| 1 | /* |
| 2 | * SPDX-License-Identifier: LGPL-2.1-or-later |
| 3 | * |
| 4 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 5 | * |
| 6 | * Userspace RCU library - sys_futex compatibility code |
| 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> |
| 19 | |
| 20 | #include "common/compat/futex.h" |
| 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 | } |