Fix: compat_futex should work-around futex signal-restart kernel bug
[urcu.git] / urcu / futex.h
1 #ifndef _URCU_FUTEX_H
2 #define _URCU_FUTEX_H
3
4 /*
5 * urcu-futex.h
6 *
7 * Userspace RCU - sys_futex/compat_futex header.
8 *
9 * Copyright 2011-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
10 *
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; either
14 * version 2.1 of the License, or (at your option) any later version.
15 *
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 */
25
26 #include <urcu/config.h>
27 #include <stdint.h>
28
29 #ifdef __cplusplus
30 extern "C" {
31 #endif
32
33 #define FUTEX_WAIT 0
34 #define FUTEX_WAKE 1
35
36 /*
37 * sys_futex compatibility header.
38 * Use *only* *either of* futex_noasync OR futex_async on a given address.
39 *
40 * futex_noasync cannot be executed in signal handlers, but ensures that
41 * it will be put in a wait queue even in compatibility mode.
42 *
43 * futex_async is signal-handler safe for the wakeup. It uses polling
44 * on the wait-side in compatibility mode.
45 *
46 * BEWARE: sys_futex() FUTEX_WAIT may return early if interrupted
47 * (returns EINTR).
48 */
49
50 extern int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
51 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
52 extern int compat_futex_async(int32_t *uaddr, int op, int32_t val,
53 const struct timespec *timeout, int32_t *uaddr2, int32_t val3);
54
55 #ifdef CONFIG_RCU_HAVE_FUTEX
56
57 #include <unistd.h>
58 #include <errno.h>
59 #include <urcu/compiler.h>
60 #include <urcu/arch.h>
61
62 static inline int futex(int32_t *uaddr, int op, int32_t val,
63 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
64 {
65 return syscall(__NR_futex, uaddr, op, val, timeout,
66 uaddr2, val3);
67 }
68
69 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
70 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
71 {
72 int ret;
73
74 ret = futex(uaddr, op, val, timeout, uaddr2, val3);
75 if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
76 /*
77 * The fallback on ENOSYS is the async-safe version of
78 * the compat futex implementation, because the
79 * async-safe compat implementation allows being used
80 * concurrently with calls to futex(). Indeed, sys_futex
81 * FUTEX_WAIT, on some architectures (mips and parisc),
82 * within a given process, spuriously return ENOSYS due
83 * to signal restart bugs on some kernel versions.
84 */
85 return compat_futex_async(uaddr, op, val, timeout,
86 uaddr2, val3);
87 }
88 return ret;
89
90 }
91
92 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
93 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
94 {
95 int ret;
96
97 ret = futex(uaddr, op, val, timeout, uaddr2, val3);
98 if (caa_unlikely(ret < 0 && errno == ENOSYS)) {
99 return compat_futex_async(uaddr, op, val, timeout,
100 uaddr2, val3);
101 }
102 return ret;
103 }
104
105 #else
106
107 static inline int futex_noasync(int32_t *uaddr, int op, int32_t val,
108 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
109 {
110 return compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3);
111 }
112
113 static inline int futex_async(int32_t *uaddr, int op, int32_t val,
114 const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
115 {
116 return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3);
117 }
118
119 #endif
120
121 #ifdef __cplusplus
122 }
123 #endif
124
125 #endif /* _URCU_FUTEX_H */
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