Fix: compat_futex.c: *uaddr should be read as volatile
[urcu.git] / compat_futex.c
CommitLineData
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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{
5b80127f 57 int ret, gret = 0;
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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 assert(!ret);
74 switch (op) {
75 case FUTEX_WAIT:
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76 /*
77 * Wait until *uaddr is changed to something else than "val".
78 * Comparing *uaddr content against val figures out which
79 * thread has been awakened.
80 */
f4fe9309 81 while (CMM_LOAD_SHARED(*uaddr) == val)
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82 pthread_cond_wait(&__urcu_compat_futex_cond,
83 &__urcu_compat_futex_lock);
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84 break;
85 case FUTEX_WAKE:
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86 /*
87 * Each wake is sending a broadcast, thus attempting wakeup of
88 * all awaiting threads, independently of their respective
89 * uaddr.
90 */
5c02e37d 91 pthread_cond_broadcast(&__urcu_compat_futex_cond);
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92 break;
93 default:
94 gret = -EINVAL;
95 }
5c02e37d 96 ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
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97 assert(!ret);
98 return gret;
99}
100
101/*
102 * _ASYNC SIGNAL-SAFE_.
103 * For now, timeout, uaddr2 and val3 are unused.
104 * Waiter will busy-loop trying to read the condition.
105 */
106
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107int compat_futex_async(int32_t *uaddr, int op, int32_t val,
108 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
49617de1 109{
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110 /*
111 * Check if NULL. Don't let users expect that they are taken into
112 * account.
113 */
114 assert(!timeout);
115 assert(!uaddr2);
116 assert(!val3);
117
118 /*
119 * Ensure previous memory operations on uaddr have completed.
120 */
5481ddb3 121 cmm_smp_mb();
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122
123 switch (op) {
124 case FUTEX_WAIT:
f4fe9309 125 while (CMM_LOAD_SHARED(*uaddr) == val)
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126 poll(NULL, 0, 10);
127 break;
128 case FUTEX_WAKE:
129 break;
130 default:
131 return -EINVAL;
132 }
1494da88 133 return 0;
49617de1 134}
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