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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, 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 CONFIG_TINY_RCU
57module_param(rcu_expedited, int, 0444);
58module_param(rcu_normal, int, 0444);
59static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
60#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)
61module_param(rcu_normal_after_boot, int, 0444);
62#endif
63#endif /* #ifndef CONFIG_TINY_RCU */
64
65#ifdef CONFIG_DEBUG_LOCK_ALLOC
66/**
67 * rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?
68 * @ret: Best guess answer if lockdep cannot be relied on
69 *
70 * Returns true if lockdep must be ignored, in which case ``*ret`` contains
71 * the best guess described below. Otherwise returns false, in which
72 * case ``*ret`` tells the caller nothing and the caller should instead
73 * consult lockdep.
74 *
75 * If CONFIG_DEBUG_LOCK_ALLOC is selected, set ``*ret`` to nonzero iff in an
76 * RCU-sched read-side critical section. In absence of
77 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
78 * critical section unless it can prove otherwise. Note that disabling
79 * of preemption (including disabling irqs) counts as an RCU-sched
80 * read-side critical section. This is useful for debug checks in functions
81 * that required that they be called within an RCU-sched read-side
82 * critical section.
83 *
84 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
85 * and while lockdep is disabled.
86 *
87 * Note that if the CPU is in the idle loop from an RCU point of view (ie:
88 * that we are in the section between ct_idle_enter() and ct_idle_exit())
89 * then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an
90 * rcu_read_lock(). The reason for this is that RCU ignores CPUs that are
91 * in such a section, considering these as in extended quiescent state,
92 * so such a CPU is effectively never in an RCU read-side critical section
93 * regardless of what RCU primitives it invokes. This state of affairs is
94 * required --- we need to keep an RCU-free window in idle where the CPU may
95 * possibly enter into low power mode. This way we can notice an extended
96 * quiescent state to other CPUs that started a grace period. Otherwise
97 * we would delay any grace period as long as we run in the idle task.
98 *
99 * Similarly, we avoid claiming an RCU read lock held if the current
100 * CPU is offline.
101 */
102static bool rcu_read_lock_held_common(bool *ret)
103{
104 if (!debug_lockdep_rcu_enabled()) {
105 *ret = true;
106 return true;
107 }
108 if (!rcu_is_watching()) {
109 *ret = false;
110 return true;
111 }
112 if (!rcu_lockdep_current_cpu_online()) {
113 *ret = false;
114 return true;
115 }
116 return false;
117}
118
119int rcu_read_lock_sched_held(void)
120{
121 bool ret;
122
123 if (rcu_read_lock_held_common(&ret))
124 return ret;
125 return lock_is_held(&rcu_sched_lock_map) || !preemptible();
126}
127EXPORT_SYMBOL(rcu_read_lock_sched_held);
128#endif
129
130#ifndef CONFIG_TINY_RCU
131
132/*
133 * Should expedited grace-period primitives always fall back to their
134 * non-expedited counterparts? Intended for use within RCU. Note
135 * that if the user specifies both rcu_expedited and rcu_normal, then
136 * rcu_normal wins. (Except during the time period during boot from
137 * when the first task is spawned until the rcu_set_runtime_mode()
138 * core_initcall() is invoked, at which point everything is expedited.)
139 */
140bool rcu_gp_is_normal(void)
141{
142 return READ_ONCE(rcu_normal) &&
143 rcu_scheduler_active != RCU_SCHEDULER_INIT;
144}
145EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
146
147static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
148
149/*
150 * Should normal grace-period primitives be expedited? Intended for
151 * use within RCU. Note that this function takes the rcu_expedited
152 * sysfs/boot variable and rcu_scheduler_active into account as well
153 * as the rcu_expedite_gp() nesting. So looping on rcu_unexpedite_gp()
154 * until rcu_gp_is_expedited() returns false is a -really- bad idea.
155 */
156bool rcu_gp_is_expedited(void)
157{
158 return rcu_expedited || atomic_read(&rcu_expedited_nesting);
159}
160EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
161
162/**
163 * rcu_expedite_gp - Expedite future RCU grace periods
164 *
165 * After a call to this function, future calls to synchronize_rcu() and
166 * friends act as the corresponding synchronize_rcu_expedited() function
167 * had instead been called.
168 */
169void rcu_expedite_gp(void)
170{
171 atomic_inc(&rcu_expedited_nesting);
172}
173EXPORT_SYMBOL_GPL(rcu_expedite_gp);
174
175/**
176 * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
177 *
178 * Undo a prior call to rcu_expedite_gp(). If all prior calls to
179 * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
180 * and if the rcu_expedited sysfs/boot parameter is not set, then all
181 * subsequent calls to synchronize_rcu() and friends will return to
182 * their normal non-expedited behavior.
183 */
184void rcu_unexpedite_gp(void)
185{
186 atomic_dec(&rcu_expedited_nesting);
187}
188EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
189
190static bool rcu_boot_ended __read_mostly;
191
192/*
193 * Inform RCU of the end of the in-kernel boot sequence.
194 */
195void rcu_end_inkernel_boot(void)
196{
197 rcu_unexpedite_gp();
198 if (rcu_normal_after_boot)
199 WRITE_ONCE(rcu_normal, 1);
200 rcu_boot_ended = true;
201}
202
203/*
204 * Let rcutorture know when it is OK to turn it up to eleven.
205 */
206bool rcu_inkernel_boot_has_ended(void)
207{
208 return rcu_boot_ended;
209}
210EXPORT_SYMBOL_GPL(rcu_inkernel_boot_has_ended);
211
212#endif /* #ifndef CONFIG_TINY_RCU */
213
214/*
215 * Test each non-SRCU synchronous grace-period wait API. This is
216 * useful just after a change in mode for these primitives, and
217 * during early boot.
218 */
219void rcu_test_sync_prims(void)
220{
221 if (!IS_ENABLED(CONFIG_PROVE_RCU))
222 return;
223 synchronize_rcu();
224 synchronize_rcu_expedited();
225}
226
227#if !defined(CONFIG_TINY_RCU)
228
229/*
230 * Switch to run-time mode once RCU has fully initialized.
231 */
232static int __init rcu_set_runtime_mode(void)
233{
234 rcu_test_sync_prims();
235 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
236 kfree_rcu_scheduler_running();
237 rcu_test_sync_prims();
238 return 0;
239}
240core_initcall(rcu_set_runtime_mode);
241
242#endif /* #if !defined(CONFIG_TINY_RCU) */
243
244#ifdef CONFIG_DEBUG_LOCK_ALLOC
245static struct lock_class_key rcu_lock_key;
246struct lockdep_map rcu_lock_map = {
247 .name = "rcu_read_lock",
248 .key = &rcu_lock_key,
249 .wait_type_outer = LD_WAIT_FREE,
250 .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT implies PREEMPT_RCU */
251};
252EXPORT_SYMBOL_GPL(rcu_lock_map);
253
254static struct lock_class_key rcu_bh_lock_key;
255struct lockdep_map rcu_bh_lock_map = {
256 .name = "rcu_read_lock_bh",
257 .key = &rcu_bh_lock_key,
258 .wait_type_outer = LD_WAIT_FREE,
259 .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */
260};
261EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
262
263static struct lock_class_key rcu_sched_lock_key;
264struct lockdep_map rcu_sched_lock_map = {
265 .name = "rcu_read_lock_sched",
266 .key = &rcu_sched_lock_key,
267 .wait_type_outer = LD_WAIT_FREE,
268 .wait_type_inner = LD_WAIT_SPIN,
269};
270EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
271
272// Tell lockdep when RCU callbacks are being invoked.
273static struct lock_class_key rcu_callback_key;
274struct lockdep_map rcu_callback_map =
275 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
276EXPORT_SYMBOL_GPL(rcu_callback_map);
277
278noinstr int notrace debug_lockdep_rcu_enabled(void)
279{
280 return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && READ_ONCE(debug_locks) &&
281 current->lockdep_recursion == 0;
282}
283EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
284
285/**
286 * rcu_read_lock_held() - might we be in RCU read-side critical section?
287 *
288 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
289 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
290 * this assumes we are in an RCU read-side critical section unless it can
291 * prove otherwise. This is useful for debug checks in functions that
292 * require that they be called within an RCU read-side critical section.
293 *
294 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
295 * and while lockdep is disabled.
296 *
297 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
298 * occur in the same context, for example, it is illegal to invoke
299 * rcu_read_unlock() in process context if the matching rcu_read_lock()
300 * was invoked from within an irq handler.
301 *
302 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
303 * offline from an RCU perspective, so check for those as well.
304 */
305int rcu_read_lock_held(void)
306{
307 bool ret;
308
309 if (rcu_read_lock_held_common(&ret))
310 return ret;
311 return lock_is_held(&rcu_lock_map);
312}
313EXPORT_SYMBOL_GPL(rcu_read_lock_held);
314
315/**
316 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
317 *
318 * Check for bottom half being disabled, which covers both the
319 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
320 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
321 * will show the situation. This is useful for debug checks in functions
322 * that require that they be called within an RCU read-side critical
323 * section.
324 *
325 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
326 *
327 * Note that rcu_read_lock_bh() is disallowed if the CPU is either idle or
328 * offline from an RCU perspective, so check for those as well.
329 */
330int rcu_read_lock_bh_held(void)
331{
332 bool ret;
333
334 if (rcu_read_lock_held_common(&ret))
335 return ret;
336 return in_softirq() || irqs_disabled();
337}
338EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
339
340int rcu_read_lock_any_held(void)
341{
342 bool ret;
343
344 if (rcu_read_lock_held_common(&ret))
345 return ret;
346 if (lock_is_held(&rcu_lock_map) ||
347 lock_is_held(&rcu_bh_lock_map) ||
348 lock_is_held(&rcu_sched_lock_map))
349 return 1;
350 return !preemptible();
351}
352EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
353
354#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
355
356/**
357 * wakeme_after_rcu() - Callback function to awaken a task after grace period
358 * @head: Pointer to rcu_head member within rcu_synchronize structure
359 *
360 * Awaken the corresponding task now that a grace period has elapsed.
361 */
362void wakeme_after_rcu(struct rcu_head *head)
363{
364 struct rcu_synchronize *rcu;
365
366 rcu = container_of(head, struct rcu_synchronize, head);
367 complete(&rcu->completion);
368}
369EXPORT_SYMBOL_GPL(wakeme_after_rcu);
370
371void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
372 struct rcu_synchronize *rs_array)
373{
374 int i;
375 int j;
376
377 /* Initialize and register callbacks for each crcu_array element. */
378 for (i = 0; i < n; i++) {
379 if (checktiny &&
380 (crcu_array[i] == call_rcu)) {
381 might_sleep();
382 continue;
383 }
384 for (j = 0; j < i; j++)
385 if (crcu_array[j] == crcu_array[i])
386 break;
387 if (j == i) {
388 init_rcu_head_on_stack(&rs_array[i].head);
389 init_completion(&rs_array[i].completion);
390 (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
391 }
392 }
393
394 /* Wait for all callbacks to be invoked. */
395 for (i = 0; i < n; i++) {
396 if (checktiny &&
397 (crcu_array[i] == call_rcu))
398 continue;
399 for (j = 0; j < i; j++)
400 if (crcu_array[j] == crcu_array[i])
401 break;
402 if (j == i) {
403 wait_for_completion(&rs_array[i].completion);
404 destroy_rcu_head_on_stack(&rs_array[i].head);
405 }
406 }
407}
408EXPORT_SYMBOL_GPL(__wait_rcu_gp);
409
410void finish_rcuwait(struct rcuwait *w)
411{
412 rcu_assign_pointer(w->task, NULL);
413 __set_current_state(TASK_RUNNING);
414}
415EXPORT_SYMBOL_GPL(finish_rcuwait);
416
417#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
418void init_rcu_head(struct rcu_head *head)
419{
420 debug_object_init(head, &rcuhead_debug_descr);
421}
422EXPORT_SYMBOL_GPL(init_rcu_head);
423
424void destroy_rcu_head(struct rcu_head *head)
425{
426 debug_object_free(head, &rcuhead_debug_descr);
427}
428EXPORT_SYMBOL_GPL(destroy_rcu_head);
429
430static bool rcuhead_is_static_object(void *addr)
431{
432 return true;
433}
434
435/**
436 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
437 * @head: pointer to rcu_head structure to be initialized
438 *
439 * This function informs debugobjects of a new rcu_head structure that
440 * has been allocated as an auto variable on the stack. This function
441 * is not required for rcu_head structures that are statically defined or
442 * that are dynamically allocated on the heap. This function has no
443 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
444 */
445void init_rcu_head_on_stack(struct rcu_head *head)
446{
447 debug_object_init_on_stack(head, &rcuhead_debug_descr);
448}
449EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
450
451/**
452 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
453 * @head: pointer to rcu_head structure to be initialized
454 *
455 * This function informs debugobjects that an on-stack rcu_head structure
456 * is about to go out of scope. As with init_rcu_head_on_stack(), this
457 * function is not required for rcu_head structures that are statically
458 * defined or that are dynamically allocated on the heap. Also as with
459 * init_rcu_head_on_stack(), this function has no effect for
460 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
461 */
462void destroy_rcu_head_on_stack(struct rcu_head *head)
463{
464 debug_object_free(head, &rcuhead_debug_descr);
465}
466EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
467
468const struct debug_obj_descr rcuhead_debug_descr = {
469 .name = "rcu_head",
470 .is_static_object = rcuhead_is_static_object,
471};
472EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
473#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
474
475#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
476void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
477 unsigned long secs,
478 unsigned long c_old, unsigned long c)
479{
480 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
481}
482EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
483#else
484#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
485 do { } while (0)
486#endif
487
488#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST)
489/* Get rcutorture access to sched_setaffinity(). */
490long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
491{
492 int ret;
493
494 ret = sched_setaffinity(pid, in_mask);
495 WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret);
496 return ret;
497}
498EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity);
499#endif
500
501#ifdef CONFIG_RCU_STALL_COMMON
502int rcu_cpu_stall_ftrace_dump __read_mostly;
503module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
504int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
505EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
506module_param(rcu_cpu_stall_suppress, int, 0644);
507int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
508module_param(rcu_cpu_stall_timeout, int, 0644);
509int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
510module_param(rcu_exp_cpu_stall_timeout, int, 0644);
511#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
512
513// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
514// warnings. Also used by rcutorture even if stall warnings are excluded.
515int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
516EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot);
517module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);
518
519/**
520 * get_completed_synchronize_rcu - Return a pre-completed polled state cookie
521 *
522 * Returns a value that will always be treated by functions like
523 * poll_state_synchronize_rcu() as a cookie whose grace period has already
524 * completed.
525 */
526unsigned long get_completed_synchronize_rcu(void)
527{
528 return RCU_GET_STATE_COMPLETED;
529}
530EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu);
531
532#ifdef CONFIG_PROVE_RCU
533
534/*
535 * Early boot self test parameters.
536 */
537static bool rcu_self_test;
538module_param(rcu_self_test, bool, 0444);
539
540static int rcu_self_test_counter;
541
542static void test_callback(struct rcu_head *r)
543{
544 rcu_self_test_counter++;
545 pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
546}
547
548DEFINE_STATIC_SRCU(early_srcu);
549static unsigned long early_srcu_cookie;
550
551struct early_boot_kfree_rcu {
552 struct rcu_head rh;
553};
554
555static void early_boot_test_call_rcu(void)
556{
557 static struct rcu_head head;
558 static struct rcu_head shead;
559 struct early_boot_kfree_rcu *rhp;
560
561 call_rcu(&head, test_callback);
562 early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
563 call_srcu(&early_srcu, &shead, test_callback);
564 rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
565 if (!WARN_ON_ONCE(!rhp))
566 kfree_rcu(rhp, rh);
567}
568
569void rcu_early_boot_tests(void)
570{
571 pr_info("Running RCU self tests\n");
572
573 if (rcu_self_test)
574 early_boot_test_call_rcu();
575 rcu_test_sync_prims();
576}
577
578static int rcu_verify_early_boot_tests(void)
579{
580 int ret = 0;
581 int early_boot_test_counter = 0;
582
583 if (rcu_self_test) {
584 early_boot_test_counter++;
585 rcu_barrier();
586 early_boot_test_counter++;
587 srcu_barrier(&early_srcu);
588 WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
589 }
590 if (rcu_self_test_counter != early_boot_test_counter) {
591 WARN_ON(1);
592 ret = -1;
593 }
594
595 return ret;
596}
597late_initcall(rcu_verify_early_boot_tests);
598#else
599void rcu_early_boot_tests(void) {}
600#endif /* CONFIG_PROVE_RCU */
601
602#include "tasks.h"
603
604#ifndef CONFIG_TINY_RCU
605
606/*
607 * Print any significant non-default boot-time settings.
608 */
609void __init rcupdate_announce_bootup_oddness(void)
610{
611 if (rcu_normal)
612 pr_info("\tNo expedited grace period (rcu_normal).\n");
613 else if (rcu_normal_after_boot)
614 pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
615 else if (rcu_expedited)
616 pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
617 if (rcu_cpu_stall_suppress)
618 pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
619 if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
620 pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
621 rcu_tasks_bootup_oddness();
622}
623
624#endif /* #ifndef CONFIG_TINY_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 */