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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> |
1da177e4 | 50 | |
29c00b4a | 51 | #define CREATE_TRACE_POINTS |
29c00b4a PM |
52 | |
53 | #include "rcu.h" | |
54 | ||
4102adab PM |
55 | MODULE_ALIAS("rcupdate"); |
56 | #ifdef MODULE_PARAM_PREFIX | |
57 | #undef MODULE_PARAM_PREFIX | |
58 | #endif | |
59 | #define MODULE_PARAM_PREFIX "rcupdate." | |
60 | ||
3705b88d AM |
61 | module_param(rcu_expedited, int, 0); |
62 | ||
9dd8fb16 PM |
63 | #ifdef CONFIG_PREEMPT_RCU |
64 | ||
2a3fa843 PM |
65 | /* |
66 | * Preemptible RCU implementation for rcu_read_lock(). | |
67 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
68 | * if we block. | |
69 | */ | |
70 | void __rcu_read_lock(void) | |
71 | { | |
72 | current->rcu_read_lock_nesting++; | |
73 | barrier(); /* critical section after entry code. */ | |
74 | } | |
75 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
76 | ||
77 | /* | |
78 | * Preemptible RCU implementation for rcu_read_unlock(). | |
79 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
80 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
81 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
82 | * in an RCU read-side critical section and other special cases. | |
83 | */ | |
84 | void __rcu_read_unlock(void) | |
85 | { | |
86 | struct task_struct *t = current; | |
87 | ||
88 | if (t->rcu_read_lock_nesting != 1) { | |
89 | --t->rcu_read_lock_nesting; | |
90 | } else { | |
91 | barrier(); /* critical section before exit code. */ | |
92 | t->rcu_read_lock_nesting = INT_MIN; | |
e3ebfb96 PM |
93 | #ifdef CONFIG_PROVE_RCU_DELAY |
94 | udelay(10); /* Make preemption more probable. */ | |
95 | #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ | |
2a3fa843 PM |
96 | barrier(); /* assign before ->rcu_read_unlock_special load */ |
97 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) | |
98 | rcu_read_unlock_special(t); | |
99 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
100 | t->rcu_read_lock_nesting = 0; | |
101 | } | |
102 | #ifdef CONFIG_PROVE_LOCKING | |
103 | { | |
104 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); | |
105 | ||
106 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
107 | } | |
108 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
109 | } | |
110 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
111 | ||
2439b696 | 112 | #endif /* #ifdef CONFIG_PREEMPT_RCU */ |
9dd8fb16 | 113 | |
162cc279 PM |
114 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
115 | static struct lock_class_key rcu_lock_key; | |
116 | struct lockdep_map rcu_lock_map = | |
117 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); | |
118 | EXPORT_SYMBOL_GPL(rcu_lock_map); | |
632ee200 PM |
119 | |
120 | static struct lock_class_key rcu_bh_lock_key; | |
121 | struct lockdep_map rcu_bh_lock_map = | |
122 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); | |
123 | EXPORT_SYMBOL_GPL(rcu_bh_lock_map); | |
124 | ||
125 | static struct lock_class_key rcu_sched_lock_key; | |
126 | struct lockdep_map rcu_sched_lock_map = | |
127 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); | |
128 | EXPORT_SYMBOL_GPL(rcu_sched_lock_map); | |
e3818b8d | 129 | |
24ef659a PM |
130 | static struct lock_class_key rcu_callback_key; |
131 | struct lockdep_map rcu_callback_map = | |
132 | STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); | |
133 | EXPORT_SYMBOL_GPL(rcu_callback_map); | |
134 | ||
a0a5a056 | 135 | int notrace debug_lockdep_rcu_enabled(void) |
bc293d62 PM |
136 | { |
137 | return rcu_scheduler_active && debug_locks && | |
138 | current->lockdep_recursion == 0; | |
139 | } | |
140 | EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); | |
141 | ||
e3818b8d | 142 | /** |
ca5ecddf | 143 | * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? |
e3818b8d PM |
144 | * |
145 | * Check for bottom half being disabled, which covers both the | |
146 | * CONFIG_PROVE_RCU and not cases. Note that if someone uses | |
147 | * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) | |
ca5ecddf PM |
148 | * will show the situation. This is useful for debug checks in functions |
149 | * that require that they be called within an RCU read-side critical | |
150 | * section. | |
e3818b8d PM |
151 | * |
152 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. | |
c0d6d01b PM |
153 | * |
154 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
155 | * offline from an RCU perspective, so check for those as well. | |
e3818b8d PM |
156 | */ |
157 | int rcu_read_lock_bh_held(void) | |
158 | { | |
159 | if (!debug_lockdep_rcu_enabled()) | |
160 | return 1; | |
5c173eb8 | 161 | if (!rcu_is_watching()) |
e6b80a3b | 162 | return 0; |
c0d6d01b PM |
163 | if (!rcu_lockdep_current_cpu_online()) |
164 | return 0; | |
773e3f93 | 165 | return in_softirq() || irqs_disabled(); |
e3818b8d PM |
166 | } |
167 | EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); | |
168 | ||
169 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
170 | ||
2c42818e PM |
171 | struct rcu_synchronize { |
172 | struct rcu_head head; | |
173 | struct completion completion; | |
174 | }; | |
175 | ||
fbf6bfca PM |
176 | /* |
177 | * Awaken the corresponding synchronize_rcu() instance now that a | |
178 | * grace period has elapsed. | |
179 | */ | |
2c42818e | 180 | static void wakeme_after_rcu(struct rcu_head *head) |
21a1ea9e | 181 | { |
01c1c660 PM |
182 | struct rcu_synchronize *rcu; |
183 | ||
184 | rcu = container_of(head, struct rcu_synchronize, head); | |
185 | complete(&rcu->completion); | |
21a1ea9e | 186 | } |
ee84b824 | 187 | |
2c42818e PM |
188 | void wait_rcu_gp(call_rcu_func_t crf) |
189 | { | |
190 | struct rcu_synchronize rcu; | |
191 | ||
192 | init_rcu_head_on_stack(&rcu.head); | |
193 | init_completion(&rcu.completion); | |
194 | /* Will wake me after RCU finished. */ | |
195 | crf(&rcu.head, wakeme_after_rcu); | |
196 | /* Wait for it. */ | |
197 | wait_for_completion(&rcu.completion); | |
198 | destroy_rcu_head_on_stack(&rcu.head); | |
199 | } | |
200 | EXPORT_SYMBOL_GPL(wait_rcu_gp); | |
201 | ||
551d55a9 MD |
202 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD |
203 | static inline void debug_init_rcu_head(struct rcu_head *head) | |
204 | { | |
205 | debug_object_init(head, &rcuhead_debug_descr); | |
206 | } | |
207 | ||
208 | static inline void debug_rcu_head_free(struct rcu_head *head) | |
209 | { | |
210 | debug_object_free(head, &rcuhead_debug_descr); | |
211 | } | |
212 | ||
551d55a9 MD |
213 | /* |
214 | * fixup_activate is called when: | |
215 | * - an active object is activated | |
216 | * - an unknown object is activated (might be a statically initialized object) | |
217 | * Activation is performed internally by call_rcu(). | |
218 | */ | |
219 | static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) | |
220 | { | |
221 | struct rcu_head *head = addr; | |
222 | ||
223 | switch (state) { | |
224 | ||
225 | case ODEBUG_STATE_NOTAVAILABLE: | |
226 | /* | |
227 | * This is not really a fixup. We just make sure that it is | |
228 | * tracked in the object tracker. | |
229 | */ | |
230 | debug_object_init(head, &rcuhead_debug_descr); | |
231 | debug_object_activate(head, &rcuhead_debug_descr); | |
232 | return 0; | |
551d55a9 | 233 | default: |
551d55a9 | 234 | return 1; |
551d55a9 MD |
235 | } |
236 | } | |
237 | ||
238 | /** | |
239 | * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects | |
240 | * @head: pointer to rcu_head structure to be initialized | |
241 | * | |
242 | * This function informs debugobjects of a new rcu_head structure that | |
243 | * has been allocated as an auto variable on the stack. This function | |
244 | * is not required for rcu_head structures that are statically defined or | |
245 | * that are dynamically allocated on the heap. This function has no | |
246 | * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
247 | */ | |
248 | void init_rcu_head_on_stack(struct rcu_head *head) | |
249 | { | |
250 | debug_object_init_on_stack(head, &rcuhead_debug_descr); | |
251 | } | |
252 | EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); | |
253 | ||
254 | /** | |
255 | * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects | |
256 | * @head: pointer to rcu_head structure to be initialized | |
257 | * | |
258 | * This function informs debugobjects that an on-stack rcu_head structure | |
259 | * is about to go out of scope. As with init_rcu_head_on_stack(), this | |
260 | * function is not required for rcu_head structures that are statically | |
261 | * defined or that are dynamically allocated on the heap. Also as with | |
262 | * init_rcu_head_on_stack(), this function has no effect for | |
263 | * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. | |
264 | */ | |
265 | void destroy_rcu_head_on_stack(struct rcu_head *head) | |
266 | { | |
267 | debug_object_free(head, &rcuhead_debug_descr); | |
268 | } | |
269 | EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); | |
270 | ||
271 | struct debug_obj_descr rcuhead_debug_descr = { | |
272 | .name = "rcu_head", | |
551d55a9 | 273 | .fixup_activate = rcuhead_fixup_activate, |
551d55a9 MD |
274 | }; |
275 | EXPORT_SYMBOL_GPL(rcuhead_debug_descr); | |
276 | #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
91afaf30 PM |
277 | |
278 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) | |
e66c33d5 | 279 | void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, |
52494535 PM |
280 | unsigned long secs, |
281 | unsigned long c_old, unsigned long c) | |
91afaf30 | 282 | { |
52494535 | 283 | trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); |
91afaf30 PM |
284 | } |
285 | EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); | |
286 | #else | |
52494535 PM |
287 | #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ |
288 | do { } while (0) | |
91afaf30 | 289 | #endif |
6bfc09e2 PM |
290 | |
291 | #ifdef CONFIG_RCU_STALL_COMMON | |
292 | ||
293 | #ifdef CONFIG_PROVE_RCU | |
294 | #define RCU_STALL_DELAY_DELTA (5 * HZ) | |
295 | #else | |
296 | #define RCU_STALL_DELAY_DELTA 0 | |
297 | #endif | |
298 | ||
299 | int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ | |
01896f7e | 300 | static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; |
6bfc09e2 PM |
301 | |
302 | module_param(rcu_cpu_stall_suppress, int, 0644); | |
303 | module_param(rcu_cpu_stall_timeout, int, 0644); | |
304 | ||
305 | int rcu_jiffies_till_stall_check(void) | |
306 | { | |
307 | int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); | |
308 | ||
309 | /* | |
310 | * Limit check must be consistent with the Kconfig limits | |
311 | * for CONFIG_RCU_CPU_STALL_TIMEOUT. | |
312 | */ | |
313 | if (till_stall_check < 3) { | |
314 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; | |
315 | till_stall_check = 3; | |
316 | } else if (till_stall_check > 300) { | |
317 | ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; | |
318 | till_stall_check = 300; | |
319 | } | |
320 | return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; | |
321 | } | |
322 | ||
61f38db3 RR |
323 | void rcu_sysrq_start(void) |
324 | { | |
325 | if (!rcu_cpu_stall_suppress) | |
326 | rcu_cpu_stall_suppress = 2; | |
327 | } | |
328 | ||
329 | void rcu_sysrq_end(void) | |
330 | { | |
331 | if (rcu_cpu_stall_suppress == 2) | |
332 | rcu_cpu_stall_suppress = 0; | |
333 | } | |
334 | ||
6bfc09e2 PM |
335 | static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) |
336 | { | |
337 | rcu_cpu_stall_suppress = 1; | |
338 | return NOTIFY_DONE; | |
339 | } | |
340 | ||
341 | static struct notifier_block rcu_panic_block = { | |
342 | .notifier_call = rcu_panic, | |
343 | }; | |
344 | ||
345 | static int __init check_cpu_stall_init(void) | |
346 | { | |
347 | atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); | |
348 | return 0; | |
349 | } | |
350 | early_initcall(check_cpu_stall_init); | |
351 | ||
352 | #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
ac1bea85 PM |
353 | |
354 | /* | |
355 | * Hooks for cond_resched() and friends to avoid RCU CPU stall warnings. | |
356 | */ | |
357 | ||
358 | DEFINE_PER_CPU(int, rcu_cond_resched_count); | |
359 | ||
360 | /* | |
361 | * Report a set of RCU quiescent states, for use by cond_resched() | |
362 | * and friends. Out of line due to being called infrequently. | |
363 | */ | |
364 | void rcu_resched(void) | |
365 | { | |
366 | preempt_disable(); | |
367 | __this_cpu_write(rcu_cond_resched_count, 0); | |
368 | rcu_note_context_switch(smp_processor_id()); | |
369 | preempt_enable(); | |
370 | } |