Root/kernel/rcupdate.c

1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright IBM Corporation, 2001
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 *
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * Papers:
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 *
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
31 *
32 */
33#include <linux/types.h>
34#include <linux/kernel.h>
35#include <linux/init.h>
36#include <linux/spinlock.h>
37#include <linux/smp.h>
38#include <linux/interrupt.h>
39#include <linux/sched.h>
40#include <linux/atomic.h>
41#include <linux/bitops.h>
42#include <linux/percpu.h>
43#include <linux/notifier.h>
44#include <linux/cpu.h>
45#include <linux/mutex.h>
46#include <linux/export.h>
47#include <linux/hardirq.h>
48
49#define CREATE_TRACE_POINTS
50#include <trace/events/rcu.h>
51
52#include "rcu.h"
53
54#ifdef CONFIG_PREEMPT_RCU
55
56/*
57 * Check for a task exiting while in a preemptible-RCU read-side
58 * critical section, clean up if so. No need to issue warnings,
59 * as debug_check_no_locks_held() already does this if lockdep
60 * is enabled.
61 */
62void exit_rcu(void)
63{
64    struct task_struct *t = current;
65
66    if (likely(list_empty(&current->rcu_node_entry)))
67        return;
68    t->rcu_read_lock_nesting = 1;
69    barrier();
70    t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
71    __rcu_read_unlock();
72}
73
74#else /* #ifdef CONFIG_PREEMPT_RCU */
75
76void exit_rcu(void)
77{
78}
79
80#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
81
82#ifdef CONFIG_DEBUG_LOCK_ALLOC
83static struct lock_class_key rcu_lock_key;
84struct lockdep_map rcu_lock_map =
85    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
86EXPORT_SYMBOL_GPL(rcu_lock_map);
87
88static struct lock_class_key rcu_bh_lock_key;
89struct lockdep_map rcu_bh_lock_map =
90    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
91EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
92
93static struct lock_class_key rcu_sched_lock_key;
94struct lockdep_map rcu_sched_lock_map =
95    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
96EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
97#endif
98
99#ifdef CONFIG_DEBUG_LOCK_ALLOC
100
101int debug_lockdep_rcu_enabled(void)
102{
103    return rcu_scheduler_active && debug_locks &&
104           current->lockdep_recursion == 0;
105}
106EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
107
108/**
109 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
110 *
111 * Check for bottom half being disabled, which covers both the
112 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
113 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
114 * will show the situation. This is useful for debug checks in functions
115 * that require that they be called within an RCU read-side critical
116 * section.
117 *
118 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
119 *
120 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
121 * offline from an RCU perspective, so check for those as well.
122 */
123int rcu_read_lock_bh_held(void)
124{
125    if (!debug_lockdep_rcu_enabled())
126        return 1;
127    if (rcu_is_cpu_idle())
128        return 0;
129    if (!rcu_lockdep_current_cpu_online())
130        return 0;
131    return in_softirq() || irqs_disabled();
132}
133EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
134
135#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
136
137struct rcu_synchronize {
138    struct rcu_head head;
139    struct completion completion;
140};
141
142/*
143 * Awaken the corresponding synchronize_rcu() instance now that a
144 * grace period has elapsed.
145 */
146static void wakeme_after_rcu(struct rcu_head *head)
147{
148    struct rcu_synchronize *rcu;
149
150    rcu = container_of(head, struct rcu_synchronize, head);
151    complete(&rcu->completion);
152}
153
154void wait_rcu_gp(call_rcu_func_t crf)
155{
156    struct rcu_synchronize rcu;
157
158    init_rcu_head_on_stack(&rcu.head);
159    init_completion(&rcu.completion);
160    /* Will wake me after RCU finished. */
161    crf(&rcu.head, wakeme_after_rcu);
162    /* Wait for it. */
163    wait_for_completion(&rcu.completion);
164    destroy_rcu_head_on_stack(&rcu.head);
165}
166EXPORT_SYMBOL_GPL(wait_rcu_gp);
167
168#ifdef CONFIG_PROVE_RCU
169/*
170 * wrapper function to avoid #include problems.
171 */
172int rcu_my_thread_group_empty(void)
173{
174    return thread_group_empty(current);
175}
176EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
177#endif /* #ifdef CONFIG_PROVE_RCU */
178
179#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
180static inline void debug_init_rcu_head(struct rcu_head *head)
181{
182    debug_object_init(head, &rcuhead_debug_descr);
183}
184
185static inline void debug_rcu_head_free(struct rcu_head *head)
186{
187    debug_object_free(head, &rcuhead_debug_descr);
188}
189
190/*
191 * fixup_init is called when:
192 * - an active object is initialized
193 */
194static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
195{
196    struct rcu_head *head = addr;
197
198    switch (state) {
199    case ODEBUG_STATE_ACTIVE:
200        /*
201         * Ensure that queued callbacks are all executed.
202         * If we detect that we are nested in a RCU read-side critical
203         * section, we should simply fail, otherwise we would deadlock.
204         * In !PREEMPT configurations, there is no way to tell if we are
205         * in a RCU read-side critical section or not, so we never
206         * attempt any fixup and just print a warning.
207         */
208#ifndef CONFIG_PREEMPT
209        WARN_ON_ONCE(1);
210        return 0;
211#endif
212        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
213            irqs_disabled()) {
214            WARN_ON_ONCE(1);
215            return 0;
216        }
217        rcu_barrier();
218        rcu_barrier_sched();
219        rcu_barrier_bh();
220        debug_object_init(head, &rcuhead_debug_descr);
221        return 1;
222    default:
223        return 0;
224    }
225}
226
227/*
228 * fixup_activate is called when:
229 * - an active object is activated
230 * - an unknown object is activated (might be a statically initialized object)
231 * Activation is performed internally by call_rcu().
232 */
233static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
234{
235    struct rcu_head *head = addr;
236
237    switch (state) {
238
239    case ODEBUG_STATE_NOTAVAILABLE:
240        /*
241         * This is not really a fixup. We just make sure that it is
242         * tracked in the object tracker.
243         */
244        debug_object_init(head, &rcuhead_debug_descr);
245        debug_object_activate(head, &rcuhead_debug_descr);
246        return 0;
247
248    case ODEBUG_STATE_ACTIVE:
249        /*
250         * Ensure that queued callbacks are all executed.
251         * If we detect that we are nested in a RCU read-side critical
252         * section, we should simply fail, otherwise we would deadlock.
253         * In !PREEMPT configurations, there is no way to tell if we are
254         * in a RCU read-side critical section or not, so we never
255         * attempt any fixup and just print a warning.
256         */
257#ifndef CONFIG_PREEMPT
258        WARN_ON_ONCE(1);
259        return 0;
260#endif
261        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
262            irqs_disabled()) {
263            WARN_ON_ONCE(1);
264            return 0;
265        }
266        rcu_barrier();
267        rcu_barrier_sched();
268        rcu_barrier_bh();
269        debug_object_activate(head, &rcuhead_debug_descr);
270        return 1;
271    default:
272        return 0;
273    }
274}
275
276/*
277 * fixup_free is called when:
278 * - an active object is freed
279 */
280static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
281{
282    struct rcu_head *head = addr;
283
284    switch (state) {
285    case ODEBUG_STATE_ACTIVE:
286        /*
287         * Ensure that queued callbacks are all executed.
288         * If we detect that we are nested in a RCU read-side critical
289         * section, we should simply fail, otherwise we would deadlock.
290         * In !PREEMPT configurations, there is no way to tell if we are
291         * in a RCU read-side critical section or not, so we never
292         * attempt any fixup and just print a warning.
293         */
294#ifndef CONFIG_PREEMPT
295        WARN_ON_ONCE(1);
296        return 0;
297#endif
298        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
299            irqs_disabled()) {
300            WARN_ON_ONCE(1);
301            return 0;
302        }
303        rcu_barrier();
304        rcu_barrier_sched();
305        rcu_barrier_bh();
306        debug_object_free(head, &rcuhead_debug_descr);
307        return 1;
308    default:
309        return 0;
310    }
311}
312
313/**
314 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
315 * @head: pointer to rcu_head structure to be initialized
316 *
317 * This function informs debugobjects of a new rcu_head structure that
318 * has been allocated as an auto variable on the stack. This function
319 * is not required for rcu_head structures that are statically defined or
320 * that are dynamically allocated on the heap. This function has no
321 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
322 */
323void init_rcu_head_on_stack(struct rcu_head *head)
324{
325    debug_object_init_on_stack(head, &rcuhead_debug_descr);
326}
327EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
328
329/**
330 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
331 * @head: pointer to rcu_head structure to be initialized
332 *
333 * This function informs debugobjects that an on-stack rcu_head structure
334 * is about to go out of scope. As with init_rcu_head_on_stack(), this
335 * function is not required for rcu_head structures that are statically
336 * defined or that are dynamically allocated on the heap. Also as with
337 * init_rcu_head_on_stack(), this function has no effect for
338 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
339 */
340void destroy_rcu_head_on_stack(struct rcu_head *head)
341{
342    debug_object_free(head, &rcuhead_debug_descr);
343}
344EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
345
346struct debug_obj_descr rcuhead_debug_descr = {
347    .name = "rcu_head",
348    .fixup_init = rcuhead_fixup_init,
349    .fixup_activate = rcuhead_fixup_activate,
350    .fixup_free = rcuhead_fixup_free,
351};
352EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
353#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
354
355#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
356void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
357{
358    trace_rcu_torture_read(rcutorturename, rhp);
359}
360EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
361#else
362#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
363#endif
364

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