->boost)) {
2947 rcu_do_batch(rsp, rdp);
2948 return;
2949 }
2950 invoke_rcu_callbacks_kthread();
2951}
2952
2953static void invoke_rcu_core(void)
2954{
2955 if (cpu_online(smp_processor_id()))
2956 raise_softirq(RCU_SOFTIRQ);
2957}
2958
2959/*
2960 * Handle any core-RCU processing required by a call_rcu() invocation.
2961 */
2962static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2963 struct rcu_head *head, unsigned long flags)
2964{
2965 bool needwake;
2966
2967 /*
2968 * If called from an extended quiescent state, invoke the RCU
2969 * core in order to force a re-evaluation of RCU's idleness.
2970 */
2971 if (!rcu_is_watching())
2972 invoke_rcu_core();
2973
2974 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2975 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2976 return;
2977
2978 /*
2979 * Force the grace period if too many callbacks or too long waiting.
2980 * Enforce hysteresis, and don't invoke force_quiescent_state()
2981 * if some other CPU has recently done so. Also, don't bother
2982 * invoking force_quiescent_state() if the newly enqueued callback
2983 * is the only one waiting for a grace period to complete.
2984 */
2985 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2986
2987 /* Are we ignoring a completed grace period? */
2988 note_gp_changes(rsp, rdp);
2989
2990 /* Start a new grace period if one not already started. */
2991 if (!rcu_gp_in_progress(rsp)) {
2992 struct rcu_node *rnp_root = rcu_get_root(rsp);
2993
2994 raw_spin_lock_rcu_node(rnp_root);
2995 needwake = rcu_start_gp(rsp);
2996 raw_spin_unlock_rcu_node(rnp_root);
2997 if (needwake)
2998 rcu_gp_kthread_wake(rsp);
2999 } else {
3000 /* Give the grace period a kick. */
3001 rdp->blimit = LONG_MAX;
3002 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
3003 *rdp->nxttail[RCU_DONE_TAIL] != head)
3004 force_quiescent_state(rsp);
3005 rdp->n_force_qs_snap = rsp->n_force_qs;
3006 rdp->qlen_last_fqs_check = rdp->qlen;
3007 }
3008 }
3009}
3010
3011/*
3012 * RCU callback function to leak a callback.
3013 */
3014static void rcu_leak_callback(struct rcu_head *rhp)
3015{
3016}
3017
3018/*
3019 * Helper function for call_rcu() and friends. The cpu argument will
3020 * normally be -1, indicating "currently running CPU". It may specify
3021 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
3022 * is expected to specify a CPU.
3023 */
3024static void
3025__call_rcu(struct rcu_head *head, rcu_callback_t func,
3026 struct rcu_state *rsp, int cpu, bool lazy)
3027{
3028 unsigned long flags;
3029 struct rcu_data *rdp;
3030
3031 WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */
3032 if (debug_rcu_head_queue(head)) {
3033 /* Probable double call_rcu(), so leak the callback. */
3034 WRITE_ONCE(head->func, rcu_leak_callback);
3035 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
3036 return;
3037 }
3038 head->func = func;
3039 head->next = NULL;
3040
3041 /*
3042 * Opportunistically note grace-period endings and beginnings.
3043 * Note that we might see a beginning right after we see an
3044 * end, but never vice versa, since this CPU has to pass through
3045 * a quiescent state betweentimes.
3046 */
3047 local_irq_save(flags);
3048 rdp = this_cpu_ptr(rsp->rda);
3049
3050 /* Add the callback to our list. */
3051 if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
3052 int offline;
3053
3054 if (cpu != -1)
3055 rdp = per_cpu_ptr(rsp->rda, cpu);
3056 if (likely(rdp->mynode)) {
3057 /* Post-boot, so this should be for a no-CBs CPU. */
3058 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
3059 WARN_ON_ONCE(offline);
3060 /* Offline CPU, _call_rcu() illegal, leak callback. */
3061 local_irq_restore(flags);
3062 return;
3063 }
3064 /*
3065 * Very early boot, before rcu_init(). Initialize if needed
3066 * and then drop through to queue the callback.
3067 */
3068 BUG_ON(cpu != -1);
3069 WARN_ON_ONCE(!rcu_is_watching());
3070 if (!likely(rdp->nxtlist))
3071 init_default_callback_list(rdp);
3072 }
3073 WRITE_ONCE(rdp->qlen, rdp->qlen + 1);
3074 if (lazy)
3075 rdp->qlen_lazy++;
3076 else
3077 rcu_idle_count_callbacks_posted();
3078 smp_mb(); /* Count before adding callback for rcu_barrier(). */
3079 *rdp->nxttail[RCU_NEXT_TAIL] = head;
3080 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
3081
3082 if (__is_kfree_rcu_offset((unsigned long)func))
3083 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3084 rdp->qlen_lazy, rdp->qlen);
3085 else
3086 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
3087
3088 /* Go handle any RCU core processing required. */
3089 __call_rcu_core(rsp, rdp, head, flags);
3090 local_irq_restore(flags);
3091}
3092
3093/*
3094 * Queue an RCU-sched callback for invocation after a grace period.
3095 */
3096void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
3097{
3098 __call_rcu(head, func, &rcu_sched_state, -1, 0);
3099}
3100EXPORT_SYMBOL_GPL(call_rcu_sched);
3101
3102/*
3103 * Queue an RCU callback for invocation after a quicker grace period.
3104 */
3105void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
3106{
3107 __call_rcu(head, func, &rcu_bh_state, -1, 0);
3108}
3109EXPORT_SYMBOL_GPL(call_rcu_bh);
3110
3111/*
3112 * Queue an RCU callback for lazy invocation after a grace period.
3113 * This will likely be later named something like "call_rcu_lazy()",
3114 * but this change will require some way of tagging the lazy RCU
3115 * callbacks in the list of pending callbacks. Until then, this
3116 * function may only be called from __kfree_rcu().
3117 */
3118void kfree_call_rcu(struct rcu_head *head,
3119 rcu_callback_t func)
3120{
3121 __call_rcu(head, func, rcu_state_p, -1, 1);
3122}
3123EXPORT_SYMBOL_GPL(kfree_call_rcu);
3124
3125/*
3126 * Because a context switch is a grace period for RCU-sched and RCU-bh,
3127 * any blocking grace-period wait automatically implies a grace period
3128 * if there is only one CPU online at any point time during execution
3129 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
3130 * occasionally incorrectly indicate that there are multiple CPUs online
3131 * when there was in fact only one the whole time, as this just adds
3132 * some overhead: RCU still operates correctly.
3133 */
3134static inline int rcu_blocking_is_gp(void)
3135{
3136 int ret;
3137
3138 might_sleep(); /* Check for RCU read-side critical section. */
3139 preempt_disable();
3140 ret = num_online_cpus() <= 1;
3141 preempt_enable();
3142 return ret;
3143}
3144
3145/**
3146 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3147 *
3148 * Control will return to the caller some time after a full rcu-sched
3149 * grace period has elapsed, in other words after all currently executing
3150 * rcu-sched read-side critical sections have completed. These read-side
3151 * critical sections are delimited by rcu_read_lock_sched() and
3152 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
3153 * local_irq_disable(), and so on may be used in place of
3154 * rcu_read_lock_sched().
3155 *
3156 * This means that all preempt_disable code sequences, including NMI and
3157 * non-threaded hardware-interrupt handlers, in progress on entry will
3158 * have completed before this primitive returns. However, this does not
3159 * guarantee that softirq handlers will have completed, since in some
3160 * kernels, these handlers can run in process context, and can block.
3161 *
3162 * Note that this guarantee implies further memory-ordering guarantees.
3163 * On systems with more than one CPU, when synchronize_sched() returns,
3164 * each CPU is guaranteed to have executed a full memory barrier since the
3165 * end of its last RCU-sched read-side critical section whose beginning
3166 * preceded the call to synchronize_sched(). In addition, each CPU having
3167 * an RCU read-side critical section that extends beyond the return from
3168 * synchronize_sched() is guaranteed to have executed a full memory barrier
3169 * after the beginning of synchronize_sched() and before the beginning of
3170 * that RCU read-side critical section. Note that these guarantees include
3171 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3172 * that are executing in the kernel.
3173 *
3174 * Furthermore, if CPU A invoked synchronize_sched(), which returned
3175 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3176 * to have executed a full memory barrier during the execution of
3177 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3178 * again only if the system has more than one CPU).
3179 *
3180 * This primitive provides the guarantees made by the (now removed)
3181 * synchronize_kernel() API. In contrast, synchronize_rcu() only
3182 * guarantees that rcu_read_lock() sections will have completed.
3183 * In "classic RCU", these two guarantees happen to be one and
3184 * the same, but can differ in realtime RCU implementations.
3185 */
3186void synchronize_sched(void)
3187{
3188 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3189 lock_is_held(&rcu_lock_map) ||
3190 lock_is_held(&rcu_sched_lock_map),
3191 "Illegal synchronize_sched() in RCU-sched read-side critical section");
3192 if (rcu_blocking_is_gp())
3193 return;
3194 if (rcu_gp_is_expedited())
3195 synchronize_sched_expedited();
3196 else
3197 wait_rcu_gp(call_rcu_sched);
3198}
3199EXPORT_SYMBOL_GPL(synchronize_sched);
3200
3201/**
3202 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3203 *
3204 * Control will return to the caller some time after a full rcu_bh grace
3205 * period has elapsed, in other words after all currently executing rcu_bh
3206 * read-side critical sections have completed. RCU read-side critical
3207 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3208 * and may be nested.
3209 *
3210 * See the description of synchronize_sched() for more detailed information
3211 * on memory ordering guarantees.
3212 */
3213void synchronize_rcu_bh(void)
3214{
3215 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3216 lock_is_held(&rcu_lock_map) ||
3217 lock_is_held(&rcu_sched_lock_map),
3218 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3219 if (rcu_blocking_is_gp())
3220 return;
3221 if (rcu_gp_is_expedited())
3222 synchronize_rcu_bh_expedited();
3223 else
3224 wait_rcu_gp(call_rcu_bh);
3225}
3226EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3227
3228/**
3229 * get_state_synchronize_rcu - Snapshot current RCU state
3230 *
3231 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3232 * to determine whether or not a full grace period has elapsed in the
3233 * meantime.
3234 */
3235unsigned long get_state_synchronize_rcu(void)
3236{
3237 /*
3238 * Any prior manipulation of RCU-protected data must happen
3239 * before the load from ->gpnum.
3240 */
3241 smp_mb(); /* ^^^ */
3242
3243 /*
3244 * Make sure this load happens before the purportedly
3245 * time-consuming work between get_state_synchronize_rcu()
3246 * and cond_synchronize_rcu().
3247 */
3248 return smp_load_acquire(&rcu_state_p->gpnum);
3249}
3250EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3251
3252/**
3253 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3254 *
3255 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3256 *
3257 * If a full RCU grace period has elapsed since the earlier call to
3258 * get_state_synchronize_rcu(), just return. Otherwise, invoke
3259 * synchronize_rcu() to wait for a full grace period.
3260 *
3261 * Yes, this function does not take counter wrap into account. But
3262 * counter wrap is harmless. If the counter wraps, we have waited for
3263 * more than 2 billion grace periods (and way more on a 64-bit system!),
3264 * so waiting for one additional grace period should be just fine.
3265 */
3266void cond_synchronize_rcu(unsigned long oldstate)
3267{
3268 unsigned long newstate;
3269
3270 /*
3271 * Ensure that this load happens before any RCU-destructive
3272 * actions the caller might carry out after we return.
3273 */
3274 newstate = smp_load_acquire(&rcu_state_p->completed);
3275 if (ULONG_CMP_GE(oldstate, newstate))
3276 synchronize_rcu();
3277}
3278EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3279
3280/**
3281 * get_state_synchronize_sched - Snapshot current RCU-sched state
3282 *
3283 * Returns a cookie that is used by a later call to cond_synchronize_sched()
3284 * to determine whether or not a full grace period has elapsed in the
3285 * meantime.
3286 */
3287unsigned long get_state_synchronize_sched(void)
3288{
3289 /*
3290 * Any prior manipulation of RCU-protected data must happen
3291 * before the load from ->gpnum.
3292 */
3293 smp_mb(); /* ^^^ */
3294
3295 /*
3296 * Make sure this load happens before the purportedly
3297 * time-consuming work between get_state_synchronize_sched()
3298 * and cond_synchronize_sched().
3299 */
3300 return smp_load_acquire(&rcu_sched_state.gpnum);
3301}
3302EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
3303
3304/**
3305 * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
3306 *
3307 * @oldstate: return value from earlier call to get_state_synchronize_sched()
3308 *
3309 * If a full RCU-sched grace period has elapsed since the earlier call to
3310 * get_state_synchronize_sched(), just return. Otherwise, invoke
3311 * synchronize_sched() to wait for a full grace period.
3312 *
3313 * Yes, this function does not take counter wrap into account. But
3314 * counter wrap is harmless. If the counter wraps, we have waited for
3315 * more than 2 billion grace periods (and way more on a 64-bit system!),
3316 * so waiting for one additional grace period should be just fine.
3317 */
3318void cond_synchronize_sched(unsigned long oldstate)
3319{
3320 unsigned long newstate;
3321
3322 /*
3323 * Ensure that this load happens before any RCU-destructive
3324 * actions the caller might carry out after we return.
3325 */
3326 newstate = smp_load_acquire(&rcu_sched_state.completed);
3327 if (ULONG_CMP_GE(oldstate, newstate))
3328 synchronize_sched();
3329}
3330EXPORT_SYMBOL_GPL(cond_synchronize_sched);
3331
3332/* Adjust sequence number for start of update-side operation. */
3333static void rcu_seq_start(unsigned long *sp)
3334{
3335 WRITE_ONCE(*sp, *sp + 1);
3336 smp_mb(); /* Ensure update-side operation after counter increment. */
3337 WARN_ON_ONCE(!(*sp & 0x1));
3338}
3339
3340/* Adjust sequence number for end of update-side operation. */
3341static void rcu_seq_end(unsigned long *sp)
3342{
3343 smp_mb(); /* Ensure update-side operation before counter increment. */
3344 WRITE_ONCE(*sp, *sp + 1);
3345 WARN_ON_ONCE(*sp & 0x1);
3346}
3347
3348/* Take a snapshot of the update side's sequence number. */
3349static unsigned long rcu_seq_snap(unsigned long *sp)
3350{
3351 unsigned long s;
3352
3353 s = (READ_ONCE(*sp) + 3) & ~0x1;
3354 smp_mb(); /* Above access must not bleed into critical section. */
3355 return s;
3356}
3357
3358/*
3359 * Given a snapshot from rcu_seq_snap(), determine whether or not a
3360 * full update-side operation has occurred.
3361 */
3362static bool rcu_seq_done(unsigned long *sp, unsigned long s)
3363{
3364 return ULONG_CMP_GE(READ_ONCE(*sp), s);
3365}
3366
3367/* Wrapper functions for expedited grace periods. */
3368static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
3369{
3370 rcu_seq_start(&rsp->expedited_sequence);
3371}
3372static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
3373{
3374 rcu_seq_end(&rsp->expedited_sequence);
3375 smp_mb(); /* Ensure that consecutive grace periods serialize. */
3376}
3377static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
3378{
3379 smp_mb(); /* Caller's modifications seen first by other CPUs. */
3380 return rcu_seq_snap(&rsp->expedited_sequence);
3381}
3382static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
3383{
3384 return rcu_seq_done(&rsp->expedited_sequence, s);
3385}
3386
3387/*
3388 * Reset the ->expmaskinit values in the rcu_node tree to reflect any
3389 * recent CPU-online activity. Note that these masks are not cleared
3390 * when CPUs go offline, so they reflect the union of all CPUs that have
3391 * ever been online. This means that this function normally takes its
3392 * no-work-to-do fastpath.
3393 */
3394static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
3395{
3396 bool done;
3397 unsigned long flags;
3398 unsigned long mask;
3399 unsigned long oldmask;
3400 int ncpus = READ_ONCE(rsp->ncpus);
3401 struct rcu_node *rnp;
3402 struct rcu_node *rnp_up;
3403
3404 /* If no new CPUs onlined since last time, nothing to do. */
3405 if (likely(ncpus == rsp->ncpus_snap))
3406 return;
3407 rsp->ncpus_snap = ncpus;
3408
3409 /*
3410 * Each pass through the following loop propagates newly onlined
3411 * CPUs for the current rcu_node structure up the rcu_node tree.
3412 */
3413 rcu_for_each_leaf_node(rsp, rnp) {
3414 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3415 if (rnp->expmaskinit == rnp->expmaskinitnext) {
3416 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3417 continue; /* No new CPUs, nothing to do. */
3418 }
3419
3420 /* Update this node's mask, track old value for propagation. */
3421 oldmask = rnp->expmaskinit;
3422 rnp->expmaskinit = rnp->expmaskinitnext;
3423 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3424
3425 /* If was already nonzero, nothing to propagate. */
3426 if (oldmask)
3427 continue;
3428
3429 /* Propagate the new CPU up the tree. */
3430 mask = rnp->grpmask;
3431 rnp_up = rnp->parent;
3432 done = false;
3433 while (rnp_up) {
3434 raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
3435 if (rnp_up->expmaskinit)
3436 done = true;
3437 rnp_up->expmaskinit |= mask;
3438 raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
3439 if (done)
3440 break;
3441 mask = rnp_up->grpmask;
3442 rnp_up = rnp_up->parent;
3443 }
3444 }
3445}
3446
3447/*
3448 * Reset the ->expmask values in the rcu_node tree in preparation for
3449 * a new expedited grace period.
3450 */
3451static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
3452{
3453 unsigned long flags;
3454 struct rcu_node *rnp;
3455
3456 sync_exp_reset_tree_hotplug(rsp);
3457 rcu_for_each_node_breadth_first(rsp, rnp) {
3458 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3459 WARN_ON_ONCE(rnp->expmask);
3460 rnp->expmask = rnp->expmaskinit;
3461 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3462 }
3463}
3464
3465/*
3466 * Return non-zero if there is no RCU expedited grace period in progress
3467 * for the specified rcu_node structure, in other words, if all CPUs and
3468 * tasks covered by the specified rcu_node structure have done their bit
3469 * for the current expedited grace period. Works only for preemptible
3470 * RCU -- other RCU implementation use other means.
3471 *
3472 * Caller must hold the root rcu_node's exp_funnel_mutex.
3473 */
3474static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
3475{
3476 return rnp->exp_tasks == NULL &&
3477 READ_ONCE(rnp->expmask) == 0;
3478}
3479
3480/*
3481 * Report the exit from RCU read-side critical section for the last task
3482 * that queued itself during or before the current expedited preemptible-RCU
3483 * grace period. This event is reported either to the rcu_node structure on
3484 * which the task was queued or to one of that rcu_node structure's ancestors,
3485 * recursively up the tree. (Calm down, calm down, we do the recursion
3486 * iteratively!)
3487 *
3488 * Caller must hold the root rcu_node's exp_funnel_mutex and the
3489 * specified rcu_node structure's ->lock.
3490 */
3491static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
3492 bool wake, unsigned long flags)
3493 __releases(rnp->lock)
3494{
3495 unsigned long mask;
3496
3497 for (;;) {
3498 if (!sync_rcu_preempt_exp_done(rnp)) {
3499 if (!rnp->expmask)
3500 rcu_initiate_boost(rnp, flags);
3501 else
3502 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3503 break;
3504 }
3505 if (rnp->parent == NULL) {
3506 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3507 if (wake) {
3508 smp_mb(); /* EGP done before wake_up(). */
3509 swake_up(&rsp->expedited_wq);
3510 }
3511 break;
3512 }
3513 mask = rnp->grpmask;
3514 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
3515 rnp = rnp->parent;
3516 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
3517 WARN_ON_ONCE(!(rnp->expmask & mask));
3518 rnp->expmask &= ~mask;
3519 }
3520}
3521
3522/*
3523 * Report expedited quiescent state for specified node. This is a
3524 * lock-acquisition wrapper function for __rcu_report_exp_rnp().
3525 *
3526 * Caller must hold the root rcu_node's exp_funnel_mutex.
3527 */
3528static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
3529 struct rcu_node *rnp, bool wake)
3530{
3531 unsigned long flags;
3532
3533 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3534 __rcu_report_exp_rnp(rsp, rnp, wake, flags);
3535}
3536
3537/*
3538 * Report expedited quiescent state for multiple CPUs, all covered by the
3539 * specified leaf rcu_node structure. Caller must hold the root
3540 * rcu_node's exp_funnel_mutex.
3541 */
3542static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
3543 unsigned long mask, bool wake)
3544{
3545 unsigned long flags;
3546
3547 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3548 if (!(rnp->expmask & mask)) {
3549 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3550 return;
3551 }
3552 rnp->expmask &= ~mask;
3553 __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
3554}
3555
3556/*
3557 * Report expedited quiescent state for specified rcu_data (CPU).
3558 * Caller must hold the root rcu_node's exp_funnel_mutex.
3559 */
3560static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
3561 bool wake)
3562{
3563 rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
3564}
3565
3566/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
3567static bool sync_exp_work_done(struct rcu_state *rsp, struct rcu_node *rnp,
3568 struct rcu_data *rdp,
3569 atomic_long_t *stat, unsigned long s)
3570{
3571 if (rcu_exp_gp_seq_done(rsp, s)) {
3572 if (rnp)
3573 mutex_unlock(&rnp->exp_funnel_mutex);
3574 else if (rdp)
3575 mutex_unlock(&rdp->exp_funnel_mutex);
3576 /* Ensure test happens before caller kfree(). */
3577 smp_mb__before_atomic(); /* ^^^ */
3578 atomic_long_inc(stat);
3579 return true;
3580 }
3581 return false;
3582}
3583
3584/*
3585 * Funnel-lock acquisition for expedited grace periods. Returns a
3586 * pointer to the root rcu_node structure, or NULL if some other
3587 * task did the expedited grace period for us.
3588 */
3589static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
3590{
3591 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
3592 struct rcu_node *rnp0;
3593 struct rcu_node *rnp1 = NULL;
3594
3595 /*
3596 * First try directly acquiring the root lock in order to reduce
3597 * latency in the common case where expedited grace periods are
3598 * rare. We check mutex_is_locked() to avoid pathological levels of
3599 * memory contention on ->exp_funnel_mutex in the heavy-load case.
3600 */
3601 rnp0 = rcu_get_root(rsp);
3602 if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) {
3603 if (mutex_trylock(&rnp0->exp_funnel_mutex)) {
3604 if (sync_exp_work_done(rsp, rnp0, NULL,
3605 &rdp->expedited_workdone0, s))
3606 return NULL;
3607 return rnp0;
3608 }
3609 }
3610
3611 /*
3612 * Each pass through the following loop works its way
3613 * up the rcu_node tree, returning if others have done the
3614 * work or otherwise falls through holding the root rnp's
3615 * ->exp_funnel_mutex. The mapping from CPU to rcu_node structure
3616 * can be inexact, as it is just promoting locality and is not
3617 * strictly needed for correctness.
3618 */
3619 if (sync_exp_work_done(rsp, NULL, NULL, &rdp->expedited_workdone1, s))
3620 return NULL;
3621 mutex_lock(&rdp->exp_funnel_mutex);
3622 rnp0 = rdp->mynode;
3623 for (; rnp0 != NULL; rnp0 = rnp0->parent) {
3624 if (sync_exp_work_done(rsp, rnp1, rdp,
3625 &rdp->expedited_workdone2, s))
3626 return NULL;
3627 mutex_lock(&rnp0->exp_funnel_mutex);
3628 if (rnp1)
3629 mutex_unlock(&rnp1->exp_funnel_mutex);
3630 else
3631 mutex_unlock(&rdp->exp_funnel_mutex);
3632 rnp1 = rnp0;
3633 }
3634 if (sync_exp_work_done(rsp, rnp1, rdp,
3635 &rdp->expedited_workdone3, s))
3636 return NULL;
3637 return rnp1;
3638}
3639
3640/* Invoked on each online non-idle CPU for expedited quiescent state. */
3641static void sync_sched_exp_handler(void *data)
3642{
3643 struct rcu_data *rdp;
3644 struct rcu_node *rnp;
3645 struct rcu_state *rsp = data;
3646
3647 rdp = this_cpu_ptr(rsp->rda);
3648 rnp = rdp->mynode;
3649 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
3650 __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
3651 return;
3652 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
3653 resched_cpu(smp_processor_id());
3654}
3655
3656/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
3657static void sync_sched_exp_online_cleanup(int cpu)
3658{
3659 struct rcu_data *rdp;
3660 int ret;
3661 struct rcu_node *rnp;
3662 struct rcu_state *rsp = &rcu_sched_state;
3663
3664 rdp = per_cpu_ptr(rsp->rda, cpu);
3665 rnp = rdp->mynode;
3666 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
3667 return;
3668 ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
3669 WARN_ON_ONCE(ret);
3670}
3671
3672/*
3673 * Select the nodes that the upcoming expedited grace period needs
3674 * to wait for.
3675 */
3676static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
3677 smp_call_func_t func)
3678{
3679 int cpu;
3680 unsigned long flags;
3681 unsigned long mask;
3682 unsigned long mask_ofl_test;
3683 unsigned long mask_ofl_ipi;
3684 int ret;
3685 struct rcu_node *rnp;
3686
3687 sync_exp_reset_tree(rsp);
3688 rcu_for_each_leaf_node(rsp, rnp) {
3689 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3690
3691 /* Each pass checks a CPU for identity, offline, and idle. */
3692 mask_ofl_test = 0;
3693 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
3694 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3695 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
3696
3697 if (raw_smp_processor_id() == cpu ||
3698 !(atomic_add_return(0, &rdtp->dynticks) & 0x1))
3699 mask_ofl_test |= rdp->grpmask;
3700 }
3701 mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
3702
3703 /*
3704 * Need to wait for any blocked tasks as well. Note that
3705 * additional blocking tasks will also block the expedited
3706 * GP until such time as the ->expmask bits are cleared.
3707 */
3708 if (rcu_preempt_has_tasks(rnp))
3709 rnp->exp_tasks = rnp->blkd_tasks.next;
3710 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3711
3712 /* IPI the remaining CPUs for expedited quiescent state. */
3713 mask = 1;
3714 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3715 if (!(mask_ofl_ipi & mask))
3716 continue;
3717retry_ipi:
3718 ret = smp_call_function_single(cpu, func, rsp, 0);
3719 if (!ret) {
3720 mask_ofl_ipi &= ~mask;
3721 continue;
3722 }
3723 /* Failed, raced with offline. */
3724 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3725 if (cpu_online(cpu) &&
3726 (rnp->expmask & mask)) {
3727 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3728 schedule_timeout_uninterruptible(1);
3729 if (cpu_online(cpu) &&
3730 (rnp->expmask & mask))
3731 goto retry_ipi;
3732 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3733 }
3734 if (!(rnp->expmask & mask))
3735 mask_ofl_ipi &= ~mask;
3736 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3737 }
3738 /* Report quiescent states for those that went offline. */
3739 mask_ofl_test |= mask_ofl_ipi;
3740 if (mask_ofl_test)
3741 rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
3742 }
3743}
3744
3745static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
3746{
3747 int cpu;
3748 unsigned long jiffies_stall;
3749 unsigned long jiffies_start;
3750 unsigned long mask;
3751 int ndetected;
3752 struct rcu_node *rnp;
3753 struct rcu_node *rnp_root = rcu_get_root(rsp);
3754 int ret;
3755
3756 jiffies_stall = rcu_jiffies_till_stall_check();
3757 jiffies_start = jiffies;
3758
3759 for (;;) {
3760 ret = swait_event_timeout(
3761 rsp->expedited_wq,
3762 sync_rcu_preempt_exp_done(rnp_root),
3763 jiffies_stall);
3764 if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
3765 return;
3766 if (ret < 0) {
3767 /* Hit a signal, disable CPU stall warnings. */
3768 swait_event(rsp->expedited_wq,
3769 sync_rcu_preempt_exp_done(rnp_root));
3770 return;
3771 }
3772 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
3773 rsp->name);
3774 ndetected = 0;
3775 rcu_for_each_leaf_node(rsp, rnp) {
3776 ndetected = rcu_print_task_exp_stall(rnp);
3777 mask = 1;
3778 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3779 struct rcu_data *rdp;
3780
3781 if (!(rnp->expmask & mask))
3782 continue;
3783 ndetected++;
3784 rdp = per_cpu_ptr(rsp->rda, cpu);
3785 pr_cont(" %d-%c%c%c", cpu,
3786 "O."[cpu_online(cpu)],
3787 "o."[!!(rdp->grpmask & rnp->expmaskinit)],
3788 "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
3789 }
3790 mask <<= 1;
3791 }
3792 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
3793 jiffies - jiffies_start, rsp->expedited_sequence,
3794 rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
3795 if (!ndetected) {
3796 pr_err("blocking rcu_node structures:");
3797 rcu_for_each_node_breadth_first(rsp, rnp) {
3798 if (rnp == rnp_root)
3799 continue; /* printed unconditionally */
3800 if (sync_rcu_preempt_exp_done(rnp))
3801 continue;
3802 pr_cont(" l=%u:%d-%d:%#lx/%c",
3803 rnp->level, rnp->grplo, rnp->grphi,
3804 rnp->expmask,
3805 ".T"[!!rnp->exp_tasks]);
3806 }
3807 pr_cont("\n");
3808 }
3809 rcu_for_each_leaf_node(rsp, rnp) {
3810 mask = 1;
3811 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask <<= 1) {
3812 if (!(rnp->expmask & mask))
3813 continue;
3814 dump_cpu_task(cpu);
3815 }
3816 }
3817 jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
3818 }
3819}
3820
3821/**
3822 * synchronize_sched_expedited - Brute-force RCU-sched grace period
3823 *
3824 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
3825 * approach to force the grace period to end quickly. This consumes
3826 * significant time on all CPUs and is unfriendly to real-time workloads,
3827 * so is thus not recommended for any sort of common-case code. In fact,
3828 * if you are using synchronize_sched_expedited() in a loop, please
3829 * restructure your code to batch your updates, and then use a single
3830 * synchronize_sched() instead.
3831 *
3832 * This implementation can be thought of as an application of sequence
3833 * locking to expedited grace periods, but using the sequence counter to
3834 * determine when someone else has already done the work instead of for
3835 * retrying readers.
3836 */
3837void synchronize_sched_expedited(void)
3838{
3839 unsigned long s;
3840 struct rcu_node *rnp;
3841 struct rcu_state *rsp = &rcu_sched_state;
3842
3843 /* If only one CPU, this is automatically a grace period. */
3844 if (rcu_blocking_is_gp())
3845 return;
3846
3847 /* If expedited grace periods are prohibited, fall back to normal. */
3848 if (rcu_gp_is_normal()) {
3849 wait_rcu_gp(call_rcu_sched);
3850 return;
3851 }
3852
3853 /* Take a snapshot of the sequence number. */
3854 s = rcu_exp_gp_seq_snap(rsp);
3855
3856 rnp = exp_funnel_lock(rsp, s);
3857 if (rnp == NULL)
3858 return; /* Someone else did our work for us. */
3859
3860 rcu_exp_gp_seq_start(rsp);
3861 sync_rcu_exp_select_cpus(rsp, sync_sched_exp_handler);
3862 synchronize_sched_expedited_wait(rsp);
3863
3864 rcu_exp_gp_seq_end(rsp);
3865 mutex_unlock(&rnp->exp_funnel_mutex);
3866}
3867EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
3868
3869/*
3870 * Check to see if there is any immediate RCU-related work to be done
3871 * by the current CPU, for the specified type of RCU, returning 1 if so.
3872 * The checks are in order of increasing expense: checks that can be
3873 * carried out against CPU-local state are performed first. However,
3874 * we must check for CPU stalls first, else we might not get a chance.
3875 */
3876static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3877{
3878 struct rcu_node *rnp = rdp->mynode;
3879
3880 rdp->n_rcu_pending++;
3881
3882 /* Check for CPU stalls, if enabled. */
3883 check_cpu_stall(rsp, rdp);
3884
3885 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3886 if (rcu_nohz_full_cpu(rsp))
3887 return 0;
3888
3889 /* Is the RCU core waiting for a quiescent state from this CPU? */
3890 if (rcu_scheduler_fully_active &&
3891 rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
3892 rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) {
3893 rdp->n_rp_core_needs_qs++;
3894 } else if (rdp->core_needs_qs &&
3895 (!rdp->cpu_no_qs.b.norm ||
3896 rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) {
3897 rdp->n_rp_report_qs++;
3898 return 1;
3899 }
3900
3901 /* Does this CPU have callbacks ready to invoke? */
3902 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
3903 rdp->n_rp_cb_ready++;
3904 return 1;
3905 }
3906
3907 /* Has RCU gone idle with this CPU needing another grace period? */
3908 if (cpu_needs_another_gp(rsp, rdp)) {
3909 rdp->n_rp_cpu_needs_gp++;
3910 return 1;
3911 }
3912
3913 /* Has another RCU grace period completed? */
3914 if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
3915 rdp->n_rp_gp_completed++;
3916 return 1;
3917 }
3918
3919 /* Has a new RCU grace period started? */
3920 if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
3921 unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
3922 rdp->n_rp_gp_started++;
3923 return 1;
3924 }
3925
3926 /* Does this CPU need a deferred NOCB wakeup? */
3927 if (rcu_nocb_need_deferred_wakeup(rdp)) {
3928 rdp->n_rp_nocb_defer_wakeup++;
3929 return 1;
3930 }
3931
3932 /* nothing to do */
3933 rdp->n_rp_need_nothing++;
3934 return 0;
3935}
3936
3937/*
3938 * Check to see if there is any immediate RCU-related work to be done
3939 * by the current CPU, returning 1 if so. This function is part of the
3940 * RCU implementation; it is -not- an exported member of the RCU API.
3941 */
3942static int rcu_pending(void)
3943{
3944 struct rcu_state *rsp;
3945
3946 for_each_rcu_flavor(rsp)
3947 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3948 return 1;
3949 return 0;
3950}
3951
3952/*
3953 * Return true if the specified CPU has any callback. If all_lazy is
3954 * non-NULL, store an indication of whether all callbacks are lazy.
3955 * (If there are no callbacks, all of them are deemed to be lazy.)
3956 */
3957static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3958{
3959 bool al = true;
3960 bool hc = false;
3961 struct rcu_data *rdp;
3962 struct rcu_state *rsp;
3963
3964 for_each_rcu_flavor(rsp) {
3965 rdp = this_cpu_ptr(rsp->rda);
3966 if (!rdp->nxtlist)
3967 continue;
3968 hc = true;
3969 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3970 al = false;
3971 break;
3972 }
3973 }
3974 if (all_lazy)
3975 *all_lazy = al;
3976 return hc;
3977}
3978
3979/*
3980 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3981 * the compiler is expected to optimize this away.
3982 */
3983static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3984 int cpu, unsigned long done)
3985{
3986 trace_rcu_barrier(rsp->name, s, cpu,
3987 atomic_read(&rsp->barrier_cpu_count), done);
3988}
3989
3990/*
3991 * RCU callback function for _rcu_barrier(). If we are last, wake
3992 * up the task executing _rcu_barrier().
3993 */
3994static void rcu_barrier_callback(struct rcu_head *rhp)
3995{
3996 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3997 struct rcu_state *rsp = rdp->rsp;
3998
3999 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
4000 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence);
4001 complete(&rsp->barrier_completion);
4002 } else {
4003 _rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence);
4004 }
4005}
4006
4007/*
4008 * Called with preemption disabled, and from cross-cpu IRQ context.
4009 */
4010static void rcu_barrier_func(void *type)
4011{
4012 struct rcu_state *rsp = type;
4013 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
4014
4015 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence);
4016 atomic_inc(&rsp->barrier_cpu_count);
4017 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
4018}
4019
4020/*
4021 * Orchestrate the specified type of RCU barrier, waiting for all
4022 * RCU callbacks of the specified type to complete.
4023 */
4024static void _rcu_barrier(struct rcu_state *rsp)
4025{
4026 int cpu;
4027 struct rcu_data *rdp;
4028 unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
4029
4030 _rcu_barrier_trace(rsp, "Begin", -1, s);
4031
4032 /* Take mutex to serialize concurrent rcu_barrier() requests. */
4033 mutex_lock(&rsp->barrier_mutex);
4034
4035 /* Did someone else do our work for us? */
4036 if (rcu_seq_done(&rsp->barrier_sequence, s)) {
4037 _rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence);
4038 smp_mb(); /* caller's subsequent code after above check. */
4039 mutex_unlock(&rsp->barrier_mutex);
4040 return;
4041 }
4042
4043 /* Mark the start of the barrier operation. */
4044 rcu_seq_start(&rsp->barrier_sequence);
4045 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence);
4046
4047 /*
4048 * Initialize the count to one rather than to zero in order to
4049 * avoid a too-soon return to zero in case of a short grace period
4050 * (or preemption of this task). Exclude CPU-hotplug operations
4051 * to ensure that no offline CPU has callbacks queued.
4052 */
4053 init_completion(&rsp->barrier_completion);
4054 atomic_set(&rsp->barrier_cpu_count, 1);
4055 get_online_cpus();
4056
4057 /*
4058 * Force each CPU with callbacks to register a new callback.
4059 * When that callback is invoked, we will know that all of the
4060 * corresponding CPU's preceding callbacks have been invoked.
4061 */
4062 for_each_possible_cpu(cpu) {
4063 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
4064 continue;
4065 rdp = per_cpu_ptr(rsp->rda, cpu);
4066 if (rcu_is_nocb_cpu(cpu)) {
4067 if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
4068 _rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
4069 rsp->barrier_sequence);
4070 } else {
4071 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
4072 rsp->barrier_sequence);
4073 smp_mb__before_atomic();
4074 atomic_inc(&rsp->barrier_cpu_count);
4075 __call_rcu(&rdp->barrier_head,
4076 rcu_barrier_callback, rsp, cpu, 0);
4077 }
4078 } else if (READ_ONCE(rdp->qlen)) {
4079 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
4080 rsp->barrier_sequence);
4081 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
4082 } else {
4083 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
4084 rsp->barrier_sequence);
4085 }
4086 }
4087 put_online_cpus();
4088
4089 /*
4090 * Now that we have an rcu_barrier_callback() callback on each
4091 * CPU, and thus each counted, remove the initial count.
4092 */
4093 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
4094 complete(&rsp->barrier_completion);
4095
4096 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4097 wait_for_completion(&rsp->barrier_completion);
4098
4099 /* Mark the end of the barrier operation. */
4100 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence);
4101 rcu_seq_end(&rsp->barrier_sequence);
4102
4103 /* Other rcu_barrier() invocations can now safely proceed. */
4104 mutex_unlock(&rsp->barrier_mutex);
4105}
4106
4107/**
4108 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
4109 */
4110void rcu_barrier_bh(void)
4111{
4112 _rcu_barrier(&rcu_bh_state);
4113}
4114EXPORT_SYMBOL_GPL(rcu_barrier_bh);
4115
4116/**
4117 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
4118 */
4119void rcu_barrier_sched(void)
4120{
4121 _rcu_barrier(&rcu_sched_state);
4122}
4123EXPORT_SYMBOL_GPL(rcu_barrier_sched);
4124
4125/*
4126 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
4127 * first CPU in a given leaf rcu_node structure coming online. The caller
4128 * must hold the corresponding leaf rcu_node ->lock with interrrupts
4129 * disabled.
4130 */
4131static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
4132{
4133 long mask;
4134 struct rcu_node *rnp = rnp_leaf;
4135
4136 for (;;) {
4137 mask = rnp->grpmask;
4138 rnp = rnp->parent;
4139 if (rnp == NULL)
4140 return;
4141 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
4142 rnp->qsmaskinit |= mask;
4143 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
4144 }
4145}
4146
4147/*
4148 * Do boot-time initialization of a CPU's per-CPU RCU data.
4149 */
4150static void __init
4151rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
4152{
4153 unsigned long flags;
4154 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4155 struct rcu_node *rnp = rcu_get_root(rsp);
4156
4157 /* Set up local state, ensuring consistent view of global state. */
4158 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4159 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
4160 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
4161 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
4162 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
4163 rdp->cpu = cpu;
4164 rdp->rsp = rsp;
4165 mutex_init(&rdp->exp_funnel_mutex);
4166 rcu_boot_init_nocb_percpu_data(rdp);
4167 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4168}
4169
4170/*
4171 * Initialize a CPU's per-CPU RCU data. Note that only one online or
4172 * offline event can be happening at a given time. Note also that we
4173 * can accept some slop in the rsp->completed access due to the fact
4174 * that this CPU cannot possibly have any RCU callbacks in flight yet.
4175 */
4176static void
4177rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
4178{
4179 unsigned long flags;
4180 unsigned long mask;
4181 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4182 struct rcu_node *rnp = rcu_get_root(rsp);
4183
4184 /* Set up local state, ensuring consistent view of global state. */
4185 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4186 rdp->qlen_last_fqs_check = 0;
4187 rdp->n_force_qs_snap = rsp->n_force_qs;
4188 rdp->blimit = blimit;
4189 if (!rdp->nxtlist)
4190 init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
4191 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
4192 rcu_sysidle_init_percpu_data(rdp->dynticks);
4193 atomic_set(&rdp->dynticks->dynticks,
4194 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
4195 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4196
4197 /*
4198 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
4199 * propagation up the rcu_node tree will happen at the beginning
4200 * of the next grace period.
4201 */
4202 rnp = rdp->mynode;
4203 mask = rdp->grpmask;
4204 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4205 rnp->qsmaskinitnext |= mask;
4206 rnp->expmaskinitnext |= mask;
4207 if (!rdp->beenonline)
4208 WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
4209 rdp->beenonline = true; /* We have now been online. */
4210 rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
4211 rdp->completed = rnp->completed;
4212 rdp->cpu_no_qs.b.norm = true;
4213 rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu);
4214 rdp->core_needs_qs = false;
4215 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
4216 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4217}
4218
4219static void rcu_prepare_cpu(int cpu)
4220{
4221 struct rcu_state *rsp;
4222
4223 for_each_rcu_flavor(rsp)
4224 rcu_init_percpu_data(cpu, rsp);
4225}
4226
4227#ifdef CONFIG_HOTPLUG_CPU
4228/*
4229 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
4230 * function. We now remove it from the rcu_node tree's ->qsmaskinit
4231 * bit masks.
4232 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
4233 * function. We now remove it from the rcu_node tree's ->qsmaskinit
4234 * bit masks.
4235 */
4236static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
4237{
4238 unsigned long flags;
4239 unsigned long mask;
4240 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
4241 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
4242
4243 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
4244 return;
4245
4246 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
4247 mask = rdp->grpmask;
4248 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
4249 rnp->qsmaskinitnext &= ~mask;
4250 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4251}
4252
4253void rcu_report_dead(unsigned int cpu)
4254{
4255 struct rcu_state *rsp;
4256
4257 /* QS for any half-done expedited RCU-sched GP. */
4258 preempt_disable();
4259 rcu_report_exp_rdp(&rcu_sched_state,
4260 this_cpu_ptr(rcu_sched_state.rda), true);
4261 preempt_enable();
4262 for_each_rcu_flavor(rsp)
4263 rcu_cleanup_dying_idle_cpu(cpu, rsp);
4264}
4265#endif
4266
4267/*
4268 * Handle CPU online/offline notification events.
4269 */
4270int rcu_cpu_notify(struct notifier_block *self,
4271 unsigned long action, void *hcpu)
4272{
4273 long cpu = (long)hcpu;
4274 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
4275 struct rcu_node *rnp = rdp->mynode;
4276 struct rcu_state *rsp;
4277
4278 switch (action) {
4279 case CPU_UP_PREPARE:
4280 case CPU_UP_PREPARE_FROZEN:
4281 rcu_prepare_cpu(cpu);
4282 rcu_prepare_kthreads(cpu);
4283 rcu_spawn_all_nocb_kthreads(cpu);
4284 break;
4285 case CPU_ONLINE:
4286 case CPU_DOWN_FAILED:
4287 sync_sched_exp_online_cleanup(cpu);
4288 rcu_boost_kthread_setaffinity(rnp, -1);
4289 break;
4290 case CPU_DOWN_PREPARE:
4291 rcu_boost_kthread_setaffinity(rnp, cpu);
4292 break;
4293 case CPU_DYING:
4294 case CPU_DYING_FROZEN:
4295 for_each_rcu_flavor(rsp)
4296 rcu_cleanup_dying_cpu(rsp);
4297 break;
4298 case CPU_DEAD:
4299 case CPU_DEAD_FROZEN:
4300 case CPU_UP_CANCELED:
4301 case CPU_UP_CANCELED_FROZEN:
4302 for_each_rcu_flavor(rsp) {
4303 rcu_cleanup_dead_cpu(cpu, rsp);
4304 do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
4305 }
4306 break;
4307 default:
4308 break;
4309 }
4310 return NOTIFY_OK;
4311}
4312
4313static int rcu_pm_notify(struct notifier_block *self,
4314 unsigned long action, void *hcpu)
4315{
4316 switch (action) {
4317 case PM_HIBERNATION_PREPARE:
4318 case PM_SUSPEND_PREPARE:
4319 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4320 rcu_expedite_gp();
4321 break;
4322 case PM_POST_HIBERNATION:
4323 case PM_POST_SUSPEND:
4324 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
4325 rcu_unexpedite_gp();
4326 break;
4327 default:
4328 break;
4329 }
4330 return NOTIFY_OK;
4331}
4332
4333/*
4334 * Spawn the kthreads that handle each RCU flavor's grace periods.
4335 */
4336static int __init rcu_spawn_gp_kthread(void)
4337{
4338 unsigned long flags;
4339 int kthread_prio_in = kthread_prio;
4340 struct rcu_node *rnp;
4341 struct rcu_state *rsp;
4342 struct sched_param sp;
4343 struct task_struct *t;
4344
4345 /* Force priority into range. */
4346 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
4347 kthread_prio = 1;
4348 else if (kthread_prio < 0)
4349 kthread_prio = 0;
4350 else if (kthread_prio > 99)
4351 kthread_prio = 99;
4352 if (kthread_prio != kthread_prio_in)
4353 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
4354 kthread_prio, kthread_prio_in);
4355
4356 rcu_scheduler_fully_active = 1;
4357 for_each_rcu_flavor(rsp) {
4358 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
4359 BUG_ON(IS_ERR(t));
4360 rnp = rcu_get_root(rsp);
4361 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4362 rsp->gp_kthread = t;
4363 if (kthread_prio) {
4364 sp.sched_priority = kthread_prio;
4365 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4366 }
4367 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4368 wake_up_process(t);
4369 }
4370 rcu_spawn_nocb_kthreads();
4371 rcu_spawn_boost_kthreads();
4372 return 0;
4373}
4374early_initcall(rcu_spawn_gp_kthread);
4375
4376/*
4377 * This function is invoked towards the end of the scheduler's initialization
4378 * process. Before this is called, the idle task might contain
4379 * RCU read-side critical sections (during which time, this idle
4380 * task is booting the system). After this function is called, the
4381 * idle tasks are prohibited from containing RCU read-side critical
4382 * sections. This function also enables RCU lockdep checking.
4383 */
4384void rcu_scheduler_starting(void)
4385{
4386 WARN_ON(num_online_cpus() != 1);
4387 WARN_ON(nr_context_switches() > 0);
4388 rcu_scheduler_active = 1;
4389}
4390
4391/*
4392 * Compute the per-level fanout, either using the exact fanout specified
4393 * or balancing the tree, depending on the rcu_fanout_exact boot parameter.
4394 */
4395static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
4396{
4397 int i;
4398
4399 if (rcu_fanout_exact) {
4400 levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
4401 for (i = rcu_num_lvls - 2; i >= 0; i--)
4402 levelspread[i] = RCU_FANOUT;
4403 } else {
4404 int ccur;
4405 int cprv;
4406
4407 cprv = nr_cpu_ids;
4408 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4409 ccur = levelcnt[i];
4410 levelspread[i] = (cprv + ccur - 1) / ccur;
4411 cprv = ccur;
4412 }
4413 }
4414}
4415
4416/*
4417 * Helper function for rcu_init() that initializes one rcu_state structure.
4418 */
4419static void __init rcu_init_one(struct rcu_state *rsp)
4420{
4421 static const char * const buf[] = RCU_NODE_NAME_INIT;
4422 static const char * const fqs[] = RCU_FQS_NAME_INIT;
4423 static const char * const exp[] = RCU_EXP_NAME_INIT;
4424 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4425 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4426 static struct lock_class_key rcu_exp_class[RCU_NUM_LVLS];
4427 static u8 fl_mask = 0x1;
4428
4429 int levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */
4430 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
4431 int cpustride = 1;
4432 int i;
4433 int j;
4434 struct rcu_node *rnp;
4435
4436 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4437
4438 /* Silence gcc 4.8 false positive about array index out of range. */
4439 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4440 panic("rcu_init_one: rcu_num_lvls out of range");
4441
4442 /* Initialize the level-tracking arrays. */
4443
4444 for (i = 0; i < rcu_num_lvls; i++)
4445 levelcnt[i] = num_rcu_lvl[i];
4446 for (i = 1; i < rcu_num_lvls; i++)
4447 rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];
4448 rcu_init_levelspread(levelspread, levelcnt);
4449 rsp->flavor_mask = fl_mask;
4450 fl_mask <<= 1;
4451
4452 /* Initialize the elements themselves, starting from the leaves. */
4453
4454 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4455 cpustride *= levelspread[i];
4456 rnp = rsp->level[i];
4457 for (j = 0; j < levelcnt[i]; j++, rnp++) {
4458 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4459 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4460 &rcu_node_class[i], buf[i]);
4461 raw_spin_lock_init(&rnp->fqslock);
4462 lockdep_set_class_and_name(&rnp->fqslock,
4463 &rcu_fqs_class[i], fqs[i]);
4464 rnp->gpnum = rsp->gpnum;
4465 rnp->completed = rsp->completed;
4466 rnp->qsmask = 0;
4467 rnp->qsmaskinit = 0;
4468 rnp->grplo = j * cpustride;
4469 rnp->grphi = (j + 1) * cpustride - 1;
4470 if (rnp->grphi >= nr_cpu_ids)
4471 rnp->grphi = nr_cpu_ids - 1;
4472 if (i == 0) {
4473 rnp->grpnum = 0;
4474 rnp->grpmask = 0;
4475 rnp->parent = NULL;
4476 } else {
4477 rnp->grpnum = j % levelspread[i - 1];
4478 rnp->grpmask = 1UL << rnp->grpnum;
4479 rnp->parent = rsp->level[i - 1] +
4480 j / levelspread[i - 1];
4481 }
4482 rnp->level = i;
4483 INIT_LIST_HEAD(&rnp->blkd_tasks);
4484 rcu_init_one_nocb(rnp);
4485 mutex_init(&rnp->exp_funnel_mutex);
4486 lockdep_set_class_and_name(&rnp->exp_funnel_mutex,
4487 &rcu_exp_class[i], exp[i]);
4488 }
4489 }
4490
4491 init_swait_queue_head(&rsp->gp_wq);
4492 init_swait_queue_head(&rsp->expedited_wq);
4493 rnp = rsp->level[rcu_num_lvls - 1];
4494 for_each_possible_cpu(i) {
4495 while (i > rnp->grphi)
4496 rnp++;
4497 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4498 rcu_boot_init_percpu_data(i, rsp);
4499 }
4500 list_add(&rsp->flavors, &rcu_struct_flavors);
4501}
4502
4503/*
4504 * Compute the rcu_node tree geometry from kernel parameters. This cannot
4505 * replace the definitions in tree.h because those are needed to size
4506 * the ->node array in the rcu_state structure.
4507 */
4508static void __init rcu_init_geometry(void)
4509{
4510 ulong d;
4511 int i;
4512 int rcu_capacity[RCU_NUM_LVLS];
4513
4514 /*
4515 * Initialize any unspecified boot parameters.
4516 * The default values of jiffies_till_first_fqs and
4517 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4518 * value, which is a function of HZ, then adding one for each
4519 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4520 */
4521 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4522 if (jiffies_till_first_fqs == ULONG_MAX)
4523 jiffies_till_first_fqs = d;
4524 if (jiffies_till_next_fqs == ULONG_MAX)
4525 jiffies_till_next_fqs = d;
4526
4527 /* If the compile-time values are accurate, just leave. */
4528 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4529 nr_cpu_ids == NR_CPUS)
4530 return;
4531 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
4532 rcu_fanout_leaf, nr_cpu_ids);
4533
4534 /*
4535 * The boot-time rcu_fanout_leaf parameter must be at least two
4536 * and cannot exceed the number of bits in the rcu_node masks.
4537 * Complain and fall back to the compile-time values if this
4538 * limit is exceeded.
4539 */
4540 if (rcu_fanout_leaf < 2 ||
4541 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4542 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4543 WARN_ON(1);
4544 return;
4545 }
4546
4547 /*
4548 * Compute number of nodes that can be handled an rcu_node tree
4549 * with the given number of levels.
4550 */
4551 rcu_capacity[0] = rcu_fanout_leaf;
4552 for (i = 1; i < RCU_NUM_LVLS; i++)
4553 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4554
4555 /*
4556 * The tree must be able to accommodate the configured number of CPUs.
4557 * If this limit is exceeded, fall back to the compile-time values.
4558 */
4559 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4560 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4561 WARN_ON(1);
4562 return;
4563 }
4564
4565 /* Calculate the number of levels in the tree. */
4566 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4567 }
4568 rcu_num_lvls = i + 1;
4569
4570 /* Calculate the number of rcu_nodes at each level of the tree. */
4571 for (i = 0; i < rcu_num_lvls; i++) {
4572 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4573 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4574 }
4575
4576 /* Calculate the total number of rcu_node structures. */
4577 rcu_num_nodes = 0;
4578 for (i = 0; i < rcu_num_lvls; i++)
4579 rcu_num_nodes += num_rcu_lvl[i];
4580}
4581
4582/*
4583 * Dump out the structure of the rcu_node combining tree associated
4584 * with the rcu_state structure referenced by rsp.
4585 */
4586static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4587{
4588 int level = 0;
4589 struct rcu_node *rnp;
4590
4591 pr_info("rcu_node tree layout dump\n");
4592 pr_info(" ");
4593 rcu_for_each_node_breadth_first(rsp, rnp) {
4594 if (rnp->level != level) {
4595 pr_cont("\n");
4596 pr_info(" ");
4597 level = rnp->level;
4598 }
4599 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4600 }
4601 pr_cont("\n");
4602}
4603
4604void __init rcu_init(void)
4605{
4606 int cpu;
4607
4608 rcu_early_boot_tests();
4609
4610 rcu_bootup_announce();
4611 rcu_init_geometry();
4612 rcu_init_one(&rcu_bh_state);
4613 rcu_init_one(&rcu_sched_state);
4614 if (dump_tree)
4615 rcu_dump_rcu_node_tree(&rcu_sched_state);
4616 __rcu_init_preempt();
4617 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4618
4619 /*
4620 * We don't need protection against CPU-hotplug here because
4621 * this is called early in boot, before either interrupts
4622 * or the scheduler are operational.
4623 */
4624 cpu_notifier(rcu_cpu_notify, 0);
4625 pm_notifier(rcu_pm_notify, 0);
4626 for_each_online_cpu(cpu)
4627 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
4628}
4629
4630#include "tree_plugin.h"