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TOMOYO Linux Cross Reference
Linux/kernel/rcu/tree.h

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  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion (tree-based version)
  3  * Internal non-public definitions.
  4  *
  5  * This program is free software; you can redistribute it and/or modify
  6  * it under the terms of the GNU General Public License as published by
  7  * the Free Software Foundation; either version 2 of the License, or
  8  * (at your option) any later version.
  9  *
 10  * This program is distributed in the hope that it will be useful,
 11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 13  * GNU General Public License for more details.
 14  *
 15  * You should have received a copy of the GNU General Public License
 16  * along with this program; if not, you can access it online at
 17  * http://www.gnu.org/licenses/gpl-2.0.html.
 18  *
 19  * Copyright IBM Corporation, 2008
 20  *
 21  * Author: Ingo Molnar <mingo@elte.hu>
 22  *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 23  */
 24 
 25 #include <linux/cache.h>
 26 #include <linux/spinlock.h>
 27 #include <linux/rtmutex.h>
 28 #include <linux/threads.h>
 29 #include <linux/cpumask.h>
 30 #include <linux/seqlock.h>
 31 #include <linux/swait.h>
 32 #include <linux/stop_machine.h>
 33 #include <linux/rcu_node_tree.h>
 34 
 35 #include "rcu_segcblist.h"
 36 
 37 /* Communicate arguments to a workqueue handler. */
 38 struct rcu_exp_work {
 39         smp_call_func_t rew_func;
 40         unsigned long rew_s;
 41         struct work_struct rew_work;
 42 };
 43 
 44 /* RCU's kthread states for tracing. */
 45 #define RCU_KTHREAD_STOPPED  0
 46 #define RCU_KTHREAD_RUNNING  1
 47 #define RCU_KTHREAD_WAITING  2
 48 #define RCU_KTHREAD_OFFCPU   3
 49 #define RCU_KTHREAD_YIELDING 4
 50 #define RCU_KTHREAD_MAX      4
 51 
 52 /*
 53  * Definition for node within the RCU grace-period-detection hierarchy.
 54  */
 55 struct rcu_node {
 56         raw_spinlock_t __private lock;  /* Root rcu_node's lock protects */
 57                                         /*  some rcu_state fields as well as */
 58                                         /*  following. */
 59         unsigned long gp_seq;   /* Track rsp->rcu_gp_seq. */
 60         unsigned long gp_seq_needed; /* Track rsp->rcu_gp_seq_needed. */
 61         unsigned long completedqs; /* All QSes done for this node. */
 62         unsigned long qsmask;   /* CPUs or groups that need to switch in */
 63                                 /*  order for current grace period to proceed.*/
 64                                 /*  In leaf rcu_node, each bit corresponds to */
 65                                 /*  an rcu_data structure, otherwise, each */
 66                                 /*  bit corresponds to a child rcu_node */
 67                                 /*  structure. */
 68         unsigned long rcu_gp_init_mask; /* Mask of offline CPUs at GP init. */
 69         unsigned long qsmaskinit;
 70                                 /* Per-GP initial value for qsmask. */
 71                                 /*  Initialized from ->qsmaskinitnext at the */
 72                                 /*  beginning of each grace period. */
 73         unsigned long qsmaskinitnext;
 74                                 /* Online CPUs for next grace period. */
 75         unsigned long expmask;  /* CPUs or groups that need to check in */
 76                                 /*  to allow the current expedited GP */
 77                                 /*  to complete. */
 78         unsigned long expmaskinit;
 79                                 /* Per-GP initial values for expmask. */
 80                                 /*  Initialized from ->expmaskinitnext at the */
 81                                 /*  beginning of each expedited GP. */
 82         unsigned long expmaskinitnext;
 83                                 /* Online CPUs for next expedited GP. */
 84                                 /*  Any CPU that has ever been online will */
 85                                 /*  have its bit set. */
 86         unsigned long ffmask;   /* Fully functional CPUs. */
 87         unsigned long grpmask;  /* Mask to apply to parent qsmask. */
 88                                 /*  Only one bit will be set in this mask. */
 89         int     grplo;          /* lowest-numbered CPU or group here. */
 90         int     grphi;          /* highest-numbered CPU or group here. */
 91         u8      grpnum;         /* CPU/group number for next level up. */
 92         u8      level;          /* root is at level 0. */
 93         bool    wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
 94                                 /*  exit RCU read-side critical sections */
 95                                 /*  before propagating offline up the */
 96                                 /*  rcu_node tree? */
 97         struct rcu_node *parent;
 98         struct list_head blkd_tasks;
 99                                 /* Tasks blocked in RCU read-side critical */
100                                 /*  section.  Tasks are placed at the head */
101                                 /*  of this list and age towards the tail. */
102         struct list_head *gp_tasks;
103                                 /* Pointer to the first task blocking the */
104                                 /*  current grace period, or NULL if there */
105                                 /*  is no such task. */
106         struct list_head *exp_tasks;
107                                 /* Pointer to the first task blocking the */
108                                 /*  current expedited grace period, or NULL */
109                                 /*  if there is no such task.  If there */
110                                 /*  is no current expedited grace period, */
111                                 /*  then there can cannot be any such task. */
112         struct list_head *boost_tasks;
113                                 /* Pointer to first task that needs to be */
114                                 /*  priority boosted, or NULL if no priority */
115                                 /*  boosting is needed for this rcu_node */
116                                 /*  structure.  If there are no tasks */
117                                 /*  queued on this rcu_node structure that */
118                                 /*  are blocking the current grace period, */
119                                 /*  there can be no such task. */
120         struct rt_mutex boost_mtx;
121                                 /* Used only for the priority-boosting */
122                                 /*  side effect, not as a lock. */
123         unsigned long boost_time;
124                                 /* When to start boosting (jiffies). */
125         struct task_struct *boost_kthread_task;
126                                 /* kthread that takes care of priority */
127                                 /*  boosting for this rcu_node structure. */
128         unsigned int boost_kthread_status;
129                                 /* State of boost_kthread_task for tracing. */
130 #ifdef CONFIG_RCU_NOCB_CPU
131         struct swait_queue_head nocb_gp_wq[2];
132                                 /* Place for rcu_nocb_kthread() to wait GP. */
133 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
134         raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
135 
136         spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
137         unsigned long exp_seq_rq;
138         wait_queue_head_t exp_wq[4];
139         struct rcu_exp_work rew;
140         bool exp_need_flush;    /* Need to flush workitem? */
141 } ____cacheline_internodealigned_in_smp;
142 
143 /*
144  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
145  * are indexed relative to this interval rather than the global CPU ID space.
146  * This generates the bit for a CPU in node-local masks.
147  */
148 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo))
149 
150 /*
151  * Union to allow "aggregate OR" operation on the need for a quiescent
152  * state by the normal and expedited grace periods.
153  */
154 union rcu_noqs {
155         struct {
156                 u8 norm;
157                 u8 exp;
158         } b; /* Bits. */
159         u16 s; /* Set of bits, aggregate OR here. */
160 };
161 
162 /* Per-CPU data for read-copy update. */
163 struct rcu_data {
164         /* 1) quiescent-state and grace-period handling : */
165         unsigned long   gp_seq;         /* Track rsp->rcu_gp_seq counter. */
166         unsigned long   gp_seq_needed;  /* Track rsp->rcu_gp_seq_needed ctr. */
167         union rcu_noqs  cpu_no_qs;      /* No QSes yet for this CPU. */
168         bool            core_needs_qs;  /* Core waits for quiesc state. */
169         bool            beenonline;     /* CPU online at least once. */
170         bool            gpwrap;         /* Possible ->gp_seq wrap. */
171         bool            deferred_qs;    /* This CPU awaiting a deferred QS? */
172         struct rcu_node *mynode;        /* This CPU's leaf of hierarchy */
173         unsigned long grpmask;          /* Mask to apply to leaf qsmask. */
174         unsigned long   ticks_this_gp;  /* The number of scheduling-clock */
175                                         /*  ticks this CPU has handled */
176                                         /*  during and after the last grace */
177                                         /* period it is aware of. */
178 
179         /* 2) batch handling */
180         struct rcu_segcblist cblist;    /* Segmented callback list, with */
181                                         /* different callbacks waiting for */
182                                         /* different grace periods. */
183         long            qlen_last_fqs_check;
184                                         /* qlen at last check for QS forcing */
185         unsigned long   n_force_qs_snap;
186                                         /* did other CPU force QS recently? */
187         long            blimit;         /* Upper limit on a processed batch */
188 
189         /* 3) dynticks interface. */
190         int dynticks_snap;              /* Per-GP tracking for dynticks. */
191         long dynticks_nesting;          /* Track process nesting level. */
192         long dynticks_nmi_nesting;      /* Track irq/NMI nesting level. */
193         atomic_t dynticks;              /* Even value for idle, else odd. */
194         bool rcu_need_heavy_qs;         /* GP old, so heavy quiescent state! */
195         bool rcu_urgent_qs;             /* GP old need light quiescent state. */
196 #ifdef CONFIG_RCU_FAST_NO_HZ
197         bool all_lazy;                  /* Are all CPU's CBs lazy? */
198         unsigned long nonlazy_posted;   /* # times non-lazy CB posted to CPU. */
199         unsigned long nonlazy_posted_snap;
200                                         /* Nonlazy_posted snapshot. */
201         unsigned long last_accelerate;  /* Last jiffy CBs were accelerated. */
202         unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */
203         int tick_nohz_enabled_snap;     /* Previously seen value from sysfs. */
204 #endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */
205 
206         /* 4) rcu_barrier(), OOM callbacks, and expediting. */
207         struct rcu_head barrier_head;
208         int exp_dynticks_snap;          /* Double-check need for IPI. */
209 
210         /* 5) Callback offloading. */
211 #ifdef CONFIG_RCU_NOCB_CPU
212         struct rcu_head *nocb_head;     /* CBs waiting for kthread. */
213         struct rcu_head **nocb_tail;
214         atomic_long_t nocb_q_count;     /* # CBs waiting for nocb */
215         atomic_long_t nocb_q_count_lazy; /*  invocation (all stages). */
216         struct rcu_head *nocb_follower_head; /* CBs ready to invoke. */
217         struct rcu_head **nocb_follower_tail;
218         struct swait_queue_head nocb_wq; /* For nocb kthreads to sleep on. */
219         struct task_struct *nocb_kthread;
220         raw_spinlock_t nocb_lock;       /* Guard following pair of fields. */
221         int nocb_defer_wakeup;          /* Defer wakeup of nocb_kthread. */
222         struct timer_list nocb_timer;   /* Enforce finite deferral. */
223 
224         /* The following fields are used by the leader, hence own cacheline. */
225         struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
226                                         /* CBs waiting for GP. */
227         struct rcu_head **nocb_gp_tail;
228         bool nocb_leader_sleep;         /* Is the nocb leader thread asleep? */
229         struct rcu_data *nocb_next_follower;
230                                         /* Next follower in wakeup chain. */
231 
232         /* The following fields are used by the follower, hence new cachline. */
233         struct rcu_data *nocb_leader ____cacheline_internodealigned_in_smp;
234                                         /* Leader CPU takes GP-end wakeups. */
235 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
236 
237         /* 6) 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 
307         /* End of fields guarded by root rcu_node's lock. */
308 
309         struct mutex barrier_mutex;             /* Guards barrier fields. */
310         atomic_t barrier_cpu_count;             /* # CPUs waiting on. */
311         struct completion barrier_completion;   /* Wake at barrier end. */
312         unsigned long barrier_sequence;         /* ++ at start and end of */
313                                                 /*  rcu_barrier(). */
314         /* End of fields guarded by barrier_mutex. */
315 
316         struct mutex exp_mutex;                 /* Serialize expedited GP. */
317         struct mutex exp_wake_mutex;            /* Serialize wakeup. */
318         unsigned long expedited_sequence;       /* Take a ticket. */
319         atomic_t expedited_need_qs;             /* # CPUs left to check in. */
320         struct swait_queue_head expedited_wq;   /* Wait for check-ins. */
321         int ncpus_snap;                         /* # CPUs seen last time. */
322 
323         unsigned long jiffies_force_qs;         /* Time at which to invoke */
324                                                 /*  force_quiescent_state(). */
325         unsigned long jiffies_kick_kthreads;    /* Time at which to kick */
326                                                 /*  kthreads, if configured. */
327         unsigned long n_force_qs;               /* Number of calls to */
328                                                 /*  force_quiescent_state(). */
329         unsigned long gp_start;                 /* Time at which GP started, */
330                                                 /*  but in jiffies. */
331         unsigned long gp_activity;              /* Time of last GP kthread */
332                                                 /*  activity in jiffies. */
333         unsigned long gp_req_activity;          /* Time of last GP request */
334                                                 /*  in jiffies. */
335         unsigned long jiffies_stall;            /* Time at which to check */
336                                                 /*  for CPU stalls. */
337         unsigned long jiffies_resched;          /* Time at which to resched */
338                                                 /*  a reluctant CPU. */
339         unsigned long n_force_qs_gpstart;       /* Snapshot of n_force_qs at */
340                                                 /*  GP start. */
341         unsigned long gp_max;                   /* Maximum GP duration in */
342                                                 /*  jiffies. */
343         const char *name;                       /* Name of structure. */
344         char abbr;                              /* Abbreviated name. */
345 
346         raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
347                                                 /* Synchronize offline with */
348                                                 /*  GP pre-initialization. */
349 };
350 
351 /* Values for rcu_state structure's gp_flags field. */
352 #define RCU_GP_FLAG_INIT 0x1    /* Need grace-period initialization. */
353 #define RCU_GP_FLAG_FQS  0x2    /* Need grace-period quiescent-state forcing. */
354 
355 /* Values for rcu_state structure's gp_state field. */
356 #define RCU_GP_IDLE      0      /* Initial state and no GP in progress. */
357 #define RCU_GP_WAIT_GPS  1      /* Wait for grace-period start. */
358 #define RCU_GP_DONE_GPS  2      /* Wait done for grace-period start. */
359 #define RCU_GP_ONOFF     3      /* Grace-period initialization hotplug. */
360 #define RCU_GP_INIT      4      /* Grace-period initialization. */
361 #define RCU_GP_WAIT_FQS  5      /* Wait for force-quiescent-state time. */
362 #define RCU_GP_DOING_FQS 6      /* Wait done for force-quiescent-state time. */
363 #define RCU_GP_CLEANUP   7      /* Grace-period cleanup started. */
364 #define RCU_GP_CLEANED   8      /* Grace-period cleanup complete. */
365 
366 static const char * const gp_state_names[] = {
367         "RCU_GP_IDLE",
368         "RCU_GP_WAIT_GPS",
369         "RCU_GP_DONE_GPS",
370         "RCU_GP_ONOFF",
371         "RCU_GP_INIT",
372         "RCU_GP_WAIT_FQS",
373         "RCU_GP_DOING_FQS",
374         "RCU_GP_CLEANUP",
375         "RCU_GP_CLEANED",
376 };
377 
378 /*
379  * In order to export the rcu_state name to the tracing tools, it
380  * needs to be added in the __tracepoint_string section.
381  * This requires defining a separate variable tp_<sname>_varname
382  * that points to the string being used, and this will allow
383  * the tracing userspace tools to be able to decipher the string
384  * address to the matching string.
385  */
386 #ifdef CONFIG_PREEMPT_RCU
387 #define RCU_ABBR 'p'
388 #define RCU_NAME_RAW "rcu_preempt"
389 #else /* #ifdef CONFIG_PREEMPT_RCU */
390 #define RCU_ABBR 's'
391 #define RCU_NAME_RAW "rcu_sched"
392 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
393 #ifndef CONFIG_TRACING
394 #define RCU_NAME RCU_NAME_RAW
395 #else /* #ifdef CONFIG_TRACING */
396 static char rcu_name[] = RCU_NAME_RAW;
397 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
398 #define RCU_NAME rcu_name
399 #endif /* #else #ifdef CONFIG_TRACING */
400 
401 /*
402  * RCU implementation internal declarations:
403  */
404 extern struct rcu_state rcu_sched_state;
405 
406 extern struct rcu_state rcu_bh_state;
407 
408 #ifdef CONFIG_PREEMPT_RCU
409 extern struct rcu_state rcu_preempt_state;
410 #endif /* #ifdef CONFIG_PREEMPT_RCU */
411 
412 int rcu_dynticks_snap(struct rcu_data *rdp);
413 
414 #ifdef CONFIG_RCU_BOOST
415 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
416 DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);
417 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
418 DECLARE_PER_CPU(char, rcu_cpu_has_work);
419 #endif /* #ifdef CONFIG_RCU_BOOST */
420 
421 /* Forward declarations for rcutree_plugin.h */
422 static void rcu_bootup_announce(void);
423 static void rcu_qs(void);
424 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
425 #ifdef CONFIG_HOTPLUG_CPU
426 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
427 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
428 static void rcu_print_detail_task_stall(void);
429 static int rcu_print_task_stall(struct rcu_node *rnp);
430 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
431 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
432 static void rcu_flavor_check_callbacks(int user);
433 void call_rcu(struct rcu_head *head, rcu_callback_t func);
434 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
435 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
436 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
437 static void invoke_rcu_callbacks_kthread(void);
438 static bool rcu_is_callbacks_kthread(void);
439 static void __init rcu_spawn_boost_kthreads(void);
440 static void rcu_prepare_kthreads(int cpu);
441 static void rcu_cleanup_after_idle(void);
442 static void rcu_prepare_for_idle(void);
443 static void rcu_idle_count_callbacks_posted(void);
444 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
445 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
446 static void rcu_preempt_deferred_qs(struct task_struct *t);
447 static void print_cpu_stall_info_begin(void);
448 static void print_cpu_stall_info(int cpu);
449 static void print_cpu_stall_info_end(void);
450 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
451 static bool rcu_nocb_cpu_needs_barrier(int cpu);
452 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
453 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
454 static void rcu_init_one_nocb(struct rcu_node *rnp);
455 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
456                             bool lazy, unsigned long flags);
457 static bool rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
458                                       struct rcu_data *rdp,
459                                       unsigned long flags);
460 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp);
461 static void do_nocb_deferred_wakeup(struct rcu_data *rdp);
462 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
463 static void rcu_spawn_all_nocb_kthreads(int cpu);
464 static void __init rcu_spawn_nocb_kthreads(void);
465 #ifdef CONFIG_RCU_NOCB_CPU
466 static void __init rcu_organize_nocb_kthreads(void);
467 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
468 static bool init_nocb_callback_list(struct rcu_data *rdp);
469 static void rcu_bind_gp_kthread(void);
470 static bool rcu_nohz_full_cpu(void);
471 static void rcu_dynticks_task_enter(void);
472 static void rcu_dynticks_task_exit(void);
473 
474 #ifdef CONFIG_SRCU
475 void srcu_online_cpu(unsigned int cpu);
476 void srcu_offline_cpu(unsigned int cpu);
477 #else /* #ifdef CONFIG_SRCU */
478 void srcu_online_cpu(unsigned int cpu) { }
479 void srcu_offline_cpu(unsigned int cpu) { }
480 #endif /* #else #ifdef CONFIG_SRCU */
481 

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