Line data Source code
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 : #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)))
38 :
39 : /* Exported common interfaces */
40 : void call_rcu(struct rcu_head *head, rcu_callback_t func);
41 : void rcu_barrier_tasks(void);
42 : void rcu_barrier_tasks_rude(void);
43 : void synchronize_rcu(void);
44 :
45 : #ifdef CONFIG_PREEMPT_RCU
46 :
47 : void __rcu_read_lock(void);
48 : void __rcu_read_unlock(void);
49 :
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 : */
56 : #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
57 :
58 : #else /* #ifdef CONFIG_PREEMPT_RCU */
59 :
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 :
66 1087909 : static inline void __rcu_read_lock(void)
67 : {
68 2176067 : preempt_disable();
69 : }
70 :
71 1088587 : static inline void __rcu_read_unlock(void)
72 : {
73 1088631 : preempt_enable();
74 1088631 : rcu_read_unlock_strict();
75 1088428 : }
76 :
77 3128469 : static inline int rcu_preempt_depth(void)
78 : {
79 3128469 : return 0;
80 : }
81 :
82 : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
83 :
84 : /* Internal to kernel */
85 : void rcu_init(void);
86 : extern int rcu_scheduler_active __read_mostly;
87 : void rcu_sched_clock_irq(int user);
88 : void rcu_report_dead(unsigned int cpu);
89 : void rcutree_migrate_callbacks(int cpu);
90 :
91 : #ifdef CONFIG_TASKS_RCU_GENERIC
92 : void rcu_init_tasks_generic(void);
93 : #else
94 1 : static inline void rcu_init_tasks_generic(void) { }
95 : #endif
96 :
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 */
101 : static inline void rcu_sysrq_start(void) { }
102 : static inline void rcu_sysrq_end(void) { }
103 : #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
104 :
105 : #ifdef CONFIG_NO_HZ_FULL
106 : void rcu_user_enter(void);
107 : void rcu_user_exit(void);
108 : #else
109 : static inline void rcu_user_enter(void) { }
110 : static inline void rcu_user_exit(void) { }
111 : #endif /* CONFIG_NO_HZ_FULL */
112 :
113 : #ifdef CONFIG_RCU_NOCB_CPU
114 : void rcu_init_nohz(void);
115 : int rcu_nocb_cpu_offload(int cpu);
116 : int rcu_nocb_cpu_deoffload(int cpu);
117 : void rcu_nocb_flush_deferred_wakeup(void);
118 : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
119 : static inline void rcu_init_nohz(void) { }
120 : static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
121 : static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
122 512765 : static inline void rcu_nocb_flush_deferred_wakeup(void) { }
123 : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
124 :
125 : /**
126 : * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
127 : * @a: Code that RCU needs to pay attention to.
128 : *
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.
133 : *
134 : * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
135 : * will tell RCU that it needs to pay attention, invoke its argument
136 : * (in this example, calling the do_something_with_RCU() function),
137 : * and then tell RCU to go back to ignoring this CPU. It is permissible
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.
142 : */
143 : #define RCU_NONIDLE(a) \
144 : do { \
145 : rcu_irq_enter_irqson(); \
146 : do { a; } while (0); \
147 : rcu_irq_exit_irqson(); \
148 : } while (0)
149 :
150 : /*
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.
153 : */
154 : #ifdef CONFIG_TASKS_RCU_GENERIC
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); \
161 : } while (0)
162 : void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
163 : void synchronize_rcu_tasks(void);
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 :
170 : # ifdef CONFIG_TASKS_RCU_TRACE
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
190 : void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
191 : void synchronize_rcu_tasks_rude(void);
192 : # endif
193 :
194 : #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
195 : void exit_tasks_rcu_start(void);
196 : void exit_tasks_rcu_finish(void);
197 : #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
198 : #define rcu_tasks_qs(t, preempt) do { } while (0)
199 : #define rcu_note_voluntary_context_switch(t) do { } while (0)
200 : #define call_rcu_tasks call_rcu
201 : #define synchronize_rcu_tasks synchronize_rcu
202 0 : static inline void exit_tasks_rcu_start(void) { }
203 0 : static inline void exit_tasks_rcu_finish(void) { }
204 : #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
205 :
206 : /**
207 : * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
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()
211 : * machinery were to be shut off, as some advocate for PREEMPTION kernels.
212 : */
213 : #define cond_resched_tasks_rcu_qs() \
214 : do { \
215 : rcu_tasks_qs(current, false); \
216 : cond_resched(); \
217 : } while (0)
218 :
219 : /*
220 : * Infrastructure to implement the synchronize_() primitives in
221 : * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
222 : */
223 :
224 : #if defined(CONFIG_TREE_RCU)
225 : #include <linux/rcutree.h>
226 : #elif defined(CONFIG_TINY_RCU)
227 : #include <linux/rcutiny.h>
228 : #else
229 : #error "Unknown RCU implementation specified to kernel configuration"
230 : #endif
231 :
232 : /*
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.
239 : */
240 : #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
241 : void init_rcu_head(struct rcu_head *head);
242 : void destroy_rcu_head(struct rcu_head *head);
243 : void init_rcu_head_on_stack(struct rcu_head *head);
244 : void destroy_rcu_head_on_stack(struct rcu_head *head);
245 : #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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) { }
250 : #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
251 :
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) */
255 : static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
256 : #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
257 :
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 :
263 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
264 :
265 1769342 : static inline void rcu_lock_acquire(struct lockdep_map *map)
266 : {
267 1769342 : lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
268 1769967 : }
269 :
270 1762681 : static inline void rcu_lock_release(struct lockdep_map *map)
271 : {
272 1738431 : lock_release(map, _THIS_IP_);
273 929 : }
274 :
275 : int debug_lockdep_rcu_enabled(void);
276 : int rcu_read_lock_held(void);
277 : int rcu_read_lock_bh_held(void);
278 : int rcu_read_lock_sched_held(void);
279 : int rcu_read_lock_any_held(void);
280 :
281 : #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
282 :
283 : # define rcu_lock_acquire(a) do { } while (0)
284 : # define rcu_lock_release(a) do { } while (0)
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 : {
298 : return !preemptible();
299 : }
300 :
301 : static inline int rcu_read_lock_any_held(void)
302 : {
303 : return !preemptible();
304 : }
305 :
306 : #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
307 :
308 : #ifdef CONFIG_PROVE_RCU
309 :
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 { \
317 : static bool __section(".data.unlikely") __warned; \
318 : if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
319 : __warned = true; \
320 : lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
321 : } \
322 : } while (0)
323 :
324 : #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
325 3157897 : static inline void rcu_preempt_sleep_check(void)
326 : {
327 6316826 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
328 : "Illegal context switch in RCU read-side critical section");
329 3160376 : }
330 : #else /* #ifdef CONFIG_PROVE_RCU */
331 : static inline void rcu_preempt_sleep_check(void) { }
332 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
333 :
334 : #define rcu_sleep_check() \
335 : do { \
336 : rcu_preempt_sleep_check(); \
337 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
338 : "Illegal context switch in RCU-bh read-side critical section"); \
339 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
340 : "Illegal context switch in RCU-sched read-side critical section"); \
341 : } while (0)
342 :
343 : #else /* #ifdef CONFIG_PROVE_RCU */
344 :
345 : #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
346 : #define rcu_sleep_check() do { } while (0)
347 :
348 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
349 :
350 : /*
351 : * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
352 : * and rcu_assign_pointer(). Some of these could be folded into their
353 : * callers, but they are left separate in order to ease introduction of
354 : * multiple pointers markings to match different RCU implementations
355 : * (e.g., __srcu), should this make sense in the future.
356 : */
357 :
358 : #ifdef __CHECKER__
359 : #define rcu_check_sparse(p, space) \
360 : ((void)(((typeof(*p) space *)p) == p))
361 : #else /* #ifdef __CHECKER__ */
362 : #define rcu_check_sparse(p, space)
363 : #endif /* #else #ifdef __CHECKER__ */
364 :
365 : #define __rcu_access_pointer(p, space) \
366 : ({ \
367 : typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
368 : rcu_check_sparse(p, space); \
369 : ((typeof(*p) __force __kernel *)(_________p1)); \
370 : })
371 : #define __rcu_dereference_check(p, c, space) \
372 : ({ \
373 : /* Dependency order vs. p above. */ \
374 : typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
375 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
376 : rcu_check_sparse(p, space); \
377 : ((typeof(*p) __force __kernel *)(________p1)); \
378 : })
379 : #define __rcu_dereference_protected(p, c, space) \
380 : ({ \
381 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
382 : rcu_check_sparse(p, space); \
383 : ((typeof(*p) __force __kernel *)(p)); \
384 : })
385 : #define rcu_dereference_raw(p) \
386 : ({ \
387 : /* Dependency order vs. p above. */ \
388 : typeof(p) ________p1 = READ_ONCE(p); \
389 : ((typeof(*p) __force __kernel *)(________p1)); \
390 : })
391 :
392 : /**
393 : * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
394 : * @v: The value to statically initialize with.
395 : */
396 : #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
397 :
398 : /**
399 : * rcu_assign_pointer() - assign to RCU-protected pointer
400 : * @p: pointer to assign to
401 : * @v: value to assign (publish)
402 : *
403 : * Assigns the specified value to the specified RCU-protected
404 : * pointer, ensuring that any concurrent RCU readers will see
405 : * any prior initialization.
406 : *
407 : * Inserts memory barriers on architectures that require them
408 : * (which is most of them), and also prevents the compiler from
409 : * reordering the code that initializes the structure after the pointer
410 : * assignment. More importantly, this call documents which pointers
411 : * will be dereferenced by RCU read-side code.
412 : *
413 : * In some special cases, you may use RCU_INIT_POINTER() instead
414 : * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
415 : * to the fact that it does not constrain either the CPU or the compiler.
416 : * That said, using RCU_INIT_POINTER() when you should have used
417 : * rcu_assign_pointer() is a very bad thing that results in
418 : * impossible-to-diagnose memory corruption. So please be careful.
419 : * See the RCU_INIT_POINTER() comment header for details.
420 : *
421 : * Note that rcu_assign_pointer() evaluates each of its arguments only
422 : * once, appearances notwithstanding. One of the "extra" evaluations
423 : * is in typeof() and the other visible only to sparse (__CHECKER__),
424 : * neither of which actually execute the argument. As with most cpp
425 : * macros, this execute-arguments-only-once property is important, so
426 : * please be careful when making changes to rcu_assign_pointer() and the
427 : * other macros that it invokes.
428 : */
429 : #define rcu_assign_pointer(p, v) \
430 : do { \
431 : uintptr_t _r_a_p__v = (uintptr_t)(v); \
432 : rcu_check_sparse(p, __rcu); \
433 : \
434 : if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
435 : WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
436 : else \
437 : smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
438 : } while (0)
439 :
440 : /**
441 : * rcu_replace_pointer() - replace an RCU pointer, returning its old value
442 : * @rcu_ptr: RCU pointer, whose old value is returned
443 : * @ptr: regular pointer
444 : * @c: the lockdep conditions under which the dereference will take place
445 : *
446 : * Perform a replacement, where @rcu_ptr is an RCU-annotated
447 : * pointer and @c is the lockdep argument that is passed to the
448 : * rcu_dereference_protected() call used to read that pointer. The old
449 : * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
450 : */
451 : #define rcu_replace_pointer(rcu_ptr, ptr, c) \
452 : ({ \
453 : typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
454 : rcu_assign_pointer((rcu_ptr), (ptr)); \
455 : __tmp; \
456 : })
457 :
458 : /**
459 : * rcu_access_pointer() - fetch RCU pointer with no dereferencing
460 : * @p: The pointer to read
461 : *
462 : * Return the value of the specified RCU-protected pointer, but omit the
463 : * lockdep checks for being in an RCU read-side critical section. This is
464 : * useful when the value of this pointer is accessed, but the pointer is
465 : * not dereferenced, for example, when testing an RCU-protected pointer
466 : * against NULL. Although rcu_access_pointer() may also be used in cases
467 : * where update-side locks prevent the value of the pointer from changing,
468 : * you should instead use rcu_dereference_protected() for this use case.
469 : *
470 : * It is also permissible to use rcu_access_pointer() when read-side
471 : * access to the pointer was removed at least one grace period ago, as
472 : * is the case in the context of the RCU callback that is freeing up
473 : * the data, or after a synchronize_rcu() returns. This can be useful
474 : * when tearing down multi-linked structures after a grace period
475 : * has elapsed.
476 : */
477 : #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
478 :
479 : /**
480 : * rcu_dereference_check() - rcu_dereference with debug checking
481 : * @p: The pointer to read, prior to dereferencing
482 : * @c: The conditions under which the dereference will take place
483 : *
484 : * Do an rcu_dereference(), but check that the conditions under which the
485 : * dereference will take place are correct. Typically the conditions
486 : * indicate the various locking conditions that should be held at that
487 : * point. The check should return true if the conditions are satisfied.
488 : * An implicit check for being in an RCU read-side critical section
489 : * (rcu_read_lock()) is included.
490 : *
491 : * For example:
492 : *
493 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
494 : *
495 : * could be used to indicate to lockdep that foo->bar may only be dereferenced
496 : * if either rcu_read_lock() is held, or that the lock required to replace
497 : * the bar struct at foo->bar is held.
498 : *
499 : * Note that the list of conditions may also include indications of when a lock
500 : * need not be held, for example during initialisation or destruction of the
501 : * target struct:
502 : *
503 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
504 : * atomic_read(&foo->usage) == 0);
505 : *
506 : * Inserts memory barriers on architectures that require them
507 : * (currently only the Alpha), prevents the compiler from refetching
508 : * (and from merging fetches), and, more importantly, documents exactly
509 : * which pointers are protected by RCU and checks that the pointer is
510 : * annotated as __rcu.
511 : */
512 : #define rcu_dereference_check(p, c) \
513 : __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
514 :
515 : /**
516 : * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
517 : * @p: The pointer to read, prior to dereferencing
518 : * @c: The conditions under which the dereference will take place
519 : *
520 : * This is the RCU-bh counterpart to rcu_dereference_check().
521 : */
522 : #define rcu_dereference_bh_check(p, c) \
523 : __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
524 :
525 : /**
526 : * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
527 : * @p: The pointer to read, prior to dereferencing
528 : * @c: The conditions under which the dereference will take place
529 : *
530 : * This is the RCU-sched counterpart to rcu_dereference_check().
531 : */
532 : #define rcu_dereference_sched_check(p, c) \
533 : __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
534 : __rcu)
535 :
536 : /*
537 : * The tracing infrastructure traces RCU (we want that), but unfortunately
538 : * some of the RCU checks causes tracing to lock up the system.
539 : *
540 : * The no-tracing version of rcu_dereference_raw() must not call
541 : * rcu_read_lock_held().
542 : */
543 : #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
544 :
545 : /**
546 : * rcu_dereference_protected() - fetch RCU pointer when updates prevented
547 : * @p: The pointer to read, prior to dereferencing
548 : * @c: The conditions under which the dereference will take place
549 : *
550 : * Return the value of the specified RCU-protected pointer, but omit
551 : * the READ_ONCE(). This is useful in cases where update-side locks
552 : * prevent the value of the pointer from changing. Please note that this
553 : * primitive does *not* prevent the compiler from repeating this reference
554 : * or combining it with other references, so it should not be used without
555 : * protection of appropriate locks.
556 : *
557 : * This function is only for update-side use. Using this function
558 : * when protected only by rcu_read_lock() will result in infrequent
559 : * but very ugly failures.
560 : */
561 : #define rcu_dereference_protected(p, c) \
562 : __rcu_dereference_protected((p), (c), __rcu)
563 :
564 :
565 : /**
566 : * rcu_dereference() - fetch RCU-protected pointer for dereferencing
567 : * @p: The pointer to read, prior to dereferencing
568 : *
569 : * This is a simple wrapper around rcu_dereference_check().
570 : */
571 : #define rcu_dereference(p) rcu_dereference_check(p, 0)
572 :
573 : /**
574 : * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
575 : * @p: The pointer to read, prior to dereferencing
576 : *
577 : * Makes rcu_dereference_check() do the dirty work.
578 : */
579 : #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
580 :
581 : /**
582 : * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
583 : * @p: The pointer to read, prior to dereferencing
584 : *
585 : * Makes rcu_dereference_check() do the dirty work.
586 : */
587 : #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
588 :
589 : /**
590 : * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
591 : * @p: The pointer to hand off
592 : *
593 : * This is simply an identity function, but it documents where a pointer
594 : * is handed off from RCU to some other synchronization mechanism, for
595 : * example, reference counting or locking. In C11, it would map to
596 : * kill_dependency(). It could be used as follows::
597 : *
598 : * rcu_read_lock();
599 : * p = rcu_dereference(gp);
600 : * long_lived = is_long_lived(p);
601 : * if (long_lived) {
602 : * if (!atomic_inc_not_zero(p->refcnt))
603 : * long_lived = false;
604 : * else
605 : * p = rcu_pointer_handoff(p);
606 : * }
607 : * rcu_read_unlock();
608 : */
609 : #define rcu_pointer_handoff(p) (p)
610 :
611 : /**
612 : * rcu_read_lock() - mark the beginning of an RCU read-side critical section
613 : *
614 : * When synchronize_rcu() is invoked on one CPU while other CPUs
615 : * are within RCU read-side critical sections, then the
616 : * synchronize_rcu() is guaranteed to block until after all the other
617 : * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
618 : * on one CPU while other CPUs are within RCU read-side critical
619 : * sections, invocation of the corresponding RCU callback is deferred
620 : * until after the all the other CPUs exit their critical sections.
621 : *
622 : * Note, however, that RCU callbacks are permitted to run concurrently
623 : * with new RCU read-side critical sections. One way that this can happen
624 : * is via the following sequence of events: (1) CPU 0 enters an RCU
625 : * read-side critical section, (2) CPU 1 invokes call_rcu() to register
626 : * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
627 : * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
628 : * callback is invoked. This is legal, because the RCU read-side critical
629 : * section that was running concurrently with the call_rcu() (and which
630 : * therefore might be referencing something that the corresponding RCU
631 : * callback would free up) has completed before the corresponding
632 : * RCU callback is invoked.
633 : *
634 : * RCU read-side critical sections may be nested. Any deferred actions
635 : * will be deferred until the outermost RCU read-side critical section
636 : * completes.
637 : *
638 : * You can avoid reading and understanding the next paragraph by
639 : * following this rule: don't put anything in an rcu_read_lock() RCU
640 : * read-side critical section that would block in a !PREEMPTION kernel.
641 : * But if you want the full story, read on!
642 : *
643 : * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
644 : * it is illegal to block while in an RCU read-side critical section.
645 : * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
646 : * kernel builds, RCU read-side critical sections may be preempted,
647 : * but explicit blocking is illegal. Finally, in preemptible RCU
648 : * implementations in real-time (with -rt patchset) kernel builds, RCU
649 : * read-side critical sections may be preempted and they may also block, but
650 : * only when acquiring spinlocks that are subject to priority inheritance.
651 : */
652 1087909 : static __always_inline void rcu_read_lock(void)
653 : {
654 1087909 : __rcu_read_lock();
655 1088158 : __acquire(RCU);
656 1088158 : rcu_lock_acquire(&rcu_lock_map);
657 1088244 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
658 : "rcu_read_lock() used illegally while idle");
659 4 : }
660 :
661 : /*
662 : * So where is rcu_write_lock()? It does not exist, as there is no
663 : * way for writers to lock out RCU readers. This is a feature, not
664 : * a bug -- this property is what provides RCU's performance benefits.
665 : * Of course, writers must coordinate with each other. The normal
666 : * spinlock primitives work well for this, but any other technique may be
667 : * used as well. RCU does not care how the writers keep out of each
668 : * others' way, as long as they do so.
669 : */
670 :
671 : /**
672 : * rcu_read_unlock() - marks the end of an RCU read-side critical section.
673 : *
674 : * In most situations, rcu_read_unlock() is immune from deadlock.
675 : * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
676 : * is responsible for deboosting, which it does via rt_mutex_unlock().
677 : * Unfortunately, this function acquires the scheduler's runqueue and
678 : * priority-inheritance spinlocks. This means that deadlock could result
679 : * if the caller of rcu_read_unlock() already holds one of these locks or
680 : * any lock that is ever acquired while holding them.
681 : *
682 : * That said, RCU readers are never priority boosted unless they were
683 : * preempted. Therefore, one way to avoid deadlock is to make sure
684 : * that preemption never happens within any RCU read-side critical
685 : * section whose outermost rcu_read_unlock() is called with one of
686 : * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
687 : * a number of ways, for example, by invoking preempt_disable() before
688 : * critical section's outermost rcu_read_lock().
689 : *
690 : * Given that the set of locks acquired by rt_mutex_unlock() might change
691 : * at any time, a somewhat more future-proofed approach is to make sure
692 : * that that preemption never happens within any RCU read-side critical
693 : * section whose outermost rcu_read_unlock() is called with irqs disabled.
694 : * This approach relies on the fact that rt_mutex_unlock() currently only
695 : * acquires irq-disabled locks.
696 : *
697 : * The second of these two approaches is best in most situations,
698 : * however, the first approach can also be useful, at least to those
699 : * developers willing to keep abreast of the set of locks acquired by
700 : * rt_mutex_unlock().
701 : *
702 : * See rcu_read_lock() for more information.
703 : */
704 1088478 : static inline void rcu_read_unlock(void)
705 : {
706 1088478 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
707 : "rcu_read_unlock() used illegally while idle");
708 1088587 : __release(RCU);
709 1088587 : __rcu_read_unlock();
710 1088460 : rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
711 1088254 : }
712 :
713 : /**
714 : * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
715 : *
716 : * This is equivalent of rcu_read_lock(), but also disables softirqs.
717 : * Note that anything else that disables softirqs can also serve as
718 : * an RCU read-side critical section.
719 : *
720 : * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
721 : * must occur in the same context, for example, it is illegal to invoke
722 : * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
723 : * was invoked from some other task.
724 : */
725 897 : static inline void rcu_read_lock_bh(void)
726 : {
727 897 : local_bh_disable();
728 897 : __acquire(RCU_BH);
729 897 : rcu_lock_acquire(&rcu_bh_lock_map);
730 897 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
731 : "rcu_read_lock_bh() used illegally while idle");
732 897 : }
733 :
734 : /**
735 : * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
736 : *
737 : * See rcu_read_lock_bh() for more information.
738 : */
739 897 : static inline void rcu_read_unlock_bh(void)
740 : {
741 897 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
742 : "rcu_read_unlock_bh() used illegally while idle");
743 897 : rcu_lock_release(&rcu_bh_lock_map);
744 897 : __release(RCU_BH);
745 897 : local_bh_enable();
746 897 : }
747 :
748 : /**
749 : * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
750 : *
751 : * This is equivalent of rcu_read_lock(), but disables preemption.
752 : * Read-side critical sections can also be introduced by anything else
753 : * that disables preemption, including local_irq_disable() and friends.
754 : *
755 : * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
756 : * must occur in the same context, for example, it is illegal to invoke
757 : * rcu_read_unlock_sched() from process context if the matching
758 : * rcu_read_lock_sched() was invoked from an NMI handler.
759 : */
760 46442 : static inline void rcu_read_lock_sched(void)
761 : {
762 46442 : preempt_disable();
763 46445 : __acquire(RCU_SCHED);
764 46445 : rcu_lock_acquire(&rcu_sched_lock_map);
765 46444 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
766 : "rcu_read_lock_sched() used illegally while idle");
767 46452 : }
768 :
769 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
770 32815884 : static inline notrace void rcu_read_lock_sched_notrace(void)
771 : {
772 32815884 : preempt_disable_notrace();
773 32821220 : __acquire(RCU_SCHED);
774 : }
775 :
776 : /**
777 : * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
778 : *
779 : * See rcu_read_lock_sched() for more information.
780 : */
781 46444 : static inline void rcu_read_unlock_sched(void)
782 : {
783 46444 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
784 : "rcu_read_unlock_sched() used illegally while idle");
785 46446 : rcu_lock_release(&rcu_sched_lock_map);
786 46441 : __release(RCU_SCHED);
787 46441 : preempt_enable();
788 46441 : }
789 :
790 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
791 32811999 : static inline notrace void rcu_read_unlock_sched_notrace(void)
792 : {
793 32811999 : __release(RCU_SCHED);
794 32811999 : preempt_enable_notrace();
795 32835935 : }
796 :
797 : /**
798 : * RCU_INIT_POINTER() - initialize an RCU protected pointer
799 : * @p: The pointer to be initialized.
800 : * @v: The value to initialized the pointer to.
801 : *
802 : * Initialize an RCU-protected pointer in special cases where readers
803 : * do not need ordering constraints on the CPU or the compiler. These
804 : * special cases are:
805 : *
806 : * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
807 : * 2. The caller has taken whatever steps are required to prevent
808 : * RCU readers from concurrently accessing this pointer *or*
809 : * 3. The referenced data structure has already been exposed to
810 : * readers either at compile time or via rcu_assign_pointer() *and*
811 : *
812 : * a. You have not made *any* reader-visible changes to
813 : * this structure since then *or*
814 : * b. It is OK for readers accessing this structure from its
815 : * new location to see the old state of the structure. (For
816 : * example, the changes were to statistical counters or to
817 : * other state where exact synchronization is not required.)
818 : *
819 : * Failure to follow these rules governing use of RCU_INIT_POINTER() will
820 : * result in impossible-to-diagnose memory corruption. As in the structures
821 : * will look OK in crash dumps, but any concurrent RCU readers might
822 : * see pre-initialized values of the referenced data structure. So
823 : * please be very careful how you use RCU_INIT_POINTER()!!!
824 : *
825 : * If you are creating an RCU-protected linked structure that is accessed
826 : * by a single external-to-structure RCU-protected pointer, then you may
827 : * use RCU_INIT_POINTER() to initialize the internal RCU-protected
828 : * pointers, but you must use rcu_assign_pointer() to initialize the
829 : * external-to-structure pointer *after* you have completely initialized
830 : * the reader-accessible portions of the linked structure.
831 : *
832 : * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
833 : * ordering guarantees for either the CPU or the compiler.
834 : */
835 : #define RCU_INIT_POINTER(p, v) \
836 : do { \
837 : rcu_check_sparse(p, __rcu); \
838 : WRITE_ONCE(p, RCU_INITIALIZER(v)); \
839 : } while (0)
840 :
841 : /**
842 : * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
843 : * @p: The pointer to be initialized.
844 : * @v: The value to initialized the pointer to.
845 : *
846 : * GCC-style initialization for an RCU-protected pointer in a structure field.
847 : */
848 : #define RCU_POINTER_INITIALIZER(p, v) \
849 : .p = RCU_INITIALIZER(v)
850 :
851 : /*
852 : * Does the specified offset indicate that the corresponding rcu_head
853 : * structure can be handled by kvfree_rcu()?
854 : */
855 : #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
856 :
857 : /**
858 : * kfree_rcu() - kfree an object after a grace period.
859 : * @ptr: pointer to kfree for both single- and double-argument invocations.
860 : * @rhf: the name of the struct rcu_head within the type of @ptr,
861 : * but only for double-argument invocations.
862 : *
863 : * Many rcu callbacks functions just call kfree() on the base structure.
864 : * These functions are trivial, but their size adds up, and furthermore
865 : * when they are used in a kernel module, that module must invoke the
866 : * high-latency rcu_barrier() function at module-unload time.
867 : *
868 : * The kfree_rcu() function handles this issue. Rather than encoding a
869 : * function address in the embedded rcu_head structure, kfree_rcu() instead
870 : * encodes the offset of the rcu_head structure within the base structure.
871 : * Because the functions are not allowed in the low-order 4096 bytes of
872 : * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
873 : * If the offset is larger than 4095 bytes, a compile-time error will
874 : * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
875 : * either fall back to use of call_rcu() or rearrange the structure to
876 : * position the rcu_head structure into the first 4096 bytes.
877 : *
878 : * Note that the allowable offset might decrease in the future, for example,
879 : * to allow something like kmem_cache_free_rcu().
880 : *
881 : * The BUILD_BUG_ON check must not involve any function calls, hence the
882 : * checks are done in macros here.
883 : */
884 : #define kfree_rcu kvfree_rcu
885 :
886 : /**
887 : * kvfree_rcu() - kvfree an object after a grace period.
888 : *
889 : * This macro consists of one or two arguments and it is
890 : * based on whether an object is head-less or not. If it
891 : * has a head then a semantic stays the same as it used
892 : * to be before:
893 : *
894 : * kvfree_rcu(ptr, rhf);
895 : *
896 : * where @ptr is a pointer to kvfree(), @rhf is the name
897 : * of the rcu_head structure within the type of @ptr.
898 : *
899 : * When it comes to head-less variant, only one argument
900 : * is passed and that is just a pointer which has to be
901 : * freed after a grace period. Therefore the semantic is
902 : *
903 : * kvfree_rcu(ptr);
904 : *
905 : * where @ptr is a pointer to kvfree().
906 : *
907 : * Please note, head-less way of freeing is permitted to
908 : * use from a context that has to follow might_sleep()
909 : * annotation. Otherwise, please switch and embed the
910 : * rcu_head structure within the type of @ptr.
911 : */
912 : #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \
913 : kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
914 :
915 : #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
916 : #define kvfree_rcu_arg_2(ptr, rhf) \
917 : do { \
918 : typeof (ptr) ___p = (ptr); \
919 : \
920 : if (___p) { \
921 : BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \
922 : kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \
923 : (offsetof(typeof(*(ptr)), rhf))); \
924 : } \
925 : } while (0)
926 :
927 : #define kvfree_rcu_arg_1(ptr) \
928 : do { \
929 : typeof(ptr) ___p = (ptr); \
930 : \
931 : if (___p) \
932 : kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
933 : } while (0)
934 :
935 : /*
936 : * Place this after a lock-acquisition primitive to guarantee that
937 : * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
938 : * if the UNLOCK and LOCK are executed by the same CPU or if the
939 : * UNLOCK and LOCK operate on the same lock variable.
940 : */
941 : #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
942 : #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
943 : #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
944 : #define smp_mb__after_unlock_lock() do { } while (0)
945 : #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
946 :
947 :
948 : /* Has the specified rcu_head structure been handed to call_rcu()? */
949 :
950 : /**
951 : * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
952 : * @rhp: The rcu_head structure to initialize.
953 : *
954 : * If you intend to invoke rcu_head_after_call_rcu() to test whether a
955 : * given rcu_head structure has already been passed to call_rcu(), then
956 : * you must also invoke this rcu_head_init() function on it just after
957 : * allocating that structure. Calls to this function must not race with
958 : * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
959 : */
960 39 : static inline void rcu_head_init(struct rcu_head *rhp)
961 : {
962 39 : rhp->func = (rcu_callback_t)~0L;
963 : }
964 :
965 : /**
966 : * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
967 : * @rhp: The rcu_head structure to test.
968 : * @f: The function passed to call_rcu() along with @rhp.
969 : *
970 : * Returns @true if the @rhp has been passed to call_rcu() with @func,
971 : * and @false otherwise. Emits a warning in any other case, including
972 : * the case where @rhp has already been invoked after a grace period.
973 : * Calls to this function must not race with callback invocation. One way
974 : * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
975 : * in an RCU read-side critical section that includes a read-side fetch
976 : * of the pointer to the structure containing @rhp.
977 : */
978 : static inline bool
979 0 : rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
980 : {
981 0 : rcu_callback_t func = READ_ONCE(rhp->func);
982 :
983 0 : if (func == f)
984 : return true;
985 0 : WARN_ON_ONCE(func != (rcu_callback_t)~0L);
986 : return false;
987 : }
988 :
989 : /* kernel/ksysfs.c definitions */
990 : extern int rcu_expedited;
991 : extern int rcu_normal;
992 :
993 : #endif /* __LINUX_RCUPDATE_H */
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