Commit | Line | Data |
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1da177e4 | 1 | /* |
a71fca58 | 2 | * Read-Copy Update mechanism for mutual exclusion |
1da177e4 LT |
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 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
a71fca58 | 21 | * |
595182bc | 22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
1da177e4 LT |
23 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
24 | * Papers: | |
25 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf | |
26 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) | |
27 | * | |
28 | * For detailed explanation of Read-Copy Update mechanism see - | |
a71fca58 | 29 | * http://lse.sourceforge.net/locking/rcupdate.html |
1da177e4 LT |
30 | * |
31 | */ | |
32 | ||
33 | #ifndef __LINUX_RCUPDATE_H | |
34 | #define __LINUX_RCUPDATE_H | |
35 | ||
99098751 | 36 | #include <linux/types.h> |
1da177e4 LT |
37 | #include <linux/cache.h> |
38 | #include <linux/spinlock.h> | |
39 | #include <linux/threads.h> | |
1da177e4 LT |
40 | #include <linux/cpumask.h> |
41 | #include <linux/seqlock.h> | |
851a67b8 | 42 | #include <linux/lockdep.h> |
4446a36f | 43 | #include <linux/completion.h> |
551d55a9 | 44 | #include <linux/debugobjects.h> |
187f1882 | 45 | #include <linux/bug.h> |
ca5ecddf | 46 | #include <linux/compiler.h> |
1da177e4 | 47 | |
e5ab6772 DY |
48 | #ifdef CONFIG_RCU_TORTURE_TEST |
49 | extern int rcutorture_runnable; /* for sysctl */ | |
50 | #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ | |
51 | ||
4a298656 PM |
52 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
53 | extern void rcutorture_record_test_transition(void); | |
54 | extern void rcutorture_record_progress(unsigned long vernum); | |
91afaf30 PM |
55 | extern void do_trace_rcu_torture_read(char *rcutorturename, |
56 | struct rcu_head *rhp); | |
4a298656 PM |
57 | #else |
58 | static inline void rcutorture_record_test_transition(void) | |
59 | { | |
60 | } | |
61 | static inline void rcutorture_record_progress(unsigned long vernum) | |
62 | { | |
63 | } | |
91afaf30 PM |
64 | #ifdef CONFIG_RCU_TRACE |
65 | extern void do_trace_rcu_torture_read(char *rcutorturename, | |
66 | struct rcu_head *rhp); | |
67 | #else | |
68 | #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) | |
69 | #endif | |
4a298656 PM |
70 | #endif |
71 | ||
e27fc964 TH |
72 | #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) |
73 | #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) | |
a3dc3fb1 PM |
74 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
75 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) | |
76 | ||
03b042bf | 77 | /* Exported common interfaces */ |
2c42818e PM |
78 | |
79 | #ifdef CONFIG_PREEMPT_RCU | |
80 | ||
81 | /** | |
82 | * call_rcu() - Queue an RCU callback for invocation after a grace period. | |
83 | * @head: structure to be used for queueing the RCU updates. | |
84 | * @func: actual callback function to be invoked after the grace period | |
85 | * | |
86 | * The callback function will be invoked some time after a full grace | |
87 | * period elapses, in other words after all pre-existing RCU read-side | |
88 | * critical sections have completed. However, the callback function | |
89 | * might well execute concurrently with RCU read-side critical sections | |
90 | * that started after call_rcu() was invoked. RCU read-side critical | |
91 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
92 | * and may be nested. | |
93 | */ | |
94 | extern void call_rcu(struct rcu_head *head, | |
95 | void (*func)(struct rcu_head *head)); | |
96 | ||
97 | #else /* #ifdef CONFIG_PREEMPT_RCU */ | |
98 | ||
99 | /* In classic RCU, call_rcu() is just call_rcu_sched(). */ | |
100 | #define call_rcu call_rcu_sched | |
101 | ||
102 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
103 | ||
104 | /** | |
105 | * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. | |
106 | * @head: structure to be used for queueing the RCU updates. | |
107 | * @func: actual callback function to be invoked after the grace period | |
108 | * | |
109 | * The callback function will be invoked some time after a full grace | |
110 | * period elapses, in other words after all currently executing RCU | |
111 | * read-side critical sections have completed. call_rcu_bh() assumes | |
112 | * that the read-side critical sections end on completion of a softirq | |
113 | * handler. This means that read-side critical sections in process | |
114 | * context must not be interrupted by softirqs. This interface is to be | |
115 | * used when most of the read-side critical sections are in softirq context. | |
116 | * RCU read-side critical sections are delimited by : | |
117 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
118 | * OR | |
119 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
120 | * These may be nested. | |
121 | */ | |
122 | extern void call_rcu_bh(struct rcu_head *head, | |
123 | void (*func)(struct rcu_head *head)); | |
124 | ||
125 | /** | |
126 | * call_rcu_sched() - Queue an RCU for invocation after sched grace period. | |
127 | * @head: structure to be used for queueing the RCU updates. | |
128 | * @func: actual callback function to be invoked after the grace period | |
129 | * | |
130 | * The callback function will be invoked some time after a full grace | |
131 | * period elapses, in other words after all currently executing RCU | |
132 | * read-side critical sections have completed. call_rcu_sched() assumes | |
133 | * that the read-side critical sections end on enabling of preemption | |
134 | * or on voluntary preemption. | |
135 | * RCU read-side critical sections are delimited by : | |
136 | * - rcu_read_lock_sched() and rcu_read_unlock_sched(), | |
137 | * OR | |
138 | * anything that disables preemption. | |
139 | * These may be nested. | |
140 | */ | |
7b0b759b PM |
141 | extern void call_rcu_sched(struct rcu_head *head, |
142 | void (*func)(struct rcu_head *rcu)); | |
2c42818e | 143 | |
7b0b759b | 144 | extern void synchronize_sched(void); |
03b042bf | 145 | |
a3dc3fb1 PM |
146 | #ifdef CONFIG_PREEMPT_RCU |
147 | ||
7b0b759b PM |
148 | extern void __rcu_read_lock(void); |
149 | extern void __rcu_read_unlock(void); | |
150 | void synchronize_rcu(void); | |
151 | ||
a3dc3fb1 PM |
152 | /* |
153 | * Defined as a macro as it is a very low level header included from | |
154 | * areas that don't even know about current. This gives the rcu_read_lock() | |
155 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
156 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
157 | */ | |
158 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
159 | ||
7b0b759b PM |
160 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
161 | ||
162 | static inline void __rcu_read_lock(void) | |
163 | { | |
164 | preempt_disable(); | |
165 | } | |
166 | ||
167 | static inline void __rcu_read_unlock(void) | |
168 | { | |
169 | preempt_enable(); | |
170 | } | |
171 | ||
172 | static inline void synchronize_rcu(void) | |
173 | { | |
174 | synchronize_sched(); | |
175 | } | |
176 | ||
177 | static inline int rcu_preempt_depth(void) | |
178 | { | |
179 | return 0; | |
180 | } | |
181 | ||
182 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
183 | ||
184 | /* Internal to kernel */ | |
7b0b759b PM |
185 | extern void rcu_sched_qs(int cpu); |
186 | extern void rcu_bh_qs(int cpu); | |
187 | extern void rcu_check_callbacks(int cpu, int user); | |
188 | struct notifier_block; | |
9b2e4f18 PM |
189 | extern void rcu_idle_enter(void); |
190 | extern void rcu_idle_exit(void); | |
191 | extern void rcu_irq_enter(void); | |
192 | extern void rcu_irq_exit(void); | |
9dd8fb16 | 193 | extern void exit_rcu(void); |
a3dc3fb1 | 194 | |
8a2ecf47 PM |
195 | /** |
196 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers | |
197 | * @a: Code that RCU needs to pay attention to. | |
198 | * | |
199 | * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden | |
200 | * in the inner idle loop, that is, between the rcu_idle_enter() and | |
201 | * the rcu_idle_exit() -- RCU will happily ignore any such read-side | |
202 | * critical sections. However, things like powertop need tracepoints | |
203 | * in the inner idle loop. | |
204 | * | |
205 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) | |
206 | * will tell RCU that it needs to pay attending, invoke its argument | |
207 | * (in this example, a call to the do_something_with_RCU() function), | |
208 | * and then tell RCU to go back to ignoring this CPU. It is permissible | |
209 | * to nest RCU_NONIDLE() wrappers, but the nesting level is currently | |
210 | * quite limited. If deeper nesting is required, it will be necessary | |
211 | * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. | |
212 | * | |
213 | * This macro may be used from process-level code only. | |
214 | */ | |
215 | #define RCU_NONIDLE(a) \ | |
216 | do { \ | |
217 | rcu_idle_exit(); \ | |
218 | do { a; } while (0); \ | |
219 | rcu_idle_enter(); \ | |
220 | } while (0) | |
221 | ||
2c42818e PM |
222 | /* |
223 | * Infrastructure to implement the synchronize_() primitives in | |
224 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
225 | */ | |
226 | ||
227 | typedef void call_rcu_func_t(struct rcu_head *head, | |
228 | void (*func)(struct rcu_head *head)); | |
229 | void wait_rcu_gp(call_rcu_func_t crf); | |
230 | ||
f41d911f | 231 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 232 | #include <linux/rcutree.h> |
a57eb940 | 233 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
9b1d82fa | 234 | #include <linux/rcutiny.h> |
64db4cff PM |
235 | #else |
236 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 237 | #endif |
01c1c660 | 238 | |
551d55a9 MD |
239 | /* |
240 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
241 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
242 | * allocated dynamically in the heap or defined statically don't need any | |
243 | * initialization. | |
244 | */ | |
245 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
246 | extern void init_rcu_head_on_stack(struct rcu_head *head); | |
247 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); | |
248 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
4376030a MD |
249 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
250 | { | |
251 | } | |
252 | ||
253 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) | |
254 | { | |
255 | } | |
551d55a9 | 256 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 257 | |
c0d6d01b PM |
258 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
259 | bool rcu_lockdep_current_cpu_online(void); | |
260 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
261 | static inline bool rcu_lockdep_current_cpu_online(void) | |
262 | { | |
263 | return 1; | |
264 | } | |
265 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
266 | ||
bc33f24b | 267 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 268 | |
e6b80a3b FW |
269 | #ifdef CONFIG_PROVE_RCU |
270 | extern int rcu_is_cpu_idle(void); | |
271 | #else /* !CONFIG_PROVE_RCU */ | |
272 | static inline int rcu_is_cpu_idle(void) | |
273 | { | |
274 | return 0; | |
275 | } | |
276 | #endif /* else !CONFIG_PROVE_RCU */ | |
277 | ||
00f49e57 FW |
278 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
279 | { | |
00f49e57 FW |
280 | lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); |
281 | } | |
282 | ||
283 | static inline void rcu_lock_release(struct lockdep_map *map) | |
284 | { | |
00f49e57 FW |
285 | lock_release(map, 1, _THIS_IP_); |
286 | } | |
287 | ||
bc33f24b | 288 | extern struct lockdep_map rcu_lock_map; |
632ee200 | 289 | extern struct lockdep_map rcu_bh_lock_map; |
632ee200 | 290 | extern struct lockdep_map rcu_sched_lock_map; |
bc293d62 | 291 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 292 | |
632ee200 | 293 | /** |
ca5ecddf | 294 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 295 | * |
d20200b5 PM |
296 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
297 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
632ee200 | 298 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
299 | * prove otherwise. This is useful for debug checks in functions that |
300 | * require that they be called within an RCU read-side critical section. | |
54dbf96c | 301 | * |
ca5ecddf | 302 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 303 | * and while lockdep is disabled. |
3842a083 PM |
304 | * |
305 | * Note that rcu_read_lock() and the matching rcu_read_unlock() must | |
306 | * occur in the same context, for example, it is illegal to invoke | |
307 | * rcu_read_unlock() in process context if the matching rcu_read_lock() | |
308 | * was invoked from within an irq handler. | |
c0d6d01b PM |
309 | * |
310 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
311 | * offline from an RCU perspective, so check for those as well. | |
632ee200 PM |
312 | */ |
313 | static inline int rcu_read_lock_held(void) | |
314 | { | |
54dbf96c PM |
315 | if (!debug_lockdep_rcu_enabled()) |
316 | return 1; | |
e6b80a3b FW |
317 | if (rcu_is_cpu_idle()) |
318 | return 0; | |
c0d6d01b PM |
319 | if (!rcu_lockdep_current_cpu_online()) |
320 | return 0; | |
54dbf96c | 321 | return lock_is_held(&rcu_lock_map); |
632ee200 PM |
322 | } |
323 | ||
e3818b8d PM |
324 | /* |
325 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
326 | * hell. | |
632ee200 | 327 | */ |
e3818b8d | 328 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
329 | |
330 | /** | |
ca5ecddf | 331 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 332 | * |
d20200b5 PM |
333 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
334 | * RCU-sched read-side critical section. In absence of | |
335 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
336 | * critical section unless it can prove otherwise. Note that disabling | |
337 | * of preemption (including disabling irqs) counts as an RCU-sched | |
ca5ecddf PM |
338 | * read-side critical section. This is useful for debug checks in functions |
339 | * that required that they be called within an RCU-sched read-side | |
340 | * critical section. | |
54dbf96c | 341 | * |
32c141a0 PM |
342 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
343 | * and while lockdep is disabled. | |
e6b80a3b FW |
344 | * |
345 | * Note that if the CPU is in the idle loop from an RCU point of | |
346 | * view (ie: that we are in the section between rcu_idle_enter() and | |
347 | * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU | |
348 | * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs | |
349 | * that are in such a section, considering these as in extended quiescent | |
350 | * state, so such a CPU is effectively never in an RCU read-side critical | |
351 | * section regardless of what RCU primitives it invokes. This state of | |
352 | * affairs is required --- we need to keep an RCU-free window in idle | |
353 | * where the CPU may possibly enter into low power mode. This way we can | |
354 | * notice an extended quiescent state to other CPUs that started a grace | |
355 | * period. Otherwise we would delay any grace period as long as we run in | |
356 | * the idle task. | |
c0d6d01b PM |
357 | * |
358 | * Similarly, we avoid claiming an SRCU read lock held if the current | |
359 | * CPU is offline. | |
632ee200 | 360 | */ |
bdd4e85d | 361 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
362 | static inline int rcu_read_lock_sched_held(void) |
363 | { | |
364 | int lockdep_opinion = 0; | |
365 | ||
54dbf96c PM |
366 | if (!debug_lockdep_rcu_enabled()) |
367 | return 1; | |
e6b80a3b FW |
368 | if (rcu_is_cpu_idle()) |
369 | return 0; | |
c0d6d01b PM |
370 | if (!rcu_lockdep_current_cpu_online()) |
371 | return 0; | |
632ee200 PM |
372 | if (debug_locks) |
373 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 374 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 375 | } |
bdd4e85d | 376 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
377 | static inline int rcu_read_lock_sched_held(void) |
378 | { | |
379 | return 1; | |
632ee200 | 380 | } |
bdd4e85d | 381 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
382 | |
383 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
384 | ||
d8ab29f8 PM |
385 | # define rcu_lock_acquire(a) do { } while (0) |
386 | # define rcu_lock_release(a) do { } while (0) | |
632ee200 PM |
387 | |
388 | static inline int rcu_read_lock_held(void) | |
389 | { | |
390 | return 1; | |
391 | } | |
392 | ||
393 | static inline int rcu_read_lock_bh_held(void) | |
394 | { | |
395 | return 1; | |
396 | } | |
397 | ||
bdd4e85d | 398 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
399 | static inline int rcu_read_lock_sched_held(void) |
400 | { | |
bbad9379 | 401 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 402 | } |
bdd4e85d | 403 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
404 | static inline int rcu_read_lock_sched_held(void) |
405 | { | |
406 | return 1; | |
632ee200 | 407 | } |
bdd4e85d | 408 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
409 | |
410 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
411 | ||
412 | #ifdef CONFIG_PROVE_RCU | |
413 | ||
ee84b824 PM |
414 | extern int rcu_my_thread_group_empty(void); |
415 | ||
4221a991 TH |
416 | /** |
417 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
418 | * @c: condition to check | |
b3fbab05 | 419 | * @s: informative message |
4221a991 | 420 | */ |
b3fbab05 | 421 | #define rcu_lockdep_assert(c, s) \ |
2b3fc35f | 422 | do { \ |
7ccaba53 | 423 | static bool __section(.data.unlikely) __warned; \ |
2b3fc35f LJ |
424 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
425 | __warned = true; \ | |
b3fbab05 | 426 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
2b3fc35f LJ |
427 | } \ |
428 | } while (0) | |
429 | ||
50406b98 PM |
430 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
431 | static inline void rcu_preempt_sleep_check(void) | |
432 | { | |
433 | rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), | |
434 | "Illegal context switch in RCU read-side " | |
435 | "critical section"); | |
436 | } | |
437 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
438 | static inline void rcu_preempt_sleep_check(void) | |
439 | { | |
440 | } | |
441 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
442 | ||
b3fbab05 PM |
443 | #define rcu_sleep_check() \ |
444 | do { \ | |
50406b98 | 445 | rcu_preempt_sleep_check(); \ |
b3fbab05 PM |
446 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ |
447 | "Illegal context switch in RCU-bh" \ | |
448 | " read-side critical section"); \ | |
449 | rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ | |
450 | "Illegal context switch in RCU-sched"\ | |
451 | " read-side critical section"); \ | |
452 | } while (0) | |
453 | ||
ca5ecddf PM |
454 | #else /* #ifdef CONFIG_PROVE_RCU */ |
455 | ||
b3fbab05 PM |
456 | #define rcu_lockdep_assert(c, s) do { } while (0) |
457 | #define rcu_sleep_check() do { } while (0) | |
ca5ecddf PM |
458 | |
459 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
460 | ||
461 | /* | |
462 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
463 | * and rcu_assign_pointer(). Some of these could be folded into their | |
464 | * callers, but they are left separate in order to ease introduction of | |
465 | * multiple flavors of pointers to match the multiple flavors of RCU | |
466 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
467 | * the future. | |
468 | */ | |
53ecfba2 PM |
469 | |
470 | #ifdef __CHECKER__ | |
471 | #define rcu_dereference_sparse(p, space) \ | |
472 | ((void)(((typeof(*p) space *)p) == p)) | |
473 | #else /* #ifdef __CHECKER__ */ | |
474 | #define rcu_dereference_sparse(p, space) | |
475 | #endif /* #else #ifdef __CHECKER__ */ | |
476 | ||
ca5ecddf PM |
477 | #define __rcu_access_pointer(p, space) \ |
478 | ({ \ | |
479 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
53ecfba2 | 480 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
481 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
482 | }) | |
483 | #define __rcu_dereference_check(p, c, space) \ | |
484 | ({ \ | |
485 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
b3fbab05 PM |
486 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
487 | " usage"); \ | |
53ecfba2 | 488 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
489 | smp_read_barrier_depends(); \ |
490 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
491 | }) | |
492 | #define __rcu_dereference_protected(p, c, space) \ | |
493 | ({ \ | |
b3fbab05 PM |
494 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
495 | " usage"); \ | |
53ecfba2 | 496 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
497 | ((typeof(*p) __force __kernel *)(p)); \ |
498 | }) | |
499 | ||
a4dd9925 PM |
500 | #define __rcu_access_index(p, space) \ |
501 | ({ \ | |
502 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
503 | rcu_dereference_sparse(p, space); \ | |
504 | (_________p1); \ | |
505 | }) | |
ca5ecddf PM |
506 | #define __rcu_dereference_index_check(p, c) \ |
507 | ({ \ | |
508 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
b3fbab05 PM |
509 | rcu_lockdep_assert(c, \ |
510 | "suspicious rcu_dereference_index_check()" \ | |
511 | " usage"); \ | |
ca5ecddf PM |
512 | smp_read_barrier_depends(); \ |
513 | (_________p1); \ | |
514 | }) | |
515 | #define __rcu_assign_pointer(p, v, space) \ | |
e9023c40 | 516 | do { \ |
d322f45c | 517 | smp_wmb(); \ |
ca5ecddf | 518 | (p) = (typeof(*v) __force space *)(v); \ |
e9023c40 | 519 | } while (0) |
ca5ecddf PM |
520 | |
521 | ||
522 | /** | |
523 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
524 | * @p: The pointer to read | |
525 | * | |
526 | * Return the value of the specified RCU-protected pointer, but omit the | |
527 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
528 | * when the value of this pointer is accessed, but the pointer is not | |
529 | * dereferenced, for example, when testing an RCU-protected pointer against | |
530 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
531 | * update-side locks prevent the value of the pointer from changing, you | |
532 | * should instead use rcu_dereference_protected() for this use case. | |
5e1ee6e1 PM |
533 | * |
534 | * It is also permissible to use rcu_access_pointer() when read-side | |
535 | * access to the pointer was removed at least one grace period ago, as | |
536 | * is the case in the context of the RCU callback that is freeing up | |
537 | * the data, or after a synchronize_rcu() returns. This can be useful | |
538 | * when tearing down multi-linked structures after a grace period | |
539 | * has elapsed. | |
ca5ecddf PM |
540 | */ |
541 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
542 | ||
632ee200 | 543 | /** |
ca5ecddf | 544 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
545 | * @p: The pointer to read, prior to dereferencing |
546 | * @c: The conditions under which the dereference will take place | |
632ee200 | 547 | * |
c08c68dd | 548 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
549 | * dereference will take place are correct. Typically the conditions |
550 | * indicate the various locking conditions that should be held at that | |
551 | * point. The check should return true if the conditions are satisfied. | |
552 | * An implicit check for being in an RCU read-side critical section | |
553 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
554 | * |
555 | * For example: | |
556 | * | |
ca5ecddf | 557 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
558 | * |
559 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 560 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
561 | * the bar struct at foo->bar is held. |
562 | * | |
563 | * Note that the list of conditions may also include indications of when a lock | |
564 | * need not be held, for example during initialisation or destruction of the | |
565 | * target struct: | |
566 | * | |
ca5ecddf | 567 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 568 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
569 | * |
570 | * Inserts memory barriers on architectures that require them | |
571 | * (currently only the Alpha), prevents the compiler from refetching | |
572 | * (and from merging fetches), and, more importantly, documents exactly | |
573 | * which pointers are protected by RCU and checks that the pointer is | |
574 | * annotated as __rcu. | |
632ee200 PM |
575 | */ |
576 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
577 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
578 | ||
579 | /** | |
580 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
581 | * @p: The pointer to read, prior to dereferencing | |
582 | * @c: The conditions under which the dereference will take place | |
583 | * | |
584 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
585 | */ | |
586 | #define rcu_dereference_bh_check(p, c) \ | |
587 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 588 | |
b62730ba | 589 | /** |
ca5ecddf PM |
590 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
591 | * @p: The pointer to read, prior to dereferencing | |
592 | * @c: The conditions under which the dereference will take place | |
593 | * | |
594 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
595 | */ | |
596 | #define rcu_dereference_sched_check(p, c) \ | |
597 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
598 | __rcu) | |
599 | ||
600 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
601 | ||
a4dd9925 PM |
602 | /** |
603 | * rcu_access_index() - fetch RCU index with no dereferencing | |
604 | * @p: The index to read | |
605 | * | |
606 | * Return the value of the specified RCU-protected index, but omit the | |
607 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
608 | * when the value of this index is accessed, but the index is not | |
609 | * dereferenced, for example, when testing an RCU-protected index against | |
610 | * -1. Although rcu_access_index() may also be used in cases where | |
611 | * update-side locks prevent the value of the index from changing, you | |
612 | * should instead use rcu_dereference_index_protected() for this use case. | |
613 | */ | |
614 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) | |
615 | ||
ca5ecddf PM |
616 | /** |
617 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
618 | * @p: The pointer to read, prior to dereferencing | |
619 | * @c: The conditions under which the dereference will take place | |
620 | * | |
621 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
622 | * This allows rcu_dereference_index_check() to be used on integers, | |
623 | * which can then be used as array indices. Attempting to use | |
624 | * rcu_dereference_check() on an integer will give compiler warnings | |
625 | * because the sparse address-space mechanism relies on dereferencing | |
626 | * the RCU-protected pointer. Dereferencing integers is not something | |
627 | * that even gcc will put up with. | |
628 | * | |
629 | * Note that this function does not implicitly check for RCU read-side | |
630 | * critical sections. If this function gains lots of uses, it might | |
631 | * make sense to provide versions for each flavor of RCU, but it does | |
632 | * not make sense as of early 2010. | |
633 | */ | |
634 | #define rcu_dereference_index_check(p, c) \ | |
635 | __rcu_dereference_index_check((p), (c)) | |
636 | ||
637 | /** | |
638 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
639 | * @p: The pointer to read, prior to dereferencing | |
640 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
641 | * |
642 | * Return the value of the specified RCU-protected pointer, but omit | |
643 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
644 | * is useful in cases where update-side locks prevent the value of the | |
645 | * pointer from changing. Please note that this primitive does -not- | |
646 | * prevent the compiler from repeating this reference or combining it | |
647 | * with other references, so it should not be used without protection | |
648 | * of appropriate locks. | |
ca5ecddf PM |
649 | * |
650 | * This function is only for update-side use. Using this function | |
651 | * when protected only by rcu_read_lock() will result in infrequent | |
652 | * but very ugly failures. | |
b62730ba PM |
653 | */ |
654 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 655 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 656 | |
bc33f24b | 657 | |
b62730ba | 658 | /** |
ca5ecddf PM |
659 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
660 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 661 | * |
ca5ecddf | 662 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 663 | */ |
ca5ecddf | 664 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 665 | |
1da177e4 | 666 | /** |
ca5ecddf PM |
667 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
668 | * @p: The pointer to read, prior to dereferencing | |
669 | * | |
670 | * Makes rcu_dereference_check() do the dirty work. | |
671 | */ | |
672 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
673 | ||
674 | /** | |
675 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
676 | * @p: The pointer to read, prior to dereferencing | |
677 | * | |
678 | * Makes rcu_dereference_check() do the dirty work. | |
679 | */ | |
680 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
681 | ||
682 | /** | |
683 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 684 | * |
9b06e818 | 685 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 686 | * are within RCU read-side critical sections, then the |
9b06e818 | 687 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
688 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
689 | * on one CPU while other CPUs are within RCU read-side critical | |
690 | * sections, invocation of the corresponding RCU callback is deferred | |
691 | * until after the all the other CPUs exit their critical sections. | |
692 | * | |
693 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 694 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
695 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
696 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
697 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
698 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
699 | * callback is invoked. This is legal, because the RCU read-side critical | |
700 | * section that was running concurrently with the call_rcu() (and which | |
701 | * therefore might be referencing something that the corresponding RCU | |
702 | * callback would free up) has completed before the corresponding | |
703 | * RCU callback is invoked. | |
704 | * | |
705 | * RCU read-side critical sections may be nested. Any deferred actions | |
706 | * will be deferred until the outermost RCU read-side critical section | |
707 | * completes. | |
708 | * | |
9079fd7c PM |
709 | * You can avoid reading and understanding the next paragraph by |
710 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
711 | * read-side critical section that would block in a !PREEMPT kernel. | |
712 | * But if you want the full story, read on! | |
713 | * | |
714 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it | |
715 | * is illegal to block while in an RCU read-side critical section. In | |
716 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) | |
717 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may | |
718 | * be preempted, but explicit blocking is illegal. Finally, in preemptible | |
719 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, | |
720 | * RCU read-side critical sections may be preempted and they may also | |
721 | * block, but only when acquiring spinlocks that are subject to priority | |
722 | * inheritance. | |
1da177e4 | 723 | */ |
bc33f24b PM |
724 | static inline void rcu_read_lock(void) |
725 | { | |
726 | __rcu_read_lock(); | |
727 | __acquire(RCU); | |
d8ab29f8 | 728 | rcu_lock_acquire(&rcu_lock_map); |
bde23c68 HC |
729 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
730 | "rcu_read_lock() used illegally while idle"); | |
bc33f24b | 731 | } |
1da177e4 | 732 | |
1da177e4 LT |
733 | /* |
734 | * So where is rcu_write_lock()? It does not exist, as there is no | |
735 | * way for writers to lock out RCU readers. This is a feature, not | |
736 | * a bug -- this property is what provides RCU's performance benefits. | |
737 | * Of course, writers must coordinate with each other. The normal | |
738 | * spinlock primitives work well for this, but any other technique may be | |
739 | * used as well. RCU does not care how the writers keep out of each | |
740 | * others' way, as long as they do so. | |
741 | */ | |
3d76c082 PM |
742 | |
743 | /** | |
ca5ecddf | 744 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
745 | * |
746 | * See rcu_read_lock() for more information. | |
747 | */ | |
bc33f24b PM |
748 | static inline void rcu_read_unlock(void) |
749 | { | |
bde23c68 HC |
750 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
751 | "rcu_read_unlock() used illegally while idle"); | |
d8ab29f8 | 752 | rcu_lock_release(&rcu_lock_map); |
bc33f24b PM |
753 | __release(RCU); |
754 | __rcu_read_unlock(); | |
755 | } | |
1da177e4 LT |
756 | |
757 | /** | |
ca5ecddf | 758 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
759 | * |
760 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
761 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
762 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
763 | * softirq handler to be a quiescent state, a process in RCU read-side | |
764 | * critical section must be protected by disabling softirqs. Read-side | |
765 | * critical sections in interrupt context can use just rcu_read_lock(), | |
766 | * though this should at least be commented to avoid confusing people | |
767 | * reading the code. | |
3842a083 PM |
768 | * |
769 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() | |
770 | * must occur in the same context, for example, it is illegal to invoke | |
771 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() | |
772 | * was invoked from some other task. | |
1da177e4 | 773 | */ |
bc33f24b PM |
774 | static inline void rcu_read_lock_bh(void) |
775 | { | |
6206ab9b | 776 | local_bh_disable(); |
bc33f24b | 777 | __acquire(RCU_BH); |
d8ab29f8 | 778 | rcu_lock_acquire(&rcu_bh_lock_map); |
bde23c68 HC |
779 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
780 | "rcu_read_lock_bh() used illegally while idle"); | |
bc33f24b | 781 | } |
1da177e4 LT |
782 | |
783 | /* | |
784 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
785 | * | |
786 | * See rcu_read_lock_bh() for more information. | |
787 | */ | |
bc33f24b PM |
788 | static inline void rcu_read_unlock_bh(void) |
789 | { | |
bde23c68 HC |
790 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
791 | "rcu_read_unlock_bh() used illegally while idle"); | |
d8ab29f8 | 792 | rcu_lock_release(&rcu_bh_lock_map); |
bc33f24b | 793 | __release(RCU_BH); |
6206ab9b | 794 | local_bh_enable(); |
bc33f24b | 795 | } |
1da177e4 | 796 | |
1c50b728 | 797 | /** |
ca5ecddf | 798 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 799 | * |
ca5ecddf PM |
800 | * This is equivalent of rcu_read_lock(), but to be used when updates |
801 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
802 | * Read-side critical sections can also be introduced by anything that | |
803 | * disables preemption, including local_irq_disable() and friends. | |
3842a083 PM |
804 | * |
805 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() | |
806 | * must occur in the same context, for example, it is illegal to invoke | |
807 | * rcu_read_unlock_sched() from process context if the matching | |
808 | * rcu_read_lock_sched() was invoked from an NMI handler. | |
1c50b728 | 809 | */ |
d6714c22 PM |
810 | static inline void rcu_read_lock_sched(void) |
811 | { | |
812 | preempt_disable(); | |
bc33f24b | 813 | __acquire(RCU_SCHED); |
d8ab29f8 | 814 | rcu_lock_acquire(&rcu_sched_lock_map); |
bde23c68 HC |
815 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
816 | "rcu_read_lock_sched() used illegally while idle"); | |
d6714c22 | 817 | } |
1eba8f84 PM |
818 | |
819 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 820 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
821 | { |
822 | preempt_disable_notrace(); | |
bc33f24b | 823 | __acquire(RCU_SCHED); |
d6714c22 | 824 | } |
1c50b728 MD |
825 | |
826 | /* | |
827 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
828 | * | |
829 | * See rcu_read_lock_sched for more information. | |
830 | */ | |
d6714c22 PM |
831 | static inline void rcu_read_unlock_sched(void) |
832 | { | |
bde23c68 HC |
833 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
834 | "rcu_read_unlock_sched() used illegally while idle"); | |
d8ab29f8 | 835 | rcu_lock_release(&rcu_sched_lock_map); |
bc33f24b | 836 | __release(RCU_SCHED); |
d6714c22 PM |
837 | preempt_enable(); |
838 | } | |
1eba8f84 PM |
839 | |
840 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 841 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 842 | { |
bc33f24b | 843 | __release(RCU_SCHED); |
d6714c22 PM |
844 | preempt_enable_notrace(); |
845 | } | |
1c50b728 | 846 | |
1da177e4 | 847 | /** |
ca5ecddf PM |
848 | * rcu_assign_pointer() - assign to RCU-protected pointer |
849 | * @p: pointer to assign to | |
850 | * @v: value to assign (publish) | |
c26d34a5 | 851 | * |
ca5ecddf PM |
852 | * Assigns the specified value to the specified RCU-protected |
853 | * pointer, ensuring that any concurrent RCU readers will see | |
e9023c40 | 854 | * any prior initialization. |
1da177e4 LT |
855 | * |
856 | * Inserts memory barriers on architectures that require them | |
6846c0c5 PM |
857 | * (which is most of them), and also prevents the compiler from |
858 | * reordering the code that initializes the structure after the pointer | |
859 | * assignment. More importantly, this call documents which pointers | |
860 | * will be dereferenced by RCU read-side code. | |
861 | * | |
862 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
863 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
864 | * to the fact that it does not constrain either the CPU or the compiler. | |
865 | * That said, using RCU_INIT_POINTER() when you should have used | |
866 | * rcu_assign_pointer() is a very bad thing that results in | |
867 | * impossible-to-diagnose memory corruption. So please be careful. | |
868 | * See the RCU_INIT_POINTER() comment header for details. | |
1da177e4 | 869 | */ |
d99c4f6b | 870 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
871 | __rcu_assign_pointer((p), (v), __rcu) |
872 | ||
873 | /** | |
874 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
875 | * | |
6846c0c5 PM |
876 | * Initialize an RCU-protected pointer in special cases where readers |
877 | * do not need ordering constraints on the CPU or the compiler. These | |
878 | * special cases are: | |
879 | * | |
880 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- | |
881 | * 2. The caller has taken whatever steps are required to prevent | |
882 | * RCU readers from concurrently accessing this pointer -or- | |
883 | * 3. The referenced data structure has already been exposed to | |
884 | * readers either at compile time or via rcu_assign_pointer() -and- | |
885 | * a. You have not made -any- reader-visible changes to | |
886 | * this structure since then -or- | |
887 | * b. It is OK for readers accessing this structure from its | |
888 | * new location to see the old state of the structure. (For | |
889 | * example, the changes were to statistical counters or to | |
890 | * other state where exact synchronization is not required.) | |
891 | * | |
892 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
893 | * result in impossible-to-diagnose memory corruption. As in the structures | |
894 | * will look OK in crash dumps, but any concurrent RCU readers might | |
895 | * see pre-initialized values of the referenced data structure. So | |
896 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
897 | * | |
898 | * If you are creating an RCU-protected linked structure that is accessed | |
899 | * by a single external-to-structure RCU-protected pointer, then you may | |
900 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
901 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
902 | * external-to-structure pointer -after- you have completely initialized | |
903 | * the reader-accessible portions of the linked structure. | |
ca5ecddf PM |
904 | */ |
905 | #define RCU_INIT_POINTER(p, v) \ | |
d1b88eb9 PM |
906 | do { \ |
907 | p = (typeof(*v) __force __rcu *)(v); \ | |
908 | } while (0) | |
1da177e4 | 909 | |
172708d0 PM |
910 | /** |
911 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer | |
912 | * | |
913 | * GCC-style initialization for an RCU-protected pointer in a structure field. | |
914 | */ | |
915 | #define RCU_POINTER_INITIALIZER(p, v) \ | |
916 | .p = (typeof(*v) __force __rcu *)(v) | |
917 | ||
9ab1544e LJ |
918 | static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) |
919 | { | |
920 | return offset < 4096; | |
921 | } | |
922 | ||
923 | static __always_inline | |
924 | void __kfree_rcu(struct rcu_head *head, unsigned long offset) | |
925 | { | |
926 | typedef void (*rcu_callback)(struct rcu_head *); | |
927 | ||
928 | BUILD_BUG_ON(!__builtin_constant_p(offset)); | |
929 | ||
930 | /* See the kfree_rcu() header comment. */ | |
931 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); | |
932 | ||
486e2593 | 933 | kfree_call_rcu(head, (rcu_callback)offset); |
9ab1544e LJ |
934 | } |
935 | ||
d8169d4c JE |
936 | /* |
937 | * Does the specified offset indicate that the corresponding rcu_head | |
938 | * structure can be handled by kfree_rcu()? | |
939 | */ | |
940 | #define __is_kfree_rcu_offset(offset) ((offset) < 4096) | |
941 | ||
942 | /* | |
943 | * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. | |
944 | */ | |
945 | #define __kfree_rcu(head, offset) \ | |
946 | do { \ | |
947 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ | |
948 | call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ | |
949 | } while (0) | |
950 | ||
9ab1544e LJ |
951 | /** |
952 | * kfree_rcu() - kfree an object after a grace period. | |
953 | * @ptr: pointer to kfree | |
954 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. | |
955 | * | |
956 | * Many rcu callbacks functions just call kfree() on the base structure. | |
957 | * These functions are trivial, but their size adds up, and furthermore | |
958 | * when they are used in a kernel module, that module must invoke the | |
959 | * high-latency rcu_barrier() function at module-unload time. | |
960 | * | |
961 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
962 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
963 | * encodes the offset of the rcu_head structure within the base structure. | |
964 | * Because the functions are not allowed in the low-order 4096 bytes of | |
965 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
966 | * If the offset is larger than 4095 bytes, a compile-time error will | |
967 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
968 | * either fall back to use of call_rcu() or rearrange the structure to | |
969 | * position the rcu_head structure into the first 4096 bytes. | |
970 | * | |
971 | * Note that the allowable offset might decrease in the future, for example, | |
972 | * to allow something like kmem_cache_free_rcu(). | |
d8169d4c JE |
973 | * |
974 | * The BUILD_BUG_ON check must not involve any function calls, hence the | |
975 | * checks are done in macros here. | |
9ab1544e LJ |
976 | */ |
977 | #define kfree_rcu(ptr, rcu_head) \ | |
978 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) | |
979 | ||
1da177e4 | 980 | #endif /* __LINUX_RCUPDATE_H */ |