Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: 065183391f75979e6bca59184f48e1126670eaad (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
// SPDX-License-Identifier: GPL-2.0+
/*
 * RCU CPU stall warnings for normal RCU grace periods
 *
 * Copyright IBM Corporation, 2019
 *
 * Author: Paul E. McKenney <paulmck@linux.ibm.com>
 */

//////////////////////////////////////////////////////////////////////////////
//
// Controlling CPU stall warnings, including delay calculation.

/* panic() on RCU Stall sysctl. */
int sysctl_panic_on_rcu_stall __read_mostly;

#ifdef CONFIG_PROVE_RCU
#define RCU_STALL_DELAY_DELTA	       (5 * HZ)
#else
#define RCU_STALL_DELAY_DELTA	       0
#endif

/* Limit-check stall timeouts specified at boottime and runtime. */
int rcu_jiffies_till_stall_check(void)
{
	int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);

	/*
	 * Limit check must be consistent with the Kconfig limits
	 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
	 */
	if (till_stall_check < 3) {
		WRITE_ONCE(rcu_cpu_stall_timeout, 3);
		till_stall_check = 3;
	} else if (till_stall_check > 300) {
		WRITE_ONCE(rcu_cpu_stall_timeout, 300);
		till_stall_check = 300;
	}
	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}
EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);

/* Don't do RCU CPU stall warnings during long sysrq printouts. */
void rcu_sysrq_start(void)
{
	if (!rcu_cpu_stall_suppress)
		rcu_cpu_stall_suppress = 2;
}

void rcu_sysrq_end(void)
{
	if (rcu_cpu_stall_suppress == 2)
		rcu_cpu_stall_suppress = 0;
}

/* Don't print RCU CPU stall warnings during a kernel panic. */
static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
{
	rcu_cpu_stall_suppress = 1;
	return NOTIFY_DONE;
}

static struct notifier_block rcu_panic_block = {
	.notifier_call = rcu_panic,
};

static int __init check_cpu_stall_init(void)
{
	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
	return 0;
}
early_initcall(check_cpu_stall_init);

/* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
static void panic_on_rcu_stall(void)
{
	if (sysctl_panic_on_rcu_stall)
		panic("RCU Stall\n");
}

/**
 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
 *
 * Set the stall-warning timeout way off into the future, thus preventing
 * any RCU CPU stall-warning messages from appearing in the current set of
 * RCU grace periods.
 *
 * The caller must disable hard irqs.
 */
void rcu_cpu_stall_reset(void)
{
	WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2);
}

//////////////////////////////////////////////////////////////////////////////
//
// Interaction with RCU grace periods

/* Start of new grace period, so record stall time (and forcing times). */
static void record_gp_stall_check_time(void)
{
	unsigned long j = jiffies;
	unsigned long j1;

	rcu_state.gp_start = j;
	j1 = rcu_jiffies_till_stall_check();
	/* Record ->gp_start before ->jiffies_stall. */
	smp_store_release(&rcu_state.jiffies_stall, j + j1); /* ^^^ */
	rcu_state.jiffies_resched = j + j1 / 2;
	rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
}

/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
	WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}

/*
 * If too much time has passed in the current grace period, and if
 * so configured, go kick the relevant kthreads.
 */
static void rcu_stall_kick_kthreads(void)
{
	unsigned long j;

	if (!rcu_kick_kthreads)
		return;
	j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
	if (time_after(jiffies, j) && rcu_state.gp_kthread &&
	    (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
		WARN_ONCE(1, "Kicking %s grace-period kthread\n",
			  rcu_state.name);
		rcu_ftrace_dump(DUMP_ALL);
		wake_up_process(rcu_state.gp_kthread);
		WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
	}
}

/*
 * Handler for the irq_work request posted about halfway into the RCU CPU
 * stall timeout, and used to detect excessive irq disabling.  Set state
 * appropriately, but just complain if there is unexpected state on entry.
 */
static void rcu_iw_handler(struct irq_work *iwp)
{
	struct rcu_data *rdp;
	struct rcu_node *rnp;

	rdp = container_of(iwp, struct rcu_data, rcu_iw);
	rnp = rdp->mynode;
	raw_spin_lock_rcu_node(rnp);
	if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
		rdp->rcu_iw_gp_seq = rnp->gp_seq;
		rdp->rcu_iw_pending = false;
	}
	raw_spin_unlock_rcu_node(rnp);
}

//////////////////////////////////////////////////////////////////////////////
//
// Printing RCU CPU stall warnings

#ifdef CONFIG_PREEMPT

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period on the specified rcu_node structure.
 */
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
	unsigned long flags;
	struct task_struct *t;

	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;
	}
	t = list_entry(rnp->gp_tasks->prev,
		       struct task_struct, rcu_node_entry);
	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
		/*
		 * We could be printing a lot while holding a spinlock.
		 * Avoid triggering hard lockup.
		 */
		touch_nmi_watchdog();
		sched_show_task(t);
	}
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}

/*
 * Scan the current list of tasks blocked within RCU read-side critical
 * sections, printing out the tid of each.
 */
static int rcu_print_task_stall(struct rcu_node *rnp)
{
	struct task_struct *t;
	int ndetected = 0;

	if (!rcu_preempt_blocked_readers_cgp(rnp))
		return 0;
	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
	       rnp->level, rnp->grplo, rnp->grphi);
	t = list_entry(rnp->gp_tasks->prev,
		       struct task_struct, rcu_node_entry);
	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
		pr_cont(" P%d", t->pid);
		ndetected++;
	}
	pr_cont("\n");
	return ndetected;
}

#else /* #ifdef CONFIG_PREEMPT */

/*
 * Because preemptible RCU does not exist, we never have to check for
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
}

/*
 * Because preemptible RCU does not exist, we never have to check for
 * tasks blocked within RCU read-side critical sections.
 */
static int rcu_print_task_stall(struct rcu_node *rnp)
{
	return 0;
}
#endif /* #else #ifdef CONFIG_PREEMPT */

/*
 * Dump stacks of all tasks running on stalled CPUs.  First try using
 * NMIs, but fall back to manual remote stack tracing on architectures
 * that don't support NMI-based stack dumps.  The NMI-triggered stack
 * traces are more accurate because they are printed by the target CPU.
 */
static void rcu_dump_cpu_stacks(void)
{
	int cpu;
	unsigned long flags;
	struct rcu_node *rnp;

	rcu_for_each_leaf_node(rnp) {
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		for_each_leaf_node_possible_cpu(rnp, cpu)
			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
				if (!trigger_single_cpu_backtrace(cpu))
					dump_cpu_task(cpu);
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	}
}

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);

	sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
		rdp->last_accelerate & 0xffff, jiffies & 0xffff,
		".l"[rdp->all_lazy],
		".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
		".D"[!!rdp->tick_nohz_enabled_snap]);
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
	*cp = '\0';
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/*
 * Print out diagnostic information for the specified stalled CPU.
 *
 * If the specified CPU is aware of the current RCU grace period, then
 * print the number of scheduling clock interrupts the CPU has taken
 * during the time that it has been aware.  Otherwise, print the number
 * of RCU grace periods that this CPU is ignorant of, for example, "1"
 * if the CPU was aware of the previous grace period.
 *
 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 */
static void print_cpu_stall_info(int cpu)
{
	unsigned long delta;
	char fast_no_hz[72];
	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
	char *ticks_title;
	unsigned long ticks_value;

	/*
	 * We could be printing a lot while holding a spinlock.  Avoid
	 * triggering hard lockup.
	 */
	touch_nmi_watchdog();

	ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
	if (ticks_value) {
		ticks_title = "GPs behind";
	} else {
		ticks_title = "ticks this GP";
		ticks_value = rdp->ticks_this_gp;
	}
	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
	delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
	       cpu,
	       "O."[!!cpu_online(cpu)],
	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
	       !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
			rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
				"!."[!delta],
	       ticks_value, ticks_title,
	       rcu_dynticks_snap(rdp) & 0xfff,
	       rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
	       READ_ONCE(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
	       fast_no_hz);
}

/* Complain about starvation of grace-period kthread.  */
static void rcu_check_gp_kthread_starvation(void)
{
	struct task_struct *gpk = rcu_state.gp_kthread;
	unsigned long j;

	j = jiffies - READ_ONCE(rcu_state.gp_activity);
	if (j > 2 * HZ) {
		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
		       rcu_state.name, j,
		       (long)rcu_seq_current(&rcu_state.gp_seq),
		       READ_ONCE(rcu_state.gp_flags),
		       gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
		       gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
		if (gpk) {
			pr_err("RCU grace-period kthread stack dump:\n");
			sched_show_task(gpk);
			wake_up_process(gpk);
		}
	}
}

static void print_other_cpu_stall(unsigned long gp_seq)
{
	int cpu;
	unsigned long flags;
	unsigned long gpa;
	unsigned long j;
	int ndetected = 0;
	struct rcu_node *rnp;
	long totqlen = 0;

	/* Kick and suppress, if so configured. */
	rcu_stall_kick_kthreads();
	if (rcu_cpu_stall_suppress)
		return;

	/*
	 * OK, time to rat on our buddy...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
	pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
	rcu_for_each_leaf_node(rnp) {
		raw_spin_lock_irqsave_rcu_node(rnp, flags);
		ndetected += rcu_print_task_stall(rnp);
		if (rnp->qsmask != 0) {
			for_each_leaf_node_possible_cpu(rnp, cpu)
				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
					print_cpu_stall_info(cpu);
					ndetected++;
				}
		}
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	}

	for_each_possible_cpu(cpu)
		totqlen += rcu_get_n_cbs_cpu(cpu);
	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
	       smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
	if (ndetected) {
		rcu_dump_cpu_stacks();

		/* Complain about tasks blocking the grace period. */
		rcu_for_each_leaf_node(rnp)
			rcu_print_detail_task_stall_rnp(rnp);
	} else {
		if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
			pr_err("INFO: Stall ended before state dump start\n");
		} else {
			j = jiffies;
			gpa = READ_ONCE(rcu_state.gp_activity);
			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
			       rcu_state.name, j - gpa, j, gpa,
			       READ_ONCE(jiffies_till_next_fqs),
			       rcu_get_root()->qsmask);
			/* In this case, the current CPU might be at fault. */
			sched_show_task(current);
		}
	}
	/* Rewrite if needed in case of slow consoles. */
	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
		WRITE_ONCE(rcu_state.jiffies_stall,
			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);

	rcu_check_gp_kthread_starvation();

	panic_on_rcu_stall();

	rcu_force_quiescent_state();  /* Kick them all. */
}

static void print_cpu_stall(void)
{
	int cpu;
	unsigned long flags;
	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
	struct rcu_node *rnp = rcu_get_root();
	long totqlen = 0;

	/* Kick and suppress, if so configured. */
	rcu_stall_kick_kthreads();
	if (rcu_cpu_stall_suppress)
		return;

	/*
	 * OK, time to rat on ourselves...
	 * See Documentation/RCU/stallwarn.txt for info on how to debug
	 * RCU CPU stall warnings.
	 */
	pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
	raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
	print_cpu_stall_info(smp_processor_id());
	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
	for_each_possible_cpu(cpu)
		totqlen += rcu_get_n_cbs_cpu(cpu);
	pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
		jiffies - rcu_state.gp_start,
		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);

	rcu_check_gp_kthread_starvation();

	rcu_dump_cpu_stacks();

	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	/* Rewrite if needed in case of slow consoles. */
	if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
		WRITE_ONCE(rcu_state.jiffies_stall,
			   jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

	panic_on_rcu_stall();

	/*
	 * Attempt to revive the RCU machinery by forcing a context switch.
	 *
	 * A context switch would normally allow the RCU state machine to make
	 * progress and it could be we're stuck in kernel space without context
	 * switches for an entirely unreasonable amount of time.
	 */
	set_tsk_need_resched(current);
	set_preempt_need_resched();
}

static void check_cpu_stall(struct rcu_data *rdp)
{
	unsigned long gs1;
	unsigned long gs2;
	unsigned long gps;
	unsigned long j;
	unsigned long jn;
	unsigned long js;
	struct rcu_node *rnp;

	if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
	    !rcu_gp_in_progress())
		return;
	rcu_stall_kick_kthreads();
	j = jiffies;

	/*
	 * Lots of memory barriers to reject false positives.
	 *
	 * The idea is to pick up rcu_state.gp_seq, then
	 * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
	 * another copy of rcu_state.gp_seq.  These values are updated in
	 * the opposite order with memory barriers (or equivalent) during
	 * grace-period initialization and cleanup.  Now, a false positive
	 * can occur if we get an new value of rcu_state.gp_start and a old
	 * value of rcu_state.jiffies_stall.  But given the memory barriers,
	 * the only way that this can happen is if one grace period ends
	 * and another starts between these two fetches.  This is detected
	 * by comparing the second fetch of rcu_state.gp_seq with the
	 * previous fetch from rcu_state.gp_seq.
	 *
	 * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
	 * and rcu_state.gp_start suffice to forestall false positives.
	 */
	gs1 = READ_ONCE(rcu_state.gp_seq);
	smp_rmb(); /* Pick up ->gp_seq first... */
	js = READ_ONCE(rcu_state.jiffies_stall);
	smp_rmb(); /* ...then ->jiffies_stall before the rest... */
	gps = READ_ONCE(rcu_state.gp_start);
	smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
	gs2 = READ_ONCE(rcu_state.gp_seq);
	if (gs1 != gs2 ||
	    ULONG_CMP_LT(j, js) ||
	    ULONG_CMP_GE(gps, js))
		return; /* No stall or GP completed since entering function. */
	rnp = rdp->mynode;
	jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
	if (rcu_gp_in_progress() &&
	    (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {

		/* We haven't checked in, so go dump stack. */
		print_cpu_stall();

	} else if (rcu_gp_in_progress() &&
		   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
		   cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {

		/* They had a few time units to dump stack, so complain. */
		print_other_cpu_stall(gs2);
	}
}

//////////////////////////////////////////////////////////////////////////////
//
// RCU forward-progress mechanisms, including of callback invocation.


/*
 * Show the state of the grace-period kthreads.
 */
void show_rcu_gp_kthreads(void)
{
	int cpu;
	unsigned long j;
	unsigned long ja;
	unsigned long jr;
	unsigned long jw;
	struct rcu_data *rdp;
	struct rcu_node *rnp;

	j = jiffies;
	ja = j - READ_ONCE(rcu_state.gp_activity);
	jr = j - READ_ONCE(rcu_state.gp_req_activity);
	jw = j - READ_ONCE(rcu_state.gp_wake_time);
	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
		rcu_state.name, gp_state_getname(rcu_state.gp_state),
		rcu_state.gp_state,
		rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL,
		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
		(long)READ_ONCE(rcu_state.gp_seq),
		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
		READ_ONCE(rcu_state.gp_flags));
	rcu_for_each_node_breadth_first(rnp) {
		if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
			continue;
		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
			rnp->grplo, rnp->grphi, (long)rnp->gp_seq,
			(long)rnp->gp_seq_needed);
		if (!rcu_is_leaf_node(rnp))
			continue;
		for_each_leaf_node_possible_cpu(rnp, cpu) {
			rdp = per_cpu_ptr(&rcu_data, cpu);
			if (rdp->gpwrap ||
			    ULONG_CMP_GE(rcu_state.gp_seq,
					 rdp->gp_seq_needed))
				continue;
			pr_info("\tcpu %d ->gp_seq_needed %ld\n",
				cpu, (long)rdp->gp_seq_needed);
		}
	}
	/* sched_show_task(rcu_state.gp_kthread); */
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);

/*
 * This function checks for grace-period requests that fail to motivate
 * RCU to come out of its idle mode.
 */
static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
				     const unsigned long gpssdelay)
{
	unsigned long flags;
	unsigned long j;
	struct rcu_node *rnp_root = rcu_get_root();
	static atomic_t warned = ATOMIC_INIT(0);

	if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
		return;
	j = jiffies; /* Expensive access, and in common case don't get here. */
	if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
	    atomic_read(&warned))
		return;

	raw_spin_lock_irqsave_rcu_node(rnp, flags);
	j = jiffies;
	if (rcu_gp_in_progress() ||
	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
	    time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
	    time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
	    atomic_read(&warned)) {
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;
	}
	/* Hold onto the leaf lock to make others see warned==1. */

	if (rnp_root != rnp)
		raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
	j = jiffies;
	if (rcu_gp_in_progress() ||
	    ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
	    time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
	    time_before(j, rcu_state.gp_activity + gpssdelay) ||
	    atomic_xchg(&warned, 1)) {
		if (rnp_root != rnp)
			/* irqs remain disabled. */
			raw_spin_unlock_rcu_node(rnp_root);
		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
		return;
	}
	WARN_ON(1);
	if (rnp_root != rnp)
		raw_spin_unlock_rcu_node(rnp_root);
	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
	show_rcu_gp_kthreads();
}

/*
 * Do a forward-progress check for rcutorture.  This is normally invoked
 * due to an OOM event.  The argument "j" gives the time period during
 * which rcutorture would like progress to have been made.
 */
void rcu_fwd_progress_check(unsigned long j)
{
	unsigned long cbs;
	int cpu;
	unsigned long max_cbs = 0;
	int max_cpu = -1;
	struct rcu_data *rdp;

	if (rcu_gp_in_progress()) {
		pr_info("%s: GP age %lu jiffies\n",
			__func__, jiffies - rcu_state.gp_start);
		show_rcu_gp_kthreads();
	} else {
		pr_info("%s: Last GP end %lu jiffies ago\n",
			__func__, jiffies - rcu_state.gp_end);
		preempt_disable();
		rdp = this_cpu_ptr(&rcu_data);
		rcu_check_gp_start_stall(rdp->mynode, rdp, j);
		preempt_enable();
	}
	for_each_possible_cpu(cpu) {
		cbs = rcu_get_n_cbs_cpu(cpu);
		if (!cbs)
			continue;
		if (max_cpu < 0)
			pr_info("%s: callbacks", __func__);
		pr_cont(" %d: %lu", cpu, cbs);
		if (cbs <= max_cbs)
			continue;
		max_cbs = cbs;
		max_cpu = cpu;
	}
	if (max_cpu >= 0)
		pr_cont("\n");
}
EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);

/* Commandeer a sysrq key to dump RCU's tree. */
static bool sysrq_rcu;
module_param(sysrq_rcu, bool, 0444);

/* Dump grace-period-request information due to commandeered sysrq. */
static void sysrq_show_rcu(int key)
{
	show_rcu_gp_kthreads();
}

static struct sysrq_key_op sysrq_rcudump_op = {
	.handler = sysrq_show_rcu,
	.help_msg = "show-rcu(y)",
	.action_msg = "Show RCU tree",
	.enable_mask = SYSRQ_ENABLE_DUMP,
};

static int __init rcu_sysrq_init(void)
{
	if (sysrq_rcu)
		return register_sysrq_key('y', &sysrq_rcudump_op);
	return 0;
}
early_initcall(rcu_sysrq_init);