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rcupdate.h
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linux-6.19.14/include/linux/rcupdate.h
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/sched.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 */ 41void call_rcu(struct rcu_head *head, rcu_callback_t func); 42void rcu_barrier_tasks(void); 43void synchronize_rcu(void); 44 45struct rcu_gp_oldstate; 46unsigned long get_completed_synchronize_rcu(void); 47void 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 */ 65static 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 72void __rcu_read_lock(void); 73void __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 88void rcu_read_unlock_strict(void); 89#endif 90 91static inline void __rcu_read_lock(void) 92{ 93 preempt_disable(); 94} 95 96static inline void __rcu_read_unlock(void) 97{ 98 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) 99 rcu_read_unlock_strict(); 100 preempt_enable(); 101} 102 103static 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 111void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func); 112#else 113static 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 */ 120void rcu_init(void); 121extern int rcu_scheduler_active; 122void rcu_sched_clock_irq(int user); 123 124#ifdef CONFIG_RCU_STALL_COMMON 125void rcu_sysrq_start(void); 126void rcu_sysrq_end(void); 127#else /* #ifdef CONFIG_RCU_STALL_COMMON */ 128static inline void rcu_sysrq_start(void) { } 129static inline void rcu_sysrq_end(void) { } 130#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ 131 132#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_VIRT_XFER_TO_GUEST_WORK)) 133void rcu_irq_work_resched(void); 134#else 135static __always_inline void rcu_irq_work_resched(void) { } 136#endif 137 138#ifdef CONFIG_RCU_NOCB_CPU 139void rcu_init_nohz(void); 140int rcu_nocb_cpu_offload(int cpu); 141int rcu_nocb_cpu_deoffload(int cpu); 142void rcu_nocb_flush_deferred_wakeup(void); 143 144#define RCU_NOCB_LOCKDEP_WARN(c, s) RCU_LOCKDEP_WARN(c, s) 145 146#else /* #ifdef CONFIG_RCU_NOCB_CPU */ 147 148static inline void rcu_init_nohz(void) { } 149static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } 150static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } 151static inline void rcu_nocb_flush_deferred_wakeup(void) { } 152 153#define RCU_NOCB_LOCKDEP_WARN(c, s) 154 155#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 156 157/* 158 * Note a quasi-voluntary context switch for RCU-tasks's benefit. 159 * This is a macro rather than an inline function to avoid #include hell. 160 */ 161#ifdef CONFIG_TASKS_RCU_GENERIC 162 163# ifdef CONFIG_TASKS_RCU 164# define rcu_tasks_classic_qs(t, preempt) \ 165 do { \ 166 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ 167 WRITE_ONCE((t)->rcu_tasks_holdout, false); \ 168 } while (0) 169void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); 170void synchronize_rcu_tasks(void); 171void rcu_tasks_torture_stats_print(char *tt, char *tf); 172# else 173# define rcu_tasks_classic_qs(t, preempt) do { } while (0) 174# define call_rcu_tasks call_rcu 175# define synchronize_rcu_tasks synchronize_rcu 176# endif 177 178# ifdef CONFIG_TASKS_TRACE_RCU 179// Bits for ->trc_reader_special.b.need_qs field. 180#define TRC_NEED_QS 0x1 // Task needs a quiescent state. 181#define TRC_NEED_QS_CHECKED 0x2 // Task has been checked for needing quiescent state. 182 183u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new); 184void rcu_tasks_trace_qs_blkd(struct task_struct *t); 185 186# define rcu_tasks_trace_qs(t) \ 187 do { \ 188 int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting); \ 189 \ 190 if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) && \ 191 likely(!___rttq_nesting)) { \ 192 rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED); \ 193 } else if (___rttq_nesting && ___rttq_nesting != INT_MIN && \ 194 !READ_ONCE((t)->trc_reader_special.b.blocked)) { \ 195 rcu_tasks_trace_qs_blkd(t); \ 196 } \ 197 } while (0) 198void rcu_tasks_trace_torture_stats_print(char *tt, char *tf); 199# else 200# define rcu_tasks_trace_qs(t) do { } while (0) 201# endif 202 203#define rcu_tasks_qs(t, preempt) \ 204do { \ 205 rcu_tasks_classic_qs((t), (preempt)); \ 206 rcu_tasks_trace_qs(t); \ 207} while (0) 208 209# ifdef CONFIG_TASKS_RUDE_RCU 210void synchronize_rcu_tasks_rude(void); 211void rcu_tasks_rude_torture_stats_print(char *tt, char *tf); 212# endif 213 214#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) 215void exit_tasks_rcu_start(void); 216void exit_tasks_rcu_finish(void); 217#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ 218#define rcu_tasks_classic_qs(t, preempt) do { } while (0) 219#define rcu_tasks_qs(t, preempt) do { } while (0) 220#define rcu_note_voluntary_context_switch(t) do { } while (0) 221#define call_rcu_tasks call_rcu 222#define synchronize_rcu_tasks synchronize_rcu 223static inline void exit_tasks_rcu_start(void) { } 224static inline void exit_tasks_rcu_finish(void) { } 225#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ 226 227/** 228 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period? 229 * 230 * As an accident of implementation, an RCU Tasks Trace grace period also 231 * acts as an RCU grace period. However, this could change at any time. 232 * Code relying on this accident must call this function to verify that 233 * this accident is still happening. 234 * 235 * You have been warned! 236 */ 237static inline bool rcu_trace_implies_rcu_gp(void) { return true; } 238 239/** 240 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU 241 * 242 * This macro resembles cond_resched(), except that it is defined to 243 * report potential quiescent states to RCU-tasks even if the cond_resched() 244 * machinery were to be shut off, as some advocate for PREEMPTION kernels. 245 */ 246#define cond_resched_tasks_rcu_qs() \ 247do { \ 248 rcu_tasks_qs(current, false); \ 249 cond_resched(); \ 250} while (0) 251 252/** 253 * rcu_softirq_qs_periodic - Report RCU and RCU-Tasks quiescent states 254 * @old_ts: jiffies at start of processing. 255 * 256 * This helper is for long-running softirq handlers, such as NAPI threads in 257 * networking. The caller should initialize the variable passed in as @old_ts 258 * at the beginning of the softirq handler. When invoked frequently, this macro 259 * will invoke rcu_softirq_qs() every 100 milliseconds thereafter, which will 260 * provide both RCU and RCU-Tasks quiescent states. Note that this macro 261 * modifies its old_ts argument. 262 * 263 * Because regions of code that have disabled softirq act as RCU read-side 264 * critical sections, this macro should be invoked with softirq (and 265 * preemption) enabled. 266 * 267 * The macro is not needed when CONFIG_PREEMPT_RT is defined. RT kernels would 268 * have more chance to invoke schedule() calls and provide necessary quiescent 269 * states. As a contrast, calling cond_resched() only won't achieve the same 270 * effect because cond_resched() does not provide RCU-Tasks quiescent states. 271 */ 272#define rcu_softirq_qs_periodic(old_ts) \ 273do { \ 274 if (!IS_ENABLED(CONFIG_PREEMPT_RT) && \ 275 time_after(jiffies, (old_ts) + HZ / 10)) { \ 276 preempt_disable(); \ 277 rcu_softirq_qs(); \ 278 preempt_enable(); \ 279 (old_ts) = jiffies; \ 280 } \ 281} while (0) 282 283/* 284 * Infrastructure to implement the synchronize_() primitives in 285 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 286 */ 287 288#if defined(CONFIG_TREE_RCU) 289#include <linux/rcutree.h> 290#elif defined(CONFIG_TINY_RCU) 291#include <linux/rcutiny.h> 292#else 293#error "Unknown RCU implementation specified to kernel configuration" 294#endif 295 296/* 297 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls 298 * are needed for dynamic initialization and destruction of rcu_head 299 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for 300 * dynamic initialization and destruction of statically allocated rcu_head 301 * structures. However, rcu_head structures allocated dynamically in the 302 * heap don't need any initialization. 303 */ 304#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 305void init_rcu_head(struct rcu_head *head); 306void destroy_rcu_head(struct rcu_head *head); 307void init_rcu_head_on_stack(struct rcu_head *head); 308void destroy_rcu_head_on_stack(struct rcu_head *head); 309#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 310static inline void init_rcu_head(struct rcu_head *head) { } 311static inline void destroy_rcu_head(struct rcu_head *head) { } 312static inline void init_rcu_head_on_stack(struct rcu_head *head) { } 313static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } 314#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 315 316#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 317bool rcu_lockdep_current_cpu_online(void); 318#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 319static inline bool rcu_lockdep_current_cpu_online(void) { return true; } 320#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 321 322extern struct lockdep_map rcu_lock_map; 323extern struct lockdep_map rcu_bh_lock_map; 324extern struct lockdep_map rcu_sched_lock_map; 325extern struct lockdep_map rcu_callback_map; 326 327#ifdef CONFIG_DEBUG_LOCK_ALLOC 328 329static inline void rcu_lock_acquire(struct lockdep_map *map) 330{ 331 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); 332} 333 334static inline void rcu_try_lock_acquire(struct lockdep_map *map) 335{ 336 lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_); 337} 338 339static inline void rcu_lock_release(struct lockdep_map *map) 340{ 341 lock_release(map, _THIS_IP_); 342} 343 344int debug_lockdep_rcu_enabled(void); 345int rcu_read_lock_held(void); 346int rcu_read_lock_bh_held(void); 347int rcu_read_lock_sched_held(void); 348int rcu_read_lock_any_held(void); 349 350#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 351 352# define rcu_lock_acquire(a) do { } while (0) 353# define rcu_try_lock_acquire(a) do { } while (0) 354# define rcu_lock_release(a) do { } while (0) 355 356static inline int rcu_read_lock_held(void) 357{ 358 return 1; 359} 360 361static inline int rcu_read_lock_bh_held(void) 362{ 363 return 1; 364} 365 366static inline int rcu_read_lock_sched_held(void) 367{ 368 return !preemptible(); 369} 370 371static inline int rcu_read_lock_any_held(void) 372{ 373 return !preemptible(); 374} 375 376static inline int debug_lockdep_rcu_enabled(void) 377{ 378 return 0; 379} 380 381#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 382 383#ifdef CONFIG_PROVE_RCU 384 385/** 386 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met 387 * @c: condition to check 388 * @s: informative message 389 * 390 * This checks debug_lockdep_rcu_enabled() before checking (c) to 391 * prevent early boot splats due to lockdep not yet being initialized, 392 * and rechecks it after checking (c) to prevent false-positive splats 393 * due to races with lockdep being disabled. See commit 3066820034b5dd 394 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail. 395 */ 396#define RCU_LOCKDEP_WARN(c, s) \ 397 do { \ 398 static bool __section(".data..unlikely") __warned; \ 399 if (debug_lockdep_rcu_enabled() && (c) && \ 400 debug_lockdep_rcu_enabled() && !__warned) { \ 401 __warned = true; \ 402 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 403 } \ 404 } while (0) 405 406#ifndef CONFIG_PREEMPT_RCU 407static inline void rcu_preempt_sleep_check(void) 408{ 409 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), 410 "Illegal context switch in RCU read-side critical section"); 411} 412#else // #ifndef CONFIG_PREEMPT_RCU 413static inline void rcu_preempt_sleep_check(void) { } 414#endif // #else // #ifndef CONFIG_PREEMPT_RCU 415 416#define rcu_sleep_check() \ 417 do { \ 418 rcu_preempt_sleep_check(); \ 419 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ 420 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ 421 "Illegal context switch in RCU-bh read-side critical section"); \ 422 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ 423 "Illegal context switch in RCU-sched read-side critical section"); \ 424 } while (0) 425 426// See RCU_LOCKDEP_WARN() for an explanation of the double call to 427// debug_lockdep_rcu_enabled(). 428static inline bool lockdep_assert_rcu_helper(bool c) 429{ 430 return debug_lockdep_rcu_enabled() && 431 (c || !rcu_is_watching() || !rcu_lockdep_current_cpu_online()) && 432 debug_lockdep_rcu_enabled(); 433} 434 435/** 436 * lockdep_assert_in_rcu_read_lock - WARN if not protected by rcu_read_lock() 437 * 438 * Splats if lockdep is enabled and there is no rcu_read_lock() in effect. 439 */ 440#define lockdep_assert_in_rcu_read_lock() \ 441 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map))) 442 443/** 444 * lockdep_assert_in_rcu_read_lock_bh - WARN if not protected by rcu_read_lock_bh() 445 * 446 * Splats if lockdep is enabled and there is no rcu_read_lock_bh() in effect. 447 * Note that local_bh_disable() and friends do not suffice here, instead an 448 * actual rcu_read_lock_bh() is required. 449 */ 450#define lockdep_assert_in_rcu_read_lock_bh() \ 451 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_bh_lock_map))) 452 453/** 454 * lockdep_assert_in_rcu_read_lock_sched - WARN if not protected by rcu_read_lock_sched() 455 * 456 * Splats if lockdep is enabled and there is no rcu_read_lock_sched() 457 * in effect. Note that preempt_disable() and friends do not suffice here, 458 * instead an actual rcu_read_lock_sched() is required. 459 */ 460#define lockdep_assert_in_rcu_read_lock_sched() \ 461 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_sched_lock_map))) 462 463/** 464 * lockdep_assert_in_rcu_reader - WARN if not within some type of RCU reader 465 * 466 * Splats if lockdep is enabled and there is no RCU reader of any 467 * type in effect. Note that regions of code protected by things like 468 * preempt_disable, local_bh_disable(), and local_irq_disable() all qualify 469 * as RCU readers. 470 * 471 * Note that this will never trigger in PREEMPT_NONE or PREEMPT_VOLUNTARY 472 * kernels that are not also built with PREEMPT_COUNT. But if you have 473 * lockdep enabled, you might as well also enable PREEMPT_COUNT. 474 */ 475#define lockdep_assert_in_rcu_reader() \ 476 WARN_ON_ONCE(lockdep_assert_rcu_helper(!lock_is_held(&rcu_lock_map) && \ 477 !lock_is_held(&rcu_bh_lock_map) && \ 478 !lock_is_held(&rcu_sched_lock_map) && \ 479 preemptible())) 480 481#else /* #ifdef CONFIG_PROVE_RCU */ 482 483#define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) 484#define rcu_sleep_check() do { } while (0) 485 486#define lockdep_assert_in_rcu_read_lock() do { } while (0) 487#define lockdep_assert_in_rcu_read_lock_bh() do { } while (0) 488#define lockdep_assert_in_rcu_read_lock_sched() do { } while (0) 489#define lockdep_assert_in_rcu_reader() do { } while (0) 490 491#endif /* #else #ifdef CONFIG_PROVE_RCU */ 492 493/* 494 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 495 * and rcu_assign_pointer(). Some of these could be folded into their 496 * callers, but they are left separate in order to ease introduction of 497 * multiple pointers markings to match different RCU implementations 498 * (e.g., __srcu), should this make sense in the future. 499 */ 500 501#ifdef __CHECKER__ 502#define rcu_check_sparse(p, space) \ 503 ((void)(((typeof(*p) space *)p) == p)) 504#else /* #ifdef __CHECKER__ */ 505#define rcu_check_sparse(p, space) 506#endif /* #else #ifdef __CHECKER__ */ 507 508#define __unrcu_pointer(p, local) \ 509({ \ 510 typeof(*p) *local = (typeof(*p) *__force)(p); \ 511 rcu_check_sparse(p, __rcu); \ 512 ((typeof(*p) __force __kernel *)(local)); \ 513}) 514/** 515 * unrcu_pointer - mark a pointer as not being RCU protected 516 * @p: pointer needing to lose its __rcu property 517 * 518 * Converts @p from an __rcu pointer to a __kernel pointer. 519 * This allows an __rcu pointer to be used with xchg() and friends. 520 */ 521#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) 522 523#define __rcu_access_pointer(p, local, space) \ 524({ \ 525 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 526 rcu_check_sparse(p, space); \ 527 ((typeof(*p) __force __kernel *)(local)); \ 528}) 529#define __rcu_dereference_check(p, local, c, space) \ 530({ \ 531 /* Dependency order vs. p above. */ \ 532 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 533 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ 534 rcu_check_sparse(p, space); \ 535 ((typeof(*p) __force __kernel *)(local)); \ 536}) 537#define __rcu_dereference_protected(p, local, c, space) \ 538({ \ 539 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ 540 rcu_check_sparse(p, space); \ 541 ((typeof(*p) __force __kernel *)(p)); \ 542}) 543#define __rcu_dereference_raw(p, local) \ 544({ \ 545 /* Dependency order vs. p above. */ \ 546 typeof(p) local = READ_ONCE(p); \ 547 ((typeof(*p) __force __kernel *)(local)); \ 548}) 549#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) 550 551/** 552 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable 553 * @v: The value to statically initialize with. 554 */ 555#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) 556 557/** 558 * rcu_assign_pointer() - assign to RCU-protected pointer 559 * @p: pointer to assign to 560 * @v: value to assign (publish) 561 * 562 * Assigns the specified value to the specified RCU-protected 563 * pointer, ensuring that any concurrent RCU readers will see 564 * any prior initialization. 565 * 566 * Inserts memory barriers on architectures that require them 567 * (which is most of them), and also prevents the compiler from 568 * reordering the code that initializes the structure after the pointer 569 * assignment. More importantly, this call documents which pointers 570 * will be dereferenced by RCU read-side code. 571 * 572 * In some special cases, you may use RCU_INIT_POINTER() instead 573 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 574 * to the fact that it does not constrain either the CPU or the compiler. 575 * That said, using RCU_INIT_POINTER() when you should have used 576 * rcu_assign_pointer() is a very bad thing that results in 577 * impossible-to-diagnose memory corruption. So please be careful. 578 * See the RCU_INIT_POINTER() comment header for details. 579 * 580 * Note that rcu_assign_pointer() evaluates each of its arguments only 581 * once, appearances notwithstanding. One of the "extra" evaluations 582 * is in typeof() and the other visible only to sparse (__CHECKER__), 583 * neither of which actually execute the argument. As with most cpp 584 * macros, this execute-arguments-only-once property is important, so 585 * please be careful when making changes to rcu_assign_pointer() and the 586 * other macros that it invokes. 587 */ 588#define rcu_assign_pointer(p, v) \ 589do { \ 590 uintptr_t _r_a_p__v = (uintptr_t)(v); \ 591 rcu_check_sparse(p, __rcu); \ 592 \ 593 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ 594 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ 595 else \ 596 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ 597} while (0) 598 599/** 600 * rcu_replace_pointer() - replace an RCU pointer, returning its old value 601 * @rcu_ptr: RCU pointer, whose old value is returned 602 * @ptr: regular pointer 603 * @c: the lockdep conditions under which the dereference will take place 604 * 605 * Perform a replacement, where @rcu_ptr is an RCU-annotated 606 * pointer and @c is the lockdep argument that is passed to the 607 * rcu_dereference_protected() call used to read that pointer. The old 608 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. 609 */ 610#define rcu_replace_pointer(rcu_ptr, ptr, c) \ 611({ \ 612 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ 613 rcu_assign_pointer((rcu_ptr), (ptr)); \ 614 __tmp; \ 615}) 616 617/** 618 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 619 * @p: The pointer to read 620 * 621 * Return the value of the specified RCU-protected pointer, but omit the 622 * lockdep checks for being in an RCU read-side critical section. This is 623 * useful when the value of this pointer is accessed, but the pointer is 624 * not dereferenced, for example, when testing an RCU-protected pointer 625 * against NULL. Although rcu_access_pointer() may also be used in cases 626 * where update-side locks prevent the value of the pointer from changing, 627 * you should instead use rcu_dereference_protected() for this use case. 628 * Within an RCU read-side critical section, there is little reason to 629 * use rcu_access_pointer(). 630 * 631 * It is usually best to test the rcu_access_pointer() return value 632 * directly in order to avoid accidental dereferences being introduced 633 * by later inattentive changes. In other words, assigning the 634 * rcu_access_pointer() return value to a local variable results in an 635 * accident waiting to happen. 636 * 637 * It is also permissible to use rcu_access_pointer() when read-side 638 * access to the pointer was removed at least one grace period ago, as is 639 * the case in the context of the RCU callback that is freeing up the data, 640 * or after a synchronize_rcu() returns. This can be useful when tearing 641 * down multi-linked structures after a grace period has elapsed. However, 642 * rcu_dereference_protected() is normally preferred for this use case. 643 */ 644#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu) 645 646/** 647 * rcu_dereference_check() - rcu_dereference with debug checking 648 * @p: The pointer to read, prior to dereferencing 649 * @c: The conditions under which the dereference will take place 650 * 651 * Do an rcu_dereference(), but check that the conditions under which the 652 * dereference will take place are correct. Typically the conditions 653 * indicate the various locking conditions that should be held at that 654 * point. The check should return true if the conditions are satisfied. 655 * An implicit check for being in an RCU read-side critical section 656 * (rcu_read_lock()) is included. 657 * 658 * For example: 659 * 660 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 661 * 662 * could be used to indicate to lockdep that foo->bar may only be dereferenced 663 * if either rcu_read_lock() is held, or that the lock required to replace 664 * the bar struct at foo->bar is held. 665 * 666 * Note that the list of conditions may also include indications of when a lock 667 * need not be held, for example during initialisation or destruction of the 668 * target struct: 669 * 670 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 671 * atomic_read(&foo->usage) == 0); 672 * 673 * Inserts memory barriers on architectures that require them 674 * (currently only the Alpha), prevents the compiler from refetching 675 * (and from merging fetches), and, more importantly, documents exactly 676 * which pointers are protected by RCU and checks that the pointer is 677 * annotated as __rcu. 678 */ 679#define rcu_dereference_check(p, c) \ 680 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 681 (c) || rcu_read_lock_held(), __rcu) 682 683/** 684 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 685 * @p: The pointer to read, prior to dereferencing 686 * @c: The conditions under which the dereference will take place 687 * 688 * This is the RCU-bh counterpart to rcu_dereference_check(). However, 689 * please note that starting in v5.0 kernels, vanilla RCU grace periods 690 * wait for local_bh_disable() regions of code in addition to regions of 691 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means 692 * that synchronize_rcu(), call_rcu, and friends all take not only 693 * rcu_read_lock() but also rcu_read_lock_bh() into account. 694 */ 695#define rcu_dereference_bh_check(p, c) \ 696 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 697 (c) || rcu_read_lock_bh_held(), __rcu) 698 699/** 700 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 701 * @p: The pointer to read, prior to dereferencing 702 * @c: The conditions under which the dereference will take place 703 * 704 * This is the RCU-sched counterpart to rcu_dereference_check(). 705 * However, please note that starting in v5.0 kernels, vanilla RCU grace 706 * periods wait for preempt_disable() regions of code in addition to 707 * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). 708 * This means that synchronize_rcu(), call_rcu, and friends all take not 709 * only rcu_read_lock() but also rcu_read_lock_sched() into account. 710 */ 711#define rcu_dereference_sched_check(p, c) \ 712 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 713 (c) || rcu_read_lock_sched_held(), \ 714 __rcu) 715 716/** 717 * rcu_dereference_all_check() - rcu_dereference_all with debug checking 718 * @p: The pointer to read, prior to dereferencing 719 * @c: The conditions under which the dereference will take place 720 * 721 * This is similar to rcu_dereference_check(), but allows protection 722 * by all forms of vanilla RCU readers, including preemption disabled, 723 * bh-disabled, and interrupt-disabled regions of code. Note that "vanilla 724 * RCU" excludes SRCU and the various Tasks RCU flavors. Please note 725 * that this macro should not be backported to any Linux-kernel version 726 * preceding v5.0 due to changes in synchronize_rcu() semantics prior 727 * to that version. 728 */ 729#define rcu_dereference_all_check(p, c) \ 730 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 731 (c) || rcu_read_lock_any_held(), \ 732 __rcu) 733 734/* 735 * The tracing infrastructure traces RCU (we want that), but unfortunately 736 * some of the RCU checks causes tracing to lock up the system. 737 * 738 * The no-tracing version of rcu_dereference_raw() must not call 739 * rcu_read_lock_held(). 740 */ 741#define rcu_dereference_raw_check(p) \ 742 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu) 743 744/** 745 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 746 * @p: The pointer to read, prior to dereferencing 747 * @c: The conditions under which the dereference will take place 748 * 749 * Return the value of the specified RCU-protected pointer, but omit 750 * the READ_ONCE(). This is useful in cases where update-side locks 751 * prevent the value of the pointer from changing. Please note that this 752 * primitive does *not* prevent the compiler from repeating this reference 753 * or combining it with other references, so it should not be used without 754 * protection of appropriate locks. 755 * 756 * This function is only for update-side use. Using this function 757 * when protected only by rcu_read_lock() will result in infrequent 758 * but very ugly failures. 759 */ 760#define rcu_dereference_protected(p, c) \ 761 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu) 762 763 764/** 765 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 766 * @p: The pointer to read, prior to dereferencing 767 * 768 * This is a simple wrapper around rcu_dereference_check(). 769 */ 770#define rcu_dereference(p) rcu_dereference_check(p, 0) 771 772/** 773 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 774 * @p: The pointer to read, prior to dereferencing 775 * 776 * Makes rcu_dereference_check() do the dirty work. 777 */ 778#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 779 780/** 781 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 782 * @p: The pointer to read, prior to dereferencing 783 * 784 * Makes rcu_dereference_check() do the dirty work. 785 */ 786#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 787 788/** 789 * rcu_dereference_all() - fetch RCU-all-protected pointer for dereferencing 790 * @p: The pointer to read, prior to dereferencing 791 * 792 * Makes rcu_dereference_check() do the dirty work. 793 */ 794#define rcu_dereference_all(p) rcu_dereference_all_check(p, 0) 795 796/** 797 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism 798 * @p: The pointer to hand off 799 * 800 * This is simply an identity function, but it documents where a pointer 801 * is handed off from RCU to some other synchronization mechanism, for 802 * example, reference counting or locking. In C11, it would map to 803 * kill_dependency(). It could be used as follows:: 804 * 805 * rcu_read_lock(); 806 * p = rcu_dereference(gp); 807 * long_lived = is_long_lived(p); 808 * if (long_lived) { 809 * if (!atomic_inc_not_zero(p->refcnt)) 810 * long_lived = false; 811 * else 812 * p = rcu_pointer_handoff(p); 813 * } 814 * rcu_read_unlock(); 815 */ 816#define rcu_pointer_handoff(p) (p) 817 818/** 819 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 820 * 821 * When synchronize_rcu() is invoked on one CPU while other CPUs 822 * are within RCU read-side critical sections, then the 823 * synchronize_rcu() is guaranteed to block until after all the other 824 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 825 * on one CPU while other CPUs are within RCU read-side critical 826 * sections, invocation of the corresponding RCU callback is deferred 827 * until after the all the other CPUs exit their critical sections. 828 * 829 * Both synchronize_rcu() and call_rcu() also wait for regions of code 830 * with preemption disabled, including regions of code with interrupts or 831 * softirqs disabled. 832 * 833 * Note, however, that RCU callbacks are permitted to run concurrently 834 * with new RCU read-side critical sections. One way that this can happen 835 * is via the following sequence of events: (1) CPU 0 enters an RCU 836 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 837 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 838 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 839 * callback is invoked. This is legal, because the RCU read-side critical 840 * section that was running concurrently with the call_rcu() (and which 841 * therefore might be referencing something that the corresponding RCU 842 * callback would free up) has completed before the corresponding 843 * RCU callback is invoked. 844 * 845 * RCU read-side critical sections may be nested. Any deferred actions 846 * will be deferred until the outermost RCU read-side critical section 847 * completes. 848 * 849 * You can avoid reading and understanding the next paragraph by 850 * following this rule: don't put anything in an rcu_read_lock() RCU 851 * read-side critical section that would block in a !PREEMPTION kernel. 852 * But if you want the full story, read on! 853 * 854 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), 855 * it is illegal to block while in an RCU read-side critical section. 856 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION 857 * kernel builds, RCU read-side critical sections may be preempted, 858 * but explicit blocking is illegal. Finally, in preemptible RCU 859 * implementations in real-time (with -rt patchset) kernel builds, RCU 860 * read-side critical sections may be preempted and they may also block, but 861 * only when acquiring spinlocks that are subject to priority inheritance. 862 */ 863static __always_inline void rcu_read_lock(void) 864{ 865 __rcu_read_lock(); 866 __acquire(RCU); 867 rcu_lock_acquire(&rcu_lock_map); 868 RCU_LOCKDEP_WARN(!rcu_is_watching(), 869 "rcu_read_lock() used illegally while idle"); 870} 871 872/* 873 * So where is rcu_write_lock()? It does not exist, as there is no 874 * way for writers to lock out RCU readers. This is a feature, not 875 * a bug -- this property is what provides RCU's performance benefits. 876 * Of course, writers must coordinate with each other. The normal 877 * spinlock primitives work well for this, but any other technique may be 878 * used as well. RCU does not care how the writers keep out of each 879 * others' way, as long as they do so. 880 */ 881 882/** 883 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 884 * 885 * In almost all situations, rcu_read_unlock() is immune from deadlock. 886 * This deadlock immunity also extends to the scheduler's runqueue 887 * and priority-inheritance spinlocks, courtesy of the quiescent-state 888 * deferral that is carried out when rcu_read_unlock() is invoked with 889 * interrupts disabled. 890 * 891 * See rcu_read_lock() for more information. 892 */ 893static inline void rcu_read_unlock(void) 894{ 895 RCU_LOCKDEP_WARN(!rcu_is_watching(), 896 "rcu_read_unlock() used illegally while idle"); 897 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ 898 __release(RCU); 899 __rcu_read_unlock(); 900} 901 902/** 903 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 904 * 905 * This is equivalent to rcu_read_lock(), but also disables softirqs. 906 * Note that anything else that disables softirqs can also serve as an RCU 907 * read-side critical section. However, please note that this equivalence 908 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and 909 * rcu_read_lock_bh() were unrelated. 910 * 911 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 912 * must occur in the same context, for example, it is illegal to invoke 913 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 914 * was invoked from some other task. 915 */ 916static inline void rcu_read_lock_bh(void) 917{ 918 local_bh_disable(); 919 __acquire(RCU_BH); 920 rcu_lock_acquire(&rcu_bh_lock_map); 921 RCU_LOCKDEP_WARN(!rcu_is_watching(), 922 "rcu_read_lock_bh() used illegally while idle"); 923} 924 925/** 926 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section 927 * 928 * See rcu_read_lock_bh() for more information. 929 */ 930static inline void rcu_read_unlock_bh(void) 931{ 932 RCU_LOCKDEP_WARN(!rcu_is_watching(), 933 "rcu_read_unlock_bh() used illegally while idle"); 934 rcu_lock_release(&rcu_bh_lock_map); 935 __release(RCU_BH); 936 local_bh_enable(); 937} 938 939/** 940 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 941 * 942 * This is equivalent to rcu_read_lock(), but also disables preemption. 943 * Read-side critical sections can also be introduced by anything else that 944 * disables preemption, including local_irq_disable() and friends. However, 945 * please note that the equivalence to rcu_read_lock() applies only to 946 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() 947 * were unrelated. 948 * 949 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 950 * must occur in the same context, for example, it is illegal to invoke 951 * rcu_read_unlock_sched() from process context if the matching 952 * rcu_read_lock_sched() was invoked from an NMI handler. 953 */ 954static inline void rcu_read_lock_sched(void) 955{ 956 preempt_disable(); 957 __acquire(RCU_SCHED); 958 rcu_lock_acquire(&rcu_sched_lock_map); 959 RCU_LOCKDEP_WARN(!rcu_is_watching(), 960 "rcu_read_lock_sched() used illegally while idle"); 961} 962 963/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 964static inline notrace void rcu_read_lock_sched_notrace(void) 965{ 966 preempt_disable_notrace(); 967 __acquire(RCU_SCHED); 968} 969 970/** 971 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section 972 * 973 * See rcu_read_lock_sched() for more information. 974 */ 975static inline void rcu_read_unlock_sched(void) 976{ 977 RCU_LOCKDEP_WARN(!rcu_is_watching(), 978 "rcu_read_unlock_sched() used illegally while idle"); 979 rcu_lock_release(&rcu_sched_lock_map); 980 __release(RCU_SCHED); 981 preempt_enable(); 982} 983 984/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 985static inline notrace void rcu_read_unlock_sched_notrace(void) 986{ 987 __release(RCU_SCHED); 988 preempt_enable_notrace(); 989} 990 991static __always_inline void rcu_read_lock_dont_migrate(void) 992{ 993 if (IS_ENABLED(CONFIG_PREEMPT_RCU)) 994 migrate_disable(); 995 rcu_read_lock(); 996} 997 998static inline void rcu_read_unlock_migrate(void) 999{ 1000 rcu_read_unlock(); 1001 if (IS_ENABLED(CONFIG_PREEMPT_RCU)) 1002 migrate_enable(); 1003} 1004 1005/** 1006 * RCU_INIT_POINTER() - initialize an RCU protected pointer 1007 * @p: The pointer to be initialized. 1008 * @v: The value to initialized the pointer to. 1009 * 1010 * Initialize an RCU-protected pointer in special cases where readers 1011 * do not need ordering constraints on the CPU or the compiler. These 1012 * special cases are: 1013 * 1014 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* 1015 * 2. The caller has taken whatever steps are required to prevent 1016 * RCU readers from concurrently accessing this pointer *or* 1017 * 3. The referenced data structure has already been exposed to 1018 * readers either at compile time or via rcu_assign_pointer() *and* 1019 * 1020 * a. You have not made *any* reader-visible changes to 1021 * this structure since then *or* 1022 * b. It is OK for readers accessing this structure from its 1023 * new location to see the old state of the structure. (For 1024 * example, the changes were to statistical counters or to 1025 * other state where exact synchronization is not required.) 1026 * 1027 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 1028 * result in impossible-to-diagnose memory corruption. As in the structures 1029 * will look OK in crash dumps, but any concurrent RCU readers might 1030 * see pre-initialized values of the referenced data structure. So 1031 * please be very careful how you use RCU_INIT_POINTER()!!! 1032 * 1033 * If you are creating an RCU-protected linked structure that is accessed 1034 * by a single external-to-structure RCU-protected pointer, then you may 1035 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 1036 * pointers, but you must use rcu_assign_pointer() to initialize the 1037 * external-to-structure pointer *after* you have completely initialized 1038 * the reader-accessible portions of the linked structure. 1039 * 1040 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no 1041 * ordering guarantees for either the CPU or the compiler. 1042 */ 1043#define RCU_INIT_POINTER(p, v) \ 1044 do { \ 1045 rcu_check_sparse(p, __rcu); \ 1046 WRITE_ONCE(p, RCU_INITIALIZER(v)); \ 1047 } while (0) 1048 1049/** 1050 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 1051 * @p: The pointer to be initialized. 1052 * @v: The value to initialized the pointer to. 1053 * 1054 * GCC-style initialization for an RCU-protected pointer in a structure field. 1055 */ 1056#define RCU_POINTER_INITIALIZER(p, v) \ 1057 .p = RCU_INITIALIZER(v) 1058 1059/** 1060 * kfree_rcu() - kfree an object after a grace period. 1061 * @ptr: pointer to kfree for double-argument invocations. 1062 * @rhf: the name of the struct rcu_head within the type of @ptr. 1063 * 1064 * Many rcu callbacks functions just call kfree() on the base structure. 1065 * These functions are trivial, but their size adds up, and furthermore 1066 * when they are used in a kernel module, that module must invoke the 1067 * high-latency rcu_barrier() function at module-unload time. 1068 * 1069 * The kfree_rcu() function handles this issue. In order to have a universal 1070 * callback function handling different offsets of rcu_head, the callback needs 1071 * to determine the starting address of the freed object, which can be a large 1072 * kmalloc or vmalloc allocation. To allow simply aligning the pointer down to 1073 * page boundary for those, only offsets up to 4095 bytes can be accommodated. 1074 * If the offset is larger than 4095 bytes, a compile-time error will 1075 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can 1076 * either fall back to use of call_rcu() or rearrange the structure to 1077 * position the rcu_head structure into the first 4096 bytes. 1078 * 1079 * The object to be freed can be allocated either by kmalloc() or 1080 * kmem_cache_alloc(). 1081 * 1082 * Note that the allowable offset might decrease in the future. 1083 * 1084 * The BUILD_BUG_ON check must not involve any function calls, hence the 1085 * checks are done in macros here. 1086 */ 1087#define kfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) 1088#define kvfree_rcu(ptr, rhf) kvfree_rcu_arg_2(ptr, rhf) 1089 1090/** 1091 * kfree_rcu_mightsleep() - kfree an object after a grace period. 1092 * @ptr: pointer to kfree for single-argument invocations. 1093 * 1094 * When it comes to head-less variant, only one argument 1095 * is passed and that is just a pointer which has to be 1096 * freed after a grace period. Therefore the semantic is 1097 * 1098 * kfree_rcu_mightsleep(ptr); 1099 * 1100 * where @ptr is the pointer to be freed by kvfree(). 1101 * 1102 * Please note, head-less way of freeing is permitted to 1103 * use from a context that has to follow might_sleep() 1104 * annotation. Otherwise, please switch and embed the 1105 * rcu_head structure within the type of @ptr. 1106 */ 1107#define kfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) 1108#define kvfree_rcu_mightsleep(ptr) kvfree_rcu_arg_1(ptr) 1109 1110/* 1111 * In mm/slab_common.c, no suitable header to include here. 1112 */ 1113void kvfree_call_rcu(struct rcu_head *head, void *ptr); 1114 1115/* 1116 * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the 1117 * comment of kfree_rcu() for details. 1118 */ 1119#define kvfree_rcu_arg_2(ptr, rhf) \ 1120do { \ 1121 typeof (ptr) ___p = (ptr); \ 1122 \ 1123 if (___p) { \ 1124 BUILD_BUG_ON(offsetof(typeof(*(ptr)), rhf) >= 4096); \ 1125 kvfree_call_rcu(&((___p)->rhf), (void *) (___p)); \ 1126 } \ 1127} while (0) 1128 1129#define kvfree_rcu_arg_1(ptr) \ 1130do { \ 1131 typeof(ptr) ___p = (ptr); \ 1132 \ 1133 if (___p) \ 1134 kvfree_call_rcu(NULL, (void *) (___p)); \ 1135} while (0) 1136 1137/* 1138 * Place this after a lock-acquisition primitive to guarantee that 1139 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies 1140 * if the UNLOCK and LOCK are executed by the same CPU or if the 1141 * UNLOCK and LOCK operate on the same lock variable. 1142 */ 1143#ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE 1144#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ 1145#else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1146#define smp_mb__after_unlock_lock() do { } while (0) 1147#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 1148 1149 1150/* Has the specified rcu_head structure been handed to call_rcu()? */ 1151 1152/** 1153 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() 1154 * @rhp: The rcu_head structure to initialize. 1155 * 1156 * If you intend to invoke rcu_head_after_call_rcu() to test whether a 1157 * given rcu_head structure has already been passed to call_rcu(), then 1158 * you must also invoke this rcu_head_init() function on it just after 1159 * allocating that structure. Calls to this function must not race with 1160 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. 1161 */ 1162static inline void rcu_head_init(struct rcu_head *rhp) 1163{ 1164 rhp->func = (rcu_callback_t)~0L; 1165} 1166 1167/** 1168 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? 1169 * @rhp: The rcu_head structure to test. 1170 * @f: The function passed to call_rcu() along with @rhp. 1171 * 1172 * Returns @true if the @rhp has been passed to call_rcu() with @func, 1173 * and @false otherwise. Emits a warning in any other case, including 1174 * the case where @rhp has already been invoked after a grace period. 1175 * Calls to this function must not race with callback invocation. One way 1176 * to avoid such races is to enclose the call to rcu_head_after_call_rcu() 1177 * in an RCU read-side critical section that includes a read-side fetch 1178 * of the pointer to the structure containing @rhp. 1179 */ 1180static inline bool 1181rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) 1182{ 1183 rcu_callback_t func = READ_ONCE(rhp->func); 1184 1185 if (func == f) 1186 return true; 1187 WARN_ON_ONCE(func != (rcu_callback_t)~0L); 1188 return false; 1189} 1190 1191/* kernel/ksysfs.c definitions */ 1192extern int rcu_expedited; 1193extern int rcu_normal; 1194 1195DEFINE_LOCK_GUARD_0(rcu, 1196 do { 1197 rcu_read_lock(); 1198 /* 1199 * sparse doesn't call the cleanup function, 1200 * so just release immediately and don't track 1201 * the context. We don't need to anyway, since 1202 * the whole point of the guard is to not need 1203 * the explicit unlock. 1204 */ 1205 __release(RCU); 1206 } while (0), 1207 rcu_read_unlock()) 1208 1209#endif /* __LINUX_RCUPDATE_H */
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