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

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