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() READ_ONCE(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 : static inline void __rcu_read_lock(void)
67 : {
68 1043 : preempt_disable();
69 : }
70 :
71 : static inline void __rcu_read_unlock(void)
72 : {
73 1136 : preempt_enable();
74 : if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
75 : rcu_read_unlock_strict();
76 : }
77 :
78 : static inline int rcu_preempt_depth(void)
79 : {
80 : return 0;
81 : }
82 :
83 : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
84 :
85 : /* Internal to kernel */
86 : void rcu_init(void);
87 : extern int rcu_scheduler_active;
88 : void rcu_sched_clock_irq(int user);
89 : void rcu_report_dead(unsigned int cpu);
90 : void rcutree_migrate_callbacks(int cpu);
91 :
92 : #ifdef CONFIG_TASKS_RCU_GENERIC
93 : void rcu_init_tasks_generic(void);
94 : #else
95 : static inline void rcu_init_tasks_generic(void) { }
96 : #endif
97 :
98 : #ifdef CONFIG_RCU_STALL_COMMON
99 : void rcu_sysrq_start(void);
100 : void rcu_sysrq_end(void);
101 : #else /* #ifdef CONFIG_RCU_STALL_COMMON */
102 : static inline void rcu_sysrq_start(void) { }
103 : static inline void rcu_sysrq_end(void) { }
104 : #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
105 :
106 : #ifdef CONFIG_NO_HZ_FULL
107 : void rcu_user_enter(void);
108 : void rcu_user_exit(void);
109 : #else
110 : static inline void rcu_user_enter(void) { }
111 : static inline void rcu_user_exit(void) { }
112 : #endif /* CONFIG_NO_HZ_FULL */
113 :
114 : #ifdef CONFIG_RCU_NOCB_CPU
115 : void rcu_init_nohz(void);
116 : int rcu_nocb_cpu_offload(int cpu);
117 : int rcu_nocb_cpu_deoffload(int cpu);
118 : void rcu_nocb_flush_deferred_wakeup(void);
119 : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
120 : static inline void rcu_init_nohz(void) { }
121 : static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
122 : static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
123 : static inline void rcu_nocb_flush_deferred_wakeup(void) { }
124 : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
125 :
126 : /**
127 : * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
128 : * @a: Code that RCU needs to pay attention to.
129 : *
130 : * RCU read-side critical sections are forbidden in the inner idle loop,
131 : * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU
132 : * will happily ignore any such read-side critical sections. However,
133 : * things like powertop need tracepoints in the inner idle loop.
134 : *
135 : * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
136 : * will tell RCU that it needs to pay attention, invoke its argument
137 : * (in this example, calling the do_something_with_RCU() function),
138 : * and then tell RCU to go back to ignoring this CPU. It is permissible
139 : * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
140 : * on the order of a million or so, even on 32-bit systems). It is
141 : * not legal to block within RCU_NONIDLE(), nor is it permissible to
142 : * transfer control either into or out of RCU_NONIDLE()'s statement.
143 : */
144 : #define RCU_NONIDLE(a) \
145 : do { \
146 : rcu_irq_enter_irqson(); \
147 : do { a; } while (0); \
148 : rcu_irq_exit_irqson(); \
149 : } while (0)
150 :
151 : /*
152 : * Note a quasi-voluntary context switch for RCU-tasks's benefit.
153 : * This is a macro rather than an inline function to avoid #include hell.
154 : */
155 : #ifdef CONFIG_TASKS_RCU_GENERIC
156 :
157 : # ifdef CONFIG_TASKS_RCU
158 : # define rcu_tasks_classic_qs(t, preempt) \
159 : do { \
160 : if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
161 : WRITE_ONCE((t)->rcu_tasks_holdout, false); \
162 : } while (0)
163 : void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
164 : void synchronize_rcu_tasks(void);
165 : # else
166 : # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
167 : # define call_rcu_tasks call_rcu
168 : # define synchronize_rcu_tasks synchronize_rcu
169 : # endif
170 :
171 : # ifdef CONFIG_TASKS_TRACE_RCU
172 : # define rcu_tasks_trace_qs(t) \
173 : do { \
174 : if (!likely(READ_ONCE((t)->trc_reader_checked)) && \
175 : !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \
176 : smp_store_release(&(t)->trc_reader_checked, true); \
177 : smp_mb(); /* Readers partitioned by store. */ \
178 : } \
179 : } while (0)
180 : # else
181 : # define rcu_tasks_trace_qs(t) do { } while (0)
182 : # endif
183 :
184 : #define rcu_tasks_qs(t, preempt) \
185 : do { \
186 : rcu_tasks_classic_qs((t), (preempt)); \
187 : rcu_tasks_trace_qs((t)); \
188 : } while (0)
189 :
190 : # ifdef CONFIG_TASKS_RUDE_RCU
191 : void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
192 : void synchronize_rcu_tasks_rude(void);
193 : # endif
194 :
195 : #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
196 : void exit_tasks_rcu_start(void);
197 : void exit_tasks_rcu_finish(void);
198 : #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
199 : #define rcu_tasks_qs(t, preempt) do { } while (0)
200 : #define rcu_note_voluntary_context_switch(t) do { } while (0)
201 : #define call_rcu_tasks call_rcu
202 : #define synchronize_rcu_tasks synchronize_rcu
203 : static inline void exit_tasks_rcu_start(void) { }
204 : static inline void exit_tasks_rcu_finish(void) { }
205 : #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
206 :
207 : /**
208 : * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
209 : *
210 : * This macro resembles cond_resched(), except that it is defined to
211 : * report potential quiescent states to RCU-tasks even if the cond_resched()
212 : * machinery were to be shut off, as some advocate for PREEMPTION kernels.
213 : */
214 : #define cond_resched_tasks_rcu_qs() \
215 : do { \
216 : rcu_tasks_qs(current, false); \
217 : cond_resched(); \
218 : } while (0)
219 :
220 : /*
221 : * Infrastructure to implement the synchronize_() primitives in
222 : * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
223 : */
224 :
225 : #if defined(CONFIG_TREE_RCU)
226 : #include <linux/rcutree.h>
227 : #elif defined(CONFIG_TINY_RCU)
228 : #include <linux/rcutiny.h>
229 : #else
230 : #error "Unknown RCU implementation specified to kernel configuration"
231 : #endif
232 :
233 : /*
234 : * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
235 : * are needed for dynamic initialization and destruction of rcu_head
236 : * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
237 : * dynamic initialization and destruction of statically allocated rcu_head
238 : * structures. However, rcu_head structures allocated dynamically in the
239 : * heap don't need any initialization.
240 : */
241 : #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
242 : void init_rcu_head(struct rcu_head *head);
243 : void destroy_rcu_head(struct rcu_head *head);
244 : void init_rcu_head_on_stack(struct rcu_head *head);
245 : void destroy_rcu_head_on_stack(struct rcu_head *head);
246 : #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
247 : static inline void init_rcu_head(struct rcu_head *head) { }
248 : static inline void destroy_rcu_head(struct rcu_head *head) { }
249 : static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
250 : static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
251 : #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
252 :
253 : #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
254 : bool rcu_lockdep_current_cpu_online(void);
255 : #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
256 : static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
257 : #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
258 :
259 : extern struct lockdep_map rcu_lock_map;
260 : extern struct lockdep_map rcu_bh_lock_map;
261 : extern struct lockdep_map rcu_sched_lock_map;
262 : extern struct lockdep_map rcu_callback_map;
263 :
264 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
265 :
266 : static inline void rcu_lock_acquire(struct lockdep_map *map)
267 : {
268 : lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
269 : }
270 :
271 : static inline void rcu_lock_release(struct lockdep_map *map)
272 : {
273 : lock_release(map, _THIS_IP_);
274 : }
275 :
276 : int debug_lockdep_rcu_enabled(void);
277 : int rcu_read_lock_held(void);
278 : int rcu_read_lock_bh_held(void);
279 : int rcu_read_lock_sched_held(void);
280 : int rcu_read_lock_any_held(void);
281 :
282 : #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
283 :
284 : # define rcu_lock_acquire(a) do { } while (0)
285 : # define rcu_lock_release(a) do { } while (0)
286 :
287 : static inline int rcu_read_lock_held(void)
288 : {
289 : return 1;
290 : }
291 :
292 : static inline int rcu_read_lock_bh_held(void)
293 : {
294 : return 1;
295 : }
296 :
297 : static inline int rcu_read_lock_sched_held(void)
298 : {
299 : return !preemptible();
300 : }
301 :
302 : static inline int rcu_read_lock_any_held(void)
303 : {
304 : return !preemptible();
305 : }
306 :
307 : #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
308 :
309 : #ifdef CONFIG_PROVE_RCU
310 :
311 : /**
312 : * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
313 : * @c: condition to check
314 : * @s: informative message
315 : */
316 : #define RCU_LOCKDEP_WARN(c, s) \
317 : do { \
318 : static bool __section(".data.unlikely") __warned; \
319 : if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \
320 : __warned = true; \
321 : lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
322 : } \
323 : } while (0)
324 :
325 : #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
326 : static inline void rcu_preempt_sleep_check(void)
327 : {
328 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
329 : "Illegal context switch in RCU read-side critical section");
330 : }
331 : #else /* #ifdef CONFIG_PROVE_RCU */
332 : static inline void rcu_preempt_sleep_check(void) { }
333 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
334 :
335 : #define rcu_sleep_check() \
336 : do { \
337 : rcu_preempt_sleep_check(); \
338 : if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
339 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
340 : "Illegal context switch in RCU-bh read-side critical section"); \
341 : RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
342 : "Illegal context switch in RCU-sched read-side critical section"); \
343 : } while (0)
344 :
345 : #else /* #ifdef CONFIG_PROVE_RCU */
346 :
347 : #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
348 : #define rcu_sleep_check() do { } while (0)
349 :
350 : #endif /* #else #ifdef CONFIG_PROVE_RCU */
351 :
352 : /*
353 : * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
354 : * and rcu_assign_pointer(). Some of these could be folded into their
355 : * callers, but they are left separate in order to ease introduction of
356 : * multiple pointers markings to match different RCU implementations
357 : * (e.g., __srcu), should this make sense in the future.
358 : */
359 :
360 : #ifdef __CHECKER__
361 : #define rcu_check_sparse(p, space) \
362 : ((void)(((typeof(*p) space *)p) == p))
363 : #else /* #ifdef __CHECKER__ */
364 : #define rcu_check_sparse(p, space)
365 : #endif /* #else #ifdef __CHECKER__ */
366 :
367 : #define __unrcu_pointer(p, local) \
368 : ({ \
369 : typeof(*p) *local = (typeof(*p) *__force)(p); \
370 : rcu_check_sparse(p, __rcu); \
371 : ((typeof(*p) __force __kernel *)(local)); \
372 : })
373 : /**
374 : * unrcu_pointer - mark a pointer as not being RCU protected
375 : * @p: pointer needing to lose its __rcu property
376 : *
377 : * Converts @p from an __rcu pointer to a __kernel pointer.
378 : * This allows an __rcu pointer to be used with xchg() and friends.
379 : */
380 : #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))
381 :
382 : #define __rcu_access_pointer(p, local, space) \
383 : ({ \
384 : typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
385 : rcu_check_sparse(p, space); \
386 : ((typeof(*p) __force __kernel *)(local)); \
387 : })
388 : #define __rcu_dereference_check(p, local, c, space) \
389 : ({ \
390 : /* Dependency order vs. p above. */ \
391 : typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
392 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
393 : rcu_check_sparse(p, space); \
394 : ((typeof(*p) __force __kernel *)(local)); \
395 : })
396 : #define __rcu_dereference_protected(p, local, c, space) \
397 : ({ \
398 : RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
399 : rcu_check_sparse(p, space); \
400 : ((typeof(*p) __force __kernel *)(p)); \
401 : })
402 : #define __rcu_dereference_raw(p, local) \
403 : ({ \
404 : /* Dependency order vs. p above. */ \
405 : typeof(p) local = READ_ONCE(p); \
406 : ((typeof(*p) __force __kernel *)(local)); \
407 : })
408 : #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))
409 :
410 : /**
411 : * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
412 : * @v: The value to statically initialize with.
413 : */
414 : #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
415 :
416 : /**
417 : * rcu_assign_pointer() - assign to RCU-protected pointer
418 : * @p: pointer to assign to
419 : * @v: value to assign (publish)
420 : *
421 : * Assigns the specified value to the specified RCU-protected
422 : * pointer, ensuring that any concurrent RCU readers will see
423 : * any prior initialization.
424 : *
425 : * Inserts memory barriers on architectures that require them
426 : * (which is most of them), and also prevents the compiler from
427 : * reordering the code that initializes the structure after the pointer
428 : * assignment. More importantly, this call documents which pointers
429 : * will be dereferenced by RCU read-side code.
430 : *
431 : * In some special cases, you may use RCU_INIT_POINTER() instead
432 : * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
433 : * to the fact that it does not constrain either the CPU or the compiler.
434 : * That said, using RCU_INIT_POINTER() when you should have used
435 : * rcu_assign_pointer() is a very bad thing that results in
436 : * impossible-to-diagnose memory corruption. So please be careful.
437 : * See the RCU_INIT_POINTER() comment header for details.
438 : *
439 : * Note that rcu_assign_pointer() evaluates each of its arguments only
440 : * once, appearances notwithstanding. One of the "extra" evaluations
441 : * is in typeof() and the other visible only to sparse (__CHECKER__),
442 : * neither of which actually execute the argument. As with most cpp
443 : * macros, this execute-arguments-only-once property is important, so
444 : * please be careful when making changes to rcu_assign_pointer() and the
445 : * other macros that it invokes.
446 : */
447 : #define rcu_assign_pointer(p, v) \
448 : do { \
449 : uintptr_t _r_a_p__v = (uintptr_t)(v); \
450 : rcu_check_sparse(p, __rcu); \
451 : \
452 : if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
453 : WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
454 : else \
455 : smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
456 : } while (0)
457 :
458 : /**
459 : * rcu_replace_pointer() - replace an RCU pointer, returning its old value
460 : * @rcu_ptr: RCU pointer, whose old value is returned
461 : * @ptr: regular pointer
462 : * @c: the lockdep conditions under which the dereference will take place
463 : *
464 : * Perform a replacement, where @rcu_ptr is an RCU-annotated
465 : * pointer and @c is the lockdep argument that is passed to the
466 : * rcu_dereference_protected() call used to read that pointer. The old
467 : * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
468 : */
469 : #define rcu_replace_pointer(rcu_ptr, ptr, c) \
470 : ({ \
471 : typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
472 : rcu_assign_pointer((rcu_ptr), (ptr)); \
473 : __tmp; \
474 : })
475 :
476 : /**
477 : * rcu_access_pointer() - fetch RCU pointer with no dereferencing
478 : * @p: The pointer to read
479 : *
480 : * Return the value of the specified RCU-protected pointer, but omit the
481 : * lockdep checks for being in an RCU read-side critical section. This is
482 : * useful when the value of this pointer is accessed, but the pointer is
483 : * not dereferenced, for example, when testing an RCU-protected pointer
484 : * against NULL. Although rcu_access_pointer() may also be used in cases
485 : * where update-side locks prevent the value of the pointer from changing,
486 : * you should instead use rcu_dereference_protected() for this use case.
487 : *
488 : * It is also permissible to use rcu_access_pointer() when read-side
489 : * access to the pointer was removed at least one grace period ago, as
490 : * is the case in the context of the RCU callback that is freeing up
491 : * the data, or after a synchronize_rcu() returns. This can be useful
492 : * when tearing down multi-linked structures after a grace period
493 : * has elapsed.
494 : */
495 : #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu)
496 :
497 : /**
498 : * rcu_dereference_check() - rcu_dereference with debug checking
499 : * @p: The pointer to read, prior to dereferencing
500 : * @c: The conditions under which the dereference will take place
501 : *
502 : * Do an rcu_dereference(), but check that the conditions under which the
503 : * dereference will take place are correct. Typically the conditions
504 : * indicate the various locking conditions that should be held at that
505 : * point. The check should return true if the conditions are satisfied.
506 : * An implicit check for being in an RCU read-side critical section
507 : * (rcu_read_lock()) is included.
508 : *
509 : * For example:
510 : *
511 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
512 : *
513 : * could be used to indicate to lockdep that foo->bar may only be dereferenced
514 : * if either rcu_read_lock() is held, or that the lock required to replace
515 : * the bar struct at foo->bar is held.
516 : *
517 : * Note that the list of conditions may also include indications of when a lock
518 : * need not be held, for example during initialisation or destruction of the
519 : * target struct:
520 : *
521 : * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
522 : * atomic_read(&foo->usage) == 0);
523 : *
524 : * Inserts memory barriers on architectures that require them
525 : * (currently only the Alpha), prevents the compiler from refetching
526 : * (and from merging fetches), and, more importantly, documents exactly
527 : * which pointers are protected by RCU and checks that the pointer is
528 : * annotated as __rcu.
529 : */
530 : #define rcu_dereference_check(p, c) \
531 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
532 : (c) || rcu_read_lock_held(), __rcu)
533 :
534 : /**
535 : * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
536 : * @p: The pointer to read, prior to dereferencing
537 : * @c: The conditions under which the dereference will take place
538 : *
539 : * This is the RCU-bh counterpart to rcu_dereference_check(). However,
540 : * please note that starting in v5.0 kernels, vanilla RCU grace periods
541 : * wait for local_bh_disable() regions of code in addition to regions of
542 : * code demarked by rcu_read_lock() and rcu_read_unlock(). This means
543 : * that synchronize_rcu(), call_rcu, and friends all take not only
544 : * rcu_read_lock() but also rcu_read_lock_bh() into account.
545 : */
546 : #define rcu_dereference_bh_check(p, c) \
547 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
548 : (c) || rcu_read_lock_bh_held(), __rcu)
549 :
550 : /**
551 : * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
552 : * @p: The pointer to read, prior to dereferencing
553 : * @c: The conditions under which the dereference will take place
554 : *
555 : * This is the RCU-sched counterpart to rcu_dereference_check().
556 : * However, please note that starting in v5.0 kernels, vanilla RCU grace
557 : * periods wait for preempt_disable() regions of code in addition to
558 : * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
559 : * This means that synchronize_rcu(), call_rcu, and friends all take not
560 : * only rcu_read_lock() but also rcu_read_lock_sched() into account.
561 : */
562 : #define rcu_dereference_sched_check(p, c) \
563 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), \
564 : (c) || rcu_read_lock_sched_held(), \
565 : __rcu)
566 :
567 : /*
568 : * The tracing infrastructure traces RCU (we want that), but unfortunately
569 : * some of the RCU checks causes tracing to lock up the system.
570 : *
571 : * The no-tracing version of rcu_dereference_raw() must not call
572 : * rcu_read_lock_held().
573 : */
574 : #define rcu_dereference_raw_check(p) \
575 : __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu)
576 :
577 : /**
578 : * rcu_dereference_protected() - fetch RCU pointer when updates prevented
579 : * @p: The pointer to read, prior to dereferencing
580 : * @c: The conditions under which the dereference will take place
581 : *
582 : * Return the value of the specified RCU-protected pointer, but omit
583 : * the READ_ONCE(). This is useful in cases where update-side locks
584 : * prevent the value of the pointer from changing. Please note that this
585 : * primitive does *not* prevent the compiler from repeating this reference
586 : * or combining it with other references, so it should not be used without
587 : * protection of appropriate locks.
588 : *
589 : * This function is only for update-side use. Using this function
590 : * when protected only by rcu_read_lock() will result in infrequent
591 : * but very ugly failures.
592 : */
593 : #define rcu_dereference_protected(p, c) \
594 : __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu)
595 :
596 :
597 : /**
598 : * rcu_dereference() - fetch RCU-protected pointer for dereferencing
599 : * @p: The pointer to read, prior to dereferencing
600 : *
601 : * This is a simple wrapper around rcu_dereference_check().
602 : */
603 : #define rcu_dereference(p) rcu_dereference_check(p, 0)
604 :
605 : /**
606 : * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
607 : * @p: The pointer to read, prior to dereferencing
608 : *
609 : * Makes rcu_dereference_check() do the dirty work.
610 : */
611 : #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
612 :
613 : /**
614 : * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
615 : * @p: The pointer to read, prior to dereferencing
616 : *
617 : * Makes rcu_dereference_check() do the dirty work.
618 : */
619 : #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
620 :
621 : /**
622 : * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
623 : * @p: The pointer to hand off
624 : *
625 : * This is simply an identity function, but it documents where a pointer
626 : * is handed off from RCU to some other synchronization mechanism, for
627 : * example, reference counting or locking. In C11, it would map to
628 : * kill_dependency(). It could be used as follows::
629 : *
630 : * rcu_read_lock();
631 : * p = rcu_dereference(gp);
632 : * long_lived = is_long_lived(p);
633 : * if (long_lived) {
634 : * if (!atomic_inc_not_zero(p->refcnt))
635 : * long_lived = false;
636 : * else
637 : * p = rcu_pointer_handoff(p);
638 : * }
639 : * rcu_read_unlock();
640 : */
641 : #define rcu_pointer_handoff(p) (p)
642 :
643 : /**
644 : * rcu_read_lock() - mark the beginning of an RCU read-side critical section
645 : *
646 : * When synchronize_rcu() is invoked on one CPU while other CPUs
647 : * are within RCU read-side critical sections, then the
648 : * synchronize_rcu() is guaranteed to block until after all the other
649 : * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
650 : * on one CPU while other CPUs are within RCU read-side critical
651 : * sections, invocation of the corresponding RCU callback is deferred
652 : * until after the all the other CPUs exit their critical sections.
653 : *
654 : * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
655 : * wait for regions of code with preemption disabled, including regions of
656 : * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which
657 : * define synchronize_sched(), only code enclosed within rcu_read_lock()
658 : * and rcu_read_unlock() are guaranteed to be waited for.
659 : *
660 : * Note, however, that RCU callbacks are permitted to run concurrently
661 : * with new RCU read-side critical sections. One way that this can happen
662 : * is via the following sequence of events: (1) CPU 0 enters an RCU
663 : * read-side critical section, (2) CPU 1 invokes call_rcu() to register
664 : * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
665 : * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
666 : * callback is invoked. This is legal, because the RCU read-side critical
667 : * section that was running concurrently with the call_rcu() (and which
668 : * therefore might be referencing something that the corresponding RCU
669 : * callback would free up) has completed before the corresponding
670 : * RCU callback is invoked.
671 : *
672 : * RCU read-side critical sections may be nested. Any deferred actions
673 : * will be deferred until the outermost RCU read-side critical section
674 : * completes.
675 : *
676 : * You can avoid reading and understanding the next paragraph by
677 : * following this rule: don't put anything in an rcu_read_lock() RCU
678 : * read-side critical section that would block in a !PREEMPTION kernel.
679 : * But if you want the full story, read on!
680 : *
681 : * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
682 : * it is illegal to block while in an RCU read-side critical section.
683 : * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
684 : * kernel builds, RCU read-side critical sections may be preempted,
685 : * but explicit blocking is illegal. Finally, in preemptible RCU
686 : * implementations in real-time (with -rt patchset) kernel builds, RCU
687 : * read-side critical sections may be preempted and they may also block, but
688 : * only when acquiring spinlocks that are subject to priority inheritance.
689 : */
690 : static __always_inline void rcu_read_lock(void)
691 : {
692 : __rcu_read_lock();
693 : __acquire(RCU);
694 : rcu_lock_acquire(&rcu_lock_map);
695 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
696 : "rcu_read_lock() used illegally while idle");
697 : }
698 :
699 : /*
700 : * So where is rcu_write_lock()? It does not exist, as there is no
701 : * way for writers to lock out RCU readers. This is a feature, not
702 : * a bug -- this property is what provides RCU's performance benefits.
703 : * Of course, writers must coordinate with each other. The normal
704 : * spinlock primitives work well for this, but any other technique may be
705 : * used as well. RCU does not care how the writers keep out of each
706 : * others' way, as long as they do so.
707 : */
708 :
709 : /**
710 : * rcu_read_unlock() - marks the end of an RCU read-side critical section.
711 : *
712 : * In almost all situations, rcu_read_unlock() is immune from deadlock.
713 : * In recent kernels that have consolidated synchronize_sched() and
714 : * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
715 : * also extends to the scheduler's runqueue and priority-inheritance
716 : * spinlocks, courtesy of the quiescent-state deferral that is carried
717 : * out when rcu_read_unlock() is invoked with interrupts disabled.
718 : *
719 : * See rcu_read_lock() for more information.
720 : */
721 : static inline void rcu_read_unlock(void)
722 : {
723 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
724 : "rcu_read_unlock() used illegally while idle");
725 : __release(RCU);
726 : __rcu_read_unlock();
727 : rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
728 : }
729 :
730 : /**
731 : * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
732 : *
733 : * This is equivalent to rcu_read_lock(), but also disables softirqs.
734 : * Note that anything else that disables softirqs can also serve as an RCU
735 : * read-side critical section. However, please note that this equivalence
736 : * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and
737 : * rcu_read_lock_bh() were unrelated.
738 : *
739 : * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
740 : * must occur in the same context, for example, it is illegal to invoke
741 : * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
742 : * was invoked from some other task.
743 : */
744 : static inline void rcu_read_lock_bh(void)
745 : {
746 : local_bh_disable();
747 : __acquire(RCU_BH);
748 : rcu_lock_acquire(&rcu_bh_lock_map);
749 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
750 : "rcu_read_lock_bh() used illegally while idle");
751 : }
752 :
753 : /**
754 : * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
755 : *
756 : * See rcu_read_lock_bh() for more information.
757 : */
758 : static inline void rcu_read_unlock_bh(void)
759 : {
760 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
761 : "rcu_read_unlock_bh() used illegally while idle");
762 : rcu_lock_release(&rcu_bh_lock_map);
763 : __release(RCU_BH);
764 : local_bh_enable();
765 : }
766 :
767 : /**
768 : * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
769 : *
770 : * This is equivalent to rcu_read_lock(), but also disables preemption.
771 : * Read-side critical sections can also be introduced by anything else that
772 : * disables preemption, including local_irq_disable() and friends. However,
773 : * please note that the equivalence to rcu_read_lock() applies only to
774 : * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched()
775 : * were unrelated.
776 : *
777 : * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
778 : * must occur in the same context, for example, it is illegal to invoke
779 : * rcu_read_unlock_sched() from process context if the matching
780 : * rcu_read_lock_sched() was invoked from an NMI handler.
781 : */
782 : static inline void rcu_read_lock_sched(void)
783 : {
784 0 : preempt_disable();
785 : __acquire(RCU_SCHED);
786 : rcu_lock_acquire(&rcu_sched_lock_map);
787 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
788 : "rcu_read_lock_sched() used illegally while idle");
789 : }
790 :
791 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
792 : static inline notrace void rcu_read_lock_sched_notrace(void)
793 : {
794 : preempt_disable_notrace();
795 : __acquire(RCU_SCHED);
796 : }
797 :
798 : /**
799 : * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
800 : *
801 : * See rcu_read_lock_sched() for more information.
802 : */
803 : static inline void rcu_read_unlock_sched(void)
804 : {
805 : RCU_LOCKDEP_WARN(!rcu_is_watching(),
806 : "rcu_read_unlock_sched() used illegally while idle");
807 : rcu_lock_release(&rcu_sched_lock_map);
808 : __release(RCU_SCHED);
809 0 : preempt_enable();
810 : }
811 :
812 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
813 : static inline notrace void rcu_read_unlock_sched_notrace(void)
814 : {
815 : __release(RCU_SCHED);
816 : preempt_enable_notrace();
817 : }
818 :
819 : /**
820 : * RCU_INIT_POINTER() - initialize an RCU protected pointer
821 : * @p: The pointer to be initialized.
822 : * @v: The value to initialized the pointer to.
823 : *
824 : * Initialize an RCU-protected pointer in special cases where readers
825 : * do not need ordering constraints on the CPU or the compiler. These
826 : * special cases are:
827 : *
828 : * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
829 : * 2. The caller has taken whatever steps are required to prevent
830 : * RCU readers from concurrently accessing this pointer *or*
831 : * 3. The referenced data structure has already been exposed to
832 : * readers either at compile time or via rcu_assign_pointer() *and*
833 : *
834 : * a. You have not made *any* reader-visible changes to
835 : * this structure since then *or*
836 : * b. It is OK for readers accessing this structure from its
837 : * new location to see the old state of the structure. (For
838 : * example, the changes were to statistical counters or to
839 : * other state where exact synchronization is not required.)
840 : *
841 : * Failure to follow these rules governing use of RCU_INIT_POINTER() will
842 : * result in impossible-to-diagnose memory corruption. As in the structures
843 : * will look OK in crash dumps, but any concurrent RCU readers might
844 : * see pre-initialized values of the referenced data structure. So
845 : * please be very careful how you use RCU_INIT_POINTER()!!!
846 : *
847 : * If you are creating an RCU-protected linked structure that is accessed
848 : * by a single external-to-structure RCU-protected pointer, then you may
849 : * use RCU_INIT_POINTER() to initialize the internal RCU-protected
850 : * pointers, but you must use rcu_assign_pointer() to initialize the
851 : * external-to-structure pointer *after* you have completely initialized
852 : * the reader-accessible portions of the linked structure.
853 : *
854 : * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
855 : * ordering guarantees for either the CPU or the compiler.
856 : */
857 : #define RCU_INIT_POINTER(p, v) \
858 : do { \
859 : rcu_check_sparse(p, __rcu); \
860 : WRITE_ONCE(p, RCU_INITIALIZER(v)); \
861 : } while (0)
862 :
863 : /**
864 : * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
865 : * @p: The pointer to be initialized.
866 : * @v: The value to initialized the pointer to.
867 : *
868 : * GCC-style initialization for an RCU-protected pointer in a structure field.
869 : */
870 : #define RCU_POINTER_INITIALIZER(p, v) \
871 : .p = RCU_INITIALIZER(v)
872 :
873 : /*
874 : * Does the specified offset indicate that the corresponding rcu_head
875 : * structure can be handled by kvfree_rcu()?
876 : */
877 : #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
878 :
879 : /**
880 : * kfree_rcu() - kfree an object after a grace period.
881 : * @ptr: pointer to kfree for both single- and double-argument invocations.
882 : * @rhf: the name of the struct rcu_head within the type of @ptr,
883 : * but only for double-argument invocations.
884 : *
885 : * Many rcu callbacks functions just call kfree() on the base structure.
886 : * These functions are trivial, but their size adds up, and furthermore
887 : * when they are used in a kernel module, that module must invoke the
888 : * high-latency rcu_barrier() function at module-unload time.
889 : *
890 : * The kfree_rcu() function handles this issue. Rather than encoding a
891 : * function address in the embedded rcu_head structure, kfree_rcu() instead
892 : * encodes the offset of the rcu_head structure within the base structure.
893 : * Because the functions are not allowed in the low-order 4096 bytes of
894 : * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
895 : * If the offset is larger than 4095 bytes, a compile-time error will
896 : * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
897 : * either fall back to use of call_rcu() or rearrange the structure to
898 : * position the rcu_head structure into the first 4096 bytes.
899 : *
900 : * Note that the allowable offset might decrease in the future, for example,
901 : * to allow something like kmem_cache_free_rcu().
902 : *
903 : * The BUILD_BUG_ON check must not involve any function calls, hence the
904 : * checks are done in macros here.
905 : */
906 : #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf)
907 :
908 : /**
909 : * kvfree_rcu() - kvfree an object after a grace period.
910 : *
911 : * This macro consists of one or two arguments and it is
912 : * based on whether an object is head-less or not. If it
913 : * has a head then a semantic stays the same as it used
914 : * to be before:
915 : *
916 : * kvfree_rcu(ptr, rhf);
917 : *
918 : * where @ptr is a pointer to kvfree(), @rhf is the name
919 : * of the rcu_head structure within the type of @ptr.
920 : *
921 : * When it comes to head-less variant, only one argument
922 : * is passed and that is just a pointer which has to be
923 : * freed after a grace period. Therefore the semantic is
924 : *
925 : * kvfree_rcu(ptr);
926 : *
927 : * where @ptr is the pointer to be freed by kvfree().
928 : *
929 : * Please note, head-less way of freeing is permitted to
930 : * use from a context that has to follow might_sleep()
931 : * annotation. Otherwise, please switch and embed the
932 : * rcu_head structure within the type of @ptr.
933 : */
934 : #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \
935 : kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
936 :
937 : #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
938 : #define kvfree_rcu_arg_2(ptr, rhf) \
939 : do { \
940 : typeof (ptr) ___p = (ptr); \
941 : \
942 : if (___p) { \
943 : BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \
944 : kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \
945 : (offsetof(typeof(*(ptr)), rhf))); \
946 : } \
947 : } while (0)
948 :
949 : #define kvfree_rcu_arg_1(ptr) \
950 : do { \
951 : typeof(ptr) ___p = (ptr); \
952 : \
953 : if (___p) \
954 : kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
955 : } while (0)
956 :
957 : /*
958 : * Place this after a lock-acquisition primitive to guarantee that
959 : * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
960 : * if the UNLOCK and LOCK are executed by the same CPU or if the
961 : * UNLOCK and LOCK operate on the same lock variable.
962 : */
963 : #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
964 : #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
965 : #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
966 : #define smp_mb__after_unlock_lock() do { } while (0)
967 : #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
968 :
969 :
970 : /* Has the specified rcu_head structure been handed to call_rcu()? */
971 :
972 : /**
973 : * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
974 : * @rhp: The rcu_head structure to initialize.
975 : *
976 : * If you intend to invoke rcu_head_after_call_rcu() to test whether a
977 : * given rcu_head structure has already been passed to call_rcu(), then
978 : * you must also invoke this rcu_head_init() function on it just after
979 : * allocating that structure. Calls to this function must not race with
980 : * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
981 : */
982 : static inline void rcu_head_init(struct rcu_head *rhp)
983 : {
984 0 : rhp->func = (rcu_callback_t)~0L;
985 : }
986 :
987 : /**
988 : * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
989 : * @rhp: The rcu_head structure to test.
990 : * @f: The function passed to call_rcu() along with @rhp.
991 : *
992 : * Returns @true if the @rhp has been passed to call_rcu() with @func,
993 : * and @false otherwise. Emits a warning in any other case, including
994 : * the case where @rhp has already been invoked after a grace period.
995 : * Calls to this function must not race with callback invocation. One way
996 : * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
997 : * in an RCU read-side critical section that includes a read-side fetch
998 : * of the pointer to the structure containing @rhp.
999 : */
1000 : static inline bool
1001 0 : rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
1002 : {
1003 0 : rcu_callback_t func = READ_ONCE(rhp->func);
1004 :
1005 0 : if (func == f)
1006 : return true;
1007 0 : WARN_ON_ONCE(func != (rcu_callback_t)~0L);
1008 : return false;
1009 : }
1010 :
1011 : /* kernel/ksysfs.c definitions */
1012 : extern int rcu_expedited;
1013 : extern int rcu_normal;
1014 :
1015 : #endif /* __LINUX_RCUPDATE_H */
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