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/kthread.h>
14 #include <linux/spinlock.h>
15 #include <linux/rtmutex.h>
16 #include <linux/threads.h>
17 #include <linux/cpumask.h>
18 #include <linux/seqlock.h>
19 #include <linux/swait.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 #ifdef CONFIG_RCU_EXP_KTHREAD
28 	struct kthread_work rew_work;
29 #else
30 	struct work_struct rew_work;
31 #endif /* CONFIG_RCU_EXP_KTHREAD */
32 };
33 
34 /* RCU's kthread states for tracing. */
35 #define RCU_KTHREAD_STOPPED  0
36 #define RCU_KTHREAD_RUNNING  1
37 #define RCU_KTHREAD_WAITING  2
38 #define RCU_KTHREAD_OFFCPU   3
39 #define RCU_KTHREAD_YIELDING 4
40 #define RCU_KTHREAD_MAX      4
41 
42 /*
43  * Definition for node within the RCU grace-period-detection hierarchy.
44  */
45 struct rcu_node {
46 	raw_spinlock_t __private lock;	/* Root rcu_node's lock protects */
47 					/*  some rcu_state fields as well as */
48 					/*  following. */
49 	unsigned long gp_seq;	/* Track rsp->gp_seq. */
50 	unsigned long gp_seq_needed; /* Track furthest future GP request. */
51 	unsigned long completedqs; /* All QSes done for this node. */
52 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
53 				/*  order for current grace period to proceed.*/
54 				/*  In leaf rcu_node, each bit corresponds to */
55 				/*  an rcu_data structure, otherwise, each */
56 				/*  bit corresponds to a child rcu_node */
57 				/*  structure. */
58 	unsigned long rcu_gp_init_mask;	/* Mask of offline CPUs at GP init. */
59 	unsigned long qsmaskinit;
60 				/* Per-GP initial value for qsmask. */
61 				/*  Initialized from ->qsmaskinitnext at the */
62 				/*  beginning of each grace period. */
63 	unsigned long qsmaskinitnext;
64 	unsigned long expmask;	/* CPUs or groups that need to check in */
65 				/*  to allow the current expedited GP */
66 				/*  to complete. */
67 	unsigned long expmaskinit;
68 				/* Per-GP initial values for expmask. */
69 				/*  Initialized from ->expmaskinitnext at the */
70 				/*  beginning of each expedited GP. */
71 	unsigned long expmaskinitnext;
72 				/* Online CPUs for next expedited GP. */
73 				/*  Any CPU that has ever been online will */
74 				/*  have its bit set. */
75 	unsigned long cbovldmask;
76 				/* CPUs experiencing callback overload. */
77 	unsigned long ffmask;	/* Fully functional CPUs. */
78 	unsigned long grpmask;	/* Mask to apply to parent qsmask. */
79 				/*  Only one bit will be set in this mask. */
80 	int	grplo;		/* lowest-numbered CPU here. */
81 	int	grphi;		/* highest-numbered CPU here. */
82 	u8	grpnum;		/* group number for next level up. */
83 	u8	level;		/* root is at level 0. */
84 	bool	wait_blkd_tasks;/* Necessary to wait for blocked tasks to */
85 				/*  exit RCU read-side critical sections */
86 				/*  before propagating offline up the */
87 				/*  rcu_node tree? */
88 	struct rcu_node *parent;
89 	struct list_head blkd_tasks;
90 				/* Tasks blocked in RCU read-side critical */
91 				/*  section.  Tasks are placed at the head */
92 				/*  of this list and age towards the tail. */
93 	struct list_head *gp_tasks;
94 				/* Pointer to the first task blocking the */
95 				/*  current grace period, or NULL if there */
96 				/*  is no such task. */
97 	struct list_head *exp_tasks;
98 				/* Pointer to the first task blocking the */
99 				/*  current expedited grace period, or NULL */
100 				/*  if there is no such task.  If there */
101 				/*  is no current expedited grace period, */
102 				/*  then there can cannot be any such task. */
103 	struct list_head *boost_tasks;
104 				/* Pointer to first task that needs to be */
105 				/*  priority boosted, or NULL if no priority */
106 				/*  boosting is needed for this rcu_node */
107 				/*  structure.  If there are no tasks */
108 				/*  queued on this rcu_node structure that */
109 				/*  are blocking the current grace period, */
110 				/*  there can be no such task. */
111 	struct rt_mutex boost_mtx;
112 				/* Used only for the priority-boosting */
113 				/*  side effect, not as a lock. */
114 	unsigned long boost_time;
115 				/* When to start boosting (jiffies). */
116 	struct mutex boost_kthread_mutex;
117 				/* Exclusion for thread spawning and affinity */
118 				/*  manipulation. */
119 	struct task_struct *boost_kthread_task;
120 				/* kthread that takes care of priority */
121 				/*  boosting for this rcu_node structure. */
122 	unsigned int boost_kthread_status;
123 				/* State of boost_kthread_task for tracing. */
124 	unsigned long n_boosts;	/* Number of boosts for this rcu_node structure. */
125 #ifdef CONFIG_RCU_NOCB_CPU
126 	struct swait_queue_head nocb_gp_wq[2];
127 				/* Place for rcu_nocb_kthread() to wait GP. */
128 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
129 	raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
130 
131 	spinlock_t exp_lock ____cacheline_internodealigned_in_smp;
132 	unsigned long exp_seq_rq;
133 	wait_queue_head_t exp_wq[4];
134 	struct rcu_exp_work rew;
135 	bool exp_need_flush;	/* Need to flush workitem? */
136 	raw_spinlock_t exp_poll_lock;
137 				/* Lock and data for polled expedited grace periods. */
138 	unsigned long exp_seq_poll_rq;
139 	struct work_struct exp_poll_wq;
140 } ____cacheline_internodealigned_in_smp;
141 
142 /*
143  * Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
144  * are indexed relative to this interval rather than the global CPU ID space.
145  * This generates the bit for a CPU in node-local masks.
146  */
147 #define leaf_node_cpu_bit(rnp, cpu) (BIT((cpu) - (rnp)->grplo))
148 
149 /*
150  * Union to allow "aggregate OR" operation on the need for a quiescent
151  * state by the normal and expedited grace periods.
152  */
153 union rcu_noqs {
154 	struct {
155 		u8 norm;
156 		u8 exp;
157 	} b; /* Bits. */
158 	u16 s; /* Set of bits, aggregate OR here. */
159 };
160 
161 /*
162  * Record the snapshot of the core stats at half of the first RCU stall timeout.
163  * The member gp_seq is used to ensure that all members are updated only once
164  * during the sampling period. The snapshot is taken only if this gp_seq is not
165  * equal to rdp->gp_seq.
166  */
167 struct rcu_snap_record {
168 	unsigned long	gp_seq;		/* Track rdp->gp_seq counter */
169 	u64		cputime_irq;	/* Accumulated cputime of hard irqs */
170 	u64		cputime_softirq;/* Accumulated cputime of soft irqs */
171 	u64		cputime_system; /* Accumulated cputime of kernel tasks */
172 	unsigned long	nr_hardirqs;	/* Accumulated number of hard irqs */
173 	unsigned int	nr_softirqs;	/* Accumulated number of soft irqs */
174 	unsigned long long nr_csw;	/* Accumulated number of task switches */
175 	unsigned long   jiffies;	/* Track jiffies value */
176 };
177 
178 /* Per-CPU data for read-copy update. */
179 struct rcu_data {
180 	/* 1) quiescent-state and grace-period handling : */
181 	unsigned long	gp_seq;		/* Track rsp->gp_seq counter. */
182 	unsigned long	gp_seq_needed;	/* Track furthest future GP request. */
183 	union rcu_noqs	cpu_no_qs;	/* No QSes yet for this CPU. */
184 	bool		core_needs_qs;	/* Core waits for quiescent state. */
185 	bool		beenonline;	/* CPU online at least once. */
186 	bool		gpwrap;		/* Possible ->gp_seq wrap. */
187 	bool		cpu_started;	/* RCU watching this onlining CPU. */
188 	struct rcu_node *mynode;	/* This CPU's leaf of hierarchy */
189 	unsigned long grpmask;		/* Mask to apply to leaf qsmask. */
190 	unsigned long	ticks_this_gp;	/* The number of scheduling-clock */
191 					/*  ticks this CPU has handled */
192 					/*  during and after the last grace */
193 					/* period it is aware of. */
194 	struct irq_work defer_qs_iw;	/* Obtain later scheduler attention. */
195 	bool defer_qs_iw_pending;	/* Scheduler attention pending? */
196 	struct work_struct strict_work;	/* Schedule readers for strict GPs. */
197 
198 	/* 2) batch handling */
199 	struct rcu_segcblist cblist;	/* Segmented callback list, with */
200 					/* different callbacks waiting for */
201 					/* different grace periods. */
202 	long		qlen_last_fqs_check;
203 					/* qlen at last check for QS forcing */
204 	unsigned long	n_cbs_invoked;	/* # callbacks invoked since boot. */
205 	unsigned long	n_force_qs_snap;
206 					/* did other CPU force QS recently? */
207 	long		blimit;		/* Upper limit on a processed batch */
208 
209 	/* 3) dynticks interface. */
210 	int dynticks_snap;		/* Per-GP tracking for dynticks. */
211 	bool rcu_need_heavy_qs;		/* GP old, so heavy quiescent state! */
212 	bool rcu_urgent_qs;		/* GP old need light quiescent state. */
213 	bool rcu_forced_tick;		/* Forced tick to provide QS. */
214 	bool rcu_forced_tick_exp;	/*   ... provide QS to expedited GP. */
215 
216 	/* 4) rcu_barrier(), OOM callbacks, and expediting. */
217 	unsigned long barrier_seq_snap;	/* Snap of rcu_state.barrier_sequence. */
218 	struct rcu_head barrier_head;
219 	int exp_dynticks_snap;		/* Double-check need for IPI. */
220 
221 	/* 5) Callback offloading. */
222 #ifdef CONFIG_RCU_NOCB_CPU
223 	struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */
224 	struct swait_queue_head nocb_state_wq; /* For offloading state changes */
225 	struct task_struct *nocb_gp_kthread;
226 	raw_spinlock_t nocb_lock;	/* Guard following pair of fields. */
227 	atomic_t nocb_lock_contended;	/* Contention experienced. */
228 	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */
229 	struct timer_list nocb_timer;	/* Enforce finite deferral. */
230 	unsigned long nocb_gp_adv_time;	/* Last call_rcu() CB adv (jiffies). */
231 	struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */
232 					    /* spawning */
233 
234 	/* The following fields are used by call_rcu, hence own cacheline. */
235 	raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;
236 	struct rcu_cblist nocb_bypass;	/* Lock-contention-bypass CB list. */
237 	unsigned long nocb_bypass_first; /* Time (jiffies) of first enqueue. */
238 	unsigned long nocb_nobypass_last; /* Last ->cblist enqueue (jiffies). */
239 	int nocb_nobypass_count;	/* # ->cblist enqueues at ^^^ time. */
240 
241 	/* The following fields are used by GP kthread, hence own cacheline. */
242 	raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp;
243 	u8 nocb_gp_sleep;		/* Is the nocb GP thread asleep? */
244 	u8 nocb_gp_bypass;		/* Found a bypass on last scan? */
245 	u8 nocb_gp_gp;			/* GP to wait for on last scan? */
246 	unsigned long nocb_gp_seq;	/*  If so, ->gp_seq to wait for. */
247 	unsigned long nocb_gp_loops;	/* # passes through wait code. */
248 	struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */
249 	bool nocb_cb_sleep;		/* Is the nocb CB thread asleep? */
250 	struct task_struct *nocb_cb_kthread;
251 	struct list_head nocb_head_rdp; /*
252 					 * Head of rcu_data list in wakeup chain,
253 					 * if rdp_gp.
254 					 */
255 	struct list_head nocb_entry_rdp; /* rcu_data node in wakeup chain. */
256 	struct rcu_data *nocb_toggling_rdp; /* rdp queued for (de-)offloading */
257 
258 	/* The following fields are used by CB kthread, hence new cacheline. */
259 	struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp;
260 					/* GP rdp takes GP-end wakeups. */
261 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
262 
263 	/* 6) RCU priority boosting. */
264 	struct task_struct *rcu_cpu_kthread_task;
265 					/* rcuc per-CPU kthread or NULL. */
266 	unsigned int rcu_cpu_kthread_status;
267 	char rcu_cpu_has_work;
268 	unsigned long rcuc_activity;
269 
270 	/* 7) Diagnostic data, including RCU CPU stall warnings. */
271 	unsigned int softirq_snap;	/* Snapshot of softirq activity. */
272 	/* ->rcu_iw* fields protected by leaf rcu_node ->lock. */
273 	struct irq_work rcu_iw;		/* Check for non-irq activity. */
274 	bool rcu_iw_pending;		/* Is ->rcu_iw pending? */
275 	unsigned long rcu_iw_gp_seq;	/* ->gp_seq associated with ->rcu_iw. */
276 	unsigned long rcu_ofl_gp_seq;	/* ->gp_seq at last offline. */
277 	short rcu_ofl_gp_flags;		/* ->gp_flags at last offline. */
278 	unsigned long rcu_onl_gp_seq;	/* ->gp_seq at last online. */
279 	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */
280 	unsigned long last_fqs_resched;	/* Time of last rcu_resched(). */
281 	unsigned long last_sched_clock;	/* Jiffies of last rcu_sched_clock_irq(). */
282 	struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */
283 					    /* the first RCU stall timeout */
284 
285 	long lazy_len;			/* Length of buffered lazy callbacks. */
286 	int cpu;
287 };
288 
289 /* Values for nocb_defer_wakeup field in struct rcu_data. */
290 #define RCU_NOCB_WAKE_NOT	0
291 #define RCU_NOCB_WAKE_BYPASS	1
292 #define RCU_NOCB_WAKE_LAZY	2
293 #define RCU_NOCB_WAKE		3
294 #define RCU_NOCB_WAKE_FORCE	4
295 
296 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
297 					/* For jiffies_till_first_fqs and */
298 					/*  and jiffies_till_next_fqs. */
299 
300 #define RCU_JIFFIES_FQS_DIV	256	/* Very large systems need more */
301 					/*  delay between bouts of */
302 					/*  quiescent-state forcing. */
303 
304 #define RCU_STALL_RAT_DELAY	2	/* Allow other CPUs time to take */
305 					/*  at least one scheduling clock */
306 					/*  irq before ratting on them. */
307 
308 #define rcu_wait(cond)							\
309 do {									\
310 	for (;;) {							\
311 		set_current_state(TASK_INTERRUPTIBLE);			\
312 		if (cond)						\
313 			break;						\
314 		schedule();						\
315 	}								\
316 	__set_current_state(TASK_RUNNING);				\
317 } while (0)
318 
319 /*
320  * RCU global state, including node hierarchy.  This hierarchy is
321  * represented in "heap" form in a dense array.  The root (first level)
322  * of the hierarchy is in ->node[0] (referenced by ->level[0]), the second
323  * level in ->node[1] through ->node[m] (->node[1] referenced by ->level[1]),
324  * and the third level in ->node[m+1] and following (->node[m+1] referenced
325  * by ->level[2]).  The number of levels is determined by the number of
326  * CPUs and by CONFIG_RCU_FANOUT.  Small systems will have a "hierarchy"
327  * consisting of a single rcu_node.
328  */
329 struct rcu_state {
330 	struct rcu_node node[NUM_RCU_NODES];	/* Hierarchy. */
331 	struct rcu_node *level[RCU_NUM_LVLS + 1];
332 						/* Hierarchy levels (+1 to */
333 						/*  shut bogus gcc warning) */
334 	int ncpus;				/* # CPUs seen so far. */
335 	int n_online_cpus;			/* # CPUs online for RCU. */
336 
337 	/* The following fields are guarded by the root rcu_node's lock. */
338 
339 	unsigned long gp_seq ____cacheline_internodealigned_in_smp;
340 						/* Grace-period sequence #. */
341 	unsigned long gp_max;			/* Maximum GP duration in */
342 						/*  jiffies. */
343 	struct task_struct *gp_kthread;		/* Task for grace periods. */
344 	struct swait_queue_head gp_wq;		/* Where GP task waits. */
345 	short gp_flags;				/* Commands for GP task. */
346 	short gp_state;				/* GP kthread sleep state. */
347 	unsigned long gp_wake_time;		/* Last GP kthread wake. */
348 	unsigned long gp_wake_seq;		/* ->gp_seq at ^^^. */
349 	unsigned long gp_seq_polled;		/* GP seq for polled API. */
350 	unsigned long gp_seq_polled_snap;	/* ->gp_seq_polled at normal GP start. */
351 	unsigned long gp_seq_polled_exp_snap;	/* ->gp_seq_polled at expedited GP start. */
352 
353 	/* End of fields guarded by root rcu_node's lock. */
354 
355 	struct mutex barrier_mutex;		/* Guards barrier fields. */
356 	atomic_t barrier_cpu_count;		/* # CPUs waiting on. */
357 	struct completion barrier_completion;	/* Wake at barrier end. */
358 	unsigned long barrier_sequence;		/* ++ at start and end of */
359 						/*  rcu_barrier(). */
360 	/* End of fields guarded by barrier_mutex. */
361 
362 	raw_spinlock_t barrier_lock;		/* Protects ->barrier_seq_snap. */
363 
364 	struct mutex exp_mutex;			/* Serialize expedited GP. */
365 	struct mutex exp_wake_mutex;		/* Serialize wakeup. */
366 	unsigned long expedited_sequence;	/* Take a ticket. */
367 	atomic_t expedited_need_qs;		/* # CPUs left to check in. */
368 	struct swait_queue_head expedited_wq;	/* Wait for check-ins. */
369 	int ncpus_snap;				/* # CPUs seen last time. */
370 	u8 cbovld;				/* Callback overload now? */
371 	u8 cbovldnext;				/* ^        ^  next time? */
372 
373 	unsigned long jiffies_force_qs;		/* Time at which to invoke */
374 						/*  force_quiescent_state(). */
375 	unsigned long jiffies_kick_kthreads;	/* Time at which to kick */
376 						/*  kthreads, if configured. */
377 	unsigned long n_force_qs;		/* Number of calls to */
378 						/*  force_quiescent_state(). */
379 	unsigned long gp_start;			/* Time at which GP started, */
380 						/*  but in jiffies. */
381 	unsigned long gp_end;			/* Time last GP ended, again */
382 						/*  in jiffies. */
383 	unsigned long gp_activity;		/* Time of last GP kthread */
384 						/*  activity in jiffies. */
385 	unsigned long gp_req_activity;		/* Time of last GP request */
386 						/*  in jiffies. */
387 	unsigned long jiffies_stall;		/* Time at which to check */
388 						/*  for CPU stalls. */
389 	int nr_fqs_jiffies_stall;		/* Number of fqs loops after
390 						 * which read jiffies and set
391 						 * jiffies_stall. Stall
392 						 * warnings disabled if !0. */
393 	unsigned long jiffies_resched;		/* Time at which to resched */
394 						/*  a reluctant CPU. */
395 	unsigned long n_force_qs_gpstart;	/* Snapshot of n_force_qs at */
396 						/*  GP start. */
397 	const char *name;			/* Name of structure. */
398 	char abbr;				/* Abbreviated name. */
399 
400 	arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
401 						/* Synchronize offline with */
402 						/*  GP pre-initialization. */
403 	int nocb_is_setup;			/* nocb is setup from boot */
404 };
405 
406 /* Values for rcu_state structure's gp_flags field. */
407 #define RCU_GP_FLAG_INIT 0x1	/* Need grace-period initialization. */
408 #define RCU_GP_FLAG_FQS  0x2	/* Need grace-period quiescent-state forcing. */
409 #define RCU_GP_FLAG_OVLD 0x4	/* Experiencing callback overload. */
410 
411 /* Values for rcu_state structure's gp_state field. */
412 #define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
413 #define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
414 #define RCU_GP_DONE_GPS  2	/* Wait done for grace-period start. */
415 #define RCU_GP_ONOFF     3	/* Grace-period initialization hotplug. */
416 #define RCU_GP_INIT      4	/* Grace-period initialization. */
417 #define RCU_GP_WAIT_FQS  5	/* Wait for force-quiescent-state time. */
418 #define RCU_GP_DOING_FQS 6	/* Wait done for force-quiescent-state time. */
419 #define RCU_GP_CLEANUP   7	/* Grace-period cleanup started. */
420 #define RCU_GP_CLEANED   8	/* Grace-period cleanup complete. */
421 
422 /*
423  * In order to export the rcu_state name to the tracing tools, it
424  * needs to be added in the __tracepoint_string section.
425  * This requires defining a separate variable tp_<sname>_varname
426  * that points to the string being used, and this will allow
427  * the tracing userspace tools to be able to decipher the string
428  * address to the matching string.
429  */
430 #ifdef CONFIG_PREEMPT_RCU
431 #define RCU_ABBR 'p'
432 #define RCU_NAME_RAW "rcu_preempt"
433 #else /* #ifdef CONFIG_PREEMPT_RCU */
434 #define RCU_ABBR 's'
435 #define RCU_NAME_RAW "rcu_sched"
436 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
437 #ifndef CONFIG_TRACING
438 #define RCU_NAME RCU_NAME_RAW
439 #else /* #ifdef CONFIG_TRACING */
440 static char rcu_name[] = RCU_NAME_RAW;
441 static const char *tp_rcu_varname __used __tracepoint_string = rcu_name;
442 #define RCU_NAME rcu_name
443 #endif /* #else #ifdef CONFIG_TRACING */
444 
445 /* Forward declarations for tree_plugin.h */
446 static void rcu_bootup_announce(void);
447 static void rcu_qs(void);
448 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
449 #ifdef CONFIG_HOTPLUG_CPU
450 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
451 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
452 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
453 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
454 static void rcu_flavor_sched_clock_irq(int user);
455 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
456 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
457 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
458 static bool rcu_is_callbacks_kthread(struct rcu_data *rdp);
459 static void rcu_cpu_kthread_setup(unsigned int cpu);
460 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp);
461 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
462 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
463 static void zero_cpu_stall_ticks(struct rcu_data *rdp);
464 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp);
465 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq);
466 static void rcu_init_one_nocb(struct rcu_node *rnp);
467 static bool wake_nocb_gp(struct rcu_data *rdp, bool force);
468 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
469 				  unsigned long j, bool lazy);
470 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
471 				bool *was_alldone, unsigned long flags,
472 				bool lazy);
473 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
474 				 unsigned long flags);
475 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
476 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
477 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
478 static void rcu_spawn_cpu_nocb_kthread(int cpu);
479 static void show_rcu_nocb_state(struct rcu_data *rdp);
480 static void rcu_nocb_lock(struct rcu_data *rdp);
481 static void rcu_nocb_unlock(struct rcu_data *rdp);
482 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
483 				       unsigned long flags);
484 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp);
485 #ifdef CONFIG_RCU_NOCB_CPU
486 static void __init rcu_organize_nocb_kthreads(void);
487 
488 /*
489  * Disable IRQs before checking offloaded state so that local
490  * locking is safe against concurrent de-offloading.
491  */
492 #define rcu_nocb_lock_irqsave(rdp, flags)			\
493 do {								\
494 	local_irq_save(flags);					\
495 	if (rcu_segcblist_is_offloaded(&(rdp)->cblist))	\
496 		raw_spin_lock(&(rdp)->nocb_lock);		\
497 } while (0)
498 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
499 #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags)
500 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
501 
502 static void rcu_bind_gp_kthread(void);
503 static bool rcu_nohz_full_cpu(void);
504 
505 /* Forward declarations for tree_stall.h */
506 static void record_gp_stall_check_time(void);
507 static void rcu_iw_handler(struct irq_work *iwp);
508 static void check_cpu_stall(struct rcu_data *rdp);
509 static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
510 				     const unsigned long gpssdelay);
511 
512 /* Forward declarations for tree_exp.h. */
513 static void sync_rcu_do_polled_gp(struct work_struct *wp);
514