Loading...
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, 2001
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 *
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * Papers:
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 *
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
31 *
32 */
33#include <linux/types.h>
34#include <linux/kernel.h>
35#include <linux/init.h>
36#include <linux/spinlock.h>
37#include <linux/smp.h>
38#include <linux/interrupt.h>
39#include <linux/sched.h>
40#include <linux/atomic.h>
41#include <linux/bitops.h>
42#include <linux/percpu.h>
43#include <linux/notifier.h>
44#include <linux/cpu.h>
45#include <linux/mutex.h>
46#include <linux/export.h>
47#include <linux/hardirq.h>
48#include <linux/delay.h>
49#include <linux/moduleparam.h>
50#include <linux/kthread.h>
51#include <linux/tick.h>
52
53#define CREATE_TRACE_POINTS
54
55#include "rcu.h"
56
57#ifdef MODULE_PARAM_PREFIX
58#undef MODULE_PARAM_PREFIX
59#endif
60#define MODULE_PARAM_PREFIX "rcupdate."
61
62#ifndef CONFIG_TINY_RCU
63module_param(rcu_expedited, int, 0);
64module_param(rcu_normal, int, 0);
65static int rcu_normal_after_boot;
66module_param(rcu_normal_after_boot, int, 0);
67#endif /* #ifndef CONFIG_TINY_RCU */
68
69#ifdef CONFIG_DEBUG_LOCK_ALLOC
70/**
71 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
72 *
73 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
74 * RCU-sched read-side critical section. In absence of
75 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
76 * critical section unless it can prove otherwise. Note that disabling
77 * of preemption (including disabling irqs) counts as an RCU-sched
78 * read-side critical section. This is useful for debug checks in functions
79 * that required that they be called within an RCU-sched read-side
80 * critical section.
81 *
82 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
83 * and while lockdep is disabled.
84 *
85 * Note that if the CPU is in the idle loop from an RCU point of
86 * view (ie: that we are in the section between rcu_idle_enter() and
87 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
88 * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
89 * that are in such a section, considering these as in extended quiescent
90 * state, so such a CPU is effectively never in an RCU read-side critical
91 * section regardless of what RCU primitives it invokes. This state of
92 * affairs is required --- we need to keep an RCU-free window in idle
93 * where the CPU may possibly enter into low power mode. This way we can
94 * notice an extended quiescent state to other CPUs that started a grace
95 * period. Otherwise we would delay any grace period as long as we run in
96 * the idle task.
97 *
98 * Similarly, we avoid claiming an SRCU read lock held if the current
99 * CPU is offline.
100 */
101int rcu_read_lock_sched_held(void)
102{
103 int lockdep_opinion = 0;
104
105 if (!debug_lockdep_rcu_enabled())
106 return 1;
107 if (!rcu_is_watching())
108 return 0;
109 if (!rcu_lockdep_current_cpu_online())
110 return 0;
111 if (debug_locks)
112 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
113 return lockdep_opinion || !preemptible();
114}
115EXPORT_SYMBOL(rcu_read_lock_sched_held);
116#endif
117
118#ifndef CONFIG_TINY_RCU
119
120/*
121 * Should expedited grace-period primitives always fall back to their
122 * non-expedited counterparts? Intended for use within RCU. Note
123 * that if the user specifies both rcu_expedited and rcu_normal, then
124 * rcu_normal wins. (Except during the time period during boot from
125 * when the first task is spawned until the rcu_exp_runtime_mode()
126 * core_initcall() is invoked, at which point everything is expedited.)
127 */
128bool rcu_gp_is_normal(void)
129{
130 return READ_ONCE(rcu_normal) &&
131 rcu_scheduler_active != RCU_SCHEDULER_INIT;
132}
133EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
134
135static atomic_t rcu_expedited_nesting =
136 ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);
137
138/*
139 * Should normal grace-period primitives be expedited? Intended for
140 * use within RCU. Note that this function takes the rcu_expedited
141 * sysfs/boot variable and rcu_scheduler_active into account as well
142 * as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp()
143 * until rcu_gp_is_expedited() returns false is a -really- bad idea.
144 */
145bool rcu_gp_is_expedited(void)
146{
147 return rcu_expedited || atomic_read(&rcu_expedited_nesting) ||
148 rcu_scheduler_active == RCU_SCHEDULER_INIT;
149}
150EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
151
152/**
153 * rcu_expedite_gp - Expedite future RCU grace periods
154 *
155 * After a call to this function, future calls to synchronize_rcu() and
156 * friends act as the corresponding synchronize_rcu_expedited() function
157 * had instead been called.
158 */
159void rcu_expedite_gp(void)
160{
161 atomic_inc(&rcu_expedited_nesting);
162}
163EXPORT_SYMBOL_GPL(rcu_expedite_gp);
164
165/**
166 * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
167 *
168 * Undo a prior call to rcu_expedite_gp(). If all prior calls to
169 * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
170 * and if the rcu_expedited sysfs/boot parameter is not set, then all
171 * subsequent calls to synchronize_rcu() and friends will return to
172 * their normal non-expedited behavior.
173 */
174void rcu_unexpedite_gp(void)
175{
176 atomic_dec(&rcu_expedited_nesting);
177}
178EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
179
180/*
181 * Inform RCU of the end of the in-kernel boot sequence.
182 */
183void rcu_end_inkernel_boot(void)
184{
185 if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
186 rcu_unexpedite_gp();
187 if (rcu_normal_after_boot)
188 WRITE_ONCE(rcu_normal, 1);
189}
190
191#endif /* #ifndef CONFIG_TINY_RCU */
192
193#ifdef CONFIG_PREEMPT_RCU
194
195/*
196 * Preemptible RCU implementation for rcu_read_lock().
197 * Just increment ->rcu_read_lock_nesting, shared state will be updated
198 * if we block.
199 */
200void __rcu_read_lock(void)
201{
202 current->rcu_read_lock_nesting++;
203 barrier(); /* critical section after entry code. */
204}
205EXPORT_SYMBOL_GPL(__rcu_read_lock);
206
207/*
208 * Preemptible RCU implementation for rcu_read_unlock().
209 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
210 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
211 * invoke rcu_read_unlock_special() to clean up after a context switch
212 * in an RCU read-side critical section and other special cases.
213 */
214void __rcu_read_unlock(void)
215{
216 struct task_struct *t = current;
217
218 if (t->rcu_read_lock_nesting != 1) {
219 --t->rcu_read_lock_nesting;
220 } else {
221 barrier(); /* critical section before exit code. */
222 t->rcu_read_lock_nesting = INT_MIN;
223 barrier(); /* assign before ->rcu_read_unlock_special load */
224 if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
225 rcu_read_unlock_special(t);
226 barrier(); /* ->rcu_read_unlock_special load before assign */
227 t->rcu_read_lock_nesting = 0;
228 }
229#ifdef CONFIG_PROVE_LOCKING
230 {
231 int rrln = READ_ONCE(t->rcu_read_lock_nesting);
232
233 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
234 }
235#endif /* #ifdef CONFIG_PROVE_LOCKING */
236}
237EXPORT_SYMBOL_GPL(__rcu_read_unlock);
238
239#endif /* #ifdef CONFIG_PREEMPT_RCU */
240
241#ifdef CONFIG_DEBUG_LOCK_ALLOC
242static struct lock_class_key rcu_lock_key;
243struct lockdep_map rcu_lock_map =
244 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
245EXPORT_SYMBOL_GPL(rcu_lock_map);
246
247static struct lock_class_key rcu_bh_lock_key;
248struct lockdep_map rcu_bh_lock_map =
249 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
250EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
251
252static struct lock_class_key rcu_sched_lock_key;
253struct lockdep_map rcu_sched_lock_map =
254 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
255EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
256
257static struct lock_class_key rcu_callback_key;
258struct lockdep_map rcu_callback_map =
259 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
260EXPORT_SYMBOL_GPL(rcu_callback_map);
261
262int notrace debug_lockdep_rcu_enabled(void)
263{
264 return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks &&
265 current->lockdep_recursion == 0;
266}
267EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
268
269/**
270 * rcu_read_lock_held() - might we be in RCU read-side critical section?
271 *
272 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
273 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
274 * this assumes we are in an RCU read-side critical section unless it can
275 * prove otherwise. This is useful for debug checks in functions that
276 * require that they be called within an RCU read-side critical section.
277 *
278 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
279 * and while lockdep is disabled.
280 *
281 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
282 * occur in the same context, for example, it is illegal to invoke
283 * rcu_read_unlock() in process context if the matching rcu_read_lock()
284 * was invoked from within an irq handler.
285 *
286 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
287 * offline from an RCU perspective, so check for those as well.
288 */
289int rcu_read_lock_held(void)
290{
291 if (!debug_lockdep_rcu_enabled())
292 return 1;
293 if (!rcu_is_watching())
294 return 0;
295 if (!rcu_lockdep_current_cpu_online())
296 return 0;
297 return lock_is_held(&rcu_lock_map);
298}
299EXPORT_SYMBOL_GPL(rcu_read_lock_held);
300
301/**
302 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
303 *
304 * Check for bottom half being disabled, which covers both the
305 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
306 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
307 * will show the situation. This is useful for debug checks in functions
308 * that require that they be called within an RCU read-side critical
309 * section.
310 *
311 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
312 *
313 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
314 * offline from an RCU perspective, so check for those as well.
315 */
316int rcu_read_lock_bh_held(void)
317{
318 if (!debug_lockdep_rcu_enabled())
319 return 1;
320 if (!rcu_is_watching())
321 return 0;
322 if (!rcu_lockdep_current_cpu_online())
323 return 0;
324 return in_softirq() || irqs_disabled();
325}
326EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
327
328#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
329
330/**
331 * wakeme_after_rcu() - Callback function to awaken a task after grace period
332 * @head: Pointer to rcu_head member within rcu_synchronize structure
333 *
334 * Awaken the corresponding task now that a grace period has elapsed.
335 */
336void wakeme_after_rcu(struct rcu_head *head)
337{
338 struct rcu_synchronize *rcu;
339
340 rcu = container_of(head, struct rcu_synchronize, head);
341 complete(&rcu->completion);
342}
343EXPORT_SYMBOL_GPL(wakeme_after_rcu);
344
345void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
346 struct rcu_synchronize *rs_array)
347{
348 int i;
349
350 /* Initialize and register callbacks for each flavor specified. */
351 for (i = 0; i < n; i++) {
352 if (checktiny &&
353 (crcu_array[i] == call_rcu ||
354 crcu_array[i] == call_rcu_bh)) {
355 might_sleep();
356 continue;
357 }
358 init_rcu_head_on_stack(&rs_array[i].head);
359 init_completion(&rs_array[i].completion);
360 (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
361 }
362
363 /* Wait for all callbacks to be invoked. */
364 for (i = 0; i < n; i++) {
365 if (checktiny &&
366 (crcu_array[i] == call_rcu ||
367 crcu_array[i] == call_rcu_bh))
368 continue;
369 wait_for_completion(&rs_array[i].completion);
370 destroy_rcu_head_on_stack(&rs_array[i].head);
371 }
372}
373EXPORT_SYMBOL_GPL(__wait_rcu_gp);
374
375#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
376void init_rcu_head(struct rcu_head *head)
377{
378 debug_object_init(head, &rcuhead_debug_descr);
379}
380
381void destroy_rcu_head(struct rcu_head *head)
382{
383 debug_object_free(head, &rcuhead_debug_descr);
384}
385
386static bool rcuhead_is_static_object(void *addr)
387{
388 return true;
389}
390
391/**
392 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
393 * @head: pointer to rcu_head structure to be initialized
394 *
395 * This function informs debugobjects of a new rcu_head structure that
396 * has been allocated as an auto variable on the stack. This function
397 * is not required for rcu_head structures that are statically defined or
398 * that are dynamically allocated on the heap. This function has no
399 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
400 */
401void init_rcu_head_on_stack(struct rcu_head *head)
402{
403 debug_object_init_on_stack(head, &rcuhead_debug_descr);
404}
405EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
406
407/**
408 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
409 * @head: pointer to rcu_head structure to be initialized
410 *
411 * This function informs debugobjects that an on-stack rcu_head structure
412 * is about to go out of scope. As with init_rcu_head_on_stack(), this
413 * function is not required for rcu_head structures that are statically
414 * defined or that are dynamically allocated on the heap. Also as with
415 * init_rcu_head_on_stack(), this function has no effect for
416 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
417 */
418void destroy_rcu_head_on_stack(struct rcu_head *head)
419{
420 debug_object_free(head, &rcuhead_debug_descr);
421}
422EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
423
424struct debug_obj_descr rcuhead_debug_descr = {
425 .name = "rcu_head",
426 .is_static_object = rcuhead_is_static_object,
427};
428EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
429#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
430
431#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
432void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
433 unsigned long secs,
434 unsigned long c_old, unsigned long c)
435{
436 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
437}
438EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
439#else
440#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
441 do { } while (0)
442#endif
443
444#ifdef CONFIG_RCU_STALL_COMMON
445
446#ifdef CONFIG_PROVE_RCU
447#define RCU_STALL_DELAY_DELTA (5 * HZ)
448#else
449#define RCU_STALL_DELAY_DELTA 0
450#endif
451
452int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
453static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
454
455module_param(rcu_cpu_stall_suppress, int, 0644);
456module_param(rcu_cpu_stall_timeout, int, 0644);
457
458int rcu_jiffies_till_stall_check(void)
459{
460 int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
461
462 /*
463 * Limit check must be consistent with the Kconfig limits
464 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
465 */
466 if (till_stall_check < 3) {
467 WRITE_ONCE(rcu_cpu_stall_timeout, 3);
468 till_stall_check = 3;
469 } else if (till_stall_check > 300) {
470 WRITE_ONCE(rcu_cpu_stall_timeout, 300);
471 till_stall_check = 300;
472 }
473 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
474}
475
476void rcu_sysrq_start(void)
477{
478 if (!rcu_cpu_stall_suppress)
479 rcu_cpu_stall_suppress = 2;
480}
481
482void rcu_sysrq_end(void)
483{
484 if (rcu_cpu_stall_suppress == 2)
485 rcu_cpu_stall_suppress = 0;
486}
487
488static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
489{
490 rcu_cpu_stall_suppress = 1;
491 return NOTIFY_DONE;
492}
493
494static struct notifier_block rcu_panic_block = {
495 .notifier_call = rcu_panic,
496};
497
498static int __init check_cpu_stall_init(void)
499{
500 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
501 return 0;
502}
503early_initcall(check_cpu_stall_init);
504
505#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
506
507#ifdef CONFIG_TASKS_RCU
508
509/*
510 * Simple variant of RCU whose quiescent states are voluntary context switch,
511 * user-space execution, and idle. As such, grace periods can take one good
512 * long time. There are no read-side primitives similar to rcu_read_lock()
513 * and rcu_read_unlock() because this implementation is intended to get
514 * the system into a safe state for some of the manipulations involved in
515 * tracing and the like. Finally, this implementation does not support
516 * high call_rcu_tasks() rates from multiple CPUs. If this is required,
517 * per-CPU callback lists will be needed.
518 */
519
520/* Global list of callbacks and associated lock. */
521static struct rcu_head *rcu_tasks_cbs_head;
522static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
523static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
524static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
525
526/* Track exiting tasks in order to allow them to be waited for. */
527DEFINE_SRCU(tasks_rcu_exit_srcu);
528
529/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
530static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
531module_param(rcu_task_stall_timeout, int, 0644);
532
533static void rcu_spawn_tasks_kthread(void);
534static struct task_struct *rcu_tasks_kthread_ptr;
535
536/*
537 * Post an RCU-tasks callback. First call must be from process context
538 * after the scheduler if fully operational.
539 */
540void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
541{
542 unsigned long flags;
543 bool needwake;
544 bool havetask = READ_ONCE(rcu_tasks_kthread_ptr);
545
546 rhp->next = NULL;
547 rhp->func = func;
548 raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
549 needwake = !rcu_tasks_cbs_head;
550 *rcu_tasks_cbs_tail = rhp;
551 rcu_tasks_cbs_tail = &rhp->next;
552 raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
553 /* We can't create the thread unless interrupts are enabled. */
554 if ((needwake && havetask) ||
555 (!havetask && !irqs_disabled_flags(flags))) {
556 rcu_spawn_tasks_kthread();
557 wake_up(&rcu_tasks_cbs_wq);
558 }
559}
560EXPORT_SYMBOL_GPL(call_rcu_tasks);
561
562/**
563 * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
564 *
565 * Control will return to the caller some time after a full rcu-tasks
566 * grace period has elapsed, in other words after all currently
567 * executing rcu-tasks read-side critical sections have elapsed. These
568 * read-side critical sections are delimited by calls to schedule(),
569 * cond_resched_rcu_qs(), idle execution, userspace execution, calls
570 * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
571 *
572 * This is a very specialized primitive, intended only for a few uses in
573 * tracing and other situations requiring manipulation of function
574 * preambles and profiling hooks. The synchronize_rcu_tasks() function
575 * is not (yet) intended for heavy use from multiple CPUs.
576 *
577 * Note that this guarantee implies further memory-ordering guarantees.
578 * On systems with more than one CPU, when synchronize_rcu_tasks() returns,
579 * each CPU is guaranteed to have executed a full memory barrier since the
580 * end of its last RCU-tasks read-side critical section whose beginning
581 * preceded the call to synchronize_rcu_tasks(). In addition, each CPU
582 * having an RCU-tasks read-side critical section that extends beyond
583 * the return from synchronize_rcu_tasks() is guaranteed to have executed
584 * a full memory barrier after the beginning of synchronize_rcu_tasks()
585 * and before the beginning of that RCU-tasks read-side critical section.
586 * Note that these guarantees include CPUs that are offline, idle, or
587 * executing in user mode, as well as CPUs that are executing in the kernel.
588 *
589 * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
590 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
591 * to have executed a full memory barrier during the execution of
592 * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
593 * (but again only if the system has more than one CPU).
594 */
595void synchronize_rcu_tasks(void)
596{
597 /* Complain if the scheduler has not started. */
598 RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
599 "synchronize_rcu_tasks called too soon");
600
601 /* Wait for the grace period. */
602 wait_rcu_gp(call_rcu_tasks);
603}
604EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
605
606/**
607 * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
608 *
609 * Although the current implementation is guaranteed to wait, it is not
610 * obligated to, for example, if there are no pending callbacks.
611 */
612void rcu_barrier_tasks(void)
613{
614 /* There is only one callback queue, so this is easy. ;-) */
615 synchronize_rcu_tasks();
616}
617EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
618
619/* See if tasks are still holding out, complain if so. */
620static void check_holdout_task(struct task_struct *t,
621 bool needreport, bool *firstreport)
622{
623 int cpu;
624
625 if (!READ_ONCE(t->rcu_tasks_holdout) ||
626 t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
627 !READ_ONCE(t->on_rq) ||
628 (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
629 !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
630 WRITE_ONCE(t->rcu_tasks_holdout, false);
631 list_del_init(&t->rcu_tasks_holdout_list);
632 put_task_struct(t);
633 return;
634 }
635 if (!needreport)
636 return;
637 if (*firstreport) {
638 pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
639 *firstreport = false;
640 }
641 cpu = task_cpu(t);
642 pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
643 t, ".I"[is_idle_task(t)],
644 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
645 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
646 t->rcu_tasks_idle_cpu, cpu);
647 sched_show_task(t);
648}
649
650/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
651static int __noreturn rcu_tasks_kthread(void *arg)
652{
653 unsigned long flags;
654 struct task_struct *g, *t;
655 unsigned long lastreport;
656 struct rcu_head *list;
657 struct rcu_head *next;
658 LIST_HEAD(rcu_tasks_holdouts);
659
660 /* Run on housekeeping CPUs by default. Sysadm can move if desired. */
661 housekeeping_affine(current);
662
663 /*
664 * Each pass through the following loop makes one check for
665 * newly arrived callbacks, and, if there are some, waits for
666 * one RCU-tasks grace period and then invokes the callbacks.
667 * This loop is terminated by the system going down. ;-)
668 */
669 for (;;) {
670
671 /* Pick up any new callbacks. */
672 raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
673 list = rcu_tasks_cbs_head;
674 rcu_tasks_cbs_head = NULL;
675 rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
676 raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
677
678 /* If there were none, wait a bit and start over. */
679 if (!list) {
680 wait_event_interruptible(rcu_tasks_cbs_wq,
681 rcu_tasks_cbs_head);
682 if (!rcu_tasks_cbs_head) {
683 WARN_ON(signal_pending(current));
684 schedule_timeout_interruptible(HZ/10);
685 }
686 continue;
687 }
688
689 /*
690 * Wait for all pre-existing t->on_rq and t->nvcsw
691 * transitions to complete. Invoking synchronize_sched()
692 * suffices because all these transitions occur with
693 * interrupts disabled. Without this synchronize_sched(),
694 * a read-side critical section that started before the
695 * grace period might be incorrectly seen as having started
696 * after the grace period.
697 *
698 * This synchronize_sched() also dispenses with the
699 * need for a memory barrier on the first store to
700 * ->rcu_tasks_holdout, as it forces the store to happen
701 * after the beginning of the grace period.
702 */
703 synchronize_sched();
704
705 /*
706 * There were callbacks, so we need to wait for an
707 * RCU-tasks grace period. Start off by scanning
708 * the task list for tasks that are not already
709 * voluntarily blocked. Mark these tasks and make
710 * a list of them in rcu_tasks_holdouts.
711 */
712 rcu_read_lock();
713 for_each_process_thread(g, t) {
714 if (t != current && READ_ONCE(t->on_rq) &&
715 !is_idle_task(t)) {
716 get_task_struct(t);
717 t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
718 WRITE_ONCE(t->rcu_tasks_holdout, true);
719 list_add(&t->rcu_tasks_holdout_list,
720 &rcu_tasks_holdouts);
721 }
722 }
723 rcu_read_unlock();
724
725 /*
726 * Wait for tasks that are in the process of exiting.
727 * This does only part of the job, ensuring that all
728 * tasks that were previously exiting reach the point
729 * where they have disabled preemption, allowing the
730 * later synchronize_sched() to finish the job.
731 */
732 synchronize_srcu(&tasks_rcu_exit_srcu);
733
734 /*
735 * Each pass through the following loop scans the list
736 * of holdout tasks, removing any that are no longer
737 * holdouts. When the list is empty, we are done.
738 */
739 lastreport = jiffies;
740 while (!list_empty(&rcu_tasks_holdouts)) {
741 bool firstreport;
742 bool needreport;
743 int rtst;
744 struct task_struct *t1;
745
746 schedule_timeout_interruptible(HZ);
747 rtst = READ_ONCE(rcu_task_stall_timeout);
748 needreport = rtst > 0 &&
749 time_after(jiffies, lastreport + rtst);
750 if (needreport)
751 lastreport = jiffies;
752 firstreport = true;
753 WARN_ON(signal_pending(current));
754 list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
755 rcu_tasks_holdout_list) {
756 check_holdout_task(t, needreport, &firstreport);
757 cond_resched();
758 }
759 }
760
761 /*
762 * Because ->on_rq and ->nvcsw are not guaranteed
763 * to have a full memory barriers prior to them in the
764 * schedule() path, memory reordering on other CPUs could
765 * cause their RCU-tasks read-side critical sections to
766 * extend past the end of the grace period. However,
767 * because these ->nvcsw updates are carried out with
768 * interrupts disabled, we can use synchronize_sched()
769 * to force the needed ordering on all such CPUs.
770 *
771 * This synchronize_sched() also confines all
772 * ->rcu_tasks_holdout accesses to be within the grace
773 * period, avoiding the need for memory barriers for
774 * ->rcu_tasks_holdout accesses.
775 *
776 * In addition, this synchronize_sched() waits for exiting
777 * tasks to complete their final preempt_disable() region
778 * of execution, cleaning up after the synchronize_srcu()
779 * above.
780 */
781 synchronize_sched();
782
783 /* Invoke the callbacks. */
784 while (list) {
785 next = list->next;
786 local_bh_disable();
787 list->func(list);
788 local_bh_enable();
789 list = next;
790 cond_resched();
791 }
792 schedule_timeout_uninterruptible(HZ/10);
793 }
794}
795
796/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */
797static void rcu_spawn_tasks_kthread(void)
798{
799 static DEFINE_MUTEX(rcu_tasks_kthread_mutex);
800 struct task_struct *t;
801
802 if (READ_ONCE(rcu_tasks_kthread_ptr)) {
803 smp_mb(); /* Ensure caller sees full kthread. */
804 return;
805 }
806 mutex_lock(&rcu_tasks_kthread_mutex);
807 if (rcu_tasks_kthread_ptr) {
808 mutex_unlock(&rcu_tasks_kthread_mutex);
809 return;
810 }
811 t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
812 BUG_ON(IS_ERR(t));
813 smp_mb(); /* Ensure others see full kthread. */
814 WRITE_ONCE(rcu_tasks_kthread_ptr, t);
815 mutex_unlock(&rcu_tasks_kthread_mutex);
816}
817
818#endif /* #ifdef CONFIG_TASKS_RCU */
819
820/*
821 * Test each non-SRCU synchronous grace-period wait API. This is
822 * useful just after a change in mode for these primitives, and
823 * during early boot.
824 */
825void rcu_test_sync_prims(void)
826{
827 if (!IS_ENABLED(CONFIG_PROVE_RCU))
828 return;
829 synchronize_rcu();
830 synchronize_rcu_bh();
831 synchronize_sched();
832 synchronize_rcu_expedited();
833 synchronize_rcu_bh_expedited();
834 synchronize_sched_expedited();
835}
836
837#ifdef CONFIG_PROVE_RCU
838
839/*
840 * Early boot self test parameters, one for each flavor
841 */
842static bool rcu_self_test;
843static bool rcu_self_test_bh;
844static bool rcu_self_test_sched;
845
846module_param(rcu_self_test, bool, 0444);
847module_param(rcu_self_test_bh, bool, 0444);
848module_param(rcu_self_test_sched, bool, 0444);
849
850static int rcu_self_test_counter;
851
852static void test_callback(struct rcu_head *r)
853{
854 rcu_self_test_counter++;
855 pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
856}
857
858static void early_boot_test_call_rcu(void)
859{
860 static struct rcu_head head;
861
862 call_rcu(&head, test_callback);
863}
864
865static void early_boot_test_call_rcu_bh(void)
866{
867 static struct rcu_head head;
868
869 call_rcu_bh(&head, test_callback);
870}
871
872static void early_boot_test_call_rcu_sched(void)
873{
874 static struct rcu_head head;
875
876 call_rcu_sched(&head, test_callback);
877}
878
879void rcu_early_boot_tests(void)
880{
881 pr_info("Running RCU self tests\n");
882
883 if (rcu_self_test)
884 early_boot_test_call_rcu();
885 if (rcu_self_test_bh)
886 early_boot_test_call_rcu_bh();
887 if (rcu_self_test_sched)
888 early_boot_test_call_rcu_sched();
889 rcu_test_sync_prims();
890}
891
892static int rcu_verify_early_boot_tests(void)
893{
894 int ret = 0;
895 int early_boot_test_counter = 0;
896
897 if (rcu_self_test) {
898 early_boot_test_counter++;
899 rcu_barrier();
900 }
901 if (rcu_self_test_bh) {
902 early_boot_test_counter++;
903 rcu_barrier_bh();
904 }
905 if (rcu_self_test_sched) {
906 early_boot_test_counter++;
907 rcu_barrier_sched();
908 }
909
910 if (rcu_self_test_counter != early_boot_test_counter) {
911 WARN_ON(1);
912 ret = -1;
913 }
914
915 return ret;
916}
917late_initcall(rcu_verify_early_boot_tests);
918#else
919void rcu_early_boot_tests(void) {}
920#endif /* CONFIG_PROVE_RCU */
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion
4 *
5 * Copyright IBM Corporation, 2001
6 *
7 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
8 * Manfred Spraul <manfred@colorfullife.com>
9 *
10 * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
11 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
12 * Papers:
13 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
14 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
15 *
16 * For detailed explanation of Read-Copy Update mechanism see -
17 * http://lse.sourceforge.net/locking/rcupdate.html
18 *
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/interrupt.h>
26#include <linux/sched/signal.h>
27#include <linux/sched/debug.h>
28#include <linux/atomic.h>
29#include <linux/bitops.h>
30#include <linux/percpu.h>
31#include <linux/notifier.h>
32#include <linux/cpu.h>
33#include <linux/mutex.h>
34#include <linux/export.h>
35#include <linux/hardirq.h>
36#include <linux/delay.h>
37#include <linux/moduleparam.h>
38#include <linux/kthread.h>
39#include <linux/tick.h>
40#include <linux/rcupdate_wait.h>
41#include <linux/sched/isolation.h>
42#include <linux/kprobes.h>
43#include <linux/slab.h>
44#include <linux/irq_work.h>
45#include <linux/rcupdate_trace.h>
46
47#define CREATE_TRACE_POINTS
48
49#include "rcu.h"
50
51#ifdef MODULE_PARAM_PREFIX
52#undef MODULE_PARAM_PREFIX
53#endif
54#define MODULE_PARAM_PREFIX "rcupdate."
55
56#ifndef data_race
57#define data_race(expr) \
58 ({ \
59 expr; \
60 })
61#endif
62#ifndef ASSERT_EXCLUSIVE_WRITER
63#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
64#endif
65#ifndef ASSERT_EXCLUSIVE_ACCESS
66#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
67#endif
68
69#ifndef CONFIG_TINY_RCU
70module_param(rcu_expedited, int, 0);
71module_param(rcu_normal, int, 0);
72static int rcu_normal_after_boot;
73module_param(rcu_normal_after_boot, int, 0);
74#endif /* #ifndef CONFIG_TINY_RCU */
75
76#ifdef CONFIG_DEBUG_LOCK_ALLOC
77/**
78 * rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?
79 * @ret: Best guess answer if lockdep cannot be relied on
80 *
81 * Returns true if lockdep must be ignored, in which case ``*ret`` contains
82 * the best guess described below. Otherwise returns false, in which
83 * case ``*ret`` tells the caller nothing and the caller should instead
84 * consult lockdep.
85 *
86 * If CONFIG_DEBUG_LOCK_ALLOC is selected, set ``*ret`` to nonzero iff in an
87 * RCU-sched read-side critical section. In absence of
88 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
89 * critical section unless it can prove otherwise. Note that disabling
90 * of preemption (including disabling irqs) counts as an RCU-sched
91 * read-side critical section. This is useful for debug checks in functions
92 * that required that they be called within an RCU-sched read-side
93 * critical section.
94 *
95 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
96 * and while lockdep is disabled.
97 *
98 * Note that if the CPU is in the idle loop from an RCU point of view (ie:
99 * that we are in the section between rcu_idle_enter() and rcu_idle_exit())
100 * then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an
101 * rcu_read_lock(). The reason for this is that RCU ignores CPUs that are
102 * in such a section, considering these as in extended quiescent state,
103 * so such a CPU is effectively never in an RCU read-side critical section
104 * regardless of what RCU primitives it invokes. This state of affairs is
105 * required --- we need to keep an RCU-free window in idle where the CPU may
106 * possibly enter into low power mode. This way we can notice an extended
107 * quiescent state to other CPUs that started a grace period. Otherwise
108 * we would delay any grace period as long as we run in the idle task.
109 *
110 * Similarly, we avoid claiming an RCU read lock held if the current
111 * CPU is offline.
112 */
113static bool rcu_read_lock_held_common(bool *ret)
114{
115 if (!debug_lockdep_rcu_enabled()) {
116 *ret = true;
117 return true;
118 }
119 if (!rcu_is_watching()) {
120 *ret = false;
121 return true;
122 }
123 if (!rcu_lockdep_current_cpu_online()) {
124 *ret = false;
125 return true;
126 }
127 return false;
128}
129
130int rcu_read_lock_sched_held(void)
131{
132 bool ret;
133
134 if (rcu_read_lock_held_common(&ret))
135 return ret;
136 return lock_is_held(&rcu_sched_lock_map) || !preemptible();
137}
138EXPORT_SYMBOL(rcu_read_lock_sched_held);
139#endif
140
141#ifndef CONFIG_TINY_RCU
142
143/*
144 * Should expedited grace-period primitives always fall back to their
145 * non-expedited counterparts? Intended for use within RCU. Note
146 * that if the user specifies both rcu_expedited and rcu_normal, then
147 * rcu_normal wins. (Except during the time period during boot from
148 * when the first task is spawned until the rcu_set_runtime_mode()
149 * core_initcall() is invoked, at which point everything is expedited.)
150 */
151bool rcu_gp_is_normal(void)
152{
153 return READ_ONCE(rcu_normal) &&
154 rcu_scheduler_active != RCU_SCHEDULER_INIT;
155}
156EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
157
158static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
159
160/*
161 * Should normal grace-period primitives be expedited? Intended for
162 * use within RCU. Note that this function takes the rcu_expedited
163 * sysfs/boot variable and rcu_scheduler_active into account as well
164 * as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp()
165 * until rcu_gp_is_expedited() returns false is a -really- bad idea.
166 */
167bool rcu_gp_is_expedited(void)
168{
169 return rcu_expedited || atomic_read(&rcu_expedited_nesting);
170}
171EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
172
173/**
174 * rcu_expedite_gp - Expedite future RCU grace periods
175 *
176 * After a call to this function, future calls to synchronize_rcu() and
177 * friends act as the corresponding synchronize_rcu_expedited() function
178 * had instead been called.
179 */
180void rcu_expedite_gp(void)
181{
182 atomic_inc(&rcu_expedited_nesting);
183}
184EXPORT_SYMBOL_GPL(rcu_expedite_gp);
185
186/**
187 * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
188 *
189 * Undo a prior call to rcu_expedite_gp(). If all prior calls to
190 * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
191 * and if the rcu_expedited sysfs/boot parameter is not set, then all
192 * subsequent calls to synchronize_rcu() and friends will return to
193 * their normal non-expedited behavior.
194 */
195void rcu_unexpedite_gp(void)
196{
197 atomic_dec(&rcu_expedited_nesting);
198}
199EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
200
201static bool rcu_boot_ended __read_mostly;
202
203/*
204 * Inform RCU of the end of the in-kernel boot sequence.
205 */
206void rcu_end_inkernel_boot(void)
207{
208 rcu_unexpedite_gp();
209 if (rcu_normal_after_boot)
210 WRITE_ONCE(rcu_normal, 1);
211 rcu_boot_ended = true;
212}
213
214/*
215 * Let rcutorture know when it is OK to turn it up to eleven.
216 */
217bool rcu_inkernel_boot_has_ended(void)
218{
219 return rcu_boot_ended;
220}
221EXPORT_SYMBOL_GPL(rcu_inkernel_boot_has_ended);
222
223#endif /* #ifndef CONFIG_TINY_RCU */
224
225/*
226 * Test each non-SRCU synchronous grace-period wait API. This is
227 * useful just after a change in mode for these primitives, and
228 * during early boot.
229 */
230void rcu_test_sync_prims(void)
231{
232 if (!IS_ENABLED(CONFIG_PROVE_RCU))
233 return;
234 synchronize_rcu();
235 synchronize_rcu_expedited();
236}
237
238#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
239
240/*
241 * Switch to run-time mode once RCU has fully initialized.
242 */
243static int __init rcu_set_runtime_mode(void)
244{
245 rcu_test_sync_prims();
246 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
247 kfree_rcu_scheduler_running();
248 rcu_test_sync_prims();
249 return 0;
250}
251core_initcall(rcu_set_runtime_mode);
252
253#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
254
255#ifdef CONFIG_DEBUG_LOCK_ALLOC
256static struct lock_class_key rcu_lock_key;
257struct lockdep_map rcu_lock_map = {
258 .name = "rcu_read_lock",
259 .key = &rcu_lock_key,
260 .wait_type_outer = LD_WAIT_FREE,
261 .wait_type_inner = LD_WAIT_CONFIG, /* XXX PREEMPT_RCU ? */
262};
263EXPORT_SYMBOL_GPL(rcu_lock_map);
264
265static struct lock_class_key rcu_bh_lock_key;
266struct lockdep_map rcu_bh_lock_map = {
267 .name = "rcu_read_lock_bh",
268 .key = &rcu_bh_lock_key,
269 .wait_type_outer = LD_WAIT_FREE,
270 .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_LOCK also makes BH preemptible */
271};
272EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
273
274static struct lock_class_key rcu_sched_lock_key;
275struct lockdep_map rcu_sched_lock_map = {
276 .name = "rcu_read_lock_sched",
277 .key = &rcu_sched_lock_key,
278 .wait_type_outer = LD_WAIT_FREE,
279 .wait_type_inner = LD_WAIT_SPIN,
280};
281EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
282
283// Tell lockdep when RCU callbacks are being invoked.
284static struct lock_class_key rcu_callback_key;
285struct lockdep_map rcu_callback_map =
286 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
287EXPORT_SYMBOL_GPL(rcu_callback_map);
288
289noinstr int notrace debug_lockdep_rcu_enabled(void)
290{
291 return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks &&
292 current->lockdep_recursion == 0;
293}
294EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
295
296/**
297 * rcu_read_lock_held() - might we be in RCU read-side critical section?
298 *
299 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
300 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
301 * this assumes we are in an RCU read-side critical section unless it can
302 * prove otherwise. This is useful for debug checks in functions that
303 * require that they be called within an RCU read-side critical section.
304 *
305 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
306 * and while lockdep is disabled.
307 *
308 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
309 * occur in the same context, for example, it is illegal to invoke
310 * rcu_read_unlock() in process context if the matching rcu_read_lock()
311 * was invoked from within an irq handler.
312 *
313 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
314 * offline from an RCU perspective, so check for those as well.
315 */
316int rcu_read_lock_held(void)
317{
318 bool ret;
319
320 if (rcu_read_lock_held_common(&ret))
321 return ret;
322 return lock_is_held(&rcu_lock_map);
323}
324EXPORT_SYMBOL_GPL(rcu_read_lock_held);
325
326/**
327 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
328 *
329 * Check for bottom half being disabled, which covers both the
330 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
331 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
332 * will show the situation. This is useful for debug checks in functions
333 * that require that they be called within an RCU read-side critical
334 * section.
335 *
336 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
337 *
338 * Note that rcu_read_lock_bh() is disallowed if the CPU is either idle or
339 * offline from an RCU perspective, so check for those as well.
340 */
341int rcu_read_lock_bh_held(void)
342{
343 bool ret;
344
345 if (rcu_read_lock_held_common(&ret))
346 return ret;
347 return in_softirq() || irqs_disabled();
348}
349EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
350
351int rcu_read_lock_any_held(void)
352{
353 bool ret;
354
355 if (rcu_read_lock_held_common(&ret))
356 return ret;
357 if (lock_is_held(&rcu_lock_map) ||
358 lock_is_held(&rcu_bh_lock_map) ||
359 lock_is_held(&rcu_sched_lock_map))
360 return 1;
361 return !preemptible();
362}
363EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
364
365#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
366
367/**
368 * wakeme_after_rcu() - Callback function to awaken a task after grace period
369 * @head: Pointer to rcu_head member within rcu_synchronize structure
370 *
371 * Awaken the corresponding task now that a grace period has elapsed.
372 */
373void wakeme_after_rcu(struct rcu_head *head)
374{
375 struct rcu_synchronize *rcu;
376
377 rcu = container_of(head, struct rcu_synchronize, head);
378 complete(&rcu->completion);
379}
380EXPORT_SYMBOL_GPL(wakeme_after_rcu);
381
382void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
383 struct rcu_synchronize *rs_array)
384{
385 int i;
386 int j;
387
388 /* Initialize and register callbacks for each crcu_array element. */
389 for (i = 0; i < n; i++) {
390 if (checktiny &&
391 (crcu_array[i] == call_rcu)) {
392 might_sleep();
393 continue;
394 }
395 for (j = 0; j < i; j++)
396 if (crcu_array[j] == crcu_array[i])
397 break;
398 if (j == i) {
399 init_rcu_head_on_stack(&rs_array[i].head);
400 init_completion(&rs_array[i].completion);
401 (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
402 }
403 }
404
405 /* Wait for all callbacks to be invoked. */
406 for (i = 0; i < n; i++) {
407 if (checktiny &&
408 (crcu_array[i] == call_rcu))
409 continue;
410 for (j = 0; j < i; j++)
411 if (crcu_array[j] == crcu_array[i])
412 break;
413 if (j == i) {
414 wait_for_completion(&rs_array[i].completion);
415 destroy_rcu_head_on_stack(&rs_array[i].head);
416 }
417 }
418}
419EXPORT_SYMBOL_GPL(__wait_rcu_gp);
420
421#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
422void init_rcu_head(struct rcu_head *head)
423{
424 debug_object_init(head, &rcuhead_debug_descr);
425}
426EXPORT_SYMBOL_GPL(init_rcu_head);
427
428void destroy_rcu_head(struct rcu_head *head)
429{
430 debug_object_free(head, &rcuhead_debug_descr);
431}
432EXPORT_SYMBOL_GPL(destroy_rcu_head);
433
434static bool rcuhead_is_static_object(void *addr)
435{
436 return true;
437}
438
439/**
440 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
441 * @head: pointer to rcu_head structure to be initialized
442 *
443 * This function informs debugobjects of a new rcu_head structure that
444 * has been allocated as an auto variable on the stack. This function
445 * is not required for rcu_head structures that are statically defined or
446 * that are dynamically allocated on the heap. This function has no
447 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
448 */
449void init_rcu_head_on_stack(struct rcu_head *head)
450{
451 debug_object_init_on_stack(head, &rcuhead_debug_descr);
452}
453EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
454
455/**
456 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
457 * @head: pointer to rcu_head structure to be initialized
458 *
459 * This function informs debugobjects that an on-stack rcu_head structure
460 * is about to go out of scope. As with init_rcu_head_on_stack(), this
461 * function is not required for rcu_head structures that are statically
462 * defined or that are dynamically allocated on the heap. Also as with
463 * init_rcu_head_on_stack(), this function has no effect for
464 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
465 */
466void destroy_rcu_head_on_stack(struct rcu_head *head)
467{
468 debug_object_free(head, &rcuhead_debug_descr);
469}
470EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
471
472struct debug_obj_descr rcuhead_debug_descr = {
473 .name = "rcu_head",
474 .is_static_object = rcuhead_is_static_object,
475};
476EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
477#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
478
479#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
480void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
481 unsigned long secs,
482 unsigned long c_old, unsigned long c)
483{
484 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
485}
486EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
487#else
488#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
489 do { } while (0)
490#endif
491
492#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)
493/* Get rcutorture access to sched_setaffinity(). */
494long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
495{
496 int ret;
497
498 ret = sched_setaffinity(pid, in_mask);
499 WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret);
500 return ret;
501}
502EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);
503#endif
504
505#ifdef CONFIG_RCU_STALL_COMMON
506int rcu_cpu_stall_ftrace_dump __read_mostly;
507module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
508int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
509EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
510module_param(rcu_cpu_stall_suppress, int, 0644);
511int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
512module_param(rcu_cpu_stall_timeout, int, 0644);
513#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
514
515// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
516// warnings. Also used by rcutorture even if stall warnings are excluded.
517int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
518EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot);
519module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);
520
521#ifdef CONFIG_PROVE_RCU
522
523/*
524 * Early boot self test parameters.
525 */
526static bool rcu_self_test;
527module_param(rcu_self_test, bool, 0444);
528
529static int rcu_self_test_counter;
530
531static void test_callback(struct rcu_head *r)
532{
533 rcu_self_test_counter++;
534 pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
535}
536
537DEFINE_STATIC_SRCU(early_srcu);
538
539struct early_boot_kfree_rcu {
540 struct rcu_head rh;
541};
542
543static void early_boot_test_call_rcu(void)
544{
545 static struct rcu_head head;
546 static struct rcu_head shead;
547 struct early_boot_kfree_rcu *rhp;
548
549 call_rcu(&head, test_callback);
550 if (IS_ENABLED(CONFIG_SRCU))
551 call_srcu(&early_srcu, &shead, test_callback);
552 rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
553 if (!WARN_ON_ONCE(!rhp))
554 kfree_rcu(rhp, rh);
555}
556
557void rcu_early_boot_tests(void)
558{
559 pr_info("Running RCU self tests\n");
560
561 if (rcu_self_test)
562 early_boot_test_call_rcu();
563 rcu_test_sync_prims();
564}
565
566static int rcu_verify_early_boot_tests(void)
567{
568 int ret = 0;
569 int early_boot_test_counter = 0;
570
571 if (rcu_self_test) {
572 early_boot_test_counter++;
573 rcu_barrier();
574 if (IS_ENABLED(CONFIG_SRCU)) {
575 early_boot_test_counter++;
576 srcu_barrier(&early_srcu);
577 }
578 }
579 if (rcu_self_test_counter != early_boot_test_counter) {
580 WARN_ON(1);
581 ret = -1;
582 }
583
584 return ret;
585}
586late_initcall(rcu_verify_early_boot_tests);
587#else
588void rcu_early_boot_tests(void) {}
589#endif /* CONFIG_PROVE_RCU */
590
591#include "tasks.h"
592
593#ifndef CONFIG_TINY_RCU
594
595/*
596 * Print any significant non-default boot-time settings.
597 */
598void __init rcupdate_announce_bootup_oddness(void)
599{
600 if (rcu_normal)
601 pr_info("\tNo expedited grace period (rcu_normal).\n");
602 else if (rcu_normal_after_boot)
603 pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
604 else if (rcu_expedited)
605 pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
606 if (rcu_cpu_stall_suppress)
607 pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
608 if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
609 pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
610 rcu_tasks_bootup_oddness();
611}
612
613#endif /* #ifndef CONFIG_TINY_RCU */