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/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 #ifdef CONFIG_RCU_NOCB_CPU
 119         struct swait_queue_head nocb_gp_wq[2];
 120                                 /* Place for rcu_nocb_kthread() to wait GP. */
 121 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 122         raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
 123
 124         spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
 125         unsigned long exp_seq_rq;
 126         wait_queue_head_t exp_wq[4];
 127         struct rcu_exp_work rew;
 128         bool exp_need_flush;    /* Need to flush workitem? */
 129 } ____cacheline_internodealigned_in_smp;
 130
 131 /*
 132  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
 133  * are indexed relative to this interval rather than the global CPU ID space.
 134  * This generates the bit for a CPU in node-local masks.
 135  */
 136 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo))
 137
 138 /*
 139  * Union to allow "aggregate OR" operation on the need for a quiescent
 140  * state by the normal and expedited grace periods.
 141  */
 142 union rcu_noqs {
 143         struct {
 144                 u8 norm;
 145                 u8 exp;
 146         } b; /* Bits. */
 147         u16 s; /* Set of bits, aggregate OR here. */
 148 };
 149
 150 /* Per-CPU data for read-copy update. */
 151 struct rcu_data {
 152         /* 1) quiescent-state and grace-period handling : */
 153         unsigned long   gp_seq;         /* Track rsp->gp_seq counter. */
 154         unsigned long   gp_seq_needed;  /* Track furthest future GP request. */
 155         union rcu_noqs  cpu_no_qs;      /* No QSes yet for this CPU. */
 156         bool            core_needs_qs;  /* Core waits for quiesc state. */
 157         bool            beenonline;     /* CPU online at least once. */
 158         bool            gpwrap;         /* Possible ->gp_seq wrap. */
 159         bool            exp_deferred_qs; /* This CPU awaiting a deferred QS? */
 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 #ifdef CONFIG_RCU_FAST_NO_HZ
 192         unsigned long last_accelerate;  /* Last jiffy CBs were accelerated. */
 193         unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */
 194         int tick_nohz_enabled_snap;     /* Previously seen value from sysfs. */
 195 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
 196
 197         /* 4) rcu_barrier(), OOM callbacks, and expediting. */
 198         struct rcu_head barrier_head;
 199         int exp_dynticks_snap;          /* Double-check need for IPI. */
 200
 201         /* 5) Callback offloading. */
 202 #ifdef CONFIG_RCU_NOCB_CPU
 203         struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
 204         struct task_struct *nocb_gp_kthread;
 205         raw_spinlock_t nocb_lock;       /* Guard following pair of fields. */
 206         atomic_t nocb_lock_contended;   /* Contention experienced. */
 207         int nocb_defer_wakeup;          /* Defer wakeup of nocb_kthread. */
 208         struct timer_list nocb_timer;   /* Enforce finite deferral. */
 209         unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */
 210
 211         /* The following fields are used by call_rcu, hence own cacheline. */
 212         raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
 213         struct rcu_cblist nocb_bypass;  /* Lock-contention-bypass CB list. */
 214         unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */
 215         unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */
 216         int nocb_nobypass_count;        /* # ->cblist enqueues at ^^^ time. */
 217
 218         /* The following fields are used by GP kthread, hence own cacheline. */
 219         raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
 220         struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */
 221         u8 nocb_gp_sleep;               /* Is the nocb GP thread asleep? */
 222         u8 nocb_gp_bypass;              /* Found a bypass on last scan? */
 223         u8 nocb_gp_gp;                  /* GP to wait for on last scan? */
 224         unsigned long nocb_gp_seq;      /*  If so, ->gp_seq to wait for. */
 225         unsigned long nocb_gp_loops;    /* # passes through wait code. */
 226         struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
 227         bool nocb_cb_sleep;             /* Is the nocb CB thread asleep? */
 228         struct task_struct *nocb_cb_kthread;
 229         struct rcu_data *nocb_next_cb_rdp;
 230                                         /* Next rcu_data 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           1
 261 #define RCU_NOCB_WAKE_FORCE     2
 262
 263 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
 264                                         /* For jiffies_till_first_fqs and */
 265                                         /*  and jiffies_till_next_fqs. */
 266
 267 #define RCU_JIFFIES_FQS_DIV     256     /* Very large systems need more */
 268                                         /*  delay between bouts of */
 269                                         /*  quiescent-state forcing. */
 270
 271 #define RCU_STALL_RAT_DELAY     2       /* Allow other CPUs time to take */
 272                                         /*  at least one scheduling clock */
 273                                         /*  irq before ratting on them. */
 274
 275 #define rcu_wait(cond)                                                  \
 276 do {                                                                    \
 277         for (;;) {                                                      \
 278                 set_current_state(TASK_INTERRUPTIBLE);                  \
 279                 if (cond)                                               \
 280                         break;                                          \
 281                 schedule();                                             \
 282         }                                                               \
 283         __set_current_state(TASK_RUNNING);                              \
 284 } while (0)
 285
 286 /*
 287  * RCU global state, including node hierarchy.  This hierarchy is
 288  * represented in "heap" form in a dense array.  The root (first level)
 289  * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
 290  * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
 291  * and the third level in ->node[m+1] and following (->node[m+1] referenced
 292  * by ->level[2]).  The number of levels is determined by the number of
 293  * CPUs and by CONFIG_RCU_FANOUT.  Small systems will have a "hierarchy"
 294  * consisting of a single rcu_node.
 295  */
 296 struct rcu_state {
 297         struct rcu_node node[NUM_RCU_NODES];    /* Hierarchy. */
 298         struct rcu_node *level[RCU_NUM_LVLS + 1];
 299                                                 /* Hierarchy levels (+1 to */
 300                                                 /*  shut bogus gcc warning) */
 301         int ncpus;                              /* # CPUs seen so far. */
 302         int n_online_cpus;                      /* # CPUs online for RCU. */
 303
 304         /* The following fields are guarded by the root rcu_node's lock. */
 305
 306         u8      boost ____cacheline_internodealigned_in_smp;
 307                                                 /* Subject to priority boost. */
 308         unsigned long gp_seq;                   /* Grace-period sequence #. */
 309         unsigned long gp_max;                   /* Maximum GP duration in */
 310                                                 /*  jiffies. */
 311         struct task_struct *gp_kthread;         /* Task for grace periods. */
 312         struct swait_queue_head gp_wq;          /* Where GP task waits. */
 313         short gp_flags;                         /* Commands for GP task. */
 314         short gp_state;                         /* GP kthread sleep state. */
 315         unsigned long gp_wake_time;             /* Last GP kthread wake. */
 316         unsigned long gp_wake_seq;              /* ->gp_seq at ^^^. */
 317
 318         /* End of fields guarded by root rcu_node's lock. */
 319
 320         struct mutex barrier_mutex;             /* Guards barrier fields. */
 321         atomic_t barrier_cpu_count;             /* # CPUs waiting on. */
 322         struct completion barrier_completion;   /* Wake at barrier end. */
 323         unsigned long barrier_sequence;         /* ++ at start and end of */
 324                                                 /*  rcu_barrier(). */
 325         /* End of fields guarded by barrier_mutex. */
 326
 327         struct mutex exp_mutex;                 /* Serialize expedited GP. */
 328         struct mutex exp_wake_mutex;            /* Serialize wakeup. */
 329         unsigned long expedited_sequence;       /* Take a ticket. */
 330         atomic_t expedited_need_qs;             /* # CPUs left to check in. */
 331         struct swait_queue_head expedited_wq;   /* Wait for check-ins. */
 332         int ncpus_snap;                         /* # CPUs seen last time. */
 333         u8 cbovld;                              /* Callback overload now? */
 334         u8 cbovldnext;                          /* ^        ^  next time? */
 335
 336         unsigned long jiffies_force_qs;         /* Time at which to invoke */
 337                                                 /*  force_quiescent_state(). */
 338         unsigned long jiffies_kick_kthreads;    /* Time at which to kick */
 339                                                 /*  kthreads, if configured. */
 340         unsigned long n_force_qs;               /* Number of calls to */
 341                                                 /*  force_quiescent_state(). */
 342         unsigned long gp_start;                 /* Time at which GP started, */
 343                                                 /*  but in jiffies. */
 344         unsigned long gp_end;                   /* Time last GP ended, again */
 345                                                 /*  in jiffies. */
 346         unsigned long gp_activity;              /* Time of last GP kthread */
 347                                                 /*  activity in jiffies. */
 348         unsigned long gp_req_activity;          /* Time of last GP request */
 349                                                 /*  in jiffies. */
 350         unsigned long jiffies_stall;            /* Time at which to check */
 351                                                 /*  for CPU stalls. */
 352         unsigned long jiffies_resched;          /* Time at which to resched */
 353                                                 /*  a reluctant CPU. */
 354         unsigned long n_force_qs_gpstart;       /* Snapshot of n_force_qs at */
 355                                                 /*  GP start. */
 356         const char *name;                       /* Name of structure. */
 357         char abbr;                              /* Abbreviated name. */
 358
 359         raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
 360                                                 /* Synchronize offline with */
 361                                                 /*  GP pre-initialization. */
 362 };
 363
 364 /* Values for rcu_state structure's gp_flags field. */
 365 #define RCU_GP_FLAG_INIT 0x1    /* Need grace-period initialization. */
 366 #define RCU_GP_FLAG_FQS  0x2    /* Need grace-period quiescent-state forcing. */
 367 #define RCU_GP_FLAG_OVLD 0x4    /* Experiencing callback overload. */
 368
 369 /* Values for rcu_state structure's gp_state field. */
 370 #define RCU_GP_IDLE      0      /* Initial state and no GP in progress. */
 371 #define RCU_GP_WAIT_GPS  1      /* Wait for grace-period start. */
 372 #define RCU_GP_DONE_GPS  2      /* Wait done for grace-period start. */
 373 #define RCU_GP_ONOFF     3      /* Grace-period initialization hotplug. */
 374 #define RCU_GP_INIT      4      /* Grace-period initialization. */
 375 #define RCU_GP_WAIT_FQS  5      /* Wait for force-quiescent-state time. */
 376 #define RCU_GP_DOING_FQS 6      /* Wait done for force-quiescent-state time. */
 377 #define RCU_GP_CLEANUP   7      /* Grace-period cleanup started. */
 378 #define RCU_GP_CLEANED   8      /* Grace-period cleanup complete. */
 379
 380 /*
 381  * In order to export the rcu_state name to the tracing tools, it
 382  * needs to be added in the __tracepoint_string section.
 383  * This requires defining a separate variable tp_<sname>_varname
 384  * that points to the string being used, and this will allow
 385  * the tracing userspace tools to be able to decipher the string
 386  * address to the matching string.
 387  */
 388 #ifdef CONFIG_PREEMPT_RCU
 389 #define RCU_ABBR 'p'
 390 #define RCU_NAME_RAW "rcu_preempt"
 391 #else /* #ifdef CONFIG_PREEMPT_RCU */
 392 #define RCU_ABBR 's'
 393 #define RCU_NAME_RAW "rcu_sched"
 394 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 395 #ifndef CONFIG_TRACING
 396 #define RCU_NAME RCU_NAME_RAW
 397 #else /* #ifdef CONFIG_TRACING */
 398 static char rcu_name[] = RCU_NAME_RAW;
 399 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
 400 #define RCU_NAME rcu_name
 401 #endif /* #else #ifdef CONFIG_TRACING */
 402
 403 /* Forward declarations for tree_plugin.h */
 404 static void rcu_bootup_announce(void);
 405 static void rcu_qs(void);
 406 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
 407 #ifdef CONFIG_HOTPLUG_CPU
 408 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 409 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 410 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 411 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
 412 static void rcu_flavor_sched_clock_irq(int user);
 413 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
 414 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
 415 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 416 static bool rcu_is_callbacks_kthread(void);
 417 static void rcu_cpu_kthread_setup(unsigned int cpu);
 418 static void __init rcu_spawn_boost_kthreads(void);
 419 static void rcu_prepare_kthreads(int cpu);
 420 static void rcu_cleanup_after_idle(void);
 421 static void rcu_prepare_for_idle(void);
 422 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 423 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 424 static void rcu_preempt_deferred_qs(struct task_struct *t);
 425 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
 426 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
 427 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
 428 static void rcu_init_one_nocb(struct rcu_node *rnp);
 429 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 430                                   unsigned long j);
 431 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 432                                 bool *was_alldone, unsigned long flags);
 433 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
 434                                  unsigned long flags);
 435 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
 436 static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
 437 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
 438 static void rcu_spawn_cpu_nocb_kthread(int cpu);
 439 static void __init rcu_spawn_nocb_kthreads(void);
 440 static void show_rcu_nocb_state(struct rcu_data *rdp);
 441 static void rcu_nocb_lock(struct rcu_data *rdp);
 442 static void rcu_nocb_unlock(struct rcu_data *rdp);
 443 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
 444                                        unsigned long flags);
 445 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp);
 446 #ifdef CONFIG_RCU_NOCB_CPU
 447 static void __init rcu_organize_nocb_kthreads(void);
 448 #define rcu_nocb_lock_irqsave(rdp, flags)                               \
 449 do {                                                                    \
 450         if (!rcu_segcblist_is_offloaded(&(rdp)->cblist))                \
 451                 local_irq_save(flags);                                  \
 452         else                                                            \
 453                 raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags));      \
 454 } while (0)
 455 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 456 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags)
 457 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
 458
 459 static void rcu_bind_gp_kthread(void);
 460 static bool rcu_nohz_full_cpu(void);
 461 static void rcu_dynticks_task_enter(void);
 462 static void rcu_dynticks_task_exit(void);
 463 static void rcu_dynticks_task_trace_enter(void);
 464 static void rcu_dynticks_task_trace_exit(void);
 465
 466 /* Forward declarations for tree_stall.h */
 467 static void record_gp_stall_check_time(void);
 468 static void rcu_iw_handler(struct irq_work *iwp);
 469 static void check_cpu_stall(struct rcu_data *rdp);
 470 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
 471                                      const unsigned long gpssdelay);