rcupdate.h 35 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574575576577578579580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639640641642643644645646647648649650651652653654655656657658659660661662663664665666667668669670671672673674675676677678679680681682683684685686687688689690691692693694695696697698699700701702703704705706707708709710711712713714715716717718719720721722723724725726727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775776777778779780781782783784785786787788789790791792793794795796797798799800801802803804805806807808809810811812813814815816817818819820821822823824825826827828829830831832833834835836837838839840841842843844845846847848849850851852853854855856857858859860861862863864865866867868869870871872873874875876877878879880881882883884885886887888889890891892893894895896897898899900901902903904905906907908909910911912913914915916917918919920921922923924925926927928929930931932933934935936937938939940941942943944945946947948949950951952953954955956957958959960961962963964965966967968969970971972973974975976977978979980981982983984985986987988989990991992
  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. #ifndef __LINUX_RCUPDATE_H
  20. #define __LINUX_RCUPDATE_H
  21. #include <linux/types.h>
  22. #include <linux/compiler.h>
  23. #include <linux/atomic.h>
  24. #include <linux/irqflags.h>
  25. #include <linux/preempt.h>
  26. #include <linux/bottom_half.h>
  27. #include <linux/lockdep.h>
  28. #include <asm/processor.h>
  29. #include <linux/cpumask.h>
  30. #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
  31. #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
  32. #define ulong2long(a) (*(long *)(&(a)))
  33. #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
  34. #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
  35. /* Exported common interfaces */
  36. void call_rcu(struct rcu_head *head, rcu_callback_t func);
  37. void rcu_barrier_tasks(void);
  38. void rcu_barrier_tasks_rude(void);
  39. void synchronize_rcu(void);
  40. #ifdef CONFIG_PREEMPT_RCU
  41. void __rcu_read_lock(void);
  42. void __rcu_read_unlock(void);
  43. /*
  44. * Defined as a macro as it is a very low level header included from
  45. * areas that don't even know about current. This gives the rcu_read_lock()
  46. * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
  47. * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
  48. */
  49. #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
  50. #else /* #ifdef CONFIG_PREEMPT_RCU */
  51. #ifdef CONFIG_TINY_RCU
  52. #define rcu_read_unlock_strict() do { } while (0)
  53. #else
  54. void rcu_read_unlock_strict(void);
  55. #endif
  56. static inline void __rcu_read_lock(void)
  57. {
  58. preempt_disable();
  59. }
  60. static inline void __rcu_read_unlock(void)
  61. {
  62. preempt_enable();
  63. rcu_read_unlock_strict();
  64. }
  65. static inline int rcu_preempt_depth(void)
  66. {
  67. return 0;
  68. }
  69. #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
  70. /* Internal to kernel */
  71. void rcu_init(void);
  72. extern int rcu_scheduler_active __read_mostly;
  73. void rcu_sched_clock_irq(int user);
  74. void rcu_report_dead(unsigned int cpu);
  75. void rcutree_migrate_callbacks(int cpu);
  76. #ifdef CONFIG_TASKS_RCU_GENERIC
  77. void rcu_init_tasks_generic(void);
  78. #else
  79. static inline void rcu_init_tasks_generic(void) { }
  80. #endif
  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. #ifdef CONFIG_NO_HZ_FULL
  89. void rcu_user_enter(void);
  90. void rcu_user_exit(void);
  91. #else
  92. static inline void rcu_user_enter(void) { }
  93. static inline void rcu_user_exit(void) { }
  94. #endif /* CONFIG_NO_HZ_FULL */
  95. #ifdef CONFIG_RCU_NOCB_CPU
  96. void rcu_init_nohz(void);
  97. void rcu_nocb_flush_deferred_wakeup(void);
  98. #else /* #ifdef CONFIG_RCU_NOCB_CPU */
  99. static inline void rcu_init_nohz(void) { }
  100. static inline void rcu_nocb_flush_deferred_wakeup(void) { }
  101. #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
  102. /**
  103. * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
  104. * @a: Code that RCU needs to pay attention to.
  105. *
  106. * RCU read-side critical sections are forbidden in the inner idle loop,
  107. * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU
  108. * will happily ignore any such read-side critical sections. However,
  109. * things like powertop need tracepoints in the inner idle loop.
  110. *
  111. * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
  112. * will tell RCU that it needs to pay attention, invoke its argument
  113. * (in this example, calling the do_something_with_RCU() function),
  114. * and then tell RCU to go back to ignoring this CPU. It is permissible
  115. * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
  116. * on the order of a million or so, even on 32-bit systems). It is
  117. * not legal to block within RCU_NONIDLE(), nor is it permissible to
  118. * transfer control either into or out of RCU_NONIDLE()'s statement.
  119. */
  120. #define RCU_NONIDLE(a) \
  121. do { \
  122. rcu_irq_enter_irqson(); \
  123. do { a; } while (0); \
  124. rcu_irq_exit_irqson(); \
  125. } while (0)
  126. /*
  127. * Note a quasi-voluntary context switch for RCU-tasks's benefit.
  128. * This is a macro rather than an inline function to avoid #include hell.
  129. */
  130. #ifdef CONFIG_TASKS_RCU_GENERIC
  131. # ifdef CONFIG_TASKS_RCU
  132. # define rcu_tasks_classic_qs(t, preempt) \
  133. do { \
  134. if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
  135. WRITE_ONCE((t)->rcu_tasks_holdout, false); \
  136. } while (0)
  137. void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
  138. void synchronize_rcu_tasks(void);
  139. # else
  140. # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
  141. # define call_rcu_tasks call_rcu
  142. # define synchronize_rcu_tasks synchronize_rcu
  143. # endif
  144. # ifdef CONFIG_TASKS_TRACE_RCU
  145. # define rcu_tasks_trace_qs(t) \
  146. do { \
  147. if (!likely(READ_ONCE((t)->trc_reader_checked)) && \
  148. !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \
  149. smp_store_release(&(t)->trc_reader_checked, true); \
  150. smp_mb(); /* Readers partitioned by store. */ \
  151. } \
  152. } while (0)
  153. # else
  154. # define rcu_tasks_trace_qs(t) do { } while (0)
  155. # endif
  156. #define rcu_tasks_qs(t, preempt) \
  157. do { \
  158. rcu_tasks_classic_qs((t), (preempt)); \
  159. rcu_tasks_trace_qs((t)); \
  160. } while (0)
  161. # ifdef CONFIG_TASKS_RUDE_RCU
  162. void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
  163. void synchronize_rcu_tasks_rude(void);
  164. # endif
  165. #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
  166. void exit_tasks_rcu_start(void);
  167. void exit_tasks_rcu_finish(void);
  168. #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
  169. #define rcu_tasks_qs(t, preempt) do { } while (0)
  170. #define rcu_note_voluntary_context_switch(t) do { } while (0)
  171. #define call_rcu_tasks call_rcu
  172. #define synchronize_rcu_tasks synchronize_rcu
  173. static inline void exit_tasks_rcu_start(void) { }
  174. static inline void exit_tasks_rcu_finish(void) { }
  175. #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
  176. /**
  177. * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
  178. *
  179. * This macro resembles cond_resched(), except that it is defined to
  180. * report potential quiescent states to RCU-tasks even if the cond_resched()
  181. * machinery were to be shut off, as some advocate for PREEMPTION kernels.
  182. */
  183. #define cond_resched_tasks_rcu_qs() \
  184. do { \
  185. rcu_tasks_qs(current, false); \
  186. cond_resched(); \
  187. } while (0)
  188. /*
  189. * Infrastructure to implement the synchronize_() primitives in
  190. * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
  191. */
  192. #if defined(CONFIG_TREE_RCU)
  193. #include <linux/rcutree.h>
  194. #elif defined(CONFIG_TINY_RCU)
  195. #include <linux/rcutiny.h>
  196. #else
  197. #error "Unknown RCU implementation specified to kernel configuration"
  198. #endif
  199. /*
  200. * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
  201. * are needed for dynamic initialization and destruction of rcu_head
  202. * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
  203. * dynamic initialization and destruction of statically allocated rcu_head
  204. * structures. However, rcu_head structures allocated dynamically in the
  205. * heap don't need any initialization.
  206. */
  207. #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
  208. void init_rcu_head(struct rcu_head *head);
  209. void destroy_rcu_head(struct rcu_head *head);
  210. void init_rcu_head_on_stack(struct rcu_head *head);
  211. void destroy_rcu_head_on_stack(struct rcu_head *head);
  212. #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
  213. static inline void init_rcu_head(struct rcu_head *head) { }
  214. static inline void destroy_rcu_head(struct rcu_head *head) { }
  215. static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
  216. static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
  217. #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
  218. #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
  219. bool rcu_lockdep_current_cpu_online(void);
  220. #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
  221. static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
  222. #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
  223. #ifdef CONFIG_DEBUG_LOCK_ALLOC
  224. static inline void rcu_lock_acquire(struct lockdep_map *map)
  225. {
  226. lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
  227. }
  228. static inline void rcu_lock_release(struct lockdep_map *map)
  229. {
  230. lock_release(map, _THIS_IP_);
  231. }
  232. extern struct lockdep_map rcu_lock_map;
  233. extern struct lockdep_map rcu_bh_lock_map;
  234. extern struct lockdep_map rcu_sched_lock_map;
  235. extern struct lockdep_map rcu_callback_map;
  236. int debug_lockdep_rcu_enabled(void);
  237. int rcu_read_lock_held(void);
  238. int rcu_read_lock_bh_held(void);
  239. int rcu_read_lock_sched_held(void);
  240. int rcu_read_lock_any_held(void);
  241. #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  242. # define rcu_lock_acquire(a) do { } while (0)
  243. # define rcu_lock_release(a) do { } while (0)
  244. static inline int rcu_read_lock_held(void)
  245. {
  246. return 1;
  247. }
  248. static inline int rcu_read_lock_bh_held(void)
  249. {
  250. return 1;
  251. }
  252. static inline int rcu_read_lock_sched_held(void)
  253. {
  254. return !preemptible();
  255. }
  256. static inline int rcu_read_lock_any_held(void)
  257. {
  258. return !preemptible();
  259. }
  260. #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  261. #ifdef CONFIG_PROVE_RCU
  262. /**
  263. * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
  264. * @c: condition to check
  265. * @s: informative message
  266. */
  267. #define RCU_LOCKDEP_WARN(c, s) \
  268. do { \
  269. static bool __section(".data.unlikely") __warned; \
  270. if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \
  271. __warned = true; \
  272. lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
  273. } \
  274. } while (0)
  275. #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
  276. static inline void rcu_preempt_sleep_check(void)
  277. {
  278. RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
  279. "Illegal context switch in RCU read-side critical section");
  280. }
  281. #else /* #ifdef CONFIG_PROVE_RCU */
  282. static inline void rcu_preempt_sleep_check(void) { }
  283. #endif /* #else #ifdef CONFIG_PROVE_RCU */
  284. #define rcu_sleep_check() \
  285. do { \
  286. rcu_preempt_sleep_check(); \
  287. RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
  288. "Illegal context switch in RCU-bh read-side critical section"); \
  289. RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
  290. "Illegal context switch in RCU-sched read-side critical section"); \
  291. } while (0)
  292. #else /* #ifdef CONFIG_PROVE_RCU */
  293. #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
  294. #define rcu_sleep_check() do { } while (0)
  295. #endif /* #else #ifdef CONFIG_PROVE_RCU */
  296. /*
  297. * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
  298. * and rcu_assign_pointer(). Some of these could be folded into their
  299. * callers, but they are left separate in order to ease introduction of
  300. * multiple pointers markings to match different RCU implementations
  301. * (e.g., __srcu), should this make sense in the future.
  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. #define __rcu_access_pointer(p, space) \
  310. ({ \
  311. typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
  312. rcu_check_sparse(p, space); \
  313. ((typeof(*p) __force __kernel *)(_________p1)); \
  314. })
  315. #define __rcu_dereference_check(p, c, space) \
  316. ({ \
  317. /* Dependency order vs. p above. */ \
  318. typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
  319. RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
  320. rcu_check_sparse(p, space); \
  321. ((typeof(*p) __force __kernel *)(________p1)); \
  322. })
  323. #define __rcu_dereference_protected(p, c, space) \
  324. ({ \
  325. RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
  326. rcu_check_sparse(p, space); \
  327. ((typeof(*p) __force __kernel *)(p)); \
  328. })
  329. #define rcu_dereference_raw(p) \
  330. ({ \
  331. /* Dependency order vs. p above. */ \
  332. typeof(p) ________p1 = READ_ONCE(p); \
  333. ((typeof(*p) __force __kernel *)(________p1)); \
  334. })
  335. /**
  336. * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
  337. * @v: The value to statically initialize with.
  338. */
  339. #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
  340. /**
  341. * rcu_assign_pointer() - assign to RCU-protected pointer
  342. * @p: pointer to assign to
  343. * @v: value to assign (publish)
  344. *
  345. * Assigns the specified value to the specified RCU-protected
  346. * pointer, ensuring that any concurrent RCU readers will see
  347. * any prior initialization.
  348. *
  349. * Inserts memory barriers on architectures that require them
  350. * (which is most of them), and also prevents the compiler from
  351. * reordering the code that initializes the structure after the pointer
  352. * assignment. More importantly, this call documents which pointers
  353. * will be dereferenced by RCU read-side code.
  354. *
  355. * In some special cases, you may use RCU_INIT_POINTER() instead
  356. * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
  357. * to the fact that it does not constrain either the CPU or the compiler.
  358. * That said, using RCU_INIT_POINTER() when you should have used
  359. * rcu_assign_pointer() is a very bad thing that results in
  360. * impossible-to-diagnose memory corruption. So please be careful.
  361. * See the RCU_INIT_POINTER() comment header for details.
  362. *
  363. * Note that rcu_assign_pointer() evaluates each of its arguments only
  364. * once, appearances notwithstanding. One of the "extra" evaluations
  365. * is in typeof() and the other visible only to sparse (__CHECKER__),
  366. * neither of which actually execute the argument. As with most cpp
  367. * macros, this execute-arguments-only-once property is important, so
  368. * please be careful when making changes to rcu_assign_pointer() and the
  369. * other macros that it invokes.
  370. */
  371. #define rcu_assign_pointer(p, v) \
  372. do { \
  373. uintptr_t _r_a_p__v = (uintptr_t)(v); \
  374. rcu_check_sparse(p, __rcu); \
  375. \
  376. if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \
  377. WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \
  378. else \
  379. smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
  380. } while (0)
  381. /**
  382. * rcu_replace_pointer() - replace an RCU pointer, returning its old value
  383. * @rcu_ptr: RCU pointer, whose old value is returned
  384. * @ptr: regular pointer
  385. * @c: the lockdep conditions under which the dereference will take place
  386. *
  387. * Perform a replacement, where @rcu_ptr is an RCU-annotated
  388. * pointer and @c is the lockdep argument that is passed to the
  389. * rcu_dereference_protected() call used to read that pointer. The old
  390. * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
  391. */
  392. #define rcu_replace_pointer(rcu_ptr, ptr, c) \
  393. ({ \
  394. typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \
  395. rcu_assign_pointer((rcu_ptr), (ptr)); \
  396. __tmp; \
  397. })
  398. /**
  399. * rcu_access_pointer() - fetch RCU pointer with no dereferencing
  400. * @p: The pointer to read
  401. *
  402. * Return the value of the specified RCU-protected pointer, but omit the
  403. * lockdep checks for being in an RCU read-side critical section. This is
  404. * useful when the value of this pointer is accessed, but the pointer is
  405. * not dereferenced, for example, when testing an RCU-protected pointer
  406. * against NULL. Although rcu_access_pointer() may also be used in cases
  407. * where update-side locks prevent the value of the pointer from changing,
  408. * you should instead use rcu_dereference_protected() for this use case.
  409. *
  410. * It is also permissible to use rcu_access_pointer() when read-side
  411. * access to the pointer was removed at least one grace period ago, as
  412. * is the case in the context of the RCU callback that is freeing up
  413. * the data, or after a synchronize_rcu() returns. This can be useful
  414. * when tearing down multi-linked structures after a grace period
  415. * has elapsed.
  416. */
  417. #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
  418. /**
  419. * rcu_dereference_check() - rcu_dereference with debug checking
  420. * @p: The pointer to read, prior to dereferencing
  421. * @c: The conditions under which the dereference will take place
  422. *
  423. * Do an rcu_dereference(), but check that the conditions under which the
  424. * dereference will take place are correct. Typically the conditions
  425. * indicate the various locking conditions that should be held at that
  426. * point. The check should return true if the conditions are satisfied.
  427. * An implicit check for being in an RCU read-side critical section
  428. * (rcu_read_lock()) is included.
  429. *
  430. * For example:
  431. *
  432. * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
  433. *
  434. * could be used to indicate to lockdep that foo->bar may only be dereferenced
  435. * if either rcu_read_lock() is held, or that the lock required to replace
  436. * the bar struct at foo->bar is held.
  437. *
  438. * Note that the list of conditions may also include indications of when a lock
  439. * need not be held, for example during initialisation or destruction of the
  440. * target struct:
  441. *
  442. * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
  443. * atomic_read(&foo->usage) == 0);
  444. *
  445. * Inserts memory barriers on architectures that require them
  446. * (currently only the Alpha), prevents the compiler from refetching
  447. * (and from merging fetches), and, more importantly, documents exactly
  448. * which pointers are protected by RCU and checks that the pointer is
  449. * annotated as __rcu.
  450. */
  451. #define rcu_dereference_check(p, c) \
  452. __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
  453. /**
  454. * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
  455. * @p: The pointer to read, prior to dereferencing
  456. * @c: The conditions under which the dereference will take place
  457. *
  458. * This is the RCU-bh counterpart to rcu_dereference_check().
  459. */
  460. #define rcu_dereference_bh_check(p, c) \
  461. __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
  462. /**
  463. * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
  464. * @p: The pointer to read, prior to dereferencing
  465. * @c: The conditions under which the dereference will take place
  466. *
  467. * This is the RCU-sched counterpart to rcu_dereference_check().
  468. */
  469. #define rcu_dereference_sched_check(p, c) \
  470. __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
  471. __rcu)
  472. /*
  473. * The tracing infrastructure traces RCU (we want that), but unfortunately
  474. * some of the RCU checks causes tracing to lock up the system.
  475. *
  476. * The no-tracing version of rcu_dereference_raw() must not call
  477. * rcu_read_lock_held().
  478. */
  479. #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
  480. /**
  481. * rcu_dereference_protected() - fetch RCU pointer when updates prevented
  482. * @p: The pointer to read, prior to dereferencing
  483. * @c: The conditions under which the dereference will take place
  484. *
  485. * Return the value of the specified RCU-protected pointer, but omit
  486. * the READ_ONCE(). This is useful in cases where update-side locks
  487. * prevent the value of the pointer from changing. Please note that this
  488. * primitive does *not* prevent the compiler from repeating this reference
  489. * or combining it with other references, so it should not be used without
  490. * protection of appropriate locks.
  491. *
  492. * This function is only for update-side use. Using this function
  493. * when protected only by rcu_read_lock() will result in infrequent
  494. * but very ugly failures.
  495. */
  496. #define rcu_dereference_protected(p, c) \
  497. __rcu_dereference_protected((p), (c), __rcu)
  498. /**
  499. * rcu_dereference() - fetch RCU-protected pointer for dereferencing
  500. * @p: The pointer to read, prior to dereferencing
  501. *
  502. * This is a simple wrapper around rcu_dereference_check().
  503. */
  504. #define rcu_dereference(p) rcu_dereference_check(p, 0)
  505. /**
  506. * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
  507. * @p: The pointer to read, prior to dereferencing
  508. *
  509. * Makes rcu_dereference_check() do the dirty work.
  510. */
  511. #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
  512. /**
  513. * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
  514. * @p: The pointer to read, prior to dereferencing
  515. *
  516. * Makes rcu_dereference_check() do the dirty work.
  517. */
  518. #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
  519. /**
  520. * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
  521. * @p: The pointer to hand off
  522. *
  523. * This is simply an identity function, but it documents where a pointer
  524. * is handed off from RCU to some other synchronization mechanism, for
  525. * example, reference counting or locking. In C11, it would map to
  526. * kill_dependency(). It could be used as follows::
  527. *
  528. * rcu_read_lock();
  529. * p = rcu_dereference(gp);
  530. * long_lived = is_long_lived(p);
  531. * if (long_lived) {
  532. * if (!atomic_inc_not_zero(p->refcnt))
  533. * long_lived = false;
  534. * else
  535. * p = rcu_pointer_handoff(p);
  536. * }
  537. * rcu_read_unlock();
  538. */
  539. #define rcu_pointer_handoff(p) (p)
  540. /**
  541. * rcu_read_lock() - mark the beginning of an RCU read-side critical section
  542. *
  543. * When synchronize_rcu() is invoked on one CPU while other CPUs
  544. * are within RCU read-side critical sections, then the
  545. * synchronize_rcu() is guaranteed to block until after all the other
  546. * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
  547. * on one CPU while other CPUs are within RCU read-side critical
  548. * sections, invocation of the corresponding RCU callback is deferred
  549. * until after the all the other CPUs exit their critical sections.
  550. *
  551. * Note, however, that RCU callbacks are permitted to run concurrently
  552. * with new RCU read-side critical sections. One way that this can happen
  553. * is via the following sequence of events: (1) CPU 0 enters an RCU
  554. * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  555. * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  556. * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  557. * callback is invoked. This is legal, because the RCU read-side critical
  558. * section that was running concurrently with the call_rcu() (and which
  559. * therefore might be referencing something that the corresponding RCU
  560. * callback would free up) has completed before the corresponding
  561. * RCU callback is invoked.
  562. *
  563. * RCU read-side critical sections may be nested. Any deferred actions
  564. * will be deferred until the outermost RCU read-side critical section
  565. * completes.
  566. *
  567. * You can avoid reading and understanding the next paragraph by
  568. * following this rule: don't put anything in an rcu_read_lock() RCU
  569. * read-side critical section that would block in a !PREEMPTION kernel.
  570. * But if you want the full story, read on!
  571. *
  572. * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
  573. * it is illegal to block while in an RCU read-side critical section.
  574. * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
  575. * kernel builds, RCU read-side critical sections may be preempted,
  576. * but explicit blocking is illegal. Finally, in preemptible RCU
  577. * implementations in real-time (with -rt patchset) kernel builds, RCU
  578. * read-side critical sections may be preempted and they may also block, but
  579. * only when acquiring spinlocks that are subject to priority inheritance.
  580. */
  581. static __always_inline void rcu_read_lock(void)
  582. {
  583. __rcu_read_lock();
  584. __acquire(RCU);
  585. rcu_lock_acquire(&rcu_lock_map);
  586. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  587. "rcu_read_lock() used illegally while idle");
  588. }
  589. /*
  590. * So where is rcu_write_lock()? It does not exist, as there is no
  591. * way for writers to lock out RCU readers. This is a feature, not
  592. * a bug -- this property is what provides RCU's performance benefits.
  593. * Of course, writers must coordinate with each other. The normal
  594. * spinlock primitives work well for this, but any other technique may be
  595. * used as well. RCU does not care how the writers keep out of each
  596. * others' way, as long as they do so.
  597. */
  598. /**
  599. * rcu_read_unlock() - marks the end of an RCU read-side critical section.
  600. *
  601. * In most situations, rcu_read_unlock() is immune from deadlock.
  602. * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
  603. * is responsible for deboosting, which it does via rt_mutex_unlock().
  604. * Unfortunately, this function acquires the scheduler's runqueue and
  605. * priority-inheritance spinlocks. This means that deadlock could result
  606. * if the caller of rcu_read_unlock() already holds one of these locks or
  607. * any lock that is ever acquired while holding them.
  608. *
  609. * That said, RCU readers are never priority boosted unless they were
  610. * preempted. Therefore, one way to avoid deadlock is to make sure
  611. * that preemption never happens within any RCU read-side critical
  612. * section whose outermost rcu_read_unlock() is called with one of
  613. * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
  614. * a number of ways, for example, by invoking preempt_disable() before
  615. * critical section's outermost rcu_read_lock().
  616. *
  617. * Given that the set of locks acquired by rt_mutex_unlock() might change
  618. * at any time, a somewhat more future-proofed approach is to make sure
  619. * that that preemption never happens within any RCU read-side critical
  620. * section whose outermost rcu_read_unlock() is called with irqs disabled.
  621. * This approach relies on the fact that rt_mutex_unlock() currently only
  622. * acquires irq-disabled locks.
  623. *
  624. * The second of these two approaches is best in most situations,
  625. * however, the first approach can also be useful, at least to those
  626. * developers willing to keep abreast of the set of locks acquired by
  627. * rt_mutex_unlock().
  628. *
  629. * See rcu_read_lock() for more information.
  630. */
  631. static inline void rcu_read_unlock(void)
  632. {
  633. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  634. "rcu_read_unlock() used illegally while idle");
  635. __release(RCU);
  636. __rcu_read_unlock();
  637. rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
  638. }
  639. /**
  640. * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
  641. *
  642. * This is equivalent of rcu_read_lock(), but also disables softirqs.
  643. * Note that anything else that disables softirqs can also serve as
  644. * an RCU read-side critical section.
  645. *
  646. * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
  647. * must occur in the same context, for example, it is illegal to invoke
  648. * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
  649. * was invoked from some other task.
  650. */
  651. static inline void rcu_read_lock_bh(void)
  652. {
  653. local_bh_disable();
  654. __acquire(RCU_BH);
  655. rcu_lock_acquire(&rcu_bh_lock_map);
  656. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  657. "rcu_read_lock_bh() used illegally while idle");
  658. }
  659. /**
  660. * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
  661. *
  662. * See rcu_read_lock_bh() for more information.
  663. */
  664. static inline void rcu_read_unlock_bh(void)
  665. {
  666. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  667. "rcu_read_unlock_bh() used illegally while idle");
  668. rcu_lock_release(&rcu_bh_lock_map);
  669. __release(RCU_BH);
  670. local_bh_enable();
  671. }
  672. /**
  673. * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
  674. *
  675. * This is equivalent of rcu_read_lock(), but disables preemption.
  676. * Read-side critical sections can also be introduced by anything else
  677. * that disables preemption, including local_irq_disable() and friends.
  678. *
  679. * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
  680. * must occur in the same context, for example, it is illegal to invoke
  681. * rcu_read_unlock_sched() from process context if the matching
  682. * rcu_read_lock_sched() was invoked from an NMI handler.
  683. */
  684. static inline void rcu_read_lock_sched(void)
  685. {
  686. preempt_disable();
  687. __acquire(RCU_SCHED);
  688. rcu_lock_acquire(&rcu_sched_lock_map);
  689. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  690. "rcu_read_lock_sched() used illegally while idle");
  691. }
  692. /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
  693. static inline notrace void rcu_read_lock_sched_notrace(void)
  694. {
  695. preempt_disable_notrace();
  696. __acquire(RCU_SCHED);
  697. }
  698. /**
  699. * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
  700. *
  701. * See rcu_read_lock_sched() for more information.
  702. */
  703. static inline void rcu_read_unlock_sched(void)
  704. {
  705. RCU_LOCKDEP_WARN(!rcu_is_watching(),
  706. "rcu_read_unlock_sched() used illegally while idle");
  707. rcu_lock_release(&rcu_sched_lock_map);
  708. __release(RCU_SCHED);
  709. preempt_enable();
  710. }
  711. /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
  712. static inline notrace void rcu_read_unlock_sched_notrace(void)
  713. {
  714. __release(RCU_SCHED);
  715. preempt_enable_notrace();
  716. }
  717. /**
  718. * RCU_INIT_POINTER() - initialize an RCU protected pointer
  719. * @p: The pointer to be initialized.
  720. * @v: The value to initialized the pointer to.
  721. *
  722. * Initialize an RCU-protected pointer in special cases where readers
  723. * do not need ordering constraints on the CPU or the compiler. These
  724. * special cases are:
  725. *
  726. * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
  727. * 2. The caller has taken whatever steps are required to prevent
  728. * RCU readers from concurrently accessing this pointer *or*
  729. * 3. The referenced data structure has already been exposed to
  730. * readers either at compile time or via rcu_assign_pointer() *and*
  731. *
  732. * a. You have not made *any* reader-visible changes to
  733. * this structure since then *or*
  734. * b. It is OK for readers accessing this structure from its
  735. * new location to see the old state of the structure. (For
  736. * example, the changes were to statistical counters or to
  737. * other state where exact synchronization is not required.)
  738. *
  739. * Failure to follow these rules governing use of RCU_INIT_POINTER() will
  740. * result in impossible-to-diagnose memory corruption. As in the structures
  741. * will look OK in crash dumps, but any concurrent RCU readers might
  742. * see pre-initialized values of the referenced data structure. So
  743. * please be very careful how you use RCU_INIT_POINTER()!!!
  744. *
  745. * If you are creating an RCU-protected linked structure that is accessed
  746. * by a single external-to-structure RCU-protected pointer, then you may
  747. * use RCU_INIT_POINTER() to initialize the internal RCU-protected
  748. * pointers, but you must use rcu_assign_pointer() to initialize the
  749. * external-to-structure pointer *after* you have completely initialized
  750. * the reader-accessible portions of the linked structure.
  751. *
  752. * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
  753. * ordering guarantees for either the CPU or the compiler.
  754. */
  755. #define RCU_INIT_POINTER(p, v) \
  756. do { \
  757. rcu_check_sparse(p, __rcu); \
  758. WRITE_ONCE(p, RCU_INITIALIZER(v)); \
  759. } while (0)
  760. /**
  761. * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
  762. * @p: The pointer to be initialized.
  763. * @v: The value to initialized the pointer to.
  764. *
  765. * GCC-style initialization for an RCU-protected pointer in a structure field.
  766. */
  767. #define RCU_POINTER_INITIALIZER(p, v) \
  768. .p = RCU_INITIALIZER(v)
  769. /*
  770. * Does the specified offset indicate that the corresponding rcu_head
  771. * structure can be handled by kvfree_rcu()?
  772. */
  773. #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
  774. /*
  775. * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
  776. */
  777. #define __kvfree_rcu(head, offset) \
  778. do { \
  779. BUILD_BUG_ON(!__is_kvfree_rcu_offset(offset)); \
  780. kvfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
  781. } while (0)
  782. /**
  783. * kfree_rcu() - kfree an object after a grace period.
  784. * @ptr: pointer to kfree
  785. * @rhf: the name of the struct rcu_head within the type of @ptr.
  786. *
  787. * Many rcu callbacks functions just call kfree() on the base structure.
  788. * These functions are trivial, but their size adds up, and furthermore
  789. * when they are used in a kernel module, that module must invoke the
  790. * high-latency rcu_barrier() function at module-unload time.
  791. *
  792. * The kfree_rcu() function handles this issue. Rather than encoding a
  793. * function address in the embedded rcu_head structure, kfree_rcu() instead
  794. * encodes the offset of the rcu_head structure within the base structure.
  795. * Because the functions are not allowed in the low-order 4096 bytes of
  796. * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
  797. * If the offset is larger than 4095 bytes, a compile-time error will
  798. * be generated in __kvfree_rcu(). If this error is triggered, you can
  799. * either fall back to use of call_rcu() or rearrange the structure to
  800. * position the rcu_head structure into the first 4096 bytes.
  801. *
  802. * Note that the allowable offset might decrease in the future, for example,
  803. * to allow something like kmem_cache_free_rcu().
  804. *
  805. * The BUILD_BUG_ON check must not involve any function calls, hence the
  806. * checks are done in macros here.
  807. */
  808. #define kfree_rcu(ptr, rhf) \
  809. do { \
  810. typeof (ptr) ___p = (ptr); \
  811. \
  812. if (___p) \
  813. __kvfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
  814. } while (0)
  815. /**
  816. * kvfree_rcu() - kvfree an object after a grace period.
  817. *
  818. * This macro consists of one or two arguments and it is
  819. * based on whether an object is head-less or not. If it
  820. * has a head then a semantic stays the same as it used
  821. * to be before:
  822. *
  823. * kvfree_rcu(ptr, rhf);
  824. *
  825. * where @ptr is a pointer to kvfree(), @rhf is the name
  826. * of the rcu_head structure within the type of @ptr.
  827. *
  828. * When it comes to head-less variant, only one argument
  829. * is passed and that is just a pointer which has to be
  830. * freed after a grace period. Therefore the semantic is
  831. *
  832. * kvfree_rcu(ptr);
  833. *
  834. * where @ptr is a pointer to kvfree().
  835. *
  836. * Please note, head-less way of freeing is permitted to
  837. * use from a context that has to follow might_sleep()
  838. * annotation. Otherwise, please switch and embed the
  839. * rcu_head structure within the type of @ptr.
  840. */
  841. #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \
  842. kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
  843. #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
  844. #define kvfree_rcu_arg_2(ptr, rhf) kfree_rcu(ptr, rhf)
  845. #define kvfree_rcu_arg_1(ptr) \
  846. do { \
  847. typeof(ptr) ___p = (ptr); \
  848. \
  849. if (___p) \
  850. kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
  851. } while (0)
  852. /*
  853. * Place this after a lock-acquisition primitive to guarantee that
  854. * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
  855. * if the UNLOCK and LOCK are executed by the same CPU or if the
  856. * UNLOCK and LOCK operate on the same lock variable.
  857. */
  858. #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
  859. #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */
  860. #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
  861. #define smp_mb__after_unlock_lock() do { } while (0)
  862. #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
  863. /* Has the specified rcu_head structure been handed to call_rcu()? */
  864. /**
  865. * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
  866. * @rhp: The rcu_head structure to initialize.
  867. *
  868. * If you intend to invoke rcu_head_after_call_rcu() to test whether a
  869. * given rcu_head structure has already been passed to call_rcu(), then
  870. * you must also invoke this rcu_head_init() function on it just after
  871. * allocating that structure. Calls to this function must not race with
  872. * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
  873. */
  874. static inline void rcu_head_init(struct rcu_head *rhp)
  875. {
  876. rhp->func = (rcu_callback_t)~0L;
  877. }
  878. /**
  879. * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
  880. * @rhp: The rcu_head structure to test.
  881. * @f: The function passed to call_rcu() along with @rhp.
  882. *
  883. * Returns @true if the @rhp has been passed to call_rcu() with @func,
  884. * and @false otherwise. Emits a warning in any other case, including
  885. * the case where @rhp has already been invoked after a grace period.
  886. * Calls to this function must not race with callback invocation. One way
  887. * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
  888. * in an RCU read-side critical section that includes a read-side fetch
  889. * of the pointer to the structure containing @rhp.
  890. */
  891. static inline bool
  892. rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
  893. {
  894. rcu_callback_t func = READ_ONCE(rhp->func);
  895. if (func == f)
  896. return true;
  897. WARN_ON_ONCE(func != (rcu_callback_t)~0L);
  898. return false;
  899. }
  900. /* kernel/ksysfs.c definitions */
  901. extern int rcu_expedited;
  902. extern int rcu_normal;
  903. #endif /* __LINUX_RCUPDATE_H */