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/rcu_node_tree.h> 20 21 #include "rcu_segcblist.h" 22 23 /* Communicate arguments to a workqueue handler. */ 24 struct rcu_exp_work { 25 unsigned long rew_s; 26 struct work_struct rew_work; 27 }; 28 29 /* RCU's kthread states for tracing. */ 30 #define RCU_KTHREAD_STOPPED 0 31 #define RCU_KTHREAD_RUNNING 1 32 #define RCU_KTHREAD_WAITING 2 33 #define RCU_KTHREAD_OFFCPU 3 34 #define RCU_KTHREAD_YIELDING 4 35 #define RCU_KTHREAD_MAX 4 36 37 /* 38 * Definition for node within the RCU grace-period-detection hierarchy. 39 */ 40 struct rcu_node { 41 raw_spinlock_t __private lock; /* Root rcu_node's lock protects */ 42 /* some rcu_state fields as well as */ 43 /* following. */ 44 unsigned long gp_seq; /* Track rsp->gp_seq. */ 45 unsigned long gp_seq_needed; /* Track furthest future GP request. */ 46 unsigned long completedqs; /* All QSes done for this node. */ 47 unsigned long qsmask; /* CPUs or groups that need to switch in */ 48 /* order for current grace period to proceed.*/ 49 /* In leaf rcu_node, each bit corresponds to */ 50 /* an rcu_data structure, otherwise, each */ 51 /* bit corresponds to a child rcu_node */ 52 /* structure. */ 53 unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */ 54 unsigned long qsmaskinit; 55 /* Per-GP initial value for qsmask. */ 56 /* Initialized from ->qsmaskinitnext at the */ 57 /* beginning of each grace period. */ 58 unsigned long qsmaskinitnext; 59 unsigned long ofl_seq; /* CPU-hotplug operation sequence count. */ 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 cbovldmask; 73 /* CPUs experiencing callback overload. */ 74 unsigned long ffmask; /* Fully functional CPUs. */ 75 unsigned long grpmask; /* Mask to apply to parent qsmask. */ 76 /* Only one bit will be set in this mask. */ 77 int grplo; /* lowest-numbered CPU here. */ 78 int grphi; /* highest-numbered CPU here. */ 79 u8 grpnum; /* group number for next level up. */ 80 u8 level; /* root is at level 0. */ 81 bool wait_blkd_tasks;/* Necessary to wait for blocked tasks to */ 82 /* exit RCU read-side critical sections */ 83 /* before propagating offline up the */ 84 /* rcu_node tree? */ 85 struct rcu_node *parent; 86 struct list_head blkd_tasks; 87 /* Tasks blocked in RCU read-side critical */ 88 /* section. Tasks are placed at the head */ 89 /* of this list and age towards the tail. */ 90 struct list_head *gp_tasks; 91 /* Pointer to the first task blocking the */ 92 /* current grace period, or NULL if there */ 93 /* is no such task. */ 94 struct list_head *exp_tasks; 95 /* Pointer to the first task blocking the */ 96 /* current expedited grace period, or NULL */ 97 /* if there is no such task. If there */ 98 /* is no current expedited grace period, */ 99 /* then there can cannot be any such task. */ 100 struct list_head *boost_tasks; 101 /* Pointer to first task that needs to be */ 102 /* priority boosted, or NULL if no priority */ 103 /* boosting is needed for this rcu_node */ 104 /* structure. If there are no tasks */ 105 /* queued on this rcu_node structure that */ 106 /* are blocking the current grace period, */ 107 /* there can be no such task. */ 108 struct rt_mutex boost_mtx; 109 /* Used only for the priority-boosting */ 110 /* side effect, not as a lock. */ 111 unsigned long boost_time; 112 /* When to start boosting (jiffies). */ 113 struct task_struct *boost_kthread_task; 114 /* kthread that takes care of priority */ 115 /* boosting for this rcu_node structure. */ 116 unsigned int boost_kthread_status; 117 /* State of boost_kthread_task for tracing. */ 118 unsigned long n_boosts; /* Number of boosts for this rcu_node structure. */ 119 #ifdef CONFIG_RCU_NOCB_CPU 120 struct swait_queue_head nocb_gp_wq[2]; 121 /* Place for rcu_nocb_kthread() to wait GP. */ 122 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 123 raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp; 124 125 spinlock_t exp_lock ____cacheline_internodealigned_in_smp; 126 unsigned long exp_seq_rq; 127 wait_queue_head_t exp_wq[4]; 128 struct rcu_exp_work rew; 129 bool exp_need_flush; /* Need to flush workitem? */ 130 } ____cacheline_internodealigned_in_smp; 131 132 /* 133 * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and 134 * are indexed relative to this interval rather than the global CPU ID space. 135 * This generates the bit for a CPU in node-local masks. 136 */ 137 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo)) 138 139 /* 140 * Union to allow "aggregate OR" operation on the need for a quiescent 141 * state by the normal and expedited grace periods. 142 */ 143 union rcu_noqs { 144 struct { 145 u8 norm; 146 u8 exp; 147 } b; /* Bits. */ 148 u16 s; /* Set of bits, aggregate OR here. */ 149 }; 150 151 /* Per-CPU data for read-copy update. */ 152 struct rcu_data { 153 /* 1) quiescent-state and grace-period handling : */ 154 unsigned long gp_seq; /* Track rsp->gp_seq counter. */ 155 unsigned long gp_seq_needed; /* Track furthest future GP request. */ 156 union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */ 157 bool core_needs_qs; /* Core waits for quiescent state. */ 158 bool beenonline; /* CPU online at least once. */ 159 bool gpwrap; /* Possible ->gp_seq wrap. */ 160 bool cpu_started; /* RCU watching this onlining CPU. */ 161 struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ 162 unsigned long grpmask; /* Mask to apply to leaf qsmask. */ 163 unsigned long ticks_this_gp; /* The number of scheduling-clock */ 164 /* ticks this CPU has handled */ 165 /* during and after the last grace */ 166 /* period it is aware of. */ 167 struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */ 168 bool defer_qs_iw_pending; /* Scheduler attention pending? */ 169 struct work_struct strict_work; /* Schedule readers for strict GPs. */ 170 171 /* 2) batch handling */ 172 struct rcu_segcblist cblist; /* Segmented callback list, with */ 173 /* different callbacks waiting for */ 174 /* different grace periods. */ 175 long qlen_last_fqs_check; 176 /* qlen at last check for QS forcing */ 177 unsigned long n_cbs_invoked; /* # callbacks invoked since boot. */ 178 unsigned long n_force_qs_snap; 179 /* did other CPU force QS recently? */ 180 long blimit; /* Upper limit on a processed batch */ 181 182 /* 3) dynticks interface. */ 183 int dynticks_snap; /* Per-GP tracking for dynticks. */ 184 long dynticks_nesting; /* Track process nesting level. */ 185 long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */ 186 atomic_t dynticks; /* Even value for idle, else odd. */ 187 bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */ 188 bool rcu_urgent_qs; /* GP old need light quiescent state. */ 189 bool rcu_forced_tick; /* Forced tick to provide QS. */ 190 bool rcu_forced_tick_exp; /* ... provide QS to expedited GP. */ 191 192 /* 4) rcu_barrier(), OOM callbacks, and expediting. */ 193 struct rcu_head barrier_head; 194 int exp_dynticks_snap; /* Double-check need for IPI. */ 195 196 /* 5) Callback offloading. */ 197 #ifdef CONFIG_RCU_NOCB_CPU 198 struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */ 199 struct swait_queue_head nocb_state_wq; /* For offloading state changes */ 200 struct task_struct *nocb_gp_kthread; 201 raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ 202 atomic_t nocb_lock_contended; /* Contention experienced. */ 203 int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ 204 struct timer_list nocb_timer; /* Enforce finite deferral. */ 205 unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ 206 struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */ 207 /* spawning */ 208 209 /* The following fields are used by call_rcu, hence own cacheline. */ 210 raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp; 211 struct rcu_cblist nocb_bypass; /* Lock-contention-bypass CB list. */ 212 unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */ 213 unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */ 214 int nocb_nobypass_count; /* # ->cblist enqueues at ^^^ time. */ 215 216 /* The following fields are used by GP kthread, hence own cacheline. */ 217 raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp; 218 u8 nocb_gp_sleep; /* Is the nocb GP thread asleep? */ 219 u8 nocb_gp_bypass; /* Found a bypass on last scan? */ 220 u8 nocb_gp_gp; /* GP to wait for on last scan? */ 221 unsigned long nocb_gp_seq; /* If so, ->gp_seq to wait for. */ 222 unsigned long nocb_gp_loops; /* # passes through wait code. */ 223 struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ 224 bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ 225 struct task_struct *nocb_cb_kthread; 226 struct list_head nocb_head_rdp; /* 227 * Head of rcu_data list in wakeup chain, 228 * if rdp_gp. 229 */ 230 struct list_head nocb_entry_rdp; /* rcu_data node in wakeup chain. */ 231 232 /* The following fields are used by CB kthread, hence new cacheline. */ 233 struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp; 234 /* GP rdp takes GP-end wakeups. */ 235 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 236 237 /* 6) RCU priority boosting. */ 238 struct task_struct *rcu_cpu_kthread_task; 239 /* rcuc per-CPU kthread or NULL. */ 240 unsigned int rcu_cpu_kthread_status; 241 char rcu_cpu_has_work; 242 243 /* 7) Diagnostic data, including RCU CPU stall warnings. */ 244 unsigned int softirq_snap; /* Snapshot of softirq activity. */ 245 /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */ 246 struct irq_work rcu_iw; /* Check for non-irq activity. */ 247 bool rcu_iw_pending; /* Is ->rcu_iw pending? */ 248 unsigned long rcu_iw_gp_seq; /* ->gp_seq associated with ->rcu_iw. */ 249 unsigned long rcu_ofl_gp_seq; /* ->gp_seq at last offline. */ 250 short rcu_ofl_gp_flags; /* ->gp_flags at last offline. */ 251 unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ 252 short rcu_onl_gp_flags; /* ->gp_flags at last online. */ 253 unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ 254 255 int cpu; 256 }; 257 258 /* Values for nocb_defer_wakeup field in struct rcu_data. */ 259 #define RCU_NOCB_WAKE_NOT 0 260 #define RCU_NOCB_WAKE_BYPASS 1 261 #define RCU_NOCB_WAKE 2 262 #define RCU_NOCB_WAKE_FORCE 3 263 264 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) 265 /* For jiffies_till_first_fqs and */ 266 /* and jiffies_till_next_fqs. */ 267 268 #define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */ 269 /* delay between bouts of */ 270 /* quiescent-state forcing. */ 271 272 #define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */ 273 /* at least one scheduling clock */ 274 /* irq before ratting on them. */ 275 276 #define rcu_wait(cond) \ 277 do { \ 278 for (;;) { \ 279 set_current_state(TASK_INTERRUPTIBLE); \ 280 if (cond) \ 281 break; \ 282 schedule(); \ 283 } \ 284 __set_current_state(TASK_RUNNING); \ 285 } while (0) 286 287 /* 288 * RCU global state, including node hierarchy. This hierarchy is 289 * represented in "heap" form in a dense array. The root (first level) 290 * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second 291 * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]), 292 * and the third level in ->node[m+1] and following (->node[m+1] referenced 293 * by ->level[2]). The number of levels is determined by the number of 294 * CPUs and by CONFIG_RCU_FANOUT. Small systems will have a "hierarchy" 295 * consisting of a single rcu_node. 296 */ 297 struct rcu_state { 298 struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */ 299 struct rcu_node *level[RCU_NUM_LVLS + 1]; 300 /* Hierarchy levels (+1 to */ 301 /* shut bogus gcc warning) */ 302 int ncpus; /* # CPUs seen so far. */ 303 int n_online_cpus; /* # CPUs online for RCU. */ 304 305 /* The following fields are guarded by the root rcu_node's lock. */ 306 307 u8 boost ____cacheline_internodealigned_in_smp; 308 /* Subject to priority boost. */ 309 unsigned long gp_seq; /* Grace-period sequence #. */ 310 unsigned long gp_max; /* Maximum GP duration in */ 311 /* jiffies. */ 312 struct task_struct *gp_kthread; /* Task for grace periods. */ 313 struct swait_queue_head gp_wq; /* Where GP task waits. */ 314 short gp_flags; /* Commands for GP task. */ 315 short gp_state; /* GP kthread sleep state. */ 316 unsigned long gp_wake_time; /* Last GP kthread wake. */ 317 unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ 318 319 /* End of fields guarded by root rcu_node's lock. */ 320 321 struct mutex barrier_mutex; /* Guards barrier fields. */ 322 atomic_t barrier_cpu_count; /* # CPUs waiting on. */ 323 struct completion barrier_completion; /* Wake at barrier end. */ 324 unsigned long barrier_sequence; /* ++ at start and end of */ 325 /* rcu_barrier(). */ 326 /* End of fields guarded by barrier_mutex. */ 327 328 struct mutex exp_mutex; /* Serialize expedited GP. */ 329 struct mutex exp_wake_mutex; /* Serialize wakeup. */ 330 unsigned long expedited_sequence; /* Take a ticket. */ 331 atomic_t expedited_need_qs; /* # CPUs left to check in. */ 332 struct swait_queue_head expedited_wq; /* Wait for check-ins. */ 333 int ncpus_snap; /* # CPUs seen last time. */ 334 u8 cbovld; /* Callback overload now? */ 335 u8 cbovldnext; /* ^ ^ next time? */ 336 337 unsigned long jiffies_force_qs; /* Time at which to invoke */ 338 /* force_quiescent_state(). */ 339 unsigned long jiffies_kick_kthreads; /* Time at which to kick */ 340 /* kthreads, if configured. */ 341 unsigned long n_force_qs; /* Number of calls to */ 342 /* force_quiescent_state(). */ 343 unsigned long gp_start; /* Time at which GP started, */ 344 /* but in jiffies. */ 345 unsigned long gp_end; /* Time last GP ended, again */ 346 /* in jiffies. */ 347 unsigned long gp_activity; /* Time of last GP kthread */ 348 /* activity in jiffies. */ 349 unsigned long gp_req_activity; /* Time of last GP request */ 350 /* in jiffies. */ 351 unsigned long jiffies_stall; /* Time at which to check */ 352 /* for CPU stalls. */ 353 unsigned long jiffies_resched; /* Time at which to resched */ 354 /* a reluctant CPU. */ 355 unsigned long n_force_qs_gpstart; /* Snapshot of n_force_qs at */ 356 /* GP start. */ 357 const char *name; /* Name of structure. */ 358 char abbr; /* Abbreviated name. */ 359 360 raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; 361 /* Synchronize offline with */ 362 /* GP pre-initialization. */ 363 }; 364 365 /* Values for rcu_state structure's gp_flags field. */ 366 #define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */ 367 #define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */ 368 #define RCU_GP_FLAG_OVLD 0x4 /* Experiencing callback overload. */ 369 370 /* Values for rcu_state structure's gp_state field. */ 371 #define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */ 372 #define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */ 373 #define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */ 374 #define RCU_GP_ONOFF 3 /* Grace-period initialization hotplug. */ 375 #define RCU_GP_INIT 4 /* Grace-period initialization. */ 376 #define RCU_GP_WAIT_FQS 5 /* Wait for force-quiescent-state time. */ 377 #define RCU_GP_DOING_FQS 6 /* Wait done for force-quiescent-state time. */ 378 #define RCU_GP_CLEANUP 7 /* Grace-period cleanup started. */ 379 #define RCU_GP_CLEANED 8 /* Grace-period cleanup complete. */ 380 381 /* 382 * In order to export the rcu_state name to the tracing tools, it 383 * needs to be added in the __tracepoint_string section. 384 * This requires defining a separate variable tp_<sname>_varname 385 * that points to the string being used, and this will allow 386 * the tracing userspace tools to be able to decipher the string 387 * address to the matching string. 388 */ 389 #ifdef CONFIG_PREEMPT_RCU 390 #define RCU_ABBR 'p' 391 #define RCU_NAME_RAW "rcu_preempt" 392 #else /* #ifdef CONFIG_PREEMPT_RCU */ 393 #define RCU_ABBR 's' 394 #define RCU_NAME_RAW "rcu_sched" 395 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 396 #ifndef CONFIG_TRACING 397 #define RCU_NAME RCU_NAME_RAW 398 #else /* #ifdef CONFIG_TRACING */ 399 static char rcu_name[] = RCU_NAME_RAW; 400 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name; 401 #define RCU_NAME rcu_name 402 #endif /* #else #ifdef CONFIG_TRACING */ 403 404 /* Forward declarations for tree_plugin.h */ 405 static void rcu_bootup_announce(void); 406 static void rcu_qs(void); 407 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); 408 #ifdef CONFIG_HOTPLUG_CPU 409 static bool rcu_preempt_has_tasks(struct rcu_node *rnp); 410 #endif /* #ifdef CONFIG_HOTPLUG_CPU */ 411 static int rcu_print_task_exp_stall(struct rcu_node *rnp); 412 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp); 413 static void rcu_flavor_sched_clock_irq(int user); 414 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck); 415 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); 416 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); 417 static bool rcu_is_callbacks_kthread(void); 418 static void rcu_cpu_kthread_setup(unsigned int cpu); 419 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp); 420 static void __init rcu_spawn_boost_kthreads(void); 421 static bool rcu_preempt_has_tasks(struct rcu_node *rnp); 422 static bool rcu_preempt_need_deferred_qs(struct task_struct *t); 423 static void rcu_preempt_deferred_qs(struct task_struct *t); 424 static void zero_cpu_stall_ticks(struct rcu_data *rdp); 425 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp); 426 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq); 427 static void rcu_init_one_nocb(struct rcu_node *rnp); 428 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, 429 unsigned long j); 430 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, 431 bool *was_alldone, unsigned long flags); 432 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, 433 unsigned long flags); 434 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); 435 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp); 436 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); 437 static void rcu_spawn_cpu_nocb_kthread(int cpu); 438 static void __init rcu_spawn_nocb_kthreads(void); 439 static void show_rcu_nocb_state(struct rcu_data *rdp); 440 static void rcu_nocb_lock(struct rcu_data *rdp); 441 static void rcu_nocb_unlock(struct rcu_data *rdp); 442 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, 443 unsigned long flags); 444 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp); 445 #ifdef CONFIG_RCU_NOCB_CPU 446 static void __init rcu_organize_nocb_kthreads(void); 447 448 /* 449 * Disable IRQs before checking offloaded state so that local 450 * locking is safe against concurrent de-offloading. 451 */ 452 #define rcu_nocb_lock_irqsave(rdp, flags) \ 453 do { \ 454 local_irq_save(flags); \ 455 if (rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ 456 raw_spin_lock(&(rdp)->nocb_lock); \ 457 } while (0) 458 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 459 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags) 460 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 461 462 static void rcu_bind_gp_kthread(void); 463 static bool rcu_nohz_full_cpu(void); 464 static void rcu_dynticks_task_enter(void); 465 static void rcu_dynticks_task_exit(void); 466 static void rcu_dynticks_task_trace_enter(void); 467 static void rcu_dynticks_task_trace_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