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         * In !PREEMPT configurations, there is no way to tell if we are
146         * in a RCU read-side critical section or not, so we never
147         * attempt any fixup and just print a warning.
148         */
149#ifndef CONFIG_PREEMPT
150        WARN_ON_ONCE(1);
151        return 0;
152#endif
153        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
154            irqs_disabled()) {
155            WARN_ON_ONCE(1);
156            return 0;
157        }
158        rcu_barrier();
159        rcu_barrier_sched();
160        rcu_barrier_bh();
161        debug_object_init(head, &rcuhead_debug_descr);
162        return 1;
163    default:
164        return 0;
165    }
166}
167
168/*
169 * fixup_activate is called when:
170 * - an active object is activated
171 * - an unknown object is activated (might be a statically initialized object)
172 * Activation is performed internally by call_rcu().
173 */
174static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
175{
176    struct rcu_head *head = addr;
177
178    switch (state) {
179
180    case ODEBUG_STATE_NOTAVAILABLE:
181        /*
182         * This is not really a fixup. We just make sure that it is
183         * tracked in the object tracker.
184         */
185        debug_object_init(head, &rcuhead_debug_descr);
186        debug_object_activate(head, &rcuhead_debug_descr);
187        return 0;
188
189    case ODEBUG_STATE_ACTIVE:
190        /*
191         * Ensure that queued callbacks are all executed.
192         * If we detect that we are nested in a RCU read-side critical
193         * section, we should simply fail, otherwise we would deadlock.
194         * In !PREEMPT configurations, there is no way to tell if we are
195         * in a RCU read-side critical section or not, so we never
196         * attempt any fixup and just print a warning.
197         */
198#ifndef CONFIG_PREEMPT
199        WARN_ON_ONCE(1);
200        return 0;
201#endif
202        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
203            irqs_disabled()) {
204            WARN_ON_ONCE(1);
205            return 0;
206        }
207        rcu_barrier();
208        rcu_barrier_sched();
209        rcu_barrier_bh();
210        debug_object_activate(head, &rcuhead_debug_descr);
211        return 1;
212    default:
213        return 0;
214    }
215}
216
217/*
218 * fixup_free is called when:
219 * - an active object is freed
220 */
221static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
222{
223    struct rcu_head *head = addr;
224
225    switch (state) {
226    case ODEBUG_STATE_ACTIVE:
227        /*
228         * Ensure that queued callbacks are all executed.
229         * If we detect that we are nested in a RCU read-side critical
230         * section, we should simply fail, otherwise we would deadlock.
231         * In !PREEMPT configurations, there is no way to tell if we are
232         * in a RCU read-side critical section or not, so we never
233         * attempt any fixup and just print a warning.
234         */
235#ifndef CONFIG_PREEMPT
236        WARN_ON_ONCE(1);
237        return 0;
238#endif
239        if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
240            irqs_disabled()) {
241            WARN_ON_ONCE(1);
242            return 0;
243        }
244        rcu_barrier();
245        rcu_barrier_sched();
246        rcu_barrier_bh();
247        debug_object_free(head, &rcuhead_debug_descr);
248        return 1;
249    default:
250        return 0;
251    }
252}
253
254/**
255 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
256 * @head: pointer to rcu_head structure to be initialized
257 *
258 * This function informs debugobjects of a new rcu_head structure that
259 * has been allocated as an auto variable on the stack. This function
260 * is not required for rcu_head structures that are statically defined or
261 * that are dynamically allocated on the heap. This function has no
262 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
263 */
264void init_rcu_head_on_stack(struct rcu_head *head)
265{
266    debug_object_init_on_stack(head, &rcuhead_debug_descr);
267}
268EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
269
270/**
271 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
272 * @head: pointer to rcu_head structure to be initialized
273 *
274 * This function informs debugobjects that an on-stack rcu_head structure
275 * is about to go out of scope. As with init_rcu_head_on_stack(), this
276 * function is not required for rcu_head structures that are statically
277 * defined or that are dynamically allocated on the heap. Also as with
278 * init_rcu_head_on_stack(), this function has no effect for
279 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
280 */
281void destroy_rcu_head_on_stack(struct rcu_head *head)
282{
283    debug_object_free(head, &rcuhead_debug_descr);
284}
285EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
286
287struct debug_obj_descr rcuhead_debug_descr = {
288    .name = "rcu_head",
289    .fixup_init = rcuhead_fixup_init,
290    .fixup_activate = rcuhead_fixup_activate,
291    .fixup_free = rcuhead_fixup_free,
292};
293EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
294#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
295

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