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1 : : /* SPDX-License-Identifier: GPL-2.0+ */
2 : : /*
3 : : * Read-Copy Update mechanism for mutual exclusion
4 : : *
5 : : * Copyright IBM Corporation, 2001
6 : : *
7 : : * Author: Dipankar Sarma <dipankar@in.ibm.com>
8 : : *
9 : : * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
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 -
16 : : * http://lse.sourceforge.net/locking/rcupdate.html
17 : : *
18 : : */
19 : :
20 : : #ifndef __LINUX_RCUPDATE_H
21 : : #define __LINUX_RCUPDATE_H
22 : :
23 : : #include <linux/types.h>
24 : : #include <linux/compiler.h>
25 : : #include <linux/atomic.h>
26 : : #include <linux/irqflags.h>
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>
32 : :
33 : : #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
34 : : #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
35 : : #define ulong2long(a) (*(long *)(&(a)))
36 : :
37 : : /* Exported common interfaces */
38 : : void call_rcu(struct rcu_head *head, rcu_callback_t func);
39 : : void rcu_barrier_tasks(void);
40 : : void synchronize_rcu(void);
41 : :
42 : : #ifdef CONFIG_PREEMPT_RCU
43 : :
44 : : void __rcu_read_lock(void);
45 : : void __rcu_read_unlock(void);
46 : :
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 : :
55 : : #else /* #ifdef CONFIG_PREEMPT_RCU */
56 : :
57 : 784782749 : static inline void __rcu_read_lock(void)
58 : : {
59 : 784782749 : preempt_disable();
60 : 784162275 : }
61 : :
62 : : static inline void __rcu_read_unlock(void)
63 : : {
64 : 776414905 : preempt_enable();
65 : : }
66 : :
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 */
75 : : void rcu_init(void);
76 : : extern int rcu_scheduler_active __read_mostly;
77 : : void rcu_sched_clock_irq(int user);
78 : : void rcu_report_dead(unsigned int cpu);
79 : : void rcutree_migrate_callbacks(int cpu);
80 : :
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 */
85 : : static inline void rcu_sysrq_start(void) { }
86 : : static inline void rcu_sysrq_end(void) { }
87 : : #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
88 : :
89 : : #ifdef CONFIG_NO_HZ_FULL
90 : : void rcu_user_enter(void);
91 : : void rcu_user_exit(void);
92 : : #else
93 : : static inline void rcu_user_enter(void) { }
94 : : static inline void rcu_user_exit(void) { }
95 : : #endif /* CONFIG_NO_HZ_FULL */
96 : :
97 : : #ifdef CONFIG_RCU_NOCB_CPU
98 : : void rcu_init_nohz(void);
99 : : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
100 : : static inline void rcu_init_nohz(void) { }
101 : : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
102 : :
103 : : /**
104 : : * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
105 : : * @a: Code that RCU needs to pay attention to.
106 : : *
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.
111 : : *
112 : : * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
113 : : * will tell RCU that it needs to pay attention, invoke its argument
114 : : * (in this example, calling the do_something_with_RCU() function),
115 : : * and then tell RCU to go back to ignoring this CPU. It is permissible
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.
120 : : */
121 : : #define RCU_NONIDLE(a) \
122 : : do { \
123 : : rcu_irq_enter_irqson(); \
124 : : do { a; } while (0); \
125 : : rcu_irq_exit_irqson(); \
126 : : } while (0)
127 : :
128 : : /*
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.
131 : : */
132 : : #ifdef CONFIG_TASKS_RCU
133 : : #define rcu_tasks_qs(t) \
134 : : do { \
135 : : if (READ_ONCE((t)->rcu_tasks_holdout)) \
136 : : WRITE_ONCE((t)->rcu_tasks_holdout, false); \
137 : : } while (0)
138 : : #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t)
139 : : void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
140 : : void synchronize_rcu_tasks(void);
141 : : void exit_tasks_rcu_start(void);
142 : : void exit_tasks_rcu_finish(void);
143 : : #else /* #ifdef CONFIG_TASKS_RCU */
144 : : #define rcu_tasks_qs(t) do { } while (0)
145 : : #define rcu_note_voluntary_context_switch(t) do { } while (0)
146 : : #define call_rcu_tasks call_rcu
147 : : #define synchronize_rcu_tasks synchronize_rcu
148 : : static inline void exit_tasks_rcu_start(void) { }
149 : : static inline void exit_tasks_rcu_finish(void) { }
150 : : #endif /* #else #ifdef CONFIG_TASKS_RCU */
151 : :
152 : : /**
153 : : * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
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()
157 : : * machinery were to be shut off, as some advocate for PREEMPT kernels.
158 : : */
159 : : #define cond_resched_tasks_rcu_qs() \
160 : : do { \
161 : : rcu_tasks_qs(current); \
162 : : cond_resched(); \
163 : : } while (0)
164 : :
165 : : /*
166 : : * Infrastructure to implement the synchronize_() primitives in
167 : : * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
168 : : */
169 : :
170 : : #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
171 : : #include <linux/rcutree.h>
172 : : #elif defined(CONFIG_TINY_RCU)
173 : : #include <linux/rcutiny.h>
174 : : #else
175 : : #error "Unknown RCU implementation specified to kernel configuration"
176 : : #endif
177 : :
178 : : /*
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.
185 : : */
186 : : #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
187 : : void init_rcu_head(struct rcu_head *head);
188 : : void destroy_rcu_head(struct rcu_head *head);
189 : : void init_rcu_head_on_stack(struct rcu_head *head);
190 : : void destroy_rcu_head_on_stack(struct rcu_head *head);
191 : : #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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) { }
196 : : #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
197 : :
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) */
201 : : static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
202 : : #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
203 : :
204 : : #ifdef CONFIG_DEBUG_LOCK_ALLOC
205 : :
206 : : static inline void rcu_lock_acquire(struct lockdep_map *map)
207 : : {
208 : : lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
209 : : }
210 : :
211 : : static inline void rcu_lock_release(struct lockdep_map *map)
212 : : {
213 : : lock_release(map, 1, _THIS_IP_);
214 : : }
215 : :
216 : : extern struct lockdep_map rcu_lock_map;
217 : : extern struct lockdep_map rcu_bh_lock_map;
218 : : extern struct lockdep_map rcu_sched_lock_map;
219 : : extern struct lockdep_map rcu_callback_map;
220 : : int debug_lockdep_rcu_enabled(void);
221 : : int rcu_read_lock_held(void);
222 : : int rcu_read_lock_bh_held(void);
223 : : int rcu_read_lock_sched_held(void);
224 : : int rcu_read_lock_any_held(void);
225 : :
226 : : #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
227 : :
228 : : # define rcu_lock_acquire(a) do { } while (0)
229 : : # define rcu_lock_release(a) do { } while (0)
230 : :
231 : 0 : static inline int rcu_read_lock_held(void)
232 : : {
233 : 0 : 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 : : {
243 : : return !preemptible();
244 : : }
245 : :
246 : : static inline int rcu_read_lock_any_held(void)
247 : : {
248 : : return !preemptible();
249 : : }
250 : :
251 : : #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
252 : :
253 : : #ifdef CONFIG_PROVE_RCU
254 : :
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 : :
269 : : #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
270 : : static inline void rcu_preempt_sleep_check(void)
271 : : {
272 : : RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
273 : : "Illegal context switch in RCU read-side critical section");
274 : : }
275 : : #else /* #ifdef CONFIG_PROVE_RCU */
276 : : static inline void rcu_preempt_sleep_check(void) { }
277 : : #endif /* #else #ifdef CONFIG_PROVE_RCU */
278 : :
279 : : #define rcu_sleep_check() \
280 : : do { \
281 : : rcu_preempt_sleep_check(); \
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"); \
286 : : } while (0)
287 : :
288 : : #else /* #ifdef CONFIG_PROVE_RCU */
289 : :
290 : : #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
291 : : #define rcu_sleep_check() do { } while (0)
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
299 : : * multiple pointers markings to match different RCU implementations
300 : : * (e.g., __srcu), should this make sense in the future.
301 : : */
302 : :
303 : : #ifdef __CHECKER__
304 : : #define rcu_check_sparse(p, space) \
305 : : ((void)(((typeof(*p) space *)p) == p))
306 : : #else /* #ifdef __CHECKER__ */
307 : : #define rcu_check_sparse(p, space)
308 : : #endif /* #else #ifdef __CHECKER__ */
309 : :
310 : : #define __rcu_access_pointer(p, space) \
311 : : ({ \
312 : : typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
313 : : rcu_check_sparse(p, space); \
314 : : ((typeof(*p) __force __kernel *)(_________p1)); \
315 : : })
316 : : #define __rcu_dereference_check(p, c, space) \
317 : : ({ \
318 : : /* Dependency order vs. p above. */ \
319 : : typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
320 : : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
321 : : rcu_check_sparse(p, space); \
322 : : ((typeof(*p) __force __kernel *)(________p1)); \
323 : : })
324 : : #define __rcu_dereference_protected(p, c, space) \
325 : : ({ \
326 : : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
327 : : rcu_check_sparse(p, space); \
328 : : ((typeof(*p) __force __kernel *)(p)); \
329 : : })
330 : : #define rcu_dereference_raw(p) \
331 : : ({ \
332 : : /* Dependency order vs. p above. */ \
333 : : typeof(p) ________p1 = READ_ONCE(p); \
334 : : ((typeof(*p) __force __kernel *)(________p1)); \
335 : : })
336 : :
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 : : */
374 : : #define rcu_assign_pointer(p, v) \
375 : : do { \
376 : : uintptr_t _r_a_p__v = (uintptr_t)(v); \
377 : : rcu_check_sparse(p, __rcu); \
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)); \
383 : : } while (0)
384 : :
385 : : /**
386 : : * rcu_swap_protected() - swap an RCU and a regular pointer
387 : : * @rcu_ptr: RCU pointer
388 : : * @ptr: regular pointer
389 : : * @c: the conditions under which the dereference will take place
390 : : *
391 : : * Perform swap(@rcu_ptr, @ptr) where @rcu_ptr is an RCU-annotated pointer and
392 : : * @c is the argument that is passed to the rcu_dereference_protected() call
393 : : * used to read that pointer.
394 : : */
395 : : #define rcu_swap_protected(rcu_ptr, ptr, c) do { \
396 : : typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
397 : : rcu_assign_pointer((rcu_ptr), (ptr)); \
398 : : (ptr) = __tmp; \
399 : : } while (0)
400 : :
401 : : /**
402 : : * rcu_access_pointer() - fetch RCU pointer with no dereferencing
403 : : * @p: The pointer to read
404 : : *
405 : : * Return the value of the specified RCU-protected pointer, but omit the
406 : : * lockdep checks for being in an RCU read-side critical section. This is
407 : : * useful when the value of this pointer is accessed, but the pointer is
408 : : * not dereferenced, for example, when testing an RCU-protected pointer
409 : : * against NULL. Although rcu_access_pointer() may also be used in cases
410 : : * where update-side locks prevent the value of the pointer from changing,
411 : : * you should instead use rcu_dereference_protected() for this use case.
412 : : *
413 : : * It is also permissible to use rcu_access_pointer() when read-side
414 : : * access to the pointer was removed at least one grace period ago, as
415 : : * is the case in the context of the RCU callback that is freeing up
416 : : * the data, or after a synchronize_rcu() returns. This can be useful
417 : : * when tearing down multi-linked structures after a grace period
418 : : * has elapsed.
419 : : */
420 : : #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
421 : :
422 : : /**
423 : : * rcu_dereference_check() - rcu_dereference with debug checking
424 : : * @p: The pointer to read, prior to dereferencing
425 : : * @c: The conditions under which the dereference will take place
426 : : *
427 : : * Do an rcu_dereference(), but check that the conditions under which the
428 : : * dereference will take place are correct. Typically the conditions
429 : : * indicate the various locking conditions that should be held at that
430 : : * point. The check should return true if the conditions are satisfied.
431 : : * An implicit check for being in an RCU read-side critical section
432 : : * (rcu_read_lock()) is included.
433 : : *
434 : : * For example:
435 : : *
436 : : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
437 : : *
438 : : * could be used to indicate to lockdep that foo->bar may only be dereferenced
439 : : * if either rcu_read_lock() is held, or that the lock required to replace
440 : : * the bar struct at foo->bar is held.
441 : : *
442 : : * Note that the list of conditions may also include indications of when a lock
443 : : * need not be held, for example during initialisation or destruction of the
444 : : * target struct:
445 : : *
446 : : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
447 : : * atomic_read(&foo->usage) == 0);
448 : : *
449 : : * Inserts memory barriers on architectures that require them
450 : : * (currently only the Alpha), prevents the compiler from refetching
451 : : * (and from merging fetches), and, more importantly, documents exactly
452 : : * which pointers are protected by RCU and checks that the pointer is
453 : : * annotated as __rcu.
454 : : */
455 : : #define rcu_dereference_check(p, c) \
456 : : __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
457 : :
458 : : /**
459 : : * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
460 : : * @p: The pointer to read, prior to dereferencing
461 : : * @c: The conditions under which the dereference will take place
462 : : *
463 : : * This is the RCU-bh counterpart to rcu_dereference_check().
464 : : */
465 : : #define rcu_dereference_bh_check(p, c) \
466 : : __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
467 : :
468 : : /**
469 : : * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
470 : : * @p: The pointer to read, prior to dereferencing
471 : : * @c: The conditions under which the dereference will take place
472 : : *
473 : : * This is the RCU-sched counterpart to rcu_dereference_check().
474 : : */
475 : : #define rcu_dereference_sched_check(p, c) \
476 : : __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
477 : : __rcu)
478 : :
479 : : /*
480 : : * The tracing infrastructure traces RCU (we want that), but unfortunately
481 : : * some of the RCU checks causes tracing to lock up the system.
482 : : *
483 : : * The no-tracing version of rcu_dereference_raw() must not call
484 : : * rcu_read_lock_held().
485 : : */
486 : : #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
487 : :
488 : : /**
489 : : * rcu_dereference_protected() - fetch RCU pointer when updates prevented
490 : : * @p: The pointer to read, prior to dereferencing
491 : : * @c: The conditions under which the dereference will take place
492 : : *
493 : : * Return the value of the specified RCU-protected pointer, but omit
494 : : * the READ_ONCE(). This is useful in cases where update-side locks
495 : : * prevent the value of the pointer from changing. Please note that this
496 : : * primitive does *not* prevent the compiler from repeating this reference
497 : : * or combining it with other references, so it should not be used without
498 : : * protection of appropriate locks.
499 : : *
500 : : * This function is only for update-side use. Using this function
501 : : * when protected only by rcu_read_lock() will result in infrequent
502 : : * but very ugly failures.
503 : : */
504 : : #define rcu_dereference_protected(p, c) \
505 : : __rcu_dereference_protected((p), (c), __rcu)
506 : :
507 : :
508 : : /**
509 : : * rcu_dereference() - fetch RCU-protected pointer for dereferencing
510 : : * @p: The pointer to read, prior to dereferencing
511 : : *
512 : : * This is a simple wrapper around rcu_dereference_check().
513 : : */
514 : : #define rcu_dereference(p) rcu_dereference_check(p, 0)
515 : :
516 : : /**
517 : : * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
518 : : * @p: The pointer to read, prior to dereferencing
519 : : *
520 : : * Makes rcu_dereference_check() do the dirty work.
521 : : */
522 : : #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
523 : :
524 : : /**
525 : : * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
526 : : * @p: The pointer to read, prior to dereferencing
527 : : *
528 : : * Makes rcu_dereference_check() do the dirty work.
529 : : */
530 : : #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
531 : :
532 : : /**
533 : : * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
534 : : * @p: The pointer to hand off
535 : : *
536 : : * This is simply an identity function, but it documents where a pointer
537 : : * is handed off from RCU to some other synchronization mechanism, for
538 : : * example, reference counting or locking. In C11, it would map to
539 : : * kill_dependency(). It could be used as follows::
540 : : *
541 : : * rcu_read_lock();
542 : : * p = rcu_dereference(gp);
543 : : * long_lived = is_long_lived(p);
544 : : * if (long_lived) {
545 : : * if (!atomic_inc_not_zero(p->refcnt))
546 : : * long_lived = false;
547 : : * else
548 : : * p = rcu_pointer_handoff(p);
549 : : * }
550 : : * rcu_read_unlock();
551 : : */
552 : : #define rcu_pointer_handoff(p) (p)
553 : :
554 : : /**
555 : : * rcu_read_lock() - mark the beginning of an RCU read-side critical section
556 : : *
557 : : * When synchronize_rcu() is invoked on one CPU while other CPUs
558 : : * are within RCU read-side critical sections, then the
559 : : * synchronize_rcu() is guaranteed to block until after all the other
560 : : * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
561 : : * on one CPU while other CPUs are within RCU read-side critical
562 : : * sections, invocation of the corresponding RCU callback is deferred
563 : : * until after the all the other CPUs exit their critical sections.
564 : : *
565 : : * Note, however, that RCU callbacks are permitted to run concurrently
566 : : * with new RCU read-side critical sections. One way that this can happen
567 : : * is via the following sequence of events: (1) CPU 0 enters an RCU
568 : : * read-side critical section, (2) CPU 1 invokes call_rcu() to register
569 : : * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
570 : : * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
571 : : * callback is invoked. This is legal, because the RCU read-side critical
572 : : * section that was running concurrently with the call_rcu() (and which
573 : : * therefore might be referencing something that the corresponding RCU
574 : : * callback would free up) has completed before the corresponding
575 : : * RCU callback is invoked.
576 : : *
577 : : * RCU read-side critical sections may be nested. Any deferred actions
578 : : * will be deferred until the outermost RCU read-side critical section
579 : : * completes.
580 : : *
581 : : * You can avoid reading and understanding the next paragraph by
582 : : * following this rule: don't put anything in an rcu_read_lock() RCU
583 : : * read-side critical section that would block in a !PREEMPT kernel.
584 : : * But if you want the full story, read on!
585 : : *
586 : : * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
587 : : * it is illegal to block while in an RCU read-side critical section.
588 : : * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
589 : : * kernel builds, RCU read-side critical sections may be preempted,
590 : : * but explicit blocking is illegal. Finally, in preemptible RCU
591 : : * implementations in real-time (with -rt patchset) kernel builds, RCU
592 : : * read-side critical sections may be preempted and they may also block, but
593 : : * only when acquiring spinlocks that are subject to priority inheritance.
594 : : */
595 : : static __always_inline void rcu_read_lock(void)
596 : : {
597 : 784764104 : __rcu_read_lock();
598 : : __acquire(RCU);
599 : : rcu_lock_acquire(&rcu_lock_map);
600 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
601 : : "rcu_read_lock() used illegally while idle");
602 : : }
603 : :
604 : : /*
605 : : * So where is rcu_write_lock()? It does not exist, as there is no
606 : : * way for writers to lock out RCU readers. This is a feature, not
607 : : * a bug -- this property is what provides RCU's performance benefits.
608 : : * Of course, writers must coordinate with each other. The normal
609 : : * spinlock primitives work well for this, but any other technique may be
610 : : * used as well. RCU does not care how the writers keep out of each
611 : : * others' way, as long as they do so.
612 : : */
613 : :
614 : : /**
615 : : * rcu_read_unlock() - marks the end of an RCU read-side critical section.
616 : : *
617 : : * In most situations, rcu_read_unlock() is immune from deadlock.
618 : : * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
619 : : * is responsible for deboosting, which it does via rt_mutex_unlock().
620 : : * Unfortunately, this function acquires the scheduler's runqueue and
621 : : * priority-inheritance spinlocks. This means that deadlock could result
622 : : * if the caller of rcu_read_unlock() already holds one of these locks or
623 : : * any lock that is ever acquired while holding them.
624 : : *
625 : : * That said, RCU readers are never priority boosted unless they were
626 : : * preempted. Therefore, one way to avoid deadlock is to make sure
627 : : * that preemption never happens within any RCU read-side critical
628 : : * section whose outermost rcu_read_unlock() is called with one of
629 : : * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
630 : : * a number of ways, for example, by invoking preempt_disable() before
631 : : * critical section's outermost rcu_read_lock().
632 : : *
633 : : * Given that the set of locks acquired by rt_mutex_unlock() might change
634 : : * at any time, a somewhat more future-proofed approach is to make sure
635 : : * that that preemption never happens within any RCU read-side critical
636 : : * section whose outermost rcu_read_unlock() is called with irqs disabled.
637 : : * This approach relies on the fact that rt_mutex_unlock() currently only
638 : : * acquires irq-disabled locks.
639 : : *
640 : : * The second of these two approaches is best in most situations,
641 : : * however, the first approach can also be useful, at least to those
642 : : * developers willing to keep abreast of the set of locks acquired by
643 : : * rt_mutex_unlock().
644 : : *
645 : : * See rcu_read_lock() for more information.
646 : : */
647 : 0 : static inline void rcu_read_unlock(void)
648 : : {
649 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
650 : : "rcu_read_unlock() used illegally while idle");
651 : : __release(RCU);
652 : : __rcu_read_unlock();
653 : : rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
654 : 0 : }
655 : :
656 : : /**
657 : : * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
658 : : *
659 : : * This is equivalent of rcu_read_lock(), but also disables softirqs.
660 : : * Note that anything else that disables softirqs can also serve as
661 : : * an RCU read-side critical section.
662 : : *
663 : : * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
664 : : * must occur in the same context, for example, it is illegal to invoke
665 : : * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
666 : : * was invoked from some other task.
667 : : */
668 : : static inline void rcu_read_lock_bh(void)
669 : : {
670 : : local_bh_disable();
671 : : __acquire(RCU_BH);
672 : : rcu_lock_acquire(&rcu_bh_lock_map);
673 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
674 : : "rcu_read_lock_bh() used illegally while idle");
675 : : }
676 : :
677 : : /*
678 : : * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
679 : : *
680 : : * See rcu_read_lock_bh() for more information.
681 : : */
682 : : static inline void rcu_read_unlock_bh(void)
683 : : {
684 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
685 : : "rcu_read_unlock_bh() used illegally while idle");
686 : : rcu_lock_release(&rcu_bh_lock_map);
687 : : __release(RCU_BH);
688 : : local_bh_enable();
689 : : }
690 : :
691 : : /**
692 : : * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
693 : : *
694 : : * This is equivalent of rcu_read_lock(), but disables preemption.
695 : : * Read-side critical sections can also be introduced by anything else
696 : : * that disables preemption, including local_irq_disable() and friends.
697 : : *
698 : : * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
699 : : * must occur in the same context, for example, it is illegal to invoke
700 : : * rcu_read_unlock_sched() from process context if the matching
701 : : * rcu_read_lock_sched() was invoked from an NMI handler.
702 : : */
703 : : static inline void rcu_read_lock_sched(void)
704 : : {
705 : 35801910 : preempt_disable();
706 : : __acquire(RCU_SCHED);
707 : : rcu_lock_acquire(&rcu_sched_lock_map);
708 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
709 : : "rcu_read_lock_sched() used illegally while idle");
710 : : }
711 : :
712 : : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
713 : : static inline notrace void rcu_read_lock_sched_notrace(void)
714 : : {
715 : : preempt_disable_notrace();
716 : : __acquire(RCU_SCHED);
717 : : }
718 : :
719 : : /*
720 : : * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
721 : : *
722 : : * See rcu_read_lock_sched for more information.
723 : : */
724 : : static inline void rcu_read_unlock_sched(void)
725 : : {
726 : : RCU_LOCKDEP_WARN(!rcu_is_watching(),
727 : : "rcu_read_unlock_sched() used illegally while idle");
728 : : rcu_lock_release(&rcu_sched_lock_map);
729 : : __release(RCU_SCHED);
730 : 35793793 : preempt_enable();
731 : : }
732 : :
733 : : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
734 : : static inline notrace void rcu_read_unlock_sched_notrace(void)
735 : : {
736 : : __release(RCU_SCHED);
737 : : preempt_enable_notrace();
738 : : }
739 : :
740 : : /**
741 : : * RCU_INIT_POINTER() - initialize an RCU protected pointer
742 : : * @p: The pointer to be initialized.
743 : : * @v: The value to initialized the pointer to.
744 : : *
745 : : * Initialize an RCU-protected pointer in special cases where readers
746 : : * do not need ordering constraints on the CPU or the compiler. These
747 : : * special cases are:
748 : : *
749 : : * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
750 : : * 2. The caller has taken whatever steps are required to prevent
751 : : * RCU readers from concurrently accessing this pointer *or*
752 : : * 3. The referenced data structure has already been exposed to
753 : : * readers either at compile time or via rcu_assign_pointer() *and*
754 : : *
755 : : * a. You have not made *any* reader-visible changes to
756 : : * this structure since then *or*
757 : : * b. It is OK for readers accessing this structure from its
758 : : * new location to see the old state of the structure. (For
759 : : * example, the changes were to statistical counters or to
760 : : * other state where exact synchronization is not required.)
761 : : *
762 : : * Failure to follow these rules governing use of RCU_INIT_POINTER() will
763 : : * result in impossible-to-diagnose memory corruption. As in the structures
764 : : * will look OK in crash dumps, but any concurrent RCU readers might
765 : : * see pre-initialized values of the referenced data structure. So
766 : : * please be very careful how you use RCU_INIT_POINTER()!!!
767 : : *
768 : : * If you are creating an RCU-protected linked structure that is accessed
769 : : * by a single external-to-structure RCU-protected pointer, then you may
770 : : * use RCU_INIT_POINTER() to initialize the internal RCU-protected
771 : : * pointers, but you must use rcu_assign_pointer() to initialize the
772 : : * external-to-structure pointer *after* you have completely initialized
773 : : * the reader-accessible portions of the linked structure.
774 : : *
775 : : * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
776 : : * ordering guarantees for either the CPU or the compiler.
777 : : */
778 : : #define RCU_INIT_POINTER(p, v) \
779 : : do { \
780 : : rcu_check_sparse(p, __rcu); \
781 : : WRITE_ONCE(p, RCU_INITIALIZER(v)); \
782 : : } while (0)
783 : :
784 : : /**
785 : : * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
786 : : * @p: The pointer to be initialized.
787 : : * @v: The value to initialized the pointer to.
788 : : *
789 : : * GCC-style initialization for an RCU-protected pointer in a structure field.
790 : : */
791 : : #define RCU_POINTER_INITIALIZER(p, v) \
792 : : .p = RCU_INITIALIZER(v)
793 : :
794 : : /*
795 : : * Does the specified offset indicate that the corresponding rcu_head
796 : : * structure can be handled by kfree_rcu()?
797 : : */
798 : : #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
799 : :
800 : : /*
801 : : * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
802 : : */
803 : : #define __kfree_rcu(head, offset) \
804 : : do { \
805 : : BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
806 : : kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
807 : : } while (0)
808 : :
809 : : /**
810 : : * kfree_rcu() - kfree an object after a grace period.
811 : : * @ptr: pointer to kfree
812 : : * @rhf: the name of the struct rcu_head within the type of @ptr.
813 : : *
814 : : * Many rcu callbacks functions just call kfree() on the base structure.
815 : : * These functions are trivial, but their size adds up, and furthermore
816 : : * when they are used in a kernel module, that module must invoke the
817 : : * high-latency rcu_barrier() function at module-unload time.
818 : : *
819 : : * The kfree_rcu() function handles this issue. Rather than encoding a
820 : : * function address in the embedded rcu_head structure, kfree_rcu() instead
821 : : * encodes the offset of the rcu_head structure within the base structure.
822 : : * Because the functions are not allowed in the low-order 4096 bytes of
823 : : * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
824 : : * If the offset is larger than 4095 bytes, a compile-time error will
825 : : * be generated in __kfree_rcu(). If this error is triggered, you can
826 : : * either fall back to use of call_rcu() or rearrange the structure to
827 : : * position the rcu_head structure into the first 4096 bytes.
828 : : *
829 : : * Note that the allowable offset might decrease in the future, for example,
830 : : * to allow something like kmem_cache_free_rcu().
831 : : *
832 : : * The BUILD_BUG_ON check must not involve any function calls, hence the
833 : : * checks are done in macros here.
834 : : */
835 : : #define kfree_rcu(ptr, rhf) \
836 : : do { \
837 : : typeof (ptr) ___p = (ptr); \
838 : : \
839 : : if (___p) \
840 : : __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
841 : : } while (0)
842 : :
843 : : /*
844 : : * Place this after a lock-acquisition primitive to guarantee that
845 : : * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
846 : : * if the UNLOCK and LOCK are executed by the same CPU or if the
847 : : * UNLOCK and LOCK operate on the same lock variable.
848 : : */
849 : : #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
850 : : #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
851 : : #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
852 : : #define smp_mb__after_unlock_lock() do { } while (0)
853 : : #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
854 : :
855 : :
856 : : /* Has the specified rcu_head structure been handed to call_rcu()? */
857 : :
858 : : /**
859 : : * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
860 : : * @rhp: The rcu_head structure to initialize.
861 : : *
862 : : * If you intend to invoke rcu_head_after_call_rcu() to test whether a
863 : : * given rcu_head structure has already been passed to call_rcu(), then
864 : : * you must also invoke this rcu_head_init() function on it just after
865 : : * allocating that structure. Calls to this function must not race with
866 : : * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
867 : : */
868 : : static inline void rcu_head_init(struct rcu_head *rhp)
869 : : {
870 : 9964 : rhp->func = (rcu_callback_t)~0L;
871 : : }
872 : :
873 : : /**
874 : : * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
875 : : * @rhp: The rcu_head structure to test.
876 : : * @f: The function passed to call_rcu() along with @rhp.
877 : : *
878 : : * Returns @true if the @rhp has been passed to call_rcu() with @func,
879 : : * and @false otherwise. Emits a warning in any other case, including
880 : : * the case where @rhp has already been invoked after a grace period.
881 : : * Calls to this function must not race with callback invocation. One way
882 : : * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
883 : : * in an RCU read-side critical section that includes a read-side fetch
884 : : * of the pointer to the structure containing @rhp.
885 : : */
886 : : static inline bool
887 : 0 : rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
888 : : {
889 : 0 : rcu_callback_t func = READ_ONCE(rhp->func);
890 : :
891 [ # # ]: 0 : if (func == f)
892 : : return true;
893 [ # # # # ]: 0 : WARN_ON_ONCE(func != (rcu_callback_t)~0L);
894 : : return false;
895 : : }
896 : :
897 : : #endif /* __LINUX_RCUPDATE_H */
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