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10544ee8 MD |
1 | /* |
2 | * compat_futex.c | |
3 | * | |
4 | * Userspace RCU library - sys_futex compatibility code | |
5 | * | |
6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
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> | |
29 | #include <stdint.h> | |
30 | ||
31 | #include <urcu/arch.h> | |
32 | #include <urcu/system.h> | |
33 | #include "futex.h" | |
34 | ||
35 | /* | |
36 | * Using attribute "weak" for __lttng_ust_compat_futex_lock and | |
37 | * __lttng_ust_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)) | |
44 | pthread_mutex_t __lttng_ust_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER; | |
45 | __attribute__((weak)) | |
46 | pthread_cond_t __lttng_ust_compat_futex_cond = PTHREAD_COND_INITIALIZER; | |
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 | ||
54 | int lttng_ust_compat_futex_noasync(int32_t *uaddr, int op, int32_t val, | |
55 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
56 | { | |
57 | int ret = 0, lockret; | |
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 | */ | |
70 | cmm_smp_mb(); | |
71 | ||
72 | lockret = pthread_mutex_lock(&__lttng_ust_compat_futex_lock); | |
73 | if (lockret) { | |
74 | errno = lockret; | |
75 | ret = -1; | |
76 | goto end; | |
77 | } | |
78 | switch (op) { | |
79 | case FUTEX_WAIT: | |
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 | */ | |
85 | while (CMM_LOAD_SHARED(*uaddr) == val) | |
86 | pthread_cond_wait(&__lttng_ust_compat_futex_cond, | |
87 | &__lttng_ust_compat_futex_lock); | |
88 | break; | |
89 | case FUTEX_WAKE: | |
90 | /* | |
91 | * Each wake is sending a broadcast, thus attempting wakeup of | |
92 | * all awaiting threads, independently of their respective | |
93 | * uaddr. | |
94 | */ | |
95 | pthread_cond_broadcast(&__lttng_ust_compat_futex_cond); | |
96 | break; | |
97 | default: | |
98 | errno = EINVAL; | |
99 | ret = -1; | |
100 | } | |
101 | lockret = pthread_mutex_unlock(&__lttng_ust_compat_futex_lock); | |
102 | if (lockret) { | |
103 | errno = lockret; | |
104 | ret = -1; | |
105 | } | |
106 | end: | |
107 | return ret; | |
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 | * It is OK to use compat_futex_async() on a futex address on which | |
115 | * futex() WAKE operations are also performed. | |
116 | */ | |
117 | ||
118 | int lttng_ust_compat_futex_async(int32_t *uaddr, int op, int32_t val, | |
119 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
120 | { | |
121 | int ret = 0; | |
122 | ||
123 | /* | |
124 | * Check if NULL. Don't let users expect that they are taken into | |
125 | * account. | |
126 | */ | |
127 | assert(!timeout); | |
128 | assert(!uaddr2); | |
129 | assert(!val3); | |
130 | ||
131 | /* | |
132 | * Ensure previous memory operations on uaddr have completed. | |
133 | */ | |
134 | cmm_smp_mb(); | |
135 | ||
136 | switch (op) { | |
137 | case FUTEX_WAIT: | |
138 | while (CMM_LOAD_SHARED(*uaddr) == val) { | |
139 | if (poll(NULL, 0, 10) < 0) { | |
140 | ret = -1; | |
141 | /* Keep poll errno. Caller handles EINTR. */ | |
142 | goto end; | |
143 | } | |
144 | } | |
145 | break; | |
146 | case FUTEX_WAKE: | |
147 | break; | |
148 | default: | |
149 | errno = EINVAL; | |
150 | ret = -1; | |
151 | } | |
152 | end: | |
153 | return ret; | |
154 | } |