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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 | ||
d5671f6b DV |
65 | #if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT) |
66 | /** | |
67 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? | |
68 | * | |
69 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an | |
70 | * RCU-sched read-side critical section. In absence of | |
71 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
72 | * critical section unless it can prove otherwise. Note that disabling | |
73 | * of preemption (including disabling irqs) counts as an RCU-sched | |
74 | * read-side critical section. This is useful for debug checks in functions | |
75 | * that required that they be called within an RCU-sched read-side | |
76 | * critical section. | |
77 | * | |
78 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot | |
79 | * and while lockdep is disabled. | |
80 | * | |
81 | * Note that if the CPU is in the idle loop from an RCU point of | |
82 | * view (ie: that we are in the section between rcu_idle_enter() and | |
83 | * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU | |
84 | * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs | |
85 | * that are in such a section, considering these as in extended quiescent | |
86 | * state, so such a CPU is effectively never in an RCU read-side critical | |
87 | * section regardless of what RCU primitives it invokes. This state of | |
88 | * affairs is required --- we need to keep an RCU-free window in idle | |
89 | * where the CPU may possibly enter into low power mode. This way we can | |
90 | * notice an extended quiescent state to other CPUs that started a grace | |
91 | * period. Otherwise we would delay any grace period as long as we run in | |
92 | * the idle task. | |
93 | * | |
94 | * Similarly, we avoid claiming an SRCU read lock held if the current | |
95 | * CPU is offline. | |
96 | */ | |
97 | int rcu_read_lock_sched_held(void) | |
98 | { | |
99 | int lockdep_opinion = 0; | |
100 | ||
101 | if (!debug_lockdep_rcu_enabled()) | |
102 | return 1; | |
103 | if (!rcu_is_watching()) | |
104 | return 0; | |
105 | if (!rcu_lockdep_current_cpu_online()) | |
106 | return 0; | |
107 | if (debug_locks) | |
108 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
109 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); | |
110 | } | |
111 | EXPORT_SYMBOL(rcu_read_lock_sched_held); | |
112 | #endif | |
113 | ||
0d39482c PM |
114 | #ifndef CONFIG_TINY_RCU |
115 | ||
ee42571f PM |
116 | static atomic_t rcu_expedited_nesting = |
117 | ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0); | |
0d39482c PM |
118 | |
119 | /* | |
120 | * Should normal grace-period primitives be expedited? Intended for | |
121 | * use within RCU. Note that this function takes the rcu_expedited | |
122 | * sysfs/boot variable into account as well as the rcu_expedite_gp() | |
123 | * nesting. So looping on rcu_unexpedite_gp() until rcu_gp_is_expedited() | |
124 | * returns false is a -really- bad idea. | |
125 | */ | |
126 | bool rcu_gp_is_expedited(void) | |
127 | { | |
128 | return rcu_expedited || atomic_read(&rcu_expedited_nesting); | |
129 | } | |
130 | EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); | |
131 | ||
132 | /** | |
133 | * rcu_expedite_gp - Expedite future RCU grace periods | |
134 | * | |
135 | * After a call to this function, future calls to synchronize_rcu() and | |
136 | * friends act as the corresponding synchronize_rcu_expedited() function | |
137 | * had instead been called. | |
138 | */ | |
139 | void rcu_expedite_gp(void) | |
140 | { | |
141 | atomic_inc(&rcu_expedited_nesting); | |
142 | } | |
143 | EXPORT_SYMBOL_GPL(rcu_expedite_gp); | |
144 | ||
145 | /** | |
146 | * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation | |
147 | * | |
148 | * Undo a prior call to rcu_expedite_gp(). If all prior calls to | |
149 | * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(), | |
150 | * and if the rcu_expedited sysfs/boot parameter is not set, then all | |
151 | * subsequent calls to synchronize_rcu() and friends will return to | |
152 | * their normal non-expedited behavior. | |
153 | */ | |
154 | void rcu_unexpedite_gp(void) | |
155 | { | |
156 | atomic_dec(&rcu_expedited_nesting); | |
157 | } | |
158 | EXPORT_SYMBOL_GPL(rcu_unexpedite_gp); | |
159 | ||
160 | #endif /* #ifndef CONFIG_TINY_RCU */ | |
161 | ||
ee42571f PM |
162 | /* |
163 | * Inform RCU of the end of the in-kernel boot sequence. | |
164 | */ | |
165 | void rcu_end_inkernel_boot(void) | |
166 | { | |
167 | if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT)) | |
168 | rcu_unexpedite_gp(); | |
169 | } | |
0d39482c | 170 | |
9dd8fb16 PM |
171 | #ifdef CONFIG_PREEMPT_RCU |
172 | ||
2a3fa843 PM |
173 | /* |
174 | * Preemptible RCU implementation for rcu_read_lock(). | |
175 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
176 | * if we block. | |
177 | */ | |
178 | void __rcu_read_lock(void) | |
179 | { | |
180 | current->rcu_read_lock_nesting++; | |
181 | barrier(); /* critical section after entry code. */ | |
182 | } | |
183 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
184 | ||
185 | /* | |
186 | * Preemptible RCU implementation for rcu_read_unlock(). | |
187 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
188 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
189 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
190 | * in an RCU read-side critical section and other special cases. | |
191 | */ | |
192 | void __rcu_read_unlock(void) | |
193 | { | |
194 | struct task_struct *t = current; | |
195 | ||
196 | if (t->rcu_read_lock_nesting != 1) { | |
197 | --t->rcu_read_lock_nesting; | |
198 | } else { | |
199 | barrier(); /* critical section before exit code. */ | |
200 | t->rcu_read_lock_nesting = INT_MIN; | |
201 | barrier(); /* assign before ->rcu_read_unlock_special load */ | |
7d0ae808 | 202 | if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) |
2a3fa843 PM |
203 | rcu_read_unlock_special(t); |
204 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
205 | t->rcu_read_lock_nesting = 0; | |
206 | } | |
207 | #ifdef CONFIG_PROVE_LOCKING | |
208 | { | |
7d0ae808 | 209 | int rrln = READ_ONCE(t->rcu_read_lock_nesting); |
2a3fa843 PM |
210 | |
211 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
212 | } | |
213 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
214 | } | |
215 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
216 | ||
2439b696 | 217 | #endif /* #ifdef CONFIG_PREEMPT_RCU */ |
9dd8fb16 | 218 | |
162cc279 PM |
219 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
220 | static struct lock_class_key rcu_lock_key; | |
221 | struct lockdep_map rcu_lock_map = | |
222 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); | |
223 | EXPORT_SYMBOL_GPL(rcu_lock_map); | |
632ee200 PM |
224 | |
225 | static struct lock_class_key rcu_bh_lock_key; | |
226 | struct lockdep_map rcu_bh_lock_map = | |
227 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); | |
228 | EXPORT_SYMBOL_GPL(rcu_bh_lock_map); | |
229 | ||
230 | static struct lock_class_key rcu_sched_lock_key; | |
231 | struct lockdep_map rcu_sched_lock_map = | |
232 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); | |
233 | EXPORT_SYMBOL_GPL(rcu_sched_lock_map); | |
e3818b8d | 234 | |
24ef659a PM |
235 | static struct lock_class_key rcu_callback_key; |
236 | struct lockdep_map rcu_callback_map = | |
237 | STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); | |
238 | EXPORT_SYMBOL_GPL(rcu_callback_map); | |
239 | ||
a0a5a056 | 240 | int notrace debug_lockdep_rcu_enabled(void) |
bc293d62 PM |
241 | { |
242 | return rcu_scheduler_active && debug_locks && | |
243 | current->lockdep_recursion == 0; | |
244 | } | |
245 | EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); | |
246 | ||
85b39d30 ON |
247 | /** |
248 | * rcu_read_lock_held() - might we be in RCU read-side critical section? | |
249 | * | |
250 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU | |
251 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
252 | * this assumes we are in an RCU read-side critical section unless it can | |
253 | * prove otherwise. This is useful for debug checks in functions that | |
254 | * require that they be called within an RCU read-side critical section. | |
255 | * | |
256 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot | |
257 | * and while lockdep is disabled. | |
258 | * | |
259 | * Note that rcu_read_lock() and the matching rcu_read_unlock() must | |
260 | * occur in the same context, for example, it is illegal to invoke | |
261 | * rcu_read_unlock() in process context if the matching rcu_read_lock() | |
262 | * was invoked from within an irq handler. | |
263 | * | |
264 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
265 | * offline from an RCU perspective, so check for those as well. | |
266 | */ | |
267 | int rcu_read_lock_held(void) | |
268 | { | |
269 | if (!debug_lockdep_rcu_enabled()) | |
270 | return 1; | |
271 | if (!rcu_is_watching()) | |
272 | return 0; | |
273 | if (!rcu_lockdep_current_cpu_online()) | |
274 | return 0; | |
275 | return lock_is_held(&rcu_lock_map); | |
276 | } | |
277 | EXPORT_SYMBOL_GPL(rcu_read_lock_held); | |
278 | ||
e3818b8d | 279 | /** |
ca5ecddf | 280 | * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
e3818b8d PM |
281 | * |
282 | * Check for bottom half being disabled, which covers both the | |
283 | * CONFIG_PROVE_RCU and not cases. Note that if someone uses | |
284 | * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) | |
ca5ecddf PM |
285 | * will show the situation. This is useful for debug checks in functions |
286 | * that require that they be called within an RCU read-side critical | |
287 | * section. | |
e3818b8d PM |
288 | * |
289 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. | |
c0d6d01b PM |
290 | * |
291 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
292 | * offline from an RCU perspective, so check for those as well. | |
e3818b8d PM |
293 | */ |
294 | int rcu_read_lock_bh_held(void) | |
295 | { | |
296 | if (!debug_lockdep_rcu_enabled()) | |
297 | return 1; | |
5c173eb8 | 298 | if (!rcu_is_watching()) |
e6b80a3b | 299 | return 0; |
c0d6d01b PM |
300 | if (!rcu_lockdep_current_cpu_online()) |
301 | return 0; | |
773e3f93 | 302 | return in_softirq() || irqs_disabled(); |
e3818b8d PM |
303 | } |
304 | EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); | |
305 | ||
306 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
307 | ||
ee376dbd PM |
308 | /** |
309 | * wakeme_after_rcu() - Callback function to awaken a task after grace period | |
310 | * @head: Pointer to rcu_head member within rcu_synchronize structure | |
311 | * | |
312 | * Awaken the corresponding task now that a grace period has elapsed. | |
fbf6bfca | 313 | */ |
ee376dbd | 314 | void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 315 | { |
01c1c660 PM |
316 | struct rcu_synchronize *rcu; |
317 | ||
318 | rcu = container_of(head, struct rcu_synchronize, head); | |
319 | complete(&rcu->completion); | |
21a1ea9e | 320 | } |
ec90a194 | 321 | EXPORT_SYMBOL_GPL(wakeme_after_rcu); |
ee84b824 | 322 | |
ec90a194 PM |
323 | void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array, |
324 | struct rcu_synchronize *rs_array) | |
2c42818e | 325 | { |
ec90a194 PM |
326 | int i; |
327 | ||
328 | /* Initialize and register callbacks for each flavor specified. */ | |
329 | for (i = 0; i < n; i++) { | |
330 | if (checktiny && | |
331 | (crcu_array[i] == call_rcu || | |
332 | crcu_array[i] == call_rcu_bh)) { | |
333 | might_sleep(); | |
334 | continue; | |
335 | } | |
336 | init_rcu_head_on_stack(&rs_array[i].head); | |
337 | init_completion(&rs_array[i].completion); | |
338 | (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu); | |
339 | } | |
340 | ||
341 | /* Wait for all callbacks to be invoked. */ | |
342 | for (i = 0; i < n; i++) { | |
343 | if (checktiny && | |
344 | (crcu_array[i] == call_rcu || | |
345 | crcu_array[i] == call_rcu_bh)) | |
346 | continue; | |
347 | wait_for_completion(&rs_array[i].completion); | |
348 | destroy_rcu_head_on_stack(&rs_array[i].head); | |
349 | } | |
2c42818e | 350 | } |
ec90a194 | 351 | EXPORT_SYMBOL_GPL(__wait_rcu_gp); |
2c42818e | 352 | |
551d55a9 | 353 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
546a9d85 | 354 | void init_rcu_head(struct rcu_head *head) |
551d55a9 MD |
355 | { |
356 | debug_object_init(head, &rcuhead_debug_descr); | |
357 | } | |
358 | ||
546a9d85 | 359 | void destroy_rcu_head(struct rcu_head *head) |
551d55a9 MD |
360 | { |
361 | debug_object_free(head, &rcuhead_debug_descr); | |
362 | } | |
363 | ||
551d55a9 MD |
364 | /* |
365 | * fixup_activate is called when: | |
366 | * - an active object is activated | |
367 | * - an unknown object is activated (might be a statically initialized object) | |
368 | * Activation is performed internally by call_rcu(). | |
369 | */ | |
370 | static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) | |
371 | { | |
372 | struct rcu_head *head = addr; | |
373 | ||
374 | switch (state) { | |
375 | ||
376 | case ODEBUG_STATE_NOTAVAILABLE: | |
377 | /* | |
378 | * This is not really a fixup. We just make sure that it is | |
379 | * tracked in the object tracker. | |
380 | */ | |
381 | debug_object_init(head, &rcuhead_debug_descr); | |
382 | debug_object_activate(head, &rcuhead_debug_descr); | |
383 | return 0; | |
551d55a9 | 384 | default: |
551d55a9 | 385 | return 1; |
551d55a9 MD |
386 | } |
387 | } | |
388 | ||
389 | /** | |
390 | * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects | |
391 | * @head: pointer to rcu_head structure to be initialized | |
392 | * | |
393 | * This function informs debugobjects of a new rcu_head structure that | |
394 | * has been allocated as an auto variable on the stack. This function | |
395 | * is not required for rcu_head structures that are statically defined or | |
396 | * that are dynamically allocated on the heap. This function has no | |
397 | * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
398 | */ | |
399 | void init_rcu_head_on_stack(struct rcu_head *head) | |
400 | { | |
401 | debug_object_init_on_stack(head, &rcuhead_debug_descr); | |
402 | } | |
403 | EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); | |
404 | ||
405 | /** | |
406 | * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects | |
407 | * @head: pointer to rcu_head structure to be initialized | |
408 | * | |
409 | * This function informs debugobjects that an on-stack rcu_head structure | |
410 | * is about to go out of scope. As with init_rcu_head_on_stack(), this | |
411 | * function is not required for rcu_head structures that are statically | |
412 | * defined or that are dynamically allocated on the heap. Also as with | |
413 | * init_rcu_head_on_stack(), this function has no effect for | |
414 | * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
415 | */ | |
416 | void destroy_rcu_head_on_stack(struct rcu_head *head) | |
417 | { | |
418 | debug_object_free(head, &rcuhead_debug_descr); | |
419 | } | |
420 | EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); | |
421 | ||
422 | struct debug_obj_descr rcuhead_debug_descr = { | |
423 | .name = "rcu_head", | |
551d55a9 | 424 | .fixup_activate = rcuhead_fixup_activate, |
551d55a9 MD |
425 | }; |
426 | EXPORT_SYMBOL_GPL(rcuhead_debug_descr); | |
427 | #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
91afaf30 | 428 | |
28f6569a | 429 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) |
e66c33d5 | 430 | void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, |
52494535 PM |
431 | unsigned long secs, |
432 | unsigned long c_old, unsigned long c) | |
91afaf30 | 433 | { |
52494535 | 434 | trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); |
91afaf30 PM |
435 | } |
436 | EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); | |
437 | #else | |
52494535 PM |
438 | #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ |
439 | do { } while (0) | |
91afaf30 | 440 | #endif |
6bfc09e2 PM |
441 | |
442 | #ifdef CONFIG_RCU_STALL_COMMON | |
443 | ||
444 | #ifdef CONFIG_PROVE_RCU | |
445 | #define RCU_STALL_DELAY_DELTA (5 * HZ) | |
446 | #else | |
447 | #define RCU_STALL_DELAY_DELTA 0 | |
448 | #endif | |
449 | ||
450 | int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ | |
01896f7e | 451 | static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; |
6bfc09e2 PM |
452 | |
453 | module_param(rcu_cpu_stall_suppress, int, 0644); | |
454 | module_param(rcu_cpu_stall_timeout, int, 0644); | |
455 | ||
456 | int rcu_jiffies_till_stall_check(void) | |
457 | { | |
7d0ae808 | 458 | int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout); |
6bfc09e2 PM |
459 | |
460 | /* | |
461 | * Limit check must be consistent with the Kconfig limits | |
462 | * for CONFIG_RCU_CPU_STALL_TIMEOUT. | |
463 | */ | |
464 | if (till_stall_check < 3) { | |
7d0ae808 | 465 | WRITE_ONCE(rcu_cpu_stall_timeout, 3); |
6bfc09e2 PM |
466 | till_stall_check = 3; |
467 | } else if (till_stall_check > 300) { | |
7d0ae808 | 468 | WRITE_ONCE(rcu_cpu_stall_timeout, 300); |
6bfc09e2 PM |
469 | till_stall_check = 300; |
470 | } | |
471 | return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; | |
472 | } | |
473 | ||
61f38db3 RR |
474 | void rcu_sysrq_start(void) |
475 | { | |
476 | if (!rcu_cpu_stall_suppress) | |
477 | rcu_cpu_stall_suppress = 2; | |
478 | } | |
479 | ||
480 | void rcu_sysrq_end(void) | |
481 | { | |
482 | if (rcu_cpu_stall_suppress == 2) | |
483 | rcu_cpu_stall_suppress = 0; | |
484 | } | |
485 | ||
6bfc09e2 PM |
486 | static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) |
487 | { | |
488 | rcu_cpu_stall_suppress = 1; | |
489 | return NOTIFY_DONE; | |
490 | } | |
491 | ||
492 | static struct notifier_block rcu_panic_block = { | |
493 | .notifier_call = rcu_panic, | |
494 | }; | |
495 | ||
496 | static int __init check_cpu_stall_init(void) | |
497 | { | |
498 | atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); | |
499 | return 0; | |
500 | } | |
501 | early_initcall(check_cpu_stall_init); | |
502 | ||
503 | #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
8315f422 PM |
504 | |
505 | #ifdef CONFIG_TASKS_RCU | |
506 | ||
507 | /* | |
508 | * Simple variant of RCU whose quiescent states are voluntary context switch, | |
509 | * user-space execution, and idle. As such, grace periods can take one good | |
510 | * long time. There are no read-side primitives similar to rcu_read_lock() | |
511 | * and rcu_read_unlock() because this implementation is intended to get | |
512 | * the system into a safe state for some of the manipulations involved in | |
513 | * tracing and the like. Finally, this implementation does not support | |
514 | * high call_rcu_tasks() rates from multiple CPUs. If this is required, | |
515 | * per-CPU callback lists will be needed. | |
516 | */ | |
517 | ||
518 | /* Global list of callbacks and associated lock. */ | |
519 | static struct rcu_head *rcu_tasks_cbs_head; | |
520 | static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; | |
c7b24d2b | 521 | static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq); |
8315f422 PM |
522 | static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock); |
523 | ||
3f95aa81 PM |
524 | /* Track exiting tasks in order to allow them to be waited for. */ |
525 | DEFINE_SRCU(tasks_rcu_exit_srcu); | |
526 | ||
527 | /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ | |
52db30ab | 528 | static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10; |
3f95aa81 PM |
529 | module_param(rcu_task_stall_timeout, int, 0644); |
530 | ||
84a8f446 PM |
531 | static void rcu_spawn_tasks_kthread(void); |
532 | ||
533 | /* | |
534 | * Post an RCU-tasks callback. First call must be from process context | |
535 | * after the scheduler if fully operational. | |
536 | */ | |
8315f422 PM |
537 | void call_rcu_tasks(struct rcu_head *rhp, void (*func)(struct rcu_head *rhp)) |
538 | { | |
539 | unsigned long flags; | |
c7b24d2b | 540 | bool needwake; |
8315f422 PM |
541 | |
542 | rhp->next = NULL; | |
543 | rhp->func = func; | |
544 | raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); | |
c7b24d2b | 545 | needwake = !rcu_tasks_cbs_head; |
8315f422 PM |
546 | *rcu_tasks_cbs_tail = rhp; |
547 | rcu_tasks_cbs_tail = &rhp->next; | |
548 | raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); | |
84a8f446 PM |
549 | if (needwake) { |
550 | rcu_spawn_tasks_kthread(); | |
c7b24d2b | 551 | wake_up(&rcu_tasks_cbs_wq); |
84a8f446 | 552 | } |
8315f422 PM |
553 | } |
554 | EXPORT_SYMBOL_GPL(call_rcu_tasks); | |
555 | ||
53c6d4ed PM |
556 | /** |
557 | * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. | |
558 | * | |
559 | * Control will return to the caller some time after a full rcu-tasks | |
560 | * grace period has elapsed, in other words after all currently | |
561 | * executing rcu-tasks read-side critical sections have elapsed. These | |
562 | * read-side critical sections are delimited by calls to schedule(), | |
563 | * cond_resched_rcu_qs(), idle execution, userspace execution, calls | |
564 | * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). | |
565 | * | |
566 | * This is a very specialized primitive, intended only for a few uses in | |
567 | * tracing and other situations requiring manipulation of function | |
568 | * preambles and profiling hooks. The synchronize_rcu_tasks() function | |
569 | * is not (yet) intended for heavy use from multiple CPUs. | |
570 | * | |
571 | * Note that this guarantee implies further memory-ordering guarantees. | |
572 | * On systems with more than one CPU, when synchronize_rcu_tasks() returns, | |
573 | * each CPU is guaranteed to have executed a full memory barrier since the | |
574 | * end of its last RCU-tasks read-side critical section whose beginning | |
575 | * preceded the call to synchronize_rcu_tasks(). In addition, each CPU | |
576 | * having an RCU-tasks read-side critical section that extends beyond | |
577 | * the return from synchronize_rcu_tasks() is guaranteed to have executed | |
578 | * a full memory barrier after the beginning of synchronize_rcu_tasks() | |
579 | * and before the beginning of that RCU-tasks read-side critical section. | |
580 | * Note that these guarantees include CPUs that are offline, idle, or | |
581 | * executing in user mode, as well as CPUs that are executing in the kernel. | |
582 | * | |
583 | * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned | |
584 | * to its caller on CPU B, then both CPU A and CPU B are guaranteed | |
585 | * to have executed a full memory barrier during the execution of | |
586 | * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU | |
587 | * (but again only if the system has more than one CPU). | |
588 | */ | |
589 | void synchronize_rcu_tasks(void) | |
590 | { | |
591 | /* Complain if the scheduler has not started. */ | |
a76a9a48 | 592 | RCU_LOCKDEP_WARN(!rcu_scheduler_active, |
f78f5b90 | 593 | "synchronize_rcu_tasks called too soon"); |
53c6d4ed PM |
594 | |
595 | /* Wait for the grace period. */ | |
596 | wait_rcu_gp(call_rcu_tasks); | |
597 | } | |
06c2a923 | 598 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); |
53c6d4ed PM |
599 | |
600 | /** | |
601 | * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. | |
602 | * | |
603 | * Although the current implementation is guaranteed to wait, it is not | |
604 | * obligated to, for example, if there are no pending callbacks. | |
605 | */ | |
606 | void rcu_barrier_tasks(void) | |
607 | { | |
608 | /* There is only one callback queue, so this is easy. ;-) */ | |
609 | synchronize_rcu_tasks(); | |
610 | } | |
06c2a923 | 611 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks); |
53c6d4ed | 612 | |
52db30ab PM |
613 | /* See if tasks are still holding out, complain if so. */ |
614 | static void check_holdout_task(struct task_struct *t, | |
615 | bool needreport, bool *firstreport) | |
8315f422 | 616 | { |
4ff475ed PM |
617 | int cpu; |
618 | ||
7d0ae808 PM |
619 | if (!READ_ONCE(t->rcu_tasks_holdout) || |
620 | t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || | |
621 | !READ_ONCE(t->on_rq) || | |
176f8f7a PM |
622 | (IS_ENABLED(CONFIG_NO_HZ_FULL) && |
623 | !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { | |
7d0ae808 | 624 | WRITE_ONCE(t->rcu_tasks_holdout, false); |
8f20a5e8 | 625 | list_del_init(&t->rcu_tasks_holdout_list); |
8315f422 | 626 | put_task_struct(t); |
52db30ab | 627 | return; |
8315f422 | 628 | } |
52db30ab PM |
629 | if (!needreport) |
630 | return; | |
631 | if (*firstreport) { | |
632 | pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); | |
633 | *firstreport = false; | |
634 | } | |
4ff475ed PM |
635 | cpu = task_cpu(t); |
636 | pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", | |
637 | t, ".I"[is_idle_task(t)], | |
638 | "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], | |
639 | t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, | |
640 | t->rcu_tasks_idle_cpu, cpu); | |
52db30ab | 641 | sched_show_task(t); |
8315f422 PM |
642 | } |
643 | ||
644 | /* RCU-tasks kthread that detects grace periods and invokes callbacks. */ | |
645 | static int __noreturn rcu_tasks_kthread(void *arg) | |
646 | { | |
647 | unsigned long flags; | |
648 | struct task_struct *g, *t; | |
52db30ab | 649 | unsigned long lastreport; |
8315f422 PM |
650 | struct rcu_head *list; |
651 | struct rcu_head *next; | |
652 | LIST_HEAD(rcu_tasks_holdouts); | |
653 | ||
60ced495 PM |
654 | /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ |
655 | housekeeping_affine(current); | |
8315f422 PM |
656 | |
657 | /* | |
658 | * Each pass through the following loop makes one check for | |
659 | * newly arrived callbacks, and, if there are some, waits for | |
660 | * one RCU-tasks grace period and then invokes the callbacks. | |
661 | * This loop is terminated by the system going down. ;-) | |
662 | */ | |
663 | for (;;) { | |
664 | ||
665 | /* Pick up any new callbacks. */ | |
666 | raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags); | |
667 | list = rcu_tasks_cbs_head; | |
668 | rcu_tasks_cbs_head = NULL; | |
669 | rcu_tasks_cbs_tail = &rcu_tasks_cbs_head; | |
670 | raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); | |
671 | ||
672 | /* If there were none, wait a bit and start over. */ | |
673 | if (!list) { | |
c7b24d2b PM |
674 | wait_event_interruptible(rcu_tasks_cbs_wq, |
675 | rcu_tasks_cbs_head); | |
676 | if (!rcu_tasks_cbs_head) { | |
677 | WARN_ON(signal_pending(current)); | |
678 | schedule_timeout_interruptible(HZ/10); | |
679 | } | |
8315f422 PM |
680 | continue; |
681 | } | |
682 | ||
683 | /* | |
684 | * Wait for all pre-existing t->on_rq and t->nvcsw | |
685 | * transitions to complete. Invoking synchronize_sched() | |
686 | * suffices because all these transitions occur with | |
687 | * interrupts disabled. Without this synchronize_sched(), | |
688 | * a read-side critical section that started before the | |
689 | * grace period might be incorrectly seen as having started | |
690 | * after the grace period. | |
691 | * | |
692 | * This synchronize_sched() also dispenses with the | |
693 | * need for a memory barrier on the first store to | |
694 | * ->rcu_tasks_holdout, as it forces the store to happen | |
695 | * after the beginning of the grace period. | |
696 | */ | |
697 | synchronize_sched(); | |
698 | ||
699 | /* | |
700 | * There were callbacks, so we need to wait for an | |
701 | * RCU-tasks grace period. Start off by scanning | |
702 | * the task list for tasks that are not already | |
703 | * voluntarily blocked. Mark these tasks and make | |
704 | * a list of them in rcu_tasks_holdouts. | |
705 | */ | |
706 | rcu_read_lock(); | |
707 | for_each_process_thread(g, t) { | |
7d0ae808 | 708 | if (t != current && READ_ONCE(t->on_rq) && |
8315f422 PM |
709 | !is_idle_task(t)) { |
710 | get_task_struct(t); | |
7d0ae808 PM |
711 | t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); |
712 | WRITE_ONCE(t->rcu_tasks_holdout, true); | |
8315f422 PM |
713 | list_add(&t->rcu_tasks_holdout_list, |
714 | &rcu_tasks_holdouts); | |
715 | } | |
716 | } | |
717 | rcu_read_unlock(); | |
718 | ||
3f95aa81 PM |
719 | /* |
720 | * Wait for tasks that are in the process of exiting. | |
721 | * This does only part of the job, ensuring that all | |
722 | * tasks that were previously exiting reach the point | |
723 | * where they have disabled preemption, allowing the | |
724 | * later synchronize_sched() to finish the job. | |
725 | */ | |
726 | synchronize_srcu(&tasks_rcu_exit_srcu); | |
727 | ||
8315f422 PM |
728 | /* |
729 | * Each pass through the following loop scans the list | |
730 | * of holdout tasks, removing any that are no longer | |
731 | * holdouts. When the list is empty, we are done. | |
732 | */ | |
52db30ab | 733 | lastreport = jiffies; |
8315f422 | 734 | while (!list_empty(&rcu_tasks_holdouts)) { |
52db30ab PM |
735 | bool firstreport; |
736 | bool needreport; | |
737 | int rtst; | |
8f20a5e8 | 738 | struct task_struct *t1; |
52db30ab | 739 | |
8315f422 | 740 | schedule_timeout_interruptible(HZ); |
7d0ae808 | 741 | rtst = READ_ONCE(rcu_task_stall_timeout); |
52db30ab PM |
742 | needreport = rtst > 0 && |
743 | time_after(jiffies, lastreport + rtst); | |
744 | if (needreport) | |
745 | lastreport = jiffies; | |
746 | firstreport = true; | |
8315f422 | 747 | WARN_ON(signal_pending(current)); |
8f20a5e8 PM |
748 | list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts, |
749 | rcu_tasks_holdout_list) { | |
52db30ab | 750 | check_holdout_task(t, needreport, &firstreport); |
8f20a5e8 PM |
751 | cond_resched(); |
752 | } | |
8315f422 PM |
753 | } |
754 | ||
755 | /* | |
756 | * Because ->on_rq and ->nvcsw are not guaranteed | |
757 | * to have a full memory barriers prior to them in the | |
758 | * schedule() path, memory reordering on other CPUs could | |
759 | * cause their RCU-tasks read-side critical sections to | |
760 | * extend past the end of the grace period. However, | |
761 | * because these ->nvcsw updates are carried out with | |
762 | * interrupts disabled, we can use synchronize_sched() | |
763 | * to force the needed ordering on all such CPUs. | |
764 | * | |
765 | * This synchronize_sched() also confines all | |
766 | * ->rcu_tasks_holdout accesses to be within the grace | |
767 | * period, avoiding the need for memory barriers for | |
768 | * ->rcu_tasks_holdout accesses. | |
3f95aa81 PM |
769 | * |
770 | * In addition, this synchronize_sched() waits for exiting | |
771 | * tasks to complete their final preempt_disable() region | |
772 | * of execution, cleaning up after the synchronize_srcu() | |
773 | * above. | |
8315f422 PM |
774 | */ |
775 | synchronize_sched(); | |
776 | ||
777 | /* Invoke the callbacks. */ | |
778 | while (list) { | |
779 | next = list->next; | |
780 | local_bh_disable(); | |
781 | list->func(list); | |
782 | local_bh_enable(); | |
783 | list = next; | |
784 | cond_resched(); | |
785 | } | |
c7b24d2b | 786 | schedule_timeout_uninterruptible(HZ/10); |
8315f422 PM |
787 | } |
788 | } | |
789 | ||
84a8f446 PM |
790 | /* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */ |
791 | static void rcu_spawn_tasks_kthread(void) | |
8315f422 | 792 | { |
84a8f446 PM |
793 | static DEFINE_MUTEX(rcu_tasks_kthread_mutex); |
794 | static struct task_struct *rcu_tasks_kthread_ptr; | |
795 | struct task_struct *t; | |
8315f422 | 796 | |
7d0ae808 | 797 | if (READ_ONCE(rcu_tasks_kthread_ptr)) { |
84a8f446 PM |
798 | smp_mb(); /* Ensure caller sees full kthread. */ |
799 | return; | |
800 | } | |
801 | mutex_lock(&rcu_tasks_kthread_mutex); | |
802 | if (rcu_tasks_kthread_ptr) { | |
803 | mutex_unlock(&rcu_tasks_kthread_mutex); | |
804 | return; | |
805 | } | |
8315f422 PM |
806 | t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread"); |
807 | BUG_ON(IS_ERR(t)); | |
84a8f446 | 808 | smp_mb(); /* Ensure others see full kthread. */ |
7d0ae808 | 809 | WRITE_ONCE(rcu_tasks_kthread_ptr, t); |
84a8f446 | 810 | mutex_unlock(&rcu_tasks_kthread_mutex); |
8315f422 | 811 | } |
8315f422 PM |
812 | |
813 | #endif /* #ifdef CONFIG_TASKS_RCU */ | |
aa23c6fb PK |
814 | |
815 | #ifdef CONFIG_PROVE_RCU | |
816 | ||
817 | /* | |
818 | * Early boot self test parameters, one for each flavor | |
819 | */ | |
820 | static bool rcu_self_test; | |
821 | static bool rcu_self_test_bh; | |
822 | static bool rcu_self_test_sched; | |
823 | ||
824 | module_param(rcu_self_test, bool, 0444); | |
825 | module_param(rcu_self_test_bh, bool, 0444); | |
826 | module_param(rcu_self_test_sched, bool, 0444); | |
827 | ||
828 | static int rcu_self_test_counter; | |
829 | ||
830 | static void test_callback(struct rcu_head *r) | |
831 | { | |
832 | rcu_self_test_counter++; | |
833 | pr_info("RCU test callback executed %d\n", rcu_self_test_counter); | |
834 | } | |
835 | ||
836 | static void early_boot_test_call_rcu(void) | |
837 | { | |
838 | static struct rcu_head head; | |
839 | ||
840 | call_rcu(&head, test_callback); | |
841 | } | |
842 | ||
843 | static void early_boot_test_call_rcu_bh(void) | |
844 | { | |
845 | static struct rcu_head head; | |
846 | ||
847 | call_rcu_bh(&head, test_callback); | |
848 | } | |
849 | ||
850 | static void early_boot_test_call_rcu_sched(void) | |
851 | { | |
852 | static struct rcu_head head; | |
853 | ||
854 | call_rcu_sched(&head, test_callback); | |
855 | } | |
856 | ||
857 | void rcu_early_boot_tests(void) | |
858 | { | |
859 | pr_info("Running RCU self tests\n"); | |
860 | ||
861 | if (rcu_self_test) | |
862 | early_boot_test_call_rcu(); | |
863 | if (rcu_self_test_bh) | |
864 | early_boot_test_call_rcu_bh(); | |
865 | if (rcu_self_test_sched) | |
866 | early_boot_test_call_rcu_sched(); | |
867 | } | |
868 | ||
869 | static int rcu_verify_early_boot_tests(void) | |
870 | { | |
871 | int ret = 0; | |
872 | int early_boot_test_counter = 0; | |
873 | ||
874 | if (rcu_self_test) { | |
875 | early_boot_test_counter++; | |
876 | rcu_barrier(); | |
877 | } | |
878 | if (rcu_self_test_bh) { | |
879 | early_boot_test_counter++; | |
880 | rcu_barrier_bh(); | |
881 | } | |
882 | if (rcu_self_test_sched) { | |
883 | early_boot_test_counter++; | |
884 | rcu_barrier_sched(); | |
885 | } | |
886 | ||
887 | if (rcu_self_test_counter != early_boot_test_counter) { | |
888 | WARN_ON(1); | |
889 | ret = -1; | |
890 | } | |
891 | ||
892 | return ret; | |
893 | } | |
894 | late_initcall(rcu_verify_early_boot_tests); | |
895 | #else | |
896 | void rcu_early_boot_tests(void) {} | |
897 | #endif /* CONFIG_PROVE_RCU */ |