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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); | |
2a3fa843 | 150 | extern void rcu_read_unlock_special(struct task_struct *t); |
7b0b759b PM |
151 | void synchronize_rcu(void); |
152 | ||
a3dc3fb1 PM |
153 | /* |
154 | * Defined as a macro as it is a very low level header included from | |
155 | * areas that don't even know about current. This gives the rcu_read_lock() | |
156 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
157 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
158 | */ | |
159 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
160 | ||
7b0b759b PM |
161 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
162 | ||
163 | static inline void __rcu_read_lock(void) | |
164 | { | |
165 | preempt_disable(); | |
166 | } | |
167 | ||
168 | static inline void __rcu_read_unlock(void) | |
169 | { | |
170 | preempt_enable(); | |
171 | } | |
172 | ||
173 | static inline void synchronize_rcu(void) | |
174 | { | |
175 | synchronize_sched(); | |
176 | } | |
177 | ||
178 | static inline int rcu_preempt_depth(void) | |
179 | { | |
180 | return 0; | |
181 | } | |
182 | ||
183 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
184 | ||
185 | /* Internal to kernel */ | |
7b0b759b PM |
186 | extern void rcu_sched_qs(int cpu); |
187 | extern void rcu_bh_qs(int cpu); | |
188 | extern void rcu_check_callbacks(int cpu, int user); | |
189 | struct notifier_block; | |
9b2e4f18 PM |
190 | extern void rcu_idle_enter(void); |
191 | extern void rcu_idle_exit(void); | |
192 | extern void rcu_irq_enter(void); | |
193 | extern void rcu_irq_exit(void); | |
9dd8fb16 | 194 | extern void exit_rcu(void); |
a3dc3fb1 | 195 | |
8a2ecf47 PM |
196 | /** |
197 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers | |
198 | * @a: Code that RCU needs to pay attention to. | |
199 | * | |
200 | * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden | |
201 | * in the inner idle loop, that is, between the rcu_idle_enter() and | |
202 | * the rcu_idle_exit() -- RCU will happily ignore any such read-side | |
203 | * critical sections. However, things like powertop need tracepoints | |
204 | * in the inner idle loop. | |
205 | * | |
206 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) | |
207 | * will tell RCU that it needs to pay attending, invoke its argument | |
208 | * (in this example, a call to the do_something_with_RCU() function), | |
209 | * and then tell RCU to go back to ignoring this CPU. It is permissible | |
210 | * to nest RCU_NONIDLE() wrappers, but the nesting level is currently | |
211 | * quite limited. If deeper nesting is required, it will be necessary | |
212 | * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. | |
213 | * | |
214 | * This macro may be used from process-level code only. | |
215 | */ | |
216 | #define RCU_NONIDLE(a) \ | |
217 | do { \ | |
218 | rcu_idle_exit(); \ | |
219 | do { a; } while (0); \ | |
220 | rcu_idle_enter(); \ | |
221 | } while (0) | |
222 | ||
2c42818e PM |
223 | /* |
224 | * Infrastructure to implement the synchronize_() primitives in | |
225 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
226 | */ | |
227 | ||
228 | typedef void call_rcu_func_t(struct rcu_head *head, | |
229 | void (*func)(struct rcu_head *head)); | |
230 | void wait_rcu_gp(call_rcu_func_t crf); | |
231 | ||
f41d911f | 232 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
64db4cff | 233 | #include <linux/rcutree.h> |
a57eb940 | 234 | #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) |
9b1d82fa | 235 | #include <linux/rcutiny.h> |
64db4cff PM |
236 | #else |
237 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 238 | #endif |
01c1c660 | 239 | |
551d55a9 MD |
240 | /* |
241 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
242 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
243 | * allocated dynamically in the heap or defined statically don't need any | |
244 | * initialization. | |
245 | */ | |
246 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
247 | extern void init_rcu_head_on_stack(struct rcu_head *head); | |
248 | extern void destroy_rcu_head_on_stack(struct rcu_head *head); | |
249 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ | |
4376030a MD |
250 | static inline void init_rcu_head_on_stack(struct rcu_head *head) |
251 | { | |
252 | } | |
253 | ||
254 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) | |
255 | { | |
256 | } | |
551d55a9 | 257 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 258 | |
62fde6ed PM |
259 | #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) |
260 | extern int rcu_is_cpu_idle(void); | |
261 | #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */ | |
262 | ||
c0d6d01b PM |
263 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
264 | bool rcu_lockdep_current_cpu_online(void); | |
265 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
266 | static inline bool rcu_lockdep_current_cpu_online(void) | |
267 | { | |
268 | return 1; | |
269 | } | |
270 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
271 | ||
bc33f24b | 272 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 273 | |
00f49e57 FW |
274 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
275 | { | |
00f49e57 FW |
276 | lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); |
277 | } | |
278 | ||
279 | static inline void rcu_lock_release(struct lockdep_map *map) | |
280 | { | |
00f49e57 FW |
281 | lock_release(map, 1, _THIS_IP_); |
282 | } | |
283 | ||
bc33f24b | 284 | extern struct lockdep_map rcu_lock_map; |
632ee200 | 285 | extern struct lockdep_map rcu_bh_lock_map; |
632ee200 | 286 | extern struct lockdep_map rcu_sched_lock_map; |
bc293d62 | 287 | extern int debug_lockdep_rcu_enabled(void); |
54dbf96c | 288 | |
632ee200 | 289 | /** |
ca5ecddf | 290 | * rcu_read_lock_held() - might we be in RCU read-side critical section? |
632ee200 | 291 | * |
d20200b5 PM |
292 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU |
293 | * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, | |
632ee200 | 294 | * this assumes we are in an RCU read-side critical section unless it can |
ca5ecddf PM |
295 | * prove otherwise. This is useful for debug checks in functions that |
296 | * require that they be called within an RCU read-side critical section. | |
54dbf96c | 297 | * |
ca5ecddf | 298 | * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot |
32c141a0 | 299 | * and while lockdep is disabled. |
3842a083 PM |
300 | * |
301 | * Note that rcu_read_lock() and the matching rcu_read_unlock() must | |
302 | * occur in the same context, for example, it is illegal to invoke | |
303 | * rcu_read_unlock() in process context if the matching rcu_read_lock() | |
304 | * was invoked from within an irq handler. | |
c0d6d01b PM |
305 | * |
306 | * Note that rcu_read_lock() is disallowed if the CPU is either idle or | |
307 | * offline from an RCU perspective, so check for those as well. | |
632ee200 PM |
308 | */ |
309 | static inline int rcu_read_lock_held(void) | |
310 | { | |
54dbf96c PM |
311 | if (!debug_lockdep_rcu_enabled()) |
312 | return 1; | |
e6b80a3b FW |
313 | if (rcu_is_cpu_idle()) |
314 | return 0; | |
c0d6d01b PM |
315 | if (!rcu_lockdep_current_cpu_online()) |
316 | return 0; | |
54dbf96c | 317 | return lock_is_held(&rcu_lock_map); |
632ee200 PM |
318 | } |
319 | ||
e3818b8d PM |
320 | /* |
321 | * rcu_read_lock_bh_held() is defined out of line to avoid #include-file | |
322 | * hell. | |
632ee200 | 323 | */ |
e3818b8d | 324 | extern int rcu_read_lock_bh_held(void); |
632ee200 PM |
325 | |
326 | /** | |
ca5ecddf | 327 | * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? |
632ee200 | 328 | * |
d20200b5 PM |
329 | * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an |
330 | * RCU-sched read-side critical section. In absence of | |
331 | * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side | |
332 | * critical section unless it can prove otherwise. Note that disabling | |
333 | * of preemption (including disabling irqs) counts as an RCU-sched | |
ca5ecddf PM |
334 | * read-side critical section. This is useful for debug checks in functions |
335 | * that required that they be called within an RCU-sched read-side | |
336 | * critical section. | |
54dbf96c | 337 | * |
32c141a0 PM |
338 | * Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
339 | * and while lockdep is disabled. | |
e6b80a3b FW |
340 | * |
341 | * Note that if the CPU is in the idle loop from an RCU point of | |
342 | * view (ie: that we are in the section between rcu_idle_enter() and | |
343 | * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU | |
344 | * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs | |
345 | * that are in such a section, considering these as in extended quiescent | |
346 | * state, so such a CPU is effectively never in an RCU read-side critical | |
347 | * section regardless of what RCU primitives it invokes. This state of | |
348 | * affairs is required --- we need to keep an RCU-free window in idle | |
349 | * where the CPU may possibly enter into low power mode. This way we can | |
350 | * notice an extended quiescent state to other CPUs that started a grace | |
351 | * period. Otherwise we would delay any grace period as long as we run in | |
352 | * the idle task. | |
c0d6d01b PM |
353 | * |
354 | * Similarly, we avoid claiming an SRCU read lock held if the current | |
355 | * CPU is offline. | |
632ee200 | 356 | */ |
bdd4e85d | 357 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
358 | static inline int rcu_read_lock_sched_held(void) |
359 | { | |
360 | int lockdep_opinion = 0; | |
361 | ||
54dbf96c PM |
362 | if (!debug_lockdep_rcu_enabled()) |
363 | return 1; | |
e6b80a3b FW |
364 | if (rcu_is_cpu_idle()) |
365 | return 0; | |
c0d6d01b PM |
366 | if (!rcu_lockdep_current_cpu_online()) |
367 | return 0; | |
632ee200 PM |
368 | if (debug_locks) |
369 | lockdep_opinion = lock_is_held(&rcu_sched_lock_map); | |
0cff810f | 370 | return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); |
632ee200 | 371 | } |
bdd4e85d | 372 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
373 | static inline int rcu_read_lock_sched_held(void) |
374 | { | |
375 | return 1; | |
632ee200 | 376 | } |
bdd4e85d | 377 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
378 | |
379 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
380 | ||
d8ab29f8 PM |
381 | # define rcu_lock_acquire(a) do { } while (0) |
382 | # define rcu_lock_release(a) do { } while (0) | |
632ee200 PM |
383 | |
384 | static inline int rcu_read_lock_held(void) | |
385 | { | |
386 | return 1; | |
387 | } | |
388 | ||
389 | static inline int rcu_read_lock_bh_held(void) | |
390 | { | |
391 | return 1; | |
392 | } | |
393 | ||
bdd4e85d | 394 | #ifdef CONFIG_PREEMPT_COUNT |
632ee200 PM |
395 | static inline int rcu_read_lock_sched_held(void) |
396 | { | |
bbad9379 | 397 | return preempt_count() != 0 || irqs_disabled(); |
632ee200 | 398 | } |
bdd4e85d | 399 | #else /* #ifdef CONFIG_PREEMPT_COUNT */ |
e6033e3b PM |
400 | static inline int rcu_read_lock_sched_held(void) |
401 | { | |
402 | return 1; | |
632ee200 | 403 | } |
bdd4e85d | 404 | #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ |
632ee200 PM |
405 | |
406 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
407 | ||
408 | #ifdef CONFIG_PROVE_RCU | |
409 | ||
ee84b824 PM |
410 | extern int rcu_my_thread_group_empty(void); |
411 | ||
4221a991 TH |
412 | /** |
413 | * rcu_lockdep_assert - emit lockdep splat if specified condition not met | |
414 | * @c: condition to check | |
b3fbab05 | 415 | * @s: informative message |
4221a991 | 416 | */ |
b3fbab05 | 417 | #define rcu_lockdep_assert(c, s) \ |
2b3fc35f | 418 | do { \ |
7ccaba53 | 419 | static bool __section(.data.unlikely) __warned; \ |
2b3fc35f LJ |
420 | if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ |
421 | __warned = true; \ | |
b3fbab05 | 422 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ |
2b3fc35f LJ |
423 | } \ |
424 | } while (0) | |
425 | ||
50406b98 PM |
426 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
427 | static inline void rcu_preempt_sleep_check(void) | |
428 | { | |
429 | rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), | |
430 | "Illegal context switch in RCU read-side " | |
431 | "critical section"); | |
432 | } | |
433 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
434 | static inline void rcu_preempt_sleep_check(void) | |
435 | { | |
436 | } | |
437 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
438 | ||
b3fbab05 PM |
439 | #define rcu_sleep_check() \ |
440 | do { \ | |
50406b98 | 441 | rcu_preempt_sleep_check(); \ |
b3fbab05 PM |
442 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ |
443 | "Illegal context switch in RCU-bh" \ | |
444 | " read-side critical section"); \ | |
445 | rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ | |
446 | "Illegal context switch in RCU-sched"\ | |
447 | " read-side critical section"); \ | |
448 | } while (0) | |
449 | ||
ca5ecddf PM |
450 | #else /* #ifdef CONFIG_PROVE_RCU */ |
451 | ||
b3fbab05 PM |
452 | #define rcu_lockdep_assert(c, s) do { } while (0) |
453 | #define rcu_sleep_check() do { } while (0) | |
ca5ecddf PM |
454 | |
455 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
456 | ||
457 | /* | |
458 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
459 | * and rcu_assign_pointer(). Some of these could be folded into their | |
460 | * callers, but they are left separate in order to ease introduction of | |
461 | * multiple flavors of pointers to match the multiple flavors of RCU | |
462 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
463 | * the future. | |
464 | */ | |
53ecfba2 PM |
465 | |
466 | #ifdef __CHECKER__ | |
467 | #define rcu_dereference_sparse(p, space) \ | |
468 | ((void)(((typeof(*p) space *)p) == p)) | |
469 | #else /* #ifdef __CHECKER__ */ | |
470 | #define rcu_dereference_sparse(p, space) | |
471 | #endif /* #else #ifdef __CHECKER__ */ | |
472 | ||
ca5ecddf PM |
473 | #define __rcu_access_pointer(p, space) \ |
474 | ({ \ | |
475 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
53ecfba2 | 476 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
477 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
478 | }) | |
479 | #define __rcu_dereference_check(p, c, space) \ | |
480 | ({ \ | |
481 | typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ | |
b3fbab05 PM |
482 | rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ |
483 | " usage"); \ | |
53ecfba2 | 484 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
485 | smp_read_barrier_depends(); \ |
486 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
487 | }) | |
488 | #define __rcu_dereference_protected(p, c, space) \ | |
489 | ({ \ | |
b3fbab05 PM |
490 | rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ |
491 | " usage"); \ | |
53ecfba2 | 492 | rcu_dereference_sparse(p, space); \ |
ca5ecddf PM |
493 | ((typeof(*p) __force __kernel *)(p)); \ |
494 | }) | |
495 | ||
a4dd9925 PM |
496 | #define __rcu_access_index(p, space) \ |
497 | ({ \ | |
498 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
499 | rcu_dereference_sparse(p, space); \ | |
500 | (_________p1); \ | |
501 | }) | |
ca5ecddf PM |
502 | #define __rcu_dereference_index_check(p, c) \ |
503 | ({ \ | |
504 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
b3fbab05 PM |
505 | rcu_lockdep_assert(c, \ |
506 | "suspicious rcu_dereference_index_check()" \ | |
507 | " usage"); \ | |
ca5ecddf PM |
508 | smp_read_barrier_depends(); \ |
509 | (_________p1); \ | |
510 | }) | |
511 | #define __rcu_assign_pointer(p, v, space) \ | |
e9023c40 | 512 | do { \ |
d322f45c | 513 | smp_wmb(); \ |
ca5ecddf | 514 | (p) = (typeof(*v) __force space *)(v); \ |
e9023c40 | 515 | } while (0) |
ca5ecddf PM |
516 | |
517 | ||
518 | /** | |
519 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
520 | * @p: The pointer to read | |
521 | * | |
522 | * Return the value of the specified RCU-protected pointer, but omit the | |
523 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
524 | * when the value of this pointer is accessed, but the pointer is not | |
525 | * dereferenced, for example, when testing an RCU-protected pointer against | |
526 | * NULL. Although rcu_access_pointer() may also be used in cases where | |
527 | * update-side locks prevent the value of the pointer from changing, you | |
528 | * should instead use rcu_dereference_protected() for this use case. | |
5e1ee6e1 PM |
529 | * |
530 | * It is also permissible to use rcu_access_pointer() when read-side | |
531 | * access to the pointer was removed at least one grace period ago, as | |
532 | * is the case in the context of the RCU callback that is freeing up | |
533 | * the data, or after a synchronize_rcu() returns. This can be useful | |
534 | * when tearing down multi-linked structures after a grace period | |
535 | * has elapsed. | |
ca5ecddf PM |
536 | */ |
537 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
538 | ||
632ee200 | 539 | /** |
ca5ecddf | 540 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
541 | * @p: The pointer to read, prior to dereferencing |
542 | * @c: The conditions under which the dereference will take place | |
632ee200 | 543 | * |
c08c68dd | 544 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
545 | * dereference will take place are correct. Typically the conditions |
546 | * indicate the various locking conditions that should be held at that | |
547 | * point. The check should return true if the conditions are satisfied. | |
548 | * An implicit check for being in an RCU read-side critical section | |
549 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
550 | * |
551 | * For example: | |
552 | * | |
ca5ecddf | 553 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
554 | * |
555 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 556 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
557 | * the bar struct at foo->bar is held. |
558 | * | |
559 | * Note that the list of conditions may also include indications of when a lock | |
560 | * need not be held, for example during initialisation or destruction of the | |
561 | * target struct: | |
562 | * | |
ca5ecddf | 563 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 564 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
565 | * |
566 | * Inserts memory barriers on architectures that require them | |
567 | * (currently only the Alpha), prevents the compiler from refetching | |
568 | * (and from merging fetches), and, more importantly, documents exactly | |
569 | * which pointers are protected by RCU and checks that the pointer is | |
570 | * annotated as __rcu. | |
632ee200 PM |
571 | */ |
572 | #define rcu_dereference_check(p, c) \ | |
ca5ecddf PM |
573 | __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) |
574 | ||
575 | /** | |
576 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
577 | * @p: The pointer to read, prior to dereferencing | |
578 | * @c: The conditions under which the dereference will take place | |
579 | * | |
580 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
581 | */ | |
582 | #define rcu_dereference_bh_check(p, c) \ | |
583 | __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) | |
632ee200 | 584 | |
b62730ba | 585 | /** |
ca5ecddf PM |
586 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
587 | * @p: The pointer to read, prior to dereferencing | |
588 | * @c: The conditions under which the dereference will take place | |
589 | * | |
590 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
591 | */ | |
592 | #define rcu_dereference_sched_check(p, c) \ | |
593 | __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ | |
594 | __rcu) | |
595 | ||
596 | #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ | |
597 | ||
a4dd9925 PM |
598 | /** |
599 | * rcu_access_index() - fetch RCU index with no dereferencing | |
600 | * @p: The index to read | |
601 | * | |
602 | * Return the value of the specified RCU-protected index, but omit the | |
603 | * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful | |
604 | * when the value of this index is accessed, but the index is not | |
605 | * dereferenced, for example, when testing an RCU-protected index against | |
606 | * -1. Although rcu_access_index() may also be used in cases where | |
607 | * update-side locks prevent the value of the index from changing, you | |
608 | * should instead use rcu_dereference_index_protected() for this use case. | |
609 | */ | |
610 | #define rcu_access_index(p) __rcu_access_index((p), __rcu) | |
611 | ||
ca5ecddf PM |
612 | /** |
613 | * rcu_dereference_index_check() - rcu_dereference for indices with debug checking | |
614 | * @p: The pointer to read, prior to dereferencing | |
615 | * @c: The conditions under which the dereference will take place | |
616 | * | |
617 | * Similar to rcu_dereference_check(), but omits the sparse checking. | |
618 | * This allows rcu_dereference_index_check() to be used on integers, | |
619 | * which can then be used as array indices. Attempting to use | |
620 | * rcu_dereference_check() on an integer will give compiler warnings | |
621 | * because the sparse address-space mechanism relies on dereferencing | |
622 | * the RCU-protected pointer. Dereferencing integers is not something | |
623 | * that even gcc will put up with. | |
624 | * | |
625 | * Note that this function does not implicitly check for RCU read-side | |
626 | * critical sections. If this function gains lots of uses, it might | |
627 | * make sense to provide versions for each flavor of RCU, but it does | |
628 | * not make sense as of early 2010. | |
629 | */ | |
630 | #define rcu_dereference_index_check(p, c) \ | |
631 | __rcu_dereference_index_check((p), (c)) | |
632 | ||
633 | /** | |
634 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
635 | * @p: The pointer to read, prior to dereferencing | |
636 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
637 | * |
638 | * Return the value of the specified RCU-protected pointer, but omit | |
639 | * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This | |
640 | * is useful in cases where update-side locks prevent the value of the | |
641 | * pointer from changing. Please note that this primitive does -not- | |
642 | * prevent the compiler from repeating this reference or combining it | |
643 | * with other references, so it should not be used without protection | |
644 | * of appropriate locks. | |
ca5ecddf PM |
645 | * |
646 | * This function is only for update-side use. Using this function | |
647 | * when protected only by rcu_read_lock() will result in infrequent | |
648 | * but very ugly failures. | |
b62730ba PM |
649 | */ |
650 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 651 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 652 | |
bc33f24b | 653 | |
b62730ba | 654 | /** |
ca5ecddf PM |
655 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
656 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 657 | * |
ca5ecddf | 658 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 659 | */ |
ca5ecddf | 660 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 661 | |
1da177e4 | 662 | /** |
ca5ecddf PM |
663 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
664 | * @p: The pointer to read, prior to dereferencing | |
665 | * | |
666 | * Makes rcu_dereference_check() do the dirty work. | |
667 | */ | |
668 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
669 | ||
670 | /** | |
671 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
672 | * @p: The pointer to read, prior to dereferencing | |
673 | * | |
674 | * Makes rcu_dereference_check() do the dirty work. | |
675 | */ | |
676 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
677 | ||
678 | /** | |
679 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 680 | * |
9b06e818 | 681 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 682 | * are within RCU read-side critical sections, then the |
9b06e818 | 683 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
684 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
685 | * on one CPU while other CPUs are within RCU read-side critical | |
686 | * sections, invocation of the corresponding RCU callback is deferred | |
687 | * until after the all the other CPUs exit their critical sections. | |
688 | * | |
689 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 690 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
691 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
692 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
693 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
694 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
695 | * callback is invoked. This is legal, because the RCU read-side critical | |
696 | * section that was running concurrently with the call_rcu() (and which | |
697 | * therefore might be referencing something that the corresponding RCU | |
698 | * callback would free up) has completed before the corresponding | |
699 | * RCU callback is invoked. | |
700 | * | |
701 | * RCU read-side critical sections may be nested. Any deferred actions | |
702 | * will be deferred until the outermost RCU read-side critical section | |
703 | * completes. | |
704 | * | |
9079fd7c PM |
705 | * You can avoid reading and understanding the next paragraph by |
706 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
707 | * read-side critical section that would block in a !PREEMPT kernel. | |
708 | * But if you want the full story, read on! | |
709 | * | |
710 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it | |
711 | * is illegal to block while in an RCU read-side critical section. In | |
712 | * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) | |
713 | * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may | |
714 | * be preempted, but explicit blocking is illegal. Finally, in preemptible | |
715 | * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, | |
716 | * RCU read-side critical sections may be preempted and they may also | |
717 | * block, but only when acquiring spinlocks that are subject to priority | |
718 | * inheritance. | |
1da177e4 | 719 | */ |
bc33f24b PM |
720 | static inline void rcu_read_lock(void) |
721 | { | |
722 | __rcu_read_lock(); | |
723 | __acquire(RCU); | |
d8ab29f8 | 724 | rcu_lock_acquire(&rcu_lock_map); |
bde23c68 HC |
725 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
726 | "rcu_read_lock() used illegally while idle"); | |
bc33f24b | 727 | } |
1da177e4 | 728 | |
1da177e4 LT |
729 | /* |
730 | * So where is rcu_write_lock()? It does not exist, as there is no | |
731 | * way for writers to lock out RCU readers. This is a feature, not | |
732 | * a bug -- this property is what provides RCU's performance benefits. | |
733 | * Of course, writers must coordinate with each other. The normal | |
734 | * spinlock primitives work well for this, but any other technique may be | |
735 | * used as well. RCU does not care how the writers keep out of each | |
736 | * others' way, as long as they do so. | |
737 | */ | |
3d76c082 PM |
738 | |
739 | /** | |
ca5ecddf | 740 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 PM |
741 | * |
742 | * See rcu_read_lock() for more information. | |
743 | */ | |
bc33f24b PM |
744 | static inline void rcu_read_unlock(void) |
745 | { | |
bde23c68 HC |
746 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
747 | "rcu_read_unlock() used illegally while idle"); | |
d8ab29f8 | 748 | rcu_lock_release(&rcu_lock_map); |
bc33f24b PM |
749 | __release(RCU); |
750 | __rcu_read_unlock(); | |
751 | } | |
1da177e4 LT |
752 | |
753 | /** | |
ca5ecddf | 754 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
755 | * |
756 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
757 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
758 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
759 | * softirq handler to be a quiescent state, a process in RCU read-side | |
760 | * critical section must be protected by disabling softirqs. Read-side | |
761 | * critical sections in interrupt context can use just rcu_read_lock(), | |
762 | * though this should at least be commented to avoid confusing people | |
763 | * reading the code. | |
3842a083 PM |
764 | * |
765 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() | |
766 | * must occur in the same context, for example, it is illegal to invoke | |
767 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() | |
768 | * was invoked from some other task. | |
1da177e4 | 769 | */ |
bc33f24b PM |
770 | static inline void rcu_read_lock_bh(void) |
771 | { | |
6206ab9b | 772 | local_bh_disable(); |
bc33f24b | 773 | __acquire(RCU_BH); |
d8ab29f8 | 774 | rcu_lock_acquire(&rcu_bh_lock_map); |
bde23c68 HC |
775 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
776 | "rcu_read_lock_bh() used illegally while idle"); | |
bc33f24b | 777 | } |
1da177e4 LT |
778 | |
779 | /* | |
780 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
781 | * | |
782 | * See rcu_read_lock_bh() for more information. | |
783 | */ | |
bc33f24b PM |
784 | static inline void rcu_read_unlock_bh(void) |
785 | { | |
bde23c68 HC |
786 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
787 | "rcu_read_unlock_bh() used illegally while idle"); | |
d8ab29f8 | 788 | rcu_lock_release(&rcu_bh_lock_map); |
bc33f24b | 789 | __release(RCU_BH); |
6206ab9b | 790 | local_bh_enable(); |
bc33f24b | 791 | } |
1da177e4 | 792 | |
1c50b728 | 793 | /** |
ca5ecddf | 794 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 795 | * |
ca5ecddf PM |
796 | * This is equivalent of rcu_read_lock(), but to be used when updates |
797 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
798 | * Read-side critical sections can also be introduced by anything that | |
799 | * disables preemption, including local_irq_disable() and friends. | |
3842a083 PM |
800 | * |
801 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() | |
802 | * must occur in the same context, for example, it is illegal to invoke | |
803 | * rcu_read_unlock_sched() from process context if the matching | |
804 | * rcu_read_lock_sched() was invoked from an NMI handler. | |
1c50b728 | 805 | */ |
d6714c22 PM |
806 | static inline void rcu_read_lock_sched(void) |
807 | { | |
808 | preempt_disable(); | |
bc33f24b | 809 | __acquire(RCU_SCHED); |
d8ab29f8 | 810 | rcu_lock_acquire(&rcu_sched_lock_map); |
bde23c68 HC |
811 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
812 | "rcu_read_lock_sched() used illegally while idle"); | |
d6714c22 | 813 | } |
1eba8f84 PM |
814 | |
815 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 816 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
817 | { |
818 | preempt_disable_notrace(); | |
bc33f24b | 819 | __acquire(RCU_SCHED); |
d6714c22 | 820 | } |
1c50b728 MD |
821 | |
822 | /* | |
823 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
824 | * | |
825 | * See rcu_read_lock_sched for more information. | |
826 | */ | |
d6714c22 PM |
827 | static inline void rcu_read_unlock_sched(void) |
828 | { | |
bde23c68 HC |
829 | rcu_lockdep_assert(!rcu_is_cpu_idle(), |
830 | "rcu_read_unlock_sched() used illegally while idle"); | |
d8ab29f8 | 831 | rcu_lock_release(&rcu_sched_lock_map); |
bc33f24b | 832 | __release(RCU_SCHED); |
d6714c22 PM |
833 | preempt_enable(); |
834 | } | |
1eba8f84 PM |
835 | |
836 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 837 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 838 | { |
bc33f24b | 839 | __release(RCU_SCHED); |
d6714c22 PM |
840 | preempt_enable_notrace(); |
841 | } | |
1c50b728 | 842 | |
1da177e4 | 843 | /** |
ca5ecddf PM |
844 | * rcu_assign_pointer() - assign to RCU-protected pointer |
845 | * @p: pointer to assign to | |
846 | * @v: value to assign (publish) | |
c26d34a5 | 847 | * |
ca5ecddf PM |
848 | * Assigns the specified value to the specified RCU-protected |
849 | * pointer, ensuring that any concurrent RCU readers will see | |
e9023c40 | 850 | * any prior initialization. |
1da177e4 LT |
851 | * |
852 | * Inserts memory barriers on architectures that require them | |
6846c0c5 PM |
853 | * (which is most of them), and also prevents the compiler from |
854 | * reordering the code that initializes the structure after the pointer | |
855 | * assignment. More importantly, this call documents which pointers | |
856 | * will be dereferenced by RCU read-side code. | |
857 | * | |
858 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
859 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
860 | * to the fact that it does not constrain either the CPU or the compiler. | |
861 | * That said, using RCU_INIT_POINTER() when you should have used | |
862 | * rcu_assign_pointer() is a very bad thing that results in | |
863 | * impossible-to-diagnose memory corruption. So please be careful. | |
864 | * See the RCU_INIT_POINTER() comment header for details. | |
1da177e4 | 865 | */ |
d99c4f6b | 866 | #define rcu_assign_pointer(p, v) \ |
ca5ecddf PM |
867 | __rcu_assign_pointer((p), (v), __rcu) |
868 | ||
869 | /** | |
870 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
871 | * | |
6846c0c5 PM |
872 | * Initialize an RCU-protected pointer in special cases where readers |
873 | * do not need ordering constraints on the CPU or the compiler. These | |
874 | * special cases are: | |
875 | * | |
876 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- | |
877 | * 2. The caller has taken whatever steps are required to prevent | |
878 | * RCU readers from concurrently accessing this pointer -or- | |
879 | * 3. The referenced data structure has already been exposed to | |
880 | * readers either at compile time or via rcu_assign_pointer() -and- | |
881 | * a. You have not made -any- reader-visible changes to | |
882 | * this structure since then -or- | |
883 | * b. It is OK for readers accessing this structure from its | |
884 | * new location to see the old state of the structure. (For | |
885 | * example, the changes were to statistical counters or to | |
886 | * other state where exact synchronization is not required.) | |
887 | * | |
888 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
889 | * result in impossible-to-diagnose memory corruption. As in the structures | |
890 | * will look OK in crash dumps, but any concurrent RCU readers might | |
891 | * see pre-initialized values of the referenced data structure. So | |
892 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
893 | * | |
894 | * If you are creating an RCU-protected linked structure that is accessed | |
895 | * by a single external-to-structure RCU-protected pointer, then you may | |
896 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
897 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
898 | * external-to-structure pointer -after- you have completely initialized | |
899 | * the reader-accessible portions of the linked structure. | |
ca5ecddf PM |
900 | */ |
901 | #define RCU_INIT_POINTER(p, v) \ | |
d1b88eb9 PM |
902 | do { \ |
903 | p = (typeof(*v) __force __rcu *)(v); \ | |
904 | } while (0) | |
9ab1544e | 905 | |
172708d0 PM |
906 | /** |
907 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer | |
908 | * | |
909 | * GCC-style initialization for an RCU-protected pointer in a structure field. | |
910 | */ | |
911 | #define RCU_POINTER_INITIALIZER(p, v) \ | |
912 | .p = (typeof(*v) __force __rcu *)(v) | |
9ab1544e | 913 | |
d8169d4c JE |
914 | /* |
915 | * Does the specified offset indicate that the corresponding rcu_head | |
916 | * structure can be handled by kfree_rcu()? | |
917 | */ | |
918 | #define __is_kfree_rcu_offset(offset) ((offset) < 4096) | |
919 | ||
920 | /* | |
921 | * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. | |
922 | */ | |
923 | #define __kfree_rcu(head, offset) \ | |
924 | do { \ | |
925 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ | |
4fa3b6cb | 926 | kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ |
d8169d4c JE |
927 | } while (0) |
928 | ||
9ab1544e LJ |
929 | /** |
930 | * kfree_rcu() - kfree an object after a grace period. | |
931 | * @ptr: pointer to kfree | |
932 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. | |
933 | * | |
934 | * Many rcu callbacks functions just call kfree() on the base structure. | |
935 | * These functions are trivial, but their size adds up, and furthermore | |
936 | * when they are used in a kernel module, that module must invoke the | |
937 | * high-latency rcu_barrier() function at module-unload time. | |
938 | * | |
939 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
940 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
941 | * encodes the offset of the rcu_head structure within the base structure. | |
942 | * Because the functions are not allowed in the low-order 4096 bytes of | |
943 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
944 | * If the offset is larger than 4095 bytes, a compile-time error will | |
945 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
946 | * either fall back to use of call_rcu() or rearrange the structure to | |
947 | * position the rcu_head structure into the first 4096 bytes. | |
948 | * | |
949 | * Note that the allowable offset might decrease in the future, for example, | |
950 | * to allow something like kmem_cache_free_rcu(). | |
d8169d4c JE |
951 | * |
952 | * The BUILD_BUG_ON check must not involve any function calls, hence the | |
953 | * checks are done in macros here. | |
9ab1544e LJ |
954 | */ |
955 | #define kfree_rcu(ptr, rcu_head) \ | |
956 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) | |
957 | ||
1da177e4 | 958 | #endif /* __LINUX_RCUPDATE_H */ |