1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Read-Copy Update mechanism for mutual exclusion (tree-based version) 4 * Internal non-public definitions. 5 * 6 * Copyright IBM Corporation, 2008 7 * 8 * Author: Ingo Molnar <mingo@elte.hu> 9 * Paul E. McKenney <paulmck@linux.ibm.com> 10 */ 11 12 #include <linux/cache.h> 13 #include <linux/spinlock.h> 14 #include <linux/rtmutex.h> 15 #include <linux/threads.h> 16 #include <linux/cpumask.h> 17 #include <linux/seqlock.h> 18 #include <linux/swait.h> 19 #include <linux/stop_machine.h> 20 #include <linux/rcu_node_tree.h> 21 22 #include "rcu_segcblist.h" 23 24 /* Communicate arguments to a workqueue handler. */ 25 struct rcu_exp_work { 26 unsigned long rew_s; 27 struct work_struct rew_work; 28 }; 29 30 /* RCU's kthread states for tracing. */ 31 #define RCU_KTHREAD_STOPPED 0 32 #define RCU_KTHREAD_RUNNING 1 33 #define RCU_KTHREAD_WAITING 2 34 #define RCU_KTHREAD_OFFCPU 3 35 #define RCU_KTHREAD_YIELDING 4 36 #define RCU_KTHREAD_MAX 4 37 38 /* 39 * Definition for node within the RCU grace-period-detection hierarchy. 40 */ 41 struct rcu_node { 42 raw_spinlock_t __private lock; /* Root rcu_node's lock protects */ 43 /* some rcu_state fields as well as */ 44 /* following. */ 45 unsigned long gp_seq; /* Track rsp->rcu_gp_seq. */ 46 unsigned long gp_seq_needed; /* Track furthest future GP request. */ 47 unsigned long completedqs; /* All QSes done for this node. */ 48 unsigned long qsmask; /* CPUs or groups that need to switch in */ 49 /* order for current grace period to proceed.*/ 50 /* In leaf rcu_node, each bit corresponds to */ 51 /* an rcu_data structure, otherwise, each */ 52 /* bit corresponds to a child rcu_node */ 53 /* structure. */ 54 unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */ 55 unsigned long qsmaskinit; 56 /* Per-GP initial value for qsmask. */ 57 /* Initialized from ->qsmaskinitnext at the */ 58 /* beginning of each grace period. */ 59 unsigned long qsmaskinitnext; 60 /* Online CPUs for next grace period. */ 61 unsigned long expmask; /* CPUs or groups that need to check in */ 62 /* to allow the current expedited GP */ 63 /* to complete. */ 64 unsigned long expmaskinit; 65 /* Per-GP initial values for expmask. */ 66 /* Initialized from ->expmaskinitnext at the */ 67 /* beginning of each expedited GP. */ 68 unsigned long expmaskinitnext; 69 /* Online CPUs for next expedited GP. */ 70 /* Any CPU that has ever been online will */ 71 /* have its bit set. */ 72 unsigned long ffmask; /* Fully functional CPUs. */ 73 unsigned long grpmask; /* Mask to apply to parent qsmask. */ 74 /* Only one bit will be set in this mask. */ 75 int grplo; /* lowest-numbered CPU or group here. */ 76 int grphi; /* highest-numbered CPU or group here. */ 77 u8 grpnum; /* CPU/group number for next level up. */ 78 u8 level; /* root is at level 0. */ 79 bool wait_blkd_tasks;/* Necessary to wait for blocked tasks to */ 80 /* exit RCU read-side critical sections */ 81 /* before propagating offline up the */ 82 /* rcu_node tree? */ 83 struct rcu_node *parent; 84 struct list_head blkd_tasks; 85 /* Tasks blocked in RCU read-side critical */ 86 /* section. Tasks are placed at the head */ 87 /* of this list and age towards the tail. */ 88 struct list_head *gp_tasks; 89 /* Pointer to the first task blocking the */ 90 /* current grace period, or NULL if there */ 91 /* is no such task. */ 92 struct list_head *exp_tasks; 93 /* Pointer to the first task blocking the */ 94 /* current expedited grace period, or NULL */ 95 /* if there is no such task. If there */ 96 /* is no current expedited grace period, */ 97 /* then there can cannot be any such task. */ 98 struct list_head *boost_tasks; 99 /* Pointer to first task that needs to be */ 100 /* priority boosted, or NULL if no priority */ 101 /* boosting is needed for this rcu_node */ 102 /* structure. If there are no tasks */ 103 /* queued on this rcu_node structure that */ 104 /* are blocking the current grace period, */ 105 /* there can be no such task. */ 106 struct rt_mutex boost_mtx; 107 /* Used only for the priority-boosting */ 108 /* side effect, not as a lock. */ 109 unsigned long boost_time; 110 /* When to start boosting (jiffies). */ 111 struct task_struct *boost_kthread_task; 112 /* kthread that takes care of priority */ 113 /* boosting for this rcu_node structure. */ 114 unsigned int boost_kthread_status; 115 /* State of boost_kthread_task for tracing. */ 116 #ifdef CONFIG_RCU_NOCB_CPU 117 struct swait_queue_head nocb_gp_wq[2]; 118 /* Place for rcu_nocb_kthread() to wait GP. */ 119 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 120 raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp; 121 122 spinlock_t exp_lock ____cacheline_internodealigned_in_smp; 123 unsigned long exp_seq_rq; 124 wait_queue_head_t exp_wq[4]; 125 struct rcu_exp_work rew; 126 bool exp_need_flush; /* Need to flush workitem? */ 127 } ____cacheline_internodealigned_in_smp; 128 129 /* 130 * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and 131 * are indexed relative to this interval rather than the global CPU ID space. 132 * This generates the bit for a CPU in node-local masks. 133 */ 134 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo)) 135 136 /* 137 * Union to allow "aggregate OR" operation on the need for a quiescent 138 * state by the normal and expedited grace periods. 139 */ 140 union rcu_noqs { 141 struct { 142 u8 norm; 143 u8 exp; 144 } b; /* Bits. */ 145 u16 s; /* Set of bits, aggregate OR here. */ 146 }; 147 148 /* Per-CPU data for read-copy update. */ 149 struct rcu_data { 150 /* 1) quiescent-state and grace-period handling : */ 151 unsigned long gp_seq; /* Track rsp->rcu_gp_seq counter. */ 152 unsigned long gp_seq_needed; /* Track furthest future GP request. */ 153 union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */ 154 bool core_needs_qs; /* Core waits for quiesc state. */ 155 bool beenonline; /* CPU online at least once. */ 156 bool gpwrap; /* Possible ->gp_seq wrap. */ 157 bool exp_deferred_qs; /* This CPU awaiting a deferred QS? */ 158 struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ 159 unsigned long grpmask; /* Mask to apply to leaf qsmask. */ 160 unsigned long ticks_this_gp; /* The number of scheduling-clock */ 161 /* ticks this CPU has handled */ 162 /* during and after the last grace */ 163 /* period it is aware of. */ 164 struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */ 165 bool defer_qs_iw_pending; /* Scheduler attention pending? */ 166 167 /* 2) batch handling */ 168 struct rcu_segcblist cblist; /* Segmented callback list, with */ 169 /* different callbacks waiting for */ 170 /* different grace periods. */ 171 long qlen_last_fqs_check; 172 /* qlen at last check for QS forcing */ 173 unsigned long n_force_qs_snap; 174 /* did other CPU force QS recently? */ 175 long blimit; /* Upper limit on a processed batch */ 176 177 /* 3) dynticks interface. */ 178 int dynticks_snap; /* Per-GP tracking for dynticks. */ 179 long dynticks_nesting; /* Track process nesting level. */ 180 long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */ 181 atomic_t dynticks; /* Even value for idle, else odd. */ 182 bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */ 183 bool rcu_urgent_qs; /* GP old need light quiescent state. */ 184 #ifdef CONFIG_RCU_FAST_NO_HZ 185 bool all_lazy; /* All CPU's CBs lazy at idle start? */ 186 unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */ 187 unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */ 188 int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */ 189 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ 190 191 /* 4) rcu_barrier(), OOM callbacks, and expediting. */ 192 struct rcu_head barrier_head; 193 int exp_dynticks_snap; /* Double-check need for IPI. */ 194 195 /* 5) Callback offloading. */ 196 #ifdef CONFIG_RCU_NOCB_CPU 197 struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */ 198 struct task_struct *nocb_gp_kthread; 199 raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ 200 atomic_t nocb_lock_contended; /* Contention experienced. */ 201 int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ 202 struct timer_list nocb_timer; /* Enforce finite deferral. */ 203 unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ 204 205 /* The following fields are used by call_rcu, hence own cacheline. */ 206 raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp; 207 struct rcu_cblist nocb_bypass; /* Lock-contention-bypass CB list. */ 208 unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */ 209 unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */ 210 int nocb_nobypass_count; /* # ->cblist enqueues at ^^^ time. */ 211 212 /* The following fields are used by GP kthread, hence own cacheline. */ 213 raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp; 214 struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */ 215 u8 nocb_gp_sleep; /* Is the nocb GP thread asleep? */ 216 u8 nocb_gp_bypass; /* Found a bypass on last scan? */ 217 u8 nocb_gp_gp; /* GP to wait for on last scan? */ 218 unsigned long nocb_gp_seq; /* If so, ->gp_seq to wait for. */ 219 unsigned long nocb_gp_loops; /* # passes through wait code. */ 220 struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ 221 bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ 222 struct task_struct *nocb_cb_kthread; 223 struct rcu_data *nocb_next_cb_rdp; 224 /* Next rcu_data in wakeup chain. */ 225 226 /* The following fields are used by CB kthread, hence new cacheline. */ 227 struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp; 228 /* GP rdp takes GP-end wakeups. */ 229 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 230 231 /* 6) RCU priority boosting. */ 232 struct task_struct *rcu_cpu_kthread_task; 233 /* rcuc per-CPU kthread or NULL. */ 234 unsigned int rcu_cpu_kthread_status; 235 char rcu_cpu_has_work; 236 237 /* 7) Diagnostic data, including RCU CPU stall warnings. */ 238 unsigned int softirq_snap; /* Snapshot of softirq activity. */ 239 /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */ 240 struct irq_work rcu_iw; /* Check for non-irq activity. */ 241 bool rcu_iw_pending; /* Is ->rcu_iw pending? */ 242 unsigned long rcu_iw_gp_seq; /* ->gp_seq associated with ->rcu_iw. */ 243 unsigned long rcu_ofl_gp_seq; /* ->gp_seq at last offline. */ 244 short rcu_ofl_gp_flags; /* ->gp_flags at last offline. */ 245 unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ 246 short rcu_onl_gp_flags; /* ->gp_flags at last online. */ 247 unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ 248 249 int cpu; 250 }; 251 252 /* Values for nocb_defer_wakeup field in struct rcu_data. */ 253 #define RCU_NOCB_WAKE_NOT 0 254 #define RCU_NOCB_WAKE 1 255 #define RCU_NOCB_WAKE_FORCE 2 256 257 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) 258 /* For jiffies_till_first_fqs and */ 259 /* and jiffies_till_next_fqs. */ 260 261 #define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */ 262 /* delay between bouts of */ 263 /* quiescent-state forcing. */ 264 265 #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */ 266 /* at least one scheduling clock */ 267 /* irq before ratting on them. */ 268 269 #define rcu_wait(cond) \ 270 do { \ 271 for (;;) { \ 272 set_current_state(TASK_INTERRUPTIBLE); \ 273 if (cond) \ 274 break; \ 275 schedule(); \ 276 } \ 277 __set_current_state(TASK_RUNNING); \ 278 } while (0) 279 280 /* 281 * RCU global state, including node hierarchy. This hierarchy is 282 * represented in "heap" form in a dense array. The root (first level) 283 * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second 284 * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]), 285 * and the third level in ->node[m+1] and following (->node[m+1] referenced 286 * by ->level[2]). The number of levels is determined by the number of 287 * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy" 288 * consisting of a single rcu_node. 289 */ 290 struct rcu_state { 291 struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */ 292 struct rcu_node *level[RCU_NUM_LVLS + 1]; 293 /* Hierarchy levels (+1 to */ 294 /* shut bogus gcc warning) */ 295 int ncpus; /* # CPUs seen so far. */ 296 297 /* The following fields are guarded by the root rcu_node's lock. */ 298 299 u8 boost ____cacheline_internodealigned_in_smp; 300 /* Subject to priority boost. */ 301 unsigned long gp_seq; /* Grace-period sequence #. */ 302 struct task_struct *gp_kthread; /* Task for grace periods. */ 303 struct swait_queue_head gp_wq; /* Where GP task waits. */ 304 short gp_flags; /* Commands for GP task. */ 305 short gp_state; /* GP kthread sleep state. */ 306 unsigned long gp_wake_time; /* Last GP kthread wake. */ 307 unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ 308 309 /* End of fields guarded by root rcu_node's lock. */ 310 311 struct mutex barrier_mutex; /* Guards barrier fields. */ 312 atomic_t barrier_cpu_count; /* # CPUs waiting on. */ 313 struct completion barrier_completion; /* Wake at barrier end. */ 314 unsigned long barrier_sequence; /* ++ at start and end of */ 315 /* rcu_barrier(). */ 316 /* End of fields guarded by barrier_mutex. */ 317 318 struct mutex exp_mutex; /* Serialize expedited GP. */ 319 struct mutex exp_wake_mutex; /* Serialize wakeup. */ 320 unsigned long expedited_sequence; /* Take a ticket. */ 321 atomic_t expedited_need_qs; /* # CPUs left to check in. */ 322 struct swait_queue_head expedited_wq; /* Wait for check-ins. */ 323 int ncpus_snap; /* # CPUs seen last time. */ 324 325 unsigned long jiffies_force_qs; /* Time at which to invoke */ 326 /* force_quiescent_state(). */ 327 unsigned long jiffies_kick_kthreads; /* Time at which to kick */ 328 /* kthreads, if configured. */ 329 unsigned long n_force_qs; /* Number of calls to */ 330 /* force_quiescent_state(). */ 331 unsigned long gp_start; /* Time at which GP started, */ 332 /* but in jiffies. */ 333 unsigned long gp_end; /* Time last GP ended, again */ 334 /* in jiffies. */ 335 unsigned long gp_activity; /* Time of last GP kthread */ 336 /* activity in jiffies. */ 337 unsigned long gp_req_activity; /* Time of last GP request */ 338 /* in jiffies. */ 339 unsigned long jiffies_stall; /* Time at which to check */ 340 /* for CPU stalls. */ 341 unsigned long jiffies_resched; /* Time at which to resched */ 342 /* a reluctant CPU. */ 343 unsigned long n_force_qs_gpstart; /* Snapshot of n_force_qs at */ 344 /* GP start. */ 345 unsigned long gp_max; /* Maximum GP duration in */ 346 /* jiffies. */ 347 const char *name; /* Name of structure. */ 348 char abbr; /* Abbreviated name. */ 349 350 raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; 351 /* Synchronize offline with */ 352 /* GP pre-initialization. */ 353 }; 354 355 /* Values for rcu_state structure's gp_flags field. */ 356 #define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */ 357 #define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */ 358 359 /* Values for rcu_state structure's gp_state field. */ 360 #define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */ 361 #define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */ 362 #define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */ 363 #define RCU_GP_ONOFF 3 /* Grace-period initialization hotplug. */ 364 #define RCU_GP_INIT 4 /* Grace-period initialization. */ 365 #define RCU_GP_WAIT_FQS 5 /* Wait for force-quiescent-state time. */ 366 #define RCU_GP_DOING_FQS 6 /* Wait done for force-quiescent-state time. */ 367 #define RCU_GP_CLEANUP 7 /* Grace-period cleanup started. */ 368 #define RCU_GP_CLEANED 8 /* Grace-period cleanup complete. */ 369 370 static const char * const gp_state_names[] = { 371 "RCU_GP_IDLE", 372 "RCU_GP_WAIT_GPS", 373 "RCU_GP_DONE_GPS", 374 "RCU_GP_ONOFF", 375 "RCU_GP_INIT", 376 "RCU_GP_WAIT_FQS", 377 "RCU_GP_DOING_FQS", 378 "RCU_GP_CLEANUP", 379 "RCU_GP_CLEANED", 380 }; 381 382 /* 383 * In order to export the rcu_state name to the tracing tools, it 384 * needs to be added in the __tracepoint_string section. 385 * This requires defining a separate variable tp_<sname>_varname 386 * that points to the string being used, and this will allow 387 * the tracing userspace tools to be able to decipher the string 388 * address to the matching string. 389 */ 390 #ifdef CONFIG_PREEMPT_RCU 391 #define RCU_ABBR 'p' 392 #define RCU_NAME_RAW "rcu_preempt" 393 #else /* #ifdef CONFIG_PREEMPT_RCU */ 394 #define RCU_ABBR 's' 395 #define RCU_NAME_RAW "rcu_sched" 396 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 397 #ifndef CONFIG_TRACING 398 #define RCU_NAME RCU_NAME_RAW 399 #else /* #ifdef CONFIG_TRACING */ 400 static char rcu_name[] = RCU_NAME_RAW; 401 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name; 402 #define RCU_NAME rcu_name 403 #endif /* #else #ifdef CONFIG_TRACING */ 404 405 int rcu_dynticks_snap(struct rcu_data *rdp); 406 407 /* Forward declarations for tree_plugin.h */ 408 static void rcu_bootup_announce(void); 409 static void rcu_qs(void); 410 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); 411 #ifdef CONFIG_HOTPLUG_CPU 412 static bool rcu_preempt_has_tasks(struct rcu_node *rnp); 413 #endif /* #ifdef CONFIG_HOTPLUG_CPU */ 414 static int rcu_print_task_exp_stall(struct rcu_node *rnp); 415 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); 416 static void rcu_flavor_sched_clock_irq(int user); 417 void call_rcu(struct rcu_head *head, rcu_callback_t func); 418 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck); 419 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); 420 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); 421 static bool rcu_is_callbacks_kthread(void); 422 static void rcu_cpu_kthread_setup(unsigned int cpu); 423 static void __init rcu_spawn_boost_kthreads(void); 424 static void rcu_prepare_kthreads(int cpu); 425 static void rcu_cleanup_after_idle(void); 426 static void rcu_prepare_for_idle(void); 427 static bool rcu_preempt_has_tasks(struct rcu_node *rnp); 428 static bool rcu_preempt_need_deferred_qs(struct task_struct *t); 429 static void rcu_preempt_deferred_qs(struct task_struct *t); 430 static void zero_cpu_stall_ticks(struct rcu_data *rdp); 431 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp); 432 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq); 433 static void rcu_init_one_nocb(struct rcu_node *rnp); 434 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, 435 unsigned long j); 436 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, 437 bool *was_alldone, unsigned long flags); 438 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, 439 unsigned long flags); 440 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp); 441 static void do_nocb_deferred_wakeup(struct rcu_data *rdp); 442 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); 443 static void rcu_spawn_cpu_nocb_kthread(int cpu); 444 static void __init rcu_spawn_nocb_kthreads(void); 445 static void show_rcu_nocb_state(struct rcu_data *rdp); 446 static void rcu_nocb_lock(struct rcu_data *rdp); 447 static void rcu_nocb_unlock(struct rcu_data *rdp); 448 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, 449 unsigned long flags); 450 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp); 451 #ifdef CONFIG_RCU_NOCB_CPU 452 static void __init rcu_organize_nocb_kthreads(void); 453 #define rcu_nocb_lock_irqsave(rdp, flags) \ 454 do { \ 455 if (!rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ 456 local_irq_save(flags); \ 457 else \ 458 raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags)); \ 459 } while (0) 460 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 461 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags) 462 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 463 464 static void rcu_bind_gp_kthread(void); 465 static bool rcu_nohz_full_cpu(void); 466 static void rcu_dynticks_task_enter(void); 467 static void rcu_dynticks_task_exit(void); 468 469 /* Forward declarations for tree_stall.h */ 470 static void record_gp_stall_check_time(void); 471 static void rcu_iw_handler(struct irq_work *iwp); 472 static void check_cpu_stall(struct rcu_data *rdp); 473 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, 474 const unsigned long gpssdelay); 475
