kernel/rcu/tree.h

   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         bool rcu_forced_tick;           /* Forced tick to provide QS. */
 185 #ifdef CONFIG_RCU_FAST_NO_HZ
 186         bool all_lazy;                  /* All CPU's CBs lazy at idle start? */
 187         unsigned long last_accelerate;  /* Last jiffy CBs were accelerated. */
 188         unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */
 189         int tick_nohz_enabled_snap;     /* Previously seen value from sysfs. */
 190 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
 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 task_struct *nocb_gp_kthread;
 200         raw_spinlock_t nocb_lock;       /* Guard following pair of fields. */
 201         atomic_t nocb_lock_contended;   /* Contention experienced. */
 202         int nocb_defer_wakeup;          /* Defer wakeup of nocb_kthread. */
 203         struct timer_list nocb_timer;   /* Enforce finite deferral. */
 204         unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */
 205
 206         /* The following fields are used by call_rcu, hence own cacheline. */
 207         raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
 208         struct rcu_cblist nocb_bypass;  /* Lock-contention-bypass CB list. */
 209         unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */
 210         unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */
 211         int nocb_nobypass_count;        /* # ->cblist enqueues at ^^^ time. */
 212
 213         /* The following fields are used by GP kthread, hence own cacheline. */
 214         raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
 215         struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */
 216         u8 nocb_gp_sleep;               /* Is the nocb GP thread asleep? */
 217         u8 nocb_gp_bypass;              /* Found a bypass on last scan? */
 218         u8 nocb_gp_gp;                  /* GP to wait for on last scan? */
 219         unsigned long nocb_gp_seq;      /*  If so, ->gp_seq to wait for. */
 220         unsigned long nocb_gp_loops;    /* # passes through wait code. */
 221         struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
 222         bool nocb_cb_sleep;             /* Is the nocb CB thread asleep? */
 223         struct task_struct *nocb_cb_kthread;
 224         struct rcu_data *nocb_next_cb_rdp;
 225                                         /* Next rcu_data in wakeup chain. */
 226
 227         /* The following fields are used by CB kthread, hence new cacheline. */
 228         struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp;
 229                                         /* GP rdp takes GP-end wakeups. */
 230 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 231
 232         /* 6) RCU priority boosting. */
 233         struct task_struct *rcu_cpu_kthread_task;
 234                                         /* rcuc per-CPU kthread or NULL. */
 235         unsigned int rcu_cpu_kthread_status;
 236         char rcu_cpu_has_work;
 237
 238         /* 7) Diagnostic data, including RCU CPU stall warnings. */
 239         unsigned int softirq_snap;      /* Snapshot of softirq activity. */
 240         /* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
 241         struct irq_work rcu_iw;         /* Check for non-irq activity. */
 242         bool rcu_iw_pending;            /* Is ->rcu_iw pending? */
 243         unsigned long rcu_iw_gp_seq;    /* ->gp_seq associated with ->rcu_iw. */
 244         unsigned long rcu_ofl_gp_seq;   /* ->gp_seq at last offline. */
 245         short rcu_ofl_gp_flags;         /* ->gp_flags at last offline. */
 246         unsigned long rcu_onl_gp_seq;   /* ->gp_seq at last online. */
 247         short rcu_onl_gp_flags;         /* ->gp_flags at last online. */
 248         unsigned long last_fqs_resched; /* Time of last rcu_resched(). */
 249
 250         int cpu;
 251 };
 252
 253 /* Values for nocb_defer_wakeup field in struct rcu_data. */
 254 #define RCU_NOCB_WAKE_NOT       0
 255 #define RCU_NOCB_WAKE           1
 256 #define RCU_NOCB_WAKE_FORCE     2
 257
 258 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
 259                                         /* For jiffies_till_first_fqs and */
 260                                         /*  and jiffies_till_next_fqs. */
 261
 262 #define RCU_JIFFIES_FQS_DIV     256     /* Very large systems need more */
 263                                         /*  delay between bouts of */
 264                                         /*  quiescent-state forcing. */
 265
 266 #define RCU_STALL_RAT_DELAY     2       /* Allow other CPUs time to take */
 267                                         /*  at least one scheduling clock */
 268                                         /*  irq before ratting on them. */
 269
 270 #define rcu_wait(cond)                                                  \
 271 do {                                                                    \
 272         for (;;) {                                                      \
 273                 set_current_state(TASK_INTERRUPTIBLE);                  \
 274                 if (cond)                                               \
 275                         break;                                          \
 276                 schedule();                                             \
 277         }                                                               \
 278         __set_current_state(TASK_RUNNING);                              \
 279 } while (0)
 280
 281 /*
 282  * RCU global state, including node hierarchy.  This hierarchy is
 283  * represented in "heap" form in a dense array.  The root (first level)
 284  * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
 285  * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
 286  * and the third level in ->node[m+1] and following (->node[m+1] referenced
 287  * by ->level[2]).  The number of levels is determined by the number of
 288  * CPUs and by CONFIG_RCU_FANOUT.  Small systems will have a "hierarchy"
 289  * consisting of a single rcu_node.
 290  */
 291 struct rcu_state {
 292         struct rcu_node node[NUM_RCU_NODES];    /* Hierarchy. */
 293         struct rcu_node *level[RCU_NUM_LVLS + 1];
 294                                                 /* Hierarchy levels (+1 to */
 295                                                 /*  shut bogus gcc warning) */
 296         int ncpus;                              /* # CPUs seen so far. */
 297
 298         /* The following fields are guarded by the root rcu_node's lock. */
 299
 300         u8      boost ____cacheline_internodealigned_in_smp;
 301                                                 /* Subject to priority boost. */
 302         unsigned long gp_seq;                   /* Grace-period sequence #. */
 303         struct task_struct *gp_kthread;         /* Task for grace periods. */
 304         struct swait_queue_head gp_wq;          /* Where GP task waits. */
 305         short gp_flags;                         /* Commands for GP task. */
 306         short gp_state;                         /* GP kthread sleep state. */
 307         unsigned long gp_wake_time;             /* Last GP kthread wake. */
 308         unsigned long gp_wake_seq;              /* ->gp_seq at ^^^. */
 309
 310         /* End of fields guarded by root rcu_node's lock. */
 311
 312         struct mutex barrier_mutex;             /* Guards barrier fields. */
 313         atomic_t barrier_cpu_count;             /* # CPUs waiting on. */
 314         struct completion barrier_completion;   /* Wake at barrier end. */
 315         unsigned long barrier_sequence;         /* ++ at start and end of */
 316                                                 /*  rcu_barrier(). */
 317         /* End of fields guarded by barrier_mutex. */
 318
 319         struct mutex exp_mutex;                 /* Serialize expedited GP. */
 320         struct mutex exp_wake_mutex;            /* Serialize wakeup. */
 321         unsigned long expedited_sequence;       /* Take a ticket. */
 322         atomic_t expedited_need_qs;             /* # CPUs left to check in. */
 323         struct swait_queue_head expedited_wq;   /* Wait for check-ins. */
 324         int ncpus_snap;                         /* # CPUs seen last time. */
 325
 326         unsigned long jiffies_force_qs;         /* Time at which to invoke */
 327                                                 /*  force_quiescent_state(). */
 328         unsigned long jiffies_kick_kthreads;    /* Time at which to kick */
 329                                                 /*  kthreads, if configured. */
 330         unsigned long n_force_qs;               /* Number of calls to */
 331                                                 /*  force_quiescent_state(). */
 332         unsigned long gp_start;                 /* Time at which GP started, */
 333                                                 /*  but in jiffies. */
 334         unsigned long gp_end;                   /* Time last GP ended, again */
 335                                                 /*  in jiffies. */
 336         unsigned long gp_activity;              /* Time of last GP kthread */
 337                                                 /*  activity in jiffies. */
 338         unsigned long gp_req_activity;          /* Time of last GP request */
 339                                                 /*  in jiffies. */
 340         unsigned long jiffies_stall;            /* Time at which to check */
 341                                                 /*  for CPU stalls. */
 342         unsigned long jiffies_resched;          /* Time at which to resched */
 343                                                 /*  a reluctant CPU. */
 344         unsigned long n_force_qs_gpstart;       /* Snapshot of n_force_qs at */
 345                                                 /*  GP start. */
 346         unsigned long gp_max;                   /* Maximum GP duration in */
 347                                                 /*  jiffies. */
 348         const char *name;                       /* Name of structure. */
 349         char abbr;                              /* Abbreviated name. */
 350
 351         raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
 352                                                 /* Synchronize offline with */
 353                                                 /*  GP pre-initialization. */
 354 };
 355
 356 /* Values for rcu_state structure's gp_flags field. */
 357 #define RCU_GP_FLAG_INIT 0x1    /* Need grace-period initialization. */
 358 #define RCU_GP_FLAG_FQS  0x2    /* Need grace-period quiescent-state forcing. */
 359
 360 /* Values for rcu_state structure's gp_state field. */
 361 #define RCU_GP_IDLE      0      /* Initial state and no GP in progress. */
 362 #define RCU_GP_WAIT_GPS  1      /* Wait for grace-period start. */
 363 #define RCU_GP_DONE_GPS  2      /* Wait done for grace-period start. */
 364 #define RCU_GP_ONOFF     3      /* Grace-period initialization hotplug. */
 365 #define RCU_GP_INIT      4      /* Grace-period initialization. */
 366 #define RCU_GP_WAIT_FQS  5      /* Wait for force-quiescent-state time. */
 367 #define RCU_GP_DOING_FQS 6      /* Wait done for force-quiescent-state time. */
 368 #define RCU_GP_CLEANUP   7      /* Grace-period cleanup started. */
 369 #define RCU_GP_CLEANED   8      /* Grace-period cleanup complete. */
 370
 371 static const char * const gp_state_names[] = {
 372         "RCU_GP_IDLE",
 373         "RCU_GP_WAIT_GPS",
 374         "RCU_GP_DONE_GPS",
 375         "RCU_GP_ONOFF",
 376         "RCU_GP_INIT",
 377         "RCU_GP_WAIT_FQS",
 378         "RCU_GP_DOING_FQS",
 379         "RCU_GP_CLEANUP",
 380         "RCU_GP_CLEANED",
 381 };
 382
 383 /*
 384  * In order to export the rcu_state name to the tracing tools, it
 385  * needs to be added in the __tracepoint_string section.
 386  * This requires defining a separate variable tp_<sname>_varname
 387  * that points to the string being used, and this will allow
 388  * the tracing userspace tools to be able to decipher the string
 389  * address to the matching string.
 390  */
 391 #ifdef CONFIG_PREEMPT_RCU
 392 #define RCU_ABBR 'p'
 393 #define RCU_NAME_RAW "rcu_preempt"
 394 #else /* #ifdef CONFIG_PREEMPT_RCU */
 395 #define RCU_ABBR 's'
 396 #define RCU_NAME_RAW "rcu_sched"
 397 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 398 #ifndef CONFIG_TRACING
 399 #define RCU_NAME RCU_NAME_RAW
 400 #else /* #ifdef CONFIG_TRACING */
 401 static char rcu_name[] = RCU_NAME_RAW;
 402 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
 403 #define RCU_NAME rcu_name
 404 #endif /* #else #ifdef CONFIG_TRACING */
 405
 406 int rcu_dynticks_snap(struct rcu_data *rdp);
 407
 408 /* Forward declarations for tree_plugin.h */
 409 static void rcu_bootup_announce(void);
 410 static void rcu_qs(void);
 411 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
 412 #ifdef CONFIG_HOTPLUG_CPU
 413 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 414 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 415 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 416 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
 417 static void rcu_flavor_sched_clock_irq(int user);
 418 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 419 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
 420 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 421 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 422 static bool rcu_is_callbacks_kthread(void);
 423 static void rcu_cpu_kthread_setup(unsigned int cpu);
 424 static void __init rcu_spawn_boost_kthreads(void);
 425 static void rcu_prepare_kthreads(int cpu);
 426 static void rcu_cleanup_after_idle(void);
 427 static void rcu_prepare_for_idle(void);
 428 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 429 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 430 static void rcu_preempt_deferred_qs(struct task_struct *t);
 431 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 432 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
 433 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 434 static void rcu_init_one_nocb(struct rcu_node *rnp);
 435 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 436                                   unsigned long j);
 437 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 438                                 bool *was_alldone, unsigned long flags);
 439 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
 440                                  unsigned long flags);
 441 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
 442 static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
 443 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
 444 static void rcu_spawn_cpu_nocb_kthread(int cpu);
 445 static void __init rcu_spawn_nocb_kthreads(void);
 446 static void show_rcu_nocb_state(struct rcu_data *rdp);
 447 static void rcu_nocb_lock(struct rcu_data *rdp);
 448 static void rcu_nocb_unlock(struct rcu_data *rdp);
 449 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
 450                                        unsigned long flags);
 451 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp);
 452 #ifdef CONFIG_RCU_NOCB_CPU
 453 static void __init rcu_organize_nocb_kthreads(void);
 454 #define rcu_nocb_lock_irqsave(rdp, flags)                               \
 455 do {                                                                    \
 456         if (!rcu_segcblist_is_offloaded(&(rdp)->cblist))                \
 457                 local_irq_save(flags);                                  \
 458         else                                                            \
 459                 raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags));      \
 460 } while (0)
 461 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 462 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags)
 463 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 464
 465 static void rcu_bind_gp_kthread(void);
 466 static bool rcu_nohz_full_cpu(void);
 467 static void rcu_dynticks_task_enter(void);
 468 static void rcu_dynticks_task_exit(void);
 469
 470 /* Forward declarations for tree_stall.h */
 471 static void record_gp_stall_check_time(void);
 472 static void rcu_iw_handler(struct irq_work *iwp);
 473 static void check_cpu_stall(struct rcu_data *rdp);
 474 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 475                                      const unsigned long gpssdelay);