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1da177e4 LT |
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 | |
87de1cfd PM |
15 | * along with this program; if not, you can access it online at |
16 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
1da177e4 | 17 | * |
01c1c660 | 18 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
19 | * |
20 | * Authors: Dipankar Sarma <dipankar@in.ibm.com> | |
21 | * Manfred Spraul <manfred@colorfullife.com> | |
a71fca58 | 22 | * |
1da177e4 LT |
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 - | |
a71fca58 | 30 | * http://lse.sourceforge.net/locking/rcupdate.html |
1da177e4 LT |
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> | |
60063497 | 40 | #include <linux/atomic.h> |
1da177e4 | 41 | #include <linux/bitops.h> |
1da177e4 LT |
42 | #include <linux/percpu.h> |
43 | #include <linux/notifier.h> | |
1da177e4 | 44 | #include <linux/cpu.h> |
9331b315 | 45 | #include <linux/mutex.h> |
9984de1a | 46 | #include <linux/export.h> |
e3818b8d | 47 | #include <linux/hardirq.h> |
e3ebfb96 | 48 | #include <linux/delay.h> |
3705b88d | 49 | #include <linux/module.h> |
8315f422 | 50 | #include <linux/kthread.h> |
4ff475ed | 51 | #include <linux/tick.h> |
1da177e4 | 52 | |
29c00b4a | 53 | #define CREATE_TRACE_POINTS |
29c00b4a PM |
54 | |
55 | #include "rcu.h" | |
56 | ||
4102adab PM |
57 | MODULE_ALIAS("rcupdate"); |
58 | #ifdef MODULE_PARAM_PREFIX | |
59 | #undef MODULE_PARAM_PREFIX | |
60 | #endif | |
61 | #define MODULE_PARAM_PREFIX "rcupdate." | |
62 | ||
3705b88d AM |
63 | module_param(rcu_expedited, int, 0); |
64 | ||
0d39482c PM |
65 | #ifndef CONFIG_TINY_RCU |
66 | ||
ee42571f PM |
67 | static atomic_t rcu_expedited_nesting = |
68 | ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0); | |
0d39482c PM |
69 | |
70 | /* | |
71 | * Should normal grace-period primitives be expedited? Intended for | |
72 | * use within RCU. Note that this function takes the rcu_expedited | |
73 | * sysfs/boot variable into account as well as the rcu_expedite_gp() | |
74 | * nesting. So looping on rcu_unexpedite_gp() until rcu_gp_is_expedited() | |
75 | * returns false is a -really- bad idea. | |
76 | */ | |
77 | bool rcu_gp_is_expedited(void) | |
78 | { | |
79 | return rcu_expedited || atomic_read(&rcu_expedited_nesting); | |
80 | } | |
81 | EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); | |
82 | ||
83 | /** | |
84 | * rcu_expedite_gp - Expedite future RCU grace periods | |
85 | * | |
86 | * After a call to this function, future calls to synchronize_rcu() and | |
87 | * friends act as the corresponding synchronize_rcu_expedited() function | |
88 | * had instead been called. | |
89 | */ | |
90 | void rcu_expedite_gp(void) | |
91 | { | |
92 | atomic_inc(&rcu_expedited_nesting); | |
93 | } | |
94 | EXPORT_SYMBOL_GPL(rcu_expedite_gp); | |
95 | ||
96 | /** | |
97 | * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation | |
98 | * | |
99 | * Undo a prior call to rcu_expedite_gp(). If all prior calls to | |
100 | * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(), | |
101 | * and if the rcu_expedited sysfs/boot parameter is not set, then all | |
102 | * subsequent calls to synchronize_rcu() and friends will return to | |
103 | * their normal non-expedited behavior. | |
104 | */ | |
105 | void rcu_unexpedite_gp(void) | |
106 | { | |
107 | atomic_dec(&rcu_expedited_nesting); | |
108 | } | |
109 | EXPORT_SYMBOL_GPL(rcu_unexpedite_gp); | |
110 | ||
111 | #endif /* #ifndef CONFIG_TINY_RCU */ | |
112 | ||
ee42571f PM |
113 | /* |
114 | * Inform RCU of the end of the in-kernel boot sequence. | |
115 | */ | |
116 | void rcu_end_inkernel_boot(void) | |
117 | { | |
118 | if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT)) | |
119 | rcu_unexpedite_gp(); | |
120 | } | |
0d39482c | 121 | |
9dd8fb16 PM |
122 | #ifdef CONFIG_PREEMPT_RCU |
123 | ||
2a3fa843 PM |
124 | /* |
125 | * Preemptible RCU implementation for rcu_read_lock(). | |
126 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
127 | * if we block. | |
128 | */ | |
129 | void __rcu_read_lock(void) | |
130 | { | |
131 | current->rcu_read_lock_nesting++; | |
132 | barrier(); /* critical section after entry code. */ | |
133 | } | |
134 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
135 | ||
136 | /* | |
137 | * Preemptible RCU implementation for rcu_read_unlock(). | |
138 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
139 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
140 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
141 | * in an RCU read-side critical section and other special cases. | |
142 | */ | |
143 | void __rcu_read_unlock(void) | |
144 | { | |
145 | struct task_struct *t = current; | |
146 | ||
147 | if (t->rcu_read_lock_nesting != 1) { | |
148 | --t->rcu_read_lock_nesting; | |
149 | } else { | |
150 | barrier(); /* critical section before exit code. */ | |
151 | t->rcu_read_lock_nesting = INT_MIN; | |
152 | barrier(); /* assign before ->rcu_read_unlock_special load */ | |
1d082fd0 | 153 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special.s))) |
2a3fa843 PM |
154 | rcu_read_unlock_special(t); |
155 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
156 | t->rcu_read_lock_nesting = 0; | |
157 | } | |
158 | #ifdef CONFIG_PROVE_LOCKING | |
159 | { | |
160 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); | |
161 | ||
162 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
163 | } | |
164 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
165 | } | |
166 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
167 | ||
2439b696 | 168 | #endif /* #ifdef CONFIG_PREEMPT_RCU */ |
9dd8fb16 | 169 | |
162cc279 PM |
170 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
171 | static struct lock_class_key rcu_lock_key; | |
172 | struct lockdep_map rcu_lock_map = | |
173 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); | |
174 | EXPORT_SYMBOL_GPL(rcu_lock_map); | |
632ee200 PM |
175 | |
176 | static struct lock_class_key rcu_bh_lock_key; | |
177 | struct lockdep_map rcu_bh_lock_map = | |
178 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); | |
179 | EXPORT_SYMBOL_GPL(rcu_bh_lock_map); | |
180 | ||
181 | static struct lock_class_key rcu_sched_lock_key; | |
182 | struct lockdep_map rcu_sched_lock_map = | |
183 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); | |
184 | EXPORT_SYMBOL_GPL(rcu_sched_lock_map); | |
e3818b8d | 185 | |
24ef659a PM |
186 | static struct lock_class_key rcu_callback_key; |
187 | struct lockdep_map rcu_callback_map = | |
188 | STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); | |
189 | EXPORT_SYMBOL_GPL(rcu_callback_map); | |
190 | ||
a0a5a056 | 191 | int notrace debug_lockdep_rcu_enabled(void) |
bc293d62 PM |
192 | { |
193 | return rcu_scheduler_active && debug_locks && | |
194 | current->lockdep_recursion == 0; | |
195 | } | |
196 | EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); | |
197 | ||
85b39d30 ON |
198 | /** |
199 | * rcu_read_lock_held() - might we be in RCU read-side critical section? | |
200 | * | |
201 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU | |
202 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
203 | * this assumes we are in an RCU read-side critical section unless it can | |
204 | * prove otherwise. This is useful for debug checks in functions that | |
205 | * require that they be called within an RCU read-side critical section. | |
206 | * | |
207 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot | |
208 | * and while lockdep is disabled. | |
209 | * | |
210 | * Note that rcu_read_lock() and the matching rcu_read_unlock() must | |
211 | * occur in the same context, for example, it is illegal to invoke | |
212 | * rcu_read_unlock() in process context if the matching rcu_read_lock() | |
213 | * was invoked from within an irq handler. | |
214 | * | |
215 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
216 | * offline from an RCU perspective, so check for those as well. | |
217 | */ | |
218 | int rcu_read_lock_held(void) | |
219 | { | |
220 | if (!debug_lockdep_rcu_enabled()) | |
221 | return 1; | |
222 | if (!rcu_is_watching()) | |
223 | return 0; | |
224 | if (!rcu_lockdep_current_cpu_online()) | |
225 | return 0; | |
226 | return lock_is_held(&rcu_lock_map); | |
227 | } | |
228 | EXPORT_SYMBOL_GPL(rcu_read_lock_held); | |
229 | ||
e3818b8d | 230 | /** |
ca5ecddf | 231 | * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
e3818b8d PM |
232 | * |
233 | * Check for bottom half being disabled, which covers both the | |
234 | * CONFIG_PROVE_RCU and not cases. Note that if someone uses | |
235 | * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) | |
ca5ecddf PM |
236 | * will show the situation. This is useful for debug checks in functions |
237 | * that require that they be called within an RCU read-side critical | |
238 | * section. | |
e3818b8d PM |
239 | * |
240 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. | |
c0d6d01b PM |
241 | * |
242 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
243 | * offline from an RCU perspective, so check for those as well. | |
e3818b8d PM |
244 | */ |
245 | int rcu_read_lock_bh_held(void) | |
246 | { | |
247 | if (!debug_lockdep_rcu_enabled()) | |
248 | return 1; | |
5c173eb8 | 249 | if (!rcu_is_watching()) |
e6b80a3b | 250 | return 0; |
c0d6d01b PM |
251 | if (!rcu_lockdep_current_cpu_online()) |
252 | return 0; | |
773e3f93 | 253 | return in_softirq() || irqs_disabled(); |
e3818b8d PM |
254 | } |
255 | EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); | |
256 | ||
257 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
258 | ||
ee376dbd PM |
259 | /** |
260 | * wakeme_after_rcu() - Callback function to awaken a task after grace period | |
261 | * @head: Pointer to rcu_head member within rcu_synchronize structure | |
262 | * | |
263 | * Awaken the corresponding task now that a grace period has elapsed. | |
fbf6bfca | 264 | */ |
ee376dbd | 265 | void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 266 | { |
01c1c660 PM |
267 | struct rcu_synchronize *rcu; |
268 | ||
269 | rcu = container_of(head, struct rcu_synchronize, head); | |
270 | complete(&rcu->completion); | |
21a1ea9e | 271 | } |
ee84b824 | 272 | |
2c42818e PM |
273 | void wait_rcu_gp(call_rcu_func_t crf) |
274 | { | |
275 | struct rcu_synchronize rcu; | |
276 | ||
277 | init_rcu_head_on_stack(&rcu.head); | |
278 | init_completion(&rcu.completion); | |
279 | /* Will wake me after RCU finished. */ | |
280 | crf(&rcu.head, wakeme_after_rcu); | |
281 | /* Wait for it. */ | |
282 | wait_for_completion(&rcu.completion); | |
283 | destroy_rcu_head_on_stack(&rcu.head); | |
284 | } | |
285 | EXPORT_SYMBOL_GPL(wait_rcu_gp); | |
286 | ||
551d55a9 | 287 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
546a9d85 | 288 | void init_rcu_head(struct rcu_head *head) |
551d55a9 MD |
289 | { |
290 | debug_object_init(head, &rcuhead_debug_descr); | |
291 | } | |
292 | ||
546a9d85 | 293 | void destroy_rcu_head(struct rcu_head *head) |
551d55a9 MD |
294 | { |
295 | debug_object_free(head, &rcuhead_debug_descr); | |
296 | } | |
297 | ||
551d55a9 MD |
298 | /* |
299 | * fixup_activate is called when: | |
300 | * - an active object is activated | |
301 | * - an unknown object is activated (might be a statically initialized object) | |
302 | * Activation is performed internally by call_rcu(). | |
303 | */ | |
304 | static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) | |
305 | { | |
306 | struct rcu_head *head = addr; | |
307 | ||
308 | switch (state) { | |
309 | ||
310 | case ODEBUG_STATE_NOTAVAILABLE: | |
311 | /* | |
312 | * This is not really a fixup. We just make sure that it is | |
313 | * tracked in the object tracker. | |
314 | */ | |
315 | debug_object_init(head, &rcuhead_debug_descr); | |
316 | debug_object_activate(head, &rcuhead_debug_descr); | |
317 | return 0; | |
551d55a9 | 318 | default: |
551d55a9 | 319 | return 1; |
551d55a9 MD |
320 | } |
321 | } | |
322 | ||
323 | /** | |
324 | * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects | |
325 | * @head: pointer to rcu_head structure to be initialized | |
326 | * | |
327 | * This function informs debugobjects of a new rcu_head structure that | |
328 | * has been allocated as an auto variable on the stack. This function | |
329 | * is not required for rcu_head structures that are statically defined or | |
330 | * that are dynamically allocated on the heap. This function has no | |
331 | * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
332 | */ | |
333 | void init_rcu_head_on_stack(struct rcu_head *head) | |
334 | { | |
335 | debug_object_init_on_stack(head, &rcuhead_debug_descr); | |
336 | } | |
337 | EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); | |
338 | ||
339 | /** | |
340 | * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects | |
341 | * @head: pointer to rcu_head structure to be initialized | |
342 | * | |
343 | * This function informs debugobjects that an on-stack rcu_head structure | |
344 | * is about to go out of scope. As with init_rcu_head_on_stack(), this | |
345 | * function is not required for rcu_head structures that are statically | |
346 | * defined or that are dynamically allocated on the heap. Also as with | |
347 | * init_rcu_head_on_stack(), this function has no effect for | |
348 | * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
349 | */ | |
350 | void destroy_rcu_head_on_stack(struct rcu_head *head) | |
351 | { | |
352 | debug_object_free(head, &rcuhead_debug_descr); | |
353 | } | |
354 | EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); | |
355 | ||
356 | struct debug_obj_descr rcuhead_debug_descr = { | |
357 | .name = "rcu_head", | |
551d55a9 | 358 | .fixup_activate = rcuhead_fixup_activate, |
551d55a9 MD |
359 | }; |
360 | EXPORT_SYMBOL_GPL(rcuhead_debug_descr); | |
361 | #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
91afaf30 | 362 | |
28f6569a | 363 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) |
e66c33d5 | 364 | void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, |
52494535 PM |
365 | unsigned long secs, |
366 | unsigned long c_old, unsigned long c) | |
91afaf30 | 367 | { |
52494535 | 368 | trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); |
91afaf30 PM |
369 | } |
370 | EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); | |
371 | #else | |
52494535 PM |
372 | #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ |
373 | do { } while (0) | |
91afaf30 | 374 | #endif |
6bfc09e2 PM |
375 | |
376 | #ifdef CONFIG_RCU_STALL_COMMON | |
377 | ||
378 | #ifdef CONFIG_PROVE_RCU | |
379 | #define RCU_STALL_DELAY_DELTA (5 * HZ) | |
380 | #else | |
381 | #define RCU_STALL_DELAY_DELTA 0 | |
382 | #endif | |
383 | ||
384 | int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ | |
01896f7e | 385 | static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; |
6bfc09e2 PM |
386 | |
387 | module_param(rcu_cpu_stall_suppress, int, 0644); | |
388 | module_param(rcu_cpu_stall_timeout, int, 0644); | |
389 | ||
390 | int rcu_jiffies_till_stall_check(void) | |
391 | { | |
392 | int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); | |
393 | ||
394 | /* | |
395 | * Limit check must be consistent with the Kconfig limits | |
396 | * for CONFIG_RCU_CPU_STALL_TIMEOUT. | |
397 | */ | |
398 | if (till_stall_check < 3) { | |
399 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; | |
400 | till_stall_check = 3; | |
401 | } else if (till_stall_check > 300) { | |
402 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; | |
403 | till_stall_check = 300; | |
404 | } | |
405 | return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; | |
406 | } | |
407 | ||
61f38db3 RR |
408 | void rcu_sysrq_start(void) |
409 | { | |
410 | if (!rcu_cpu_stall_suppress) | |
411 | rcu_cpu_stall_suppress = 2; | |
412 | } | |
413 | ||
414 | void rcu_sysrq_end(void) | |
415 | { | |
416 | if (rcu_cpu_stall_suppress == 2) | |
417 | rcu_cpu_stall_suppress = 0; | |
418 | } | |
419 | ||
6bfc09e2 PM |
420 | static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) |
421 | { | |
422 | rcu_cpu_stall_suppress = 1; | |
423 | return NOTIFY_DONE; | |
424 | } | |
425 | ||
426 | static struct notifier_block rcu_panic_block = { | |
427 | .notifier_call = rcu_panic, | |
428 | }; | |
429 | ||
430 | static int __init check_cpu_stall_init(void) | |
431 | { | |
432 | atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); | |
433 | return 0; | |
434 | } | |
435 | early_initcall(check_cpu_stall_init); | |
436 | ||
437 | #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
8315f422 PM |
438 | |
439 | #ifdef CONFIG_TASKS_RCU | |
440 | ||
441 | /* | |
442 | * Simple variant of RCU whose quiescent states are voluntary context switch, | |
443 | * user-space execution, and idle. As such, grace periods can take one good | |
444 | * long time. There are no read-side primitives similar to rcu_read_lock() | |
445 | * and rcu_read_unlock() because this implementation is intended to get | |
446 | * the system into a safe state for some of the manipulations involved in | |
447 | * tracing and the like. Finally, this implementation does not support | |
448 | * high call_rcu_tasks() rates from multiple CPUs. If this is required, | |
449 | * per-CPU callback lists will be needed. | |
450 | */ | |
451 | ||
452 | /* Global list of callbacks and associated lock. */ | |
453 | static struct rcu_head *rcu_tasks_cbs_head; | |
454 | static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; | |
c7b24d2b | 455 | static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); |
8315f422 PM |
456 | static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); |
457 | ||
3f95aa81 PM |
458 | /* Track exiting tasks in order to allow them to be waited for. */ |
459 | DEFINE_SRCU(tasks_rcu_exit_srcu); | |
460 | ||
461 | /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ | |
52db30ab | 462 | static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10; |
3f95aa81 PM |
463 | module_param(rcu_task_stall_timeout, int, 0644); |
464 | ||
84a8f446 PM |
465 | static void rcu_spawn_tasks_kthread(void); |
466 | ||
467 | /* | |
468 | * Post an RCU-tasks callback. First call must be from process context | |
469 | * after the scheduler if fully operational. | |
470 | */ | |
8315f422 PM |
471 | void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp)) |
472 | { | |
473 | unsigned long flags; | |
c7b24d2b | 474 | bool needwake; |
8315f422 PM |
475 | |
476 | rhp->next = NULL; | |
477 | rhp->func = func; | |
478 | raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); | |
c7b24d2b | 479 | needwake = !rcu_tasks_cbs_head; |
8315f422 PM |
480 | *rcu_tasks_cbs_tail = rhp; |
481 | rcu_tasks_cbs_tail = &rhp->next; | |
482 | raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); | |
84a8f446 PM |
483 | if (needwake) { |
484 | rcu_spawn_tasks_kthread(); | |
c7b24d2b | 485 | wake_up(&rcu_tasks_cbs_wq); |
84a8f446 | 486 | } |
8315f422 PM |
487 | } |
488 | EXPORT_SYMBOL_GPL(call_rcu_tasks); | |
489 | ||
53c6d4ed PM |
490 | /** |
491 | * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. | |
492 | * | |
493 | * Control will return to the caller some time after a full rcu-tasks | |
494 | * grace period has elapsed, in other words after all currently | |
495 | * executing rcu-tasks read-side critical sections have elapsed. These | |
496 | * read-side critical sections are delimited by calls to schedule(), | |
497 | * cond_resched_rcu_qs(), idle execution, userspace execution, calls | |
498 | * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). | |
499 | * | |
500 | * This is a very specialized primitive, intended only for a few uses in | |
501 | * tracing and other situations requiring manipulation of function | |
502 | * preambles and profiling hooks. The synchronize_rcu_tasks() function | |
503 | * is not (yet) intended for heavy use from multiple CPUs. | |
504 | * | |
505 | * Note that this guarantee implies further memory-ordering guarantees. | |
506 | * On systems with more than one CPU, when synchronize_rcu_tasks() returns, | |
507 | * each CPU is guaranteed to have executed a full memory barrier since the | |
508 | * end of its last RCU-tasks read-side critical section whose beginning | |
509 | * preceded the call to synchronize_rcu_tasks(). In addition, each CPU | |
510 | * having an RCU-tasks read-side critical section that extends beyond | |
511 | * the return from synchronize_rcu_tasks() is guaranteed to have executed | |
512 | * a full memory barrier after the beginning of synchronize_rcu_tasks() | |
513 | * and before the beginning of that RCU-tasks read-side critical section. | |
514 | * Note that these guarantees include CPUs that are offline, idle, or | |
515 | * executing in user mode, as well as CPUs that are executing in the kernel. | |
516 | * | |
517 | * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned | |
518 | * to its caller on CPU B, then both CPU A and CPU B are guaranteed | |
519 | * to have executed a full memory barrier during the execution of | |
520 | * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU | |
521 | * (but again only if the system has more than one CPU). | |
522 | */ | |
523 | void synchronize_rcu_tasks(void) | |
524 | { | |
525 | /* Complain if the scheduler has not started. */ | |
526 | rcu_lockdep_assert(!rcu_scheduler_active, | |
527 | "synchronize_rcu_tasks called too soon"); | |
528 | ||
529 | /* Wait for the grace period. */ | |
530 | wait_rcu_gp(call_rcu_tasks); | |
531 | } | |
06c2a923 | 532 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); |
53c6d4ed PM |
533 | |
534 | /** | |
535 | * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. | |
536 | * | |
537 | * Although the current implementation is guaranteed to wait, it is not | |
538 | * obligated to, for example, if there are no pending callbacks. | |
539 | */ | |
540 | void rcu_barrier_tasks(void) | |
541 | { | |
542 | /* There is only one callback queue, so this is easy. ;-) */ | |
543 | synchronize_rcu_tasks(); | |
544 | } | |
06c2a923 | 545 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks); |
53c6d4ed | 546 | |
52db30ab PM |
547 | /* See if tasks are still holding out, complain if so. */ |
548 | static void check_holdout_task(struct task_struct *t, | |
549 | bool needreport, bool *firstreport) | |
8315f422 | 550 | { |
4ff475ed PM |
551 | int cpu; |
552 | ||
8315f422 PM |
553 | if (!ACCESS_ONCE(t->rcu_tasks_holdout) || |
554 | t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) || | |
176f8f7a PM |
555 | !ACCESS_ONCE(t->on_rq) || |
556 | (IS_ENABLED(CONFIG_NO_HZ_FULL) && | |
557 | !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { | |
8315f422 | 558 | ACCESS_ONCE(t->rcu_tasks_holdout) = false; |
8f20a5e8 | 559 | list_del_init(&t->rcu_tasks_holdout_list); |
8315f422 | 560 | put_task_struct(t); |
52db30ab | 561 | return; |
8315f422 | 562 | } |
52db30ab PM |
563 | if (!needreport) |
564 | return; | |
565 | if (*firstreport) { | |
566 | pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); | |
567 | *firstreport = false; | |
568 | } | |
4ff475ed PM |
569 | cpu = task_cpu(t); |
570 | pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", | |
571 | t, ".I"[is_idle_task(t)], | |
572 | "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], | |
573 | t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, | |
574 | t->rcu_tasks_idle_cpu, cpu); | |
52db30ab | 575 | sched_show_task(t); |
8315f422 PM |
576 | } |
577 | ||
578 | /* RCU-tasks kthread that detects grace periods and invokes callbacks. */ | |
579 | static int __noreturn rcu_tasks_kthread(void *arg) | |
580 | { | |
581 | unsigned long flags; | |
582 | struct task_struct *g, *t; | |
52db30ab | 583 | unsigned long lastreport; |
8315f422 PM |
584 | struct rcu_head *list; |
585 | struct rcu_head *next; | |
586 | LIST_HEAD(rcu_tasks_holdouts); | |
587 | ||
60ced495 PM |
588 | /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ |
589 | housekeeping_affine(current); | |
8315f422 PM |
590 | |
591 | /* | |
592 | * Each pass through the following loop makes one check for | |
593 | * newly arrived callbacks, and, if there are some, waits for | |
594 | * one RCU-tasks grace period and then invokes the callbacks. | |
595 | * This loop is terminated by the system going down. ;-) | |
596 | */ | |
597 | for (;;) { | |
598 | ||
599 | /* Pick up any new callbacks. */ | |
600 | raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); | |
601 | list = rcu_tasks_cbs_head; | |
602 | rcu_tasks_cbs_head = NULL; | |
603 | rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; | |
604 | raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); | |
605 | ||
606 | /* If there were none, wait a bit and start over. */ | |
607 | if (!list) { | |
c7b24d2b PM |
608 | wait_event_interruptible(rcu_tasks_cbs_wq, |
609 | rcu_tasks_cbs_head); | |
610 | if (!rcu_tasks_cbs_head) { | |
611 | WARN_ON(signal_pending(current)); | |
612 | schedule_timeout_interruptible(HZ/10); | |
613 | } | |
8315f422 PM |
614 | continue; |
615 | } | |
616 | ||
617 | /* | |
618 | * Wait for all pre-existing t->on_rq and t->nvcsw | |
619 | * transitions to complete. Invoking synchronize_sched() | |
620 | * suffices because all these transitions occur with | |
621 | * interrupts disabled. Without this synchronize_sched(), | |
622 | * a read-side critical section that started before the | |
623 | * grace period might be incorrectly seen as having started | |
624 | * after the grace period. | |
625 | * | |
626 | * This synchronize_sched() also dispenses with the | |
627 | * need for a memory barrier on the first store to | |
628 | * ->rcu_tasks_holdout, as it forces the store to happen | |
629 | * after the beginning of the grace period. | |
630 | */ | |
631 | synchronize_sched(); | |
632 | ||
633 | /* | |
634 | * There were callbacks, so we need to wait for an | |
635 | * RCU-tasks grace period. Start off by scanning | |
636 | * the task list for tasks that are not already | |
637 | * voluntarily blocked. Mark these tasks and make | |
638 | * a list of them in rcu_tasks_holdouts. | |
639 | */ | |
640 | rcu_read_lock(); | |
641 | for_each_process_thread(g, t) { | |
642 | if (t != current && ACCESS_ONCE(t->on_rq) && | |
643 | !is_idle_task(t)) { | |
644 | get_task_struct(t); | |
645 | t->rcu_tasks_nvcsw = ACCESS_ONCE(t->nvcsw); | |
646 | ACCESS_ONCE(t->rcu_tasks_holdout) = true; | |
647 | list_add(&t->rcu_tasks_holdout_list, | |
648 | &rcu_tasks_holdouts); | |
649 | } | |
650 | } | |
651 | rcu_read_unlock(); | |
652 | ||
3f95aa81 PM |
653 | /* |
654 | * Wait for tasks that are in the process of exiting. | |
655 | * This does only part of the job, ensuring that all | |
656 | * tasks that were previously exiting reach the point | |
657 | * where they have disabled preemption, allowing the | |
658 | * later synchronize_sched() to finish the job. | |
659 | */ | |
660 | synchronize_srcu(&tasks_rcu_exit_srcu); | |
661 | ||
8315f422 PM |
662 | /* |
663 | * Each pass through the following loop scans the list | |
664 | * of holdout tasks, removing any that are no longer | |
665 | * holdouts. When the list is empty, we are done. | |
666 | */ | |
52db30ab | 667 | lastreport = jiffies; |
8315f422 | 668 | while (!list_empty(&rcu_tasks_holdouts)) { |
52db30ab PM |
669 | bool firstreport; |
670 | bool needreport; | |
671 | int rtst; | |
8f20a5e8 | 672 | struct task_struct *t1; |
52db30ab | 673 | |
8315f422 | 674 | schedule_timeout_interruptible(HZ); |
52db30ab PM |
675 | rtst = ACCESS_ONCE(rcu_task_stall_timeout); |
676 | needreport = rtst > 0 && | |
677 | time_after(jiffies, lastreport + rtst); | |
678 | if (needreport) | |
679 | lastreport = jiffies; | |
680 | firstreport = true; | |
8315f422 | 681 | WARN_ON(signal_pending(current)); |
8f20a5e8 PM |
682 | list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts, |
683 | rcu_tasks_holdout_list) { | |
52db30ab | 684 | check_holdout_task(t, needreport, &firstreport); |
8f20a5e8 PM |
685 | cond_resched(); |
686 | } | |
8315f422 PM |
687 | } |
688 | ||
689 | /* | |
690 | * Because ->on_rq and ->nvcsw are not guaranteed | |
691 | * to have a full memory barriers prior to them in the | |
692 | * schedule() path, memory reordering on other CPUs could | |
693 | * cause their RCU-tasks read-side critical sections to | |
694 | * extend past the end of the grace period. However, | |
695 | * because these ->nvcsw updates are carried out with | |
696 | * interrupts disabled, we can use synchronize_sched() | |
697 | * to force the needed ordering on all such CPUs. | |
698 | * | |
699 | * This synchronize_sched() also confines all | |
700 | * ->rcu_tasks_holdout accesses to be within the grace | |
701 | * period, avoiding the need for memory barriers for | |
702 | * ->rcu_tasks_holdout accesses. | |
3f95aa81 PM |
703 | * |
704 | * In addition, this synchronize_sched() waits for exiting | |
705 | * tasks to complete their final preempt_disable() region | |
706 | * of execution, cleaning up after the synchronize_srcu() | |
707 | * above. | |
8315f422 PM |
708 | */ |
709 | synchronize_sched(); | |
710 | ||
711 | /* Invoke the callbacks. */ | |
712 | while (list) { | |
713 | next = list->next; | |
714 | local_bh_disable(); | |
715 | list->func(list); | |
716 | local_bh_enable(); | |
717 | list = next; | |
718 | cond_resched(); | |
719 | } | |
c7b24d2b | 720 | schedule_timeout_uninterruptible(HZ/10); |
8315f422 PM |
721 | } |
722 | } | |
723 | ||
84a8f446 PM |
724 | /* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */ |
725 | static void rcu_spawn_tasks_kthread(void) | |
8315f422 | 726 | { |
84a8f446 PM |
727 | static DEFINE_MUTEX(rcu_tasks_kthread_mutex); |
728 | static struct task_struct *rcu_tasks_kthread_ptr; | |
729 | struct task_struct *t; | |
8315f422 | 730 | |
84a8f446 PM |
731 | if (ACCESS_ONCE(rcu_tasks_kthread_ptr)) { |
732 | smp_mb(); /* Ensure caller sees full kthread. */ | |
733 | return; | |
734 | } | |
735 | mutex_lock(&rcu_tasks_kthread_mutex); | |
736 | if (rcu_tasks_kthread_ptr) { | |
737 | mutex_unlock(&rcu_tasks_kthread_mutex); | |
738 | return; | |
739 | } | |
8315f422 PM |
740 | t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread"); |
741 | BUG_ON(IS_ERR(t)); | |
84a8f446 PM |
742 | smp_mb(); /* Ensure others see full kthread. */ |
743 | ACCESS_ONCE(rcu_tasks_kthread_ptr) = t; | |
744 | mutex_unlock(&rcu_tasks_kthread_mutex); | |
8315f422 | 745 | } |
8315f422 PM |
746 | |
747 | #endif /* #ifdef CONFIG_TASKS_RCU */ | |
aa23c6fb PK |
748 | |
749 | #ifdef CONFIG_PROVE_RCU | |
750 | ||
751 | /* | |
752 | * Early boot self test parameters, one for each flavor | |
753 | */ | |
754 | static bool rcu_self_test; | |
755 | static bool rcu_self_test_bh; | |
756 | static bool rcu_self_test_sched; | |
757 | ||
758 | module_param(rcu_self_test, bool, 0444); | |
759 | module_param(rcu_self_test_bh, bool, 0444); | |
760 | module_param(rcu_self_test_sched, bool, 0444); | |
761 | ||
762 | static int rcu_self_test_counter; | |
763 | ||
764 | static void test_callback(struct rcu_head *r) | |
765 | { | |
766 | rcu_self_test_counter++; | |
767 | pr_info("RCU test callback executed %d\n", rcu_self_test_counter); | |
768 | } | |
769 | ||
770 | static void early_boot_test_call_rcu(void) | |
771 | { | |
772 | static struct rcu_head head; | |
773 | ||
774 | call_rcu(&head, test_callback); | |
775 | } | |
776 | ||
777 | static void early_boot_test_call_rcu_bh(void) | |
778 | { | |
779 | static struct rcu_head head; | |
780 | ||
781 | call_rcu_bh(&head, test_callback); | |
782 | } | |
783 | ||
784 | static void early_boot_test_call_rcu_sched(void) | |
785 | { | |
786 | static struct rcu_head head; | |
787 | ||
788 | call_rcu_sched(&head, test_callback); | |
789 | } | |
790 | ||
791 | void rcu_early_boot_tests(void) | |
792 | { | |
793 | pr_info("Running RCU self tests\n"); | |
794 | ||
795 | if (rcu_self_test) | |
796 | early_boot_test_call_rcu(); | |
797 | if (rcu_self_test_bh) | |
798 | early_boot_test_call_rcu_bh(); | |
799 | if (rcu_self_test_sched) | |
800 | early_boot_test_call_rcu_sched(); | |
801 | } | |
802 | ||
803 | static int rcu_verify_early_boot_tests(void) | |
804 | { | |
805 | int ret = 0; | |
806 | int early_boot_test_counter = 0; | |
807 | ||
808 | if (rcu_self_test) { | |
809 | early_boot_test_counter++; | |
810 | rcu_barrier(); | |
811 | } | |
812 | if (rcu_self_test_bh) { | |
813 | early_boot_test_counter++; | |
814 | rcu_barrier_bh(); | |
815 | } | |
816 | if (rcu_self_test_sched) { | |
817 | early_boot_test_counter++; | |
818 | rcu_barrier_sched(); | |
819 | } | |
820 | ||
821 | if (rcu_self_test_counter != early_boot_test_counter) { | |
822 | WARN_ON(1); | |
823 | ret = -1; | |
824 | } | |
825 | ||
826 | return ret; | |
827 | } | |
828 | late_initcall(rcu_verify_early_boot_tests); | |
829 | #else | |
830 | void rcu_early_boot_tests(void) {} | |
831 | #endif /* CONFIG_PROVE_RCU */ |