1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Read-Copy Update definitions shared among RCU implementations. 4 * 5 * Copyright IBM Corporation, 2011 6 * 7 * Author: Paul E. McKenney <paulmck@linux.ibm.com> 8 */ 9 10 #ifndef __LINUX_RCU_H 11 #define __LINUX_RCU_H 12 13 #include <trace/events/rcu.h> 14 15 /* Offset to allow distinguishing irq vs. task-based idle entry/exit. */ 16 #define DYNTICK_IRQ_NONIDLE ((LONG_MAX / 2) + 1) 17 18 19 /* 20 * Grace-period counter management. 21 */ 22 23 #define RCU_SEQ_CTR_SHIFT 2 24 #define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1) 25 26 extern int sysctl_sched_rt_runtime; 27 28 /* 29 * Return the counter portion of a sequence number previously returned 30 * by rcu_seq_snap() or rcu_seq_current(). 31 */ 32 static inline unsigned long rcu_seq_ctr(unsigned long s) 33 { 34 return s >> RCU_SEQ_CTR_SHIFT; 35 } 36 37 /* 38 * Return the state portion of a sequence number previously returned 39 * by rcu_seq_snap() or rcu_seq_current(). 40 */ 41 static inline int rcu_seq_state(unsigned long s) 42 { 43 return s & RCU_SEQ_STATE_MASK; 44 } 45 46 /* 47 * Set the state portion of the pointed-to sequence number. 48 * The caller is responsible for preventing conflicting updates. 49 */ 50 static inline void rcu_seq_set_state(unsigned long *sp, int newstate) 51 { 52 WARN_ON_ONCE(newstate & ~RCU_SEQ_STATE_MASK); 53 WRITE_ONCE(*sp, (*sp & ~RCU_SEQ_STATE_MASK) + newstate); 54 } 55 56 /* Adjust sequence number for start of update-side operation. */ 57 static inline void rcu_seq_start(unsigned long *sp) 58 { 59 WRITE_ONCE(*sp, *sp + 1); 60 smp_mb(); /* Ensure update-side operation after counter increment. */ 61 WARN_ON_ONCE(rcu_seq_state(*sp) != 1); 62 } 63 64 /* Compute the end-of-grace-period value for the specified sequence number. */ 65 static inline unsigned long rcu_seq_endval(unsigned long *sp) 66 { 67 return (*sp | RCU_SEQ_STATE_MASK) + 1; 68 } 69 70 /* Adjust sequence number for end of update-side operation. */ 71 static inline void rcu_seq_end(unsigned long *sp) 72 { 73 smp_mb(); /* Ensure update-side operation before counter increment. */ 74 WARN_ON_ONCE(!rcu_seq_state(*sp)); 75 WRITE_ONCE(*sp, rcu_seq_endval(sp)); 76 } 77 78 /* 79 * rcu_seq_snap - Take a snapshot of the update side's sequence number. 80 * 81 * This function returns the earliest value of the grace-period sequence number 82 * that will indicate that a full grace period has elapsed since the current 83 * time. Once the grace-period sequence number has reached this value, it will 84 * be safe to invoke all callbacks that have been registered prior to the 85 * current time. This value is the current grace-period number plus two to the 86 * power of the number of low-order bits reserved for state, then rounded up to 87 * the next value in which the state bits are all zero. 88 */ 89 static inline unsigned long rcu_seq_snap(unsigned long *sp) 90 { 91 unsigned long s; 92 93 s = (READ_ONCE(*sp) + 2 * RCU_SEQ_STATE_MASK + 1) & ~RCU_SEQ_STATE_MASK; 94 smp_mb(); /* Above access must not bleed into critical section. */ 95 return s; 96 } 97 98 /* Return the current value the update side's sequence number, no ordering. */ 99 static inline unsigned long rcu_seq_current(unsigned long *sp) 100 { 101 return READ_ONCE(*sp); 102 } 103 104 /* 105 * Given a snapshot from rcu_seq_snap(), determine whether or not the 106 * corresponding update-side operation has started. 107 */ 108 static inline bool rcu_seq_started(unsigned long *sp, unsigned long s) 109 { 110 return ULONG_CMP_LT((s - 1) & ~RCU_SEQ_STATE_MASK, READ_ONCE(*sp)); 111 } 112 113 /* 114 * Given a snapshot from rcu_seq_snap(), determine whether or not a 115 * full update-side operation has occurred. 116 */ 117 static inline bool rcu_seq_done(unsigned long *sp, unsigned long s) 118 { 119 return ULONG_CMP_GE(READ_ONCE(*sp), s); 120 } 121 122 /* 123 * Has a grace period completed since the time the old gp_seq was collected? 124 */ 125 static inline bool rcu_seq_completed_gp(unsigned long old, unsigned long new) 126 { 127 return ULONG_CMP_LT(old, new & ~RCU_SEQ_STATE_MASK); 128 } 129 130 /* 131 * Has a grace period started since the time the old gp_seq was collected? 132 */ 133 static inline bool rcu_seq_new_gp(unsigned long old, unsigned long new) 134 { 135 return ULONG_CMP_LT((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK, 136 new); 137 } 138 139 /* 140 * Roughly how many full grace periods have elapsed between the collection 141 * of the two specified grace periods? 142 */ 143 static inline unsigned long rcu_seq_diff(unsigned long new, unsigned long old) 144 { 145 unsigned long rnd_diff; 146 147 if (old == new) 148 return 0; 149 /* 150 * Compute the number of grace periods (still shifted up), plus 151 * one if either of new and old is not an exact grace period. 152 */ 153 rnd_diff = (new & ~RCU_SEQ_STATE_MASK) - 154 ((old + RCU_SEQ_STATE_MASK) & ~RCU_SEQ_STATE_MASK) + 155 ((new & RCU_SEQ_STATE_MASK) || (old & RCU_SEQ_STATE_MASK)); 156 if (ULONG_CMP_GE(RCU_SEQ_STATE_MASK, rnd_diff)) 157 return 1; /* Definitely no grace period has elapsed. */ 158 return ((rnd_diff - RCU_SEQ_STATE_MASK - 1) >> RCU_SEQ_CTR_SHIFT) + 2; 159 } 160 161 /* 162 * debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally 163 * by call_rcu() and rcu callback execution, and are therefore not part 164 * of the RCU API. These are in rcupdate.h because they are used by all 165 * RCU implementations. 166 */ 167 168 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 169 # define STATE_RCU_HEAD_READY 0 170 # define STATE_RCU_HEAD_QUEUED 1 171 172 extern const struct debug_obj_descr rcuhead_debug_descr; 173 174 static inline int debug_rcu_head_queue(struct rcu_head *head) 175 { 176 int r1; 177 178 r1 = debug_object_activate(head, &rcuhead_debug_descr); 179 debug_object_active_state(head, &rcuhead_debug_descr, 180 STATE_RCU_HEAD_READY, 181 STATE_RCU_HEAD_QUEUED); 182 return r1; 183 } 184 185 static inline void debug_rcu_head_unqueue(struct rcu_head *head) 186 { 187 debug_object_active_state(head, &rcuhead_debug_descr, 188 STATE_RCU_HEAD_QUEUED, 189 STATE_RCU_HEAD_READY); 190 debug_object_deactivate(head, &rcuhead_debug_descr); 191 } 192 #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 193 static inline int debug_rcu_head_queue(struct rcu_head *head) 194 { 195 return 0; 196 } 197 198 static inline void debug_rcu_head_unqueue(struct rcu_head *head) 199 { 200 } 201 #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 202 203 extern int rcu_cpu_stall_suppress_at_boot; 204 205 static inline bool rcu_stall_is_suppressed_at_boot(void) 206 { 207 return rcu_cpu_stall_suppress_at_boot && !rcu_inkernel_boot_has_ended(); 208 } 209 210 #ifdef CONFIG_RCU_STALL_COMMON 211 212 extern int rcu_cpu_stall_ftrace_dump; 213 extern int rcu_cpu_stall_suppress; 214 extern int rcu_cpu_stall_timeout; 215 extern int rcu_exp_cpu_stall_timeout; 216 int rcu_jiffies_till_stall_check(void); 217 int rcu_exp_jiffies_till_stall_check(void); 218 219 static inline bool rcu_stall_is_suppressed(void) 220 { 221 return rcu_stall_is_suppressed_at_boot() || rcu_cpu_stall_suppress; 222 } 223 224 #define rcu_ftrace_dump_stall_suppress() \ 225 do { \ 226 if (!rcu_cpu_stall_suppress) \ 227 rcu_cpu_stall_suppress = 3; \ 228 } while (0) 229 230 #define rcu_ftrace_dump_stall_unsuppress() \ 231 do { \ 232 if (rcu_cpu_stall_suppress == 3) \ 233 rcu_cpu_stall_suppress = 0; \ 234 } while (0) 235 236 #else /* #endif #ifdef CONFIG_RCU_STALL_COMMON */ 237 238 static inline bool rcu_stall_is_suppressed(void) 239 { 240 return rcu_stall_is_suppressed_at_boot(); 241 } 242 #define rcu_ftrace_dump_stall_suppress() 243 #define rcu_ftrace_dump_stall_unsuppress() 244 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ 245 246 /* 247 * Strings used in tracepoints need to be exported via the 248 * tracing system such that tools like perf and trace-cmd can 249 * translate the string address pointers to actual text. 250 */ 251 #define TPS(x) tracepoint_string(x) 252 253 /* 254 * Dump the ftrace buffer, but only one time per callsite per boot. 255 */ 256 #define rcu_ftrace_dump(oops_dump_mode) \ 257 do { \ 258 static atomic_t ___rfd_beenhere = ATOMIC_INIT(0); \ 259 \ 260 if (!atomic_read(&___rfd_beenhere) && \ 261 !atomic_xchg(&___rfd_beenhere, 1)) { \ 262 tracing_off(); \ 263 rcu_ftrace_dump_stall_suppress(); \ 264 ftrace_dump(oops_dump_mode); \ 265 rcu_ftrace_dump_stall_unsuppress(); \ 266 } \ 267 } while (0) 268 269 void rcu_early_boot_tests(void); 270 void rcu_test_sync_prims(void); 271 272 /* 273 * This function really isn't for public consumption, but RCU is special in 274 * that context switches can allow the state machine to make progress. 275 */ 276 extern void resched_cpu(int cpu); 277 278 #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) 279 280 #include <linux/rcu_node_tree.h> 281 282 extern int rcu_num_lvls; 283 extern int num_rcu_lvl[]; 284 extern int rcu_num_nodes; 285 static bool rcu_fanout_exact; 286 static int rcu_fanout_leaf; 287 288 /* 289 * Compute the per-level fanout, either using the exact fanout specified 290 * or balancing the tree, depending on the rcu_fanout_exact boot parameter. 291 */ 292 static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) 293 { 294 int i; 295 296 for (i = 0; i < RCU_NUM_LVLS; i++) 297 levelspread[i] = INT_MIN; 298 if (rcu_fanout_exact) { 299 levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf; 300 for (i = rcu_num_lvls - 2; i >= 0; i--) 301 levelspread[i] = RCU_FANOUT; 302 } else { 303 int ccur; 304 int cprv; 305 306 cprv = nr_cpu_ids; 307 for (i = rcu_num_lvls - 1; i >= 0; i--) { 308 ccur = levelcnt[i]; 309 levelspread[i] = (cprv + ccur - 1) / ccur; 310 cprv = ccur; 311 } 312 } 313 } 314 315 extern void rcu_init_geometry(void); 316 317 /* Returns a pointer to the first leaf rcu_node structure. */ 318 #define rcu_first_leaf_node() (rcu_state.level[rcu_num_lvls - 1]) 319 320 /* Is this rcu_node a leaf? */ 321 #define rcu_is_leaf_node(rnp) ((rnp)->level == rcu_num_lvls - 1) 322 323 /* Is this rcu_node the last leaf? */ 324 #define rcu_is_last_leaf_node(rnp) ((rnp) == &rcu_state.node[rcu_num_nodes - 1]) 325 326 /* 327 * Do a full breadth-first scan of the {s,}rcu_node structures for the 328 * specified state structure (for SRCU) or the only rcu_state structure 329 * (for RCU). 330 */ 331 #define srcu_for_each_node_breadth_first(sp, rnp) \ 332 for ((rnp) = &(sp)->node[0]; \ 333 (rnp) < &(sp)->node[rcu_num_nodes]; (rnp)++) 334 #define rcu_for_each_node_breadth_first(rnp) \ 335 srcu_for_each_node_breadth_first(&rcu_state, rnp) 336 337 /* 338 * Scan the leaves of the rcu_node hierarchy for the rcu_state structure. 339 * Note that if there is a singleton rcu_node tree with but one rcu_node 340 * structure, this loop -will- visit the rcu_node structure. It is still 341 * a leaf node, even if it is also the root node. 342 */ 343 #define rcu_for_each_leaf_node(rnp) \ 344 for ((rnp) = rcu_first_leaf_node(); \ 345 (rnp) < &rcu_state.node[rcu_num_nodes]; (rnp)++) 346 347 /* 348 * Iterate over all possible CPUs in a leaf RCU node. 349 */ 350 #define for_each_leaf_node_possible_cpu(rnp, cpu) \ 351 for (WARN_ON_ONCE(!rcu_is_leaf_node(rnp)), \ 352 (cpu) = cpumask_next((rnp)->grplo - 1, cpu_possible_mask); \ 353 (cpu) <= rnp->grphi; \ 354 (cpu) = cpumask_next((cpu), cpu_possible_mask)) 355 356 /* 357 * Iterate over all CPUs in a leaf RCU node's specified mask. 358 */ 359 #define rcu_find_next_bit(rnp, cpu, mask) \ 360 ((rnp)->grplo + find_next_bit(&(mask), BITS_PER_LONG, (cpu))) 361 #define for_each_leaf_node_cpu_mask(rnp, cpu, mask) \ 362 for (WARN_ON_ONCE(!rcu_is_leaf_node(rnp)), \ 363 (cpu) = rcu_find_next_bit((rnp), 0, (mask)); \ 364 (cpu) <= rnp->grphi; \ 365 (cpu) = rcu_find_next_bit((rnp), (cpu) + 1 - (rnp->grplo), (mask))) 366 367 /* 368 * Wrappers for the rcu_node::lock acquire and release. 369 * 370 * Because the rcu_nodes form a tree, the tree traversal locking will observe 371 * different lock values, this in turn means that an UNLOCK of one level 372 * followed by a LOCK of another level does not imply a full memory barrier; 373 * and most importantly transitivity is lost. 374 * 375 * In order to restore full ordering between tree levels, augment the regular 376 * lock acquire functions with smp_mb__after_unlock_lock(). 377 * 378 * As ->lock of struct rcu_node is a __private field, therefore one should use 379 * these wrappers rather than directly call raw_spin_{lock,unlock}* on ->lock. 380 */ 381 #define raw_spin_lock_rcu_node(p) \ 382 do { \ 383 raw_spin_lock(&ACCESS_PRIVATE(p, lock)); \ 384 smp_mb__after_unlock_lock(); \ 385 } while (0) 386 387 #define raw_spin_unlock_rcu_node(p) \ 388 do { \ 389 lockdep_assert_irqs_disabled(); \ 390 raw_spin_unlock(&ACCESS_PRIVATE(p, lock)); \ 391 } while (0) 392 393 #define raw_spin_lock_irq_rcu_node(p) \ 394 do { \ 395 raw_spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ 396 smp_mb__after_unlock_lock(); \ 397 } while (0) 398 399 #define raw_spin_unlock_irq_rcu_node(p) \ 400 do { \ 401 lockdep_assert_irqs_disabled(); \ 402 raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)); \ 403 } while (0) 404 405 #define raw_spin_lock_irqsave_rcu_node(p, flags) \ 406 do { \ 407 raw_spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ 408 smp_mb__after_unlock_lock(); \ 409 } while (0) 410 411 #define raw_spin_unlock_irqrestore_rcu_node(p, flags) \ 412 do { \ 413 lockdep_assert_irqs_disabled(); \ 414 raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags); \ 415 } while (0) 416 417 #define raw_spin_trylock_rcu_node(p) \ 418 ({ \ 419 bool ___locked = raw_spin_trylock(&ACCESS_PRIVATE(p, lock)); \ 420 \ 421 if (___locked) \ 422 smp_mb__after_unlock_lock(); \ 423 ___locked; \ 424 }) 425 426 #define raw_lockdep_assert_held_rcu_node(p) \ 427 lockdep_assert_held(&ACCESS_PRIVATE(p, lock)) 428 429 #endif /* #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) */ 430 431 #ifdef CONFIG_TINY_RCU 432 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */ 433 static inline bool rcu_gp_is_normal(void) { return true; } 434 static inline bool rcu_gp_is_expedited(void) { return false; } 435 static inline void rcu_expedite_gp(void) { } 436 static inline void rcu_unexpedite_gp(void) { } 437 static inline void rcu_request_urgent_qs_task(struct task_struct *t) { } 438 #else /* #ifdef CONFIG_TINY_RCU */ 439 bool rcu_gp_is_normal(void); /* Internal RCU use. */ 440 bool rcu_gp_is_expedited(void); /* Internal RCU use. */ 441 void rcu_expedite_gp(void); 442 void rcu_unexpedite_gp(void); 443 void rcupdate_announce_bootup_oddness(void); 444 #ifdef CONFIG_TASKS_RCU_GENERIC 445 void show_rcu_tasks_gp_kthreads(void); 446 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ 447 static inline void show_rcu_tasks_gp_kthreads(void) {} 448 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ 449 void rcu_request_urgent_qs_task(struct task_struct *t); 450 #endif /* #else #ifdef CONFIG_TINY_RCU */ 451 452 #define RCU_SCHEDULER_INACTIVE 0 453 #define RCU_SCHEDULER_INIT 1 454 #define RCU_SCHEDULER_RUNNING 2 455 456 enum rcutorture_type { 457 RCU_FLAVOR, 458 RCU_TASKS_FLAVOR, 459 RCU_TASKS_RUDE_FLAVOR, 460 RCU_TASKS_TRACING_FLAVOR, 461 RCU_TRIVIAL_FLAVOR, 462 SRCU_FLAVOR, 463 INVALID_RCU_FLAVOR 464 }; 465 466 #if defined(CONFIG_TREE_RCU) 467 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, 468 unsigned long *gp_seq); 469 void do_trace_rcu_torture_read(const char *rcutorturename, 470 struct rcu_head *rhp, 471 unsigned long secs, 472 unsigned long c_old, 473 unsigned long c); 474 void rcu_gp_set_torture_wait(int duration); 475 #else 476 static inline void rcutorture_get_gp_data(enum rcutorture_type test_type, 477 int *flags, unsigned long *gp_seq) 478 { 479 *flags = 0; 480 *gp_seq = 0; 481 } 482 #ifdef CONFIG_RCU_TRACE 483 void do_trace_rcu_torture_read(const char *rcutorturename, 484 struct rcu_head *rhp, 485 unsigned long secs, 486 unsigned long c_old, 487 unsigned long c); 488 #else 489 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ 490 do { } while (0) 491 #endif 492 static inline void rcu_gp_set_torture_wait(int duration) { } 493 #endif 494 495 #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) 496 long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask); 497 #endif 498 499 #ifdef CONFIG_TINY_SRCU 500 501 static inline void srcutorture_get_gp_data(enum rcutorture_type test_type, 502 struct srcu_struct *sp, int *flags, 503 unsigned long *gp_seq) 504 { 505 if (test_type != SRCU_FLAVOR) 506 return; 507 *flags = 0; 508 *gp_seq = sp->srcu_idx; 509 } 510 511 #elif defined(CONFIG_TREE_SRCU) 512 513 void srcutorture_get_gp_data(enum rcutorture_type test_type, 514 struct srcu_struct *sp, int *flags, 515 unsigned long *gp_seq); 516 517 #endif 518 519 #ifdef CONFIG_TINY_RCU 520 static inline bool rcu_dynticks_zero_in_eqs(int cpu, int *vp) { return false; } 521 static inline unsigned long rcu_get_gp_seq(void) { return 0; } 522 static inline unsigned long rcu_exp_batches_completed(void) { return 0; } 523 static inline unsigned long 524 srcu_batches_completed(struct srcu_struct *sp) { return 0; } 525 static inline void rcu_force_quiescent_state(void) { } 526 static inline bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) { return true; } 527 static inline void show_rcu_gp_kthreads(void) { } 528 static inline int rcu_get_gp_kthreads_prio(void) { return 0; } 529 static inline void rcu_fwd_progress_check(unsigned long j) { } 530 static inline void rcu_gp_slow_register(atomic_t *rgssp) { } 531 static inline void rcu_gp_slow_unregister(atomic_t *rgssp) { } 532 #else /* #ifdef CONFIG_TINY_RCU */ 533 bool rcu_dynticks_zero_in_eqs(int cpu, int *vp); 534 unsigned long rcu_get_gp_seq(void); 535 unsigned long rcu_exp_batches_completed(void); 536 unsigned long srcu_batches_completed(struct srcu_struct *sp); 537 bool rcu_check_boost_fail(unsigned long gp_state, int *cpup); 538 void show_rcu_gp_kthreads(void); 539 int rcu_get_gp_kthreads_prio(void); 540 void rcu_fwd_progress_check(unsigned long j); 541 void rcu_force_quiescent_state(void); 542 extern struct workqueue_struct *rcu_gp_wq; 543 #ifdef CONFIG_RCU_EXP_KTHREAD 544 extern struct kthread_worker *rcu_exp_gp_kworker; 545 extern struct kthread_worker *rcu_exp_par_gp_kworker; 546 #else /* !CONFIG_RCU_EXP_KTHREAD */ 547 extern struct workqueue_struct *rcu_par_gp_wq; 548 #endif /* CONFIG_RCU_EXP_KTHREAD */ 549 void rcu_gp_slow_register(atomic_t *rgssp); 550 void rcu_gp_slow_unregister(atomic_t *rgssp); 551 #endif /* #else #ifdef CONFIG_TINY_RCU */ 552 553 #ifdef CONFIG_RCU_NOCB_CPU 554 void rcu_bind_current_to_nocb(void); 555 #else 556 static inline void rcu_bind_current_to_nocb(void) { } 557 #endif 558 559 #if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_RCU) 560 void show_rcu_tasks_classic_gp_kthread(void); 561 #else 562 static inline void show_rcu_tasks_classic_gp_kthread(void) {} 563 #endif 564 #if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_RUDE_RCU) 565 void show_rcu_tasks_rude_gp_kthread(void); 566 #else 567 static inline void show_rcu_tasks_rude_gp_kthread(void) {} 568 #endif 569 #if !defined(CONFIG_TINY_RCU) && defined(CONFIG_TASKS_TRACE_RCU) 570 void show_rcu_tasks_trace_gp_kthread(void); 571 #else 572 static inline void show_rcu_tasks_trace_gp_kthread(void) {} 573 #endif 574 575 #endif /* __LINUX_RCU_H */ 576