1/* 2 * Read-Copy Update mechanism for mutual exclusion 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, write to the Free Software 16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 17 * 18 * Copyright IBM Corporation, 2001 19 * 20 * Author: Dipankar Sarma <dipankar@in.ibm.com> 21 * 22 * Based on the original work by Paul McKenney <paulmck@us.ibm.com> 23 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 24 * Papers: 25 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 26 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 27 * 28 * For detailed explanation of Read-Copy Update mechanism see - 29 * http://lse.sourceforge.net/locking/rcupdate.html 30 * 31 */ 32 33#ifndef __LINUX_RCUPDATE_H 34#define __LINUX_RCUPDATE_H 35 36#include <linux/types.h> 37#include <linux/cache.h> 38#include <linux/spinlock.h> 39#include <linux/threads.h> 40#include <linux/cpumask.h> 41#include <linux/seqlock.h> 42#include <linux/lockdep.h> 43#include <linux/completion.h> 44#include <linux/debugobjects.h> 45#include <linux/bug.h> 46#include <linux/compiler.h> 47 48#ifdef CONFIG_RCU_TORTURE_TEST 49extern int rcutorture_runnable; /* for sysctl */ 50#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ 51 52#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 53extern void rcutorture_record_test_transition(void); 54extern void rcutorture_record_progress(unsigned long vernum); 55extern void do_trace_rcu_torture_read(char *rcutorturename, 56 struct rcu_head *rhp); 57#else 58static inline void rcutorture_record_test_transition(void) 59{ 60} 61static inline void rcutorture_record_progress(unsigned long vernum) 62{ 63} 64#ifdef CONFIG_RCU_TRACE 65extern void do_trace_rcu_torture_read(char *rcutorturename, 66 struct rcu_head *rhp); 67#else 68#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0) 69#endif 70#endif 71 72#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) 73#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) 74#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 75#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 76 77/* Exported common interfaces */ 78 79#ifdef CONFIG_PREEMPT_RCU 80 81/** 82 * call_rcu() - Queue an RCU callback for invocation after a grace period. 83 * @head: structure to be used for queueing the RCU updates. 84 * @func: actual callback function to be invoked after the grace period 85 * 86 * The callback function will be invoked some time after a full grace 87 * period elapses, in other words after all pre-existing RCU read-side 88 * critical sections have completed. However, the callback function 89 * might well execute concurrently with RCU read-side critical sections 90 * that started after call_rcu() was invoked. RCU read-side critical 91 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), 92 * and may be nested. 93 */ 94extern void call_rcu(struct rcu_head *head, 95 void (*func)(struct rcu_head *head)); 96 97#else /* #ifdef CONFIG_PREEMPT_RCU */ 98 99/* In classic RCU, call_rcu() is just call_rcu_sched(). */ 100#define call_rcu call_rcu_sched 101 102#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 103 104/** 105 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. 106 * @head: structure to be used for queueing the RCU updates. 107 * @func: actual callback function to be invoked after the grace period 108 * 109 * The callback function will be invoked some time after a full grace 110 * period elapses, in other words after all currently executing RCU 111 * read-side critical sections have completed. call_rcu_bh() assumes 112 * that the read-side critical sections end on completion of a softirq 113 * handler. This means that read-side critical sections in process 114 * context must not be interrupted by softirqs. This interface is to be 115 * used when most of the read-side critical sections are in softirq context. 116 * RCU read-side critical sections are delimited by : 117 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. 118 * OR 119 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. 120 * These may be nested. 121 */ 122extern void call_rcu_bh(struct rcu_head *head, 123 void (*func)(struct rcu_head *head)); 124 125/** 126 * call_rcu_sched() - Queue an RCU for invocation after sched grace period. 127 * @head: structure to be used for queueing the RCU updates. 128 * @func: actual callback function to be invoked after the grace period 129 * 130 * The callback function will be invoked some time after a full grace 131 * period elapses, in other words after all currently executing RCU 132 * read-side critical sections have completed. call_rcu_sched() assumes 133 * that the read-side critical sections end on enabling of preemption 134 * or on voluntary preemption. 135 * RCU read-side critical sections are delimited by : 136 * - rcu_read_lock_sched() and rcu_read_unlock_sched(), 137 * OR 138 * anything that disables preemption. 139 * These may be nested. 140 */ 141extern void call_rcu_sched(struct rcu_head *head, 142 void (*func)(struct rcu_head *rcu)); 143 144extern void synchronize_sched(void); 145 146#ifdef CONFIG_PREEMPT_RCU 147 148extern void __rcu_read_lock(void); 149extern void __rcu_read_unlock(void); 150extern void rcu_read_unlock_special(struct task_struct *t); 151void synchronize_rcu(void); 152 153/* 154 * Defined as a macro as it is a very low level header included from 155 * areas that don't even know about current. This gives the rcu_read_lock() 156 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 157 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 158 */ 159#define rcu_preempt_depth() (current->rcu_read_lock_nesting) 160 161#else /* #ifdef CONFIG_PREEMPT_RCU */ 162 163static inline void __rcu_read_lock(void) 164{ 165 preempt_disable(); 166} 167 168static inline void __rcu_read_unlock(void) 169{ 170 preempt_enable(); 171} 172 173static inline void synchronize_rcu(void) 174{ 175 synchronize_sched(); 176} 177 178static inline int rcu_preempt_depth(void) 179{ 180 return 0; 181} 182 183#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 184 185/* Internal to kernel */ 186extern void rcu_sched_qs(int cpu); 187extern void rcu_bh_qs(int cpu); 188extern void rcu_check_callbacks(int cpu, int user); 189struct notifier_block; 190extern void rcu_idle_enter(void); 191extern void rcu_idle_exit(void); 192extern void rcu_irq_enter(void); 193extern void rcu_irq_exit(void); 194extern void exit_rcu(void); 195 196/** 197 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers 198 * @a: Code that RCU needs to pay attention to. 199 * 200 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden 201 * in the inner idle loop, that is, between the rcu_idle_enter() and 202 * the rcu_idle_exit() -- RCU will happily ignore any such read-side 203 * critical sections. However, things like powertop need tracepoints 204 * in the inner idle loop. 205 * 206 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) 207 * will tell RCU that it needs to pay attending, invoke its argument 208 * (in this example, a call to the do_something_with_RCU() function), 209 * and then tell RCU to go back to ignoring this CPU. It is permissible 210 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently 211 * quite limited. If deeper nesting is required, it will be necessary 212 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. 213 * 214 * This macro may be used from process-level code only. 215 */ 216#define RCU_NONIDLE(a) \ 217 do { \ 218 rcu_idle_exit(); \ 219 do { a; } while (0); \ 220 rcu_idle_enter(); \ 221 } while (0) 222 223/* 224 * Infrastructure to implement the synchronize_() primitives in 225 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 226 */ 227 228typedef void call_rcu_func_t(struct rcu_head *head, 229 void (*func)(struct rcu_head *head)); 230void wait_rcu_gp(call_rcu_func_t crf); 231 232#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 233#include <linux/rcutree.h> 234#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) 235#include <linux/rcutiny.h> 236#else 237#error "Unknown RCU implementation specified to kernel configuration" 238#endif 239 240/* 241 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic 242 * initialization and destruction of rcu_head on the stack. rcu_head structures 243 * allocated dynamically in the heap or defined statically don't need any 244 * initialization. 245 */ 246#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 247extern void init_rcu_head_on_stack(struct rcu_head *head); 248extern void destroy_rcu_head_on_stack(struct rcu_head *head); 249#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 250static inline void init_rcu_head_on_stack(struct rcu_head *head) 251{ 252} 253 254static inline void destroy_rcu_head_on_stack(struct rcu_head *head) 255{ 256} 257#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 258 259#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) 260extern int rcu_is_cpu_idle(void); 261#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */ 262 263#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 264bool rcu_lockdep_current_cpu_online(void); 265#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 266static inline bool rcu_lockdep_current_cpu_online(void) 267{ 268 return 1; 269} 270#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 271 272#ifdef CONFIG_DEBUG_LOCK_ALLOC 273 274static inline void rcu_lock_acquire(struct lockdep_map *map) 275{ 276 lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); 277} 278 279static inline void rcu_lock_release(struct lockdep_map *map) 280{ 281 lock_release(map, 1, _THIS_IP_); 282} 283 284extern struct lockdep_map rcu_lock_map; 285extern struct lockdep_map rcu_bh_lock_map; 286extern struct lockdep_map rcu_sched_lock_map; 287extern int debug_lockdep_rcu_enabled(void); 288 289/** 290 * rcu_read_lock_held() - might we be in RCU read-side critical section? 291 * 292 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU 293 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 294 * this assumes we are in an RCU read-side critical section unless it can 295 * prove otherwise. This is useful for debug checks in functions that 296 * require that they be called within an RCU read-side critical section. 297 * 298 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 299 * and while lockdep is disabled. 300 * 301 * Note that rcu_read_lock() and the matching rcu_read_unlock() must 302 * occur in the same context, for example, it is illegal to invoke 303 * rcu_read_unlock() in process context if the matching rcu_read_lock() 304 * was invoked from within an irq handler. 305 * 306 * Note that rcu_read_lock() is disallowed if the CPU is either idle or 307 * offline from an RCU perspective, so check for those as well. 308 */ 309static inline int rcu_read_lock_held(void) 310{ 311 if (!debug_lockdep_rcu_enabled()) 312 return 1; 313 if (rcu_is_cpu_idle()) 314 return 0; 315 if (!rcu_lockdep_current_cpu_online()) 316 return 0; 317 return lock_is_held(&rcu_lock_map); 318} 319 320/* 321 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file 322 * hell. 323 */ 324extern int rcu_read_lock_bh_held(void); 325 326/** 327 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? 328 * 329 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an 330 * RCU-sched read-side critical section. In absence of 331 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side 332 * critical section unless it can prove otherwise. Note that disabling 333 * of preemption (including disabling irqs) counts as an RCU-sched 334 * read-side critical section. This is useful for debug checks in functions 335 * that required that they be called within an RCU-sched read-side 336 * critical section. 337 * 338 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot 339 * and while lockdep is disabled. 340 * 341 * Note that if the CPU is in the idle loop from an RCU point of 342 * view (ie: that we are in the section between rcu_idle_enter() and 343 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU 344 * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs 345 * that are in such a section, considering these as in extended quiescent 346 * state, so such a CPU is effectively never in an RCU read-side critical 347 * section regardless of what RCU primitives it invokes. This state of 348 * affairs is required --- we need to keep an RCU-free window in idle 349 * where the CPU may possibly enter into low power mode. This way we can 350 * notice an extended quiescent state to other CPUs that started a grace 351 * period. Otherwise we would delay any grace period as long as we run in 352 * the idle task. 353 * 354 * Similarly, we avoid claiming an SRCU read lock held if the current 355 * CPU is offline. 356 */ 357#ifdef CONFIG_PREEMPT_COUNT 358static inline int rcu_read_lock_sched_held(void) 359{ 360 int lockdep_opinion = 0; 361 362 if (!debug_lockdep_rcu_enabled()) 363 return 1; 364 if (rcu_is_cpu_idle()) 365 return 0; 366 if (!rcu_lockdep_current_cpu_online()) 367 return 0; 368 if (debug_locks) 369 lockdep_opinion = lock_is_held(&rcu_sched_lock_map); 370 return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); 371} 372#else /* #ifdef CONFIG_PREEMPT_COUNT */ 373static inline int rcu_read_lock_sched_held(void) 374{ 375 return 1; 376} 377#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ 378 379#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 380 381# define rcu_lock_acquire(a) do { } while (0) 382# define rcu_lock_release(a) do { } while (0) 383 384static inline int rcu_read_lock_held(void) 385{ 386 return 1; 387} 388 389static inline int rcu_read_lock_bh_held(void) 390{ 391 return 1; 392} 393 394#ifdef CONFIG_PREEMPT_COUNT 395static inline int rcu_read_lock_sched_held(void) 396{ 397 return preempt_count() != 0 || irqs_disabled(); 398} 399#else /* #ifdef CONFIG_PREEMPT_COUNT */ 400static inline int rcu_read_lock_sched_held(void) 401{ 402 return 1; 403} 404#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ 405 406#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 407 408#ifdef CONFIG_PROVE_RCU 409 410extern int rcu_my_thread_group_empty(void); 411 412/** 413 * rcu_lockdep_assert - emit lockdep splat if specified condition not met 414 * @c: condition to check 415 * @s: informative message 416 */ 417#define rcu_lockdep_assert(c, s) \ 418 do { \ 419 static bool __section(.data.unlikely) __warned; \ 420 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ 421 __warned = true; \ 422 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 423 } \ 424 } while (0) 425 426#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) 427static inline void rcu_preempt_sleep_check(void) 428{ 429 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), 430 "Illegal context switch in RCU read-side critical section"); 431} 432#else /* #ifdef CONFIG_PROVE_RCU */ 433static inline void rcu_preempt_sleep_check(void) 434{ 435} 436#endif /* #else #ifdef CONFIG_PROVE_RCU */ 437 438#define rcu_sleep_check() \ 439 do { \ 440 rcu_preempt_sleep_check(); \ 441 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ 442 "Illegal context switch in RCU-bh" \ 443 " read-side critical section"); \ 444 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ 445 "Illegal context switch in RCU-sched"\ 446 " read-side critical section"); \ 447 } while (0) 448 449#else /* #ifdef CONFIG_PROVE_RCU */ 450 451#define rcu_lockdep_assert(c, s) do { } while (0) 452#define rcu_sleep_check() do { } while (0) 453 454#endif /* #else #ifdef CONFIG_PROVE_RCU */ 455 456/* 457 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 458 * and rcu_assign_pointer(). Some of these could be folded into their 459 * callers, but they are left separate in order to ease introduction of 460 * multiple flavors of pointers to match the multiple flavors of RCU 461 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in 462 * the future. 463 */ 464 465#ifdef __CHECKER__ 466#define rcu_dereference_sparse(p, space) \ 467 ((void)(((typeof(*p) space *)p) == p)) 468#else /* #ifdef __CHECKER__ */ 469#define rcu_dereference_sparse(p, space) 470#endif /* #else #ifdef __CHECKER__ */ 471 472#define __rcu_access_pointer(p, space) \ 473 ({ \ 474 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 475 rcu_dereference_sparse(p, space); \ 476 ((typeof(*p) __force __kernel *)(_________p1)); \ 477 }) 478#define __rcu_dereference_check(p, c, space) \ 479 ({ \ 480 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 481 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ 482 " usage"); \ 483 rcu_dereference_sparse(p, space); \ 484 smp_read_barrier_depends(); \ 485 ((typeof(*p) __force __kernel *)(_________p1)); \ 486 }) 487#define __rcu_dereference_protected(p, c, space) \ 488 ({ \ 489 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ 490 " usage"); \ 491 rcu_dereference_sparse(p, space); \ 492 ((typeof(*p) __force __kernel *)(p)); \ 493 }) 494 495#define __rcu_access_index(p, space) \ 496 ({ \ 497 typeof(p) _________p1 = ACCESS_ONCE(p); \ 498 rcu_dereference_sparse(p, space); \ 499 (_________p1); \ 500 }) 501#define __rcu_dereference_index_check(p, c) \ 502 ({ \ 503 typeof(p) _________p1 = ACCESS_ONCE(p); \ 504 rcu_lockdep_assert(c, \ 505 "suspicious rcu_dereference_index_check()" \ 506 " usage"); \ 507 smp_read_barrier_depends(); \ 508 (_________p1); \ 509 }) 510#define __rcu_assign_pointer(p, v, space) \ 511 do { \ 512 smp_wmb(); \ 513 (p) = (typeof(*v) __force space *)(v); \ 514 } while (0) 515 516 517/** 518 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 519 * @p: The pointer to read 520 * 521 * Return the value of the specified RCU-protected pointer, but omit the 522 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 523 * when the value of this pointer is accessed, but the pointer is not 524 * dereferenced, for example, when testing an RCU-protected pointer against 525 * NULL. Although rcu_access_pointer() may also be used in cases where 526 * update-side locks prevent the value of the pointer from changing, you 527 * should instead use rcu_dereference_protected() for this use case. 528 * 529 * It is also permissible to use rcu_access_pointer() when read-side 530 * access to the pointer was removed at least one grace period ago, as 531 * is the case in the context of the RCU callback that is freeing up 532 * the data, or after a synchronize_rcu() returns. This can be useful 533 * when tearing down multi-linked structures after a grace period 534 * has elapsed. 535 */ 536#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) 537 538/** 539 * rcu_dereference_check() - rcu_dereference with debug checking 540 * @p: The pointer to read, prior to dereferencing 541 * @c: The conditions under which the dereference will take place 542 * 543 * Do an rcu_dereference(), but check that the conditions under which the 544 * dereference will take place are correct. Typically the conditions 545 * indicate the various locking conditions that should be held at that 546 * point. The check should return true if the conditions are satisfied. 547 * An implicit check for being in an RCU read-side critical section 548 * (rcu_read_lock()) is included. 549 * 550 * For example: 551 * 552 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 553 * 554 * could be used to indicate to lockdep that foo->bar may only be dereferenced 555 * if either rcu_read_lock() is held, or that the lock required to replace 556 * the bar struct at foo->bar is held. 557 * 558 * Note that the list of conditions may also include indications of when a lock 559 * need not be held, for example during initialisation or destruction of the 560 * target struct: 561 * 562 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 563 * atomic_read(&foo->usage) == 0); 564 * 565 * Inserts memory barriers on architectures that require them 566 * (currently only the Alpha), prevents the compiler from refetching 567 * (and from merging fetches), and, more importantly, documents exactly 568 * which pointers are protected by RCU and checks that the pointer is 569 * annotated as __rcu. 570 */ 571#define rcu_dereference_check(p, c) \ 572 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) 573 574/** 575 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 576 * @p: The pointer to read, prior to dereferencing 577 * @c: The conditions under which the dereference will take place 578 * 579 * This is the RCU-bh counterpart to rcu_dereference_check(). 580 */ 581#define rcu_dereference_bh_check(p, c) \ 582 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) 583 584/** 585 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 586 * @p: The pointer to read, prior to dereferencing 587 * @c: The conditions under which the dereference will take place 588 * 589 * This is the RCU-sched counterpart to rcu_dereference_check(). 590 */ 591#define rcu_dereference_sched_check(p, c) \ 592 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ 593 __rcu) 594 595#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ 596 597/** 598 * rcu_access_index() - fetch RCU index with no dereferencing 599 * @p: The index to read 600 * 601 * Return the value of the specified RCU-protected index, but omit the 602 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 603 * when the value of this index is accessed, but the index is not 604 * dereferenced, for example, when testing an RCU-protected index against 605 * -1. Although rcu_access_index() may also be used in cases where 606 * update-side locks prevent the value of the index from changing, you 607 * should instead use rcu_dereference_index_protected() for this use case. 608 */ 609#define rcu_access_index(p) __rcu_access_index((p), __rcu) 610 611/** 612 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking 613 * @p: The pointer to read, prior to dereferencing 614 * @c: The conditions under which the dereference will take place 615 * 616 * Similar to rcu_dereference_check(), but omits the sparse checking. 617 * This allows rcu_dereference_index_check() to be used on integers, 618 * which can then be used as array indices. Attempting to use 619 * rcu_dereference_check() on an integer will give compiler warnings 620 * because the sparse address-space mechanism relies on dereferencing 621 * the RCU-protected pointer. Dereferencing integers is not something 622 * that even gcc will put up with. 623 * 624 * Note that this function does not implicitly check for RCU read-side 625 * critical sections. If this function gains lots of uses, it might 626 * make sense to provide versions for each flavor of RCU, but it does 627 * not make sense as of early 2010. 628 */ 629#define rcu_dereference_index_check(p, c) \ 630 __rcu_dereference_index_check((p), (c)) 631 632/** 633 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 634 * @p: The pointer to read, prior to dereferencing 635 * @c: The conditions under which the dereference will take place 636 * 637 * Return the value of the specified RCU-protected pointer, but omit 638 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This 639 * is useful in cases where update-side locks prevent the value of the 640 * pointer from changing. Please note that this primitive does -not- 641 * prevent the compiler from repeating this reference or combining it 642 * with other references, so it should not be used without protection 643 * of appropriate locks. 644 * 645 * This function is only for update-side use. Using this function 646 * when protected only by rcu_read_lock() will result in infrequent 647 * but very ugly failures. 648 */ 649#define rcu_dereference_protected(p, c) \ 650 __rcu_dereference_protected((p), (c), __rcu) 651 652 653/** 654 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 655 * @p: The pointer to read, prior to dereferencing 656 * 657 * This is a simple wrapper around rcu_dereference_check(). 658 */ 659#define rcu_dereference(p) rcu_dereference_check(p, 0) 660 661/** 662 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 663 * @p: The pointer to read, prior to dereferencing 664 * 665 * Makes rcu_dereference_check() do the dirty work. 666 */ 667#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 668 669/** 670 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 671 * @p: The pointer to read, prior to dereferencing 672 * 673 * Makes rcu_dereference_check() do the dirty work. 674 */ 675#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 676 677/** 678 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 679 * 680 * When synchronize_rcu() is invoked on one CPU while other CPUs 681 * are within RCU read-side critical sections, then the 682 * synchronize_rcu() is guaranteed to block until after all the other 683 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 684 * on one CPU while other CPUs are within RCU read-side critical 685 * sections, invocation of the corresponding RCU callback is deferred 686 * until after the all the other CPUs exit their critical sections. 687 * 688 * Note, however, that RCU callbacks are permitted to run concurrently 689 * with new RCU read-side critical sections. One way that this can happen 690 * is via the following sequence of events: (1) CPU 0 enters an RCU 691 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 692 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 693 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 694 * callback is invoked. This is legal, because the RCU read-side critical 695 * section that was running concurrently with the call_rcu() (and which 696 * therefore might be referencing something that the corresponding RCU 697 * callback would free up) has completed before the corresponding 698 * RCU callback is invoked. 699 * 700 * RCU read-side critical sections may be nested. Any deferred actions 701 * will be deferred until the outermost RCU read-side critical section 702 * completes. 703 * 704 * You can avoid reading and understanding the next paragraph by 705 * following this rule: don't put anything in an rcu_read_lock() RCU 706 * read-side critical section that would block in a !PREEMPT kernel. 707 * But if you want the full story, read on! 708 * 709 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it 710 * is illegal to block while in an RCU read-side critical section. In 711 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) 712 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may 713 * be preempted, but explicit blocking is illegal. Finally, in preemptible 714 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, 715 * RCU read-side critical sections may be preempted and they may also 716 * block, but only when acquiring spinlocks that are subject to priority 717 * inheritance. 718 */ 719static inline void rcu_read_lock(void) 720{ 721 __rcu_read_lock(); 722 __acquire(RCU); 723 rcu_lock_acquire(&rcu_lock_map); 724 rcu_lockdep_assert(!rcu_is_cpu_idle(), 725 "rcu_read_lock() used illegally while idle"); 726} 727 728/* 729 * So where is rcu_write_lock()? It does not exist, as there is no 730 * way for writers to lock out RCU readers. This is a feature, not 731 * a bug -- this property is what provides RCU's performance benefits. 732 * Of course, writers must coordinate with each other. The normal 733 * spinlock primitives work well for this, but any other technique may be 734 * used as well. RCU does not care how the writers keep out of each 735 * others' way, as long as they do so. 736 */ 737 738/** 739 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 740 * 741 * See rcu_read_lock() for more information. 742 */ 743static inline void rcu_read_unlock(void) 744{ 745 rcu_lockdep_assert(!rcu_is_cpu_idle(), 746 "rcu_read_unlock() used illegally while idle"); 747 rcu_lock_release(&rcu_lock_map); 748 __release(RCU); 749 __rcu_read_unlock(); 750} 751 752/** 753 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 754 * 755 * This is equivalent of rcu_read_lock(), but to be used when updates 756 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since 757 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a 758 * softirq handler to be a quiescent state, a process in RCU read-side 759 * critical section must be protected by disabling softirqs. Read-side 760 * critical sections in interrupt context can use just rcu_read_lock(), 761 * though this should at least be commented to avoid confusing people 762 * reading the code. 763 * 764 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 765 * must occur in the same context, for example, it is illegal to invoke 766 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 767 * was invoked from some other task. 768 */ 769static inline void rcu_read_lock_bh(void) 770{ 771 local_bh_disable(); 772 __acquire(RCU_BH); 773 rcu_lock_acquire(&rcu_bh_lock_map); 774 rcu_lockdep_assert(!rcu_is_cpu_idle(), 775 "rcu_read_lock_bh() used illegally while idle"); 776} 777 778/* 779 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 780 * 781 * See rcu_read_lock_bh() for more information. 782 */ 783static inline void rcu_read_unlock_bh(void) 784{ 785 rcu_lockdep_assert(!rcu_is_cpu_idle(), 786 "rcu_read_unlock_bh() used illegally while idle"); 787 rcu_lock_release(&rcu_bh_lock_map); 788 __release(RCU_BH); 789 local_bh_enable(); 790} 791 792/** 793 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 794 * 795 * This is equivalent of rcu_read_lock(), but to be used when updates 796 * are being done using call_rcu_sched() or synchronize_rcu_sched(). 797 * Read-side critical sections can also be introduced by anything that 798 * disables preemption, including local_irq_disable() and friends. 799 * 800 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 801 * must occur in the same context, for example, it is illegal to invoke 802 * rcu_read_unlock_sched() from process context if the matching 803 * rcu_read_lock_sched() was invoked from an NMI handler. 804 */ 805static inline void rcu_read_lock_sched(void) 806{ 807 preempt_disable(); 808 __acquire(RCU_SCHED); 809 rcu_lock_acquire(&rcu_sched_lock_map); 810 rcu_lockdep_assert(!rcu_is_cpu_idle(), 811 "rcu_read_lock_sched() used illegally while idle"); 812} 813 814/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 815static inline notrace void rcu_read_lock_sched_notrace(void) 816{ 817 preempt_disable_notrace(); 818 __acquire(RCU_SCHED); 819} 820 821/* 822 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section 823 * 824 * See rcu_read_lock_sched for more information. 825 */ 826static inline void rcu_read_unlock_sched(void) 827{ 828 rcu_lockdep_assert(!rcu_is_cpu_idle(), 829 "rcu_read_unlock_sched() used illegally while idle"); 830 rcu_lock_release(&rcu_sched_lock_map); 831 __release(RCU_SCHED); 832 preempt_enable(); 833} 834 835/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 836static inline notrace void rcu_read_unlock_sched_notrace(void) 837{ 838 __release(RCU_SCHED); 839 preempt_enable_notrace(); 840} 841 842/** 843 * rcu_assign_pointer() - assign to RCU-protected pointer 844 * @p: pointer to assign to 845 * @v: value to assign (publish) 846 * 847 * Assigns the specified value to the specified RCU-protected 848 * pointer, ensuring that any concurrent RCU readers will see 849 * any prior initialization. 850 * 851 * Inserts memory barriers on architectures that require them 852 * (which is most of them), and also prevents the compiler from 853 * reordering the code that initializes the structure after the pointer 854 * assignment. More importantly, this call documents which pointers 855 * will be dereferenced by RCU read-side code. 856 * 857 * In some special cases, you may use RCU_INIT_POINTER() instead 858 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 859 * to the fact that it does not constrain either the CPU or the compiler. 860 * That said, using RCU_INIT_POINTER() when you should have used 861 * rcu_assign_pointer() is a very bad thing that results in 862 * impossible-to-diagnose memory corruption. So please be careful. 863 * See the RCU_INIT_POINTER() comment header for details. 864 */ 865#define rcu_assign_pointer(p, v) \ 866 __rcu_assign_pointer((p), (v), __rcu) 867 868/** 869 * RCU_INIT_POINTER() - initialize an RCU protected pointer 870 * 871 * Initialize an RCU-protected pointer in special cases where readers 872 * do not need ordering constraints on the CPU or the compiler. These 873 * special cases are: 874 * 875 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- 876 * 2. The caller has taken whatever steps are required to prevent 877 * RCU readers from concurrently accessing this pointer -or- 878 * 3. The referenced data structure has already been exposed to 879 * readers either at compile time or via rcu_assign_pointer() -and- 880 * a. You have not made -any- reader-visible changes to 881 * this structure since then -or- 882 * b. It is OK for readers accessing this structure from its 883 * new location to see the old state of the structure. (For 884 * example, the changes were to statistical counters or to 885 * other state where exact synchronization is not required.) 886 * 887 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 888 * result in impossible-to-diagnose memory corruption. As in the structures 889 * will look OK in crash dumps, but any concurrent RCU readers might 890 * see pre-initialized values of the referenced data structure. So 891 * please be very careful how you use RCU_INIT_POINTER()!!! 892 * 893 * If you are creating an RCU-protected linked structure that is accessed 894 * by a single external-to-structure RCU-protected pointer, then you may 895 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 896 * pointers, but you must use rcu_assign_pointer() to initialize the 897 * external-to-structure pointer -after- you have completely initialized 898 * the reader-accessible portions of the linked structure. 899 */ 900#define RCU_INIT_POINTER(p, v) \ 901 do { \ 902 p = (typeof(*v) __force __rcu *)(v); \ 903 } while (0) 904 905/** 906 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 907 * 908 * GCC-style initialization for an RCU-protected pointer in a structure field. 909 */ 910#define RCU_POINTER_INITIALIZER(p, v) \ 911 .p = (typeof(*v) __force __rcu *)(v) 912 913/* 914 * Does the specified offset indicate that the corresponding rcu_head 915 * structure can be handled by kfree_rcu()? 916 */ 917#define __is_kfree_rcu_offset(offset) ((offset) < 4096) 918 919/* 920 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. 921 */ 922#define __kfree_rcu(head, offset) \ 923 do { \ 924 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ 925 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ 926 } while (0) 927 928/** 929 * kfree_rcu() - kfree an object after a grace period. 930 * @ptr: pointer to kfree 931 * @rcu_head: the name of the struct rcu_head within the type of @ptr. 932 * 933 * Many rcu callbacks functions just call kfree() on the base structure. 934 * These functions are trivial, but their size adds up, and furthermore 935 * when they are used in a kernel module, that module must invoke the 936 * high-latency rcu_barrier() function at module-unload time. 937 * 938 * The kfree_rcu() function handles this issue. Rather than encoding a 939 * function address in the embedded rcu_head structure, kfree_rcu() instead 940 * encodes the offset of the rcu_head structure within the base structure. 941 * Because the functions are not allowed in the low-order 4096 bytes of 942 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 943 * If the offset is larger than 4095 bytes, a compile-time error will 944 * be generated in __kfree_rcu(). If this error is triggered, you can 945 * either fall back to use of call_rcu() or rearrange the structure to 946 * position the rcu_head structure into the first 4096 bytes. 947 * 948 * Note that the allowable offset might decrease in the future, for example, 949 * to allow something like kmem_cache_free_rcu(). 950 * 951 * The BUILD_BUG_ON check must not involve any function calls, hence the 952 * checks are done in macros here. 953 */ 954#define kfree_rcu(ptr, rcu_head) \ 955 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) 956 957#endif /* __LINUX_RCUPDATE_H */ 958