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 <asm/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/module.h>
47#include <linux/hardirq.h>
48
49#ifdef CONFIG_DEBUG_LOCK_ALLOC
50static struct lock_class_key rcu_lock_key;
51struct lockdep_map rcu_lock_map =
52    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
53EXPORT_SYMBOL_GPL(rcu_lock_map);
54
55static struct lock_class_key rcu_bh_lock_key;
56struct lockdep_map rcu_bh_lock_map =
57    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
58EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
59
60static struct lock_class_key rcu_sched_lock_key;
61struct lockdep_map rcu_sched_lock_map =
62    STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
63EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
64#endif
65
66#ifdef CONFIG_DEBUG_LOCK_ALLOC
67
68int debug_lockdep_rcu_enabled(void)
69{
70    return rcu_scheduler_active && debug_locks &&
71           current->lockdep_recursion == 0;
72}
73EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
74
75/**
76 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
77 *
78 * Check for bottom half being disabled, which covers both the
79 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
80 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
81 * will show the situation. This is useful for debug checks in functions
82 * that require that they be called within an RCU read-side critical
83 * section.
84 *
85 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
86 */
87int rcu_read_lock_bh_held(void)
88{
89    if (!debug_lockdep_rcu_enabled())
90        return 1;
91    return in_softirq() || irqs_disabled();
92}
93EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
94
95#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
96
97/*
98 * Awaken the corresponding synchronize_rcu() instance now that a
99 * grace period has elapsed.
100 */
101void wakeme_after_rcu(struct rcu_head *head)
102{
103    struct rcu_synchronize *rcu;
104
105    rcu = container_of(head, struct rcu_synchronize, head);
106    complete(&rcu->completion);
107}
108
109#ifdef CONFIG_PROVE_RCU
110/*
111 * wrapper function to avoid #include problems.
112 */
113int rcu_my_thread_group_empty(void)
114{
115    return thread_group_empty(current);
116}
117EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
118#endif /* #ifdef CONFIG_PROVE_RCU */
119
120#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
121static inline void debug_init_rcu_head(struct rcu_head *head)
122{
123    debug_object_init(head, &rcuhead_debug_descr);
124}
125
126static inline void debug_rcu_head_free(struct rcu_head *head)
127{
128    debug_object_free(head, &rcuhead_debug_descr);
129}
130
131/*
132 * fixup_init is called when:
133 * - an active object is initialized
134 */
135static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
136{
137    struct rcu_head *head = addr;
138
139    switch (state) {
140    case ODEBUG_STATE_ACTIVE:
141        /*
142         * Ensure that queued callbacks are all executed.
143         * If we detect that we are nested in a RCU read-side critical
144         * section, we should simply fail, otherwise we would deadlock.
145         */
146        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
147            irqs_disabled()) {
148            WARN_ON(1);
149            return 0;
150        }
151        rcu_barrier();
152        rcu_barrier_sched();
153        rcu_barrier_bh();
154        debug_object_init(head, &rcuhead_debug_descr);
155        return 1;
156    default:
157        return 0;
158    }
159}
160
161/*
162 * fixup_activate is called when:
163 * - an active object is activated
164 * - an unknown object is activated (might be a statically initialized object)
165 * Activation is performed internally by call_rcu().
166 */
167static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
168{
169    struct rcu_head *head = addr;
170
171    switch (state) {
172
173    case ODEBUG_STATE_NOTAVAILABLE:
174        /*
175         * This is not really a fixup. We just make sure that it is
176         * tracked in the object tracker.
177         */
178        debug_object_init(head, &rcuhead_debug_descr);
179        debug_object_activate(head, &rcuhead_debug_descr);
180        return 0;
181
182    case ODEBUG_STATE_ACTIVE:
183        /*
184         * Ensure that queued callbacks are all executed.
185         * If we detect that we are nested in a RCU read-side critical
186         * section, we should simply fail, otherwise we would deadlock.
187         */
188        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
189            irqs_disabled()) {
190            WARN_ON(1);
191            return 0;
192        }
193        rcu_barrier();
194        rcu_barrier_sched();
195        rcu_barrier_bh();
196        debug_object_activate(head, &rcuhead_debug_descr);
197        return 1;
198    default:
199        return 0;
200    }
201}
202
203/*
204 * fixup_free is called when:
205 * - an active object is freed
206 */
207static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
208{
209    struct rcu_head *head = addr;
210
211    switch (state) {
212    case ODEBUG_STATE_ACTIVE:
213        /*
214         * Ensure that queued callbacks are all executed.
215         * If we detect that we are nested in a RCU read-side critical
216         * section, we should simply fail, otherwise we would deadlock.
217         */
218#ifndef CONFIG_PREEMPT
219        WARN_ON(1);
220        return 0;
221#else
222        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
223            irqs_disabled()) {
224            WARN_ON(1);
225            return 0;
226        }
227        rcu_barrier();
228        rcu_barrier_sched();
229        rcu_barrier_bh();
230        debug_object_free(head, &rcuhead_debug_descr);
231        return 1;
232#endif
233    default:
234        return 0;
235    }
236}
237
238/**
239 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
240 * @head: pointer to rcu_head structure to be initialized
241 *
242 * This function informs debugobjects of a new rcu_head structure that
243 * has been allocated as an auto variable on the stack. This function
244 * is not required for rcu_head structures that are statically defined or
245 * that are dynamically allocated on the heap. This function has no
246 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
247 */
248void init_rcu_head_on_stack(struct rcu_head *head)
249{
250    debug_object_init_on_stack(head, &rcuhead_debug_descr);
251}
252EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
253
254/**
255 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
256 * @head: pointer to rcu_head structure to be initialized
257 *
258 * This function informs debugobjects that an on-stack rcu_head structure
259 * is about to go out of scope. As with init_rcu_head_on_stack(), this
260 * function is not required for rcu_head structures that are statically
261 * defined or that are dynamically allocated on the heap. Also as with
262 * init_rcu_head_on_stack(), this function has no effect for
263 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
264 */
265void destroy_rcu_head_on_stack(struct rcu_head *head)
266{
267    debug_object_free(head, &rcuhead_debug_descr);
268}
269EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
270
271struct debug_obj_descr rcuhead_debug_descr = {
272    .name = "rcu_head",
273    .fixup_init = rcuhead_fixup_init,
274    .fixup_activate = rcuhead_fixup_activate,
275    .fixup_free = rcuhead_fixup_free,
276};
277EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
278#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
279

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