Fix: handle sys_futex() FUTEX_WAIT interrupted by signal
[urcu.git] / compat_futex.c
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1/*
2 * compat_futex.c
3 *
4 * Userspace RCU library - sys_futex compatibility code
5 *
6982d6d7 6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
23#include <stdio.h>
24#include <pthread.h>
25#include <signal.h>
26#include <assert.h>
27#include <errno.h>
28#include <poll.h>
6d841bc2 29#include <stdint.h>
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30
31#include <urcu/arch.h>
41849996 32#include <urcu/futex.h>
f4fe9309 33#include <urcu/system.h>
49617de1 34
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35/*
36 * Using attribute "weak" for __urcu_compat_futex_lock and
37 * __urcu_compat_futex_cond. Those are globally visible by the entire
38 * program, even though many shared objects may have their own version.
39 * The first version that gets loaded will be used by the entire program
40 * (executable and all shared objects).
41 */
42
43__attribute__((weak))
44pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
45__attribute__((weak))
46pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
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47
48/*
49 * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
50 * For now, timeout, uaddr2 and val3 are unused.
51 * Waiter will relinquish the CPU until woken up.
52 */
53
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54int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
55 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
49617de1 56{
b0a841b4 57 int ret;
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58
59 /*
60 * Check if NULL. Don't let users expect that they are taken into
61 * account.
62 */
63 assert(!timeout);
64 assert(!uaddr2);
65 assert(!val3);
66
67 /*
68 * memory barriers to serialize with the previous uaddr modification.
69 */
5481ddb3 70 cmm_smp_mb();
49617de1 71
5c02e37d 72 ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
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73 if (ret) {
74 errno = ret;
75 ret = -1;
76 goto end;
77 }
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78 switch (op) {
79 case FUTEX_WAIT:
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80 /*
81 * Wait until *uaddr is changed to something else than "val".
82 * Comparing *uaddr content against val figures out which
83 * thread has been awakened.
84 */
f4fe9309 85 while (CMM_LOAD_SHARED(*uaddr) == val)
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86 pthread_cond_wait(&__urcu_compat_futex_cond,
87 &__urcu_compat_futex_lock);
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88 break;
89 case FUTEX_WAKE:
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90 /*
91 * Each wake is sending a broadcast, thus attempting wakeup of
92 * all awaiting threads, independently of their respective
93 * uaddr.
94 */
5c02e37d 95 pthread_cond_broadcast(&__urcu_compat_futex_cond);
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96 break;
97 default:
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98 errno = EINVAL;
99 ret = -1;
49617de1 100 }
5c02e37d 101 ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
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102 if (ret) {
103 errno = ret;
104 ret = -1;
105 }
106end:
107 return ret;
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108}
109
110/*
111 * _ASYNC SIGNAL-SAFE_.
112 * For now, timeout, uaddr2 and val3 are unused.
113 * Waiter will busy-loop trying to read the condition.
114 */
115
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116int compat_futex_async(int32_t *uaddr, int op, int32_t val,
117 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
49617de1 118{
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119 int ret = 0;
120
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121 /*
122 * Check if NULL. Don't let users expect that they are taken into
123 * account.
124 */
125 assert(!timeout);
126 assert(!uaddr2);
127 assert(!val3);
128
129 /*
130 * Ensure previous memory operations on uaddr have completed.
131 */
5481ddb3 132 cmm_smp_mb();
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133
134 switch (op) {
135 case FUTEX_WAIT:
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136 while (CMM_LOAD_SHARED(*uaddr) == val) {
137 if (poll(NULL, 0, 10) < 0) {
138 ret = -1;
139 /* Keep poll errno. Caller handles EINTR. */
140 goto end;
141 }
142 }
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143 break;
144 case FUTEX_WAKE:
145 break;
146 default:
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147 errno = EINVAL;
148 ret = -1;
49617de1 149 }
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150end:
151 return ret;
49617de1 152}
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