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 49 extern int rcutorture_runnable; /* for sysctl */ 50 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */ 51 52 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 53 extern void rcutorture_record_test_transition(void); 54 extern void rcutorture_record_progress(unsigned long vernum); 55 extern void do_trace_rcu_torture_read(char *rcutorturename, 56 struct rcu_head *rhp, 57 unsigned long secs, 58 unsigned long c_old, 59 unsigned long c); 60 #else 61 static inline void rcutorture_record_test_transition(void) 62 { 63 } 64 static inline void rcutorture_record_progress(unsigned long vernum) 65 { 66 } 67 #ifdef CONFIG_RCU_TRACE 68 extern void do_trace_rcu_torture_read(char *rcutorturename, 69 struct rcu_head *rhp, 70 unsigned long secs, 71 unsigned long c_old, 72 unsigned long c); 73 #else 74 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ 75 do { } while (0) 76 #endif 77 #endif 78 79 #define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b)) 80 #define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b)) 81 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 82 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 83 84 /* Exported common interfaces */ 85 86 #ifdef CONFIG_PREEMPT_RCU 87 88 /** 89 * call_rcu() - Queue an RCU callback for invocation after a grace period. 90 * @head: structure to be used for queueing the RCU updates. 91 * @func: actual callback function to be invoked after the grace period 92 * 93 * The callback function will be invoked some time after a full grace 94 * period elapses, in other words after all pre-existing RCU read-side 95 * critical sections have completed. However, the callback function 96 * might well execute concurrently with RCU read-side critical sections 97 * that started after call_rcu() was invoked. RCU read-side critical 98 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), 99 * and may be nested. 100 * 101 * Note that all CPUs must agree that the grace period extended beyond 102 * all pre-existing RCU read-side critical section. On systems with more 103 * than one CPU, this means that when "func()" is invoked, each CPU is 104 * guaranteed to have executed a full memory barrier since the end of its 105 * last RCU read-side critical section whose beginning preceded the call 106 * to call_rcu(). It also means that each CPU executing an RCU read-side 107 * critical section that continues beyond the start of "func()" must have 108 * executed a memory barrier after the call_rcu() but before the beginning 109 * of that RCU read-side critical section. Note that these guarantees 110 * include CPUs that are offline, idle, or executing in user mode, as 111 * well as CPUs that are executing in the kernel. 112 * 113 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the 114 * resulting RCU callback function "func()", then both CPU A and CPU B are 115 * guaranteed to execute a full memory barrier during the time interval 116 * between the call to call_rcu() and the invocation of "func()" -- even 117 * if CPU A and CPU B are the same CPU (but again only if the system has 118 * more than one CPU). 119 */ 120 extern void call_rcu(struct rcu_head *head, 121 void (*func)(struct rcu_head *head)); 122 123 #else /* #ifdef CONFIG_PREEMPT_RCU */ 124 125 /* In classic RCU, call_rcu() is just call_rcu_sched(). */ 126 #define call_rcu call_rcu_sched 127 128 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 129 130 /** 131 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period. 132 * @head: structure to be used for queueing the RCU updates. 133 * @func: actual callback function to be invoked after the grace period 134 * 135 * The callback function will be invoked some time after a full grace 136 * period elapses, in other words after all currently executing RCU 137 * read-side critical sections have completed. call_rcu_bh() assumes 138 * that the read-side critical sections end on completion of a softirq 139 * handler. This means that read-side critical sections in process 140 * context must not be interrupted by softirqs. This interface is to be 141 * used when most of the read-side critical sections are in softirq context. 142 * RCU read-side critical sections are delimited by : 143 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. 144 * OR 145 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. 146 * These may be nested. 147 * 148 * See the description of call_rcu() for more detailed information on 149 * memory ordering guarantees. 150 */ 151 extern void call_rcu_bh(struct rcu_head *head, 152 void (*func)(struct rcu_head *head)); 153 154 /** 155 * call_rcu_sched() - Queue an RCU for invocation after sched grace period. 156 * @head: structure to be used for queueing the RCU updates. 157 * @func: actual callback function to be invoked after the grace period 158 * 159 * The callback function will be invoked some time after a full grace 160 * period elapses, in other words after all currently executing RCU 161 * read-side critical sections have completed. call_rcu_sched() assumes 162 * that the read-side critical sections end on enabling of preemption 163 * or on voluntary preemption. 164 * RCU read-side critical sections are delimited by : 165 * - rcu_read_lock_sched() and rcu_read_unlock_sched(), 166 * OR 167 * anything that disables preemption. 168 * These may be nested. 169 * 170 * See the description of call_rcu() for more detailed information on 171 * memory ordering guarantees. 172 */ 173 extern void call_rcu_sched(struct rcu_head *head, 174 void (*func)(struct rcu_head *rcu)); 175 176 extern void synchronize_sched(void); 177 178 #ifdef CONFIG_PREEMPT_RCU 179 180 extern void __rcu_read_lock(void); 181 extern void __rcu_read_unlock(void); 182 extern void rcu_read_unlock_special(struct task_struct *t); 183 void synchronize_rcu(void); 184 185 /* 186 * Defined as a macro as it is a very low level header included from 187 * areas that don't even know about current. This gives the rcu_read_lock() 188 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 189 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 190 */ 191 #define rcu_preempt_depth() (current->rcu_read_lock_nesting) 192 193 #else /* #ifdef CONFIG_PREEMPT_RCU */ 194 195 static inline void __rcu_read_lock(void) 196 { 197 preempt_disable(); 198 } 199 200 static inline void __rcu_read_unlock(void) 201 { 202 preempt_enable(); 203 } 204 205 static inline void synchronize_rcu(void) 206 { 207 synchronize_sched(); 208 } 209 210 static inline int rcu_preempt_depth(void) 211 { 212 return 0; 213 } 214 215 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 216 217 /* Internal to kernel */ 218 extern void rcu_sched_qs(int cpu); 219 extern void rcu_bh_qs(int cpu); 220 extern void rcu_check_callbacks(int cpu, int user); 221 struct notifier_block; 222 extern void rcu_idle_enter(void); 223 extern void rcu_idle_exit(void); 224 extern void rcu_irq_enter(void); 225 extern void rcu_irq_exit(void); 226 227 #ifdef CONFIG_RCU_USER_QS 228 extern void rcu_user_enter(void); 229 extern void rcu_user_exit(void); 230 extern void rcu_user_enter_after_irq(void); 231 extern void rcu_user_exit_after_irq(void); 232 #else 233 static inline void rcu_user_enter(void) { } 234 static inline void rcu_user_exit(void) { } 235 static inline void rcu_user_enter_after_irq(void) { } 236 static inline void rcu_user_exit_after_irq(void) { } 237 static inline void rcu_user_hooks_switch(struct task_struct *prev, 238 struct task_struct *next) { } 239 #endif /* CONFIG_RCU_USER_QS */ 240 241 extern void exit_rcu(void); 242 243 /** 244 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers 245 * @a: Code that RCU needs to pay attention to. 246 * 247 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden 248 * in the inner idle loop, that is, between the rcu_idle_enter() and 249 * the rcu_idle_exit() -- RCU will happily ignore any such read-side 250 * critical sections. However, things like powertop need tracepoints 251 * in the inner idle loop. 252 * 253 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) 254 * will tell RCU that it needs to pay attending, invoke its argument 255 * (in this example, a call to the do_something_with_RCU() function), 256 * and then tell RCU to go back to ignoring this CPU. It is permissible 257 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently 258 * quite limited. If deeper nesting is required, it will be necessary 259 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. 260 */ 261 #define RCU_NONIDLE(a) \ 262 do { \ 263 rcu_irq_enter(); \ 264 do { a; } while (0); \ 265 rcu_irq_exit(); \ 266 } while (0) 267 268 /* 269 * Infrastructure to implement the synchronize_() primitives in 270 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 271 */ 272 273 typedef void call_rcu_func_t(struct rcu_head *head, 274 void (*func)(struct rcu_head *head)); 275 void wait_rcu_gp(call_rcu_func_t crf); 276 277 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) 278 #include <linux/rcutree.h> 279 #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU) 280 #include <linux/rcutiny.h> 281 #else 282 #error "Unknown RCU implementation specified to kernel configuration" 283 #endif 284 285 /* 286 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic 287 * initialization and destruction of rcu_head on the stack. rcu_head structures 288 * allocated dynamically in the heap or defined statically don't need any 289 * initialization. 290 */ 291 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 292 extern void init_rcu_head_on_stack(struct rcu_head *head); 293 extern void destroy_rcu_head_on_stack(struct rcu_head *head); 294 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 295 static inline void init_rcu_head_on_stack(struct rcu_head *head) 296 { 297 } 298 299 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) 300 { 301 } 302 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 303 304 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) 305 extern int rcu_is_cpu_idle(void); 306 #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */ 307 308 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 309 bool rcu_lockdep_current_cpu_online(void); 310 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 311 static inline bool rcu_lockdep_current_cpu_online(void) 312 { 313 return 1; 314 } 315 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 316 317 #ifdef CONFIG_DEBUG_LOCK_ALLOC 318 319 static inline void rcu_lock_acquire(struct lockdep_map *map) 320 { 321 lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_); 322 } 323 324 static inline void rcu_lock_release(struct lockdep_map *map) 325 { 326 lock_release(map, 1, _THIS_IP_); 327 } 328 329 extern struct lockdep_map rcu_lock_map; 330 extern struct lockdep_map rcu_bh_lock_map; 331 extern struct lockdep_map rcu_sched_lock_map; 332 extern int debug_lockdep_rcu_enabled(void); 333 334 /** 335 * rcu_read_lock_held() - might we be in RCU read-side critical section? 336 * 337 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU 338 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC, 339 * this assumes we are in an RCU read-side critical section unless it can 340 * prove otherwise. This is useful for debug checks in functions that 341 * require that they be called within an RCU read-side critical section. 342 * 343 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot 344 * and while lockdep is disabled. 345 * 346 * Note that rcu_read_lock() and the matching rcu_read_unlock() must 347 * occur in the same context, for example, it is illegal to invoke 348 * rcu_read_unlock() in process context if the matching rcu_read_lock() 349 * was invoked from within an irq handler. 350 * 351 * Note that rcu_read_lock() is disallowed if the CPU is either idle or 352 * offline from an RCU perspective, so check for those as well. 353 */ 354 static inline int rcu_read_lock_held(void) 355 { 356 if (!debug_lockdep_rcu_enabled()) 357 return 1; 358 if (rcu_is_cpu_idle()) 359 return 0; 360 if (!rcu_lockdep_current_cpu_online()) 361 return 0; 362 return lock_is_held(&rcu_lock_map); 363 } 364 365 /* 366 * rcu_read_lock_bh_held() is defined out of line to avoid #include-file 367 * hell. 368 */ 369 extern int rcu_read_lock_bh_held(void); 370 371 /** 372 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section? 373 * 374 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an 375 * RCU-sched read-side critical section. In absence of 376 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side 377 * critical section unless it can prove otherwise. Note that disabling 378 * of preemption (including disabling irqs) counts as an RCU-sched 379 * read-side critical section. This is useful for debug checks in functions 380 * that required that they be called within an RCU-sched read-side 381 * critical section. 382 * 383 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot 384 * and while lockdep is disabled. 385 * 386 * Note that if the CPU is in the idle loop from an RCU point of 387 * view (ie: that we are in the section between rcu_idle_enter() and 388 * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU 389 * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs 390 * that are in such a section, considering these as in extended quiescent 391 * state, so such a CPU is effectively never in an RCU read-side critical 392 * section regardless of what RCU primitives it invokes. This state of 393 * affairs is required --- we need to keep an RCU-free window in idle 394 * where the CPU may possibly enter into low power mode. This way we can 395 * notice an extended quiescent state to other CPUs that started a grace 396 * period. Otherwise we would delay any grace period as long as we run in 397 * the idle task. 398 * 399 * Similarly, we avoid claiming an SRCU read lock held if the current 400 * CPU is offline. 401 */ 402 #ifdef CONFIG_PREEMPT_COUNT 403 static inline int rcu_read_lock_sched_held(void) 404 { 405 int lockdep_opinion = 0; 406 407 if (!debug_lockdep_rcu_enabled()) 408 return 1; 409 if (rcu_is_cpu_idle()) 410 return 0; 411 if (!rcu_lockdep_current_cpu_online()) 412 return 0; 413 if (debug_locks) 414 lockdep_opinion = lock_is_held(&rcu_sched_lock_map); 415 return lockdep_opinion || preempt_count() != 0 || irqs_disabled(); 416 } 417 #else /* #ifdef CONFIG_PREEMPT_COUNT */ 418 static inline int rcu_read_lock_sched_held(void) 419 { 420 return 1; 421 } 422 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ 423 424 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 425 426 # define rcu_lock_acquire(a) do { } while (0) 427 # define rcu_lock_release(a) do { } while (0) 428 429 static inline int rcu_read_lock_held(void) 430 { 431 return 1; 432 } 433 434 static inline int rcu_read_lock_bh_held(void) 435 { 436 return 1; 437 } 438 439 #ifdef CONFIG_PREEMPT_COUNT 440 static inline int rcu_read_lock_sched_held(void) 441 { 442 return preempt_count() != 0 || irqs_disabled(); 443 } 444 #else /* #ifdef CONFIG_PREEMPT_COUNT */ 445 static inline int rcu_read_lock_sched_held(void) 446 { 447 return 1; 448 } 449 #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */ 450 451 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 452 453 #ifdef CONFIG_PROVE_RCU 454 455 extern int rcu_my_thread_group_empty(void); 456 457 /** 458 * rcu_lockdep_assert - emit lockdep splat if specified condition not met 459 * @c: condition to check 460 * @s: informative message 461 */ 462 #define rcu_lockdep_assert(c, s) \ 463 do { \ 464 static bool __section(.data.unlikely) __warned; \ 465 if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ 466 __warned = true; \ 467 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 468 } \ 469 } while (0) 470 471 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) 472 static inline void rcu_preempt_sleep_check(void) 473 { 474 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), 475 "Illegal context switch in RCU read-side critical section"); 476 } 477 #else /* #ifdef CONFIG_PROVE_RCU */ 478 static inline void rcu_preempt_sleep_check(void) 479 { 480 } 481 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 482 483 #define rcu_sleep_check() \ 484 do { \ 485 rcu_preempt_sleep_check(); \ 486 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \ 487 "Illegal context switch in RCU-bh" \ 488 " read-side critical section"); \ 489 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \ 490 "Illegal context switch in RCU-sched"\ 491 " read-side critical section"); \ 492 } while (0) 493 494 #else /* #ifdef CONFIG_PROVE_RCU */ 495 496 #define rcu_lockdep_assert(c, s) do { } while (0) 497 #define rcu_sleep_check() do { } while (0) 498 499 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 500 501 /* 502 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 503 * and rcu_assign_pointer(). Some of these could be folded into their 504 * callers, but they are left separate in order to ease introduction of 505 * multiple flavors of pointers to match the multiple flavors of RCU 506 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in 507 * the future. 508 */ 509 510 #ifdef __CHECKER__ 511 #define rcu_dereference_sparse(p, space) \ 512 ((void)(((typeof(*p) space *)p) == p)) 513 #else /* #ifdef __CHECKER__ */ 514 #define rcu_dereference_sparse(p, space) 515 #endif /* #else #ifdef __CHECKER__ */ 516 517 #define __rcu_access_pointer(p, space) \ 518 ({ \ 519 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 520 rcu_dereference_sparse(p, space); \ 521 ((typeof(*p) __force __kernel *)(_________p1)); \ 522 }) 523 #define __rcu_dereference_check(p, c, space) \ 524 ({ \ 525 typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \ 526 rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \ 527 " usage"); \ 528 rcu_dereference_sparse(p, space); \ 529 smp_read_barrier_depends(); \ 530 ((typeof(*p) __force __kernel *)(_________p1)); \ 531 }) 532 #define __rcu_dereference_protected(p, c, space) \ 533 ({ \ 534 rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \ 535 " usage"); \ 536 rcu_dereference_sparse(p, space); \ 537 ((typeof(*p) __force __kernel *)(p)); \ 538 }) 539 540 #define __rcu_access_index(p, space) \ 541 ({ \ 542 typeof(p) _________p1 = ACCESS_ONCE(p); \ 543 rcu_dereference_sparse(p, space); \ 544 (_________p1); \ 545 }) 546 #define __rcu_dereference_index_check(p, c) \ 547 ({ \ 548 typeof(p) _________p1 = ACCESS_ONCE(p); \ 549 rcu_lockdep_assert(c, \ 550 "suspicious rcu_dereference_index_check()" \ 551 " usage"); \ 552 smp_read_barrier_depends(); \ 553 (_________p1); \ 554 }) 555 #define __rcu_assign_pointer(p, v, space) \ 556 do { \ 557 smp_wmb(); \ 558 (p) = (typeof(*v) __force space *)(v); \ 559 } while (0) 560 561 562 /** 563 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 564 * @p: The pointer to read 565 * 566 * Return the value of the specified RCU-protected pointer, but omit the 567 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 568 * when the value of this pointer is accessed, but the pointer is not 569 * dereferenced, for example, when testing an RCU-protected pointer against 570 * NULL. Although rcu_access_pointer() may also be used in cases where 571 * update-side locks prevent the value of the pointer from changing, you 572 * should instead use rcu_dereference_protected() for this use case. 573 * 574 * It is also permissible to use rcu_access_pointer() when read-side 575 * access to the pointer was removed at least one grace period ago, as 576 * is the case in the context of the RCU callback that is freeing up 577 * the data, or after a synchronize_rcu() returns. This can be useful 578 * when tearing down multi-linked structures after a grace period 579 * has elapsed. 580 */ 581 #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu) 582 583 /** 584 * rcu_dereference_check() - rcu_dereference with debug checking 585 * @p: The pointer to read, prior to dereferencing 586 * @c: The conditions under which the dereference will take place 587 * 588 * Do an rcu_dereference(), but check that the conditions under which the 589 * dereference will take place are correct. Typically the conditions 590 * indicate the various locking conditions that should be held at that 591 * point. The check should return true if the conditions are satisfied. 592 * An implicit check for being in an RCU read-side critical section 593 * (rcu_read_lock()) is included. 594 * 595 * For example: 596 * 597 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 598 * 599 * could be used to indicate to lockdep that foo->bar may only be dereferenced 600 * if either rcu_read_lock() is held, or that the lock required to replace 601 * the bar struct at foo->bar is held. 602 * 603 * Note that the list of conditions may also include indications of when a lock 604 * need not be held, for example during initialisation or destruction of the 605 * target struct: 606 * 607 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 608 * atomic_read(&foo->usage) == 0); 609 * 610 * Inserts memory barriers on architectures that require them 611 * (currently only the Alpha), prevents the compiler from refetching 612 * (and from merging fetches), and, more importantly, documents exactly 613 * which pointers are protected by RCU and checks that the pointer is 614 * annotated as __rcu. 615 */ 616 #define rcu_dereference_check(p, c) \ 617 __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu) 618 619 /** 620 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 621 * @p: The pointer to read, prior to dereferencing 622 * @c: The conditions under which the dereference will take place 623 * 624 * This is the RCU-bh counterpart to rcu_dereference_check(). 625 */ 626 #define rcu_dereference_bh_check(p, c) \ 627 __rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu) 628 629 /** 630 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 631 * @p: The pointer to read, prior to dereferencing 632 * @c: The conditions under which the dereference will take place 633 * 634 * This is the RCU-sched counterpart to rcu_dereference_check(). 635 */ 636 #define rcu_dereference_sched_check(p, c) \ 637 __rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \ 638 __rcu) 639 640 #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ 641 642 /** 643 * rcu_access_index() - fetch RCU index with no dereferencing 644 * @p: The index to read 645 * 646 * Return the value of the specified RCU-protected index, but omit the 647 * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful 648 * when the value of this index is accessed, but the index is not 649 * dereferenced, for example, when testing an RCU-protected index against 650 * -1. Although rcu_access_index() may also be used in cases where 651 * update-side locks prevent the value of the index from changing, you 652 * should instead use rcu_dereference_index_protected() for this use case. 653 */ 654 #define rcu_access_index(p) __rcu_access_index((p), __rcu) 655 656 /** 657 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking 658 * @p: The pointer to read, prior to dereferencing 659 * @c: The conditions under which the dereference will take place 660 * 661 * Similar to rcu_dereference_check(), but omits the sparse checking. 662 * This allows rcu_dereference_index_check() to be used on integers, 663 * which can then be used as array indices. Attempting to use 664 * rcu_dereference_check() on an integer will give compiler warnings 665 * because the sparse address-space mechanism relies on dereferencing 666 * the RCU-protected pointer. Dereferencing integers is not something 667 * that even gcc will put up with. 668 * 669 * Note that this function does not implicitly check for RCU read-side 670 * critical sections. If this function gains lots of uses, it might 671 * make sense to provide versions for each flavor of RCU, but it does 672 * not make sense as of early 2010. 673 */ 674 #define rcu_dereference_index_check(p, c) \ 675 __rcu_dereference_index_check((p), (c)) 676 677 /** 678 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 679 * @p: The pointer to read, prior to dereferencing 680 * @c: The conditions under which the dereference will take place 681 * 682 * Return the value of the specified RCU-protected pointer, but omit 683 * both the smp_read_barrier_depends() and the ACCESS_ONCE(). This 684 * is useful in cases where update-side locks prevent the value of the 685 * pointer from changing. Please note that this primitive does -not- 686 * prevent the compiler from repeating this reference or combining it 687 * with other references, so it should not be used without protection 688 * of appropriate locks. 689 * 690 * This function is only for update-side use. Using this function 691 * when protected only by rcu_read_lock() will result in infrequent 692 * but very ugly failures. 693 */ 694 #define rcu_dereference_protected(p, c) \ 695 __rcu_dereference_protected((p), (c), __rcu) 696 697 698 /** 699 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 700 * @p: The pointer to read, prior to dereferencing 701 * 702 * This is a simple wrapper around rcu_dereference_check(). 703 */ 704 #define rcu_dereference(p) rcu_dereference_check(p, 0) 705 706 /** 707 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 708 * @p: The pointer to read, prior to dereferencing 709 * 710 * Makes rcu_dereference_check() do the dirty work. 711 */ 712 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 713 714 /** 715 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 716 * @p: The pointer to read, prior to dereferencing 717 * 718 * Makes rcu_dereference_check() do the dirty work. 719 */ 720 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 721 722 /** 723 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 724 * 725 * When synchronize_rcu() is invoked on one CPU while other CPUs 726 * are within RCU read-side critical sections, then the 727 * synchronize_rcu() is guaranteed to block until after all the other 728 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 729 * on one CPU while other CPUs are within RCU read-side critical 730 * sections, invocation of the corresponding RCU callback is deferred 731 * until after the all the other CPUs exit their critical sections. 732 * 733 * Note, however, that RCU callbacks are permitted to run concurrently 734 * with new RCU read-side critical sections. One way that this can happen 735 * is via the following sequence of events: (1) CPU 0 enters an RCU 736 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 737 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 738 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 739 * callback is invoked. This is legal, because the RCU read-side critical 740 * section that was running concurrently with the call_rcu() (and which 741 * therefore might be referencing something that the corresponding RCU 742 * callback would free up) has completed before the corresponding 743 * RCU callback is invoked. 744 * 745 * RCU read-side critical sections may be nested. Any deferred actions 746 * will be deferred until the outermost RCU read-side critical section 747 * completes. 748 * 749 * You can avoid reading and understanding the next paragraph by 750 * following this rule: don't put anything in an rcu_read_lock() RCU 751 * read-side critical section that would block in a !PREEMPT kernel. 752 * But if you want the full story, read on! 753 * 754 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it 755 * is illegal to block while in an RCU read-side critical section. In 756 * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU) 757 * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may 758 * be preempted, but explicit blocking is illegal. Finally, in preemptible 759 * RCU implementations in real-time (with -rt patchset) kernel builds, 760 * RCU read-side critical sections may be preempted and they may also 761 * block, but only when acquiring spinlocks that are subject to priority 762 * inheritance. 763 */ 764 static inline void rcu_read_lock(void) 765 { 766 __rcu_read_lock(); 767 __acquire(RCU); 768 rcu_lock_acquire(&rcu_lock_map); 769 rcu_lockdep_assert(!rcu_is_cpu_idle(), 770 "rcu_read_lock() used illegally while idle"); 771 } 772 773 /* 774 * So where is rcu_write_lock()? It does not exist, as there is no 775 * way for writers to lock out RCU readers. This is a feature, not 776 * a bug -- this property is what provides RCU's performance benefits. 777 * Of course, writers must coordinate with each other. The normal 778 * spinlock primitives work well for this, but any other technique may be 779 * used as well. RCU does not care how the writers keep out of each 780 * others' way, as long as they do so. 781 */ 782 783 /** 784 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 785 * 786 * See rcu_read_lock() for more information. 787 */ 788 static inline void rcu_read_unlock(void) 789 { 790 rcu_lockdep_assert(!rcu_is_cpu_idle(), 791 "rcu_read_unlock() used illegally while idle"); 792 rcu_lock_release(&rcu_lock_map); 793 __release(RCU); 794 __rcu_read_unlock(); 795 } 796 797 /** 798 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 799 * 800 * This is equivalent of rcu_read_lock(), but to be used when updates 801 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since 802 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a 803 * softirq handler to be a quiescent state, a process in RCU read-side 804 * critical section must be protected by disabling softirqs. Read-side 805 * critical sections in interrupt context can use just rcu_read_lock(), 806 * though this should at least be commented to avoid confusing people 807 * reading the code. 808 * 809 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 810 * must occur in the same context, for example, it is illegal to invoke 811 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 812 * was invoked from some other task. 813 */ 814 static inline void rcu_read_lock_bh(void) 815 { 816 local_bh_disable(); 817 __acquire(RCU_BH); 818 rcu_lock_acquire(&rcu_bh_lock_map); 819 rcu_lockdep_assert(!rcu_is_cpu_idle(), 820 "rcu_read_lock_bh() used illegally while idle"); 821 } 822 823 /* 824 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section 825 * 826 * See rcu_read_lock_bh() for more information. 827 */ 828 static inline void rcu_read_unlock_bh(void) 829 { 830 rcu_lockdep_assert(!rcu_is_cpu_idle(), 831 "rcu_read_unlock_bh() used illegally while idle"); 832 rcu_lock_release(&rcu_bh_lock_map); 833 __release(RCU_BH); 834 local_bh_enable(); 835 } 836 837 /** 838 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 839 * 840 * This is equivalent of rcu_read_lock(), but to be used when updates 841 * are being done using call_rcu_sched() or synchronize_rcu_sched(). 842 * Read-side critical sections can also be introduced by anything that 843 * disables preemption, including local_irq_disable() and friends. 844 * 845 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 846 * must occur in the same context, for example, it is illegal to invoke 847 * rcu_read_unlock_sched() from process context if the matching 848 * rcu_read_lock_sched() was invoked from an NMI handler. 849 */ 850 static inline void rcu_read_lock_sched(void) 851 { 852 preempt_disable(); 853 __acquire(RCU_SCHED); 854 rcu_lock_acquire(&rcu_sched_lock_map); 855 rcu_lockdep_assert(!rcu_is_cpu_idle(), 856 "rcu_read_lock_sched() used illegally while idle"); 857 } 858 859 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 860 static inline notrace void rcu_read_lock_sched_notrace(void) 861 { 862 preempt_disable_notrace(); 863 __acquire(RCU_SCHED); 864 } 865 866 /* 867 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section 868 * 869 * See rcu_read_lock_sched for more information. 870 */ 871 static inline void rcu_read_unlock_sched(void) 872 { 873 rcu_lockdep_assert(!rcu_is_cpu_idle(), 874 "rcu_read_unlock_sched() used illegally while idle"); 875 rcu_lock_release(&rcu_sched_lock_map); 876 __release(RCU_SCHED); 877 preempt_enable(); 878 } 879 880 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 881 static inline notrace void rcu_read_unlock_sched_notrace(void) 882 { 883 __release(RCU_SCHED); 884 preempt_enable_notrace(); 885 } 886 887 /** 888 * rcu_assign_pointer() - assign to RCU-protected pointer 889 * @p: pointer to assign to 890 * @v: value to assign (publish) 891 * 892 * Assigns the specified value to the specified RCU-protected 893 * pointer, ensuring that any concurrent RCU readers will see 894 * any prior initialization. 895 * 896 * Inserts memory barriers on architectures that require them 897 * (which is most of them), and also prevents the compiler from 898 * reordering the code that initializes the structure after the pointer 899 * assignment. More importantly, this call documents which pointers 900 * will be dereferenced by RCU read-side code. 901 * 902 * In some special cases, you may use RCU_INIT_POINTER() instead 903 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 904 * to the fact that it does not constrain either the CPU or the compiler. 905 * That said, using RCU_INIT_POINTER() when you should have used 906 * rcu_assign_pointer() is a very bad thing that results in 907 * impossible-to-diagnose memory corruption. So please be careful. 908 * See the RCU_INIT_POINTER() comment header for details. 909 */ 910 #define rcu_assign_pointer(p, v) \ 911 __rcu_assign_pointer((p), (v), __rcu) 912 913 /** 914 * RCU_INIT_POINTER() - initialize an RCU protected pointer 915 * 916 * Initialize an RCU-protected pointer in special cases where readers 917 * do not need ordering constraints on the CPU or the compiler. These 918 * special cases are: 919 * 920 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or- 921 * 2. The caller has taken whatever steps are required to prevent 922 * RCU readers from concurrently accessing this pointer -or- 923 * 3. The referenced data structure has already been exposed to 924 * readers either at compile time or via rcu_assign_pointer() -and- 925 * a. You have not made -any- reader-visible changes to 926 * this structure since then -or- 927 * b. It is OK for readers accessing this structure from its 928 * new location to see the old state of the structure. (For 929 * example, the changes were to statistical counters or to 930 * other state where exact synchronization is not required.) 931 * 932 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 933 * result in impossible-to-diagnose memory corruption. As in the structures 934 * will look OK in crash dumps, but any concurrent RCU readers might 935 * see pre-initialized values of the referenced data structure. So 936 * please be very careful how you use RCU_INIT_POINTER()!!! 937 * 938 * If you are creating an RCU-protected linked structure that is accessed 939 * by a single external-to-structure RCU-protected pointer, then you may 940 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 941 * pointers, but you must use rcu_assign_pointer() to initialize the 942 * external-to-structure pointer -after- you have completely initialized 943 * the reader-accessible portions of the linked structure. 944 */ 945 #define RCU_INIT_POINTER(p, v) \ 946 do { \ 947 p = (typeof(*v) __force __rcu *)(v); \ 948 } while (0) 949 950 /** 951 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 952 * 953 * GCC-style initialization for an RCU-protected pointer in a structure field. 954 */ 955 #define RCU_POINTER_INITIALIZER(p, v) \ 956 .p = (typeof(*v) __force __rcu *)(v) 957 958 /* 959 * Does the specified offset indicate that the corresponding rcu_head 960 * structure can be handled by kfree_rcu()? 961 */ 962 #define __is_kfree_rcu_offset(offset) ((offset) < 4096) 963 964 /* 965 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain. 966 */ 967 #define __kfree_rcu(head, offset) \ 968 do { \ 969 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \ 970 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \ 971 } while (0) 972 973 /** 974 * kfree_rcu() - kfree an object after a grace period. 975 * @ptr: pointer to kfree 976 * @rcu_head: the name of the struct rcu_head within the type of @ptr. 977 * 978 * Many rcu callbacks functions just call kfree() on the base structure. 979 * These functions are trivial, but their size adds up, and furthermore 980 * when they are used in a kernel module, that module must invoke the 981 * high-latency rcu_barrier() function at module-unload time. 982 * 983 * The kfree_rcu() function handles this issue. Rather than encoding a 984 * function address in the embedded rcu_head structure, kfree_rcu() instead 985 * encodes the offset of the rcu_head structure within the base structure. 986 * Because the functions are not allowed in the low-order 4096 bytes of 987 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 988 * If the offset is larger than 4095 bytes, a compile-time error will 989 * be generated in __kfree_rcu(). If this error is triggered, you can 990 * either fall back to use of call_rcu() or rearrange the structure to 991 * position the rcu_head structure into the first 4096 bytes. 992 * 993 * Note that the allowable offset might decrease in the future, for example, 994 * to allow something like kmem_cache_free_rcu(). 995 * 996 * The BUILD_BUG_ON check must not involve any function calls, hence the 997 * checks are done in macros here. 998 */ 999 #define kfree_rcu(ptr, rcu_head) \ 1000 __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head)) 1001 1002 #endif /* __LINUX_RCUPDATE_H */ 1003