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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 | 19 | |
08ba2503 | 20 | #include "lib/lttng-ust/futex.h" |
10544ee8 MD |
21 | |
22 | /* | |
08ba2503 MJ |
23 | * This compat header originated in userspace RCU where it's used across |
24 | * multiple shared objects hence the need to have the mutexes as public weak | |
25 | * symbols, in our case here, it's only used internally by liblttng-ust so we | |
26 | * can hide them. If we end up using this compat header in another library in | |
27 | * this project we will have to use the same scheme, but in the meantime, don't | |
28 | * expose those symbols in the ABI. | |
29 | */ | |
30 | ||
31 | /* | |
32 | * This comment will apply if we start using this compat header in multiple | |
33 | * libraires. | |
34 | * | |
10544ee8 MD |
35 | * Using attribute "weak" for __lttng_ust_compat_futex_lock and |
36 | * __lttng_ust_compat_futex_cond. Those are globally visible by the entire | |
37 | * program, even though many shared objects may have their own version. | |
38 | * The first version that gets loaded will be used by the entire program | |
39 | * (executable and all shared objects). | |
40 | */ | |
41 | ||
08ba2503 MJ |
42 | static pthread_mutex_t __lttng_ust_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER; |
43 | static pthread_cond_t __lttng_ust_compat_futex_cond = PTHREAD_COND_INITIALIZER; | |
10544ee8 MD |
44 | |
45 | /* | |
46 | * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though. | |
47 | * For now, timeout, uaddr2 and val3 are unused. | |
48 | * Waiter will relinquish the CPU until woken up. | |
49 | */ | |
50 | ||
51 | int lttng_ust_compat_futex_noasync(int32_t *uaddr, int op, int32_t val, | |
52 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
53 | { | |
54 | int ret = 0, lockret; | |
55 | ||
56 | /* | |
57 | * Check if NULL. Don't let users expect that they are taken into | |
58 | * account. | |
59 | */ | |
60 | assert(!timeout); | |
61 | assert(!uaddr2); | |
62 | assert(!val3); | |
63 | ||
64 | /* | |
65 | * memory barriers to serialize with the previous uaddr modification. | |
66 | */ | |
67 | cmm_smp_mb(); | |
68 | ||
69 | lockret = pthread_mutex_lock(&__lttng_ust_compat_futex_lock); | |
70 | if (lockret) { | |
71 | errno = lockret; | |
72 | ret = -1; | |
73 | goto end; | |
74 | } | |
75 | switch (op) { | |
76 | case FUTEX_WAIT: | |
77 | /* | |
78 | * Wait until *uaddr is changed to something else than "val". | |
79 | * Comparing *uaddr content against val figures out which | |
80 | * thread has been awakened. | |
81 | */ | |
82 | while (CMM_LOAD_SHARED(*uaddr) == val) | |
83 | pthread_cond_wait(&__lttng_ust_compat_futex_cond, | |
84 | &__lttng_ust_compat_futex_lock); | |
85 | break; | |
86 | case FUTEX_WAKE: | |
87 | /* | |
88 | * Each wake is sending a broadcast, thus attempting wakeup of | |
89 | * all awaiting threads, independently of their respective | |
90 | * uaddr. | |
91 | */ | |
92 | pthread_cond_broadcast(&__lttng_ust_compat_futex_cond); | |
93 | break; | |
94 | default: | |
95 | errno = EINVAL; | |
96 | ret = -1; | |
97 | } | |
98 | lockret = pthread_mutex_unlock(&__lttng_ust_compat_futex_lock); | |
99 | if (lockret) { | |
100 | errno = lockret; | |
101 | ret = -1; | |
102 | } | |
103 | end: | |
104 | return ret; | |
105 | } | |
106 | ||
107 | /* | |
108 | * _ASYNC SIGNAL-SAFE_. | |
109 | * For now, timeout, uaddr2 and val3 are unused. | |
110 | * Waiter will busy-loop trying to read the condition. | |
111 | * It is OK to use compat_futex_async() on a futex address on which | |
112 | * futex() WAKE operations are also performed. | |
113 | */ | |
114 | ||
115 | int lttng_ust_compat_futex_async(int32_t *uaddr, int op, int32_t val, | |
116 | const struct timespec *timeout, int32_t *uaddr2, int32_t val3) | |
117 | { | |
118 | int ret = 0; | |
119 | ||
120 | /* | |
121 | * Check if NULL. Don't let users expect that they are taken into | |
122 | * account. | |
123 | */ | |
124 | assert(!timeout); | |
125 | assert(!uaddr2); | |
126 | assert(!val3); | |
127 | ||
128 | /* | |
129 | * Ensure previous memory operations on uaddr have completed. | |
130 | */ | |
131 | cmm_smp_mb(); | |
132 | ||
133 | switch (op) { | |
134 | case FUTEX_WAIT: | |
135 | while (CMM_LOAD_SHARED(*uaddr) == val) { | |
136 | if (poll(NULL, 0, 10) < 0) { | |
137 | ret = -1; | |
138 | /* Keep poll errno. Caller handles EINTR. */ | |
139 | goto end; | |
140 | } | |
141 | } | |
142 | break; | |
143 | case FUTEX_WAKE: | |
144 | break; | |
145 | default: | |
146 | errno = EINVAL; | |
147 | ret = -1; | |
148 | } | |
149 | end: | |
150 | return ret; | |
151 | } |