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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 51extern void rcutorture_record_test_transition(void); 52extern void rcutorture_record_progress(unsigned long vernum); 53#else 54static inline void rcutorture_record_test_transition(void) 55{ 56} 57static inline void rcutorture_record_progress(unsigned long vernum) 58{ 59} 60#endif 61 62#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) 63#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) 64#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 65#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 66 67/** 68 * struct rcu_head - callback structure for use with RCU 69 * @next: next update requests in a list 70 * @func: actual update function to call after the grace period. 71 */ 72struct rcu_head { 73 struct rcu_head *next; 74 void (*func)(struct rcu_head *head); 75}; 76 77/* Exported common interfaces */ 78extern void call_rcu_sched(struct rcu_head *head, 79 void (*func)(struct rcu_head *rcu)); 80extern void synchronize_sched(void); 81extern void rcu_barrier_bh(void); 82extern void rcu_barrier_sched(void); 83 84static inline void __rcu_read_lock_bh(void) 85{ 86 local_bh_disable(); 87} 88 89static inline void __rcu_read_unlock_bh(void) 90{ 91 local_bh_enable(); 92} 93 94#ifdef CONFIG_PREEMPT_RCU 95 96extern void __rcu_read_lock(void); 97extern void __rcu_read_unlock(void); 98void synchronize_rcu(void); 99 100/* 101 * Defined as a macro as it is a very low level header included from 102 * areas that don't even know about current. This gives the rcu_read_lock() 103 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 104 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 105 */ 106#define rcu_preempt_depth() (current->rcu_read_lock_nesting) 107 108#else /* #ifdef CONFIG_PREEMPT_RCU */ 109 110static inline void __rcu_read_lock(void) 111{ 112 preempt_disable(); 113} 114 115static inline void __rcu_read_unlock(void) 116{ 117 preempt_enable(); 118} 119 120static inline void synchronize_rcu(void) 121{ 122 synchronize_sched(); 123} 124 125static inline int rcu_preempt_depth(void) 126{ 127 return 0; 128} 129 130#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 131 132/* Internal to kernel */ 133extern void rcu_sched_qs(int cpu); 134extern void rcu_bh_qs(int cpu); 135extern void rcu_check_callbacks(int cpu, int user); 136struct notifier_block; 137 138#ifdef CONFIG_NO_HZ 139 140extern void rcu_enter_nohz(void); 141extern void rcu_exit_nohz(void); 142 143#else /* #ifdef CONFIG_NO_HZ */ 144 145static inline void rcu_enter_nohz(void) 146{ 147} 148 149static inline void rcu_exit_nohz(void) 150{ 151} 152 153#endif /* #else #ifdef CONFIG_NO_HZ */ 154 155#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 156#include <linux/rcutree.h> 157#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) 158#include <linux/rcutiny.h> 159#else 160#error "Unknown RCU implementation specified to kernel configuration" 161#endif 162 163/* 164 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic 165 * initialization and destruction of rcu_head on the stack. rcu_head structures 166 * allocated dynamically in the heap or defined statically don't need any 167 * initialization. 168 */ 169#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 170extern void init_rcu_head_on_stack(struct rcu_head *head); 171extern void destroy_rcu_head_on_stack(struct rcu_head *head); 172#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 173static inline void init_rcu_head_on_stack(struct rcu_head *head) 174{ 175} 176 177static inline void destroy_rcu_head_on_stack(struct rcu_head *head) 178{ 179} 180#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 181 182#ifdef CONFIG_DEBUG_LOCK_ALLOC 183 184extern struct lockdep_map rcu_lock_map; 185# define rcu_read_acquire() \ 186 lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 187# define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) 188 189extern struct lockdep_map rcu_bh_lock_map; 190# define rcu_read_acquire_bh() \ 191 lock_acquire(&rcu_bh_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 192# define rcu_read_release_bh() lock_release(&rcu_bh_lock_map, 1, _THIS_IP_) 193 194extern struct lockdep_map rcu_sched_lock_map; 195# define rcu_read_acquire_sched() \ 196 lock_acquire(&rcu_sched_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) 197# define rcu_read_release_sched() \ 198 lock_release(&rcu_sched_lock_map, 1, _THIS_IP_) 199 200extern int debug_lockdep_rcu_enabled(void); 201 202/** 203 * rcu_read_lock_held() - might we be in RCU read-side critical section? 204 * 205 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU 206 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 207 * this assumes we are in an RCU read-side critical section unless it can 208 * prove otherwise. This is useful for debug checks in functions that 209 * require that they be called within an RCU read-side critical section. 210 * 211 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 212 * and while lockdep is disabled. 213 */ 214static inline int rcu_read_lock_held(void) 215{ 216 if (!debug_lockdep_rcu_enabled()) 217 return 1; 218 return lock_is_held(&rcu_lock_map); 219} 220 221/* 222 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file 223 * hell. 224 */ 225extern int rcu_read_lock_bh_held(void); 226 227/** 228 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? 229 * 230 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an 231 * RCU-sched read-side critical section. In absence of 232 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side 233 * critical section unless it can prove otherwise. Note that disabling 234 * of preemption (including disabling irqs) counts as an RCU-sched 235 * read-side critical section. This is useful for debug checks in functions 236 * that required that they be called within an RCU-sched read-side 237 * critical section. 238 * 239 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot 240 * and while lockdep is disabled. 241 */ 242#ifdef CONFIG_PREEMPT 243static inline int rcu_read_lock_sched_held(void) 244{ 245 int lockdep_opinion = 0; 246 247 if (!debug_lockdep_rcu_enabled()) 248 return 1; 249 if (debug_locks) 250 lockdep_opinion = lock_is_held(&rcu_sched_lock_map); 251 return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); 252} 253#else /* #ifdef CONFIG_PREEMPT */ 254static inline int rcu_read_lock_sched_held(void) 255{ 256 return 1; 257} 258#endif /* #else #ifdef CONFIG_PREEMPT */ 259 260#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 261 262# define rcu_read_acquire() do { } while (0) 263# define rcu_read_release() do { } while (0) 264# define rcu_read_acquire_bh() do { } while (0) 265# define rcu_read_release_bh() do { } while (0) 266# define rcu_read_acquire_sched() do { } while (0) 267# define rcu_read_release_sched() do { } while (0) 268 269static inline int rcu_read_lock_held(void) 270{ 271 return 1; 272} 273 274static inline int rcu_read_lock_bh_held(void) 275{ 276 return 1; 277} 278 279#ifdef CONFIG_PREEMPT 280static inline int rcu_read_lock_sched_held(void) 281{ 282 return preempt_count() != 0 || irqs_disabled(); 283} 284#else /* #ifdef CONFIG_PREEMPT */ 285static inline int rcu_read_lock_sched_held(void) 286{ 287 return 1; 288} 289#endif /* #else #ifdef CONFIG_PREEMPT */ 290 291#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 292 293#ifdef CONFIG_PROVE_RCU 294 295extern int rcu_my_thread_group_empty(void); 296 297/** 298 * rcu_lockdep_assert - emit lockdep splat if specified condition not met 299 * @c: condition to check 300 */ 301#define rcu_lockdep_assert(c) \ 302 do { \ 303 static bool __warned; \ 304 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ 305 __warned = true; \ 306 lockdep_rcu_dereference(__FILE__, __LINE__); \ 307 } \ 308 } while (0) 309 310#else /* #ifdef CONFIG_PROVE_RCU */ 311 312#define rcu_lockdep_assert(c) do { } while (0) 313 314#endif /* #else #ifdef CONFIG_PROVE_RCU */ 315 316/* 317 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 318 * and rcu_assign_pointer(). Some of these could be folded into their 319 * callers, but they are left separate in order to ease introduction of 320 * multiple flavors of pointers to match the multiple flavors of RCU 321 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in 322 * the future. 323 */ 324 325#ifdef __CHECKER__ 326#define rcu_dereference_sparse(p, space) \ 327 ((void)(((typeof(*p) space *)p) == p)) 328#else /* #ifdef __CHECKER__ */ 329#define rcu_dereference_sparse(p, space) 330#endif /* #else #ifdef __CHECKER__ */ 331 332#define __rcu_access_pointer(p, space) \ 333 ({ \ 334 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 335 rcu_dereference_sparse(p, space); \ 336 ((typeof(*p) __force __kernel *)(_________p1)); \ 337 }) 338#define __rcu_dereference_check(p, c, space) \ 339 ({ \ 340 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 341 rcu_lockdep_assert(c); \ 342 rcu_dereference_sparse(p, space); \ 343 smp_read_barrier_depends(); \ 344 ((typeof(*p) __force __kernel *)(_________p1)); \ 345 }) 346#define __rcu_dereference_protected(p, c, space) \ 347 ({ \ 348 rcu_lockdep_assert(c); \ 349 rcu_dereference_sparse(p, space); \ 350 ((typeof(*p) __force __kernel *)(p)); \ 351 }) 352 353#define __rcu_access_index(p, space) \ 354 ({ \ 355 typeof(p) _________p1 = ACCESS_ONCE(p); \ 356 rcu_dereference_sparse(p, space); \ 357 (_________p1); \ 358 }) 359#define __rcu_dereference_index_check(p, c) \ 360 ({ \ 361 typeof(p) _________p1 = ACCESS_ONCE(p); \ 362 rcu_lockdep_assert(c); \ 363 smp_read_barrier_depends(); \ 364 (_________p1); \ 365 }) 366#define __rcu_assign_pointer(p, v, space) \ 367 ({ \ 368 if (!__builtin_constant_p(v) || \ 369 ((v) != NULL)) \ 370 smp_wmb(); \ 371 (p) = (typeof(*v) __force space *)(v); \ 372 }) 373 374 375/** 376 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 377 * @p: The pointer to read 378 * 379 * Return the value of the specified RCU-protected pointer, but omit the 380 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 381 * when the value of this pointer is accessed, but the pointer is not 382 * dereferenced, for example, when testing an RCU-protected pointer against 383 * NULL. Although rcu_access_pointer() may also be used in cases where 384 * update-side locks prevent the value of the pointer from changing, you 385 * should instead use rcu_dereference_protected() for this use case. 386 */ 387#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) 388 389/** 390 * rcu_dereference_check() - rcu_dereference with debug checking 391 * @p: The pointer to read, prior to dereferencing 392 * @c: The conditions under which the dereference will take place 393 * 394 * Do an rcu_dereference(), but check that the conditions under which the 395 * dereference will take place are correct. Typically the conditions 396 * indicate the various locking conditions that should be held at that 397 * point. The check should return true if the conditions are satisfied. 398 * An implicit check for being in an RCU read-side critical section 399 * (rcu_read_lock()) is included. 400 * 401 * For example: 402 * 403 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 404 * 405 * could be used to indicate to lockdep that foo->bar may only be dereferenced 406 * if either rcu_read_lock() is held, or that the lock required to replace 407 * the bar struct at foo->bar is held. 408 * 409 * Note that the list of conditions may also include indications of when a lock 410 * need not be held, for example during initialisation or destruction of the 411 * target struct: 412 * 413 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 414 * atomic_read(&foo->usage) == 0); 415 * 416 * Inserts memory barriers on architectures that require them 417 * (currently only the Alpha), prevents the compiler from refetching 418 * (and from merging fetches), and, more importantly, documents exactly 419 * which pointers are protected by RCU and checks that the pointer is 420 * annotated as __rcu. 421 */ 422#define rcu_dereference_check(p, c) \ 423 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) 424 425/** 426 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 427 * @p: The pointer to read, prior to dereferencing 428 * @c: The conditions under which the dereference will take place 429 * 430 * This is the RCU-bh counterpart to rcu_dereference_check(). 431 */ 432#define rcu_dereference_bh_check(p, c) \ 433 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) 434 435/** 436 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 437 * @p: The pointer to read, prior to dereferencing 438 * @c: The conditions under which the dereference will take place 439 * 440 * This is the RCU-sched counterpart to rcu_dereference_check(). 441 */ 442#define rcu_dereference_sched_check(p, c) \ 443 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ 444 __rcu) 445 446#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ 447 448/** 449 * rcu_access_index() - fetch RCU index with no dereferencing 450 * @p: The index to read 451 * 452 * Return the value of the specified RCU-protected index, but omit the 453 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 454 * when the value of this index is accessed, but the index is not 455 * dereferenced, for example, when testing an RCU-protected index against 456 * -1. Although rcu_access_index() may also be used in cases where 457 * update-side locks prevent the value of the index from changing, you 458 * should instead use rcu_dereference_index_protected() for this use case. 459 */ 460#define rcu_access_index(p) __rcu_access_index((p), __rcu) 461 462/** 463 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking 464 * @p: The pointer to read, prior to dereferencing 465 * @c: The conditions under which the dereference will take place 466 * 467 * Similar to rcu_dereference_check(), but omits the sparse checking. 468 * This allows rcu_dereference_index_check() to be used on integers, 469 * which can then be used as array indices. Attempting to use 470 * rcu_dereference_check() on an integer will give compiler warnings 471 * because the sparse address-space mechanism relies on dereferencing 472 * the RCU-protected pointer. Dereferencing integers is not something 473 * that even gcc will put up with. 474 * 475 * Note that this function does not implicitly check for RCU read-side 476 * critical sections. If this function gains lots of uses, it might 477 * make sense to provide versions for each flavor of RCU, but it does 478 * not make sense as of early 2010. 479 */ 480#define rcu_dereference_index_check(p, c) \ 481 __rcu_dereference_index_check((p), (c)) 482 483/** 484 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 485 * @p: The pointer to read, prior to dereferencing 486 * @c: The conditions under which the dereference will take place 487 * 488 * Return the value of the specified RCU-protected pointer, but omit 489 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This 490 * is useful in cases where update-side locks prevent the value of the 491 * pointer from changing. Please note that this primitive does -not- 492 * prevent the compiler from repeating this reference or combining it 493 * with other references, so it should not be used without protection 494 * of appropriate locks. 495 * 496 * This function is only for update-side use. Using this function 497 * when protected only by rcu_read_lock() will result in infrequent 498 * but very ugly failures. 499 */ 500#define rcu_dereference_protected(p, c) \ 501 __rcu_dereference_protected((p), (c), __rcu) 502 503/** 504 * rcu_dereference_bh_protected() - fetch RCU-bh pointer when updates prevented 505 * @p: The pointer to read, prior to dereferencing 506 * @c: The conditions under which the dereference will take place 507 * 508 * This is the RCU-bh counterpart to rcu_dereference_protected(). 509 */ 510#define rcu_dereference_bh_protected(p, c) \ 511 __rcu_dereference_protected((p), (c), __rcu) 512 513/** 514 * rcu_dereference_sched_protected() - fetch RCU-sched pointer when updates prevented 515 * @p: The pointer to read, prior to dereferencing 516 * @c: The conditions under which the dereference will take place 517 * 518 * This is the RCU-sched counterpart to rcu_dereference_protected(). 519 */ 520#define rcu_dereference_sched_protected(p, c) \ 521 __rcu_dereference_protected((p), (c), __rcu) 522 523 524/** 525 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 526 * @p: The pointer to read, prior to dereferencing 527 * 528 * This is a simple wrapper around rcu_dereference_check(). 529 */ 530#define rcu_dereference(p) rcu_dereference_check(p, 0) 531 532/** 533 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 534 * @p: The pointer to read, prior to dereferencing 535 * 536 * Makes rcu_dereference_check() do the dirty work. 537 */ 538#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 539 540/** 541 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 542 * @p: The pointer to read, prior to dereferencing 543 * 544 * Makes rcu_dereference_check() do the dirty work. 545 */ 546#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 547 548/** 549 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 550 * 551 * When synchronize_rcu() is invoked on one CPU while other CPUs 552 * are within RCU read-side critical sections, then the 553 * synchronize_rcu() is guaranteed to block until after all the other 554 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 555 * on one CPU while other CPUs are within RCU read-side critical 556 * sections, invocation of the corresponding RCU callback is deferred 557 * until after the all the other CPUs exit their critical sections. 558 * 559 * Note, however, that RCU callbacks are permitted to run concurrently 560 * with new RCU read-side critical sections. One way that this can happen 561 * is via the following sequence of events: (1) CPU 0 enters an RCU 562 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 563 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 564 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 565 * callback is invoked. This is legal, because the RCU read-side critical 566 * section that was running concurrently with the call_rcu() (and which 567 * therefore might be referencing something that the corresponding RCU 568 * callback would free up) has completed before the corresponding 569 * RCU callback is invoked. 570 * 571 * RCU read-side critical sections may be nested. Any deferred actions 572 * will be deferred until the outermost RCU read-side critical section 573 * completes. 574 * 575 * You can avoid reading and understanding the next paragraph by 576 * following this rule: don't put anything in an rcu_read_lock() RCU 577 * read-side critical section that would block in a !PREEMPT kernel. 578 * But if you want the full story, read on! 579 * 580 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it 581 * is illegal to block while in an RCU read-side critical section. In 582 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) 583 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may 584 * be preempted, but explicit blocking is illegal. Finally, in preemptible 585 * RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds, 586 * RCU read-side critical sections may be preempted and they may also 587 * block, but only when acquiring spinlocks that are subject to priority 588 * inheritance. 589 */ 590static inline void rcu_read_lock(void) 591{ 592 __rcu_read_lock(); 593 __acquire(RCU); 594 rcu_read_acquire(); 595} 596 597/* 598 * So where is rcu_write_lock()? It does not exist, as there is no 599 * way for writers to lock out RCU readers. This is a feature, not 600 * a bug -- this property is what provides RCU's performance benefits. 601 * Of course, writers must coordinate with each other. The normal 602 * spinlock primitives work well for this, but any other technique may be 603 * used as well. RCU does not care how the writers keep out of each 604 * others' way, as long as they do so. 605 */ 606 607/** 608 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 609 * 610 * See rcu_read_lock() for more information. 611 */ 612static inline void rcu_read_unlock(void) 613{ 614 rcu_read_release(); 615 __release(RCU); 616 __rcu_read_unlock(); 617} 618 619/** 620 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 621 * 622 * This is equivalent of rcu_read_lock(), but to be used when updates 623 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since 624 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a 625 * softirq handler to be a quiescent state, a process in RCU read-side 626 * critical section must be protected by disabling softirqs. Read-side 627 * critical sections in interrupt context can use just rcu_read_lock(), 628 * though this should at least be commented to avoid confusing people 629 * reading the code. 630 */ 631static inline void rcu_read_lock_bh(void) 632{ 633 __rcu_read_lock_bh(); 634 __acquire(RCU_BH); 635 rcu_read_acquire_bh(); 636} 637 638/* 639 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 640 * 641 * See rcu_read_lock_bh() for more information. 642 */ 643static inline void rcu_read_unlock_bh(void) 644{ 645 rcu_read_release_bh(); 646 __release(RCU_BH); 647 __rcu_read_unlock_bh(); 648} 649 650/** 651 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 652 * 653 * This is equivalent of rcu_read_lock(), but to be used when updates 654 * are being done using call_rcu_sched() or synchronize_rcu_sched(). 655 * Read-side critical sections can also be introduced by anything that 656 * disables preemption, including local_irq_disable() and friends. 657 */ 658static inline void rcu_read_lock_sched(void) 659{ 660 preempt_disable(); 661 __acquire(RCU_SCHED); 662 rcu_read_acquire_sched(); 663} 664 665/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 666static inline notrace void rcu_read_lock_sched_notrace(void) 667{ 668 preempt_disable_notrace(); 669 __acquire(RCU_SCHED); 670} 671 672/* 673 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section 674 * 675 * See rcu_read_lock_sched for more information. 676 */ 677static inline void rcu_read_unlock_sched(void) 678{ 679 rcu_read_release_sched(); 680 __release(RCU_SCHED); 681 preempt_enable(); 682} 683 684/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 685static inline notrace void rcu_read_unlock_sched_notrace(void) 686{ 687 __release(RCU_SCHED); 688 preempt_enable_notrace(); 689} 690 691/** 692 * rcu_assign_pointer() - assign to RCU-protected pointer 693 * @p: pointer to assign to 694 * @v: value to assign (publish) 695 * 696 * Assigns the specified value to the specified RCU-protected 697 * pointer, ensuring that any concurrent RCU readers will see 698 * any prior initialization. Returns the value assigned. 699 * 700 * Inserts memory barriers on architectures that require them 701 * (pretty much all of them other than x86), and also prevents 702 * the compiler from reordering the code that initializes the 703 * structure after the pointer assignment. More importantly, this 704 * call documents which pointers will be dereferenced by RCU read-side 705 * code. 706 */ 707#define rcu_assign_pointer(p, v) \ 708 __rcu_assign_pointer((p), (v), __rcu) 709 710/** 711 * RCU_INIT_POINTER() - initialize an RCU protected pointer 712 * 713 * Initialize an RCU-protected pointer in such a way to avoid RCU-lockdep 714 * splats. 715 */ 716#define RCU_INIT_POINTER(p, v) \ 717 p = (typeof(*v) __force __rcu *)(v) 718 719/* Infrastructure to implement the synchronize_() primitives. */ 720 721struct rcu_synchronize { 722 struct rcu_head head; 723 struct completion completion; 724}; 725 726extern void wakeme_after_rcu(struct rcu_head *head); 727 728#ifdef CONFIG_PREEMPT_RCU 729 730/** 731 * call_rcu() - Queue an RCU callback for invocation after a grace period. 732 * @head: structure to be used for queueing the RCU updates. 733 * @func: actual callback function to be invoked after the grace period 734 * 735 * The callback function will be invoked some time after a full grace 736 * period elapses, in other words after all pre-existing RCU read-side 737 * critical sections have completed. However, the callback function 738 * might well execute concurrently with RCU read-side critical sections 739 * that started after call_rcu() was invoked. RCU read-side critical 740 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), 741 * and may be nested. 742 */ 743extern void call_rcu(struct rcu_head *head, 744 void (*func)(struct rcu_head *head)); 745 746#else /* #ifdef CONFIG_PREEMPT_RCU */ 747 748/* In classic RCU, call_rcu() is just call_rcu_sched(). */ 749#define call_rcu call_rcu_sched 750 751#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 752 753/** 754 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. 755 * @head: structure to be used for queueing the RCU updates. 756 * @func: actual callback function to be invoked after the grace period 757 * 758 * The callback function will be invoked some time after a full grace 759 * period elapses, in other words after all currently executing RCU 760 * read-side critical sections have completed. call_rcu_bh() assumes 761 * that the read-side critical sections end on completion of a softirq 762 * handler. This means that read-side critical sections in process 763 * context must not be interrupted by softirqs. This interface is to be 764 * used when most of the read-side critical sections are in softirq context. 765 * RCU read-side critical sections are delimited by : 766 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. 767 * OR 768 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. 769 * These may be nested. 770 */ 771extern void call_rcu_bh(struct rcu_head *head, 772 void (*func)(struct rcu_head *head)); 773 774/* 775 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally 776 * by call_rcu() and rcu callback execution, and are therefore not part of the 777 * RCU API. Leaving in rcupdate.h because they are used by all RCU flavors. 778 */ 779 780#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 781# define STATE_RCU_HEAD_READY 0 782# define STATE_RCU_HEAD_QUEUED 1 783 784extern struct debug_obj_descr rcuhead_debug_descr; 785 786static inline void debug_rcu_head_queue(struct rcu_head *head) 787{ 788 WARN_ON_ONCE((unsigned long)head & 0x3); 789 debug_object_activate(head, &rcuhead_debug_descr); 790 debug_object_active_state(head, &rcuhead_debug_descr, 791 STATE_RCU_HEAD_READY, 792 STATE_RCU_HEAD_QUEUED); 793} 794 795static inline void debug_rcu_head_unqueue(struct rcu_head *head) 796{ 797 debug_object_active_state(head, &rcuhead_debug_descr, 798 STATE_RCU_HEAD_QUEUED, 799 STATE_RCU_HEAD_READY); 800 debug_object_deactivate(head, &rcuhead_debug_descr); 801} 802#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 803static inline void debug_rcu_head_queue(struct rcu_head *head) 804{ 805} 806 807static inline void debug_rcu_head_unqueue(struct rcu_head *head) 808{ 809} 810#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 811 812static __always_inline bool __is_kfree_rcu_offset(unsigned long offset) 813{ 814 return offset < 4096; 815} 816 817static __always_inline 818void __kfree_rcu(struct rcu_head *head, unsigned long offset) 819{ 820 typedef void (*rcu_callback)(struct rcu_head *); 821 822 BUILD_BUG_ON(!__builtin_constant_p(offset)); 823 824 /* See the kfree_rcu() header comment. */ 825 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); 826 827 call_rcu(head, (rcu_callback)offset); 828} 829 830extern void kfree(const void *); 831 832static inline void __rcu_reclaim(struct rcu_head *head) 833{ 834 unsigned long offset = (unsigned long)head->func; 835 836 if (__is_kfree_rcu_offset(offset)) 837 kfree((void *)head - offset); 838 else 839 head->func(head); 840} 841 842/** 843 * kfree_rcu() - kfree an object after a grace period. 844 * @ptr: pointer to kfree 845 * @rcu_head: the name of the struct rcu_head within the type of @ptr. 846 * 847 * Many rcu callbacks functions just call kfree() on the base structure. 848 * These functions are trivial, but their size adds up, and furthermore 849 * when they are used in a kernel module, that module must invoke the 850 * high-latency rcu_barrier() function at module-unload time. 851 * 852 * The kfree_rcu() function handles this issue. Rather than encoding a 853 * function address in the embedded rcu_head structure, kfree_rcu() instead 854 * encodes the offset of the rcu_head structure within the base structure. 855 * Because the functions are not allowed in the low-order 4096 bytes of 856 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 857 * If the offset is larger than 4095 bytes, a compile-time error will 858 * be generated in __kfree_rcu(). If this error is triggered, you can 859 * either fall back to use of call_rcu() or rearrange the structure to 860 * position the rcu_head structure into the first 4096 bytes. 861 * 862 * Note that the allowable offset might decrease in the future, for example, 863 * to allow something like kmem_cache_free_rcu(). 864 */ 865#define kfree_rcu(ptr, rcu_head) \ 866 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) 867 868#endif /* __LINUX_RCUPDATE_H */ 869