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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> |
1da177e4 | 48 | |
29c00b4a PM |
49 | #define CREATE_TRACE_POINTS |
50 | #include <trace/events/rcu.h> | |
51 | ||
52 | #include "rcu.h" | |
53 | ||
9dd8fb16 PM |
54 | #ifdef CONFIG_PREEMPT_RCU |
55 | ||
2a3fa843 PM |
56 | /* |
57 | * Preemptible RCU implementation for rcu_read_lock(). | |
58 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
59 | * if we block. | |
60 | */ | |
61 | void __rcu_read_lock(void) | |
62 | { | |
63 | current->rcu_read_lock_nesting++; | |
64 | barrier(); /* critical section after entry code. */ | |
65 | } | |
66 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
67 | ||
68 | /* | |
69 | * Preemptible RCU implementation for rcu_read_unlock(). | |
70 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
71 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
72 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
73 | * in an RCU read-side critical section and other special cases. | |
74 | */ | |
75 | void __rcu_read_unlock(void) | |
76 | { | |
77 | struct task_struct *t = current; | |
78 | ||
79 | if (t->rcu_read_lock_nesting != 1) { | |
80 | --t->rcu_read_lock_nesting; | |
81 | } else { | |
82 | barrier(); /* critical section before exit code. */ | |
83 | t->rcu_read_lock_nesting = INT_MIN; | |
84 | barrier(); /* assign before ->rcu_read_unlock_special load */ | |
85 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) | |
86 | rcu_read_unlock_special(t); | |
87 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
88 | t->rcu_read_lock_nesting = 0; | |
89 | } | |
90 | #ifdef CONFIG_PROVE_LOCKING | |
91 | { | |
92 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); | |
93 | ||
94 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
95 | } | |
96 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
97 | } | |
98 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
99 | ||
9dd8fb16 PM |
100 | /* |
101 | * Check for a task exiting while in a preemptible-RCU read-side | |
102 | * critical section, clean up if so. No need to issue warnings, | |
103 | * as debug_check_no_locks_held() already does this if lockdep | |
104 | * is enabled. | |
105 | */ | |
106 | void exit_rcu(void) | |
107 | { | |
108 | struct task_struct *t = current; | |
109 | ||
110 | if (likely(list_empty(¤t->rcu_node_entry))) | |
111 | return; | |
112 | t->rcu_read_lock_nesting = 1; | |
113 | barrier(); | |
114 | t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; | |
115 | __rcu_read_unlock(); | |
116 | } | |
117 | ||
118 | #else /* #ifdef CONFIG_PREEMPT_RCU */ | |
119 | ||
120 | void exit_rcu(void) | |
121 | { | |
122 | } | |
123 | ||
124 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
125 | ||
162cc279 PM |
126 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
127 | static struct lock_class_key rcu_lock_key; | |
128 | struct lockdep_map rcu_lock_map = | |
129 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); | |
130 | EXPORT_SYMBOL_GPL(rcu_lock_map); | |
632ee200 PM |
131 | |
132 | static struct lock_class_key rcu_bh_lock_key; | |
133 | struct lockdep_map rcu_bh_lock_map = | |
134 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); | |
135 | EXPORT_SYMBOL_GPL(rcu_bh_lock_map); | |
136 | ||
137 | static struct lock_class_key rcu_sched_lock_key; | |
138 | struct lockdep_map rcu_sched_lock_map = | |
139 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); | |
140 | EXPORT_SYMBOL_GPL(rcu_sched_lock_map); | |
162cc279 PM |
141 | #endif |
142 | ||
e3818b8d PM |
143 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
144 | ||
bc293d62 PM |
145 | int debug_lockdep_rcu_enabled(void) |
146 | { | |
147 | return rcu_scheduler_active && debug_locks && | |
148 | current->lockdep_recursion == 0; | |
149 | } | |
150 | EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); | |
151 | ||
e3818b8d | 152 | /** |
ca5ecddf | 153 | * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
e3818b8d PM |
154 | * |
155 | * Check for bottom half being disabled, which covers both the | |
156 | * CONFIG_PROVE_RCU and not cases. Note that if someone uses | |
157 | * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) | |
ca5ecddf PM |
158 | * will show the situation. This is useful for debug checks in functions |
159 | * that require that they be called within an RCU read-side critical | |
160 | * section. | |
e3818b8d PM |
161 | * |
162 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. | |
c0d6d01b PM |
163 | * |
164 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
165 | * offline from an RCU perspective, so check for those as well. | |
e3818b8d PM |
166 | */ |
167 | int rcu_read_lock_bh_held(void) | |
168 | { | |
169 | if (!debug_lockdep_rcu_enabled()) | |
170 | return 1; | |
e6b80a3b FW |
171 | if (rcu_is_cpu_idle()) |
172 | return 0; | |
c0d6d01b PM |
173 | if (!rcu_lockdep_current_cpu_online()) |
174 | return 0; | |
773e3f93 | 175 | return in_softirq() || irqs_disabled(); |
e3818b8d PM |
176 | } |
177 | EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); | |
178 | ||
179 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
180 | ||
2c42818e PM |
181 | struct rcu_synchronize { |
182 | struct rcu_head head; | |
183 | struct completion completion; | |
184 | }; | |
185 | ||
fbf6bfca PM |
186 | /* |
187 | * Awaken the corresponding synchronize_rcu() instance now that a | |
188 | * grace period has elapsed. | |
189 | */ | |
2c42818e | 190 | static void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 191 | { |
01c1c660 PM |
192 | struct rcu_synchronize *rcu; |
193 | ||
194 | rcu = container_of(head, struct rcu_synchronize, head); | |
195 | complete(&rcu->completion); | |
21a1ea9e | 196 | } |
ee84b824 | 197 | |
2c42818e PM |
198 | void wait_rcu_gp(call_rcu_func_t crf) |
199 | { | |
200 | struct rcu_synchronize rcu; | |
201 | ||
202 | init_rcu_head_on_stack(&rcu.head); | |
203 | init_completion(&rcu.completion); | |
204 | /* Will wake me after RCU finished. */ | |
205 | crf(&rcu.head, wakeme_after_rcu); | |
206 | /* Wait for it. */ | |
207 | wait_for_completion(&rcu.completion); | |
208 | destroy_rcu_head_on_stack(&rcu.head); | |
209 | } | |
210 | EXPORT_SYMBOL_GPL(wait_rcu_gp); | |
211 | ||
ee84b824 PM |
212 | #ifdef CONFIG_PROVE_RCU |
213 | /* | |
214 | * wrapper function to avoid #include problems. | |
215 | */ | |
216 | int rcu_my_thread_group_empty(void) | |
217 | { | |
218 | return thread_group_empty(current); | |
219 | } | |
220 | EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty); | |
221 | #endif /* #ifdef CONFIG_PROVE_RCU */ | |
551d55a9 MD |
222 | |
223 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
224 | static inline void debug_init_rcu_head(struct rcu_head *head) | |
225 | { | |
226 | debug_object_init(head, &rcuhead_debug_descr); | |
227 | } | |
228 | ||
229 | static inline void debug_rcu_head_free(struct rcu_head *head) | |
230 | { | |
231 | debug_object_free(head, &rcuhead_debug_descr); | |
232 | } | |
233 | ||
234 | /* | |
235 | * fixup_init is called when: | |
236 | * - an active object is initialized | |
237 | */ | |
238 | static int rcuhead_fixup_init(void *addr, enum debug_obj_state state) | |
239 | { | |
240 | struct rcu_head *head = addr; | |
241 | ||
242 | switch (state) { | |
243 | case ODEBUG_STATE_ACTIVE: | |
244 | /* | |
245 | * Ensure that queued callbacks are all executed. | |
246 | * If we detect that we are nested in a RCU read-side critical | |
247 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
248 | * In !PREEMPT configurations, there is no way to tell if we are |
249 | * in a RCU read-side critical section or not, so we never | |
250 | * attempt any fixup and just print a warning. | |
551d55a9 | 251 | */ |
fc2ecf7e | 252 | #ifndef CONFIG_PREEMPT |
108aae22 | 253 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
254 | return 0; |
255 | #endif | |
551d55a9 MD |
256 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
257 | irqs_disabled()) { | |
108aae22 | 258 | WARN_ON_ONCE(1); |
551d55a9 MD |
259 | return 0; |
260 | } | |
261 | rcu_barrier(); | |
262 | rcu_barrier_sched(); | |
263 | rcu_barrier_bh(); | |
264 | debug_object_init(head, &rcuhead_debug_descr); | |
265 | return 1; | |
266 | default: | |
267 | return 0; | |
268 | } | |
269 | } | |
270 | ||
271 | /* | |
272 | * fixup_activate is called when: | |
273 | * - an active object is activated | |
274 | * - an unknown object is activated (might be a statically initialized object) | |
275 | * Activation is performed internally by call_rcu(). | |
276 | */ | |
277 | static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) | |
278 | { | |
279 | struct rcu_head *head = addr; | |
280 | ||
281 | switch (state) { | |
282 | ||
283 | case ODEBUG_STATE_NOTAVAILABLE: | |
284 | /* | |
285 | * This is not really a fixup. We just make sure that it is | |
286 | * tracked in the object tracker. | |
287 | */ | |
288 | debug_object_init(head, &rcuhead_debug_descr); | |
289 | debug_object_activate(head, &rcuhead_debug_descr); | |
290 | return 0; | |
291 | ||
292 | case ODEBUG_STATE_ACTIVE: | |
293 | /* | |
294 | * Ensure that queued callbacks are all executed. | |
295 | * If we detect that we are nested in a RCU read-side critical | |
296 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
297 | * In !PREEMPT configurations, there is no way to tell if we are |
298 | * in a RCU read-side critical section or not, so we never | |
299 | * attempt any fixup and just print a warning. | |
551d55a9 | 300 | */ |
fc2ecf7e | 301 | #ifndef CONFIG_PREEMPT |
108aae22 | 302 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
303 | return 0; |
304 | #endif | |
551d55a9 MD |
305 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
306 | irqs_disabled()) { | |
108aae22 | 307 | WARN_ON_ONCE(1); |
551d55a9 MD |
308 | return 0; |
309 | } | |
310 | rcu_barrier(); | |
311 | rcu_barrier_sched(); | |
312 | rcu_barrier_bh(); | |
313 | debug_object_activate(head, &rcuhead_debug_descr); | |
314 | return 1; | |
315 | default: | |
316 | return 0; | |
317 | } | |
318 | } | |
319 | ||
320 | /* | |
321 | * fixup_free is called when: | |
322 | * - an active object is freed | |
323 | */ | |
324 | static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) | |
325 | { | |
326 | struct rcu_head *head = addr; | |
327 | ||
328 | switch (state) { | |
329 | case ODEBUG_STATE_ACTIVE: | |
330 | /* | |
331 | * Ensure that queued callbacks are all executed. | |
332 | * If we detect that we are nested in a RCU read-side critical | |
333 | * section, we should simply fail, otherwise we would deadlock. | |
fc2ecf7e MD |
334 | * In !PREEMPT configurations, there is no way to tell if we are |
335 | * in a RCU read-side critical section or not, so we never | |
336 | * attempt any fixup and just print a warning. | |
551d55a9 | 337 | */ |
fc2ecf7e | 338 | #ifndef CONFIG_PREEMPT |
108aae22 | 339 | WARN_ON_ONCE(1); |
fc2ecf7e MD |
340 | return 0; |
341 | #endif | |
551d55a9 MD |
342 | if (rcu_preempt_depth() != 0 || preempt_count() != 0 || |
343 | irqs_disabled()) { | |
108aae22 | 344 | WARN_ON_ONCE(1); |
551d55a9 MD |
345 | return 0; |
346 | } | |
347 | rcu_barrier(); | |
348 | rcu_barrier_sched(); | |
349 | rcu_barrier_bh(); | |
350 | debug_object_free(head, &rcuhead_debug_descr); | |
351 | return 1; | |
551d55a9 MD |
352 | default: |
353 | return 0; | |
354 | } | |
355 | } | |
356 | ||
357 | /** | |
358 | * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects | |
359 | * @head: pointer to rcu_head structure to be initialized | |
360 | * | |
361 | * This function informs debugobjects of a new rcu_head structure that | |
362 | * has been allocated as an auto variable on the stack. This function | |
363 | * is not required for rcu_head structures that are statically defined or | |
364 | * that are dynamically allocated on the heap. This function has no | |
365 | * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
366 | */ | |
367 | void init_rcu_head_on_stack(struct rcu_head *head) | |
368 | { | |
369 | debug_object_init_on_stack(head, &rcuhead_debug_descr); | |
370 | } | |
371 | EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); | |
372 | ||
373 | /** | |
374 | * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects | |
375 | * @head: pointer to rcu_head structure to be initialized | |
376 | * | |
377 | * This function informs debugobjects that an on-stack rcu_head structure | |
378 | * is about to go out of scope. As with init_rcu_head_on_stack(), this | |
379 | * function is not required for rcu_head structures that are statically | |
380 | * defined or that are dynamically allocated on the heap. Also as with | |
381 | * init_rcu_head_on_stack(), this function has no effect for | |
382 | * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
383 | */ | |
384 | void destroy_rcu_head_on_stack(struct rcu_head *head) | |
385 | { | |
386 | debug_object_free(head, &rcuhead_debug_descr); | |
387 | } | |
388 | EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); | |
389 | ||
390 | struct debug_obj_descr rcuhead_debug_descr = { | |
391 | .name = "rcu_head", | |
392 | .fixup_init = rcuhead_fixup_init, | |
393 | .fixup_activate = rcuhead_fixup_activate, | |
394 | .fixup_free = rcuhead_fixup_free, | |
395 | }; | |
396 | EXPORT_SYMBOL_GPL(rcuhead_debug_descr); | |
397 | #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
91afaf30 PM |
398 | |
399 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) | |
400 | void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp) | |
401 | { | |
402 | trace_rcu_torture_read(rcutorturename, rhp); | |
403 | } | |
404 | EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); | |
405 | #else | |
406 | #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) | |
407 | #endif |