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10544ee8 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-or-later |
10544ee8 MD |
3 | * |
4 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
5 | * | |
c0c0989a | 6 | * Userspace RCU library - sys_futex compatibility code |
10544ee8 MD |
7 | */ |
8 | ||
9 | #include <stdio.h> | |
10 | #include <pthread.h> | |
11 | #include <signal.h> | |
12 | #include <assert.h> | |
13 | #include <errno.h> | |
14 | #include <poll.h> | |
15 | #include <stdint.h> | |
16 | ||
17 | #include <urcu/arch.h> | |
18 | #include <urcu/system.h> | |
58f84478 MJ |
19 | |
20 | #include "common/compat/futex.h" | |
10544ee8 MD |
21 | |
22 | /* | |
23 | * Using attribute "weak" for __lttng_ust_compat_futex_lock and | |
24 | * __lttng_ust_compat_futex_cond. Those are globally visible by the entire | |
25 | * program, even though many shared objects may have their own version. | |
26 | * The first version that gets loaded will be used by the entire program | |
27 | * (executable and all shared objects). | |
28 | */ | |
29 | ||
30 | __attribute__((weak)) | |
31 | pthread_mutex_t __lttng_ust_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER; | |
32 | __attribute__((weak)) | |
33 | pthread_cond_t __lttng_ust_compat_futex_cond = PTHREAD_COND_INITIALIZER; | |
34 | ||
35 | /* | |
36 | * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though. | |
37 | * For now, timeout, uaddr2 and val3 are unused. | |
38 | * Waiter will relinquish the CPU until woken up. | |
39 | */ | |
40 | ||
41 | int lttng_ust_compat_futex_noasync(int32_t *uaddr, int op, int32_t val, | |
42 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
43 | { | |
44 | int ret = 0, lockret; | |
45 | ||
46 | /* | |
47 | * Check if NULL. Don't let users expect that they are taken into | |
48 | * account. | |
49 | */ | |
50 | assert(!timeout); | |
51 | assert(!uaddr2); | |
52 | assert(!val3); | |
53 | ||
54 | /* | |
55 | * memory barriers to serialize with the previous uaddr modification. | |
56 | */ | |
57 | cmm_smp_mb(); | |
58 | ||
59 | lockret = pthread_mutex_lock(&__lttng_ust_compat_futex_lock); | |
60 | if (lockret) { | |
61 | errno = lockret; | |
62 | ret = -1; | |
63 | goto end; | |
64 | } | |
65 | switch (op) { | |
66 | case FUTEX_WAIT: | |
67 | /* | |
68 | * Wait until *uaddr is changed to something else than "val". | |
69 | * Comparing *uaddr content against val figures out which | |
70 | * thread has been awakened. | |
71 | */ | |
72 | while (CMM_LOAD_SHARED(*uaddr) == val) | |
73 | pthread_cond_wait(&__lttng_ust_compat_futex_cond, | |
74 | &__lttng_ust_compat_futex_lock); | |
75 | break; | |
76 | case FUTEX_WAKE: | |
77 | /* | |
78 | * Each wake is sending a broadcast, thus attempting wakeup of | |
79 | * all awaiting threads, independently of their respective | |
80 | * uaddr. | |
81 | */ | |
82 | pthread_cond_broadcast(&__lttng_ust_compat_futex_cond); | |
83 | break; | |
84 | default: | |
85 | errno = EINVAL; | |
86 | ret = -1; | |
87 | } | |
88 | lockret = pthread_mutex_unlock(&__lttng_ust_compat_futex_lock); | |
89 | if (lockret) { | |
90 | errno = lockret; | |
91 | ret = -1; | |
92 | } | |
93 | end: | |
94 | return ret; | |
95 | } | |
96 | ||
97 | /* | |
98 | * _ASYNC SIGNAL-SAFE_. | |
99 | * For now, timeout, uaddr2 and val3 are unused. | |
100 | * Waiter will busy-loop trying to read the condition. | |
101 | * It is OK to use compat_futex_async() on a futex address on which | |
102 | * futex() WAKE operations are also performed. | |
103 | */ | |
104 | ||
105 | int lttng_ust_compat_futex_async(int32_t *uaddr, int op, int32_t val, | |
106 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
107 | { | |
108 | int ret = 0; | |
109 | ||
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 | */ | |
121 | cmm_smp_mb(); | |
122 | ||
123 | switch (op) { | |
124 | case FUTEX_WAIT: | |
125 | while (CMM_LOAD_SHARED(*uaddr) == val) { | |
126 | if (poll(NULL, 0, 10) < 0) { | |
127 | ret = -1; | |
128 | /* Keep poll errno. Caller handles EINTR. */ | |
129 | goto end; | |
130 | } | |
131 | } | |
132 | break; | |
133 | case FUTEX_WAKE: | |
134 | break; | |
135 | default: | |
136 | errno = EINVAL; | |
137 | ret = -1; | |
138 | } | |
139 | end: | |
140 | return ret; | |
141 | } |