summaryrefslogtreecommitdiffstats
path: root/kernel/context_tracking.c
blob: 77978e37237712667e1d4a32eae139c8a436ab33 (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
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Context tracking: Probe on high level context boundaries such as kernel,
 * userspace, guest or idle.
 *
 * This is used by RCU to remove its dependency on the timer tick while a CPU
 * runs in idle, userspace or guest mode.
 *
 * User/guest tracking started by Frederic Weisbecker:
 *
 * Copyright (C) 2012 Red Hat, Inc., Frederic Weisbecker
 *
 * Many thanks to Gilad Ben-Yossef, Paul McKenney, Ingo Molnar, Andrew Morton,
 * Steven Rostedt, Peter Zijlstra for suggestions and improvements.
 *
 * RCU extended quiescent state bits imported from kernel/rcu/tree.c
 * where the relevant authorship may be found.
 */

#include <linux/context_tracking.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/hardirq.h>
#include <linux/export.h>
#include <linux/kprobes.h>
#include <trace/events/rcu.h>


DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
#ifdef CONFIG_CONTEXT_TRACKING_IDLE
	.dynticks_nesting = 1,
	.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
#endif
	.state = ATOMIC_INIT(RCU_DYNTICKS_IDX),
};
EXPORT_SYMBOL_GPL(context_tracking);

#ifdef CONFIG_CONTEXT_TRACKING_IDLE
#define TPS(x)  tracepoint_string(x)

/* Record the current task on dyntick-idle entry. */
static __always_inline void rcu_dynticks_task_enter(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
	WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}

/* Record no current task on dyntick-idle exit. */
static __always_inline void rcu_dynticks_task_exit(void)
{
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
	WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
}

/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
static __always_inline void rcu_dynticks_task_trace_enter(void)
{
#ifdef CONFIG_TASKS_TRACE_RCU
	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
		current->trc_reader_special.b.need_mb = true;
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
}

/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
static __always_inline void rcu_dynticks_task_trace_exit(void)
{
#ifdef CONFIG_TASKS_TRACE_RCU
	if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
		current->trc_reader_special.b.need_mb = false;
#endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
}

/*
 * Record entry into an extended quiescent state.  This is only to be
 * called when not already in an extended quiescent state, that is,
 * RCU is watching prior to the call to this function and is no longer
 * watching upon return.
 */
static noinstr void ct_kernel_exit_state(int offset)
{
	int seq;

	/*
	 * CPUs seeing atomic_add_return() must see prior RCU read-side
	 * critical sections, and we also must force ordering with the
	 * next idle sojourn.
	 */
	rcu_dynticks_task_trace_enter();  // Before ->dynticks update!
	seq = ct_state_inc(offset);
	// RCU is no longer watching.  Better be in extended quiescent state!
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (seq & RCU_DYNTICKS_IDX));
}

/*
 * Record exit from an extended quiescent state.  This is only to be
 * called from an extended quiescent state, that is, RCU is not watching
 * prior to the call to this function and is watching upon return.
 */
static noinstr void ct_kernel_enter_state(int offset)
{
	int seq;

	/*
	 * CPUs seeing atomic_add_return() must see prior idle sojourns,
	 * and we also must force ordering with the next RCU read-side
	 * critical section.
	 */
	seq = ct_state_inc(offset);
	// RCU is now watching.  Better not be in an extended quiescent state!
	rcu_dynticks_task_trace_exit();  // After ->dynticks update!
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(seq & RCU_DYNTICKS_IDX));
}

/*
 * Enter an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 *
 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
 * the possibility of usermode upcalls having messed up our count
 * of interrupt nesting level during the prior busy period.
 */
static void noinstr ct_kernel_exit(bool user, int offset)
{
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);

	WARN_ON_ONCE(ct_dynticks_nmi_nesting() != DYNTICK_IRQ_NONIDLE);
	WRITE_ONCE(ct->dynticks_nmi_nesting, 0);
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
		     ct_dynticks_nesting() == 0);
	if (ct_dynticks_nesting() != 1) {
		// RCU will still be watching, so just do accounting and leave.
		ct->dynticks_nesting--;
		return;
	}

	instrumentation_begin();
	lockdep_assert_irqs_disabled();
	trace_rcu_dyntick(TPS("Start"), ct_dynticks_nesting(), 0, ct_dynticks());
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
	rcu_preempt_deferred_qs(current);

	// instrumentation for the noinstr ct_kernel_exit_state()
	instrument_atomic_write(&ct->state, sizeof(ct->state));

	instrumentation_end();
	WRITE_ONCE(ct->dynticks_nesting, 0); /* Avoid irq-access tearing. */
	// RCU is watching here ...
	ct_kernel_exit_state(offset);
	// ... but is no longer watching here.
	rcu_dynticks_task_enter();
}

/*
 * Exit an RCU extended quiescent state, which can be either the
 * idle loop or adaptive-tickless usermode execution.
 *
 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
 * allow for the possibility of usermode upcalls messing up our count of
 * interrupt nesting level during the busy period that is just now starting.
 */
static void noinstr ct_kernel_enter(bool user, int offset)
{
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);
	long oldval;

	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
	oldval = ct_dynticks_nesting();
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
	if (oldval) {
		// RCU was already watching, so just do accounting and leave.
		ct->dynticks_nesting++;
		return;
	}
	rcu_dynticks_task_exit();
	// RCU is not watching here ...
	ct_kernel_enter_state(offset);
	// ... but is watching here.
	instrumentation_begin();

	// instrumentation for the noinstr ct_kernel_enter_state()
	instrument_atomic_write(&ct->state, sizeof(ct->state));

	trace_rcu_dyntick(TPS("End"), ct_dynticks_nesting(), 1, ct_dynticks());
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
	WRITE_ONCE(ct->dynticks_nesting, 1);
	WARN_ON_ONCE(ct_dynticks_nmi_nesting());
	WRITE_ONCE(ct->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
	instrumentation_end();
}

/**
 * ct_nmi_exit - inform RCU of exit from NMI context
 *
 * If we are returning from the outermost NMI handler that interrupted an
 * RCU-idle period, update ct->state and ct->dynticks_nmi_nesting
 * to let the RCU grace-period handling know that the CPU is back to
 * being RCU-idle.
 *
 * If you add or remove a call to ct_nmi_exit(), be sure to test
 * with CONFIG_RCU_EQS_DEBUG=y.
 */
void noinstr ct_nmi_exit(void)
{
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);

	instrumentation_begin();
	/*
	 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
	 * (We are exiting an NMI handler, so RCU better be paying attention
	 * to us!)
	 */
	WARN_ON_ONCE(ct_dynticks_nmi_nesting() <= 0);
	WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());

	/*
	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
	 * leave it in non-RCU-idle state.
	 */
	if (ct_dynticks_nmi_nesting() != 1) {
		trace_rcu_dyntick(TPS("--="), ct_dynticks_nmi_nesting(), ct_dynticks_nmi_nesting() - 2,
				  ct_dynticks());
		WRITE_ONCE(ct->dynticks_nmi_nesting, /* No store tearing. */
			   ct_dynticks_nmi_nesting() - 2);
		instrumentation_end();
		return;
	}

	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
	trace_rcu_dyntick(TPS("Startirq"), ct_dynticks_nmi_nesting(), 0, ct_dynticks());
	WRITE_ONCE(ct->dynticks_nmi_nesting, 0); /* Avoid store tearing. */

	// instrumentation for the noinstr ct_kernel_exit_state()
	instrument_atomic_write(&ct->state, sizeof(ct->state));
	instrumentation_end();

	// RCU is watching here ...
	ct_kernel_exit_state(RCU_DYNTICKS_IDX);
	// ... but is no longer watching here.

	if (!in_nmi())
		rcu_dynticks_task_enter();
}

/**
 * ct_nmi_enter - inform RCU of entry to NMI context
 *
 * If the CPU was idle from RCU's viewpoint, update ct->state and
 * ct->dynticks_nmi_nesting to let the RCU grace-period handling know
 * that the CPU is active.  This implementation permits nested NMIs, as
 * long as the nesting level does not overflow an int.  (You will probably
 * run out of stack space first.)
 *
 * If you add or remove a call to ct_nmi_enter(), be sure to test
 * with CONFIG_RCU_EQS_DEBUG=y.
 */
void noinstr ct_nmi_enter(void)
{
	long incby = 2;
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);

	/* Complain about underflow. */
	WARN_ON_ONCE(ct_dynticks_nmi_nesting() < 0);

	/*
	 * If idle from RCU viewpoint, atomically increment ->dynticks
	 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
	 * Otherwise, increment ->dynticks_nmi_nesting by two.  This means
	 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
	 * to be in the outermost NMI handler that interrupted an RCU-idle
	 * period (observation due to Andy Lutomirski).
	 */
	if (rcu_dynticks_curr_cpu_in_eqs()) {

		if (!in_nmi())
			rcu_dynticks_task_exit();

		// RCU is not watching here ...
		ct_kernel_enter_state(RCU_DYNTICKS_IDX);
		// ... but is watching here.

		instrumentation_begin();
		// instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
		instrument_atomic_read(&ct->state, sizeof(ct->state));
		// instrumentation for the noinstr ct_kernel_enter_state()
		instrument_atomic_write(&ct->state, sizeof(ct->state));

		incby = 1;
	} else if (!in_nmi()) {
		instrumentation_begin();
		rcu_irq_enter_check_tick();
	} else  {
		instrumentation_begin();
	}

	trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
			  ct_dynticks_nmi_nesting(),
			  ct_dynticks_nmi_nesting() + incby, ct_dynticks());
	instrumentation_end();
	WRITE_ONCE(ct->dynticks_nmi_nesting, /* Prevent store tearing. */
		   ct_dynticks_nmi_nesting() + incby);
	barrier();
}

/**
 * ct_idle_enter - inform RCU that current CPU is entering idle
 *
 * Enter idle mode, in other words, -leave- the mode in which RCU
 * read-side critical sections can occur.  (Though RCU read-side
 * critical sections can occur in irq handlers in idle, a possibility
 * handled by irq_enter() and irq_exit().)
 *
 * If you add or remove a call to ct_idle_enter(), be sure to test with
 * CONFIG_RCU_EQS_DEBUG=y.
 */
void noinstr ct_idle_enter(void)
{
	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !raw_irqs_disabled());
	ct_kernel_exit(false, RCU_DYNTICKS_IDX + CONTEXT_IDLE);
}
EXPORT_SYMBOL_GPL(ct_idle_enter);

/**
 * ct_idle_exit - inform RCU that current CPU is leaving idle
 *
 * Exit idle mode, in other words, -enter- the mode in which RCU
 * read-side critical sections can occur.
 *
 * If you add or remove a call to ct_idle_exit(), be sure to test with
 * CONFIG_RCU_EQS_DEBUG=y.
 */
void noinstr ct_idle_exit(void)
{
	unsigned long flags;

	raw_local_irq_save(flags);
	ct_kernel_enter(false, RCU_DYNTICKS_IDX - CONTEXT_IDLE);
	raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(ct_idle_exit);

/**
 * ct_irq_enter - inform RCU that current CPU is entering irq away from idle
 *
 * Enter an interrupt handler, which might possibly result in exiting
 * idle mode, in other words, entering the mode in which read-side critical
 * sections can occur.  The caller must have disabled interrupts.
 *
 * Note that the Linux kernel is fully capable of entering an interrupt
 * handler that it never exits, for example when doing upcalls to user mode!
 * This code assumes that the idle loop never does upcalls to user mode.
 * If your architecture's idle loop does do upcalls to user mode (or does
 * anything else that results in unbalanced calls to the irq_enter() and
 * irq_exit() functions), RCU will give you what you deserve, good and hard.
 * But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
 *
 * If you add or remove a call to ct_irq_enter(), be sure to test with
 * CONFIG_RCU_EQS_DEBUG=y.
 */
noinstr void ct_irq_enter(void)
{
	lockdep_assert_irqs_disabled();
	ct_nmi_enter();
}

/**
 * ct_irq_exit - inform RCU that current CPU is exiting irq towards idle
 *
 * Exit from an interrupt handler, which might possibly result in entering
 * idle mode, in other words, leaving the mode in which read-side critical
 * sections can occur.  The caller must have disabled interrupts.
 *
 * This code assumes that the idle loop never does anything that might
 * result in unbalanced calls to irq_enter() and irq_exit().  If your
 * architecture's idle loop violates this assumption, RCU will give you what
 * you deserve, good and hard.  But very infrequently and irreproducibly.
 *
 * Use things like work queues to work around this limitation.
 *
 * You have been warned.
 *
 * If you add or remove a call to ct_irq_exit(), be sure to test with
 * CONFIG_RCU_EQS_DEBUG=y.
 */
noinstr void ct_irq_exit(void)
{
	lockdep_assert_irqs_disabled();
	ct_nmi_exit();
}

/*
 * Wrapper for ct_irq_enter() where interrupts are enabled.
 *
 * If you add or remove a call to ct_irq_enter_irqson(), be sure to test
 * with CONFIG_RCU_EQS_DEBUG=y.
 */
void ct_irq_enter_irqson(void)
{
	unsigned long flags;

	local_irq_save(flags);
	ct_irq_enter();
	local_irq_restore(flags);
}

/*
 * Wrapper for ct_irq_exit() where interrupts are enabled.
 *
 * If you add or remove a call to ct_irq_exit_irqson(), be sure to test
 * with CONFIG_RCU_EQS_DEBUG=y.
 */
void ct_irq_exit_irqson(void)
{
	unsigned long flags;

	local_irq_save(flags);
	ct_irq_exit();
	local_irq_restore(flags);
}
#else
static __always_inline void ct_kernel_exit(bool user, int offset) { }
static __always_inline void ct_kernel_enter(bool user, int offset) { }
#endif /* #ifdef CONFIG_CONTEXT_TRACKING_IDLE */

#ifdef CONFIG_CONTEXT_TRACKING_USER

#define CREATE_TRACE_POINTS
#include <trace/events/context_tracking.h>

DEFINE_STATIC_KEY_FALSE(context_tracking_key);
EXPORT_SYMBOL_GPL(context_tracking_key);

static noinstr bool context_tracking_recursion_enter(void)
{
	int recursion;

	recursion = __this_cpu_inc_return(context_tracking.recursion);
	if (recursion == 1)
		return true;

	WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion);
	__this_cpu_dec(context_tracking.recursion);

	return false;
}

static __always_inline void context_tracking_recursion_exit(void)
{
	__this_cpu_dec(context_tracking.recursion);
}

/**
 * __ct_user_enter - Inform the context tracking that the CPU is going
 *		     to enter user or guest space mode.
 *
 * This function must be called right before we switch from the kernel
 * to user or guest space, when it's guaranteed the remaining kernel
 * instructions to execute won't use any RCU read side critical section
 * because this function sets RCU in extended quiescent state.
 */
void noinstr __ct_user_enter(enum ctx_state state)
{
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);
	lockdep_assert_irqs_disabled();

	/* Kernel threads aren't supposed to go to userspace */
	WARN_ON_ONCE(!current->mm);

	if (!context_tracking_recursion_enter())
		return;

	if (__ct_state() != state) {
		if (ct->active) {
			/*
			 * At this stage, only low level arch entry code remains and
			 * then we'll run in userspace. We can assume there won't be
			 * any RCU read-side critical section until the next call to
			 * user_exit() or ct_irq_enter(). Let's remove RCU's dependency
			 * on the tick.
			 */
			if (state == CONTEXT_USER) {
				instrumentation_begin();
				trace_user_enter(0);
				vtime_user_enter(current);
				instrumentation_end();
			}
			/*
			 * Other than generic entry implementation, we may be past the last
			 * rescheduling opportunity in the entry code. Trigger a self IPI
			 * that will fire and reschedule once we resume in user/guest mode.
			 */
			rcu_irq_work_resched();

			/*
			 * Enter RCU idle mode right before resuming userspace.  No use of RCU
			 * is permitted between this call and rcu_eqs_exit(). This way the
			 * CPU doesn't need to maintain the tick for RCU maintenance purposes
			 * when the CPU runs in userspace.
			 */
			ct_kernel_exit(true, RCU_DYNTICKS_IDX + state);

			/*
			 * Special case if we only track user <-> kernel transitions for tickless
			 * cputime accounting but we don't support RCU extended quiescent state.
			 * In this we case we don't care about any concurrency/ordering.
			 */
			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE))
				atomic_set(&ct->state, state);
		} else {
			/*
			 * Even if context tracking is disabled on this CPU, because it's outside
			 * the full dynticks mask for example, we still have to keep track of the
			 * context transitions and states to prevent inconsistency on those of
			 * other CPUs.
			 * If a task triggers an exception in userspace, sleep on the exception
			 * handler and then migrate to another CPU, that new CPU must know where
			 * the exception returns by the time we call exception_exit().
			 * This information can only be provided by the previous CPU when it called
			 * exception_enter().
			 * OTOH we can spare the calls to vtime and RCU when context_tracking.active
			 * is false because we know that CPU is not tickless.
			 */
			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
				/* Tracking for vtime only, no concurrent RCU EQS accounting */
				atomic_set(&ct->state, state);
			} else {
				/*
				 * Tracking for vtime and RCU EQS. Make sure we don't race
				 * with NMIs. OTOH we don't care about ordering here since
				 * RCU only requires RCU_DYNTICKS_IDX increments to be fully
				 * ordered.
				 */
				atomic_add(state, &ct->state);
			}
		}
	}
	context_tracking_recursion_exit();
}
EXPORT_SYMBOL_GPL(__ct_user_enter);

/*
 * OBSOLETE:
 * This function should be noinstr but the below local_irq_restore() is
 * unsafe because it involves illegal RCU uses through tracing and lockdep.
 * This is unlikely to be fixed as this function is obsolete. The preferred
 * way is to call __context_tracking_enter() through user_enter_irqoff()
 * or context_tracking_guest_enter(). It should be the arch entry code
 * responsibility to call into context tracking with IRQs disabled.
 */
void ct_user_enter(enum ctx_state state)
{
	unsigned long flags;

	/*
	 * Some contexts may involve an exception occuring in an irq,
	 * leading to that nesting:
	 * ct_irq_enter() rcu_eqs_exit(true) rcu_eqs_enter(true) ct_irq_exit()
	 * This would mess up the dyntick_nesting count though. And rcu_irq_*()
	 * helpers are enough to protect RCU uses inside the exception. So
	 * just return immediately if we detect we are in an IRQ.
	 */
	if (in_interrupt())
		return;

	local_irq_save(flags);
	__ct_user_enter(state);
	local_irq_restore(flags);
}
NOKPROBE_SYMBOL(ct_user_enter);
EXPORT_SYMBOL_GPL(ct_user_enter);

/**
 * user_enter_callable() - Unfortunate ASM callable version of user_enter() for
 *			   archs that didn't manage to check the context tracking
 *			   static key from low level code.
 *
 * This OBSOLETE function should be noinstr but it unsafely calls
 * local_irq_restore(), involving illegal RCU uses through tracing and lockdep.
 * This is unlikely to be fixed as this function is obsolete. The preferred
 * way is to call user_enter_irqoff(). It should be the arch entry code
 * responsibility to call into context tracking with IRQs disabled.
 */
void user_enter_callable(void)
{
	user_enter();
}
NOKPROBE_SYMBOL(user_enter_callable);

/**
 * __ct_user_exit - Inform the context tracking that the CPU is
 *		    exiting user or guest mode and entering the kernel.
 *
 * This function must be called after we entered the kernel from user or
 * guest space before any use of RCU read side critical section. This
 * potentially include any high level kernel code like syscalls, exceptions,
 * signal handling, etc...
 *
 * This call supports re-entrancy. This way it can be called from any exception
 * handler without needing to know if we came from userspace or not.
 */
void noinstr __ct_user_exit(enum ctx_state state)
{
	struct context_tracking *ct = this_cpu_ptr(&context_tracking);

	if (!context_tracking_recursion_enter())
		return;

	if (__ct_state() == state) {
		if (ct->active) {
			/*
			 * Exit RCU idle mode while entering the kernel because it can
			 * run a RCU read side critical section anytime.
			 */
			ct_kernel_enter(true, RCU_DYNTICKS_IDX - state);
			if (state == CONTEXT_USER) {
				instrumentation_begin();
				vtime_user_exit(current);
				trace_user_exit(0);
				instrumentation_end();
			}

			/*
			 * Special case if we only track user <-> kernel transitions for tickless
			 * cputime accounting but we don't support RCU extended quiescent state.
			 * In this we case we don't care about any concurrency/ordering.
			 */
			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE))
				atomic_set(&ct->state, CONTEXT_KERNEL);

		} else {
			if (!IS_ENABLED(CONFIG_CONTEXT_TRACKING_IDLE)) {
				/* Tracking for vtime only, no concurrent RCU EQS accounting */
				atomic_set(&ct->state, CONTEXT_KERNEL);
			} else {
				/*
				 * Tracking for vtime and RCU EQS. Make sure we don't race
				 * with NMIs. OTOH we don't care about ordering here since
				 * RCU only requires RCU_DYNTICKS_IDX increments to be fully
				 * ordered.
				 */
				atomic_sub(state, &ct->state);
			}
		}
	}
	context_tracking_recursion_exit();
}
EXPORT_SYMBOL_GPL(__ct_user_exit);

/*
 * OBSOLETE:
 * This function should be noinstr but the below local_irq_save() is
 * unsafe because it involves illegal RCU uses through tracing and lockdep.
 * This is unlikely to be fixed as this function is obsolete. The preferred
 * way is to call __context_tracking_exit() through user_exit_irqoff()
 * or context_tracking_guest_exit(). It should be the arch entry code
 * responsibility to call into context tracking with IRQs disabled.
 */
void ct_user_exit(enum ctx_state state)
{
	unsigned long flags;

	if (in_interrupt())
		return;

	local_irq_save(flags);
	__ct_user_exit(state);
	local_irq_restore(flags);
}
NOKPROBE_SYMBOL(ct_user_exit);
EXPORT_SYMBOL_GPL(ct_user_exit);

/**
 * user_exit_callable() - Unfortunate ASM callable version of user_exit() for
 *			  archs that didn't manage to check the context tracking
 *			  static key from low level code.
 *
 * This OBSOLETE function should be noinstr but it unsafely calls local_irq_save(),
 * involving illegal RCU uses through tracing and lockdep. This is unlikely
 * to be fixed as this function is obsolete. The preferred way is to call
 * user_exit_irqoff(). It should be the arch entry code responsibility to
 * call into context tracking with IRQs disabled.
 */
void user_exit_callable(void)
{
	user_exit();
}
NOKPROBE_SYMBOL(user_exit_callable);

void __init ct_cpu_track_user(int cpu)
{
	static __initdata bool initialized = false;

	if (!per_cpu(context_tracking.active, cpu)) {
		per_cpu(context_tracking.active, cpu) = true;
		static_branch_inc(&context_tracking_key);
	}

	if (initialized)
		return;

#ifdef CONFIG_HAVE_TIF_NOHZ
	/*
	 * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork
	 * This assumes that init is the only task at this early boot stage.
	 */
	set_tsk_thread_flag(&init_task, TIF_NOHZ);
#endif
	WARN_ON_ONCE(!tasklist_empty());

	initialized = true;
}

#ifdef CONFIG_CONTEXT_TRACKING_USER_FORCE
void __init context_tracking_init(void)
{
	int cpu;

	for_each_possible_cpu(cpu)
		ct_cpu_track_user(cpu);
}
#endif

#endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */