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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 | |
15 | * along with this program; if not, write to the Free Software | |
16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
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> |
1da177e4 | 50 | |
29c00b4a PM |
51 | #define CREATE_TRACE_POINTS |
52 | #include <trace/events/rcu.h> | |
53 | ||
54 | #include "rcu.h" | |
55 | ||
3705b88d AM |
56 | module_param(rcu_expedited, int, 0); |
57 | ||
9dd8fb16 PM |
58 | #ifdef CONFIG_PREEMPT_RCU |
59 | ||
2a3fa843 PM |
60 | /* |
61 | * Preemptible RCU implementation for rcu_read_lock(). | |
62 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
63 | * if we block. | |
64 | */ | |
65 | void __rcu_read_lock(void) | |
66 | { | |
67 | current->rcu_read_lock_nesting++; | |
68 | barrier(); /* critical section after entry code. */ | |
69 | } | |
70 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
71 | ||
72 | /* | |
73 | * Preemptible RCU implementation for rcu_read_unlock(). | |
74 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
75 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
76 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
77 | * in an RCU read-side critical section and other special cases. | |
78 | */ | |
79 | void __rcu_read_unlock(void) | |
80 | { | |
81 | struct task_struct *t = current; | |
82 | ||
83 | if (t->rcu_read_lock_nesting != 1) { | |
84 | --t->rcu_read_lock_nesting; | |
85 | } else { | |
86 | barrier(); /* critical section before exit code. */ | |
87 | t->rcu_read_lock_nesting = INT_MIN; | |
e3ebfb96 PM |
88 | #ifdef CONFIG_PROVE_RCU_DELAY |
89 | udelay(10); /* Make preemption more probable. */ | |
90 | #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ | |
2a3fa843 PM |
91 | barrier(); /* assign before ->rcu_read_unlock_special load */ |
92 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) | |
93 | rcu_read_unlock_special(t); | |
94 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
95 | t->rcu_read_lock_nesting = 0; | |
96 | } | |
97 | #ifdef CONFIG_PROVE_LOCKING | |
98 | { | |
99 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); | |
100 | ||
101 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
102 | } | |
103 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
104 | } | |
105 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
106 | ||
2439b696 | 107 | #endif /* #ifdef CONFIG_PREEMPT_RCU */ |
9dd8fb16 | 108 | |
162cc279 PM |
109 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
110 | static struct lock_class_key rcu_lock_key; | |
111 | struct lockdep_map rcu_lock_map = | |
112 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); | |
113 | EXPORT_SYMBOL_GPL(rcu_lock_map); | |
632ee200 PM |
114 | |
115 | static struct lock_class_key rcu_bh_lock_key; | |
116 | struct lockdep_map rcu_bh_lock_map = | |
117 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); | |
118 | EXPORT_SYMBOL_GPL(rcu_bh_lock_map); | |
119 | ||
120 | static struct lock_class_key rcu_sched_lock_key; | |
121 | struct lockdep_map rcu_sched_lock_map = | |
122 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); | |
123 | EXPORT_SYMBOL_GPL(rcu_sched_lock_map); | |
162cc279 PM |
124 | #endif |
125 | ||
e3818b8d PM |
126 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
127 | ||
bc293d62 PM |
128 | int debug_lockdep_rcu_enabled(void) |
129 | { | |
130 | return rcu_scheduler_active && debug_locks && | |
131 | current->lockdep_recursion == 0; | |
132 | } | |
133 | EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); | |
134 | ||
e3818b8d | 135 | /** |
ca5ecddf | 136 | * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
e3818b8d PM |
137 | * |
138 | * Check for bottom half being disabled, which covers both the | |
139 | * CONFIG_PROVE_RCU and not cases. Note that if someone uses | |
140 | * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) | |
ca5ecddf PM |
141 | * will show the situation. This is useful for debug checks in functions |
142 | * that require that they be called within an RCU read-side critical | |
143 | * section. | |
e3818b8d PM |
144 | * |
145 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. | |
c0d6d01b PM |
146 | * |
147 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
148 | * offline from an RCU perspective, so check for those as well. | |
e3818b8d PM |
149 | */ |
150 | int rcu_read_lock_bh_held(void) | |
151 | { | |
152 | if (!debug_lockdep_rcu_enabled()) | |
153 | return 1; | |
e6b80a3b FW |
154 | if (rcu_is_cpu_idle()) |
155 | return 0; | |
c0d6d01b PM |
156 | if (!rcu_lockdep_current_cpu_online()) |
157 | return 0; | |
773e3f93 | 158 | return in_softirq() || irqs_disabled(); |
e3818b8d PM |
159 | } |
160 | EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); | |
161 | ||
162 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
163 | ||
2c42818e PM |
164 | struct rcu_synchronize { |
165 | struct rcu_head head; | |
166 | struct completion completion; | |
167 | }; | |
168 | ||
fbf6bfca PM |
169 | /* |
170 | * Awaken the corresponding synchronize_rcu() instance now that a | |
171 | * grace period has elapsed. | |
172 | */ | |
2c42818e | 173 | static void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 174 | { |
01c1c660 PM |
175 | struct rcu_synchronize *rcu; |
176 | ||
177 | rcu = container_of(head, struct rcu_synchronize, head); | |
178 | complete(&rcu->completion); | |
21a1ea9e | 179 | } |
ee84b824 | 180 | |
2c42818e PM |
181 | void wait_rcu_gp(call_rcu_func_t crf) |
182 | { | |
183 | struct rcu_synchronize rcu; | |
184 | ||
185 | init_rcu_head_on_stack(&rcu.head); | |
186 | init_completion(&rcu.completion); | |
187 | /* Will wake me after RCU finished. */ | |
188 | crf(&rcu.head, wakeme_after_rcu); | |
189 | /* Wait for it. */ | |
190 | wait_for_completion(&rcu.completion); | |
191 | destroy_rcu_head_on_stack(&rcu.head); | |
192 | } | |
193 | EXPORT_SYMBOL_GPL(wait_rcu_gp); | |
194 | ||
ee84b824 PM |
195 | #ifdef CONFIG_PROVE_RCU |
196 | /* | |
197 | * wrapper function to avoid #include problems. | |
198 | */ | |
199 | int rcu_my_thread_group_empty(void) | |
200 | { | |
201 | return thread_group_empty(current); | |
202 | } | |
203 | EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); | |
204 | #endif /* #ifdef CONFIG_PROVE_RCU */ | |
551d55a9 MD |
205 | |
206 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
207 | static inline void debug_init_rcu_head(struct rcu_head *head) | |
208 | { | |
209 | debug_object_init(head, &rcuhead_debug_descr); | |
210 | } | |
211 | ||
212 | static inline void debug_rcu_head_free(struct rcu_head *head) | |
213 | { | |
214 | debug_object_free(head, &rcuhead_debug_descr); | |
215 | } | |
216 | ||
217 | /* | |
218 | * fixup_init is called when: | |
219 | * - an active object is initialized | |
220 | */ | |
221 | static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) | |
222 | { | |
223 | struct rcu_head *head = addr; | |
224 | ||
225 | switch (state) { | |
226 | case ODEBUG_STATE_ACTIVE: | |
227 | /* | |
228 | * Ensure that queued callbacks are all executed. | |
229 | * If we detect that we are nested in a RCU read-side critical | |
230 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
231 | * In !PREEMPT configurations, there is no way to tell if we are |
232 | * in a RCU read-side critical section or not, so we never | |
233 | * attempt any fixup and just print a warning. | |
551d55a9 | 234 | */ |
fc2ecf7e | 235 | #ifndef CONFIG_PREEMPT |
108aae22 | 236 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
237 | return 0; |
238 | #endif | |
551d55a9 MD |
239 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
240 | irqs_disabled()) { | |
108aae22 | 241 | WARN_ON_ONCE(1); |
551d55a9 MD |
242 | return 0; |
243 | } | |
244 | rcu_barrier(); | |
245 | rcu_barrier_sched(); | |
246 | rcu_barrier_bh(); | |
247 | debug_object_init(head, &rcuhead_debug_descr); | |
248 | return 1; | |
249 | default: | |
250 | return 0; | |
251 | } | |
252 | } | |
253 | ||
254 | /* | |
255 | * fixup_activate is called when: | |
256 | * - an active object is activated | |
257 | * - an unknown object is activated (might be a statically initialized object) | |
258 | * Activation is performed internally by call_rcu(). | |
259 | */ | |
260 | static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) | |
261 | { | |
262 | struct rcu_head *head = addr; | |
263 | ||
264 | switch (state) { | |
265 | ||
266 | case ODEBUG_STATE_NOTAVAILABLE: | |
267 | /* | |
268 | * This is not really a fixup. We just make sure that it is | |
269 | * tracked in the object tracker. | |
270 | */ | |
271 | debug_object_init(head, &rcuhead_debug_descr); | |
272 | debug_object_activate(head, &rcuhead_debug_descr); | |
273 | return 0; | |
274 | ||
275 | case ODEBUG_STATE_ACTIVE: | |
276 | /* | |
277 | * Ensure that queued callbacks are all executed. | |
278 | * If we detect that we are nested in a RCU read-side critical | |
279 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
280 | * In !PREEMPT configurations, there is no way to tell if we are |
281 | * in a RCU read-side critical section or not, so we never | |
282 | * attempt any fixup and just print a warning. | |
551d55a9 | 283 | */ |
fc2ecf7e | 284 | #ifndef CONFIG_PREEMPT |
108aae22 | 285 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
286 | return 0; |
287 | #endif | |
551d55a9 MD |
288 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
289 | irqs_disabled()) { | |
108aae22 | 290 | WARN_ON_ONCE(1); |
551d55a9 MD |
291 | return 0; |
292 | } | |
293 | rcu_barrier(); | |
294 | rcu_barrier_sched(); | |
295 | rcu_barrier_bh(); | |
296 | debug_object_activate(head, &rcuhead_debug_descr); | |
297 | return 1; | |
298 | default: | |
299 | return 0; | |
300 | } | |
301 | } | |
302 | ||
303 | /* | |
304 | * fixup_free is called when: | |
305 | * - an active object is freed | |
306 | */ | |
307 | static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) | |
308 | { | |
309 | struct rcu_head *head = addr; | |
310 | ||
311 | switch (state) { | |
312 | case ODEBUG_STATE_ACTIVE: | |
313 | /* | |
314 | * Ensure that queued callbacks are all executed. | |
315 | * If we detect that we are nested in a RCU read-side critical | |
316 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
317 | * In !PREEMPT configurations, there is no way to tell if we are |
318 | * in a RCU read-side critical section or not, so we never | |
319 | * attempt any fixup and just print a warning. | |
551d55a9 | 320 | */ |
fc2ecf7e | 321 | #ifndef CONFIG_PREEMPT |
108aae22 | 322 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
323 | return 0; |
324 | #endif | |
551d55a9 MD |
325 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
326 | irqs_disabled()) { | |
108aae22 | 327 | WARN_ON_ONCE(1); |
551d55a9 MD |
328 | return 0; |
329 | } | |
330 | rcu_barrier(); | |
331 | rcu_barrier_sched(); | |
332 | rcu_barrier_bh(); | |
333 | debug_object_free(head, &rcuhead_debug_descr); | |
334 | return 1; | |
551d55a9 MD |
335 | default: |
336 | return 0; | |
337 | } | |
338 | } | |
339 | ||
340 | /** | |
341 | * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects | |
342 | * @head: pointer to rcu_head structure to be initialized | |
343 | * | |
344 | * This function informs debugobjects of a new rcu_head structure that | |
345 | * has been allocated as an auto variable on the stack. This function | |
346 | * is not required for rcu_head structures that are statically defined or | |
347 | * that are dynamically allocated on the heap. This function has no | |
348 | * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
349 | */ | |
350 | void init_rcu_head_on_stack(struct rcu_head *head) | |
351 | { | |
352 | debug_object_init_on_stack(head, &rcuhead_debug_descr); | |
353 | } | |
354 | EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); | |
355 | ||
356 | /** | |
357 | * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects | |
358 | * @head: pointer to rcu_head structure to be initialized | |
359 | * | |
360 | * This function informs debugobjects that an on-stack rcu_head structure | |
361 | * is about to go out of scope. As with init_rcu_head_on_stack(), this | |
362 | * function is not required for rcu_head structures that are statically | |
363 | * defined or that are dynamically allocated on the heap. Also as with | |
364 | * init_rcu_head_on_stack(), this function has no effect for | |
365 | * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
366 | */ | |
367 | void destroy_rcu_head_on_stack(struct rcu_head *head) | |
368 | { | |
369 | debug_object_free(head, &rcuhead_debug_descr); | |
370 | } | |
371 | EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); | |
372 | ||
373 | struct debug_obj_descr rcuhead_debug_descr = { | |
374 | .name = "rcu_head", | |
375 | .fixup_init = rcuhead_fixup_init, | |
376 | .fixup_activate = rcuhead_fixup_activate, | |
377 | .fixup_free = rcuhead_fixup_free, | |
378 | }; | |
379 | EXPORT_SYMBOL_GPL(rcuhead_debug_descr); | |
380 | #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
91afaf30 PM |
381 | |
382 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) | |
52494535 PM |
383 | void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp, |
384 | unsigned long secs, | |
385 | unsigned long c_old, unsigned long c) | |
91afaf30 | 386 | { |
52494535 | 387 | trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); |
91afaf30 PM |
388 | } |
389 | EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); | |
390 | #else | |
52494535 PM |
391 | #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ |
392 | do { } while (0) | |
91afaf30 | 393 | #endif |
6bfc09e2 PM |
394 | |
395 | #ifdef CONFIG_RCU_STALL_COMMON | |
396 | ||
397 | #ifdef CONFIG_PROVE_RCU | |
398 | #define RCU_STALL_DELAY_DELTA (5 * HZ) | |
399 | #else | |
400 | #define RCU_STALL_DELAY_DELTA 0 | |
401 | #endif | |
402 | ||
403 | int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ | |
404 | int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; | |
405 | ||
406 | module_param(rcu_cpu_stall_suppress, int, 0644); | |
407 | module_param(rcu_cpu_stall_timeout, int, 0644); | |
408 | ||
409 | int rcu_jiffies_till_stall_check(void) | |
410 | { | |
411 | int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); | |
412 | ||
413 | /* | |
414 | * Limit check must be consistent with the Kconfig limits | |
415 | * for CONFIG_RCU_CPU_STALL_TIMEOUT. | |
416 | */ | |
417 | if (till_stall_check < 3) { | |
418 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; | |
419 | till_stall_check = 3; | |
420 | } else if (till_stall_check > 300) { | |
421 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; | |
422 | till_stall_check = 300; | |
423 | } | |
424 | return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; | |
425 | } | |
426 | ||
427 | static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) | |
428 | { | |
429 | rcu_cpu_stall_suppress = 1; | |
430 | return NOTIFY_DONE; | |
431 | } | |
432 | ||
433 | static struct notifier_block rcu_panic_block = { | |
434 | .notifier_call = rcu_panic, | |
435 | }; | |
436 | ||
437 | static int __init check_cpu_stall_init(void) | |
438 | { | |
439 | atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); | |
440 | return 0; | |
441 | } | |
442 | early_initcall(check_cpu_stall_init); | |
443 | ||
444 | #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ |