aboutsummaryrefslogtreecommitdiff
path: root/kernel/rcupdate.c
blob: 48ab70384a4cda7533a65c02915ef253ea767645 (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
/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright IBM Corporation, 2001
 *
 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 *	    Manfred Spraul <manfred@colorfullife.com>
 *
 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 * Papers:
 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *		http://lse.sourceforge.net/locking/rcupdate.html
 *
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/export.h>
#include <linux/hardirq.h>
#include <linux/delay.h>
#include <linux/module.h>

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

#include "rcu.h"

module_param(rcu_expedited, int, 0);

#ifdef CONFIG_PREEMPT_RCU

/*
 * Preemptible RCU implementation for rcu_read_lock().
 * Just increment ->rcu_read_lock_nesting, shared state will be updated
 * if we block.
 */
void __rcu_read_lock(void)
{
	current->rcu_read_lock_nesting++;
	barrier();  /* critical section after entry code. */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);

/*
 * Preemptible RCU implementation for rcu_read_unlock().
 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
 * invoke rcu_read_unlock_special() to clean up after a context switch
 * in an RCU read-side critical section and other special cases.
 */
void __rcu_read_unlock(void)
{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting != 1) {
		--t->rcu_read_lock_nesting;
	} else {
		barrier();  /* critical section before exit code. */
		t->rcu_read_lock_nesting = INT_MIN;
#ifdef CONFIG_PROVE_RCU_DELAY
		udelay(10); /* Make preemption more probable. */
#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
		barrier();  /* assign before ->rcu_read_unlock_special load */
		if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
			rcu_read_unlock_special(t);
		barrier();  /* ->rcu_read_unlock_special load before assign */
		t->rcu_read_lock_nesting = 0;
	}
#ifdef CONFIG_PROVE_LOCKING
	{
		int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);

		WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
	}
#endif /* #ifdef CONFIG_PROVE_LOCKING */
}
EXPORT_SYMBOL_GPL(__rcu_read_unlock);

/*
 * Check for a task exiting while in a preemptible-RCU read-side
 * critical section, clean up if so.  No need to issue warnings,
 * as debug_check_no_locks_held() already does this if lockdep
 * is enabled.
 */
void exit_rcu(void)
{
	struct task_struct *t = current;

	if (likely(list_empty(&current->rcu_node_entry)))
		return;
	t->rcu_read_lock_nesting = 1;
	barrier();
	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
	__rcu_read_unlock();
}

#else /* #ifdef CONFIG_PREEMPT_RCU */

void exit_rcu(void)
{
}

#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
EXPORT_SYMBOL_GPL(rcu_lock_map);

static struct lock_class_key rcu_bh_lock_key;
struct lockdep_map rcu_bh_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
EXPORT_SYMBOL_GPL(rcu_bh_lock_map);

static struct lock_class_key rcu_sched_lock_key;
struct lockdep_map rcu_sched_lock_map =
	STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC

int debug_lockdep_rcu_enabled(void)
{
	return rcu_scheduler_active && debug_locks &&
	       current->lockdep_recursion == 0;
}
EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);

/**
 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 *
 * Check for bottom half being disabled, which covers both the
 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 * will show the situation.  This is useful for debug checks in functions
 * that require that they be called within an RCU read-side critical
 * section.
 *
 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 *
 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 * offline from an RCU perspective, so check for those as well.
 */
int rcu_read_lock_bh_held(void)
{
	if (!debug_lockdep_rcu_enabled())
		return 1;
	if (rcu_is_cpu_idle())
		return 0;
	if (!rcu_lockdep_current_cpu_online())
		return 0;
	return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);

#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

struct rcu_synchronize {
	struct rcu_head head;
	struct completion completion;
};

/*
 * Awaken the corresponding synchronize_rcu() instance now that a
 * grace period has elapsed.
 */
static void wakeme_after_rcu(struct rcu_head  *head)
{
	struct rcu_synchronize *rcu;

	rcu = container_of(head, struct rcu_synchronize, head);
	complete(&rcu->completion);
}

void wait_rcu_gp(call_rcu_func_t crf)
{
	struct rcu_synchronize rcu;

	init_rcu_head_on_stack(&rcu.head);
	init_completion(&rcu.completion);
	/* Will wake me after RCU finished. */
	crf(&rcu.head, wakeme_after_rcu);
	/* Wait for it. */
	wait_for_completion(&rcu.completion);
	destroy_rcu_head_on_stack(&rcu.head);
}
EXPORT_SYMBOL_GPL(wait_rcu_gp);

#ifdef CONFIG_PROVE_RCU
/*
 * wrapper function to avoid #include problems.
 */
int rcu_my_thread_group_empty(void)
{
	return thread_group_empty(current);
}
EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
#endif /* #ifdef CONFIG_PROVE_RCU */

#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
static inline void debug_init_rcu_head(struct rcu_head *head)
{
	debug_object_init(head, &rcuhead_debug_descr);
}

static inline void debug_rcu_head_free(struct rcu_head *head)
{
	debug_object_free(head, &rcuhead_debug_descr);
}

/*
 * fixup_init is called when:
 * - an active object is initialized
 */
static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
{
	struct rcu_head *head = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_init(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/*
 * fixup_activate is called when:
 * - an active object is activated
 * - an unknown object is activated (might be a statically initialized object)
 * Activation is performed internally by call_rcu().
 */
static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
{
	struct rcu_head *head = addr;

	switch (state) {

	case ODEBUG_STATE_NOTAVAILABLE:
		/*
		 * This is not really a fixup. We just make sure that it is
		 * tracked in the object tracker.
		 */
		debug_object_init(head, &rcuhead_debug_descr);
		debug_object_activate(head, &rcuhead_debug_descr);
		return 0;

	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_activate(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/*
 * fixup_free is called when:
 * - an active object is freed
 */
static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
{
	struct rcu_head *head = addr;

	switch (state) {
	case ODEBUG_STATE_ACTIVE:
		/*
		 * Ensure that queued callbacks are all executed.
		 * If we detect that we are nested in a RCU read-side critical
		 * section, we should simply fail, otherwise we would deadlock.
		 * In !PREEMPT configurations, there is no way to tell if we are
		 * in a RCU read-side critical section or not, so we never
		 * attempt any fixup and just print a warning.
		 */
#ifndef CONFIG_PREEMPT
		WARN_ON_ONCE(1);
		return 0;
#endif
		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
		    irqs_disabled()) {
			WARN_ON_ONCE(1);
			return 0;
		}
		rcu_barrier();
		rcu_barrier_sched();
		rcu_barrier_bh();
		debug_object_free(head, &rcuhead_debug_descr);
		return 1;
	default:
		return 0;
	}
}

/**
 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 * @head: pointer to rcu_head structure to be initialized
 *
 * This function informs debugobjects of a new rcu_head structure that
 * has been allocated as an auto variable on the stack.  This function
 * is not required for rcu_head structures that are statically defined or
 * that are dynamically allocated on the heap.  This function has no
 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 */
void init_rcu_head_on_stack(struct rcu_head *head)
{
	debug_object_init_on_stack(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);

/**
 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 * @head: pointer to rcu_head structure to be initialized
 *
 * This function informs debugobjects that an on-stack rcu_head structure
 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 * function is not required for rcu_head structures that are statically
 * defined or that are dynamically allocated on the heap.  Also as with
 * init_rcu_head_on_stack(), this function has no effect for
 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 */
void destroy_rcu_head_on_stack(struct rcu_head *head)
{
	debug_object_free(head, &rcuhead_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);

struct debug_obj_descr rcuhead_debug_descr = {
	.name = "rcu_head",
	.fixup_init = rcuhead_fixup_init,
	.fixup_activate = rcuhead_fixup_activate,
	.fixup_free = rcuhead_fixup_free,
};
EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
			       unsigned long secs,
			       unsigned long c_old, unsigned long c)
{
	trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
}
EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
#else
#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
	do { } while (0)
#endif

#ifdef CONFIG_RCU_STALL_COMMON

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

int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;

module_param(rcu_cpu_stall_suppress, int, 0644);
module_param(rcu_cpu_stall_timeout, int, 0644);

int rcu_jiffies_till_stall_check(void)
{
	int till_stall_check = ACCESS_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) {
		ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
		till_stall_check = 3;
	} else if (till_stall_check > 300) {
		ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
		till_stall_check = 300;
	}
	return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
}

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);

#endif /* #ifdef CONFIG_RCU_STALL_COMMON */