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 <linux/cleanup.h> 31 #include <asm/processor.h> 32 #include <linux/context_tracking_irq.h> 33 34 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 35 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 36 37 #define RCU_SEQ_CTR_SHIFT 2 38 #define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1) 39 40 /* Exported common interfaces */ 41 void call_rcu(struct rcu_head *head, rcu_callback_t func); 42 void rcu_barrier_tasks(void); 43 void synchronize_rcu(void); 44 45 struct rcu_gp_oldstate; 46 unsigned long get_completed_synchronize_rcu(void); 47 void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp); 48 49 // Maximum number of unsigned long values corresponding to 50 // not-yet-completed RCU grace periods. 51 #define NUM_ACTIVE_RCU_POLL_OLDSTATE 2 52 53 /** 54 * same_state_synchronize_rcu - Are two old-state values identical? 55 * @oldstate1: First old-state value. 56 * @oldstate2: Second old-state value. 57 * 58 * The two old-state values must have been obtained from either 59 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or 60 * get_completed_synchronize_rcu(). Returns @true if the two values are 61 * identical and @false otherwise. This allows structures whose lifetimes 62 * are tracked by old-state values to push these values to a list header, 63 * allowing those structures to be slightly smaller. 64 */ same_state_synchronize_rcu(unsigned long oldstate1,unsigned long oldstate2)65 static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2) 66 { 67 return oldstate1 == oldstate2; 68 } 69 70 #ifdef CONFIG_PREEMPT_RCU 71 72 void __rcu_read_lock(void); 73 void __rcu_read_unlock(void); 74 75 /* 76 * Defined as a macro as it is a very low level header included from 77 * areas that don't even know about current. This gives the rcu_read_lock() 78 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 79 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 80 */ 81 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) 82 83 #else /* #ifdef CONFIG_PREEMPT_RCU */ 84 85 #ifdef CONFIG_TINY_RCU 86 #define rcu_read_unlock_strict() do { } while (0) 87 #else 88 void rcu_read_unlock_strict(void); 89 #endif 90 __rcu_read_lock(void)91 static inline void __rcu_read_lock(void) 92 { 93 preempt_disable(); 94 } 95 __rcu_read_unlock(void)96 static inline void __rcu_read_unlock(void) 97 { 98 preempt_enable(); 99 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) 100 rcu_read_unlock_strict(); 101 } 102 rcu_preempt_depth(void)103 static inline int rcu_preempt_depth(void) 104 { 105 return 0; 106 } 107 108 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 109 110 #ifdef CONFIG_RCU_LAZY 111 void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func); 112 #else call_rcu_hurry(struct rcu_head * head,rcu_callback_t func)113 static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) 114 { 115 call_rcu(head, func); 116 } 117 #endif 118 119 /* Internal to kernel */ 120 void rcu_init(void); 121 extern int rcu_scheduler_active; 122 void rcu_sched_clock_irq(int user); 123 124 #ifdef CONFIG_TASKS_RCU_GENERIC 125 void rcu_init_tasks_generic(void); 126 #else rcu_init_tasks_generic(void)127 static inline void rcu_init_tasks_generic(void) { } 128 #endif 129 130 #ifdef CONFIG_RCU_STALL_COMMON 131 void rcu_sysrq_start(void); 132 void rcu_sysrq_end(void); 133 #else /* #ifdef CONFIG_RCU_STALL_COMMON */ rcu_sysrq_start(void)134 static inline void rcu_sysrq_start(void) { } rcu_sysrq_end(void)135 static inline void rcu_sysrq_end(void) { } 136 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ 137 138 #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) 139 void rcu_irq_work_resched(void); 140 #else rcu_irq_work_resched(void)141 static inline void rcu_irq_work_resched(void) { } 142 #endif 143 144 #ifdef CONFIG_RCU_NOCB_CPU 145 void rcu_init_nohz(void); 146 int rcu_nocb_cpu_offload(int cpu); 147 int rcu_nocb_cpu_deoffload(int cpu); 148 void rcu_nocb_flush_deferred_wakeup(void); 149 150 #define RCU_NOCB_LOCKDEP_WARN(c, s) RCU_LOCKDEP_WARN(c, s) 151 152 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 153 rcu_init_nohz(void)154 static inline void rcu_init_nohz(void) { } rcu_nocb_cpu_offload(int cpu)155 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } rcu_nocb_cpu_deoffload(int cpu)156 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } rcu_nocb_flush_deferred_wakeup(void)157 static inline void rcu_nocb_flush_deferred_wakeup(void) { } 158 159 #define RCU_NOCB_LOCKDEP_WARN(c, s) 160 161 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 162 163 /* 164 * Note a quasi-voluntary context switch for RCU-tasks's benefit. 165 * This is a macro rather than an inline function to avoid #include hell. 166 */ 167 #ifdef CONFIG_TASKS_RCU_GENERIC 168 169 # ifdef CONFIG_TASKS_RCU 170 # define rcu_tasks_classic_qs(t, preempt) \ 171 do { \ 172 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ 173 WRITE_ONCE((t)->rcu_tasks_holdout, false); \ 174 } while (0) 175 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); 176 void synchronize_rcu_tasks(void); 177 void rcu_tasks_torture_stats_print(char *tt, char *tf); 178 # else 179 # define rcu_tasks_classic_qs(t, preempt) do { } while (0) 180 # define call_rcu_tasks call_rcu 181 # define synchronize_rcu_tasks synchronize_rcu 182 # endif 183 184 # ifdef CONFIG_TASKS_TRACE_RCU 185 // Bits for ->trc_reader_special.b.need_qs field. 186 #define TRC_NEED_QS 0x1 // Task needs a quiescent state. 187 #define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state. 188 189 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new); 190 void rcu_tasks_trace_qs_blkd(struct task_struct *t); 191 192 # define rcu_tasks_trace_qs(t) \ 193 do { \ 194 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \ 195 \ 196 if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) && \ 197 likely(!___rttq_nesting)) { \ 198 rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED); \ 199 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \ 200 !READ_ONCE((t)->trc_reader_special.b.blocked)) { \ 201 rcu_tasks_trace_qs_blkd(t); \ 202 } \ 203 } while (0) 204 void rcu_tasks_trace_torture_stats_print(char *tt, char *tf); 205 # else 206 # define rcu_tasks_trace_qs(t) do { } while (0) 207 # endif 208 209 #define rcu_tasks_qs(t, preempt) \ 210 do { \ 211 rcu_tasks_classic_qs((t), (preempt)); \ 212 rcu_tasks_trace_qs(t); \ 213 } while (0) 214 215 # ifdef CONFIG_TASKS_RUDE_RCU 216 void synchronize_rcu_tasks_rude(void); 217 void rcu_tasks_rude_torture_stats_print(char *tt, char *tf); 218 # endif 219 220 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) 221 void exit_tasks_rcu_start(void); 222 void exit_tasks_rcu_finish(void); 223 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ 224 #define rcu_tasks_classic_qs(t, preempt) do { } while (0) 225 #define rcu_tasks_qs(t, preempt) do { } while (0) 226 #define rcu_note_voluntary_context_switch(t) do { } while (0) 227 #define call_rcu_tasks call_rcu 228 #define synchronize_rcu_tasks synchronize_rcu exit_tasks_rcu_start(void)229 static inline void exit_tasks_rcu_start(void) { } exit_tasks_rcu_finish(void)230 static inline void exit_tasks_rcu_finish(void) { } 231 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ 232 233 /** 234 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period? 235 * 236 * As an accident of implementation, an RCU Tasks Trace grace period also 237 * acts as an RCU grace period. However, this could change at any time. 238 * Code relying on this accident must call this function to verify that 239 * this accident is still happening. 240 * 241 * You have been warned! 242 */ rcu_trace_implies_rcu_gp(void)243 static inline bool rcu_trace_implies_rcu_gp(void) { return true; } 244 245 /** 246 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU 247 * 248 * This macro resembles cond_resched(), except that it is defined to 249 * report potential quiescent states to RCU-tasks even if the cond_resched() 250 * machinery were to be shut off, as some advocate for PREEMPTION kernels. 251 */ 252 #define cond_resched_tasks_rcu_qs() \ 253 do { \ 254 rcu_tasks_qs(current, false); \ 255 cond_resched(); \ 256 } while (0) 257 258 /** 259 * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states 260 * @old_ts: jiffies at start of processing. 261 * 262 * This helper is for long-running softirq handlers, such as NAPI threads in 263 * networking. The caller should initialize the variable passed in as @old_ts 264 * at the beginning of the softirq handler. When invoked frequently, this macro 265 * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will 266 * provide both RCU and RCU-Tasks quiescent states. Note that this macro 267 * modifies its old_ts argument. 268 * 269 * Because regions of code that have disabled softirq act as RCU read-side 270 * critical sections, this macro should be invoked with softirq (and 271 * preemption) enabled. 272 * 273 * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would 274 * have more chance to invoke schedule() calls and provide necessary quiescent 275 * states. As a contrast, calling cond_resched() only won't achieve the same 276 * effect because cond_resched() does not provide RCU-Tasks quiescent states. 277 */ 278 #define rcu_softirq_qs_periodic(old_ts) \ 279 do { \ 280 if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \ 281 time_after(jiffies, (old_ts) + HZ / 10)) { \ 282 preempt_disable(); \ 283 rcu_softirq_qs(); \ 284 preempt_enable(); \ 285 (old_ts) = jiffies; \ 286 } \ 287 } while (0) 288 289 /* 290 * Infrastructure to implement the synchronize_() primitives in 291 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 292 */ 293 294 #if defined(CONFIG_TREE_RCU) 295 #include <linux/rcutree.h> 296 #elif defined(CONFIG_TINY_RCU) 297 #include <linux/rcutiny.h> 298 #else 299 #error "Unknown RCU implementation specified to kernel configuration" 300 #endif 301 302 /* 303 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls 304 * are needed for dynamic initialization and destruction of rcu_head 305 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for 306 * dynamic initialization and destruction of statically allocated rcu_head 307 * structures. However, rcu_head structures allocated dynamically in the 308 * heap don't need any initialization. 309 */ 310 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 311 void init_rcu_head(struct rcu_head *head); 312 void destroy_rcu_head(struct rcu_head *head); 313 void init_rcu_head_on_stack(struct rcu_head *head); 314 void destroy_rcu_head_on_stack(struct rcu_head *head); 315 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ init_rcu_head(struct rcu_head * head)316 static inline void init_rcu_head(struct rcu_head *head) { } destroy_rcu_head(struct rcu_head * head)317 static inline void destroy_rcu_head(struct rcu_head *head) { } init_rcu_head_on_stack(struct rcu_head * head)318 static inline void init_rcu_head_on_stack(struct rcu_head *head) { } destroy_rcu_head_on_stack(struct rcu_head * head)319 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } 320 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 321 322 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 323 bool rcu_lockdep_current_cpu_online(void); 324 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ rcu_lockdep_current_cpu_online(void)325 static inline bool rcu_lockdep_current_cpu_online(void) { return true; } 326 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 327 328 extern struct lockdep_map rcu_lock_map; 329 extern struct lockdep_map rcu_bh_lock_map; 330 extern struct lockdep_map rcu_sched_lock_map; 331 extern struct lockdep_map rcu_callback_map; 332 333 #ifdef CONFIG_DEBUG_LOCK_ALLOC 334 rcu_lock_acquire(struct lockdep_map * map)335 static inline void rcu_lock_acquire(struct lockdep_map *map) 336 { 337 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); 338 } 339 rcu_try_lock_acquire(struct lockdep_map * map)340 static inline void rcu_try_lock_acquire(struct lockdep_map *map) 341 { 342 lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_); 343 } 344 rcu_lock_release(struct lockdep_map * map)345 static inline void rcu_lock_release(struct lockdep_map *map) 346 { 347 lock_release(map, _THIS_IP_); 348 } 349 350 int debug_lockdep_rcu_enabled(void); 351 int rcu_read_lock_held(void); 352 int rcu_read_lock_bh_held(void); 353 int rcu_read_lock_sched_held(void); 354 int rcu_read_lock_any_held(void); 355 356 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 357 358 # define rcu_lock_acquire(a) do { } while (0) 359 # define rcu_try_lock_acquire(a) do { } while (0) 360 # define rcu_lock_release(a) do { } while (0) 361 rcu_read_lock_held(void)362 static inline int rcu_read_lock_held(void) 363 { 364 return 1; 365 } 366 rcu_read_lock_bh_held(void)367 static inline int rcu_read_lock_bh_held(void) 368 { 369 return 1; 370 } 371 rcu_read_lock_sched_held(void)372 static inline int rcu_read_lock_sched_held(void) 373 { 374 return !preemptible(); 375 } 376 rcu_read_lock_any_held(void)377 static inline int rcu_read_lock_any_held(void) 378 { 379 return !preemptible(); 380 } 381 debug_lockdep_rcu_enabled(void)382 static inline int debug_lockdep_rcu_enabled(void) 383 { 384 return 0; 385 } 386 387 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 388 389 #ifdef CONFIG_PROVE_RCU 390 391 /** 392 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met 393 * @c: condition to check 394 * @s: informative message 395 * 396 * This checks debug_lockdep_rcu_enabled() before checking (c) to 397 * prevent early boot splats due to lockdep not yet being initialized, 398 * and rechecks it after checking (c) to prevent false-positive splats 399 * due to races with lockdep being disabled. See commit 3066820034b5dd 400 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail. 401 */ 402 #define RCU_LOCKDEP_WARN(c, s) \ 403 do { \ 404 static bool __section(".data.unlikely") __warned; \ 405 if (debug_lockdep_rcu_enabled() && (c) && \ 406 debug_lockdep_rcu_enabled() && !__warned) { \ 407 __warned = true; \ 408 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 409 } \ 410 } while (0) 411 412 #ifndef CONFIG_PREEMPT_RCU rcu_preempt_sleep_check(void)413 static inline void rcu_preempt_sleep_check(void) 414 { 415 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), 416 "Illegal context switch in RCU read-side critical section"); 417 } 418 #else // #ifndef CONFIG_PREEMPT_RCU rcu_preempt_sleep_check(void)419 static inline void rcu_preempt_sleep_check(void) { } 420 #endif // #else // #ifndef CONFIG_PREEMPT_RCU 421 422 #define rcu_sleep_check() \ 423 do { \ 424 rcu_preempt_sleep_check(); \ 425 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ 426 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ 427 "Illegal context switch in RCU-bh read-side critical section"); \ 428 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ 429 "Illegal context switch in RCU-sched read-side critical section"); \ 430 } while (0) 431 432 // See RCU_LOCKDEP_WARN() for an explanation of the double call to 433 // debug_lockdep_rcu_enabled(). lockdep_assert_rcu_helper(bool c)434 static inline bool lockdep_assert_rcu_helper(bool c) 435 { 436 return debug_lockdep_rcu_enabled() && 437 (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) && 438 debug_lockdep_rcu_enabled(); 439 } 440 441 /** 442 * lockdep_assert_in_rcu_read_lock - WARN if not protected by rcu_read_lock() 443 * 444 * Splats if lockdep is enabled and there is no rcu_read_lock() in effect. 445 */ 446 #define lockdep_assert_in_rcu_read_lock() \ 447 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map))) 448 449 /** 450 * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh() 451 * 452 * Splats if lockdep is enabled and there is no rcu_read_lock_bh() in effect. 453 * Note that local_bh_disable() and friends do not suffice here, instead an 454 * actual rcu_read_lock_bh() is required. 455 */ 456 #define lockdep_assert_in_rcu_read_lock_bh() \ 457 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map))) 458 459 /** 460 * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched() 461 * 462 * Splats if lockdep is enabled and there is no rcu_read_lock_sched() 463 * in effect. Note that preempt_disable() and friends do not suffice here, 464 * instead an actual rcu_read_lock_sched() is required. 465 */ 466 #define lockdep_assert_in_rcu_read_lock_sched() \ 467 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map))) 468 469 /** 470 * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader 471 * 472 * Splats if lockdep is enabled and there is no RCU reader of any 473 * type in effect. Note that regions of code protected by things like 474 * preempt_disable, local_bh_disable(), and local_irq_disable() all qualify 475 * as RCU readers. 476 * 477 * Note that this will never trigger in PREEMPT_NONE or PREEMPT_VOLUNTARY 478 * kernels that are not also built with PREEMPT_COUNT. But if you have 479 * lockdep enabled, you might as well also enable PREEMPT_COUNT. 480 */ 481 #define lockdep_assert_in_rcu_reader() \ 482 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) && \ 483 !lock_is_held(&rcu_bh_lock_map) && \ 484 !lock_is_held(&rcu_sched_lock_map) && \ 485 preemptible())) 486 487 #else /* #ifdef CONFIG_PROVE_RCU */ 488 489 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) 490 #define rcu_sleep_check() do { } while (0) 491 492 #define lockdep_assert_in_rcu_read_lock() do { } while (0) 493 #define lockdep_assert_in_rcu_read_lock_bh() do { } while (0) 494 #define lockdep_assert_in_rcu_read_lock_sched() do { } while (0) 495 #define lockdep_assert_in_rcu_reader() do { } while (0) 496 497 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 498 499 /* 500 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 501 * and rcu_assign_pointer(). Some of these could be folded into their 502 * callers, but they are left separate in order to ease introduction of 503 * multiple pointers markings to match different RCU implementations 504 * (e.g., __srcu), should this make sense in the future. 505 */ 506 507 #ifdef __CHECKER__ 508 #define rcu_check_sparse(p, space) \ 509 ((void)(((typeof(*p) space *)p) == p)) 510 #else /* #ifdef __CHECKER__ */ 511 #define rcu_check_sparse(p, space) 512 #endif /* #else #ifdef __CHECKER__ */ 513 514 #define __unrcu_pointer(p, local) \ 515 ({ \ 516 typeof(*p) *local = (typeof(*p) *__force)(p); \ 517 rcu_check_sparse(p, __rcu); \ 518 ((typeof(*p) __force __kernel *)(local)); \ 519 }) 520 /** 521 * unrcu_pointer - mark a pointer as not being RCU protected 522 * @p: pointer needing to lose its __rcu property 523 * 524 * Converts @p from an __rcu pointer to a __kernel pointer. 525 * This allows an __rcu pointer to be used with xchg() and friends. 526 */ 527 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) 528 529 #define __rcu_access_pointer(p, local, space) \ 530 ({ \ 531 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 532 rcu_check_sparse(p, space); \ 533 ((typeof(*p) __force __kernel *)(local)); \ 534 }) 535 #define __rcu_dereference_check(p, local, c, space) \ 536 ({ \ 537 /* Dependency order vs. p above. */ \ 538 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 539 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ 540 rcu_check_sparse(p, space); \ 541 ((typeof(*p) __force __kernel *)(local)); \ 542 }) 543 #define __rcu_dereference_protected(p, local, c, space) \ 544 ({ \ 545 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ 546 rcu_check_sparse(p, space); \ 547 ((typeof(*p) __force __kernel *)(p)); \ 548 }) 549 #define __rcu_dereference_raw(p, local) \ 550 ({ \ 551 /* Dependency order vs. p above. */ \ 552 typeof(p) local = READ_ONCE(p); \ 553 ((typeof(*p) __force __kernel *)(local)); \ 554 }) 555 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) 556 557 /** 558 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable 559 * @v: The value to statically initialize with. 560 */ 561 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) 562 563 /** 564 * rcu_assign_pointer() - assign to RCU-protected pointer 565 * @p: pointer to assign to 566 * @v: value to assign (publish) 567 * 568 * Assigns the specified value to the specified RCU-protected 569 * pointer, ensuring that any concurrent RCU readers will see 570 * any prior initialization. 571 * 572 * Inserts memory barriers on architectures that require them 573 * (which is most of them), and also prevents the compiler from 574 * reordering the code that initializes the structure after the pointer 575 * assignment. More importantly, this call documents which pointers 576 * will be dereferenced by RCU read-side code. 577 * 578 * In some special cases, you may use RCU_INIT_POINTER() instead 579 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 580 * to the fact that it does not constrain either the CPU or the compiler. 581 * That said, using RCU_INIT_POINTER() when you should have used 582 * rcu_assign_pointer() is a very bad thing that results in 583 * impossible-to-diagnose memory corruption. So please be careful. 584 * See the RCU_INIT_POINTER() comment header for details. 585 * 586 * Note that rcu_assign_pointer() evaluates each of its arguments only 587 * once, appearances notwithstanding. One of the "extra" evaluations 588 * is in typeof() and the other visible only to sparse (__CHECKER__), 589 * neither of which actually execute the argument. As with most cpp 590 * macros, this execute-arguments-only-once property is important, so 591 * please be careful when making changes to rcu_assign_pointer() and the 592 * other macros that it invokes. 593 */ 594 #define rcu_assign_pointer(p, v) \ 595 do { \ 596 uintptr_t _r_a_p__v = (uintptr_t)(v); \ 597 rcu_check_sparse(p, __rcu); \ 598 \ 599 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ 600 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ 601 else \ 602 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ 603 } while (0) 604 605 /** 606 * rcu_replace_pointer() - replace an RCU pointer, returning its old value 607 * @rcu_ptr: RCU pointer, whose old value is returned 608 * @ptr: regular pointer 609 * @c: the lockdep conditions under which the dereference will take place 610 * 611 * Perform a replacement, where @rcu_ptr is an RCU-annotated 612 * pointer and @c is the lockdep argument that is passed to the 613 * rcu_dereference_protected() call used to read that pointer. The old 614 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. 615 */ 616 #define rcu_replace_pointer(rcu_ptr, ptr, c) \ 617 ({ \ 618 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ 619 rcu_assign_pointer((rcu_ptr), (ptr)); \ 620 __tmp; \ 621 }) 622 623 /** 624 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 625 * @p: The pointer to read 626 * 627 * Return the value of the specified RCU-protected pointer, but omit the 628 * lockdep checks for being in an RCU read-side critical section. This is 629 * useful when the value of this pointer is accessed, but the pointer is 630 * not dereferenced, for example, when testing an RCU-protected pointer 631 * against NULL. Although rcu_access_pointer() may also be used in cases 632 * where update-side locks prevent the value of the pointer from changing, 633 * you should instead use rcu_dereference_protected() for this use case. 634 * Within an RCU read-side critical section, there is little reason to 635 * use rcu_access_pointer(). 636 * 637 * It is usually best to test the rcu_access_pointer() return value 638 * directly in order to avoid accidental dereferences being introduced 639 * by later inattentive changes. In other words, assigning the 640 * rcu_access_pointer() return value to a local variable results in an 641 * accident waiting to happen. 642 * 643 * It is also permissible to use rcu_access_pointer() when read-side 644 * access to the pointer was removed at least one grace period ago, as is 645 * the case in the context of the RCU callback that is freeing up the data, 646 * or after a synchronize_rcu() returns. This can be useful when tearing 647 * down multi-linked structures after a grace period has elapsed. However, 648 * rcu_dereference_protected() is normally preferred for this use case. 649 */ 650 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu) 651 652 /** 653 * rcu_dereference_check() - rcu_dereference with debug checking 654 * @p: The pointer to read, prior to dereferencing 655 * @c: The conditions under which the dereference will take place 656 * 657 * Do an rcu_dereference(), but check that the conditions under which the 658 * dereference will take place are correct. Typically the conditions 659 * indicate the various locking conditions that should be held at that 660 * point. The check should return true if the conditions are satisfied. 661 * An implicit check for being in an RCU read-side critical section 662 * (rcu_read_lock()) is included. 663 * 664 * For example: 665 * 666 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 667 * 668 * could be used to indicate to lockdep that foo->bar may only be dereferenced 669 * if either rcu_read_lock() is held, or that the lock required to replace 670 * the bar struct at foo->bar is held. 671 * 672 * Note that the list of conditions may also include indications of when a lock 673 * need not be held, for example during initialisation or destruction of the 674 * target struct: 675 * 676 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 677 * atomic_read(&foo->usage) == 0); 678 * 679 * Inserts memory barriers on architectures that require them 680 * (currently only the Alpha), prevents the compiler from refetching 681 * (and from merging fetches), and, more importantly, documents exactly 682 * which pointers are protected by RCU and checks that the pointer is 683 * annotated as __rcu. 684 */ 685 #define rcu_dereference_check(p, c) \ 686 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 687 (c) || rcu_read_lock_held(), __rcu) 688 689 /** 690 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 691 * @p: The pointer to read, prior to dereferencing 692 * @c: The conditions under which the dereference will take place 693 * 694 * This is the RCU-bh counterpart to rcu_dereference_check(). However, 695 * please note that starting in v5.0 kernels, vanilla RCU grace periods 696 * wait for local_bh_disable() regions of code in addition to regions of 697 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means 698 * that synchronize_rcu(), call_rcu, and friends all take not only 699 * rcu_read_lock() but also rcu_read_lock_bh() into account. 700 */ 701 #define rcu_dereference_bh_check(p, c) \ 702 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 703 (c) || rcu_read_lock_bh_held(), __rcu) 704 705 /** 706 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 707 * @p: The pointer to read, prior to dereferencing 708 * @c: The conditions under which the dereference will take place 709 * 710 * This is the RCU-sched counterpart to rcu_dereference_check(). 711 * However, please note that starting in v5.0 kernels, vanilla RCU grace 712 * periods wait for preempt_disable() regions of code in addition to 713 * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). 714 * This means that synchronize_rcu(), call_rcu, and friends all take not 715 * only rcu_read_lock() but also rcu_read_lock_sched() into account. 716 */ 717 #define rcu_dereference_sched_check(p, c) \ 718 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 719 (c) || rcu_read_lock_sched_held(), \ 720 __rcu) 721 722 /* 723 * The tracing infrastructure traces RCU (we want that), but unfortunately 724 * some of the RCU checks causes tracing to lock up the system. 725 * 726 * The no-tracing version of rcu_dereference_raw() must not call 727 * rcu_read_lock_held(). 728 */ 729 #define rcu_dereference_raw_check(p) \ 730 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu) 731 732 /** 733 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 734 * @p: The pointer to read, prior to dereferencing 735 * @c: The conditions under which the dereference will take place 736 * 737 * Return the value of the specified RCU-protected pointer, but omit 738 * the READ_ONCE(). This is useful in cases where update-side locks 739 * prevent the value of the pointer from changing. Please note that this 740 * primitive does *not* prevent the compiler from repeating this reference 741 * or combining it with other references, so it should not be used without 742 * protection of appropriate locks. 743 * 744 * This function is only for update-side use. Using this function 745 * when protected only by rcu_read_lock() will result in infrequent 746 * but very ugly failures. 747 */ 748 #define rcu_dereference_protected(p, c) \ 749 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu) 750 751 752 /** 753 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 754 * @p: The pointer to read, prior to dereferencing 755 * 756 * This is a simple wrapper around rcu_dereference_check(). 757 */ 758 #define rcu_dereference(p) rcu_dereference_check(p, 0) 759 760 /** 761 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 762 * @p: The pointer to read, prior to dereferencing 763 * 764 * Makes rcu_dereference_check() do the dirty work. 765 */ 766 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 767 768 /** 769 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 770 * @p: The pointer to read, prior to dereferencing 771 * 772 * Makes rcu_dereference_check() do the dirty work. 773 */ 774 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 775 776 /** 777 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism 778 * @p: The pointer to hand off 779 * 780 * This is simply an identity function, but it documents where a pointer 781 * is handed off from RCU to some other synchronization mechanism, for 782 * example, reference counting or locking. In C11, it would map to 783 * kill_dependency(). It could be used as follows:: 784 * 785 * rcu_read_lock(); 786 * p = rcu_dereference(gp); 787 * long_lived = is_long_lived(p); 788 * if (long_lived) { 789 * if (!atomic_inc_not_zero(p->refcnt)) 790 * long_lived = false; 791 * else 792 * p = rcu_pointer_handoff(p); 793 * } 794 * rcu_read_unlock(); 795 */ 796 #define rcu_pointer_handoff(p) (p) 797 798 /** 799 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 800 * 801 * When synchronize_rcu() is invoked on one CPU while other CPUs 802 * are within RCU read-side critical sections, then the 803 * synchronize_rcu() is guaranteed to block until after all the other 804 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 805 * on one CPU while other CPUs are within RCU read-side critical 806 * sections, invocation of the corresponding RCU callback is deferred 807 * until after the all the other CPUs exit their critical sections. 808 * 809 * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also 810 * wait for regions of code with preemption disabled, including regions of 811 * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which 812 * define synchronize_sched(), only code enclosed within rcu_read_lock() 813 * and rcu_read_unlock() are guaranteed to be waited for. 814 * 815 * Note, however, that RCU callbacks are permitted to run concurrently 816 * with new RCU read-side critical sections. One way that this can happen 817 * is via the following sequence of events: (1) CPU 0 enters an RCU 818 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 819 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 820 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 821 * callback is invoked. This is legal, because the RCU read-side critical 822 * section that was running concurrently with the call_rcu() (and which 823 * therefore might be referencing something that the corresponding RCU 824 * callback would free up) has completed before the corresponding 825 * RCU callback is invoked. 826 * 827 * RCU read-side critical sections may be nested. Any deferred actions 828 * will be deferred until the outermost RCU read-side critical section 829 * completes. 830 * 831 * You can avoid reading and understanding the next paragraph by 832 * following this rule: don't put anything in an rcu_read_lock() RCU 833 * read-side critical section that would block in a !PREEMPTION kernel. 834 * But if you want the full story, read on! 835 * 836 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), 837 * it is illegal to block while in an RCU read-side critical section. 838 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION 839 * kernel builds, RCU read-side critical sections may be preempted, 840 * but explicit blocking is illegal. Finally, in preemptible RCU 841 * implementations in real-time (with -rt patchset) kernel builds, RCU 842 * read-side critical sections may be preempted and they may also block, but 843 * only when acquiring spinlocks that are subject to priority inheritance. 844 */ rcu_read_lock(void)845 static __always_inline void rcu_read_lock(void) 846 { 847 __rcu_read_lock(); 848 __acquire(RCU); 849 rcu_lock_acquire(&rcu_lock_map); 850 RCU_LOCKDEP_WARN(!rcu_is_watching(), 851 "rcu_read_lock() used illegally while idle"); 852 } 853 854 /* 855 * So where is rcu_write_lock()? It does not exist, as there is no 856 * way for writers to lock out RCU readers. This is a feature, not 857 * a bug -- this property is what provides RCU's performance benefits. 858 * Of course, writers must coordinate with each other. The normal 859 * spinlock primitives work well for this, but any other technique may be 860 * used as well. RCU does not care how the writers keep out of each 861 * others' way, as long as they do so. 862 */ 863 864 /** 865 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 866 * 867 * In almost all situations, rcu_read_unlock() is immune from deadlock. 868 * In recent kernels that have consolidated synchronize_sched() and 869 * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity 870 * also extends to the scheduler's runqueue and priority-inheritance 871 * spinlocks, courtesy of the quiescent-state deferral that is carried 872 * out when rcu_read_unlock() is invoked with interrupts disabled. 873 * 874 * See rcu_read_lock() for more information. 875 */ rcu_read_unlock(void)876 static inline void rcu_read_unlock(void) 877 { 878 RCU_LOCKDEP_WARN(!rcu_is_watching(), 879 "rcu_read_unlock() used illegally while idle"); 880 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ 881 __release(RCU); 882 __rcu_read_unlock(); 883 } 884 885 /** 886 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 887 * 888 * This is equivalent to rcu_read_lock(), but also disables softirqs. 889 * Note that anything else that disables softirqs can also serve as an RCU 890 * read-side critical section. However, please note that this equivalence 891 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and 892 * rcu_read_lock_bh() were unrelated. 893 * 894 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 895 * must occur in the same context, for example, it is illegal to invoke 896 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 897 * was invoked from some other task. 898 */ rcu_read_lock_bh(void)899 static inline void rcu_read_lock_bh(void) 900 { 901 local_bh_disable(); 902 __acquire(RCU_BH); 903 rcu_lock_acquire(&rcu_bh_lock_map); 904 RCU_LOCKDEP_WARN(!rcu_is_watching(), 905 "rcu_read_lock_bh() used illegally while idle"); 906 } 907 908 /** 909 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section 910 * 911 * See rcu_read_lock_bh() for more information. 912 */ rcu_read_unlock_bh(void)913 static inline void rcu_read_unlock_bh(void) 914 { 915 RCU_LOCKDEP_WARN(!rcu_is_watching(), 916 "rcu_read_unlock_bh() used illegally while idle"); 917 rcu_lock_release(&rcu_bh_lock_map); 918 __release(RCU_BH); 919 local_bh_enable(); 920 } 921 922 /** 923 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 924 * 925 * This is equivalent to rcu_read_lock(), but also disables preemption. 926 * Read-side critical sections can also be introduced by anything else that 927 * disables preemption, including local_irq_disable() and friends. However, 928 * please note that the equivalence to rcu_read_lock() applies only to 929 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() 930 * were unrelated. 931 * 932 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 933 * must occur in the same context, for example, it is illegal to invoke 934 * rcu_read_unlock_sched() from process context if the matching 935 * rcu_read_lock_sched() was invoked from an NMI handler. 936 */ rcu_read_lock_sched(void)937 static inline void rcu_read_lock_sched(void) 938 { 939 preempt_disable(); 940 __acquire(RCU_SCHED); 941 rcu_lock_acquire(&rcu_sched_lock_map); 942 RCU_LOCKDEP_WARN(!rcu_is_watching(), 943 "rcu_read_lock_sched() used illegally while idle"); 944 } 945 946 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ rcu_read_lock_sched_notrace(void)947 static inline notrace void rcu_read_lock_sched_notrace(void) 948 { 949 preempt_disable_notrace(); 950 __acquire(RCU_SCHED); 951 } 952 953 /** 954 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section 955 * 956 * See rcu_read_lock_sched() for more information. 957 */ rcu_read_unlock_sched(void)958 static inline void rcu_read_unlock_sched(void) 959 { 960 RCU_LOCKDEP_WARN(!rcu_is_watching(), 961 "rcu_read_unlock_sched() used illegally while idle"); 962 rcu_lock_release(&rcu_sched_lock_map); 963 __release(RCU_SCHED); 964 preempt_enable(); 965 } 966 967 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ rcu_read_unlock_sched_notrace(void)968 static inline notrace void rcu_read_unlock_sched_notrace(void) 969 { 970 __release(RCU_SCHED); 971 preempt_enable_notrace(); 972 } 973 974 /** 975 * RCU_INIT_POINTER() - initialize an RCU protected pointer 976 * @p: The pointer to be initialized. 977 * @v: The value to initialized the pointer to. 978 * 979 * Initialize an RCU-protected pointer in special cases where readers 980 * do not need ordering constraints on the CPU or the compiler. These 981 * special cases are: 982 * 983 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* 984 * 2. The caller has taken whatever steps are required to prevent 985 * RCU readers from concurrently accessing this pointer *or* 986 * 3. The referenced data structure has already been exposed to 987 * readers either at compile time or via rcu_assign_pointer() *and* 988 * 989 * a. You have not made *any* reader-visible changes to 990 * this structure since then *or* 991 * b. It is OK for readers accessing this structure from its 992 * new location to see the old state of the structure. (For 993 * example, the changes were to statistical counters or to 994 * other state where exact synchronization is not required.) 995 * 996 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 997 * result in impossible-to-diagnose memory corruption. As in the structures 998 * will look OK in crash dumps, but any concurrent RCU readers might 999 * see pre-initialized values of the referenced data structure. So 1000 * please be very careful how you use RCU_INIT_POINTER()!!! 1001 * 1002 * If you are creating an RCU-protected linked structure that is accessed 1003 * by a single external-to-structure RCU-protected pointer, then you may 1004 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 1005 * pointers, but you must use rcu_assign_pointer() to initialize the 1006 * external-to-structure pointer *after* you have completely initialized 1007 * the reader-accessible portions of the linked structure. 1008 * 1009 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no 1010 * ordering guarantees for either the CPU or the compiler. 1011 */ 1012 #define RCU_INIT_POINTER(p, v) \ 1013 do { \ 1014 rcu_check_sparse(p, __rcu); \ 1015 WRITE_ONCE(p, RCU_INITIALIZER(v)); \ 1016 } while (0) 1017 1018 /** 1019 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 1020 * @p: The pointer to be initialized. 1021 * @v: The value to initialized the pointer to. 1022 * 1023 * GCC-style initialization for an RCU-protected pointer in a structure field. 1024 */ 1025 #define RCU_POINTER_INITIALIZER(p, v) \ 1026 .p = RCU_INITIALIZER(v) 1027 1028 /* 1029 * Does the specified offset indicate that the corresponding rcu_head 1030 * structure can be handled by kvfree_rcu()? 1031 */ 1032 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096) 1033 1034 /** 1035 * kfree_rcu() - kfree an object after a grace period. 1036 * @ptr: pointer to kfree for double-argument invocations. 1037 * @rhf: the name of the struct rcu_head within the type of @ptr. 1038 * 1039 * Many rcu callbacks functions just call kfree() on the base structure. 1040 * These functions are trivial, but their size adds up, and furthermore 1041 * when they are used in a kernel module, that module must invoke the 1042 * high-latency rcu_barrier() function at module-unload time. 1043 * 1044 * The kfree_rcu() function handles this issue. Rather than encoding a 1045 * function address in the embedded rcu_head structure, kfree_rcu() instead 1046 * encodes the offset of the rcu_head structure within the base structure. 1047 * Because the functions are not allowed in the low-order 4096 bytes of 1048 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 1049 * If the offset is larger than 4095 bytes, a compile-time error will 1050 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can 1051 * either fall back to use of call_rcu() or rearrange the structure to 1052 * position the rcu_head structure into the first 4096 bytes. 1053 * 1054 * The object to be freed can be allocated either by kmalloc() or 1055 * kmem_cache_alloc(). 1056 * 1057 * Note that the allowable offset might decrease in the future. 1058 * 1059 * The BUILD_BUG_ON check must not involve any function calls, hence the 1060 * checks are done in macros here. 1061 */ 1062 #define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) 1063 #define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) 1064 1065 /** 1066 * kfree_rcu_mightsleep() - kfree an object after a grace period. 1067 * @ptr: pointer to kfree for single-argument invocations. 1068 * 1069 * When it comes to head-less variant, only one argument 1070 * is passed and that is just a pointer which has to be 1071 * freed after a grace period. Therefore the semantic is 1072 * 1073 * kfree_rcu_mightsleep(ptr); 1074 * 1075 * where @ptr is the pointer to be freed by kvfree(). 1076 * 1077 * Please note, head-less way of freeing is permitted to 1078 * use from a context that has to follow might_sleep() 1079 * annotation. Otherwise, please switch and embed the 1080 * rcu_head structure within the type of @ptr. 1081 */ 1082 #define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) 1083 #define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) 1084 1085 #define kvfree_rcu_arg_2(ptr, rhf) \ 1086 do { \ 1087 typeof (ptr) ___p = (ptr); \ 1088 \ 1089 if (___p) { \ 1090 BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ 1091 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \ 1092 } \ 1093 } while (0) 1094 1095 #define kvfree_rcu_arg_1(ptr) \ 1096 do { \ 1097 typeof(ptr) ___p = (ptr); \ 1098 \ 1099 if (___p) \ 1100 kvfree_call_rcu(NULL, (void *) (___p)); \ 1101 } while (0) 1102 1103 /* 1104 * Place this after a lock-acquisition primitive to guarantee that 1105 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies 1106 * if the UNLOCK and LOCK are executed by the same CPU or if the 1107 * UNLOCK and LOCK operate on the same lock variable. 1108 */ 1109 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE 1110 #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ 1111 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1112 #define smp_mb__after_unlock_lock() do { } while (0) 1113 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1114 1115 1116 /* Has the specified rcu_head structure been handed to call_rcu()? */ 1117 1118 /** 1119 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() 1120 * @rhp: The rcu_head structure to initialize. 1121 * 1122 * If you intend to invoke rcu_head_after_call_rcu() to test whether a 1123 * given rcu_head structure has already been passed to call_rcu(), then 1124 * you must also invoke this rcu_head_init() function on it just after 1125 * allocating that structure. Calls to this function must not race with 1126 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. 1127 */ rcu_head_init(struct rcu_head * rhp)1128 static inline void rcu_head_init(struct rcu_head *rhp) 1129 { 1130 rhp->func = (rcu_callback_t)~0L; 1131 } 1132 1133 /** 1134 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? 1135 * @rhp: The rcu_head structure to test. 1136 * @f: The function passed to call_rcu() along with @rhp. 1137 * 1138 * Returns @true if the @rhp has been passed to call_rcu() with @func, 1139 * and @false otherwise. Emits a warning in any other case, including 1140 * the case where @rhp has already been invoked after a grace period. 1141 * Calls to this function must not race with callback invocation. One way 1142 * to avoid such races is to enclose the call to rcu_head_after_call_rcu() 1143 * in an RCU read-side critical section that includes a read-side fetch 1144 * of the pointer to the structure containing @rhp. 1145 */ 1146 static inline bool rcu_head_after_call_rcu(struct rcu_head * rhp,rcu_callback_t f)1147 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) 1148 { 1149 rcu_callback_t func = READ_ONCE(rhp->func); 1150 1151 if (func == f) 1152 return true; 1153 WARN_ON_ONCE(func != (rcu_callback_t)~0L); 1154 return false; 1155 } 1156 1157 /* kernel/ksysfs.c definitions */ 1158 extern int rcu_expedited; 1159 extern int rcu_normal; 1160 1161 DEFINE_LOCK_GUARD_0(rcu, 1162 do { 1163 rcu_read_lock(); 1164 /* 1165 * sparse doesn't call the cleanup function, 1166 * so just release immediately and don't track 1167 * the context. We don't need to anyway, since 1168 * the whole point of the guard is to not need 1169 * the explicit unlock. 1170 */ 1171 __release(RCU); 1172 } while (0), 1173 rcu_read_unlock()) 1174 1175 #endif /* __LINUX_RCUPDATE_H */ 1176