Commit | Line | Data |
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73604da5 | 1 | /* SPDX-License-Identifier: GPL-2.0+ */ |
1da177e4 | 2 | /* |
a71fca58 | 3 | * Read-Copy Update mechanism for mutual exclusion |
1da177e4 | 4 | * |
01c1c660 | 5 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
6 | * |
7 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
a71fca58 | 8 | * |
73604da5 | 9 | * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com> |
1da177e4 LT |
10 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
11 | * Papers: | |
12 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf | |
13 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) | |
14 | * | |
15 | * For detailed explanation of Read-Copy Update mechanism see - | |
a71fca58 | 16 | * http://lse.sourceforge.net/locking/rcupdate.html |
1da177e4 LT |
17 | * |
18 | */ | |
19 | ||
20 | #ifndef __LINUX_RCUPDATE_H | |
21 | #define __LINUX_RCUPDATE_H | |
22 | ||
99098751 | 23 | #include <linux/types.h> |
ca5ecddf | 24 | #include <linux/compiler.h> |
5f192ab0 | 25 | #include <linux/atomic.h> |
4929c913 | 26 | #include <linux/irqflags.h> |
5f192ab0 PM |
27 | #include <linux/preempt.h> |
28 | #include <linux/bottom_half.h> | |
29 | #include <linux/lockdep.h> | |
30 | #include <asm/processor.h> | |
31 | #include <linux/cpumask.h> | |
c1ad348b | 32 | |
a3dc3fb1 PM |
33 | #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) |
34 | #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) | |
c0f4dfd4 | 35 | #define ulong2long(a) (*(long *)(&(a))) |
a3dc3fb1 | 36 | |
03b042bf | 37 | /* Exported common interfaces */ |
709fdce7 | 38 | void call_rcu(struct rcu_head *head, rcu_callback_t func); |
53c6d4ed | 39 | void rcu_barrier_tasks(void); |
709fdce7 | 40 | void synchronize_rcu(void); |
8315f422 | 41 | |
a3dc3fb1 PM |
42 | #ifdef CONFIG_PREEMPT_RCU |
43 | ||
584dc4ce TB |
44 | void __rcu_read_lock(void); |
45 | void __rcu_read_unlock(void); | |
7b0b759b | 46 | |
a3dc3fb1 PM |
47 | /* |
48 | * Defined as a macro as it is a very low level header included from | |
49 | * areas that don't even know about current. This gives the rcu_read_lock() | |
50 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
51 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
52 | */ | |
53 | #define rcu_preempt_depth() (current->rcu_read_lock_nesting) | |
54 | ||
7b0b759b PM |
55 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
56 | ||
57 | static inline void __rcu_read_lock(void) | |
58 | { | |
66be4e66 | 59 | preempt_disable(); |
7b0b759b PM |
60 | } |
61 | ||
62 | static inline void __rcu_read_unlock(void) | |
63 | { | |
66be4e66 | 64 | preempt_enable(); |
7b0b759b PM |
65 | } |
66 | ||
7b0b759b PM |
67 | static inline int rcu_preempt_depth(void) |
68 | { | |
69 | return 0; | |
70 | } | |
71 | ||
72 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
73 | ||
74 | /* Internal to kernel */ | |
584dc4ce | 75 | void rcu_init(void); |
825c5bd2 | 76 | extern int rcu_scheduler_active __read_mostly; |
c98cac60 | 77 | void rcu_sched_clock_irq(int user); |
27d50c7e | 78 | void rcu_report_dead(unsigned int cpu); |
a58163d8 | 79 | void rcutree_migrate_callbacks(int cpu); |
2b1d5024 | 80 | |
61f38db3 RR |
81 | #ifdef CONFIG_RCU_STALL_COMMON |
82 | void rcu_sysrq_start(void); | |
83 | void rcu_sysrq_end(void); | |
84 | #else /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
d0df7a34 PM |
85 | static inline void rcu_sysrq_start(void) { } |
86 | static inline void rcu_sysrq_end(void) { } | |
61f38db3 RR |
87 | #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ |
88 | ||
d1ec4c34 | 89 | #ifdef CONFIG_NO_HZ_FULL |
584dc4ce TB |
90 | void rcu_user_enter(void); |
91 | void rcu_user_exit(void); | |
2b1d5024 FW |
92 | #else |
93 | static inline void rcu_user_enter(void) { } | |
94 | static inline void rcu_user_exit(void) { } | |
d1ec4c34 | 95 | #endif /* CONFIG_NO_HZ_FULL */ |
2b1d5024 | 96 | |
f4579fc5 PM |
97 | #ifdef CONFIG_RCU_NOCB_CPU |
98 | void rcu_init_nohz(void); | |
99 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ | |
d0df7a34 | 100 | static inline void rcu_init_nohz(void) { } |
f4579fc5 PM |
101 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
102 | ||
8a2ecf47 PM |
103 | /** |
104 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers | |
105 | * @a: Code that RCU needs to pay attention to. | |
106 | * | |
2bd8b1a2 PM |
107 | * RCU read-side critical sections are forbidden in the inner idle loop, |
108 | * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU | |
109 | * will happily ignore any such read-side critical sections. However, | |
110 | * things like powertop need tracepoints in the inner idle loop. | |
8a2ecf47 PM |
111 | * |
112 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) | |
810ce8b5 PM |
113 | * will tell RCU that it needs to pay attention, invoke its argument |
114 | * (in this example, calling the do_something_with_RCU() function), | |
8a2ecf47 | 115 | * and then tell RCU to go back to ignoring this CPU. It is permissible |
810ce8b5 PM |
116 | * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is |
117 | * on the order of a million or so, even on 32-bit systems). It is | |
118 | * not legal to block within RCU_NONIDLE(), nor is it permissible to | |
119 | * transfer control either into or out of RCU_NONIDLE()'s statement. | |
8a2ecf47 PM |
120 | */ |
121 | #define RCU_NONIDLE(a) \ | |
122 | do { \ | |
7c9906ca | 123 | rcu_irq_enter_irqson(); \ |
8a2ecf47 | 124 | do { a; } while (0); \ |
7c9906ca | 125 | rcu_irq_exit_irqson(); \ |
8a2ecf47 PM |
126 | } while (0) |
127 | ||
8315f422 | 128 | /* |
6f56f714 PM |
129 | * Note a quasi-voluntary context switch for RCU-tasks's benefit. |
130 | * This is a macro rather than an inline function to avoid #include hell. | |
8315f422 | 131 | */ |
5873b8a9 | 132 | #ifdef CONFIG_TASKS_RCU_GENERIC |
6f56f714 | 133 | #define rcu_tasks_qs(t) \ |
8315f422 | 134 | do { \ |
7d0ae808 PM |
135 | if (READ_ONCE((t)->rcu_tasks_holdout)) \ |
136 | WRITE_ONCE((t)->rcu_tasks_holdout, false); \ | |
8315f422 | 137 | } while (0) |
4d232dfe | 138 | #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t) |
7e42776d PM |
139 | void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
140 | void synchronize_rcu_tasks(void); | |
ccdd29ff PM |
141 | void exit_tasks_rcu_start(void); |
142 | void exit_tasks_rcu_finish(void); | |
5873b8a9 | 143 | #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ |
6f56f714 | 144 | #define rcu_tasks_qs(t) do { } while (0) |
4d232dfe | 145 | #define rcu_note_voluntary_context_switch(t) do { } while (0) |
2bd8b1a2 | 146 | #define call_rcu_tasks call_rcu |
a8bb74ac | 147 | #define synchronize_rcu_tasks synchronize_rcu |
ccdd29ff PM |
148 | static inline void exit_tasks_rcu_start(void) { } |
149 | static inline void exit_tasks_rcu_finish(void) { } | |
5873b8a9 | 150 | #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |
8315f422 | 151 | |
bde6c3aa | 152 | /** |
cee43939 | 153 | * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU |
bde6c3aa PM |
154 | * |
155 | * This macro resembles cond_resched(), except that it is defined to | |
156 | * report potential quiescent states to RCU-tasks even if the cond_resched() | |
90326f05 | 157 | * machinery were to be shut off, as some advocate for PREEMPTION kernels. |
bde6c3aa | 158 | */ |
cee43939 | 159 | #define cond_resched_tasks_rcu_qs() \ |
bde6c3aa | 160 | do { \ |
6f56f714 | 161 | rcu_tasks_qs(current); \ |
07f27570 | 162 | cond_resched(); \ |
bde6c3aa PM |
163 | } while (0) |
164 | ||
2c42818e PM |
165 | /* |
166 | * Infrastructure to implement the synchronize_() primitives in | |
167 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
168 | */ | |
169 | ||
b3e627d3 | 170 | #if defined(CONFIG_TREE_RCU) |
64db4cff | 171 | #include <linux/rcutree.h> |
127781d1 | 172 | #elif defined(CONFIG_TINY_RCU) |
9b1d82fa | 173 | #include <linux/rcutiny.h> |
64db4cff PM |
174 | #else |
175 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 176 | #endif |
01c1c660 | 177 | |
551d55a9 | 178 | /* |
b5482a06 PM |
179 | * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls |
180 | * are needed for dynamic initialization and destruction of rcu_head | |
181 | * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for | |
182 | * dynamic initialization and destruction of statically allocated rcu_head | |
183 | * structures. However, rcu_head structures allocated dynamically in the | |
184 | * heap don't need any initialization. | |
551d55a9 MD |
185 | */ |
186 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
546a9d85 PM |
187 | void init_rcu_head(struct rcu_head *head); |
188 | void destroy_rcu_head(struct rcu_head *head); | |
584dc4ce TB |
189 | void init_rcu_head_on_stack(struct rcu_head *head); |
190 | void destroy_rcu_head_on_stack(struct rcu_head *head); | |
551d55a9 | 191 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
d0df7a34 PM |
192 | static inline void init_rcu_head(struct rcu_head *head) { } |
193 | static inline void destroy_rcu_head(struct rcu_head *head) { } | |
194 | static inline void init_rcu_head_on_stack(struct rcu_head *head) { } | |
195 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } | |
551d55a9 | 196 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 197 | |
c0d6d01b PM |
198 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
199 | bool rcu_lockdep_current_cpu_online(void); | |
200 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
17a8c187 | 201 | static inline bool rcu_lockdep_current_cpu_online(void) { return true; } |
c0d6d01b PM |
202 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
203 | ||
bc33f24b | 204 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 205 | |
00f49e57 FW |
206 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
207 | { | |
fb9edbe9 | 208 | lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); |
00f49e57 FW |
209 | } |
210 | ||
211 | static inline void rcu_lock_release(struct lockdep_map *map) | |
212 | { | |
5facae4f | 213 | lock_release(map, _THIS_IP_); |
00f49e57 FW |
214 | } |
215 | ||
bc33f24b | 216 | extern struct lockdep_map rcu_lock_map; |
632ee200 | 217 | extern struct lockdep_map rcu_bh_lock_map; |
632ee200 | 218 | extern struct lockdep_map rcu_sched_lock_map; |
24ef659a | 219 | extern struct lockdep_map rcu_callback_map; |
a235c091 | 220 | int debug_lockdep_rcu_enabled(void); |
85b39d30 | 221 | int rcu_read_lock_held(void); |
584dc4ce | 222 | int rcu_read_lock_bh_held(void); |
d5671f6b | 223 | int rcu_read_lock_sched_held(void); |
28875945 | 224 | int rcu_read_lock_any_held(void); |
632ee200 PM |
225 | |
226 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
227 | ||
d8ab29f8 PM |
228 | # define rcu_lock_acquire(a) do { } while (0) |
229 | # define rcu_lock_release(a) do { } while (0) | |
632ee200 PM |
230 | |
231 | static inline int rcu_read_lock_held(void) | |
232 | { | |
233 | return 1; | |
234 | } | |
235 | ||
236 | static inline int rcu_read_lock_bh_held(void) | |
237 | { | |
238 | return 1; | |
239 | } | |
240 | ||
241 | static inline int rcu_read_lock_sched_held(void) | |
242 | { | |
293e2421 | 243 | return !preemptible(); |
632ee200 | 244 | } |
28875945 JFG |
245 | |
246 | static inline int rcu_read_lock_any_held(void) | |
247 | { | |
248 | return !preemptible(); | |
249 | } | |
250 | ||
632ee200 PM |
251 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
252 | ||
253 | #ifdef CONFIG_PROVE_RCU | |
254 | ||
f78f5b90 PM |
255 | /** |
256 | * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met | |
257 | * @c: condition to check | |
258 | * @s: informative message | |
259 | */ | |
260 | #define RCU_LOCKDEP_WARN(c, s) \ | |
261 | do { \ | |
262 | static bool __section(.data.unlikely) __warned; \ | |
263 | if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \ | |
264 | __warned = true; \ | |
265 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ | |
266 | } \ | |
267 | } while (0) | |
268 | ||
50406b98 PM |
269 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
270 | static inline void rcu_preempt_sleep_check(void) | |
271 | { | |
f78f5b90 PM |
272 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
273 | "Illegal context switch in RCU read-side critical section"); | |
50406b98 PM |
274 | } |
275 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
d0df7a34 | 276 | static inline void rcu_preempt_sleep_check(void) { } |
50406b98 PM |
277 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
278 | ||
b3fbab05 PM |
279 | #define rcu_sleep_check() \ |
280 | do { \ | |
50406b98 | 281 | rcu_preempt_sleep_check(); \ |
f78f5b90 PM |
282 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ |
283 | "Illegal context switch in RCU-bh read-side critical section"); \ | |
284 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ | |
285 | "Illegal context switch in RCU-sched read-side critical section"); \ | |
b3fbab05 PM |
286 | } while (0) |
287 | ||
ca5ecddf PM |
288 | #else /* #ifdef CONFIG_PROVE_RCU */ |
289 | ||
f78f5b90 | 290 | #define RCU_LOCKDEP_WARN(c, s) do { } while (0) |
b3fbab05 | 291 | #define rcu_sleep_check() do { } while (0) |
ca5ecddf PM |
292 | |
293 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
294 | ||
295 | /* | |
296 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
297 | * and rcu_assign_pointer(). Some of these could be folded into their | |
298 | * callers, but they are left separate in order to ease introduction of | |
2bd8b1a2 PM |
299 | * multiple pointers markings to match different RCU implementations |
300 | * (e.g., __srcu), should this make sense in the future. | |
ca5ecddf | 301 | */ |
53ecfba2 PM |
302 | |
303 | #ifdef __CHECKER__ | |
423a86a6 | 304 | #define rcu_check_sparse(p, space) \ |
53ecfba2 PM |
305 | ((void)(((typeof(*p) space *)p) == p)) |
306 | #else /* #ifdef __CHECKER__ */ | |
423a86a6 | 307 | #define rcu_check_sparse(p, space) |
53ecfba2 PM |
308 | #endif /* #else #ifdef __CHECKER__ */ |
309 | ||
ca5ecddf | 310 | #define __rcu_access_pointer(p, space) \ |
0adab9b9 | 311 | ({ \ |
7d0ae808 | 312 | typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
423a86a6 | 313 | rcu_check_sparse(p, space); \ |
0adab9b9 JP |
314 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
315 | }) | |
ca5ecddf | 316 | #define __rcu_dereference_check(p, c, space) \ |
0adab9b9 | 317 | ({ \ |
ac59853c | 318 | /* Dependency order vs. p above. */ \ |
506458ef | 319 | typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
f78f5b90 | 320 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
423a86a6 | 321 | rcu_check_sparse(p, space); \ |
ac59853c | 322 | ((typeof(*p) __force __kernel *)(________p1)); \ |
0adab9b9 | 323 | }) |
ca5ecddf | 324 | #define __rcu_dereference_protected(p, c, space) \ |
0adab9b9 | 325 | ({ \ |
f78f5b90 | 326 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
423a86a6 | 327 | rcu_check_sparse(p, space); \ |
0adab9b9 JP |
328 | ((typeof(*p) __force __kernel *)(p)); \ |
329 | }) | |
995f1405 PM |
330 | #define rcu_dereference_raw(p) \ |
331 | ({ \ | |
332 | /* Dependency order vs. p above. */ \ | |
506458ef | 333 | typeof(p) ________p1 = READ_ONCE(p); \ |
995f1405 PM |
334 | ((typeof(*p) __force __kernel *)(________p1)); \ |
335 | }) | |
ca5ecddf | 336 | |
462225ae PM |
337 | /** |
338 | * RCU_INITIALIZER() - statically initialize an RCU-protected global variable | |
339 | * @v: The value to statically initialize with. | |
340 | */ | |
341 | #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) | |
342 | ||
343 | /** | |
344 | * rcu_assign_pointer() - assign to RCU-protected pointer | |
345 | * @p: pointer to assign to | |
346 | * @v: value to assign (publish) | |
347 | * | |
348 | * Assigns the specified value to the specified RCU-protected | |
349 | * pointer, ensuring that any concurrent RCU readers will see | |
350 | * any prior initialization. | |
351 | * | |
352 | * Inserts memory barriers on architectures that require them | |
353 | * (which is most of them), and also prevents the compiler from | |
354 | * reordering the code that initializes the structure after the pointer | |
355 | * assignment. More importantly, this call documents which pointers | |
356 | * will be dereferenced by RCU read-side code. | |
357 | * | |
358 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
359 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
360 | * to the fact that it does not constrain either the CPU or the compiler. | |
361 | * That said, using RCU_INIT_POINTER() when you should have used | |
362 | * rcu_assign_pointer() is a very bad thing that results in | |
363 | * impossible-to-diagnose memory corruption. So please be careful. | |
364 | * See the RCU_INIT_POINTER() comment header for details. | |
365 | * | |
366 | * Note that rcu_assign_pointer() evaluates each of its arguments only | |
367 | * once, appearances notwithstanding. One of the "extra" evaluations | |
368 | * is in typeof() and the other visible only to sparse (__CHECKER__), | |
369 | * neither of which actually execute the argument. As with most cpp | |
370 | * macros, this execute-arguments-only-once property is important, so | |
371 | * please be careful when making changes to rcu_assign_pointer() and the | |
372 | * other macros that it invokes. | |
373 | */ | |
3a37f727 | 374 | #define rcu_assign_pointer(p, v) \ |
9129b017 | 375 | do { \ |
3a37f727 | 376 | uintptr_t _r_a_p__v = (uintptr_t)(v); \ |
b3119cde | 377 | rcu_check_sparse(p, __rcu); \ |
3a37f727 PM |
378 | \ |
379 | if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ | |
380 | WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ | |
381 | else \ | |
382 | smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ | |
9129b017 | 383 | } while (0) |
ca5ecddf | 384 | |
a63fc6b7 PM |
385 | /** |
386 | * rcu_replace_pointer() - replace an RCU pointer, returning its old value | |
387 | * @rcu_ptr: RCU pointer, whose old value is returned | |
388 | * @ptr: regular pointer | |
389 | * @c: the lockdep conditions under which the dereference will take place | |
390 | * | |
391 | * Perform a replacement, where @rcu_ptr is an RCU-annotated | |
392 | * pointer and @c is the lockdep argument that is passed to the | |
393 | * rcu_dereference_protected() call used to read that pointer. The old | |
394 | * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. | |
395 | */ | |
396 | #define rcu_replace_pointer(rcu_ptr, ptr, c) \ | |
397 | ({ \ | |
398 | typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ | |
399 | rcu_assign_pointer((rcu_ptr), (ptr)); \ | |
400 | __tmp; \ | |
401 | }) | |
402 | ||
ca5ecddf PM |
403 | /** |
404 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
405 | * @p: The pointer to read | |
406 | * | |
407 | * Return the value of the specified RCU-protected pointer, but omit the | |
137f61f6 PM |
408 | * lockdep checks for being in an RCU read-side critical section. This is |
409 | * useful when the value of this pointer is accessed, but the pointer is | |
410 | * not dereferenced, for example, when testing an RCU-protected pointer | |
411 | * against NULL. Although rcu_access_pointer() may also be used in cases | |
412 | * where update-side locks prevent the value of the pointer from changing, | |
413 | * you should instead use rcu_dereference_protected() for this use case. | |
5e1ee6e1 PM |
414 | * |
415 | * It is also permissible to use rcu_access_pointer() when read-side | |
416 | * access to the pointer was removed at least one grace period ago, as | |
417 | * is the case in the context of the RCU callback that is freeing up | |
418 | * the data, or after a synchronize_rcu() returns. This can be useful | |
419 | * when tearing down multi-linked structures after a grace period | |
420 | * has elapsed. | |
ca5ecddf PM |
421 | */ |
422 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
423 | ||
632ee200 | 424 | /** |
ca5ecddf | 425 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
426 | * @p: The pointer to read, prior to dereferencing |
427 | * @c: The conditions under which the dereference will take place | |
632ee200 | 428 | * |
c08c68dd | 429 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
430 | * dereference will take place are correct. Typically the conditions |
431 | * indicate the various locking conditions that should be held at that | |
432 | * point. The check should return true if the conditions are satisfied. | |
433 | * An implicit check for being in an RCU read-side critical section | |
434 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
435 | * |
436 | * For example: | |
437 | * | |
ca5ecddf | 438 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
439 | * |
440 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 441 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
442 | * the bar struct at foo->bar is held. |
443 | * | |
444 | * Note that the list of conditions may also include indications of when a lock | |
445 | * need not be held, for example during initialisation or destruction of the | |
446 | * target struct: | |
447 | * | |
ca5ecddf | 448 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 449 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
450 | * |
451 | * Inserts memory barriers on architectures that require them | |
452 | * (currently only the Alpha), prevents the compiler from refetching | |
453 | * (and from merging fetches), and, more importantly, documents exactly | |
454 | * which pointers are protected by RCU and checks that the pointer is | |
455 | * annotated as __rcu. | |
632ee200 PM |
456 | */ |
457 | #define rcu_dereference_check(p, c) \ | |
b826565a | 458 | __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu) |
ca5ecddf PM |
459 | |
460 | /** | |
461 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
462 | * @p: The pointer to read, prior to dereferencing | |
463 | * @c: The conditions under which the dereference will take place | |
464 | * | |
465 | * This is the RCU-bh counterpart to rcu_dereference_check(). | |
466 | */ | |
467 | #define rcu_dereference_bh_check(p, c) \ | |
b826565a | 468 | __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu) |
632ee200 | 469 | |
b62730ba | 470 | /** |
ca5ecddf PM |
471 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
472 | * @p: The pointer to read, prior to dereferencing | |
473 | * @c: The conditions under which the dereference will take place | |
474 | * | |
475 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
476 | */ | |
477 | #define rcu_dereference_sched_check(p, c) \ | |
b826565a | 478 | __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \ |
ca5ecddf PM |
479 | __rcu) |
480 | ||
12bcbe66 SR |
481 | /* |
482 | * The tracing infrastructure traces RCU (we want that), but unfortunately | |
483 | * some of the RCU checks causes tracing to lock up the system. | |
484 | * | |
f039f0af | 485 | * The no-tracing version of rcu_dereference_raw() must not call |
12bcbe66 SR |
486 | * rcu_read_lock_held(). |
487 | */ | |
0a5b99f5 | 488 | #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu) |
12bcbe66 | 489 | |
ca5ecddf PM |
490 | /** |
491 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
492 | * @p: The pointer to read, prior to dereferencing | |
493 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
494 | * |
495 | * Return the value of the specified RCU-protected pointer, but omit | |
137f61f6 PM |
496 | * the READ_ONCE(). This is useful in cases where update-side locks |
497 | * prevent the value of the pointer from changing. Please note that this | |
498 | * primitive does *not* prevent the compiler from repeating this reference | |
499 | * or combining it with other references, so it should not be used without | |
500 | * protection of appropriate locks. | |
ca5ecddf PM |
501 | * |
502 | * This function is only for update-side use. Using this function | |
503 | * when protected only by rcu_read_lock() will result in infrequent | |
504 | * but very ugly failures. | |
b62730ba PM |
505 | */ |
506 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 507 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 508 | |
bc33f24b | 509 | |
b62730ba | 510 | /** |
ca5ecddf PM |
511 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
512 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 513 | * |
ca5ecddf | 514 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 515 | */ |
ca5ecddf | 516 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 517 | |
1da177e4 | 518 | /** |
ca5ecddf PM |
519 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
520 | * @p: The pointer to read, prior to dereferencing | |
521 | * | |
522 | * Makes rcu_dereference_check() do the dirty work. | |
523 | */ | |
524 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
525 | ||
526 | /** | |
527 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
528 | * @p: The pointer to read, prior to dereferencing | |
529 | * | |
530 | * Makes rcu_dereference_check() do the dirty work. | |
531 | */ | |
532 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
533 | ||
c3ac7cf1 PM |
534 | /** |
535 | * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism | |
536 | * @p: The pointer to hand off | |
537 | * | |
538 | * This is simply an identity function, but it documents where a pointer | |
539 | * is handed off from RCU to some other synchronization mechanism, for | |
540 | * example, reference counting or locking. In C11, it would map to | |
1445e917 MCC |
541 | * kill_dependency(). It could be used as follows:: |
542 | * | |
c3ac7cf1 PM |
543 | * rcu_read_lock(); |
544 | * p = rcu_dereference(gp); | |
545 | * long_lived = is_long_lived(p); | |
546 | * if (long_lived) { | |
547 | * if (!atomic_inc_not_zero(p->refcnt)) | |
548 | * long_lived = false; | |
549 | * else | |
550 | * p = rcu_pointer_handoff(p); | |
551 | * } | |
552 | * rcu_read_unlock(); | |
553 | */ | |
554 | #define rcu_pointer_handoff(p) (p) | |
555 | ||
ca5ecddf PM |
556 | /** |
557 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 558 | * |
9b06e818 | 559 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 560 | * are within RCU read-side critical sections, then the |
9b06e818 | 561 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
562 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
563 | * on one CPU while other CPUs are within RCU read-side critical | |
564 | * sections, invocation of the corresponding RCU callback is deferred | |
565 | * until after the all the other CPUs exit their critical sections. | |
566 | * | |
567 | * Note, however, that RCU callbacks are permitted to run concurrently | |
77d8485a | 568 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
569 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
570 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
571 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
572 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
573 | * callback is invoked. This is legal, because the RCU read-side critical | |
574 | * section that was running concurrently with the call_rcu() (and which | |
575 | * therefore might be referencing something that the corresponding RCU | |
576 | * callback would free up) has completed before the corresponding | |
577 | * RCU callback is invoked. | |
578 | * | |
579 | * RCU read-side critical sections may be nested. Any deferred actions | |
580 | * will be deferred until the outermost RCU read-side critical section | |
581 | * completes. | |
582 | * | |
9079fd7c PM |
583 | * You can avoid reading and understanding the next paragraph by |
584 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
90326f05 | 585 | * read-side critical section that would block in a !PREEMPTION kernel. |
9079fd7c PM |
586 | * But if you want the full story, read on! |
587 | * | |
b3e627d3 | 588 | * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), |
ab74fdfd | 589 | * it is illegal to block while in an RCU read-side critical section. |
01b1d88b | 590 | * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION |
ab74fdfd PM |
591 | * kernel builds, RCU read-side critical sections may be preempted, |
592 | * but explicit blocking is illegal. Finally, in preemptible RCU | |
593 | * implementations in real-time (with -rt patchset) kernel builds, RCU | |
594 | * read-side critical sections may be preempted and they may also block, but | |
595 | * only when acquiring spinlocks that are subject to priority inheritance. | |
1da177e4 | 596 | */ |
6da9f775 | 597 | static __always_inline void rcu_read_lock(void) |
bc33f24b PM |
598 | { |
599 | __rcu_read_lock(); | |
600 | __acquire(RCU); | |
d8ab29f8 | 601 | rcu_lock_acquire(&rcu_lock_map); |
f78f5b90 PM |
602 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
603 | "rcu_read_lock() used illegally while idle"); | |
bc33f24b | 604 | } |
1da177e4 | 605 | |
1da177e4 LT |
606 | /* |
607 | * So where is rcu_write_lock()? It does not exist, as there is no | |
608 | * way for writers to lock out RCU readers. This is a feature, not | |
609 | * a bug -- this property is what provides RCU's performance benefits. | |
610 | * Of course, writers must coordinate with each other. The normal | |
611 | * spinlock primitives work well for this, but any other technique may be | |
612 | * used as well. RCU does not care how the writers keep out of each | |
613 | * others' way, as long as they do so. | |
614 | */ | |
3d76c082 PM |
615 | |
616 | /** | |
ca5ecddf | 617 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 | 618 | * |
f27bc487 PM |
619 | * In most situations, rcu_read_unlock() is immune from deadlock. |
620 | * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock() | |
621 | * is responsible for deboosting, which it does via rt_mutex_unlock(). | |
622 | * Unfortunately, this function acquires the scheduler's runqueue and | |
623 | * priority-inheritance spinlocks. This means that deadlock could result | |
624 | * if the caller of rcu_read_unlock() already holds one of these locks or | |
ec84b27f | 625 | * any lock that is ever acquired while holding them. |
f27bc487 PM |
626 | * |
627 | * That said, RCU readers are never priority boosted unless they were | |
628 | * preempted. Therefore, one way to avoid deadlock is to make sure | |
629 | * that preemption never happens within any RCU read-side critical | |
630 | * section whose outermost rcu_read_unlock() is called with one of | |
631 | * rt_mutex_unlock()'s locks held. Such preemption can be avoided in | |
632 | * a number of ways, for example, by invoking preempt_disable() before | |
633 | * critical section's outermost rcu_read_lock(). | |
634 | * | |
635 | * Given that the set of locks acquired by rt_mutex_unlock() might change | |
636 | * at any time, a somewhat more future-proofed approach is to make sure | |
637 | * that that preemption never happens within any RCU read-side critical | |
638 | * section whose outermost rcu_read_unlock() is called with irqs disabled. | |
639 | * This approach relies on the fact that rt_mutex_unlock() currently only | |
640 | * acquires irq-disabled locks. | |
641 | * | |
642 | * The second of these two approaches is best in most situations, | |
643 | * however, the first approach can also be useful, at least to those | |
644 | * developers willing to keep abreast of the set of locks acquired by | |
645 | * rt_mutex_unlock(). | |
646 | * | |
3d76c082 PM |
647 | * See rcu_read_lock() for more information. |
648 | */ | |
bc33f24b PM |
649 | static inline void rcu_read_unlock(void) |
650 | { | |
f78f5b90 PM |
651 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
652 | "rcu_read_unlock() used illegally while idle"); | |
bc33f24b PM |
653 | __release(RCU); |
654 | __rcu_read_unlock(); | |
d24209bb | 655 | rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
bc33f24b | 656 | } |
1da177e4 LT |
657 | |
658 | /** | |
ca5ecddf | 659 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 | 660 | * |
82fcecfa | 661 | * This is equivalent of rcu_read_lock(), but also disables softirqs. |
2bd8b1a2 PM |
662 | * Note that anything else that disables softirqs can also serve as |
663 | * an RCU read-side critical section. | |
3842a083 PM |
664 | * |
665 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() | |
666 | * must occur in the same context, for example, it is illegal to invoke | |
667 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() | |
668 | * was invoked from some other task. | |
1da177e4 | 669 | */ |
bc33f24b PM |
670 | static inline void rcu_read_lock_bh(void) |
671 | { | |
6206ab9b | 672 | local_bh_disable(); |
bc33f24b | 673 | __acquire(RCU_BH); |
d8ab29f8 | 674 | rcu_lock_acquire(&rcu_bh_lock_map); |
f78f5b90 PM |
675 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
676 | "rcu_read_lock_bh() used illegally while idle"); | |
bc33f24b | 677 | } |
1da177e4 LT |
678 | |
679 | /* | |
680 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
681 | * | |
682 | * See rcu_read_lock_bh() for more information. | |
683 | */ | |
bc33f24b PM |
684 | static inline void rcu_read_unlock_bh(void) |
685 | { | |
f78f5b90 PM |
686 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
687 | "rcu_read_unlock_bh() used illegally while idle"); | |
d8ab29f8 | 688 | rcu_lock_release(&rcu_bh_lock_map); |
bc33f24b | 689 | __release(RCU_BH); |
6206ab9b | 690 | local_bh_enable(); |
bc33f24b | 691 | } |
1da177e4 | 692 | |
1c50b728 | 693 | /** |
ca5ecddf | 694 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 695 | * |
2bd8b1a2 PM |
696 | * This is equivalent of rcu_read_lock(), but disables preemption. |
697 | * Read-side critical sections can also be introduced by anything else | |
698 | * that disables preemption, including local_irq_disable() and friends. | |
3842a083 PM |
699 | * |
700 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() | |
701 | * must occur in the same context, for example, it is illegal to invoke | |
702 | * rcu_read_unlock_sched() from process context if the matching | |
703 | * rcu_read_lock_sched() was invoked from an NMI handler. | |
1c50b728 | 704 | */ |
d6714c22 PM |
705 | static inline void rcu_read_lock_sched(void) |
706 | { | |
707 | preempt_disable(); | |
bc33f24b | 708 | __acquire(RCU_SCHED); |
d8ab29f8 | 709 | rcu_lock_acquire(&rcu_sched_lock_map); |
f78f5b90 PM |
710 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
711 | "rcu_read_lock_sched() used illegally while idle"); | |
d6714c22 | 712 | } |
1eba8f84 PM |
713 | |
714 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 715 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
716 | { |
717 | preempt_disable_notrace(); | |
bc33f24b | 718 | __acquire(RCU_SCHED); |
d6714c22 | 719 | } |
1c50b728 MD |
720 | |
721 | /* | |
722 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
723 | * | |
724 | * See rcu_read_lock_sched for more information. | |
725 | */ | |
d6714c22 PM |
726 | static inline void rcu_read_unlock_sched(void) |
727 | { | |
f78f5b90 PM |
728 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
729 | "rcu_read_unlock_sched() used illegally while idle"); | |
d8ab29f8 | 730 | rcu_lock_release(&rcu_sched_lock_map); |
bc33f24b | 731 | __release(RCU_SCHED); |
d6714c22 PM |
732 | preempt_enable(); |
733 | } | |
1eba8f84 PM |
734 | |
735 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 736 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 737 | { |
bc33f24b | 738 | __release(RCU_SCHED); |
d6714c22 PM |
739 | preempt_enable_notrace(); |
740 | } | |
1c50b728 | 741 | |
ca5ecddf PM |
742 | /** |
743 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
27fdb35f PM |
744 | * @p: The pointer to be initialized. |
745 | * @v: The value to initialized the pointer to. | |
ca5ecddf | 746 | * |
6846c0c5 PM |
747 | * Initialize an RCU-protected pointer in special cases where readers |
748 | * do not need ordering constraints on the CPU or the compiler. These | |
749 | * special cases are: | |
750 | * | |
27fdb35f | 751 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* |
6846c0c5 | 752 | * 2. The caller has taken whatever steps are required to prevent |
27fdb35f | 753 | * RCU readers from concurrently accessing this pointer *or* |
6846c0c5 | 754 | * 3. The referenced data structure has already been exposed to |
27fdb35f PM |
755 | * readers either at compile time or via rcu_assign_pointer() *and* |
756 | * | |
757 | * a. You have not made *any* reader-visible changes to | |
758 | * this structure since then *or* | |
6846c0c5 PM |
759 | * b. It is OK for readers accessing this structure from its |
760 | * new location to see the old state of the structure. (For | |
761 | * example, the changes were to statistical counters or to | |
762 | * other state where exact synchronization is not required.) | |
763 | * | |
764 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
765 | * result in impossible-to-diagnose memory corruption. As in the structures | |
766 | * will look OK in crash dumps, but any concurrent RCU readers might | |
767 | * see pre-initialized values of the referenced data structure. So | |
768 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
769 | * | |
770 | * If you are creating an RCU-protected linked structure that is accessed | |
771 | * by a single external-to-structure RCU-protected pointer, then you may | |
772 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
773 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
27fdb35f | 774 | * external-to-structure pointer *after* you have completely initialized |
6846c0c5 | 775 | * the reader-accessible portions of the linked structure. |
71a9b269 PM |
776 | * |
777 | * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no | |
778 | * ordering guarantees for either the CPU or the compiler. | |
ca5ecddf PM |
779 | */ |
780 | #define RCU_INIT_POINTER(p, v) \ | |
d1b88eb9 | 781 | do { \ |
423a86a6 | 782 | rcu_check_sparse(p, __rcu); \ |
155d1d12 | 783 | WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
d1b88eb9 | 784 | } while (0) |
9ab1544e | 785 | |
172708d0 PM |
786 | /** |
787 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer | |
27fdb35f PM |
788 | * @p: The pointer to be initialized. |
789 | * @v: The value to initialized the pointer to. | |
172708d0 PM |
790 | * |
791 | * GCC-style initialization for an RCU-protected pointer in a structure field. | |
792 | */ | |
793 | #define RCU_POINTER_INITIALIZER(p, v) \ | |
462225ae | 794 | .p = RCU_INITIALIZER(v) |
9ab1544e | 795 | |
d8169d4c JE |
796 | /* |
797 | * Does the specified offset indicate that the corresponding rcu_head | |
798 | * structure can be handled by kfree_rcu()? | |
799 | */ | |
800 | #define __is_kfree_rcu_offset(offset) ((offset) < 4096) | |
801 | ||
802 | /* | |
803 | * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. | |
804 | */ | |
805 | #define __kfree_rcu(head, offset) \ | |
806 | do { \ | |
807 | BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ | |
b6a4ae76 | 808 | kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \ |
d8169d4c JE |
809 | } while (0) |
810 | ||
9ab1544e LJ |
811 | /** |
812 | * kfree_rcu() - kfree an object after a grace period. | |
813 | * @ptr: pointer to kfree | |
12edff04 | 814 | * @rhf: the name of the struct rcu_head within the type of @ptr. |
9ab1544e LJ |
815 | * |
816 | * Many rcu callbacks functions just call kfree() on the base structure. | |
817 | * These functions are trivial, but their size adds up, and furthermore | |
818 | * when they are used in a kernel module, that module must invoke the | |
819 | * high-latency rcu_barrier() function at module-unload time. | |
820 | * | |
821 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
822 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
823 | * encodes the offset of the rcu_head structure within the base structure. | |
824 | * Because the functions are not allowed in the low-order 4096 bytes of | |
825 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
826 | * If the offset is larger than 4095 bytes, a compile-time error will | |
827 | * be generated in __kfree_rcu(). If this error is triggered, you can | |
828 | * either fall back to use of call_rcu() or rearrange the structure to | |
829 | * position the rcu_head structure into the first 4096 bytes. | |
830 | * | |
831 | * Note that the allowable offset might decrease in the future, for example, | |
832 | * to allow something like kmem_cache_free_rcu(). | |
d8169d4c JE |
833 | * |
834 | * The BUILD_BUG_ON check must not involve any function calls, hence the | |
835 | * checks are done in macros here. | |
9ab1544e | 836 | */ |
12edff04 PM |
837 | #define kfree_rcu(ptr, rhf) \ |
838 | do { \ | |
839 | typeof (ptr) ___p = (ptr); \ | |
840 | \ | |
841 | if (___p) \ | |
842 | __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \ | |
843 | } while (0) | |
0edd1b17 | 844 | |
d85b62f1 PM |
845 | /* |
846 | * Place this after a lock-acquisition primitive to guarantee that | |
847 | * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies | |
848 | * if the UNLOCK and LOCK are executed by the same CPU or if the | |
849 | * UNLOCK and LOCK operate on the same lock variable. | |
850 | */ | |
77e58496 | 851 | #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
d85b62f1 | 852 | #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
77e58496 | 853 | #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 854 | #define smp_mb__after_unlock_lock() do { } while (0) |
77e58496 | 855 | #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 856 | |
274529ba | 857 | |
74de6960 PM |
858 | /* Has the specified rcu_head structure been handed to call_rcu()? */ |
859 | ||
2aa55030 | 860 | /** |
74de6960 PM |
861 | * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() |
862 | * @rhp: The rcu_head structure to initialize. | |
863 | * | |
864 | * If you intend to invoke rcu_head_after_call_rcu() to test whether a | |
865 | * given rcu_head structure has already been passed to call_rcu(), then | |
866 | * you must also invoke this rcu_head_init() function on it just after | |
867 | * allocating that structure. Calls to this function must not race with | |
868 | * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. | |
869 | */ | |
870 | static inline void rcu_head_init(struct rcu_head *rhp) | |
871 | { | |
872 | rhp->func = (rcu_callback_t)~0L; | |
873 | } | |
874 | ||
2aa55030 | 875 | /** |
74de6960 PM |
876 | * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()? |
877 | * @rhp: The rcu_head structure to test. | |
2aa55030 | 878 | * @f: The function passed to call_rcu() along with @rhp. |
74de6960 PM |
879 | * |
880 | * Returns @true if the @rhp has been passed to call_rcu() with @func, | |
881 | * and @false otherwise. Emits a warning in any other case, including | |
882 | * the case where @rhp has already been invoked after a grace period. | |
883 | * Calls to this function must not race with callback invocation. One way | |
884 | * to avoid such races is to enclose the call to rcu_head_after_call_rcu() | |
885 | * in an RCU read-side critical section that includes a read-side fetch | |
886 | * of the pointer to the structure containing @rhp. | |
887 | */ | |
888 | static inline bool | |
889 | rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) | |
890 | { | |
b699cce1 NU |
891 | rcu_callback_t func = READ_ONCE(rhp->func); |
892 | ||
893 | if (func == f) | |
74de6960 | 894 | return true; |
b699cce1 | 895 | WARN_ON_ONCE(func != (rcu_callback_t)~0L); |
74de6960 PM |
896 | return false; |
897 | } | |
898 | ||
e1350e8e BD |
899 | /* kernel/ksysfs.c definitions */ |
900 | extern int rcu_expedited; | |
901 | extern int rcu_normal; | |
902 | ||
1da177e4 | 903 | #endif /* __LINUX_RCUPDATE_H */ |