xref: /openbmc/linux/kernel/rcu/tree_exp.h (revision eba92d62)
1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * RCU expedited grace periods
4  *
5  * Copyright IBM Corporation, 2016
6  *
7  * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
8  */
9 
10 #include <linux/lockdep.h>
11 
12 static void rcu_exp_handler(void *unused);
13 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
14 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
15 
16 /*
17  * Record the start of an expedited grace period.
18  */
rcu_exp_gp_seq_start(void)19 static void rcu_exp_gp_seq_start(void)
20 {
21 	rcu_seq_start(&rcu_state.expedited_sequence);
22 	rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
23 }
24 
25 /*
26  * Return the value that the expedited-grace-period counter will have
27  * at the end of the current grace period.
28  */
rcu_exp_gp_seq_endval(void)29 static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
30 {
31 	return rcu_seq_endval(&rcu_state.expedited_sequence);
32 }
33 
34 /*
35  * Record the end of an expedited grace period.
36  */
rcu_exp_gp_seq_end(void)37 static void rcu_exp_gp_seq_end(void)
38 {
39 	rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
40 	rcu_seq_end(&rcu_state.expedited_sequence);
41 	smp_mb(); /* Ensure that consecutive grace periods serialize. */
42 }
43 
44 /*
45  * Take a snapshot of the expedited-grace-period counter, which is the
46  * earliest value that will indicate that a full grace period has
47  * elapsed since the current time.
48  */
rcu_exp_gp_seq_snap(void)49 static unsigned long rcu_exp_gp_seq_snap(void)
50 {
51 	unsigned long s;
52 
53 	smp_mb(); /* Caller's modifications seen first by other CPUs. */
54 	s = rcu_seq_snap(&rcu_state.expedited_sequence);
55 	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
56 	return s;
57 }
58 
59 /*
60  * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
61  * if a full expedited grace period has elapsed since that snapshot
62  * was taken.
63  */
rcu_exp_gp_seq_done(unsigned long s)64 static bool rcu_exp_gp_seq_done(unsigned long s)
65 {
66 	return rcu_seq_done(&rcu_state.expedited_sequence, s);
67 }
68 
69 /*
70  * Reset the ->expmaskinit values in the rcu_node tree to reflect any
71  * recent CPU-online activity.  Note that these masks are not cleared
72  * when CPUs go offline, so they reflect the union of all CPUs that have
73  * ever been online.  This means that this function normally takes its
74  * no-work-to-do fastpath.
75  */
sync_exp_reset_tree_hotplug(void)76 static void sync_exp_reset_tree_hotplug(void)
77 {
78 	bool done;
79 	unsigned long flags;
80 	unsigned long mask;
81 	unsigned long oldmask;
82 	int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
83 	struct rcu_node *rnp;
84 	struct rcu_node *rnp_up;
85 
86 	/* If no new CPUs onlined since last time, nothing to do. */
87 	if (likely(ncpus == rcu_state.ncpus_snap))
88 		return;
89 	rcu_state.ncpus_snap = ncpus;
90 
91 	/*
92 	 * Each pass through the following loop propagates newly onlined
93 	 * CPUs for the current rcu_node structure up the rcu_node tree.
94 	 */
95 	rcu_for_each_leaf_node(rnp) {
96 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
97 		if (rnp->expmaskinit == rnp->expmaskinitnext) {
98 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
99 			continue;  /* No new CPUs, nothing to do. */
100 		}
101 
102 		/* Update this node's mask, track old value for propagation. */
103 		oldmask = rnp->expmaskinit;
104 		rnp->expmaskinit = rnp->expmaskinitnext;
105 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
106 
107 		/* If was already nonzero, nothing to propagate. */
108 		if (oldmask)
109 			continue;
110 
111 		/* Propagate the new CPU up the tree. */
112 		mask = rnp->grpmask;
113 		rnp_up = rnp->parent;
114 		done = false;
115 		while (rnp_up) {
116 			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
117 			if (rnp_up->expmaskinit)
118 				done = true;
119 			rnp_up->expmaskinit |= mask;
120 			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
121 			if (done)
122 				break;
123 			mask = rnp_up->grpmask;
124 			rnp_up = rnp_up->parent;
125 		}
126 	}
127 }
128 
129 /*
130  * Reset the ->expmask values in the rcu_node tree in preparation for
131  * a new expedited grace period.
132  */
sync_exp_reset_tree(void)133 static void __maybe_unused sync_exp_reset_tree(void)
134 {
135 	unsigned long flags;
136 	struct rcu_node *rnp;
137 
138 	sync_exp_reset_tree_hotplug();
139 	rcu_for_each_node_breadth_first(rnp) {
140 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
141 		WARN_ON_ONCE(rnp->expmask);
142 		WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
143 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
144 	}
145 }
146 
147 /*
148  * Return non-zero if there is no RCU expedited grace period in progress
149  * for the specified rcu_node structure, in other words, if all CPUs and
150  * tasks covered by the specified rcu_node structure have done their bit
151  * for the current expedited grace period.
152  */
sync_rcu_exp_done(struct rcu_node * rnp)153 static bool sync_rcu_exp_done(struct rcu_node *rnp)
154 {
155 	raw_lockdep_assert_held_rcu_node(rnp);
156 	return READ_ONCE(rnp->exp_tasks) == NULL &&
157 	       READ_ONCE(rnp->expmask) == 0;
158 }
159 
160 /*
161  * Like sync_rcu_exp_done(), but where the caller does not hold the
162  * rcu_node's ->lock.
163  */
sync_rcu_exp_done_unlocked(struct rcu_node * rnp)164 static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
165 {
166 	unsigned long flags;
167 	bool ret;
168 
169 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
170 	ret = sync_rcu_exp_done(rnp);
171 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
172 
173 	return ret;
174 }
175 
176 /*
177  * Report the exit from RCU read-side critical section for the last task
178  * that queued itself during or before the current expedited preemptible-RCU
179  * grace period.  This event is reported either to the rcu_node structure on
180  * which the task was queued or to one of that rcu_node structure's ancestors,
181  * recursively up the tree.  (Calm down, calm down, we do the recursion
182  * iteratively!)
183  */
__rcu_report_exp_rnp(struct rcu_node * rnp,bool wake,unsigned long flags)184 static void __rcu_report_exp_rnp(struct rcu_node *rnp,
185 				 bool wake, unsigned long flags)
186 	__releases(rnp->lock)
187 {
188 	unsigned long mask;
189 
190 	raw_lockdep_assert_held_rcu_node(rnp);
191 	for (;;) {
192 		if (!sync_rcu_exp_done(rnp)) {
193 			if (!rnp->expmask)
194 				rcu_initiate_boost(rnp, flags);
195 			else
196 				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
197 			break;
198 		}
199 		if (rnp->parent == NULL) {
200 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
201 			if (wake) {
202 				smp_mb(); /* EGP done before wake_up(). */
203 				swake_up_one_online(&rcu_state.expedited_wq);
204 			}
205 			break;
206 		}
207 		mask = rnp->grpmask;
208 		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
209 		rnp = rnp->parent;
210 		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
211 		WARN_ON_ONCE(!(rnp->expmask & mask));
212 		WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
213 	}
214 }
215 
216 /*
217  * Report expedited quiescent state for specified node.  This is a
218  * lock-acquisition wrapper function for __rcu_report_exp_rnp().
219  */
rcu_report_exp_rnp(struct rcu_node * rnp,bool wake)220 static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
221 {
222 	unsigned long flags;
223 
224 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
225 	__rcu_report_exp_rnp(rnp, wake, flags);
226 }
227 
228 /*
229  * Report expedited quiescent state for multiple CPUs, all covered by the
230  * specified leaf rcu_node structure.
231  */
rcu_report_exp_cpu_mult(struct rcu_node * rnp,unsigned long mask,bool wake)232 static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
233 				    unsigned long mask, bool wake)
234 {
235 	int cpu;
236 	unsigned long flags;
237 	struct rcu_data *rdp;
238 
239 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
240 	if (!(rnp->expmask & mask)) {
241 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
242 		return;
243 	}
244 	WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
245 	for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
246 		rdp = per_cpu_ptr(&rcu_data, cpu);
247 		if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
248 			continue;
249 		rdp->rcu_forced_tick_exp = false;
250 		tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
251 	}
252 	__rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
253 }
254 
255 /*
256  * Report expedited quiescent state for specified rcu_data (CPU).
257  */
rcu_report_exp_rdp(struct rcu_data * rdp)258 static void rcu_report_exp_rdp(struct rcu_data *rdp)
259 {
260 	WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
261 	rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
262 }
263 
264 /* Common code for work-done checking. */
sync_exp_work_done(unsigned long s)265 static bool sync_exp_work_done(unsigned long s)
266 {
267 	if (rcu_exp_gp_seq_done(s)) {
268 		trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
269 		smp_mb(); /* Ensure test happens before caller kfree(). */
270 		return true;
271 	}
272 	return false;
273 }
274 
275 /*
276  * Funnel-lock acquisition for expedited grace periods.  Returns true
277  * if some other task completed an expedited grace period that this task
278  * can piggy-back on, and with no mutex held.  Otherwise, returns false
279  * with the mutex held, indicating that the caller must actually do the
280  * expedited grace period.
281  */
exp_funnel_lock(unsigned long s)282 static bool exp_funnel_lock(unsigned long s)
283 {
284 	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
285 	struct rcu_node *rnp = rdp->mynode;
286 	struct rcu_node *rnp_root = rcu_get_root();
287 
288 	/* Low-contention fastpath. */
289 	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
290 	    (rnp == rnp_root ||
291 	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
292 	    mutex_trylock(&rcu_state.exp_mutex))
293 		goto fastpath;
294 
295 	/*
296 	 * Each pass through the following loop works its way up
297 	 * the rcu_node tree, returning if others have done the work or
298 	 * otherwise falls through to acquire ->exp_mutex.  The mapping
299 	 * from CPU to rcu_node structure can be inexact, as it is just
300 	 * promoting locality and is not strictly needed for correctness.
301 	 */
302 	for (; rnp != NULL; rnp = rnp->parent) {
303 		if (sync_exp_work_done(s))
304 			return true;
305 
306 		/* Work not done, either wait here or go up. */
307 		spin_lock(&rnp->exp_lock);
308 		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
309 
310 			/* Someone else doing GP, so wait for them. */
311 			spin_unlock(&rnp->exp_lock);
312 			trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
313 						  rnp->grplo, rnp->grphi,
314 						  TPS("wait"));
315 			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
316 				   sync_exp_work_done(s));
317 			return true;
318 		}
319 		WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
320 		spin_unlock(&rnp->exp_lock);
321 		trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
322 					  rnp->grplo, rnp->grphi, TPS("nxtlvl"));
323 	}
324 	mutex_lock(&rcu_state.exp_mutex);
325 fastpath:
326 	if (sync_exp_work_done(s)) {
327 		mutex_unlock(&rcu_state.exp_mutex);
328 		return true;
329 	}
330 	rcu_exp_gp_seq_start();
331 	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
332 	return false;
333 }
334 
335 /*
336  * Select the CPUs within the specified rcu_node that the upcoming
337  * expedited grace period needs to wait for.
338  */
__sync_rcu_exp_select_node_cpus(struct rcu_exp_work * rewp)339 static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
340 {
341 	int cpu;
342 	unsigned long flags;
343 	unsigned long mask_ofl_test;
344 	unsigned long mask_ofl_ipi;
345 	int ret;
346 	struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
347 
348 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
349 
350 	/* Each pass checks a CPU for identity, offline, and idle. */
351 	mask_ofl_test = 0;
352 	for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
353 		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
354 		unsigned long mask = rdp->grpmask;
355 		int snap;
356 
357 		if (raw_smp_processor_id() == cpu ||
358 		    !(rnp->qsmaskinitnext & mask)) {
359 			mask_ofl_test |= mask;
360 		} else {
361 			snap = rcu_dynticks_snap(cpu);
362 			if (rcu_dynticks_in_eqs(snap))
363 				mask_ofl_test |= mask;
364 			else
365 				rdp->exp_dynticks_snap = snap;
366 		}
367 	}
368 	mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
369 
370 	/*
371 	 * Need to wait for any blocked tasks as well.	Note that
372 	 * additional blocking tasks will also block the expedited GP
373 	 * until such time as the ->expmask bits are cleared.
374 	 */
375 	if (rcu_preempt_has_tasks(rnp))
376 		WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
377 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
378 
379 	/* IPI the remaining CPUs for expedited quiescent state. */
380 	for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
381 		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
382 		unsigned long mask = rdp->grpmask;
383 
384 retry_ipi:
385 		if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
386 			mask_ofl_test |= mask;
387 			continue;
388 		}
389 		if (get_cpu() == cpu) {
390 			mask_ofl_test |= mask;
391 			put_cpu();
392 			continue;
393 		}
394 		ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
395 		put_cpu();
396 		/* The CPU will report the QS in response to the IPI. */
397 		if (!ret)
398 			continue;
399 
400 		/* Failed, raced with CPU hotplug operation. */
401 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
402 		if ((rnp->qsmaskinitnext & mask) &&
403 		    (rnp->expmask & mask)) {
404 			/* Online, so delay for a bit and try again. */
405 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
406 			trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
407 			schedule_timeout_idle(1);
408 			goto retry_ipi;
409 		}
410 		/* CPU really is offline, so we must report its QS. */
411 		if (rnp->expmask & mask)
412 			mask_ofl_test |= mask;
413 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
414 	}
415 	/* Report quiescent states for those that went offline. */
416 	if (mask_ofl_test)
417 		rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
418 }
419 
420 static void rcu_exp_sel_wait_wake(unsigned long s);
421 
422 #ifdef CONFIG_RCU_EXP_KTHREAD
sync_rcu_exp_select_node_cpus(struct kthread_work * wp)423 static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
424 {
425 	struct rcu_exp_work *rewp =
426 		container_of(wp, struct rcu_exp_work, rew_work);
427 
428 	__sync_rcu_exp_select_node_cpus(rewp);
429 }
430 
rcu_exp_worker_started(void)431 static inline bool rcu_exp_worker_started(void)
432 {
433 	return !!READ_ONCE(rcu_exp_gp_kworker);
434 }
435 
rcu_exp_par_worker_started(void)436 static inline bool rcu_exp_par_worker_started(void)
437 {
438 	return !!READ_ONCE(rcu_exp_par_gp_kworker);
439 }
440 
sync_rcu_exp_select_cpus_queue_work(struct rcu_node * rnp)441 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
442 {
443 	kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
444 	/*
445 	 * Use rcu_exp_par_gp_kworker, because flushing a work item from
446 	 * another work item on the same kthread worker can result in
447 	 * deadlock.
448 	 */
449 	kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
450 }
451 
sync_rcu_exp_select_cpus_flush_work(struct rcu_node * rnp)452 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
453 {
454 	kthread_flush_work(&rnp->rew.rew_work);
455 }
456 
457 /*
458  * Work-queue handler to drive an expedited grace period forward.
459  */
wait_rcu_exp_gp(struct kthread_work * wp)460 static void wait_rcu_exp_gp(struct kthread_work *wp)
461 {
462 	struct rcu_exp_work *rewp;
463 
464 	rewp = container_of(wp, struct rcu_exp_work, rew_work);
465 	rcu_exp_sel_wait_wake(rewp->rew_s);
466 }
467 
synchronize_rcu_expedited_queue_work(struct rcu_exp_work * rew)468 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
469 {
470 	kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
471 	kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
472 }
473 
synchronize_rcu_expedited_destroy_work(struct rcu_exp_work * rew)474 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
475 {
476 }
477 #else /* !CONFIG_RCU_EXP_KTHREAD */
sync_rcu_exp_select_node_cpus(struct work_struct * wp)478 static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
479 {
480 	struct rcu_exp_work *rewp =
481 		container_of(wp, struct rcu_exp_work, rew_work);
482 
483 	__sync_rcu_exp_select_node_cpus(rewp);
484 }
485 
rcu_exp_worker_started(void)486 static inline bool rcu_exp_worker_started(void)
487 {
488 	return !!READ_ONCE(rcu_gp_wq);
489 }
490 
rcu_exp_par_worker_started(void)491 static inline bool rcu_exp_par_worker_started(void)
492 {
493 	return !!READ_ONCE(rcu_par_gp_wq);
494 }
495 
sync_rcu_exp_select_cpus_queue_work(struct rcu_node * rnp)496 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
497 {
498 	int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
499 
500 	INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
501 	/* If all offline, queue the work on an unbound CPU. */
502 	if (unlikely(cpu > rnp->grphi - rnp->grplo))
503 		cpu = WORK_CPU_UNBOUND;
504 	else
505 		cpu += rnp->grplo;
506 	queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
507 }
508 
sync_rcu_exp_select_cpus_flush_work(struct rcu_node * rnp)509 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
510 {
511 	flush_work(&rnp->rew.rew_work);
512 }
513 
514 /*
515  * Work-queue handler to drive an expedited grace period forward.
516  */
wait_rcu_exp_gp(struct work_struct * wp)517 static void wait_rcu_exp_gp(struct work_struct *wp)
518 {
519 	struct rcu_exp_work *rewp;
520 
521 	rewp = container_of(wp, struct rcu_exp_work, rew_work);
522 	rcu_exp_sel_wait_wake(rewp->rew_s);
523 }
524 
synchronize_rcu_expedited_queue_work(struct rcu_exp_work * rew)525 static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
526 {
527 	INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
528 	queue_work(rcu_gp_wq, &rew->rew_work);
529 }
530 
synchronize_rcu_expedited_destroy_work(struct rcu_exp_work * rew)531 static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
532 {
533 	destroy_work_on_stack(&rew->rew_work);
534 }
535 #endif /* CONFIG_RCU_EXP_KTHREAD */
536 
537 /*
538  * Select the nodes that the upcoming expedited grace period needs
539  * to wait for.
540  */
sync_rcu_exp_select_cpus(void)541 static void sync_rcu_exp_select_cpus(void)
542 {
543 	struct rcu_node *rnp;
544 
545 	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
546 	sync_exp_reset_tree();
547 	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
548 
549 	/* Schedule work for each leaf rcu_node structure. */
550 	rcu_for_each_leaf_node(rnp) {
551 		rnp->exp_need_flush = false;
552 		if (!READ_ONCE(rnp->expmask))
553 			continue; /* Avoid early boot non-existent wq. */
554 		if (!rcu_exp_par_worker_started() ||
555 		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
556 		    rcu_is_last_leaf_node(rnp)) {
557 			/* No worker started yet or last leaf, do direct call. */
558 			sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
559 			continue;
560 		}
561 		sync_rcu_exp_select_cpus_queue_work(rnp);
562 		rnp->exp_need_flush = true;
563 	}
564 
565 	/* Wait for jobs (if any) to complete. */
566 	rcu_for_each_leaf_node(rnp)
567 		if (rnp->exp_need_flush)
568 			sync_rcu_exp_select_cpus_flush_work(rnp);
569 }
570 
571 /*
572  * Wait for the expedited grace period to elapse, within time limit.
573  * If the time limit is exceeded without the grace period elapsing,
574  * return false, otherwise return true.
575  */
synchronize_rcu_expedited_wait_once(long tlimit)576 static bool synchronize_rcu_expedited_wait_once(long tlimit)
577 {
578 	int t;
579 	struct rcu_node *rnp_root = rcu_get_root();
580 
581 	t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
582 					  sync_rcu_exp_done_unlocked(rnp_root),
583 					  tlimit);
584 	// Workqueues should not be signaled.
585 	if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
586 		return true;
587 	WARN_ON(t < 0);  /* workqueues should not be signaled. */
588 	return false;
589 }
590 
591 /*
592  * Wait for the expedited grace period to elapse, issuing any needed
593  * RCU CPU stall warnings along the way.
594  */
synchronize_rcu_expedited_wait(void)595 static void synchronize_rcu_expedited_wait(void)
596 {
597 	int cpu;
598 	unsigned long j;
599 	unsigned long jiffies_stall;
600 	unsigned long jiffies_start;
601 	unsigned long mask;
602 	int ndetected;
603 	struct rcu_data *rdp;
604 	struct rcu_node *rnp;
605 	struct rcu_node *rnp_root = rcu_get_root();
606 	unsigned long flags;
607 
608 	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
609 	jiffies_stall = rcu_exp_jiffies_till_stall_check();
610 	jiffies_start = jiffies;
611 	if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
612 		if (synchronize_rcu_expedited_wait_once(1))
613 			return;
614 		rcu_for_each_leaf_node(rnp) {
615 			raw_spin_lock_irqsave_rcu_node(rnp, flags);
616 			mask = READ_ONCE(rnp->expmask);
617 			for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
618 				rdp = per_cpu_ptr(&rcu_data, cpu);
619 				if (rdp->rcu_forced_tick_exp)
620 					continue;
621 				rdp->rcu_forced_tick_exp = true;
622 				if (cpu_online(cpu))
623 					tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
624 			}
625 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
626 		}
627 		j = READ_ONCE(jiffies_till_first_fqs);
628 		if (synchronize_rcu_expedited_wait_once(j + HZ))
629 			return;
630 	}
631 
632 	for (;;) {
633 		if (synchronize_rcu_expedited_wait_once(jiffies_stall))
634 			return;
635 		if (rcu_stall_is_suppressed())
636 			continue;
637 		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
638 		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
639 		       rcu_state.name);
640 		ndetected = 0;
641 		rcu_for_each_leaf_node(rnp) {
642 			ndetected += rcu_print_task_exp_stall(rnp);
643 			for_each_leaf_node_possible_cpu(rnp, cpu) {
644 				struct rcu_data *rdp;
645 
646 				mask = leaf_node_cpu_bit(rnp, cpu);
647 				if (!(READ_ONCE(rnp->expmask) & mask))
648 					continue;
649 				ndetected++;
650 				rdp = per_cpu_ptr(&rcu_data, cpu);
651 				pr_cont(" %d-%c%c%c%c", cpu,
652 					"O."[!!cpu_online(cpu)],
653 					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
654 					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
655 					"D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
656 			}
657 		}
658 		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
659 			jiffies - jiffies_start, rcu_state.expedited_sequence,
660 			data_race(rnp_root->expmask),
661 			".T"[!!data_race(rnp_root->exp_tasks)]);
662 		if (ndetected) {
663 			pr_err("blocking rcu_node structures (internal RCU debug):");
664 			rcu_for_each_node_breadth_first(rnp) {
665 				if (rnp == rnp_root)
666 					continue; /* printed unconditionally */
667 				if (sync_rcu_exp_done_unlocked(rnp))
668 					continue;
669 				pr_cont(" l=%u:%d-%d:%#lx/%c",
670 					rnp->level, rnp->grplo, rnp->grphi,
671 					data_race(rnp->expmask),
672 					".T"[!!data_race(rnp->exp_tasks)]);
673 			}
674 			pr_cont("\n");
675 		}
676 		rcu_for_each_leaf_node(rnp) {
677 			for_each_leaf_node_possible_cpu(rnp, cpu) {
678 				mask = leaf_node_cpu_bit(rnp, cpu);
679 				if (!(READ_ONCE(rnp->expmask) & mask))
680 					continue;
681 				preempt_disable(); // For smp_processor_id() in dump_cpu_task().
682 				dump_cpu_task(cpu);
683 				preempt_enable();
684 			}
685 			rcu_exp_print_detail_task_stall_rnp(rnp);
686 		}
687 		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
688 		panic_on_rcu_stall();
689 	}
690 }
691 
692 /*
693  * Wait for the current expedited grace period to complete, and then
694  * wake up everyone who piggybacked on the just-completed expedited
695  * grace period.  Also update all the ->exp_seq_rq counters as needed
696  * in order to avoid counter-wrap problems.
697  */
rcu_exp_wait_wake(unsigned long s)698 static void rcu_exp_wait_wake(unsigned long s)
699 {
700 	struct rcu_node *rnp;
701 
702 	synchronize_rcu_expedited_wait();
703 
704 	// Switch over to wakeup mode, allowing the next GP to proceed.
705 	// End the previous grace period only after acquiring the mutex
706 	// to ensure that only one GP runs concurrently with wakeups.
707 	mutex_lock(&rcu_state.exp_wake_mutex);
708 	rcu_exp_gp_seq_end();
709 	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
710 
711 	rcu_for_each_node_breadth_first(rnp) {
712 		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
713 			spin_lock(&rnp->exp_lock);
714 			/* Recheck, avoid hang in case someone just arrived. */
715 			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
716 				WRITE_ONCE(rnp->exp_seq_rq, s);
717 			spin_unlock(&rnp->exp_lock);
718 		}
719 		smp_mb(); /* All above changes before wakeup. */
720 		wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
721 	}
722 	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
723 	mutex_unlock(&rcu_state.exp_wake_mutex);
724 }
725 
726 /*
727  * Common code to drive an expedited grace period forward, used by
728  * workqueues and mid-boot-time tasks.
729  */
rcu_exp_sel_wait_wake(unsigned long s)730 static void rcu_exp_sel_wait_wake(unsigned long s)
731 {
732 	/* Initialize the rcu_node tree in preparation for the wait. */
733 	sync_rcu_exp_select_cpus();
734 
735 	/* Wait and clean up, including waking everyone. */
736 	rcu_exp_wait_wake(s);
737 }
738 
739 #ifdef CONFIG_PREEMPT_RCU
740 
741 /*
742  * Remote handler for smp_call_function_single().  If there is an
743  * RCU read-side critical section in effect, request that the
744  * next rcu_read_unlock() record the quiescent state up the
745  * ->expmask fields in the rcu_node tree.  Otherwise, immediately
746  * report the quiescent state.
747  */
rcu_exp_handler(void * unused)748 static void rcu_exp_handler(void *unused)
749 {
750 	int depth = rcu_preempt_depth();
751 	unsigned long flags;
752 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
753 	struct rcu_node *rnp = rdp->mynode;
754 	struct task_struct *t = current;
755 
756 	/*
757 	 * First, the common case of not being in an RCU read-side
758 	 * critical section.  If also enabled or idle, immediately
759 	 * report the quiescent state, otherwise defer.
760 	 */
761 	if (!depth) {
762 		if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
763 		    rcu_is_cpu_rrupt_from_idle()) {
764 			rcu_report_exp_rdp(rdp);
765 		} else {
766 			WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
767 			set_tsk_need_resched(t);
768 			set_preempt_need_resched();
769 		}
770 		return;
771 	}
772 
773 	/*
774 	 * Second, the less-common case of being in an RCU read-side
775 	 * critical section.  In this case we can count on a future
776 	 * rcu_read_unlock().  However, this rcu_read_unlock() might
777 	 * execute on some other CPU, but in that case there will be
778 	 * a future context switch.  Either way, if the expedited
779 	 * grace period is still waiting on this CPU, set ->deferred_qs
780 	 * so that the eventual quiescent state will be reported.
781 	 * Note that there is a large group of race conditions that
782 	 * can have caused this quiescent state to already have been
783 	 * reported, so we really do need to check ->expmask.
784 	 */
785 	if (depth > 0) {
786 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
787 		if (rnp->expmask & rdp->grpmask) {
788 			WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
789 			t->rcu_read_unlock_special.b.exp_hint = true;
790 		}
791 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
792 		return;
793 	}
794 
795 	// Finally, negative nesting depth should not happen.
796 	WARN_ON_ONCE(1);
797 }
798 
799 /* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
sync_sched_exp_online_cleanup(int cpu)800 static void sync_sched_exp_online_cleanup(int cpu)
801 {
802 }
803 
804 /*
805  * Scan the current list of tasks blocked within RCU read-side critical
806  * sections, printing out the tid of each that is blocking the current
807  * expedited grace period.
808  */
rcu_print_task_exp_stall(struct rcu_node * rnp)809 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
810 {
811 	unsigned long flags;
812 	int ndetected = 0;
813 	struct task_struct *t;
814 
815 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
816 	if (!rnp->exp_tasks) {
817 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
818 		return 0;
819 	}
820 	t = list_entry(rnp->exp_tasks->prev,
821 		       struct task_struct, rcu_node_entry);
822 	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
823 		pr_cont(" P%d", t->pid);
824 		ndetected++;
825 	}
826 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
827 	return ndetected;
828 }
829 
830 /*
831  * Scan the current list of tasks blocked within RCU read-side critical
832  * sections, dumping the stack of each that is blocking the current
833  * expedited grace period.
834  */
rcu_exp_print_detail_task_stall_rnp(struct rcu_node * rnp)835 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
836 {
837 	unsigned long flags;
838 	struct task_struct *t;
839 
840 	if (!rcu_exp_stall_task_details)
841 		return;
842 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
843 	if (!READ_ONCE(rnp->exp_tasks)) {
844 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
845 		return;
846 	}
847 	t = list_entry(rnp->exp_tasks->prev,
848 		       struct task_struct, rcu_node_entry);
849 	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
850 		/*
851 		 * We could be printing a lot while holding a spinlock.
852 		 * Avoid triggering hard lockup.
853 		 */
854 		touch_nmi_watchdog();
855 		sched_show_task(t);
856 	}
857 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
858 }
859 
860 #else /* #ifdef CONFIG_PREEMPT_RCU */
861 
862 /* Request an expedited quiescent state. */
rcu_exp_need_qs(void)863 static void rcu_exp_need_qs(void)
864 {
865 	__this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
866 	/* Store .exp before .rcu_urgent_qs. */
867 	smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
868 	set_tsk_need_resched(current);
869 	set_preempt_need_resched();
870 }
871 
872 /* Invoked on each online non-idle CPU for expedited quiescent state. */
rcu_exp_handler(void * unused)873 static void rcu_exp_handler(void *unused)
874 {
875 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
876 	struct rcu_node *rnp = rdp->mynode;
877 	bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
878 
879 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
880 	    __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
881 		return;
882 	if (rcu_is_cpu_rrupt_from_idle() ||
883 	    (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
884 		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
885 		return;
886 	}
887 	rcu_exp_need_qs();
888 }
889 
890 /* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
sync_sched_exp_online_cleanup(int cpu)891 static void sync_sched_exp_online_cleanup(int cpu)
892 {
893 	unsigned long flags;
894 	int my_cpu;
895 	struct rcu_data *rdp;
896 	int ret;
897 	struct rcu_node *rnp;
898 
899 	rdp = per_cpu_ptr(&rcu_data, cpu);
900 	rnp = rdp->mynode;
901 	my_cpu = get_cpu();
902 	/* Quiescent state either not needed or already requested, leave. */
903 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
904 	    READ_ONCE(rdp->cpu_no_qs.b.exp)) {
905 		put_cpu();
906 		return;
907 	}
908 	/* Quiescent state needed on current CPU, so set it up locally. */
909 	if (my_cpu == cpu) {
910 		local_irq_save(flags);
911 		rcu_exp_need_qs();
912 		local_irq_restore(flags);
913 		put_cpu();
914 		return;
915 	}
916 	/* Quiescent state needed on some other CPU, send IPI. */
917 	ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
918 	put_cpu();
919 	WARN_ON_ONCE(ret);
920 }
921 
922 /*
923  * Because preemptible RCU does not exist, we never have to check for
924  * tasks blocked within RCU read-side critical sections that are
925  * blocking the current expedited grace period.
926  */
rcu_print_task_exp_stall(struct rcu_node * rnp)927 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
928 {
929 	return 0;
930 }
931 
932 /*
933  * Because preemptible RCU does not exist, we never have to print out
934  * tasks blocked within RCU read-side critical sections that are blocking
935  * the current expedited grace period.
936  */
rcu_exp_print_detail_task_stall_rnp(struct rcu_node * rnp)937 static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
938 {
939 }
940 
941 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
942 
943 /**
944  * synchronize_rcu_expedited - Brute-force RCU grace period
945  *
946  * Wait for an RCU grace period, but expedite it.  The basic idea is to
947  * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
948  * the CPU is in an RCU critical section, and if so, it sets a flag that
949  * causes the outermost rcu_read_unlock() to report the quiescent state
950  * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
951  * other hand, if the CPU is not in an RCU read-side critical section,
952  * the IPI handler reports the quiescent state immediately.
953  *
954  * Although this is a great improvement over previous expedited
955  * implementations, it is still unfriendly to real-time workloads, so is
956  * thus not recommended for any sort of common-case code.  In fact, if
957  * you are using synchronize_rcu_expedited() in a loop, please restructure
958  * your code to batch your updates, and then use a single synchronize_rcu()
959  * instead.
960  *
961  * This has the same semantics as (but is more brutal than) synchronize_rcu().
962  */
synchronize_rcu_expedited(void)963 void synchronize_rcu_expedited(void)
964 {
965 	bool use_worker;
966 	unsigned long flags;
967 	struct rcu_exp_work rew;
968 	struct rcu_node *rnp;
969 	unsigned long s;
970 
971 	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
972 			 lock_is_held(&rcu_lock_map) ||
973 			 lock_is_held(&rcu_sched_lock_map),
974 			 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
975 
976 	use_worker = (rcu_scheduler_active != RCU_SCHEDULER_INIT) &&
977 		      rcu_exp_worker_started();
978 
979 	/* Is the state is such that the call is a grace period? */
980 	if (rcu_blocking_is_gp()) {
981 		// Note well that this code runs with !PREEMPT && !SMP.
982 		// In addition, all code that advances grace periods runs
983 		// at process level.  Therefore, this expedited GP overlaps
984 		// with other expedited GPs only by being fully nested within
985 		// them, which allows reuse of ->gp_seq_polled_exp_snap.
986 		rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
987 		rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
988 
989 		local_irq_save(flags);
990 		WARN_ON_ONCE(num_online_cpus() > 1);
991 		rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
992 		local_irq_restore(flags);
993 		return;  // Context allows vacuous grace periods.
994 	}
995 
996 	/* If expedited grace periods are prohibited, fall back to normal. */
997 	if (rcu_gp_is_normal()) {
998 		wait_rcu_gp(call_rcu_hurry);
999 		return;
1000 	}
1001 
1002 	/* Take a snapshot of the sequence number.  */
1003 	s = rcu_exp_gp_seq_snap();
1004 	if (exp_funnel_lock(s))
1005 		return;  /* Someone else did our work for us. */
1006 
1007 	/* Ensure that load happens before action based on it. */
1008 	if (unlikely(!use_worker)) {
1009 		/* Direct call during scheduler init and early_initcalls(). */
1010 		rcu_exp_sel_wait_wake(s);
1011 	} else {
1012 		/* Marshall arguments & schedule the expedited grace period. */
1013 		rew.rew_s = s;
1014 		synchronize_rcu_expedited_queue_work(&rew);
1015 	}
1016 
1017 	/* Wait for expedited grace period to complete. */
1018 	rnp = rcu_get_root();
1019 	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
1020 		   sync_exp_work_done(s));
1021 	smp_mb(); /* Work actions happen before return. */
1022 
1023 	/* Let the next expedited grace period start. */
1024 	mutex_unlock(&rcu_state.exp_mutex);
1025 
1026 	if (likely(use_worker))
1027 		synchronize_rcu_expedited_destroy_work(&rew);
1028 }
1029 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1030 
1031 /*
1032  * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
1033  * RCU grace periods that it needs.
1034  */
sync_rcu_do_polled_gp(struct work_struct * wp)1035 static void sync_rcu_do_polled_gp(struct work_struct *wp)
1036 {
1037 	unsigned long flags;
1038 	int i = 0;
1039 	struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
1040 	unsigned long s;
1041 
1042 	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1043 	s = rnp->exp_seq_poll_rq;
1044 	rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1045 	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1046 	if (s == RCU_GET_STATE_COMPLETED)
1047 		return;
1048 	while (!poll_state_synchronize_rcu(s)) {
1049 		synchronize_rcu_expedited();
1050 		if (i == 10 || i == 20)
1051 			pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
1052 		i++;
1053 	}
1054 	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1055 	s = rnp->exp_seq_poll_rq;
1056 	if (poll_state_synchronize_rcu(s))
1057 		rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1058 	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1059 }
1060 
1061 /**
1062  * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
1063  *
1064  * Returns a cookie to pass to a call to cond_synchronize_rcu(),
1065  * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
1066  * allowing them to determine whether or not any sort of grace period has
1067  * elapsed in the meantime.  If the needed expedited grace period is not
1068  * already slated to start, initiates that grace period.
1069  */
start_poll_synchronize_rcu_expedited(void)1070 unsigned long start_poll_synchronize_rcu_expedited(void)
1071 {
1072 	unsigned long flags;
1073 	struct rcu_data *rdp;
1074 	struct rcu_node *rnp;
1075 	unsigned long s;
1076 
1077 	s = get_state_synchronize_rcu();
1078 	rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
1079 	rnp = rdp->mynode;
1080 	if (rcu_init_invoked())
1081 		raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1082 	if (!poll_state_synchronize_rcu(s)) {
1083 		if (rcu_init_invoked()) {
1084 			rnp->exp_seq_poll_rq = s;
1085 			queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
1086 		}
1087 	}
1088 	if (rcu_init_invoked())
1089 		raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1090 
1091 	return s;
1092 }
1093 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
1094 
1095 /**
1096  * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
1097  * @rgosp: Place to put snapshot of grace-period state
1098  *
1099  * Places the normal and expedited grace-period states in rgosp.  This
1100  * state value can be passed to a later call to cond_synchronize_rcu_full()
1101  * or poll_state_synchronize_rcu_full() to determine whether or not a
1102  * grace period (whether normal or expedited) has elapsed in the meantime.
1103  * If the needed expedited grace period is not already slated to start,
1104  * initiates that grace period.
1105  */
start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate * rgosp)1106 void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1107 {
1108 	get_state_synchronize_rcu_full(rgosp);
1109 	(void)start_poll_synchronize_rcu_expedited();
1110 }
1111 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
1112 
1113 /**
1114  * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
1115  *
1116  * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
1117  *
1118  * If any type of full RCU grace period has elapsed since the earlier
1119  * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
1120  * or start_poll_synchronize_rcu_expedited(), just return.  Otherwise,
1121  * invoke synchronize_rcu_expedited() to wait for a full grace period.
1122  *
1123  * Yes, this function does not take counter wrap into account.
1124  * But counter wrap is harmless.  If the counter wraps, we have waited for
1125  * more than 2 billion grace periods (and way more on a 64-bit system!),
1126  * so waiting for a couple of additional grace periods should be just fine.
1127  *
1128  * This function provides the same memory-ordering guarantees that
1129  * would be provided by a synchronize_rcu() that was invoked at the call
1130  * to the function that provided @oldstate and that returned at the end
1131  * of this function.
1132  */
cond_synchronize_rcu_expedited(unsigned long oldstate)1133 void cond_synchronize_rcu_expedited(unsigned long oldstate)
1134 {
1135 	if (!poll_state_synchronize_rcu(oldstate))
1136 		synchronize_rcu_expedited();
1137 }
1138 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
1139 
1140 /**
1141  * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
1142  * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
1143  *
1144  * If a full RCU grace period has elapsed since the call to
1145  * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
1146  * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
1147  * obtained, just return.  Otherwise, invoke synchronize_rcu_expedited()
1148  * to wait for a full grace period.
1149  *
1150  * Yes, this function does not take counter wrap into account.
1151  * But counter wrap is harmless.  If the counter wraps, we have waited for
1152  * more than 2 billion grace periods (and way more on a 64-bit system!),
1153  * so waiting for a couple of additional grace periods should be just fine.
1154  *
1155  * This function provides the same memory-ordering guarantees that
1156  * would be provided by a synchronize_rcu() that was invoked at the call
1157  * to the function that provided @rgosp and that returned at the end of
1158  * this function.
1159  */
cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate * rgosp)1160 void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1161 {
1162 	if (!poll_state_synchronize_rcu_full(rgosp))
1163 		synchronize_rcu_expedited();
1164 }
1165 EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);
1166