1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Read-Copy Update mechanism for mutual exclusion 4 * 5 * Copyright IBM Corporation, 2001 6 * 7 * Author: Dipankar Sarma <dipankar@in.ibm.com> 8 * 9 * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com> 10 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 11 * Papers: 12 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 13 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 14 * 15 * For detailed explanation of Read-Copy Update mechanism see - 16 * http://lse.sourceforge.net/locking/rcupdate.html 17 * 18 */ 19 20 #ifndef __LINUX_RCUPDATE_H 21 #define __LINUX_RCUPDATE_H 22 23 #include <linux/types.h> 24 #include <linux/compiler.h> 25 #include <linux/atomic.h> 26 #include <linux/irqflags.h> 27 #include <linux/preempt.h> 28 #include <linux/bottom_half.h> 29 #include <linux/lockdep.h> 30 #include <asm/processor.h> 31 #include <linux/cpumask.h> 32 33 #define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b)) 34 #define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b)) 35 #define ulong2long(a) (*(long *)(&(a))) 36 #define USHORT_CMP_GE(a, b) (USHRT_MAX / 2 >= (unsigned short)((a) - (b))) 37 #define USHORT_CMP_LT(a, b) (USHRT_MAX / 2 < (unsigned short)((a) - (b))) 38 39 /* Exported common interfaces */ 40 void call_rcu(struct rcu_head *head, rcu_callback_t func); 41 void rcu_barrier_tasks(void); 42 void rcu_barrier_tasks_rude(void); 43 void synchronize_rcu(void); 44 45 #ifdef CONFIG_PREEMPT_RCU 46 47 void __rcu_read_lock(void); 48 void __rcu_read_unlock(void); 49 50 /* 51 * Defined as a macro as it is a very low level header included from 52 * areas that don't even know about current. This gives the rcu_read_lock() 53 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other 54 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable. 55 */ 56 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting) 57 58 #else /* #ifdef CONFIG_PREEMPT_RCU */ 59 60 #ifdef CONFIG_TINY_RCU 61 #define rcu_read_unlock_strict() do { } while (0) 62 #else 63 void rcu_read_unlock_strict(void); 64 #endif 65 66 static inline void __rcu_read_lock(void) 67 { 68 preempt_disable(); 69 } 70 71 static inline void __rcu_read_unlock(void) 72 { 73 preempt_enable(); 74 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) 75 rcu_read_unlock_strict(); 76 } 77 78 static inline int rcu_preempt_depth(void) 79 { 80 return 0; 81 } 82 83 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 84 85 /* Internal to kernel */ 86 void rcu_init(void); 87 extern int rcu_scheduler_active __read_mostly; 88 void rcu_sched_clock_irq(int user); 89 void rcu_report_dead(unsigned int cpu); 90 void rcutree_migrate_callbacks(int cpu); 91 92 #ifdef CONFIG_TASKS_RCU_GENERIC 93 void rcu_init_tasks_generic(void); 94 #else 95 static inline void rcu_init_tasks_generic(void) { } 96 #endif 97 98 #ifdef CONFIG_RCU_STALL_COMMON 99 void rcu_sysrq_start(void); 100 void rcu_sysrq_end(void); 101 #else /* #ifdef CONFIG_RCU_STALL_COMMON */ 102 static inline void rcu_sysrq_start(void) { } 103 static inline void rcu_sysrq_end(void) { } 104 #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */ 105 106 #ifdef CONFIG_NO_HZ_FULL 107 void rcu_user_enter(void); 108 void rcu_user_exit(void); 109 #else 110 static inline void rcu_user_enter(void) { } 111 static inline void rcu_user_exit(void) { } 112 #endif /* CONFIG_NO_HZ_FULL */ 113 114 #ifdef CONFIG_RCU_NOCB_CPU 115 void rcu_init_nohz(void); 116 int rcu_nocb_cpu_offload(int cpu); 117 int rcu_nocb_cpu_deoffload(int cpu); 118 void rcu_nocb_flush_deferred_wakeup(void); 119 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 120 static inline void rcu_init_nohz(void) { } 121 static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; } 122 static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; } 123 static inline void rcu_nocb_flush_deferred_wakeup(void) { } 124 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 125 126 /** 127 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers 128 * @a: Code that RCU needs to pay attention to. 129 * 130 * RCU read-side critical sections are forbidden in the inner idle loop, 131 * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU 132 * will happily ignore any such read-side critical sections. However, 133 * things like powertop need tracepoints in the inner idle loop. 134 * 135 * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU()) 136 * will tell RCU that it needs to pay attention, invoke its argument 137 * (in this example, calling the do_something_with_RCU() function), 138 * and then tell RCU to go back to ignoring this CPU. It is permissible 139 * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is 140 * on the order of a million or so, even on 32-bit systems). It is 141 * not legal to block within RCU_NONIDLE(), nor is it permissible to 142 * transfer control either into or out of RCU_NONIDLE()'s statement. 143 */ 144 #define RCU_NONIDLE(a) \ 145 do { \ 146 rcu_irq_enter_irqson(); \ 147 do { a; } while (0); \ 148 rcu_irq_exit_irqson(); \ 149 } while (0) 150 151 /* 152 * Note a quasi-voluntary context switch for RCU-tasks's benefit. 153 * This is a macro rather than an inline function to avoid #include hell. 154 */ 155 #ifdef CONFIG_TASKS_RCU_GENERIC 156 157 # ifdef CONFIG_TASKS_RCU 158 # define rcu_tasks_classic_qs(t, preempt) \ 159 do { \ 160 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \ 161 WRITE_ONCE((t)->rcu_tasks_holdout, false); \ 162 } while (0) 163 void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func); 164 void synchronize_rcu_tasks(void); 165 # else 166 # define rcu_tasks_classic_qs(t, preempt) do { } while (0) 167 # define call_rcu_tasks call_rcu 168 # define synchronize_rcu_tasks synchronize_rcu 169 # endif 170 171 # ifdef CONFIG_TASKS_TRACE_RCU 172 # define rcu_tasks_trace_qs(t) \ 173 do { \ 174 if (!likely(READ_ONCE((t)->trc_reader_checked)) && \ 175 !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \ 176 smp_store_release(&(t)->trc_reader_checked, true); \ 177 smp_mb(); /* Readers partitioned by store. */ \ 178 } \ 179 } while (0) 180 # else 181 # define rcu_tasks_trace_qs(t) do { } while (0) 182 # endif 183 184 #define rcu_tasks_qs(t, preempt) \ 185 do { \ 186 rcu_tasks_classic_qs((t), (preempt)); \ 187 rcu_tasks_trace_qs((t)); \ 188 } while (0) 189 190 # ifdef CONFIG_TASKS_RUDE_RCU 191 void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func); 192 void synchronize_rcu_tasks_rude(void); 193 # endif 194 195 #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false) 196 void exit_tasks_rcu_start(void); 197 void exit_tasks_rcu_finish(void); 198 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ 199 #define rcu_tasks_qs(t, preempt) do { } while (0) 200 #define rcu_note_voluntary_context_switch(t) do { } while (0) 201 #define call_rcu_tasks call_rcu 202 #define synchronize_rcu_tasks synchronize_rcu 203 static inline void exit_tasks_rcu_start(void) { } 204 static inline void exit_tasks_rcu_finish(void) { } 205 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ 206 207 /** 208 * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU 209 * 210 * This macro resembles cond_resched(), except that it is defined to 211 * report potential quiescent states to RCU-tasks even if the cond_resched() 212 * machinery were to be shut off, as some advocate for PREEMPTION kernels. 213 */ 214 #define cond_resched_tasks_rcu_qs() \ 215 do { \ 216 rcu_tasks_qs(current, false); \ 217 cond_resched(); \ 218 } while (0) 219 220 /* 221 * Infrastructure to implement the synchronize_() primitives in 222 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU. 223 */ 224 225 #if defined(CONFIG_TREE_RCU) 226 #include <linux/rcutree.h> 227 #elif defined(CONFIG_TINY_RCU) 228 #include <linux/rcutiny.h> 229 #else 230 #error "Unknown RCU implementation specified to kernel configuration" 231 #endif 232 233 /* 234 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls 235 * are needed for dynamic initialization and destruction of rcu_head 236 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for 237 * dynamic initialization and destruction of statically allocated rcu_head 238 * structures. However, rcu_head structures allocated dynamically in the 239 * heap don't need any initialization. 240 */ 241 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 242 void init_rcu_head(struct rcu_head *head); 243 void destroy_rcu_head(struct rcu_head *head); 244 void init_rcu_head_on_stack(struct rcu_head *head); 245 void destroy_rcu_head_on_stack(struct rcu_head *head); 246 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 247 static inline void init_rcu_head(struct rcu_head *head) { } 248 static inline void destroy_rcu_head(struct rcu_head *head) { } 249 static inline void init_rcu_head_on_stack(struct rcu_head *head) { } 250 static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { } 251 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 252 253 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) 254 bool rcu_lockdep_current_cpu_online(void); 255 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 256 static inline bool rcu_lockdep_current_cpu_online(void) { return true; } 257 #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */ 258 259 extern struct lockdep_map rcu_lock_map; 260 extern struct lockdep_map rcu_bh_lock_map; 261 extern struct lockdep_map rcu_sched_lock_map; 262 extern struct lockdep_map rcu_callback_map; 263 264 #ifdef CONFIG_DEBUG_LOCK_ALLOC 265 266 static inline void rcu_lock_acquire(struct lockdep_map *map) 267 { 268 lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); 269 } 270 271 static inline void rcu_lock_release(struct lockdep_map *map) 272 { 273 lock_release(map, _THIS_IP_); 274 } 275 276 int debug_lockdep_rcu_enabled(void); 277 int rcu_read_lock_held(void); 278 int rcu_read_lock_bh_held(void); 279 int rcu_read_lock_sched_held(void); 280 int rcu_read_lock_any_held(void); 281 282 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 283 284 # define rcu_lock_acquire(a) do { } while (0) 285 # define rcu_lock_release(a) do { } while (0) 286 287 static inline int rcu_read_lock_held(void) 288 { 289 return 1; 290 } 291 292 static inline int rcu_read_lock_bh_held(void) 293 { 294 return 1; 295 } 296 297 static inline int rcu_read_lock_sched_held(void) 298 { 299 return !preemptible(); 300 } 301 302 static inline int rcu_read_lock_any_held(void) 303 { 304 return !preemptible(); 305 } 306 307 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 308 309 #ifdef CONFIG_PROVE_RCU 310 311 /** 312 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met 313 * @c: condition to check 314 * @s: informative message 315 */ 316 #define RCU_LOCKDEP_WARN(c, s) \ 317 do { \ 318 static bool __section(".data.unlikely") __warned; \ 319 if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \ 320 __warned = true; \ 321 lockdep_rcu_suspicious(__FILE__, __LINE__, s); \ 322 } \ 323 } while (0) 324 325 #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU) 326 static inline void rcu_preempt_sleep_check(void) 327 { 328 RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map), 329 "Illegal context switch in RCU read-side critical section"); 330 } 331 #else /* #ifdef CONFIG_PROVE_RCU */ 332 static inline void rcu_preempt_sleep_check(void) { } 333 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 334 335 #define rcu_sleep_check() \ 336 do { \ 337 rcu_preempt_sleep_check(); \ 338 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ 339 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \ 340 "Illegal context switch in RCU-bh read-side critical section"); \ 341 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \ 342 "Illegal context switch in RCU-sched read-side critical section"); \ 343 } while (0) 344 345 #else /* #ifdef CONFIG_PROVE_RCU */ 346 347 #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c)) 348 #define rcu_sleep_check() do { } while (0) 349 350 #endif /* #else #ifdef CONFIG_PROVE_RCU */ 351 352 /* 353 * Helper functions for rcu_dereference_check(), rcu_dereference_protected() 354 * and rcu_assign_pointer(). Some of these could be folded into their 355 * callers, but they are left separate in order to ease introduction of 356 * multiple pointers markings to match different RCU implementations 357 * (e.g., __srcu), should this make sense in the future. 358 */ 359 360 #ifdef __CHECKER__ 361 #define rcu_check_sparse(p, space) \ 362 ((void)(((typeof(*p) space *)p) == p)) 363 #else /* #ifdef __CHECKER__ */ 364 #define rcu_check_sparse(p, space) 365 #endif /* #else #ifdef __CHECKER__ */ 366 367 #define __unrcu_pointer(p, local) \ 368 ({ \ 369 typeof(*p) *local = (typeof(*p) *__force)(p); \ 370 rcu_check_sparse(p, __rcu); \ 371 ((typeof(*p) __force __kernel *)(local)); \ 372 }) 373 /** 374 * unrcu_pointer - mark a pointer as not being RCU protected 375 * @p: pointer needing to lose its __rcu property 376 * 377 * Converts @p from an __rcu pointer to a __kernel pointer. 378 * This allows an __rcu pointer to be used with xchg() and friends. 379 */ 380 #define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu)) 381 382 #define __rcu_access_pointer(p, local, space) \ 383 ({ \ 384 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 385 rcu_check_sparse(p, space); \ 386 ((typeof(*p) __force __kernel *)(local)); \ 387 }) 388 #define __rcu_dereference_check(p, local, c, space) \ 389 ({ \ 390 /* Dependency order vs. p above. */ \ 391 typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \ 392 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \ 393 rcu_check_sparse(p, space); \ 394 ((typeof(*p) __force __kernel *)(local)); \ 395 }) 396 #define __rcu_dereference_protected(p, local, c, space) \ 397 ({ \ 398 RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \ 399 rcu_check_sparse(p, space); \ 400 ((typeof(*p) __force __kernel *)(p)); \ 401 }) 402 #define __rcu_dereference_raw(p, local) \ 403 ({ \ 404 /* Dependency order vs. p above. */ \ 405 typeof(p) local = READ_ONCE(p); \ 406 ((typeof(*p) __force __kernel *)(local)); \ 407 }) 408 #define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu)) 409 410 /** 411 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable 412 * @v: The value to statically initialize with. 413 */ 414 #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) 415 416 /** 417 * rcu_assign_pointer() - assign to RCU-protected pointer 418 * @p: pointer to assign to 419 * @v: value to assign (publish) 420 * 421 * Assigns the specified value to the specified RCU-protected 422 * pointer, ensuring that any concurrent RCU readers will see 423 * any prior initialization. 424 * 425 * Inserts memory barriers on architectures that require them 426 * (which is most of them), and also prevents the compiler from 427 * reordering the code that initializes the structure after the pointer 428 * assignment. More importantly, this call documents which pointers 429 * will be dereferenced by RCU read-side code. 430 * 431 * In some special cases, you may use RCU_INIT_POINTER() instead 432 * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due 433 * to the fact that it does not constrain either the CPU or the compiler. 434 * That said, using RCU_INIT_POINTER() when you should have used 435 * rcu_assign_pointer() is a very bad thing that results in 436 * impossible-to-diagnose memory corruption. So please be careful. 437 * See the RCU_INIT_POINTER() comment header for details. 438 * 439 * Note that rcu_assign_pointer() evaluates each of its arguments only 440 * once, appearances notwithstanding. One of the "extra" evaluations 441 * is in typeof() and the other visible only to sparse (__CHECKER__), 442 * neither of which actually execute the argument. As with most cpp 443 * macros, this execute-arguments-only-once property is important, so 444 * please be careful when making changes to rcu_assign_pointer() and the 445 * other macros that it invokes. 446 */ 447 #define rcu_assign_pointer(p, v) \ 448 do { \ 449 uintptr_t _r_a_p__v = (uintptr_t)(v); \ 450 rcu_check_sparse(p, __rcu); \ 451 \ 452 if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL) \ 453 WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ 454 else \ 455 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ 456 } while (0) 457 458 /** 459 * rcu_replace_pointer() - replace an RCU pointer, returning its old value 460 * @rcu_ptr: RCU pointer, whose old value is returned 461 * @ptr: regular pointer 462 * @c: the lockdep conditions under which the dereference will take place 463 * 464 * Perform a replacement, where @rcu_ptr is an RCU-annotated 465 * pointer and @c is the lockdep argument that is passed to the 466 * rcu_dereference_protected() call used to read that pointer. The old 467 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. 468 */ 469 #define rcu_replace_pointer(rcu_ptr, ptr, c) \ 470 ({ \ 471 typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ 472 rcu_assign_pointer((rcu_ptr), (ptr)); \ 473 __tmp; \ 474 }) 475 476 /** 477 * rcu_access_pointer() - fetch RCU pointer with no dereferencing 478 * @p: The pointer to read 479 * 480 * Return the value of the specified RCU-protected pointer, but omit the 481 * lockdep checks for being in an RCU read-side critical section. This is 482 * useful when the value of this pointer is accessed, but the pointer is 483 * not dereferenced, for example, when testing an RCU-protected pointer 484 * against NULL. Although rcu_access_pointer() may also be used in cases 485 * where update-side locks prevent the value of the pointer from changing, 486 * you should instead use rcu_dereference_protected() for this use case. 487 * 488 * It is also permissible to use rcu_access_pointer() when read-side 489 * access to the pointer was removed at least one grace period ago, as 490 * is the case in the context of the RCU callback that is freeing up 491 * the data, or after a synchronize_rcu() returns. This can be useful 492 * when tearing down multi-linked structures after a grace period 493 * has elapsed. 494 */ 495 #define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __rcu) 496 497 /** 498 * rcu_dereference_check() - rcu_dereference with debug checking 499 * @p: The pointer to read, prior to dereferencing 500 * @c: The conditions under which the dereference will take place 501 * 502 * Do an rcu_dereference(), but check that the conditions under which the 503 * dereference will take place are correct. Typically the conditions 504 * indicate the various locking conditions that should be held at that 505 * point. The check should return true if the conditions are satisfied. 506 * An implicit check for being in an RCU read-side critical section 507 * (rcu_read_lock()) is included. 508 * 509 * For example: 510 * 511 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock)); 512 * 513 * could be used to indicate to lockdep that foo->bar may only be dereferenced 514 * if either rcu_read_lock() is held, or that the lock required to replace 515 * the bar struct at foo->bar is held. 516 * 517 * Note that the list of conditions may also include indications of when a lock 518 * need not be held, for example during initialisation or destruction of the 519 * target struct: 520 * 521 * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) || 522 * atomic_read(&foo->usage) == 0); 523 * 524 * Inserts memory barriers on architectures that require them 525 * (currently only the Alpha), prevents the compiler from refetching 526 * (and from merging fetches), and, more importantly, documents exactly 527 * which pointers are protected by RCU and checks that the pointer is 528 * annotated as __rcu. 529 */ 530 #define rcu_dereference_check(p, c) \ 531 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 532 (c) || rcu_read_lock_held(), __rcu) 533 534 /** 535 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking 536 * @p: The pointer to read, prior to dereferencing 537 * @c: The conditions under which the dereference will take place 538 * 539 * This is the RCU-bh counterpart to rcu_dereference_check(). However, 540 * please note that starting in v5.0 kernels, vanilla RCU grace periods 541 * wait for local_bh_disable() regions of code in addition to regions of 542 * code demarked by rcu_read_lock() and rcu_read_unlock(). This means 543 * that synchronize_rcu(), call_rcu, and friends all take not only 544 * rcu_read_lock() but also rcu_read_lock_bh() into account. 545 */ 546 #define rcu_dereference_bh_check(p, c) \ 547 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 548 (c) || rcu_read_lock_bh_held(), __rcu) 549 550 /** 551 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking 552 * @p: The pointer to read, prior to dereferencing 553 * @c: The conditions under which the dereference will take place 554 * 555 * This is the RCU-sched counterpart to rcu_dereference_check(). 556 * However, please note that starting in v5.0 kernels, vanilla RCU grace 557 * periods wait for preempt_disable() regions of code in addition to 558 * regions of code demarked by rcu_read_lock() and rcu_read_unlock(). 559 * This means that synchronize_rcu(), call_rcu, and friends all take not 560 * only rcu_read_lock() but also rcu_read_lock_sched() into account. 561 */ 562 #define rcu_dereference_sched_check(p, c) \ 563 __rcu_dereference_check((p), __UNIQUE_ID(rcu), \ 564 (c) || rcu_read_lock_sched_held(), \ 565 __rcu) 566 567 /* 568 * The tracing infrastructure traces RCU (we want that), but unfortunately 569 * some of the RCU checks causes tracing to lock up the system. 570 * 571 * The no-tracing version of rcu_dereference_raw() must not call 572 * rcu_read_lock_held(). 573 */ 574 #define rcu_dereference_raw_check(p) \ 575 __rcu_dereference_check((p), __UNIQUE_ID(rcu), 1, __rcu) 576 577 /** 578 * rcu_dereference_protected() - fetch RCU pointer when updates prevented 579 * @p: The pointer to read, prior to dereferencing 580 * @c: The conditions under which the dereference will take place 581 * 582 * Return the value of the specified RCU-protected pointer, but omit 583 * the READ_ONCE(). This is useful in cases where update-side locks 584 * prevent the value of the pointer from changing. Please note that this 585 * primitive does *not* prevent the compiler from repeating this reference 586 * or combining it with other references, so it should not be used without 587 * protection of appropriate locks. 588 * 589 * This function is only for update-side use. Using this function 590 * when protected only by rcu_read_lock() will result in infrequent 591 * but very ugly failures. 592 */ 593 #define rcu_dereference_protected(p, c) \ 594 __rcu_dereference_protected((p), __UNIQUE_ID(rcu), (c), __rcu) 595 596 597 /** 598 * rcu_dereference() - fetch RCU-protected pointer for dereferencing 599 * @p: The pointer to read, prior to dereferencing 600 * 601 * This is a simple wrapper around rcu_dereference_check(). 602 */ 603 #define rcu_dereference(p) rcu_dereference_check(p, 0) 604 605 /** 606 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing 607 * @p: The pointer to read, prior to dereferencing 608 * 609 * Makes rcu_dereference_check() do the dirty work. 610 */ 611 #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0) 612 613 /** 614 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing 615 * @p: The pointer to read, prior to dereferencing 616 * 617 * Makes rcu_dereference_check() do the dirty work. 618 */ 619 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0) 620 621 /** 622 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism 623 * @p: The pointer to hand off 624 * 625 * This is simply an identity function, but it documents where a pointer 626 * is handed off from RCU to some other synchronization mechanism, for 627 * example, reference counting or locking. In C11, it would map to 628 * kill_dependency(). It could be used as follows:: 629 * 630 * rcu_read_lock(); 631 * p = rcu_dereference(gp); 632 * long_lived = is_long_lived(p); 633 * if (long_lived) { 634 * if (!atomic_inc_not_zero(p->refcnt)) 635 * long_lived = false; 636 * else 637 * p = rcu_pointer_handoff(p); 638 * } 639 * rcu_read_unlock(); 640 */ 641 #define rcu_pointer_handoff(p) (p) 642 643 /** 644 * rcu_read_lock() - mark the beginning of an RCU read-side critical section 645 * 646 * When synchronize_rcu() is invoked on one CPU while other CPUs 647 * are within RCU read-side critical sections, then the 648 * synchronize_rcu() is guaranteed to block until after all the other 649 * CPUs exit their critical sections. Similarly, if call_rcu() is invoked 650 * on one CPU while other CPUs are within RCU read-side critical 651 * sections, invocation of the corresponding RCU callback is deferred 652 * until after the all the other CPUs exit their critical sections. 653 * 654 * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also 655 * wait for regions of code with preemption disabled, including regions of 656 * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which 657 * define synchronize_sched(), only code enclosed within rcu_read_lock() 658 * and rcu_read_unlock() are guaranteed to be waited for. 659 * 660 * Note, however, that RCU callbacks are permitted to run concurrently 661 * with new RCU read-side critical sections. One way that this can happen 662 * is via the following sequence of events: (1) CPU 0 enters an RCU 663 * read-side critical section, (2) CPU 1 invokes call_rcu() to register 664 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, 665 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU 666 * callback is invoked. This is legal, because the RCU read-side critical 667 * section that was running concurrently with the call_rcu() (and which 668 * therefore might be referencing something that the corresponding RCU 669 * callback would free up) has completed before the corresponding 670 * RCU callback is invoked. 671 * 672 * RCU read-side critical sections may be nested. Any deferred actions 673 * will be deferred until the outermost RCU read-side critical section 674 * completes. 675 * 676 * You can avoid reading and understanding the next paragraph by 677 * following this rule: don't put anything in an rcu_read_lock() RCU 678 * read-side critical section that would block in a !PREEMPTION kernel. 679 * But if you want the full story, read on! 680 * 681 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU), 682 * it is illegal to block while in an RCU read-side critical section. 683 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION 684 * kernel builds, RCU read-side critical sections may be preempted, 685 * but explicit blocking is illegal. Finally, in preemptible RCU 686 * implementations in real-time (with -rt patchset) kernel builds, RCU 687 * read-side critical sections may be preempted and they may also block, but 688 * only when acquiring spinlocks that are subject to priority inheritance. 689 */ 690 static __always_inline void rcu_read_lock(void) 691 { 692 __rcu_read_lock(); 693 __acquire(RCU); 694 rcu_lock_acquire(&rcu_lock_map); 695 RCU_LOCKDEP_WARN(!rcu_is_watching(), 696 "rcu_read_lock() used illegally while idle"); 697 } 698 699 /* 700 * So where is rcu_write_lock()? It does not exist, as there is no 701 * way for writers to lock out RCU readers. This is a feature, not 702 * a bug -- this property is what provides RCU's performance benefits. 703 * Of course, writers must coordinate with each other. The normal 704 * spinlock primitives work well for this, but any other technique may be 705 * used as well. RCU does not care how the writers keep out of each 706 * others' way, as long as they do so. 707 */ 708 709 /** 710 * rcu_read_unlock() - marks the end of an RCU read-side critical section. 711 * 712 * In almost all situations, rcu_read_unlock() is immune from deadlock. 713 * In recent kernels that have consolidated synchronize_sched() and 714 * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity 715 * also extends to the scheduler's runqueue and priority-inheritance 716 * spinlocks, courtesy of the quiescent-state deferral that is carried 717 * out when rcu_read_unlock() is invoked with interrupts disabled. 718 * 719 * See rcu_read_lock() for more information. 720 */ 721 static inline void rcu_read_unlock(void) 722 { 723 RCU_LOCKDEP_WARN(!rcu_is_watching(), 724 "rcu_read_unlock() used illegally while idle"); 725 __release(RCU); 726 __rcu_read_unlock(); 727 rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ 728 } 729 730 /** 731 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section 732 * 733 * This is equivalent to rcu_read_lock(), but also disables softirqs. 734 * Note that anything else that disables softirqs can also serve as an RCU 735 * read-side critical section. However, please note that this equivalence 736 * applies only to v5.0 and later. Before v5.0, rcu_read_lock() and 737 * rcu_read_lock_bh() were unrelated. 738 * 739 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh() 740 * must occur in the same context, for example, it is illegal to invoke 741 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh() 742 * was invoked from some other task. 743 */ 744 static inline void rcu_read_lock_bh(void) 745 { 746 local_bh_disable(); 747 __acquire(RCU_BH); 748 rcu_lock_acquire(&rcu_bh_lock_map); 749 RCU_LOCKDEP_WARN(!rcu_is_watching(), 750 "rcu_read_lock_bh() used illegally while idle"); 751 } 752 753 /** 754 * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section 755 * 756 * See rcu_read_lock_bh() for more information. 757 */ 758 static inline void rcu_read_unlock_bh(void) 759 { 760 RCU_LOCKDEP_WARN(!rcu_is_watching(), 761 "rcu_read_unlock_bh() used illegally while idle"); 762 rcu_lock_release(&rcu_bh_lock_map); 763 __release(RCU_BH); 764 local_bh_enable(); 765 } 766 767 /** 768 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section 769 * 770 * This is equivalent to rcu_read_lock(), but also disables preemption. 771 * Read-side critical sections can also be introduced by anything else that 772 * disables preemption, including local_irq_disable() and friends. However, 773 * please note that the equivalence to rcu_read_lock() applies only to 774 * v5.0 and later. Before v5.0, rcu_read_lock() and rcu_read_lock_sched() 775 * were unrelated. 776 * 777 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched() 778 * must occur in the same context, for example, it is illegal to invoke 779 * rcu_read_unlock_sched() from process context if the matching 780 * rcu_read_lock_sched() was invoked from an NMI handler. 781 */ 782 static inline void rcu_read_lock_sched(void) 783 { 784 preempt_disable(); 785 __acquire(RCU_SCHED); 786 rcu_lock_acquire(&rcu_sched_lock_map); 787 RCU_LOCKDEP_WARN(!rcu_is_watching(), 788 "rcu_read_lock_sched() used illegally while idle"); 789 } 790 791 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 792 static inline notrace void rcu_read_lock_sched_notrace(void) 793 { 794 preempt_disable_notrace(); 795 __acquire(RCU_SCHED); 796 } 797 798 /** 799 * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section 800 * 801 * See rcu_read_lock_sched() for more information. 802 */ 803 static inline void rcu_read_unlock_sched(void) 804 { 805 RCU_LOCKDEP_WARN(!rcu_is_watching(), 806 "rcu_read_unlock_sched() used illegally while idle"); 807 rcu_lock_release(&rcu_sched_lock_map); 808 __release(RCU_SCHED); 809 preempt_enable(); 810 } 811 812 /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ 813 static inline notrace void rcu_read_unlock_sched_notrace(void) 814 { 815 __release(RCU_SCHED); 816 preempt_enable_notrace(); 817 } 818 819 /** 820 * RCU_INIT_POINTER() - initialize an RCU protected pointer 821 * @p: The pointer to be initialized. 822 * @v: The value to initialized the pointer to. 823 * 824 * Initialize an RCU-protected pointer in special cases where readers 825 * do not need ordering constraints on the CPU or the compiler. These 826 * special cases are: 827 * 828 * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer *or* 829 * 2. The caller has taken whatever steps are required to prevent 830 * RCU readers from concurrently accessing this pointer *or* 831 * 3. The referenced data structure has already been exposed to 832 * readers either at compile time or via rcu_assign_pointer() *and* 833 * 834 * a. You have not made *any* reader-visible changes to 835 * this structure since then *or* 836 * b. It is OK for readers accessing this structure from its 837 * new location to see the old state of the structure. (For 838 * example, the changes were to statistical counters or to 839 * other state where exact synchronization is not required.) 840 * 841 * Failure to follow these rules governing use of RCU_INIT_POINTER() will 842 * result in impossible-to-diagnose memory corruption. As in the structures 843 * will look OK in crash dumps, but any concurrent RCU readers might 844 * see pre-initialized values of the referenced data structure. So 845 * please be very careful how you use RCU_INIT_POINTER()!!! 846 * 847 * If you are creating an RCU-protected linked structure that is accessed 848 * by a single external-to-structure RCU-protected pointer, then you may 849 * use RCU_INIT_POINTER() to initialize the internal RCU-protected 850 * pointers, but you must use rcu_assign_pointer() to initialize the 851 * external-to-structure pointer *after* you have completely initialized 852 * the reader-accessible portions of the linked structure. 853 * 854 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no 855 * ordering guarantees for either the CPU or the compiler. 856 */ 857 #define RCU_INIT_POINTER(p, v) \ 858 do { \ 859 rcu_check_sparse(p, __rcu); \ 860 WRITE_ONCE(p, RCU_INITIALIZER(v)); \ 861 } while (0) 862 863 /** 864 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer 865 * @p: The pointer to be initialized. 866 * @v: The value to initialized the pointer to. 867 * 868 * GCC-style initialization for an RCU-protected pointer in a structure field. 869 */ 870 #define RCU_POINTER_INITIALIZER(p, v) \ 871 .p = RCU_INITIALIZER(v) 872 873 /* 874 * Does the specified offset indicate that the corresponding rcu_head 875 * structure can be handled by kvfree_rcu()? 876 */ 877 #define __is_kvfree_rcu_offset(offset) ((offset) < 4096) 878 879 /** 880 * kfree_rcu() - kfree an object after a grace period. 881 * @ptr: pointer to kfree for both single- and double-argument invocations. 882 * @rhf: the name of the struct rcu_head within the type of @ptr, 883 * but only for double-argument invocations. 884 * 885 * Many rcu callbacks functions just call kfree() on the base structure. 886 * These functions are trivial, but their size adds up, and furthermore 887 * when they are used in a kernel module, that module must invoke the 888 * high-latency rcu_barrier() function at module-unload time. 889 * 890 * The kfree_rcu() function handles this issue. Rather than encoding a 891 * function address in the embedded rcu_head structure, kfree_rcu() instead 892 * encodes the offset of the rcu_head structure within the base structure. 893 * Because the functions are not allowed in the low-order 4096 bytes of 894 * kernel virtual memory, offsets up to 4095 bytes can be accommodated. 895 * If the offset is larger than 4095 bytes, a compile-time error will 896 * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can 897 * either fall back to use of call_rcu() or rearrange the structure to 898 * position the rcu_head structure into the first 4096 bytes. 899 * 900 * Note that the allowable offset might decrease in the future, for example, 901 * to allow something like kmem_cache_free_rcu(). 902 * 903 * The BUILD_BUG_ON check must not involve any function calls, hence the 904 * checks are done in macros here. 905 */ 906 #define kfree_rcu(ptr, rhf...) kvfree_rcu(ptr, ## rhf) 907 908 /** 909 * kvfree_rcu() - kvfree an object after a grace period. 910 * 911 * This macro consists of one or two arguments and it is 912 * based on whether an object is head-less or not. If it 913 * has a head then a semantic stays the same as it used 914 * to be before: 915 * 916 * kvfree_rcu(ptr, rhf); 917 * 918 * where @ptr is a pointer to kvfree(), @rhf is the name 919 * of the rcu_head structure within the type of @ptr. 920 * 921 * When it comes to head-less variant, only one argument 922 * is passed and that is just a pointer which has to be 923 * freed after a grace period. Therefore the semantic is 924 * 925 * kvfree_rcu(ptr); 926 * 927 * where @ptr is a pointer to kvfree(). 928 * 929 * Please note, head-less way of freeing is permitted to 930 * use from a context that has to follow might_sleep() 931 * annotation. Otherwise, please switch and embed the 932 * rcu_head structure within the type of @ptr. 933 */ 934 #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__, \ 935 kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__) 936 937 #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME 938 #define kvfree_rcu_arg_2(ptr, rhf) \ 939 do { \ 940 typeof (ptr) ___p = (ptr); \ 941 \ 942 if (___p) { \ 943 BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf))); \ 944 kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long) \ 945 (offsetof(typeof(*(ptr)), rhf))); \ 946 } \ 947 } while (0) 948 949 #define kvfree_rcu_arg_1(ptr) \ 950 do { \ 951 typeof(ptr) ___p = (ptr); \ 952 \ 953 if (___p) \ 954 kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \ 955 } while (0) 956 957 /* 958 * Place this after a lock-acquisition primitive to guarantee that 959 * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies 960 * if the UNLOCK and LOCK are executed by the same CPU or if the 961 * UNLOCK and LOCK operate on the same lock variable. 962 */ 963 #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE 964 #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ 965 #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 966 #define smp_mb__after_unlock_lock() do { } while (0) 967 #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */ 968 969 970 /* Has the specified rcu_head structure been handed to call_rcu()? */ 971 972 /** 973 * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu() 974 * @rhp: The rcu_head structure to initialize. 975 * 976 * If you intend to invoke rcu_head_after_call_rcu() to test whether a 977 * given rcu_head structure has already been passed to call_rcu(), then 978 * you must also invoke this rcu_head_init() function on it just after 979 * allocating that structure. Calls to this function must not race with 980 * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation. 981 */ 982 static inline void rcu_head_init(struct rcu_head *rhp) 983 { 984 rhp->func = (rcu_callback_t)~0L; 985 } 986 987 /** 988 * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()? 989 * @rhp: The rcu_head structure to test. 990 * @f: The function passed to call_rcu() along with @rhp. 991 * 992 * Returns @true if the @rhp has been passed to call_rcu() with @func, 993 * and @false otherwise. Emits a warning in any other case, including 994 * the case where @rhp has already been invoked after a grace period. 995 * Calls to this function must not race with callback invocation. One way 996 * to avoid such races is to enclose the call to rcu_head_after_call_rcu() 997 * in an RCU read-side critical section that includes a read-side fetch 998 * of the pointer to the structure containing @rhp. 999 */ 1000 static inline bool 1001 rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f) 1002 { 1003 rcu_callback_t func = READ_ONCE(rhp->func); 1004 1005 if (func == f) 1006 return true; 1007 WARN_ON_ONCE(func != (rcu_callback_t)~0L); 1008 return false; 1009 } 1010 1011 /* kernel/ksysfs.c definitions */ 1012 extern int rcu_expedited; 1013 extern int rcu_normal; 1014 1015 #endif /* __LINUX_RCUPDATE_H */ 1016