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/cache.h> 37#include <linux/spinlock.h> 38#include <linux/threads.h> 39#include <linux/cpumask.h> 40#include <linux/seqlock.h> 41#include <linux/lockdep.h> 42#include <linux/completion.h> 43#include <linux/debugobjects.h> 44#include <linux/compiler.h> 45 46#ifdef CONFIG_RCU_TORTURE_TEST 47extern int rcutorture_runnable; /* for sysctl */ 48#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ 49 50#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) 51#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) 52#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 53#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 54 55/** 56 * struct rcu_head - callback structure for use with RCU 57 * @next: next update requests in a list 58 * @func: actual update function to call after the grace period. 59 */ 60struct rcu_head { 61 struct rcu_head *next; 62 void (*func)(struct rcu_head *head); 63}; 64 65/* Exported common interfaces */ 66extern void call_rcu_sched(struct rcu_head *head, 67 void (*func)(struct rcu_head *rcu)); 68extern void synchronize_sched(void); 69extern void rcu_barrier_bh(void); 70extern void rcu_barrier_sched(void); 71extern int sched_expedited_torture_stats(char *page); 72 73static inline void __rcu_read_lock_bh(void) 74{ 75 local_bh_disable(); 76} 77 78static inline void __rcu_read_unlock_bh(void) 79{ 80 local_bh_enable(); 81} 82 83#ifdef CONFIG_PREEMPT_RCU 84 85extern void __rcu_read_lock(void); 86extern void __rcu_read_unlock(void); 87void synchronize_rcu(void); 88 89/* 90 * Defined as a macro as it is a very low level header included from 91 * areas that don't even know about current. This gives the rcu_read_lock() 92 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 93 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 94 */ 95#define rcu_preempt_depth() (current->rcu_read_lock_nesting) 96 97#else /* #ifdef CONFIG_PREEMPT_RCU */ 98 99static inline void __rcu_read_lock(void) 100{ 101 preempt_disable(); 102} 103 104static inline void __rcu_read_unlock(void) 105{ 106 preempt_enable(); 107} 108 109static inline void synchronize_rcu(void) 110{ 111 synchronize_sched(); 112} 113 114static inline int rcu_preempt_depth(void) 115{ 116 return 0; 117} 118 119#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 120 121/* Internal to kernel */ 122extern void rcu_sched_qs(int cpu); 123extern void rcu_bh_qs(int cpu); 124extern void rcu_check_callbacks(int cpu, int user); 125struct notifier_block; 126 127#ifdef CONFIG_NO_HZ 128 129extern void rcu_enter_nohz(void); 130extern void rcu_exit_nohz(void); 131 132#else /* #ifdef CONFIG_NO_HZ */ 133 134static inline void rcu_enter_nohz(void) 135{ 136} 137 138static inline void rcu_exit_nohz(void) 139{ 140} 141 142#endif /* #else #ifdef CONFIG_NO_HZ */ 143 144#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 145#include <linux/rcutree.h> 146#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) 147#include <linux/rcutiny.h> 148#else 149#error "Unknown RCU implementation specified to kernel configuration" 150#endif 151 152/* 153 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic 154 * initialization and destruction of rcu_head on the stack. rcu_head structures 155 * allocated dynamically in the heap or defined statically don't need any 156 * initialization. 157 */ 158#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 159extern void init_rcu_head_on_stack(struct rcu_head *head); 160extern void destroy_rcu_head_on_stack(struct rcu_head *head); 161#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 162static inline void init_rcu_head_on_stack(struct rcu_head *head) 163{ 164} 165 166static inline void destroy_rcu_head_on_stack(struct rcu_head *head) 167{ 168} 169#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 170 171#ifdef CONFIG_DEBUG_LOCK_ALLOC 172 173extern struct lockdep_map rcu_lock_map; 174# define rcu_read_acquire() \ 175 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 176# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) 177 178extern struct lockdep_map rcu_bh_lock_map; 179# define rcu_read_acquire_bh() \ 180 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 181# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) 182 183extern struct lockdep_map rcu_sched_lock_map; 184# define rcu_read_acquire_sched() \ 185 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 186# define rcu_read_release_sched() \ 187 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) 188 189extern int debug_lockdep_rcu_enabled(void); 190 191/** 192 * rcu_read_lock_held() - might we be in RCU read-side critical section? 193 * 194 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU 195 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 196 * this assumes we are in an RCU read-side critical section unless it can 197 * prove otherwise. This is useful for debug checks in functions that 198 * require that they be called within an RCU read-side critical section. 199 * 200 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 201 * and while lockdep is disabled. 202 */ 203static inline int rcu_read_lock_held(void) 204{ 205 if (!debug_lockdep_rcu_enabled()) 206 return 1; 207 return lock_is_held(&rcu_lock_map); 208} 209 210/* 211 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file 212 * hell. 213 */ 214extern int rcu_read_lock_bh_held(void); 215 216/** 217 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? 218 * 219 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an 220 * RCU-sched read-side critical section. In absence of 221 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side 222 * critical section unless it can prove otherwise. Note that disabling 223 * of preemption (including disabling irqs) counts as an RCU-sched 224 * read-side critical section. This is useful for debug checks in functions 225 * that required that they be called within an RCU-sched read-side 226 * critical section. 227 * 228 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot 229 * and while lockdep is disabled. 230 */ 231#ifdef CONFIG_PREEMPT 232static inline int rcu_read_lock_sched_held(void) 233{ 234 int lockdep_opinion = 0; 235 236 if (!debug_lockdep_rcu_enabled()) 237 return 1; 238 if (debug_locks) 239 lockdep_opinion = lock_is_held(&rcu_sched_lock_map); 240 return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); 241} 242#else /* #ifdef CONFIG_PREEMPT */ 243static inline int rcu_read_lock_sched_held(void) 244{ 245 return 1; 246} 247#endif /* #else #ifdef CONFIG_PREEMPT */ 248 249#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 250 251# define rcu_read_acquire() do { } while (0) 252# define rcu_read_release() do { } while (0) 253# define rcu_read_acquire_bh() do { } while (0) 254# define rcu_read_release_bh() do { } while (0) 255# define rcu_read_acquire_sched() do { } while (0) 256# define rcu_read_release_sched() do { } while (0) 257 258static inline int rcu_read_lock_held(void) 259{ 260 return 1; 261} 262 263static inline int rcu_read_lock_bh_held(void) 264{ 265 return 1; 266} 267 268#ifdef CONFIG_PREEMPT 269static inline int rcu_read_lock_sched_held(void) 270{ 271 return preempt_count() != 0 || irqs_disabled(); 272} 273#else /* #ifdef CONFIG_PREEMPT */ 274static inline int rcu_read_lock_sched_held(void) 275{ 276 return 1; 277} 278#endif /* #else #ifdef CONFIG_PREEMPT */ 279 280#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 281 282#ifdef CONFIG_PROVE_RCU 283 284extern int rcu_my_thread_group_empty(void); 285 286/** 287 * rcu_lockdep_assert - emit lockdep splat if specified condition not met 288 * @c: condition to check 289 */ 290#define rcu_lockdep_assert(c) \ 291 do { \ 292 static bool __warned; \ 293 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ 294 __warned = true; \ 295 lockdep_rcu_dereference(__FILE__, __LINE__); \ 296 } \ 297 } while (0) 298 299#else /* #ifdef CONFIG_PROVE_RCU */ 300 301#define rcu_lockdep_assert(c) do { } while (0) 302 303#endif /* #else #ifdef CONFIG_PROVE_RCU */ 304 305/* 306 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 307 * and rcu_assign_pointer(). Some of these could be folded into their 308 * callers, but they are left separate in order to ease introduction of 309 * multiple flavors of pointers to match the multiple flavors of RCU 310 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in 311 * the future. 312 */ 313 314#ifdef __CHECKER__ 315#define rcu_dereference_sparse(p, space) \ 316 ((void)(((typeof(*p) space *)p) == p)) 317#else /* #ifdef __CHECKER__ */ 318#define rcu_dereference_sparse(p, space) 319#endif /* #else #ifdef __CHECKER__ */ 320 321#define __rcu_access_pointer(p, space) \ 322 ({ \ 323 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 324 rcu_dereference_sparse(p, space); \ 325 ((typeof(*p) __force __kernel *)(_________p1)); \ 326 }) 327#define __rcu_dereference_check(p, c, space) \ 328 ({ \ 329 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 330 rcu_lockdep_assert(c); \ 331 rcu_dereference_sparse(p, space); \ 332 smp_read_barrier_depends(); \ 333 ((typeof(*p) __force __kernel *)(_________p1)); \ 334 }) 335#define __rcu_dereference_protected(p, c, space) \ 336 ({ \ 337 rcu_lockdep_assert(c); \ 338 rcu_dereference_sparse(p, space); \ 339 ((typeof(*p) __force __kernel *)(p)); \ 340 }) 341 342#define __rcu_dereference_index_check(p, c) \ 343 ({ \ 344 typeof(p) _________p1 = ACCESS_ONCE(p); \ 345 rcu_lockdep_assert(c); \ 346 smp_read_barrier_depends(); \ 347 (_________p1); \ 348 }) 349#define __rcu_assign_pointer(p, v, space) \ 350 ({ \ 351 if (!__builtin_constant_p(v) || \ 352 ((v) != NULL)) \ 353 smp_wmb(); \ 354 (p) = (typeof(*v) __force space *)(v); \ 355 }) 356 357 358/** 359 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 360 * @p: The pointer to read 361 * 362 * Return the value of the specified RCU-protected pointer, but omit the 363 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 364 * when the value of this pointer is accessed, but the pointer is not 365 * dereferenced, for example, when testing an RCU-protected pointer against 366 * NULL. Although rcu_access_pointer() may also be used in cases where 367 * update-side locks prevent the value of the pointer from changing, you 368 * should instead use rcu_dereference_protected() for this use case. 369 */ 370#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) 371 372/** 373 * rcu_dereference_check() - rcu_dereference with debug checking 374 * @p: The pointer to read, prior to dereferencing 375 * @c: The conditions under which the dereference will take place 376 * 377 * Do an rcu_dereference(), but check that the conditions under which the 378 * dereference will take place are correct. Typically the conditions 379 * indicate the various locking conditions that should be held at that 380 * point. The check should return true if the conditions are satisfied. 381 * An implicit check for being in an RCU read-side critical section 382 * (rcu_read_lock()) is included. 383 * 384 * For example: 385 * 386 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 387 * 388 * could be used to indicate to lockdep that foo->bar may only be dereferenced 389 * if either rcu_read_lock() is held, or that the lock required to replace 390 * the bar struct at foo->bar is held. 391 * 392 * Note that the list of conditions may also include indications of when a lock 393 * need not be held, for example during initialisation or destruction of the 394 * target struct: 395 * 396 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 397 * atomic_read(&foo->usage) == 0); 398 * 399 * Inserts memory barriers on architectures that require them 400 * (currently only the Alpha), prevents the compiler from refetching 401 * (and from merging fetches), and, more importantly, documents exactly 402 * which pointers are protected by RCU and checks that the pointer is 403 * annotated as __rcu. 404 */ 405#define rcu_dereference_check(p, c) \ 406 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) 407 408/** 409 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 410 * @p: The pointer to read, prior to dereferencing 411 * @c: The conditions under which the dereference will take place 412 * 413 * This is the RCU-bh counterpart to rcu_dereference_check(). 414 */ 415#define rcu_dereference_bh_check(p, c) \ 416 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) 417 418/** 419 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 420 * @p: The pointer to read, prior to dereferencing 421 * @c: The conditions under which the dereference will take place 422 * 423 * This is the RCU-sched counterpart to rcu_dereference_check(). 424 */ 425#define rcu_dereference_sched_check(p, c) \ 426 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ 427 __rcu) 428 429#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ 430 431/** 432 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking 433 * @p: The pointer to read, prior to dereferencing 434 * @c: The conditions under which the dereference will take place 435 * 436 * Similar to rcu_dereference_check(), but omits the sparse checking. 437 * This allows rcu_dereference_index_check() to be used on integers, 438 * which can then be used as array indices. Attempting to use 439 * rcu_dereference_check() on an integer will give compiler warnings 440 * because the sparse address-space mechanism relies on dereferencing 441 * the RCU-protected pointer. Dereferencing integers is not something 442 * that even gcc will put up with. 443 * 444 * Note that this function does not implicitly check for RCU read-side 445 * critical sections. If this function gains lots of uses, it might 446 * make sense to provide versions for each flavor of RCU, but it does 447 * not make sense as of early 2010. 448 */ 449#define rcu_dereference_index_check(p, c) \ 450 __rcu_dereference_index_check((p), (c)) 451 452/** 453 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 454 * @p: The pointer to read, prior to dereferencing 455 * @c: The conditions under which the dereference will take place 456 * 457 * Return the value of the specified RCU-protected pointer, but omit 458 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This 459 * is useful in cases where update-side locks prevent the value of the 460 * pointer from changing. Please note that this primitive does -not- 461 * prevent the compiler from repeating this reference or combining it 462 * with other references, so it should not be used without protection 463 * of appropriate locks. 464 * 465 * This function is only for update-side use. Using this function 466 * when protected only by rcu_read_lock() will result in infrequent 467 * but very ugly failures. 468 */ 469#define rcu_dereference_protected(p, c) \ 470 __rcu_dereference_protected((p), (c), __rcu) 471 472/** 473 * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented 474 * @p: The pointer to read, prior to dereferencing 475 * @c: The conditions under which the dereference will take place 476 * 477 * This is the RCU-bh counterpart to rcu_dereference_protected(). 478 */ 479#define rcu_dereference_bh_protected(p, c) \ 480 __rcu_dereference_protected((p), (c), __rcu) 481 482/** 483 * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented 484 * @p: The pointer to read, prior to dereferencing 485 * @c: The conditions under which the dereference will take place 486 * 487 * This is the RCU-sched counterpart to rcu_dereference_protected(). 488 */ 489#define rcu_dereference_sched_protected(p, c) \ 490 __rcu_dereference_protected((p), (c), __rcu) 491 492 493/** 494 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 495 * @p: The pointer to read, prior to dereferencing 496 * 497 * This is a simple wrapper around rcu_dereference_check(). 498 */ 499#define rcu_dereference(p) rcu_dereference_check(p, 0) 500 501/** 502 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 503 * @p: The pointer to read, prior to dereferencing 504 * 505 * Makes rcu_dereference_check() do the dirty work. 506 */ 507#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 508 509/** 510 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 511 * @p: The pointer to read, prior to dereferencing 512 * 513 * Makes rcu_dereference_check() do the dirty work. 514 */ 515#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 516 517/** 518 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 519 * 520 * When synchronize_rcu() is invoked on one CPU while other CPUs 521 * are within RCU read-side critical sections, then the 522 * synchronize_rcu() is guaranteed to block until after all the other 523 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 524 * on one CPU while other CPUs are within RCU read-side critical 525 * sections, invocation of the corresponding RCU callback is deferred 526 * until after the all the other CPUs exit their critical sections. 527 * 528 * Note, however, that RCU callbacks are permitted to run concurrently 529 * with new RCU read-side critical sections. One way that this can happen 530 * is via the following sequence of events: (1) CPU 0 enters an RCU 531 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 532 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 533 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 534 * callback is invoked. This is legal, because the RCU read-side critical 535 * section that was running concurrently with the call_rcu() (and which 536 * therefore might be referencing something that the corresponding RCU 537 * callback would free up) has completed before the corresponding 538 * RCU callback is invoked. 539 * 540 * RCU read-side critical sections may be nested. Any deferred actions 541 * will be deferred until the outermost RCU read-side critical section 542 * completes. 543 * 544 * You can avoid reading and understanding the next paragraph by 545 * following this rule: don't put anything in an rcu_read_lock() RCU 546 * read-side critical section that would block in a !PREEMPT kernel. 547 * But if you want the full story, read on! 548 * 549 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it 550 * is illegal to block while in an RCU read-side critical section. In 551 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) 552 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may 553 * be preempted, but explicit blocking is illegal. Finally, in preemptible 554 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, 555 * RCU read-side critical sections may be preempted and they may also 556 * block, but only when acquiring spinlocks that are subject to priority 557 * inheritance. 558 */ 559static inline void rcu_read_lock(void) 560{ 561 __rcu_read_lock(); 562 __acquire(RCU); 563 rcu_read_acquire(); 564} 565 566/* 567 * So where is rcu_write_lock()? It does not exist, as there is no 568 * way for writers to lock out RCU readers. This is a feature, not 569 * a bug -- this property is what provides RCU's performance benefits. 570 * Of course, writers must coordinate with each other. The normal 571 * spinlock primitives work well for this, but any other technique may be 572 * used as well. RCU does not care how the writers keep out of each 573 * others' way, as long as they do so. 574 */ 575 576/** 577 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 578 * 579 * See rcu_read_lock() for more information. 580 */ 581static inline void rcu_read_unlock(void) 582{ 583 rcu_read_release(); 584 __release(RCU); 585 __rcu_read_unlock(); 586} 587 588/** 589 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 590 * 591 * This is equivalent of rcu_read_lock(), but to be used when updates 592 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since 593 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a 594 * softirq handler to be a quiescent state, a process in RCU read-side 595 * critical section must be protected by disabling softirqs. Read-side 596 * critical sections in interrupt context can use just rcu_read_lock(), 597 * though this should at least be commented to avoid confusing people 598 * reading the code. 599 */ 600static inline void rcu_read_lock_bh(void) 601{ 602 __rcu_read_lock_bh(); 603 __acquire(RCU_BH); 604 rcu_read_acquire_bh(); 605} 606 607/* 608 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 609 * 610 * See rcu_read_lock_bh() for more information. 611 */ 612static inline void rcu_read_unlock_bh(void) 613{ 614 rcu_read_release_bh(); 615 __release(RCU_BH); 616 __rcu_read_unlock_bh(); 617} 618 619/** 620 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 621 * 622 * This is equivalent of rcu_read_lock(), but to be used when updates 623 * are being done using call_rcu_sched() or synchronize_rcu_sched(). 624 * Read-side critical sections can also be introduced by anything that 625 * disables preemption, including local_irq_disable() and friends. 626 */ 627static inline void rcu_read_lock_sched(void) 628{ 629 preempt_disable(); 630 __acquire(RCU_SCHED); 631 rcu_read_acquire_sched(); 632} 633 634/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 635static inline notrace void rcu_read_lock_sched_notrace(void) 636{ 637 preempt_disable_notrace(); 638 __acquire(RCU_SCHED); 639} 640 641/* 642 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section 643 * 644 * See rcu_read_lock_sched for more information. 645 */ 646static inline void rcu_read_unlock_sched(void) 647{ 648 rcu_read_release_sched(); 649 __release(RCU_SCHED); 650 preempt_enable(); 651} 652 653/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 654static inline notrace void rcu_read_unlock_sched_notrace(void) 655{ 656 __release(RCU_SCHED); 657 preempt_enable_notrace(); 658} 659 660/** 661 * rcu_assign_pointer() - assign to RCU-protected pointer 662 * @p: pointer to assign to 663 * @v: value to assign (publish) 664 * 665 * Assigns the specified value to the specified RCU-protected 666 * pointer, ensuring that any concurrent RCU readers will see 667 * any prior initialization. Returns the value assigned. 668 * 669 * Inserts memory barriers on architectures that require them 670 * (pretty much all of them other than x86), and also prevents 671 * the compiler from reordering the code that initializes the 672 * structure after the pointer assignment. More importantly, this 673 * call documents which pointers will be dereferenced by RCU read-side 674 * code. 675 */ 676#define rcu_assign_pointer(p, v) \ 677 __rcu_assign_pointer((p), (v), __rcu) 678 679/** 680 * RCU_INIT_POINTER() - initialize an RCU protected pointer 681 * 682 * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep 683 * splats. 684 */ 685#define RCU_INIT_POINTER(p, v) \ 686 p = (typeof(*v) __force __rcu *)(v) 687 688/* Infrastructure to implement the synchronize_() primitives. */ 689 690struct rcu_synchronize { 691 struct rcu_head head; 692 struct completion completion; 693}; 694 695extern void wakeme_after_rcu(struct rcu_head *head); 696 697#ifdef CONFIG_PREEMPT_RCU 698 699/** 700 * call_rcu() - Queue an RCU callback for invocation after a grace period. 701 * @head: structure to be used for queueing the RCU updates. 702 * @func: actual callback function to be invoked after the grace period 703 * 704 * The callback function will be invoked some time after a full grace 705 * period elapses, in other words after all pre-existing RCU read-side 706 * critical sections have completed. However, the callback function 707 * might well execute concurrently with RCU read-side critical sections 708 * that started after call_rcu() was invoked. RCU read-side critical 709 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), 710 * and may be nested. 711 */ 712extern void call_rcu(struct rcu_head *head, 713 void (*func)(struct rcu_head *head)); 714 715#else /* #ifdef CONFIG_PREEMPT_RCU */ 716 717/* In classic RCU, call_rcu() is just call_rcu_sched(). */ 718#define call_rcu call_rcu_sched 719 720#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 721 722/** 723 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. 724 * @head: structure to be used for queueing the RCU updates. 725 * @func: actual callback function to be invoked after the grace period 726 * 727 * The callback function will be invoked some time after a full grace 728 * period elapses, in other words after all currently executing RCU 729 * read-side critical sections have completed. call_rcu_bh() assumes 730 * that the read-side critical sections end on completion of a softirq 731 * handler. This means that read-side critical sections in process 732 * context must not be interrupted by softirqs. This interface is to be 733 * used when most of the read-side critical sections are in softirq context. 734 * RCU read-side critical sections are delimited by : 735 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. 736 * OR 737 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. 738 * These may be nested. 739 */ 740extern void call_rcu_bh(struct rcu_head *head, 741 void (*func)(struct rcu_head *head)); 742 743/* 744 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally 745 * by call_rcu() and rcu callback execution, and are therefore not part of the 746 * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors. 747 */ 748 749#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 750# define STATE_RCU_HEAD_READY 0 751# define STATE_RCU_HEAD_QUEUED 1 752 753extern struct debug_obj_descr rcuhead_debug_descr; 754 755static inline void debug_rcu_head_queue(struct rcu_head *head) 756{ 757 debug_object_activate(head, &rcuhead_debug_descr); 758 debug_object_active_state(head, &rcuhead_debug_descr, 759 STATE_RCU_HEAD_READY, 760 STATE_RCU_HEAD_QUEUED); 761} 762 763static inline void debug_rcu_head_unqueue(struct rcu_head *head) 764{ 765 debug_object_active_state(head, &rcuhead_debug_descr, 766 STATE_RCU_HEAD_QUEUED, 767 STATE_RCU_HEAD_READY); 768 debug_object_deactivate(head, &rcuhead_debug_descr); 769} 770#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 771static inline void debug_rcu_head_queue(struct rcu_head *head) 772{ 773} 774 775static inline void debug_rcu_head_unqueue(struct rcu_head *head) 776{ 777} 778#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 779 780#endif /* __LINUX_RCUPDATE_H */ 781