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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))) |
8b5bd67c PM |
36 | #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) |
37 | #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) | |
a3dc3fb1 | 38 | |
03b042bf | 39 | /* Exported common interfaces */ |
709fdce7 | 40 | void call_rcu(struct rcu_head *head, rcu_callback_t func); |
53c6d4ed | 41 | void rcu_barrier_tasks(void); |
c84aad76 | 42 | void rcu_barrier_tasks_rude(void); |
709fdce7 | 43 | void synchronize_rcu(void); |
8315f422 | 44 | |
a3dc3fb1 PM |
45 | #ifdef CONFIG_PREEMPT_RCU |
46 | ||
584dc4ce TB |
47 | void __rcu_read_lock(void); |
48 | void __rcu_read_unlock(void); | |
7b0b759b | 49 | |
a3dc3fb1 PM |
50 | /* |
51 | * Defined as a macro as it is a very low level header included from | |
52 | * areas that don't even know about current. This gives the rcu_read_lock() | |
53 | * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other | |
54 | * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. | |
55 | */ | |
5fcb3a5f | 56 | #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) |
a3dc3fb1 | 57 | |
7b0b759b PM |
58 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
59 | ||
aa40c138 PM |
60 | #ifdef CONFIG_TINY_RCU |
61 | #define rcu_read_unlock_strict() do { } while (0) | |
62 | #else | |
63 | void rcu_read_unlock_strict(void); | |
64 | #endif | |
65 | ||
7b0b759b PM |
66 | static inline void __rcu_read_lock(void) |
67 | { | |
66be4e66 | 68 | preempt_disable(); |
7b0b759b PM |
69 | } |
70 | ||
71 | static inline void __rcu_read_unlock(void) | |
72 | { | |
66be4e66 | 73 | preempt_enable(); |
aa40c138 | 74 | rcu_read_unlock_strict(); |
7b0b759b PM |
75 | } |
76 | ||
7b0b759b PM |
77 | static inline int rcu_preempt_depth(void) |
78 | { | |
79 | return 0; | |
80 | } | |
81 | ||
82 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ | |
83 | ||
84 | /* Internal to kernel */ | |
584dc4ce | 85 | void rcu_init(void); |
825c5bd2 | 86 | extern int rcu_scheduler_active __read_mostly; |
c98cac60 | 87 | void rcu_sched_clock_irq(int user); |
27d50c7e | 88 | void rcu_report_dead(unsigned int cpu); |
a58163d8 | 89 | void rcutree_migrate_callbacks(int cpu); |
2b1d5024 | 90 | |
1b04fa99 URS |
91 | #ifdef CONFIG_TASKS_RCU_GENERIC |
92 | void rcu_init_tasks_generic(void); | |
93 | #else | |
94 | static inline void rcu_init_tasks_generic(void) { } | |
95 | #endif | |
96 | ||
61f38db3 RR |
97 | #ifdef CONFIG_RCU_STALL_COMMON |
98 | void rcu_sysrq_start(void); | |
99 | void rcu_sysrq_end(void); | |
100 | #else /* #ifdef CONFIG_RCU_STALL_COMMON */ | |
d0df7a34 PM |
101 | static inline void rcu_sysrq_start(void) { } |
102 | static inline void rcu_sysrq_end(void) { } | |
61f38db3 RR |
103 | #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ |
104 | ||
d1ec4c34 | 105 | #ifdef CONFIG_NO_HZ_FULL |
584dc4ce TB |
106 | void rcu_user_enter(void); |
107 | void rcu_user_exit(void); | |
2b1d5024 FW |
108 | #else |
109 | static inline void rcu_user_enter(void) { } | |
110 | static inline void rcu_user_exit(void) { } | |
d1ec4c34 | 111 | #endif /* CONFIG_NO_HZ_FULL */ |
2b1d5024 | 112 | |
f4579fc5 PM |
113 | #ifdef CONFIG_RCU_NOCB_CPU |
114 | void rcu_init_nohz(void); | |
254e11ef | 115 | int rcu_nocb_cpu_offload(int cpu); |
d97b0781 | 116 | int rcu_nocb_cpu_deoffload(int cpu); |
43789ef3 | 117 | void rcu_nocb_flush_deferred_wakeup(void); |
f4579fc5 | 118 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
d0df7a34 | 119 | static inline void rcu_init_nohz(void) { } |
254e11ef | 120 | static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } |
d97b0781 | 121 | static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } |
43789ef3 | 122 | static inline void rcu_nocb_flush_deferred_wakeup(void) { } |
f4579fc5 PM |
123 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ |
124 | ||
8a2ecf47 PM |
125 | /** |
126 | * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers | |
127 | * @a: Code that RCU needs to pay attention to. | |
128 | * | |
2bd8b1a2 PM |
129 | * RCU read-side critical sections are forbidden in the inner idle loop, |
130 | * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU | |
131 | * will happily ignore any such read-side critical sections. However, | |
132 | * things like powertop need tracepoints in the inner idle loop. | |
8a2ecf47 PM |
133 | * |
134 | * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) | |
810ce8b5 PM |
135 | * will tell RCU that it needs to pay attention, invoke its argument |
136 | * (in this example, calling the do_something_with_RCU() function), | |
8a2ecf47 | 137 | * and then tell RCU to go back to ignoring this CPU. It is permissible |
810ce8b5 PM |
138 | * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is |
139 | * on the order of a million or so, even on 32-bit systems). It is | |
140 | * not legal to block within RCU_NONIDLE(), nor is it permissible to | |
141 | * transfer control either into or out of RCU_NONIDLE()'s statement. | |
8a2ecf47 PM |
142 | */ |
143 | #define RCU_NONIDLE(a) \ | |
144 | do { \ | |
7c9906ca | 145 | rcu_irq_enter_irqson(); \ |
8a2ecf47 | 146 | do { a; } while (0); \ |
7c9906ca | 147 | rcu_irq_exit_irqson(); \ |
8a2ecf47 PM |
148 | } while (0) |
149 | ||
8315f422 | 150 | /* |
6f56f714 PM |
151 | * Note a quasi-voluntary context switch for RCU-tasks's benefit. |
152 | * This is a macro rather than an inline function to avoid #include hell. | |
8315f422 | 153 | */ |
5873b8a9 | 154 | #ifdef CONFIG_TASKS_RCU_GENERIC |
43766c3e PM |
155 | |
156 | # ifdef CONFIG_TASKS_RCU | |
157 | # define rcu_tasks_classic_qs(t, preempt) \ | |
158 | do { \ | |
159 | if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ | |
160 | WRITE_ONCE((t)->rcu_tasks_holdout, false); \ | |
8315f422 | 161 | } while (0) |
7e42776d PM |
162 | void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); |
163 | void synchronize_rcu_tasks(void); | |
43766c3e PM |
164 | # else |
165 | # define rcu_tasks_classic_qs(t, preempt) do { } while (0) | |
166 | # define call_rcu_tasks call_rcu | |
167 | # define synchronize_rcu_tasks synchronize_rcu | |
168 | # endif | |
169 | ||
fed31a4d | 170 | # ifdef CONFIG_TASKS_TRACE_RCU |
43766c3e PM |
171 | # define rcu_tasks_trace_qs(t) \ |
172 | do { \ | |
173 | if (!likely(READ_ONCE((t)->trc_reader_checked)) && \ | |
174 | !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \ | |
175 | smp_store_release(&(t)->trc_reader_checked, true); \ | |
176 | smp_mb(); /* Readers partitioned by store. */ \ | |
177 | } \ | |
178 | } while (0) | |
179 | # else | |
180 | # define rcu_tasks_trace_qs(t) do { } while (0) | |
181 | # endif | |
182 | ||
183 | #define rcu_tasks_qs(t, preempt) \ | |
184 | do { \ | |
185 | rcu_tasks_classic_qs((t), (preempt)); \ | |
186 | rcu_tasks_trace_qs((t)); \ | |
187 | } while (0) | |
188 | ||
189 | # ifdef CONFIG_TASKS_RUDE_RCU | |
c84aad76 PM |
190 | void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); |
191 | void synchronize_rcu_tasks_rude(void); | |
43766c3e PM |
192 | # endif |
193 | ||
194 | #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) | |
ccdd29ff PM |
195 | void exit_tasks_rcu_start(void); |
196 | void exit_tasks_rcu_finish(void); | |
5873b8a9 | 197 | #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ |
43766c3e | 198 | #define rcu_tasks_qs(t, preempt) do { } while (0) |
4d232dfe | 199 | #define rcu_note_voluntary_context_switch(t) do { } while (0) |
2bd8b1a2 | 200 | #define call_rcu_tasks call_rcu |
a8bb74ac | 201 | #define synchronize_rcu_tasks synchronize_rcu |
ccdd29ff PM |
202 | static inline void exit_tasks_rcu_start(void) { } |
203 | static inline void exit_tasks_rcu_finish(void) { } | |
5873b8a9 | 204 | #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |
8315f422 | 205 | |
bde6c3aa | 206 | /** |
cee43939 | 207 | * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU |
bde6c3aa PM |
208 | * |
209 | * This macro resembles cond_resched(), except that it is defined to | |
210 | * report potential quiescent states to RCU-tasks even if the cond_resched() | |
90326f05 | 211 | * machinery were to be shut off, as some advocate for PREEMPTION kernels. |
bde6c3aa | 212 | */ |
cee43939 | 213 | #define cond_resched_tasks_rcu_qs() \ |
bde6c3aa | 214 | do { \ |
43766c3e | 215 | rcu_tasks_qs(current, false); \ |
07f27570 | 216 | cond_resched(); \ |
bde6c3aa PM |
217 | } while (0) |
218 | ||
2c42818e PM |
219 | /* |
220 | * Infrastructure to implement the synchronize_() primitives in | |
221 | * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. | |
222 | */ | |
223 | ||
b3e627d3 | 224 | #if defined(CONFIG_TREE_RCU) |
64db4cff | 225 | #include <linux/rcutree.h> |
127781d1 | 226 | #elif defined(CONFIG_TINY_RCU) |
9b1d82fa | 227 | #include <linux/rcutiny.h> |
64db4cff PM |
228 | #else |
229 | #error "Unknown RCU implementation specified to kernel configuration" | |
6b3ef48a | 230 | #endif |
01c1c660 | 231 | |
551d55a9 | 232 | /* |
b5482a06 PM |
233 | * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls |
234 | * are needed for dynamic initialization and destruction of rcu_head | |
235 | * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for | |
236 | * dynamic initialization and destruction of statically allocated rcu_head | |
237 | * structures. However, rcu_head structures allocated dynamically in the | |
238 | * heap don't need any initialization. | |
551d55a9 MD |
239 | */ |
240 | #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD | |
546a9d85 PM |
241 | void init_rcu_head(struct rcu_head *head); |
242 | void destroy_rcu_head(struct rcu_head *head); | |
584dc4ce TB |
243 | void init_rcu_head_on_stack(struct rcu_head *head); |
244 | void destroy_rcu_head_on_stack(struct rcu_head *head); | |
551d55a9 | 245 | #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
d0df7a34 PM |
246 | static inline void init_rcu_head(struct rcu_head *head) { } |
247 | static inline void destroy_rcu_head(struct rcu_head *head) { } | |
248 | static inline void init_rcu_head_on_stack(struct rcu_head *head) { } | |
249 | static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } | |
551d55a9 | 250 | #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ |
4376030a | 251 | |
c0d6d01b PM |
252 | #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) |
253 | bool rcu_lockdep_current_cpu_online(void); | |
254 | #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ | |
17a8c187 | 255 | static inline bool rcu_lockdep_current_cpu_online(void) { return true; } |
c0d6d01b PM |
256 | #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ |
257 | ||
891cd1f9 JK |
258 | extern struct lockdep_map rcu_lock_map; |
259 | extern struct lockdep_map rcu_bh_lock_map; | |
260 | extern struct lockdep_map rcu_sched_lock_map; | |
261 | extern struct lockdep_map rcu_callback_map; | |
262 | ||
bc33f24b | 263 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
632ee200 | 264 | |
00f49e57 FW |
265 | static inline void rcu_lock_acquire(struct lockdep_map *map) |
266 | { | |
fb9edbe9 | 267 | lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); |
00f49e57 FW |
268 | } |
269 | ||
270 | static inline void rcu_lock_release(struct lockdep_map *map) | |
271 | { | |
5facae4f | 272 | lock_release(map, _THIS_IP_); |
00f49e57 FW |
273 | } |
274 | ||
a235c091 | 275 | int debug_lockdep_rcu_enabled(void); |
85b39d30 | 276 | int rcu_read_lock_held(void); |
584dc4ce | 277 | int rcu_read_lock_bh_held(void); |
d5671f6b | 278 | int rcu_read_lock_sched_held(void); |
28875945 | 279 | int rcu_read_lock_any_held(void); |
632ee200 PM |
280 | |
281 | #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
282 | ||
d8ab29f8 PM |
283 | # define rcu_lock_acquire(a) do { } while (0) |
284 | # define rcu_lock_release(a) do { } while (0) | |
632ee200 PM |
285 | |
286 | static inline int rcu_read_lock_held(void) | |
287 | { | |
288 | return 1; | |
289 | } | |
290 | ||
291 | static inline int rcu_read_lock_bh_held(void) | |
292 | { | |
293 | return 1; | |
294 | } | |
295 | ||
296 | static inline int rcu_read_lock_sched_held(void) | |
297 | { | |
293e2421 | 298 | return !preemptible(); |
632ee200 | 299 | } |
28875945 JFG |
300 | |
301 | static inline int rcu_read_lock_any_held(void) | |
302 | { | |
303 | return !preemptible(); | |
304 | } | |
305 | ||
632ee200 PM |
306 | #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
307 | ||
308 | #ifdef CONFIG_PROVE_RCU | |
309 | ||
f78f5b90 PM |
310 | /** |
311 | * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met | |
312 | * @c: condition to check | |
313 | * @s: informative message | |
314 | */ | |
315 | #define RCU_LOCKDEP_WARN(c, s) \ | |
316 | do { \ | |
33def849 | 317 | static bool __section(".data.unlikely") __warned; \ |
30668200 | 318 | if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ |
f78f5b90 PM |
319 | __warned = true; \ |
320 | lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ | |
321 | } \ | |
322 | } while (0) | |
323 | ||
50406b98 PM |
324 | #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) |
325 | static inline void rcu_preempt_sleep_check(void) | |
326 | { | |
f78f5b90 PM |
327 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), |
328 | "Illegal context switch in RCU read-side critical section"); | |
50406b98 PM |
329 | } |
330 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
d0df7a34 | 331 | static inline void rcu_preempt_sleep_check(void) { } |
50406b98 PM |
332 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ |
333 | ||
b3fbab05 PM |
334 | #define rcu_sleep_check() \ |
335 | do { \ | |
50406b98 | 336 | rcu_preempt_sleep_check(); \ |
ba9e6cab TG |
337 | if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ |
338 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ | |
f78f5b90 PM |
339 | "Illegal context switch in RCU-bh read-side critical section"); \ |
340 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ | |
341 | "Illegal context switch in RCU-sched read-side critical section"); \ | |
b3fbab05 PM |
342 | } while (0) |
343 | ||
ca5ecddf PM |
344 | #else /* #ifdef CONFIG_PROVE_RCU */ |
345 | ||
65e9eb1c | 346 | #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) |
b3fbab05 | 347 | #define rcu_sleep_check() do { } while (0) |
ca5ecddf PM |
348 | |
349 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
350 | ||
351 | /* | |
352 | * Helper functions for rcu_dereference_check(), rcu_dereference_protected() | |
353 | * and rcu_assign_pointer(). Some of these could be folded into their | |
354 | * callers, but they are left separate in order to ease introduction of | |
2bd8b1a2 PM |
355 | * multiple pointers markings to match different RCU implementations |
356 | * (e.g., __srcu), should this make sense in the future. | |
ca5ecddf | 357 | */ |
53ecfba2 PM |
358 | |
359 | #ifdef __CHECKER__ | |
423a86a6 | 360 | #define rcu_check_sparse(p, space) \ |
53ecfba2 PM |
361 | ((void)(((typeof(*p) space *)p) == p)) |
362 | #else /* #ifdef __CHECKER__ */ | |
423a86a6 | 363 | #define rcu_check_sparse(p, space) |
53ecfba2 PM |
364 | #endif /* #else #ifdef __CHECKER__ */ |
365 | ||
76c8eaaf PM |
366 | /** |
367 | * unrcu_pointer - mark a pointer as not being RCU protected | |
368 | * @p: pointer needing to lose its __rcu property | |
369 | * | |
370 | * Converts @p from an __rcu pointer to a __kernel pointer. | |
371 | * This allows an __rcu pointer to be used with xchg() and friends. | |
372 | */ | |
373 | #define unrcu_pointer(p) \ | |
374 | ({ \ | |
375 | typeof(*p) *_________p1 = (typeof(*p) *__force)(p); \ | |
376 | rcu_check_sparse(p, __rcu); \ | |
377 | ((typeof(*p) __force __kernel *)(_________p1)); \ | |
378 | }) | |
379 | ||
ca5ecddf | 380 | #define __rcu_access_pointer(p, space) \ |
0adab9b9 | 381 | ({ \ |
7d0ae808 | 382 | typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
423a86a6 | 383 | rcu_check_sparse(p, space); \ |
0adab9b9 JP |
384 | ((typeof(*p) __force __kernel *)(_________p1)); \ |
385 | }) | |
ca5ecddf | 386 | #define __rcu_dereference_check(p, c, space) \ |
0adab9b9 | 387 | ({ \ |
ac59853c | 388 | /* Dependency order vs. p above. */ \ |
506458ef | 389 | typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \ |
f78f5b90 | 390 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ |
423a86a6 | 391 | rcu_check_sparse(p, space); \ |
ac59853c | 392 | ((typeof(*p) __force __kernel *)(________p1)); \ |
0adab9b9 | 393 | }) |
ca5ecddf | 394 | #define __rcu_dereference_protected(p, c, space) \ |
0adab9b9 | 395 | ({ \ |
f78f5b90 | 396 | RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ |
423a86a6 | 397 | rcu_check_sparse(p, space); \ |
0adab9b9 JP |
398 | ((typeof(*p) __force __kernel *)(p)); \ |
399 | }) | |
995f1405 PM |
400 | #define rcu_dereference_raw(p) \ |
401 | ({ \ | |
402 | /* Dependency order vs. p above. */ \ | |
506458ef | 403 | typeof(p) ________p1 = READ_ONCE(p); \ |
995f1405 PM |
404 | ((typeof(*p) __force __kernel *)(________p1)); \ |
405 | }) | |
ca5ecddf | 406 | |
462225ae PM |
407 | /** |
408 | * RCU_INITIALIZER() - statically initialize an RCU-protected global variable | |
409 | * @v: The value to statically initialize with. | |
410 | */ | |
411 | #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) | |
412 | ||
413 | /** | |
414 | * rcu_assign_pointer() - assign to RCU-protected pointer | |
415 | * @p: pointer to assign to | |
416 | * @v: value to assign (publish) | |
417 | * | |
418 | * Assigns the specified value to the specified RCU-protected | |
419 | * pointer, ensuring that any concurrent RCU readers will see | |
420 | * any prior initialization. | |
421 | * | |
422 | * Inserts memory barriers on architectures that require them | |
423 | * (which is most of them), and also prevents the compiler from | |
424 | * reordering the code that initializes the structure after the pointer | |
425 | * assignment. More importantly, this call documents which pointers | |
426 | * will be dereferenced by RCU read-side code. | |
427 | * | |
428 | * In some special cases, you may use RCU_INIT_POINTER() instead | |
429 | * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due | |
430 | * to the fact that it does not constrain either the CPU or the compiler. | |
431 | * That said, using RCU_INIT_POINTER() when you should have used | |
432 | * rcu_assign_pointer() is a very bad thing that results in | |
433 | * impossible-to-diagnose memory corruption. So please be careful. | |
434 | * See the RCU_INIT_POINTER() comment header for details. | |
435 | * | |
436 | * Note that rcu_assign_pointer() evaluates each of its arguments only | |
437 | * once, appearances notwithstanding. One of the "extra" evaluations | |
438 | * is in typeof() and the other visible only to sparse (__CHECKER__), | |
439 | * neither of which actually execute the argument. As with most cpp | |
440 | * macros, this execute-arguments-only-once property is important, so | |
441 | * please be careful when making changes to rcu_assign_pointer() and the | |
442 | * other macros that it invokes. | |
443 | */ | |
3a37f727 | 444 | #define rcu_assign_pointer(p, v) \ |
9129b017 | 445 | do { \ |
3a37f727 | 446 | uintptr_t _r_a_p__v = (uintptr_t)(v); \ |
b3119cde | 447 | rcu_check_sparse(p, __rcu); \ |
3a37f727 PM |
448 | \ |
449 | if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ | |
450 | WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ | |
451 | else \ | |
452 | smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ | |
9129b017 | 453 | } while (0) |
ca5ecddf | 454 | |
a63fc6b7 PM |
455 | /** |
456 | * rcu_replace_pointer() - replace an RCU pointer, returning its old value | |
457 | * @rcu_ptr: RCU pointer, whose old value is returned | |
458 | * @ptr: regular pointer | |
459 | * @c: the lockdep conditions under which the dereference will take place | |
460 | * | |
461 | * Perform a replacement, where @rcu_ptr is an RCU-annotated | |
462 | * pointer and @c is the lockdep argument that is passed to the | |
463 | * rcu_dereference_protected() call used to read that pointer. The old | |
464 | * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. | |
465 | */ | |
466 | #define rcu_replace_pointer(rcu_ptr, ptr, c) \ | |
467 | ({ \ | |
468 | typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ | |
469 | rcu_assign_pointer((rcu_ptr), (ptr)); \ | |
470 | __tmp; \ | |
471 | }) | |
472 | ||
ca5ecddf PM |
473 | /** |
474 | * rcu_access_pointer() - fetch RCU pointer with no dereferencing | |
475 | * @p: The pointer to read | |
476 | * | |
477 | * Return the value of the specified RCU-protected pointer, but omit the | |
137f61f6 PM |
478 | * lockdep checks for being in an RCU read-side critical section. This is |
479 | * useful when the value of this pointer is accessed, but the pointer is | |
480 | * not dereferenced, for example, when testing an RCU-protected pointer | |
481 | * against NULL. Although rcu_access_pointer() may also be used in cases | |
482 | * where update-side locks prevent the value of the pointer from changing, | |
483 | * you should instead use rcu_dereference_protected() for this use case. | |
5e1ee6e1 PM |
484 | * |
485 | * It is also permissible to use rcu_access_pointer() when read-side | |
486 | * access to the pointer was removed at least one grace period ago, as | |
487 | * is the case in the context of the RCU callback that is freeing up | |
488 | * the data, or after a synchronize_rcu() returns. This can be useful | |
489 | * when tearing down multi-linked structures after a grace period | |
490 | * has elapsed. | |
ca5ecddf PM |
491 | */ |
492 | #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) | |
493 | ||
632ee200 | 494 | /** |
ca5ecddf | 495 | * rcu_dereference_check() - rcu_dereference with debug checking |
c08c68dd DH |
496 | * @p: The pointer to read, prior to dereferencing |
497 | * @c: The conditions under which the dereference will take place | |
632ee200 | 498 | * |
c08c68dd | 499 | * Do an rcu_dereference(), but check that the conditions under which the |
ca5ecddf PM |
500 | * dereference will take place are correct. Typically the conditions |
501 | * indicate the various locking conditions that should be held at that | |
502 | * point. The check should return true if the conditions are satisfied. | |
503 | * An implicit check for being in an RCU read-side critical section | |
504 | * (rcu_read_lock()) is included. | |
c08c68dd DH |
505 | * |
506 | * For example: | |
507 | * | |
ca5ecddf | 508 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); |
c08c68dd DH |
509 | * |
510 | * could be used to indicate to lockdep that foo->bar may only be dereferenced | |
ca5ecddf | 511 | * if either rcu_read_lock() is held, or that the lock required to replace |
c08c68dd DH |
512 | * the bar struct at foo->bar is held. |
513 | * | |
514 | * Note that the list of conditions may also include indications of when a lock | |
515 | * need not be held, for example during initialisation or destruction of the | |
516 | * target struct: | |
517 | * | |
ca5ecddf | 518 | * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || |
c08c68dd | 519 | * atomic_read(&foo->usage) == 0); |
ca5ecddf PM |
520 | * |
521 | * Inserts memory barriers on architectures that require them | |
522 | * (currently only the Alpha), prevents the compiler from refetching | |
523 | * (and from merging fetches), and, more importantly, documents exactly | |
524 | * which pointers are protected by RCU and checks that the pointer is | |
525 | * annotated as __rcu. | |
632ee200 PM |
526 | */ |
527 | #define rcu_dereference_check(p, c) \ | |
b826565a | 528 | __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu) |
ca5ecddf PM |
529 | |
530 | /** | |
531 | * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking | |
532 | * @p: The pointer to read, prior to dereferencing | |
533 | * @c: The conditions under which the dereference will take place | |
534 | * | |
1893afd6 PM |
535 | * This is the RCU-bh counterpart to rcu_dereference_check(). However, |
536 | * please note that starting in v5.0 kernels, vanilla RCU grace periods | |
537 | * wait for local_bh_disable() regions of code in addition to regions of | |
538 | * code demarked by rcu_read_lock() and rcu_read_unlock(). This means | |
539 | * that synchronize_rcu(), call_rcu, and friends all take not only | |
540 | * rcu_read_lock() but also rcu_read_lock_bh() into account. | |
ca5ecddf PM |
541 | */ |
542 | #define rcu_dereference_bh_check(p, c) \ | |
b826565a | 543 | __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu) |
632ee200 | 544 | |
b62730ba | 545 | /** |
ca5ecddf PM |
546 | * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking |
547 | * @p: The pointer to read, prior to dereferencing | |
548 | * @c: The conditions under which the dereference will take place | |
549 | * | |
550 | * This is the RCU-sched counterpart to rcu_dereference_check(). | |
1893afd6 PM |
551 | * However, please note that starting in v5.0 kernels, vanilla RCU grace |
552 | * periods wait for preempt_disable() regions of code in addition to | |
553 | * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). | |
554 | * This means that synchronize_rcu(), call_rcu, and friends all take not | |
555 | * only rcu_read_lock() but also rcu_read_lock_sched() into account. | |
ca5ecddf PM |
556 | */ |
557 | #define rcu_dereference_sched_check(p, c) \ | |
b826565a | 558 | __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \ |
ca5ecddf PM |
559 | __rcu) |
560 | ||
12bcbe66 SR |
561 | /* |
562 | * The tracing infrastructure traces RCU (we want that), but unfortunately | |
563 | * some of the RCU checks causes tracing to lock up the system. | |
564 | * | |
f039f0af | 565 | * The no-tracing version of rcu_dereference_raw() must not call |
12bcbe66 SR |
566 | * rcu_read_lock_held(). |
567 | */ | |
0a5b99f5 | 568 | #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu) |
12bcbe66 | 569 | |
ca5ecddf PM |
570 | /** |
571 | * rcu_dereference_protected() - fetch RCU pointer when updates prevented | |
572 | * @p: The pointer to read, prior to dereferencing | |
573 | * @c: The conditions under which the dereference will take place | |
b62730ba PM |
574 | * |
575 | * Return the value of the specified RCU-protected pointer, but omit | |
137f61f6 PM |
576 | * the READ_ONCE(). This is useful in cases where update-side locks |
577 | * prevent the value of the pointer from changing. Please note that this | |
578 | * primitive does *not* prevent the compiler from repeating this reference | |
579 | * or combining it with other references, so it should not be used without | |
580 | * protection of appropriate locks. | |
ca5ecddf PM |
581 | * |
582 | * This function is only for update-side use. Using this function | |
583 | * when protected only by rcu_read_lock() will result in infrequent | |
584 | * but very ugly failures. | |
b62730ba PM |
585 | */ |
586 | #define rcu_dereference_protected(p, c) \ | |
ca5ecddf | 587 | __rcu_dereference_protected((p), (c), __rcu) |
b62730ba | 588 | |
bc33f24b | 589 | |
b62730ba | 590 | /** |
ca5ecddf PM |
591 | * rcu_dereference() - fetch RCU-protected pointer for dereferencing |
592 | * @p: The pointer to read, prior to dereferencing | |
b62730ba | 593 | * |
ca5ecddf | 594 | * This is a simple wrapper around rcu_dereference_check(). |
b62730ba | 595 | */ |
ca5ecddf | 596 | #define rcu_dereference(p) rcu_dereference_check(p, 0) |
b62730ba | 597 | |
1da177e4 | 598 | /** |
ca5ecddf PM |
599 | * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing |
600 | * @p: The pointer to read, prior to dereferencing | |
601 | * | |
602 | * Makes rcu_dereference_check() do the dirty work. | |
603 | */ | |
604 | #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) | |
605 | ||
606 | /** | |
607 | * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing | |
608 | * @p: The pointer to read, prior to dereferencing | |
609 | * | |
610 | * Makes rcu_dereference_check() do the dirty work. | |
611 | */ | |
612 | #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) | |
613 | ||
c3ac7cf1 PM |
614 | /** |
615 | * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism | |
616 | * @p: The pointer to hand off | |
617 | * | |
618 | * This is simply an identity function, but it documents where a pointer | |
619 | * is handed off from RCU to some other synchronization mechanism, for | |
620 | * example, reference counting or locking. In C11, it would map to | |
1445e917 MCC |
621 | * kill_dependency(). It could be used as follows:: |
622 | * | |
c3ac7cf1 PM |
623 | * rcu_read_lock(); |
624 | * p = rcu_dereference(gp); | |
625 | * long_lived = is_long_lived(p); | |
626 | * if (long_lived) { | |
627 | * if (!atomic_inc_not_zero(p->refcnt)) | |
628 | * long_lived = false; | |
629 | * else | |
630 | * p = rcu_pointer_handoff(p); | |
631 | * } | |
632 | * rcu_read_unlock(); | |
633 | */ | |
634 | #define rcu_pointer_handoff(p) (p) | |
635 | ||
ca5ecddf PM |
636 | /** |
637 | * rcu_read_lock() - mark the beginning of an RCU read-side critical section | |
1da177e4 | 638 | * |
9b06e818 | 639 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 640 | * are within RCU read-side critical sections, then the |
9b06e818 | 641 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
642 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
643 | * on one CPU while other CPUs are within RCU read-side critical | |
644 | * sections, invocation of the corresponding RCU callback is deferred | |
645 | * until after the all the other CPUs exit their critical sections. | |
646 | * | |
1893afd6 PM |
647 | * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also |
648 | * wait for regions of code with preemption disabled, including regions of | |
649 | * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which | |
650 | * define synchronize_sched(), only code enclosed within rcu_read_lock() | |
651 | * and rcu_read_unlock() are guaranteed to be waited for. | |
652 | * | |
1da177e4 | 653 | * Note, however, that RCU callbacks are permitted to run concurrently |
77d8485a | 654 | * with new RCU read-side critical sections. One way that this can happen |
1da177e4 LT |
655 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
656 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
657 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
658 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
659 | * callback is invoked. This is legal, because the RCU read-side critical | |
660 | * section that was running concurrently with the call_rcu() (and which | |
661 | * therefore might be referencing something that the corresponding RCU | |
662 | * callback would free up) has completed before the corresponding | |
663 | * RCU callback is invoked. | |
664 | * | |
665 | * RCU read-side critical sections may be nested. Any deferred actions | |
666 | * will be deferred until the outermost RCU read-side critical section | |
667 | * completes. | |
668 | * | |
9079fd7c PM |
669 | * You can avoid reading and understanding the next paragraph by |
670 | * following this rule: don't put anything in an rcu_read_lock() RCU | |
90326f05 | 671 | * read-side critical section that would block in a !PREEMPTION kernel. |
9079fd7c PM |
672 | * But if you want the full story, read on! |
673 | * | |
b3e627d3 | 674 | * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), |
ab74fdfd | 675 | * it is illegal to block while in an RCU read-side critical section. |
01b1d88b | 676 | * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION |
ab74fdfd PM |
677 | * kernel builds, RCU read-side critical sections may be preempted, |
678 | * but explicit blocking is illegal. Finally, in preemptible RCU | |
679 | * implementations in real-time (with -rt patchset) kernel builds, RCU | |
680 | * read-side critical sections may be preempted and they may also block, but | |
681 | * only when acquiring spinlocks that are subject to priority inheritance. | |
1da177e4 | 682 | */ |
6da9f775 | 683 | static __always_inline void rcu_read_lock(void) |
bc33f24b PM |
684 | { |
685 | __rcu_read_lock(); | |
686 | __acquire(RCU); | |
d8ab29f8 | 687 | rcu_lock_acquire(&rcu_lock_map); |
f78f5b90 PM |
688 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
689 | "rcu_read_lock() used illegally while idle"); | |
bc33f24b | 690 | } |
1da177e4 | 691 | |
1da177e4 LT |
692 | /* |
693 | * So where is rcu_write_lock()? It does not exist, as there is no | |
694 | * way for writers to lock out RCU readers. This is a feature, not | |
695 | * a bug -- this property is what provides RCU's performance benefits. | |
696 | * Of course, writers must coordinate with each other. The normal | |
697 | * spinlock primitives work well for this, but any other technique may be | |
698 | * used as well. RCU does not care how the writers keep out of each | |
699 | * others' way, as long as they do so. | |
700 | */ | |
3d76c082 PM |
701 | |
702 | /** | |
ca5ecddf | 703 | * rcu_read_unlock() - marks the end of an RCU read-side critical section. |
3d76c082 | 704 | * |
02238460 PM |
705 | * In almost all situations, rcu_read_unlock() is immune from deadlock. |
706 | * In recent kernels that have consolidated synchronize_sched() and | |
707 | * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity | |
708 | * also extends to the scheduler's runqueue and priority-inheritance | |
709 | * spinlocks, courtesy of the quiescent-state deferral that is carried | |
710 | * out when rcu_read_unlock() is invoked with interrupts disabled. | |
f27bc487 | 711 | * |
3d76c082 PM |
712 | * See rcu_read_lock() for more information. |
713 | */ | |
bc33f24b PM |
714 | static inline void rcu_read_unlock(void) |
715 | { | |
f78f5b90 PM |
716 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
717 | "rcu_read_unlock() used illegally while idle"); | |
bc33f24b PM |
718 | __release(RCU); |
719 | __rcu_read_unlock(); | |
d24209bb | 720 | rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ |
bc33f24b | 721 | } |
1da177e4 LT |
722 | |
723 | /** | |
ca5ecddf | 724 | * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section |
1da177e4 | 725 | * |
1893afd6 PM |
726 | * This is equivalent to rcu_read_lock(), but also disables softirqs. |
727 | * Note that anything else that disables softirqs can also serve as an RCU | |
728 | * read-side critical section. However, please note that this equivalence | |
729 | * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and | |
730 | * rcu_read_lock_bh() were unrelated. | |
3842a083 PM |
731 | * |
732 | * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() | |
733 | * must occur in the same context, for example, it is illegal to invoke | |
734 | * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() | |
735 | * was invoked from some other task. | |
1da177e4 | 736 | */ |
bc33f24b PM |
737 | static inline void rcu_read_lock_bh(void) |
738 | { | |
6206ab9b | 739 | local_bh_disable(); |
bc33f24b | 740 | __acquire(RCU_BH); |
d8ab29f8 | 741 | rcu_lock_acquire(&rcu_bh_lock_map); |
f78f5b90 PM |
742 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
743 | "rcu_read_lock_bh() used illegally while idle"); | |
bc33f24b | 744 | } |
1da177e4 | 745 | |
000601bb TK |
746 | /** |
747 | * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section | |
1da177e4 LT |
748 | * |
749 | * See rcu_read_lock_bh() for more information. | |
750 | */ | |
bc33f24b PM |
751 | static inline void rcu_read_unlock_bh(void) |
752 | { | |
f78f5b90 PM |
753 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
754 | "rcu_read_unlock_bh() used illegally while idle"); | |
d8ab29f8 | 755 | rcu_lock_release(&rcu_bh_lock_map); |
bc33f24b | 756 | __release(RCU_BH); |
6206ab9b | 757 | local_bh_enable(); |
bc33f24b | 758 | } |
1da177e4 | 759 | |
1c50b728 | 760 | /** |
ca5ecddf | 761 | * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section |
1c50b728 | 762 | * |
1893afd6 PM |
763 | * This is equivalent to rcu_read_lock(), but also disables preemption. |
764 | * Read-side critical sections can also be introduced by anything else that | |
765 | * disables preemption, including local_irq_disable() and friends. However, | |
766 | * please note that the equivalence to rcu_read_lock() applies only to | |
767 | * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() | |
768 | * were unrelated. | |
3842a083 PM |
769 | * |
770 | * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() | |
771 | * must occur in the same context, for example, it is illegal to invoke | |
772 | * rcu_read_unlock_sched() from process context if the matching | |
773 | * rcu_read_lock_sched() was invoked from an NMI handler. | |
1c50b728 | 774 | */ |
d6714c22 PM |
775 | static inline void rcu_read_lock_sched(void) |
776 | { | |
777 | preempt_disable(); | |
bc33f24b | 778 | __acquire(RCU_SCHED); |
d8ab29f8 | 779 | rcu_lock_acquire(&rcu_sched_lock_map); |
f78f5b90 PM |
780 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
781 | "rcu_read_lock_sched() used illegally while idle"); | |
d6714c22 | 782 | } |
1eba8f84 PM |
783 | |
784 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 785 | static inline notrace void rcu_read_lock_sched_notrace(void) |
d6714c22 PM |
786 | { |
787 | preempt_disable_notrace(); | |
bc33f24b | 788 | __acquire(RCU_SCHED); |
d6714c22 | 789 | } |
1c50b728 | 790 | |
000601bb TK |
791 | /** |
792 | * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section | |
1c50b728 | 793 | * |
000601bb | 794 | * See rcu_read_lock_sched() for more information. |
1c50b728 | 795 | */ |
d6714c22 PM |
796 | static inline void rcu_read_unlock_sched(void) |
797 | { | |
f78f5b90 PM |
798 | RCU_LOCKDEP_WARN(!rcu_is_watching(), |
799 | "rcu_read_unlock_sched() used illegally while idle"); | |
d8ab29f8 | 800 | rcu_lock_release(&rcu_sched_lock_map); |
bc33f24b | 801 | __release(RCU_SCHED); |
d6714c22 PM |
802 | preempt_enable(); |
803 | } | |
1eba8f84 PM |
804 | |
805 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ | |
7c614d64 | 806 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
d6714c22 | 807 | { |
bc33f24b | 808 | __release(RCU_SCHED); |
d6714c22 PM |
809 | preempt_enable_notrace(); |
810 | } | |
1c50b728 | 811 | |
ca5ecddf PM |
812 | /** |
813 | * RCU_INIT_POINTER() - initialize an RCU protected pointer | |
27fdb35f PM |
814 | * @p: The pointer to be initialized. |
815 | * @v: The value to initialized the pointer to. | |
ca5ecddf | 816 | * |
6846c0c5 PM |
817 | * Initialize an RCU-protected pointer in special cases where readers |
818 | * do not need ordering constraints on the CPU or the compiler. These | |
819 | * special cases are: | |
820 | * | |
27fdb35f | 821 | * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* |
6846c0c5 | 822 | * 2. The caller has taken whatever steps are required to prevent |
27fdb35f | 823 | * RCU readers from concurrently accessing this pointer *or* |
6846c0c5 | 824 | * 3. The referenced data structure has already been exposed to |
27fdb35f PM |
825 | * readers either at compile time or via rcu_assign_pointer() *and* |
826 | * | |
827 | * a. You have not made *any* reader-visible changes to | |
828 | * this structure since then *or* | |
6846c0c5 PM |
829 | * b. It is OK for readers accessing this structure from its |
830 | * new location to see the old state of the structure. (For | |
831 | * example, the changes were to statistical counters or to | |
832 | * other state where exact synchronization is not required.) | |
833 | * | |
834 | * Failure to follow these rules governing use of RCU_INIT_POINTER() will | |
835 | * result in impossible-to-diagnose memory corruption. As in the structures | |
836 | * will look OK in crash dumps, but any concurrent RCU readers might | |
837 | * see pre-initialized values of the referenced data structure. So | |
838 | * please be very careful how you use RCU_INIT_POINTER()!!! | |
839 | * | |
840 | * If you are creating an RCU-protected linked structure that is accessed | |
841 | * by a single external-to-structure RCU-protected pointer, then you may | |
842 | * use RCU_INIT_POINTER() to initialize the internal RCU-protected | |
843 | * pointers, but you must use rcu_assign_pointer() to initialize the | |
27fdb35f | 844 | * external-to-structure pointer *after* you have completely initialized |
6846c0c5 | 845 | * the reader-accessible portions of the linked structure. |
71a9b269 PM |
846 | * |
847 | * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no | |
848 | * ordering guarantees for either the CPU or the compiler. | |
ca5ecddf PM |
849 | */ |
850 | #define RCU_INIT_POINTER(p, v) \ | |
d1b88eb9 | 851 | do { \ |
423a86a6 | 852 | rcu_check_sparse(p, __rcu); \ |
155d1d12 | 853 | WRITE_ONCE(p, RCU_INITIALIZER(v)); \ |
d1b88eb9 | 854 | } while (0) |
9ab1544e | 855 | |
172708d0 PM |
856 | /** |
857 | * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer | |
27fdb35f PM |
858 | * @p: The pointer to be initialized. |
859 | * @v: The value to initialized the pointer to. | |
172708d0 PM |
860 | * |
861 | * GCC-style initialization for an RCU-protected pointer in a structure field. | |
862 | */ | |
863 | #define RCU_POINTER_INITIALIZER(p, v) \ | |
462225ae | 864 | .p = RCU_INITIALIZER(v) |
9ab1544e | 865 | |
d8169d4c JE |
866 | /* |
867 | * Does the specified offset indicate that the corresponding rcu_head | |
c408b215 | 868 | * structure can be handled by kvfree_rcu()? |
d8169d4c | 869 | */ |
c408b215 | 870 | #define __is_kvfree_rcu_offset(offset) ((offset) < 4096) |
d8169d4c | 871 | |
9ab1544e LJ |
872 | /** |
873 | * kfree_rcu() - kfree an object after a grace period. | |
5130b8fd URS |
874 | * @ptr: pointer to kfree for both single- and double-argument invocations. |
875 | * @rhf: the name of the struct rcu_head within the type of @ptr, | |
876 | * but only for double-argument invocations. | |
9ab1544e LJ |
877 | * |
878 | * Many rcu callbacks functions just call kfree() on the base structure. | |
879 | * These functions are trivial, but their size adds up, and furthermore | |
880 | * when they are used in a kernel module, that module must invoke the | |
881 | * high-latency rcu_barrier() function at module-unload time. | |
882 | * | |
883 | * The kfree_rcu() function handles this issue. Rather than encoding a | |
884 | * function address in the embedded rcu_head structure, kfree_rcu() instead | |
885 | * encodes the offset of the rcu_head structure within the base structure. | |
886 | * Because the functions are not allowed in the low-order 4096 bytes of | |
887 | * kernel virtual memory, offsets up to 4095 bytes can be accommodated. | |
888 | * If the offset is larger than 4095 bytes, a compile-time error will | |
5ea5d1ed | 889 | * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can |
9ab1544e LJ |
890 | * either fall back to use of call_rcu() or rearrange the structure to |
891 | * position the rcu_head structure into the first 4096 bytes. | |
892 | * | |
893 | * Note that the allowable offset might decrease in the future, for example, | |
894 | * to allow something like kmem_cache_free_rcu(). | |
d8169d4c JE |
895 | * |
896 | * The BUILD_BUG_ON check must not involve any function calls, hence the | |
897 | * checks are done in macros here. | |
9ab1544e | 898 | */ |
e75956bd | 899 | #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf) |
0edd1b17 | 900 | |
ce4dce12 URS |
901 | /** |
902 | * kvfree_rcu() - kvfree an object after a grace period. | |
ce4dce12 | 903 | * |
1835f475 URS |
904 | * This macro consists of one or two arguments and it is |
905 | * based on whether an object is head-less or not. If it | |
906 | * has a head then a semantic stays the same as it used | |
907 | * to be before: | |
908 | * | |
909 | * kvfree_rcu(ptr, rhf); | |
910 | * | |
911 | * where @ptr is a pointer to kvfree(), @rhf is the name | |
912 | * of the rcu_head structure within the type of @ptr. | |
913 | * | |
914 | * When it comes to head-less variant, only one argument | |
915 | * is passed and that is just a pointer which has to be | |
916 | * freed after a grace period. Therefore the semantic is | |
917 | * | |
918 | * kvfree_rcu(ptr); | |
919 | * | |
920 | * where @ptr is a pointer to kvfree(). | |
921 | * | |
922 | * Please note, head-less way of freeing is permitted to | |
923 | * use from a context that has to follow might_sleep() | |
924 | * annotation. Otherwise, please switch and embed the | |
925 | * rcu_head structure within the type of @ptr. | |
ce4dce12 | 926 | */ |
1835f475 URS |
927 | #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \ |
928 | kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__) | |
929 | ||
930 | #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME | |
5130b8fd URS |
931 | #define kvfree_rcu_arg_2(ptr, rhf) \ |
932 | do { \ | |
933 | typeof (ptr) ___p = (ptr); \ | |
934 | \ | |
5ea5d1ed URS |
935 | if (___p) { \ |
936 | BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ | |
937 | kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \ | |
938 | (offsetof(typeof(*(ptr)), rhf))); \ | |
939 | } \ | |
5130b8fd URS |
940 | } while (0) |
941 | ||
1835f475 URS |
942 | #define kvfree_rcu_arg_1(ptr) \ |
943 | do { \ | |
944 | typeof(ptr) ___p = (ptr); \ | |
945 | \ | |
946 | if (___p) \ | |
947 | kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \ | |
948 | } while (0) | |
ce4dce12 | 949 | |
d85b62f1 PM |
950 | /* |
951 | * Place this after a lock-acquisition primitive to guarantee that | |
952 | * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies | |
953 | * if the UNLOCK and LOCK are executed by the same CPU or if the | |
954 | * UNLOCK and LOCK operate on the same lock variable. | |
955 | */ | |
77e58496 | 956 | #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE |
d85b62f1 | 957 | #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ |
77e58496 | 958 | #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 959 | #define smp_mb__after_unlock_lock() do { } while (0) |
77e58496 | 960 | #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ |
d85b62f1 | 961 | |
274529ba | 962 | |
74de6960 PM |
963 | /* Has the specified rcu_head structure been handed to call_rcu()? */ |
964 | ||
2aa55030 | 965 | /** |
74de6960 PM |
966 | * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() |
967 | * @rhp: The rcu_head structure to initialize. | |
968 | * | |
969 | * If you intend to invoke rcu_head_after_call_rcu() to test whether a | |
970 | * given rcu_head structure has already been passed to call_rcu(), then | |
971 | * you must also invoke this rcu_head_init() function on it just after | |
972 | * allocating that structure. Calls to this function must not race with | |
973 | * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. | |
974 | */ | |
975 | static inline void rcu_head_init(struct rcu_head *rhp) | |
976 | { | |
977 | rhp->func = (rcu_callback_t)~0L; | |
978 | } | |
979 | ||
2aa55030 | 980 | /** |
000601bb | 981 | * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? |
74de6960 | 982 | * @rhp: The rcu_head structure to test. |
2aa55030 | 983 | * @f: The function passed to call_rcu() along with @rhp. |
74de6960 PM |
984 | * |
985 | * Returns @true if the @rhp has been passed to call_rcu() with @func, | |
986 | * and @false otherwise. Emits a warning in any other case, including | |
987 | * the case where @rhp has already been invoked after a grace period. | |
988 | * Calls to this function must not race with callback invocation. One way | |
989 | * to avoid such races is to enclose the call to rcu_head_after_call_rcu() | |
990 | * in an RCU read-side critical section that includes a read-side fetch | |
991 | * of the pointer to the structure containing @rhp. | |
992 | */ | |
993 | static inline bool | |
994 | rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) | |
995 | { | |
b699cce1 NU |
996 | rcu_callback_t func = READ_ONCE(rhp->func); |
997 | ||
998 | if (func == f) | |
74de6960 | 999 | return true; |
b699cce1 | 1000 | WARN_ON_ONCE(func != (rcu_callback_t)~0L); |
74de6960 PM |
1001 | return false; |
1002 | } | |
1003 | ||
e1350e8e BD |
1004 | /* kernel/ksysfs.c definitions */ |
1005 | extern int rcu_expedited; | |
1006 | extern int rcu_normal; | |
1007 | ||
1da177e4 | 1008 | #endif /* __LINUX_RCUPDATE_H */ |