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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 | |
87de1cfd PM |
15 | * along with this program; if not, you can access it online at |
16 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
1da177e4 | 17 | * |
01c1c660 | 18 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
19 | * |
20 | * 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> |
ca5ecddf | 37 | #include <linux/compiler.h> |
5f192ab0 | 38 | #include <linux/atomic.h> |
4929c913 | 39 | #include <linux/irqflags.h> |
5f192ab0 PM |
40 | #include <linux/preempt.h> |
41 | #include <linux/bottom_half.h> | |
42 | #include <linux/lockdep.h> | |
43 | #include <asm/processor.h> | |
44 | #include <linux/cpumask.h> | |
c1ad348b | 45 | |
a3dc3fb1 PM |
46 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
47 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) | |
c0f4dfd4 | 48 | #define ulong2long(a) (*(long *)(&(a))) |
a3dc3fb1 | 49 | |
03b042bf | 50 | /* Exported common interfaces */ |
2c42818e PM |
51 | |
52 | #ifdef CONFIG_PREEMPT_RCU | |
a68a2bb2 | 53 | void call_rcu(struct rcu_head *head, rcu_callback_t func); |
2c42818e | 54 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
2c42818e | 55 | #define call_rcu call_rcu_sched |
2c42818e PM |
56 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
57 | ||
a68a2bb2 PM |
58 | void call_rcu_bh(struct rcu_head *head, rcu_callback_t func); |
59 | void call_rcu_sched(struct rcu_head *head, rcu_callback_t func); | |
584dc4ce | 60 | void synchronize_sched(void); |
53c6d4ed | 61 | void rcu_barrier_tasks(void); |
8315f422 | 62 | |
a3dc3fb1 PM |
63 | #ifdef CONFIG_PREEMPT_RCU |
64 | ||
584dc4ce TB |
65 | void __rcu_read_lock(void); |
66 | void __rcu_read_unlock(void); | |
67 | void rcu_read_unlock_special(struct task_struct *t); | |
7b0b759b PM |
68 | void synchronize_rcu(void); |
69 | ||
a3dc3fb1 PM |
70 | /* |
71 | * Defined as a macro as it is a very low level header included from | |
72 | * areas that don't even know about current. This gives the rcu_read_lock() | |
73 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
74 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
75 | */ | |
76 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
77 | ||
7b0b759b PM |
78 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
79 | ||
80 | static inline void __rcu_read_lock(void) | |
81 | { | |
bb73c52b BF |
82 | if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) |
83 | preempt_disable(); | |
7b0b759b PM |
84 | } |
85 | ||
86 | static inline void __rcu_read_unlock(void) | |
87 | { | |
bb73c52b BF |
88 | if (IS_ENABLED(CONFIG_PREEMPT_COUNT)) |
89 | preempt_enable(); | |
7b0b759b PM |
90 | } |
91 | ||
92 | static inline void synchronize_rcu(void) | |
93 | { | |
94 | synchronize_sched(); | |
95 | } | |
96 | ||
97 | static inline int rcu_preempt_depth(void) | |
98 | { | |
99 | return 0; | |
100 | } | |
101 | ||
102 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
103 | ||
104 | /* Internal to kernel */ | |
584dc4ce | 105 | void rcu_init(void); |
825c5bd2 | 106 | extern int rcu_scheduler_active __read_mostly; |
284a8c93 PM |
107 | void rcu_sched_qs(void); |
108 | void rcu_bh_qs(void); | |
c3377c2d | 109 | void rcu_check_callbacks(int user); |
27d50c7e | 110 | void rcu_report_dead(unsigned int cpu); |
7ec99de3 | 111 | void rcu_cpu_starting(unsigned int cpu); |
a58163d8 | 112 | void rcutree_migrate_callbacks(int cpu); |
2b1d5024 | 113 | |
61f38db3 RR |
114 | #ifdef CONFIG_RCU_STALL_COMMON |
115 | void rcu_sysrq_start(void); | |
116 | void rcu_sysrq_end(void); | |
117 | #else /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
d0df7a34 PM |
118 | static inline void rcu_sysrq_start(void) { } |
119 | static inline void rcu_sysrq_end(void) { } | |
61f38db3 RR |
120 | #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ |
121 | ||
d1ec4c34 | 122 | #ifdef CONFIG_NO_HZ_FULL |
584dc4ce TB |
123 | void rcu_user_enter(void); |
124 | void rcu_user_exit(void); | |
2b1d5024 FW |
125 | #else |
126 | static inline void rcu_user_enter(void) { } | |
127 | static inline void rcu_user_exit(void) { } | |
d1ec4c34 | 128 | #endif /* CONFIG_NO_HZ_FULL */ |
2b1d5024 | 129 | |
f4579fc5 PM |
130 | #ifdef CONFIG_RCU_NOCB_CPU |
131 | void rcu_init_nohz(void); | |
132 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
d0df7a34 | 133 | static inline void rcu_init_nohz(void) { } |
f4579fc5 PM |
134 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
135 | ||
8a2ecf47 PM |
136 | /** |
137 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers | |
138 | * @a: Code that RCU needs to pay attention to. | |
139 | * | |
140 | * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden | |
141 | * in the inner idle loop, that is, between the rcu_idle_enter() and | |
142 | * the rcu_idle_exit() -- RCU will happily ignore any such read-side | |
143 | * critical sections. However, things like powertop need tracepoints | |
144 | * in the inner idle loop. | |
145 | * | |
146 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) | |
810ce8b5 PM |
147 | * will tell RCU that it needs to pay attention, invoke its argument |
148 | * (in this example, calling the do_something_with_RCU() function), | |
8a2ecf47 | 149 | * and then tell RCU to go back to ignoring this CPU. It is permissible |
810ce8b5 PM |
150 | * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is |
151 | * on the order of a million or so, even on 32-bit systems). It is | |
152 | * not legal to block within RCU_NONIDLE(), nor is it permissible to | |
153 | * transfer control either into or out of RCU_NONIDLE()'s statement. | |
8a2ecf47 PM |
154 | */ |
155 | #define RCU_NONIDLE(a) \ | |
156 | do { \ | |
7c9906ca | 157 | rcu_irq_enter_irqson(); \ |
8a2ecf47 | 158 | do { a; } while (0); \ |
7c9906ca | 159 | rcu_irq_exit_irqson(); \ |
8a2ecf47 PM |
160 | } while (0) |
161 | ||
8315f422 PM |
162 | /* |
163 | * Note a voluntary context switch for RCU-tasks benefit. This is a | |
164 | * macro rather than an inline function to avoid #include hell. | |
165 | */ | |
166 | #ifdef CONFIG_TASKS_RCU | |
bcbfdd01 | 167 | #define rcu_note_voluntary_context_switch_lite(t) \ |
8315f422 | 168 | do { \ |
7d0ae808 PM |
169 | if (READ_ONCE((t)->rcu_tasks_holdout)) \ |
170 | WRITE_ONCE((t)->rcu_tasks_holdout, false); \ | |
8315f422 | 171 | } while (0) |
bcbfdd01 PM |
172 | #define rcu_note_voluntary_context_switch(t) \ |
173 | do { \ | |
174 | rcu_all_qs(); \ | |
175 | rcu_note_voluntary_context_switch_lite(t); \ | |
176 | } while (0) | |
7e42776d PM |
177 | void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
178 | void synchronize_rcu_tasks(void); | |
ccdd29ff PM |
179 | void exit_tasks_rcu_start(void); |
180 | void exit_tasks_rcu_finish(void); | |
8315f422 | 181 | #else /* #ifdef CONFIG_TASKS_RCU */ |
bcbfdd01 PM |
182 | #define rcu_note_voluntary_context_switch_lite(t) do { } while (0) |
183 | #define rcu_note_voluntary_context_switch(t) rcu_all_qs() | |
7e42776d PM |
184 | #define call_rcu_tasks call_rcu_sched |
185 | #define synchronize_rcu_tasks synchronize_sched | |
ccdd29ff PM |
186 | static inline void exit_tasks_rcu_start(void) { } |
187 | static inline void exit_tasks_rcu_finish(void) { } | |
8315f422 PM |
188 | #endif /* #else #ifdef CONFIG_TASKS_RCU */ |
189 | ||
bde6c3aa PM |
190 | /** |
191 | * cond_resched_rcu_qs - Report potential quiescent states to RCU | |
192 | * | |
193 | * This macro resembles cond_resched(), except that it is defined to | |
194 | * report potential quiescent states to RCU-tasks even if the cond_resched() | |
195 | * machinery were to be shut off, as some advocate for PREEMPT kernels. | |
196 | */ | |
197 | #define cond_resched_rcu_qs() \ | |
198 | do { \ | |
b6331ae8 | 199 | if (!cond_resched()) \ |
dc259acc | 200 | rcu_note_voluntary_context_switch_lite(current); \ |
bde6c3aa PM |
201 | } while (0) |
202 | ||
2c42818e PM |
203 | /* |
204 | * Infrastructure to implement the synchronize_() primitives in | |
205 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
206 | */ | |
207 | ||
28f6569a | 208 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) |
64db4cff | 209 | #include <linux/rcutree.h> |
127781d1 | 210 | #elif defined(CONFIG_TINY_RCU) |
9b1d82fa | 211 | #include <linux/rcutiny.h> |
64db4cff PM |
212 | #else |
213 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 214 | #endif |
01c1c660 | 215 | |
551d55a9 MD |
216 | /* |
217 | * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic | |
218 | * initialization and destruction of rcu_head on the stack. rcu_head structures | |
219 | * allocated dynamically in the heap or defined statically don't need any | |
220 | * initialization. | |
221 | */ | |
222 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
546a9d85 PM |
223 | void init_rcu_head(struct rcu_head *head); |
224 | void destroy_rcu_head(struct rcu_head *head); | |
584dc4ce TB |
225 | void init_rcu_head_on_stack(struct rcu_head *head); |
226 | void destroy_rcu_head_on_stack(struct rcu_head *head); | |
551d55a9 | 227 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
d0df7a34 PM |
228 | static inline void init_rcu_head(struct rcu_head *head) { } |
229 | static inline void destroy_rcu_head(struct rcu_head *head) { } | |
230 | static inline void init_rcu_head_on_stack(struct rcu_head *head) { } | |
231 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } | |
551d55a9 | 232 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 233 | |
c0d6d01b PM |
234 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
235 | bool rcu_lockdep_current_cpu_online(void); | |
236 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
17a8c187 | 237 | static inline bool rcu_lockdep_current_cpu_online(void) { return true; } |
c0d6d01b PM |
238 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
239 | ||
bc33f24b | 240 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 241 | |
00f49e57 FW |
242 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
243 | { | |
fb9edbe9 | 244 | lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); |
00f49e57 FW |
245 | } |
246 | ||
247 | static inline void rcu_lock_release(struct lockdep_map *map) | |
248 | { | |
00f49e57 FW |
249 | lock_release(map, 1, _THIS_IP_); |
250 | } | |
251 | ||
bc33f24b | 252 | extern struct lockdep_map rcu_lock_map; |
632ee200 | 253 | extern struct lockdep_map rcu_bh_lock_map; |
632ee200 | 254 | extern struct lockdep_map rcu_sched_lock_map; |
24ef659a | 255 | extern struct lockdep_map rcu_callback_map; |
a235c091 | 256 | int debug_lockdep_rcu_enabled(void); |
85b39d30 | 257 | int rcu_read_lock_held(void); |
584dc4ce | 258 | int rcu_read_lock_bh_held(void); |
d5671f6b | 259 | int rcu_read_lock_sched_held(void); |
632ee200 PM |
260 | |
261 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
262 | ||
d8ab29f8 PM |
263 | # define rcu_lock_acquire(a) do { } while (0) |
264 | # define rcu_lock_release(a) do { } while (0) | |
632ee200 PM |
265 | |
266 | static inline int rcu_read_lock_held(void) | |
267 | { | |
268 | return 1; | |
269 | } | |
270 | ||
271 | static inline int rcu_read_lock_bh_held(void) | |
272 | { | |
273 | return 1; | |
274 | } | |
275 | ||
276 | static inline int rcu_read_lock_sched_held(void) | |
277 | { | |
293e2421 | 278 | return !preemptible(); |
632ee200 | 279 | } |
632ee200 PM |
280 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
281 | ||
282 | #ifdef CONFIG_PROVE_RCU | |
283 | ||
f78f5b90 PM |
284 | /** |
285 | * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met | |
286 | * @c: condition to check | |
287 | * @s: informative message | |
288 | */ | |
289 | #define RCU_LOCKDEP_WARN(c, s) \ | |
290 | do { \ | |
291 | static bool __section(.data.unlikely) __warned; \ | |
292 | if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \ | |
293 | __warned = true; \ | |
294 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ | |
295 | } \ | |
296 | } while (0) | |
297 | ||
50406b98 PM |
298 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
299 | static inline void rcu_preempt_sleep_check(void) | |
300 | { | |
f78f5b90 PM |
301 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
302 | "Illegal context switch in RCU read-side critical section"); | |
50406b98 PM |
303 | } |
304 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
d0df7a34 | 305 | static inline void rcu_preempt_sleep_check(void) { } |
50406b98 PM |
306 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
307 | ||
b3fbab05 PM |
308 | #define rcu_sleep_check() \ |
309 | do { \ | |
50406b98 | 310 | rcu_preempt_sleep_check(); \ |
f78f5b90 PM |
311 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ |
312 | "Illegal context switch in RCU-bh read-side critical section"); \ | |
313 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ | |
314 | "Illegal context switch in RCU-sched read-side critical section"); \ | |
b3fbab05 PM |
315 | } while (0) |
316 | ||
ca5ecddf PM |
317 | #else /* #ifdef CONFIG_PROVE_RCU */ |
318 | ||
f78f5b90 | 319 | #define RCU_LOCKDEP_WARN(c, s) do { } while (0) |
b3fbab05 | 320 | #define rcu_sleep_check() do { } while (0) |
ca5ecddf PM |
321 | |
322 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
323 | ||
324 | /* | |
325 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
326 | * and rcu_assign_pointer(). Some of these could be folded into their | |
327 | * callers, but they are left separate in order to ease introduction of | |
328 | * multiple flavors of pointers to match the multiple flavors of RCU | |
329 | * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in | |
330 | * the future. | |
331 | */ | |
53ecfba2 PM |
332 | |
333 | #ifdef __CHECKER__ | |
334 | #define rcu_dereference_sparse(p, space) \ | |
335 | ((void)(((typeof(*p) space *)p) == p)) | |
336 | #else /* #ifdef __CHECKER__ */ | |
337 | #define rcu_dereference_sparse(p, space) | |
338 | #endif /* #else #ifdef __CHECKER__ */ | |
339 | ||
ca5ecddf | 340 | #define __rcu_access_pointer(p, space) \ |
0adab9b9 | 341 | ({ \ |
7d0ae808 | 342 | typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
0adab9b9 JP |
343 | rcu_dereference_sparse(p, space); \ |
344 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
345 | }) | |
ca5ecddf | 346 | #define __rcu_dereference_check(p, c, space) \ |
0adab9b9 | 347 | ({ \ |
ac59853c | 348 | /* Dependency order vs. p above. */ \ |
506458ef | 349 | typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
f78f5b90 | 350 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
0adab9b9 | 351 | rcu_dereference_sparse(p, space); \ |
ac59853c | 352 | ((typeof(*p) __force __kernel *)(________p1)); \ |
0adab9b9 | 353 | }) |
ca5ecddf | 354 | #define __rcu_dereference_protected(p, c, space) \ |
0adab9b9 | 355 | ({ \ |
f78f5b90 | 356 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
0adab9b9 JP |
357 | rcu_dereference_sparse(p, space); \ |
358 | ((typeof(*p) __force __kernel *)(p)); \ | |
359 | }) | |
995f1405 PM |
360 | #define rcu_dereference_raw(p) \ |
361 | ({ \ | |
362 | /* Dependency order vs. p above. */ \ | |
506458ef | 363 | typeof(p) ________p1 = READ_ONCE(p); \ |
995f1405 PM |
364 | ((typeof(*p) __force __kernel *)(________p1)); \ |
365 | }) | |
ca5ecddf | 366 | |
462225ae PM |
367 | /** |
368 | * RCU_INITIALIZER() - statically initialize an RCU-protected global variable | |
369 | * @v: The value to statically initialize with. | |
370 | */ | |
371 | #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) | |
372 | ||
373 | /** | |
374 | * rcu_assign_pointer() - assign to RCU-protected pointer | |
375 | * @p: pointer to assign to | |
376 | * @v: value to assign (publish) | |
377 | * | |
378 | * Assigns the specified value to the specified RCU-protected | |
379 | * pointer, ensuring that any concurrent RCU readers will see | |
380 | * any prior initialization. | |
381 | * | |
382 | * Inserts memory barriers on architectures that require them | |
383 | * (which is most of them), and also prevents the compiler from | |
384 | * reordering the code that initializes the structure after the pointer | |
385 | * assignment. More importantly, this call documents which pointers | |
386 | * will be dereferenced by RCU read-side code. | |
387 | * | |
388 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
389 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
390 | * to the fact that it does not constrain either the CPU or the compiler. | |
391 | * That said, using RCU_INIT_POINTER() when you should have used | |
392 | * rcu_assign_pointer() is a very bad thing that results in | |
393 | * impossible-to-diagnose memory corruption. So please be careful. | |
394 | * See the RCU_INIT_POINTER() comment header for details. | |
395 | * | |
396 | * Note that rcu_assign_pointer() evaluates each of its arguments only | |
397 | * once, appearances notwithstanding. One of the "extra" evaluations | |
398 | * is in typeof() and the other visible only to sparse (__CHECKER__), | |
399 | * neither of which actually execute the argument. As with most cpp | |
400 | * macros, this execute-arguments-only-once property is important, so | |
401 | * please be careful when making changes to rcu_assign_pointer() and the | |
402 | * other macros that it invokes. | |
403 | */ | |
3a37f727 PM |
404 | #define rcu_assign_pointer(p, v) \ |
405 | ({ \ | |
406 | uintptr_t _r_a_p__v = (uintptr_t)(v); \ | |
407 | \ | |
408 | if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ | |
409 | WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ | |
410 | else \ | |
411 | smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ | |
412 | _r_a_p__v; \ | |
413 | }) | |
ca5ecddf | 414 | |
26e3e3cb BVA |
415 | /** |
416 | * rcu_swap_protected() - swap an RCU and a regular pointer | |
417 | * @rcu_ptr: RCU pointer | |
418 | * @ptr: regular pointer | |
419 | * @c: the conditions under which the dereference will take place | |
420 | * | |
421 | * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and | |
422 | * @c is the argument that is passed to the rcu_dereference_protected() call | |
423 | * used to read that pointer. | |
424 | */ | |
425 | #define rcu_swap_protected(rcu_ptr, ptr, c) do { \ | |
426 | typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ | |
427 | rcu_assign_pointer((rcu_ptr), (ptr)); \ | |
428 | (ptr) = __tmp; \ | |
429 | } while (0) | |
430 | ||
ca5ecddf PM |
431 | /** |
432 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
433 | * @p: The pointer to read | |
434 | * | |
435 | * Return the value of the specified RCU-protected pointer, but omit the | |
137f61f6 PM |
436 | * lockdep checks for being in an RCU read-side critical section. This is |
437 | * useful when the value of this pointer is accessed, but the pointer is | |
438 | * not dereferenced, for example, when testing an RCU-protected pointer | |
439 | * against NULL. Although rcu_access_pointer() may also be used in cases | |
440 | * where update-side locks prevent the value of the pointer from changing, | |
441 | * you should instead use rcu_dereference_protected() for this use case. | |
5e1ee6e1 PM |
442 | * |
443 | * It is also permissible to use rcu_access_pointer() when read-side | |
444 | * access to the pointer was removed at least one grace period ago, as | |
445 | * is the case in the context of the RCU callback that is freeing up | |
446 | * the data, or after a synchronize_rcu() returns. This can be useful | |
447 | * when tearing down multi-linked structures after a grace period | |
448 | * has elapsed. | |
ca5ecddf PM |
449 | */ |
450 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
451 | ||
632ee200 | 452 | /** |
ca5ecddf | 453 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
454 | * @p: The pointer to read, prior to dereferencing |
455 | * @c: The conditions under which the dereference will take place | |
632ee200 | 456 | * |
c08c68dd | 457 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
458 | * dereference will take place are correct. Typically the conditions |
459 | * indicate the various locking conditions that should be held at that | |
460 | * point. The check should return true if the conditions are satisfied. | |
461 | * An implicit check for being in an RCU read-side critical section | |
462 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
463 | * |
464 | * For example: | |
465 | * | |
ca5ecddf | 466 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
467 | * |
468 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 469 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
470 | * the bar struct at foo->bar is held. |
471 | * | |
472 | * Note that the list of conditions may also include indications of when a lock | |
473 | * need not be held, for example during initialisation or destruction of the | |
474 | * target struct: | |
475 | * | |
ca5ecddf | 476 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 477 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
478 | * |
479 | * Inserts memory barriers on architectures that require them | |
480 | * (currently only the Alpha), prevents the compiler from refetching | |
481 | * (and from merging fetches), and, more importantly, documents exactly | |
482 | * which pointers are protected by RCU and checks that the pointer is | |
483 | * annotated as __rcu. | |
632ee200 PM |
484 | */ |
485 | #define rcu_dereference_check(p, c) \ | |
b826565a | 486 | __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu) |
ca5ecddf PM |
487 | |
488 | /** | |
489 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
490 | * @p: The pointer to read, prior to dereferencing | |
491 | * @c: The conditions under which the dereference will take place | |
492 | * | |
493 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
494 | */ | |
495 | #define rcu_dereference_bh_check(p, c) \ | |
b826565a | 496 | __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu) |
632ee200 | 497 | |
b62730ba | 498 | /** |
ca5ecddf PM |
499 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
500 | * @p: The pointer to read, prior to dereferencing | |
501 | * @c: The conditions under which the dereference will take place | |
502 | * | |
503 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
504 | */ | |
505 | #define rcu_dereference_sched_check(p, c) \ | |
b826565a | 506 | __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \ |
ca5ecddf PM |
507 | __rcu) |
508 | ||
12bcbe66 SR |
509 | /* |
510 | * The tracing infrastructure traces RCU (we want that), but unfortunately | |
511 | * some of the RCU checks causes tracing to lock up the system. | |
512 | * | |
f039f0af | 513 | * The no-tracing version of rcu_dereference_raw() must not call |
12bcbe66 SR |
514 | * rcu_read_lock_held(). |
515 | */ | |
516 | #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu) | |
517 | ||
ca5ecddf PM |
518 | /** |
519 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
520 | * @p: The pointer to read, prior to dereferencing | |
521 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
522 | * |
523 | * Return the value of the specified RCU-protected pointer, but omit | |
137f61f6 PM |
524 | * the READ_ONCE(). This is useful in cases where update-side locks |
525 | * prevent the value of the pointer from changing. Please note that this | |
526 | * primitive does *not* prevent the compiler from repeating this reference | |
527 | * or combining it with other references, so it should not be used without | |
528 | * protection of appropriate locks. | |
ca5ecddf PM |
529 | * |
530 | * This function is only for update-side use. Using this function | |
531 | * when protected only by rcu_read_lock() will result in infrequent | |
532 | * but very ugly failures. | |
b62730ba PM |
533 | */ |
534 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 535 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 536 | |
bc33f24b | 537 | |
b62730ba | 538 | /** |
ca5ecddf PM |
539 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
540 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 541 | * |
ca5ecddf | 542 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 543 | */ |
ca5ecddf | 544 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 545 | |
1da177e4 | 546 | /** |
ca5ecddf PM |
547 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
548 | * @p: The pointer to read, prior to dereferencing | |
549 | * | |
550 | * Makes rcu_dereference_check() do the dirty work. | |
551 | */ | |
552 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
553 | ||
554 | /** | |
555 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
556 | * @p: The pointer to read, prior to dereferencing | |
557 | * | |
558 | * Makes rcu_dereference_check() do the dirty work. | |
559 | */ | |
560 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
561 | ||
c3ac7cf1 PM |
562 | /** |
563 | * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism | |
564 | * @p: The pointer to hand off | |
565 | * | |
566 | * This is simply an identity function, but it documents where a pointer | |
567 | * is handed off from RCU to some other synchronization mechanism, for | |
568 | * example, reference counting or locking. In C11, it would map to | |
569 | * kill_dependency(). It could be used as follows: | |
27fdb35f | 570 | * `` |
c3ac7cf1 PM |
571 | * rcu_read_lock(); |
572 | * p = rcu_dereference(gp); | |
573 | * long_lived = is_long_lived(p); | |
574 | * if (long_lived) { | |
575 | * if (!atomic_inc_not_zero(p->refcnt)) | |
576 | * long_lived = false; | |
577 | * else | |
578 | * p = rcu_pointer_handoff(p); | |
579 | * } | |
580 | * rcu_read_unlock(); | |
27fdb35f | 581 | *`` |
c3ac7cf1 PM |
582 | */ |
583 | #define rcu_pointer_handoff(p) (p) | |
584 | ||
ca5ecddf PM |
585 | /** |
586 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 587 | * |
9b06e818 | 588 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 589 | * are within RCU read-side critical sections, then the |
9b06e818 | 590 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
591 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
592 | * on one CPU while other CPUs are within RCU read-side critical | |
593 | * sections, invocation of the corresponding RCU callback is deferred | |
594 | * until after the all the other CPUs exit their critical sections. | |
595 | * | |
596 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 597 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
598 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
599 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
600 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
601 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
602 | * callback is invoked. This is legal, because the RCU read-side critical | |
603 | * section that was running concurrently with the call_rcu() (and which | |
604 | * therefore might be referencing something that the corresponding RCU | |
605 | * callback would free up) has completed before the corresponding | |
606 | * RCU callback is invoked. | |
607 | * | |
608 | * RCU read-side critical sections may be nested. Any deferred actions | |
609 | * will be deferred until the outermost RCU read-side critical section | |
610 | * completes. | |
611 | * | |
9079fd7c PM |
612 | * You can avoid reading and understanding the next paragraph by |
613 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
614 | * read-side critical section that would block in a !PREEMPT kernel. | |
615 | * But if you want the full story, read on! | |
616 | * | |
ab74fdfd PM |
617 | * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), |
618 | * it is illegal to block while in an RCU read-side critical section. | |
28f6569a | 619 | * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT |
ab74fdfd PM |
620 | * kernel builds, RCU read-side critical sections may be preempted, |
621 | * but explicit blocking is illegal. Finally, in preemptible RCU | |
622 | * implementations in real-time (with -rt patchset) kernel builds, RCU | |
623 | * read-side critical sections may be preempted and they may also block, but | |
624 | * only when acquiring spinlocks that are subject to priority inheritance. | |
1da177e4 | 625 | */ |
bc33f24b PM |
626 | static inline void rcu_read_lock(void) |
627 | { | |
628 | __rcu_read_lock(); | |
629 | __acquire(RCU); | |
d8ab29f8 | 630 | rcu_lock_acquire(&rcu_lock_map); |
f78f5b90 PM |
631 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
632 | "rcu_read_lock() used illegally while idle"); | |
bc33f24b | 633 | } |
1da177e4 | 634 | |
1da177e4 LT |
635 | /* |
636 | * So where is rcu_write_lock()? It does not exist, as there is no | |
637 | * way for writers to lock out RCU readers. This is a feature, not | |
638 | * a bug -- this property is what provides RCU's performance benefits. | |
639 | * Of course, writers must coordinate with each other. The normal | |
640 | * spinlock primitives work well for this, but any other technique may be | |
641 | * used as well. RCU does not care how the writers keep out of each | |
642 | * others' way, as long as they do so. | |
643 | */ | |
3d76c082 PM |
644 | |
645 | /** | |
ca5ecddf | 646 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 | 647 | * |
f27bc487 PM |
648 | * In most situations, rcu_read_unlock() is immune from deadlock. |
649 | * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock() | |
650 | * is responsible for deboosting, which it does via rt_mutex_unlock(). | |
651 | * Unfortunately, this function acquires the scheduler's runqueue and | |
652 | * priority-inheritance spinlocks. This means that deadlock could result | |
653 | * if the caller of rcu_read_unlock() already holds one of these locks or | |
ce36f2f3 ON |
654 | * any lock that is ever acquired while holding them; or any lock which |
655 | * can be taken from interrupt context because rcu_boost()->rt_mutex_lock() | |
656 | * does not disable irqs while taking ->wait_lock. | |
f27bc487 PM |
657 | * |
658 | * That said, RCU readers are never priority boosted unless they were | |
659 | * preempted. Therefore, one way to avoid deadlock is to make sure | |
660 | * that preemption never happens within any RCU read-side critical | |
661 | * section whose outermost rcu_read_unlock() is called with one of | |
662 | * rt_mutex_unlock()'s locks held. Such preemption can be avoided in | |
663 | * a number of ways, for example, by invoking preempt_disable() before | |
664 | * critical section's outermost rcu_read_lock(). | |
665 | * | |
666 | * Given that the set of locks acquired by rt_mutex_unlock() might change | |
667 | * at any time, a somewhat more future-proofed approach is to make sure | |
668 | * that that preemption never happens within any RCU read-side critical | |
669 | * section whose outermost rcu_read_unlock() is called with irqs disabled. | |
670 | * This approach relies on the fact that rt_mutex_unlock() currently only | |
671 | * acquires irq-disabled locks. | |
672 | * | |
673 | * The second of these two approaches is best in most situations, | |
674 | * however, the first approach can also be useful, at least to those | |
675 | * developers willing to keep abreast of the set of locks acquired by | |
676 | * rt_mutex_unlock(). | |
677 | * | |
3d76c082 PM |
678 | * See rcu_read_lock() for more information. |
679 | */ | |
bc33f24b PM |
680 | static inline void rcu_read_unlock(void) |
681 | { | |
f78f5b90 PM |
682 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
683 | "rcu_read_unlock() used illegally while idle"); | |
bc33f24b PM |
684 | __release(RCU); |
685 | __rcu_read_unlock(); | |
d24209bb | 686 | rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
bc33f24b | 687 | } |
1da177e4 LT |
688 | |
689 | /** | |
ca5ecddf | 690 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 LT |
691 | * |
692 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
ca5ecddf PM |
693 | * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since |
694 | * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a | |
695 | * softirq handler to be a quiescent state, a process in RCU read-side | |
696 | * critical section must be protected by disabling softirqs. Read-side | |
697 | * critical sections in interrupt context can use just rcu_read_lock(), | |
698 | * though this should at least be commented to avoid confusing people | |
699 | * reading the code. | |
3842a083 PM |
700 | * |
701 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() | |
702 | * must occur in the same context, for example, it is illegal to invoke | |
703 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() | |
704 | * was invoked from some other task. | |
1da177e4 | 705 | */ |
bc33f24b PM |
706 | static inline void rcu_read_lock_bh(void) |
707 | { | |
6206ab9b | 708 | local_bh_disable(); |
bc33f24b | 709 | __acquire(RCU_BH); |
d8ab29f8 | 710 | rcu_lock_acquire(&rcu_bh_lock_map); |
f78f5b90 PM |
711 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
712 | "rcu_read_lock_bh() used illegally while idle"); | |
bc33f24b | 713 | } |
1da177e4 LT |
714 | |
715 | /* | |
716 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
717 | * | |
718 | * See rcu_read_lock_bh() for more information. | |
719 | */ | |
bc33f24b PM |
720 | static inline void rcu_read_unlock_bh(void) |
721 | { | |
f78f5b90 PM |
722 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
723 | "rcu_read_unlock_bh() used illegally while idle"); | |
d8ab29f8 | 724 | rcu_lock_release(&rcu_bh_lock_map); |
bc33f24b | 725 | __release(RCU_BH); |
6206ab9b | 726 | local_bh_enable(); |
bc33f24b | 727 | } |
1da177e4 | 728 | |
1c50b728 | 729 | /** |
ca5ecddf | 730 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 731 | * |
ca5ecddf PM |
732 | * This is equivalent of rcu_read_lock(), but to be used when updates |
733 | * are being done using call_rcu_sched() or synchronize_rcu_sched(). | |
734 | * Read-side critical sections can also be introduced by anything that | |
735 | * disables preemption, including local_irq_disable() and friends. | |
3842a083 PM |
736 | * |
737 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() | |
738 | * must occur in the same context, for example, it is illegal to invoke | |
739 | * rcu_read_unlock_sched() from process context if the matching | |
740 | * rcu_read_lock_sched() was invoked from an NMI handler. | |
1c50b728 | 741 | */ |
d6714c22 PM |
742 | static inline void rcu_read_lock_sched(void) |
743 | { | |
744 | preempt_disable(); | |
bc33f24b | 745 | __acquire(RCU_SCHED); |
d8ab29f8 | 746 | rcu_lock_acquire(&rcu_sched_lock_map); |
f78f5b90 PM |
747 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
748 | "rcu_read_lock_sched() used illegally while idle"); | |
d6714c22 | 749 | } |
1eba8f84 PM |
750 | |
751 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 752 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
753 | { |
754 | preempt_disable_notrace(); | |
bc33f24b | 755 | __acquire(RCU_SCHED); |
d6714c22 | 756 | } |
1c50b728 MD |
757 | |
758 | /* | |
759 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
760 | * | |
761 | * See rcu_read_lock_sched for more information. | |
762 | */ | |
d6714c22 PM |
763 | static inline void rcu_read_unlock_sched(void) |
764 | { | |
f78f5b90 PM |
765 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
766 | "rcu_read_unlock_sched() used illegally while idle"); | |
d8ab29f8 | 767 | rcu_lock_release(&rcu_sched_lock_map); |
bc33f24b | 768 | __release(RCU_SCHED); |
d6714c22 PM |
769 | preempt_enable(); |
770 | } | |
1eba8f84 PM |
771 | |
772 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 773 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 774 | { |
bc33f24b | 775 | __release(RCU_SCHED); |
d6714c22 PM |
776 | preempt_enable_notrace(); |
777 | } | |
1c50b728 | 778 | |
ca5ecddf PM |
779 | /** |
780 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
27fdb35f PM |
781 | * @p: The pointer to be initialized. |
782 | * @v: The value to initialized the pointer to. | |
ca5ecddf | 783 | * |
6846c0c5 PM |
784 | * Initialize an RCU-protected pointer in special cases where readers |
785 | * do not need ordering constraints on the CPU or the compiler. These | |
786 | * special cases are: | |
787 | * | |
27fdb35f | 788 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* |
6846c0c5 | 789 | * 2. The caller has taken whatever steps are required to prevent |
27fdb35f | 790 | * RCU readers from concurrently accessing this pointer *or* |
6846c0c5 | 791 | * 3. The referenced data structure has already been exposed to |
27fdb35f PM |
792 | * readers either at compile time or via rcu_assign_pointer() *and* |
793 | * | |
794 | * a. You have not made *any* reader-visible changes to | |
795 | * this structure since then *or* | |
6846c0c5 PM |
796 | * b. It is OK for readers accessing this structure from its |
797 | * new location to see the old state of the structure. (For | |
798 | * example, the changes were to statistical counters or to | |
799 | * other state where exact synchronization is not required.) | |
800 | * | |
801 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
802 | * result in impossible-to-diagnose memory corruption. As in the structures | |
803 | * will look OK in crash dumps, but any concurrent RCU readers might | |
804 | * see pre-initialized values of the referenced data structure. So | |
805 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
806 | * | |
807 | * If you are creating an RCU-protected linked structure that is accessed | |
808 | * by a single external-to-structure RCU-protected pointer, then you may | |
809 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
810 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
27fdb35f | 811 | * external-to-structure pointer *after* you have completely initialized |
6846c0c5 | 812 | * the reader-accessible portions of the linked structure. |
71a9b269 PM |
813 | * |
814 | * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no | |
815 | * ordering guarantees for either the CPU or the compiler. | |
ca5ecddf PM |
816 | */ |
817 | #define RCU_INIT_POINTER(p, v) \ | |
d1b88eb9 | 818 | do { \ |
1a6c9b26 | 819 | rcu_dereference_sparse(p, __rcu); \ |
155d1d12 | 820 | WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
d1b88eb9 | 821 | } while (0) |
9ab1544e | 822 | |
172708d0 PM |
823 | /** |
824 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer | |
27fdb35f PM |
825 | * @p: The pointer to be initialized. |
826 | * @v: The value to initialized the pointer to. | |
172708d0 PM |
827 | * |
828 | * GCC-style initialization for an RCU-protected pointer in a structure field. | |
829 | */ | |
830 | #define RCU_POINTER_INITIALIZER(p, v) \ | |
462225ae | 831 | .p = RCU_INITIALIZER(v) |
9ab1544e | 832 | |
d8169d4c JE |
833 | /* |
834 | * Does the specified offset indicate that the corresponding rcu_head | |
835 | * structure can be handled by kfree_rcu()? | |
836 | */ | |
837 | #define __is_kfree_rcu_offset(offset) ((offset) < 4096) | |
838 | ||
839 | /* | |
840 | * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. | |
841 | */ | |
842 | #define __kfree_rcu(head, offset) \ | |
843 | do { \ | |
844 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ | |
b6a4ae76 | 845 | kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ |
d8169d4c JE |
846 | } while (0) |
847 | ||
9ab1544e LJ |
848 | /** |
849 | * kfree_rcu() - kfree an object after a grace period. | |
850 | * @ptr: pointer to kfree | |
851 | * @rcu_head: the name of the struct rcu_head within the type of @ptr. | |
852 | * | |
853 | * Many rcu callbacks functions just call kfree() on the base structure. | |
854 | * These functions are trivial, but their size adds up, and furthermore | |
855 | * when they are used in a kernel module, that module must invoke the | |
856 | * high-latency rcu_barrier() function at module-unload time. | |
857 | * | |
858 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
859 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
860 | * encodes the offset of the rcu_head structure within the base structure. | |
861 | * Because the functions are not allowed in the low-order 4096 bytes of | |
862 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
863 | * If the offset is larger than 4095 bytes, a compile-time error will | |
864 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
865 | * either fall back to use of call_rcu() or rearrange the structure to | |
866 | * position the rcu_head structure into the first 4096 bytes. | |
867 | * | |
868 | * Note that the allowable offset might decrease in the future, for example, | |
869 | * to allow something like kmem_cache_free_rcu(). | |
d8169d4c JE |
870 | * |
871 | * The BUILD_BUG_ON check must not involve any function calls, hence the | |
872 | * checks are done in macros here. | |
9ab1544e LJ |
873 | */ |
874 | #define kfree_rcu(ptr, rcu_head) \ | |
875 | __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) | |
876 | ||
0edd1b17 | 877 | |
d85b62f1 PM |
878 | /* |
879 | * Place this after a lock-acquisition primitive to guarantee that | |
880 | * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies | |
881 | * if the UNLOCK and LOCK are executed by the same CPU or if the | |
882 | * UNLOCK and LOCK operate on the same lock variable. | |
883 | */ | |
77e58496 | 884 | #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
d85b62f1 | 885 | #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
77e58496 | 886 | #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 887 | #define smp_mb__after_unlock_lock() do { } while (0) |
77e58496 | 888 | #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 889 | |
274529ba | 890 | |
1da177e4 | 891 | #endif /* __LINUX_RCUPDATE_H */ |