Commit | Line | Data |
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287a512f | 1 | /* |
ab5be9fa MJ |
2 | * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
3 | * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com> | |
287a512f | 4 | * |
ab5be9fa | 5 | * SPDX-License-Identifier: LGPL-2.1-only |
287a512f | 6 | * |
287a512f JG |
7 | */ |
8 | ||
c9e313bc | 9 | #include "error.hpp" |
f40b76ae | 10 | #include "macros.hpp" |
28ab034a JG |
11 | #include "waiter.hpp" |
12 | ||
287a512f | 13 | #include <poll.h> |
28ab034a JG |
14 | #include <urcu/futex.h> |
15 | #include <urcu/uatomic.h> | |
287a512f JG |
16 | |
17 | /* | |
18 | * Number of busy-loop attempts before waiting on futex. | |
19 | */ | |
20 | #define WAIT_ATTEMPTS 1000 | |
21 | ||
22 | enum waiter_state { | |
23 | /* WAITER_WAITING is compared directly (futex compares it). */ | |
28ab034a | 24 | WAITER_WAITING = 0, |
287a512f | 25 | /* non-zero are used as masks. */ |
28ab034a JG |
26 | WAITER_WOKEN_UP = (1 << 0), |
27 | WAITER_RUNNING = (1 << 1), | |
28 | WAITER_TEARDOWN = (1 << 2), | |
287a512f JG |
29 | }; |
30 | ||
287a512f JG |
31 | void lttng_waiter_init(struct lttng_waiter *waiter) |
32 | { | |
33 | cds_wfs_node_init(&waiter->wait_queue_node); | |
34 | uatomic_set(&waiter->state, WAITER_WAITING); | |
35 | cmm_smp_mb(); | |
36 | } | |
37 | ||
38 | /* | |
39 | * User must init "waiter" before passing its memory to waker thread. | |
40 | */ | |
287a512f JG |
41 | void lttng_waiter_wait(struct lttng_waiter *waiter) |
42 | { | |
43 | unsigned int i; | |
44 | ||
f40b76ae JG |
45 | DBG("Beginning of waiter \"wait\" period"); |
46 | ||
47 | /* Load and test condition before read state. */ | |
287a512f JG |
48 | cmm_smp_rmb(); |
49 | for (i = 0; i < WAIT_ATTEMPTS; i++) { | |
50 | if (uatomic_read(&waiter->state) != WAITER_WAITING) { | |
51 | goto skip_futex_wait; | |
52 | } | |
f40b76ae | 53 | |
287a512f JG |
54 | caa_cpu_relax(); |
55 | } | |
f40b76ae | 56 | |
6e5438dc | 57 | while (uatomic_read(&waiter->state) == WAITER_WAITING) { |
cd9adb8b JG |
58 | if (!futex_noasync( |
59 | &waiter->state, FUTEX_WAIT, WAITER_WAITING, nullptr, nullptr, 0)) { | |
6e5438dc MD |
60 | /* |
61 | * Prior queued wakeups queued by unrelated code | |
62 | * using the same address can cause futex wait to | |
63 | * return 0 even through the futex value is still | |
64 | * WAITER_WAITING (spurious wakeups). Check | |
65 | * the value again in user-space to validate | |
66 | * whether it really differs from WAITER_WAITING. | |
67 | */ | |
68 | continue; | |
69 | } | |
f40b76ae | 70 | |
287a512f | 71 | switch (errno) { |
6e5438dc | 72 | case EAGAIN: |
287a512f JG |
73 | /* Value already changed. */ |
74 | goto skip_futex_wait; | |
75 | case EINTR: | |
76 | /* Retry if interrupted by signal. */ | |
28ab034a | 77 | break; /* Get out of switch. Check again. */ |
287a512f JG |
78 | default: |
79 | /* Unexpected error. */ | |
80 | PERROR("futex_noasync"); | |
81 | abort(); | |
82 | } | |
83 | } | |
84 | skip_futex_wait: | |
85 | ||
86 | /* Tell waker thread than we are running. */ | |
87 | uatomic_or(&waiter->state, WAITER_RUNNING); | |
88 | ||
89 | /* | |
90 | * Wait until waker thread lets us know it's ok to tear down | |
91 | * memory allocated for struct lttng_waiter. | |
92 | */ | |
93 | for (i = 0; i < WAIT_ATTEMPTS; i++) { | |
94 | if (uatomic_read(&waiter->state) & WAITER_TEARDOWN) { | |
95 | break; | |
96 | } | |
f40b76ae | 97 | |
287a512f JG |
98 | caa_cpu_relax(); |
99 | } | |
f40b76ae | 100 | |
287a512f | 101 | while (!(uatomic_read(&waiter->state) & WAITER_TEARDOWN)) { |
cd9adb8b | 102 | poll(nullptr, 0, 10); |
287a512f | 103 | } |
f40b76ae | 104 | |
a0377dfe | 105 | LTTNG_ASSERT(uatomic_read(&waiter->state) & WAITER_TEARDOWN); |
f40b76ae | 106 | DBG("End of waiter \"wait\" period"); |
287a512f JG |
107 | } |
108 | ||
109 | /* | |
110 | * Note: lttng_waiter_wake needs waiter to stay allocated throughout its | |
111 | * execution. In this scheme, the waiter owns the node memory, and we only allow | |
112 | * it to free this memory when it sees the WAITER_TEARDOWN flag. | |
113 | */ | |
f40b76ae | 114 | void lttng_waiter_wake(struct lttng_waiter *waiter) |
287a512f JG |
115 | { |
116 | cmm_smp_mb(); | |
a0377dfe | 117 | LTTNG_ASSERT(uatomic_read(&waiter->state) == WAITER_WAITING); |
287a512f JG |
118 | uatomic_set(&waiter->state, WAITER_WOKEN_UP); |
119 | if (!(uatomic_read(&waiter->state) & WAITER_RUNNING)) { | |
cd9adb8b | 120 | if (futex_noasync(&waiter->state, FUTEX_WAKE, 1, nullptr, nullptr, 0) < 0) { |
287a512f JG |
121 | PERROR("futex_noasync"); |
122 | abort(); | |
123 | } | |
124 | } | |
f40b76ae | 125 | |
287a512f JG |
126 | /* Allow teardown of struct urcu_wait memory. */ |
127 | uatomic_or(&waiter->state, WAITER_TEARDOWN); | |
128 | } | |
f40b76ae JG |
129 | |
130 | void lttng_wait_queue_init(struct lttng_wait_queue *queue) | |
131 | { | |
132 | cds_wfs_init(&queue->stack); | |
133 | } | |
134 | ||
135 | void lttng_wait_queue_add(struct lttng_wait_queue *queue, struct lttng_waiter *waiter) | |
136 | { | |
137 | (void) cds_wfs_push(&queue->stack, &waiter->wait_queue_node); | |
138 | } | |
139 | ||
140 | void lttng_wait_queue_wake_all(struct lttng_wait_queue *queue) | |
141 | { | |
142 | cds_wfs_head *waiters; | |
143 | cds_wfs_node *iter, *iter_n; | |
144 | ||
145 | /* Move all waiters from the queue to our local stack. */ | |
146 | waiters = __cds_wfs_pop_all(&queue->stack); | |
147 | ||
148 | /* Wake all waiters in our stack head. */ | |
149 | cds_wfs_for_each_blocking_safe (waiters, iter, iter_n) { | |
150 | auto *waiter = lttng::utils::container_of(iter, <tng_waiter::wait_queue_node); | |
151 | ||
152 | /* Don't wake already running threads. */ | |
153 | if (waiter->state & WAITER_RUNNING) { | |
154 | continue; | |
155 | } | |
156 | ||
157 | lttng_waiter_wake(waiter); | |
158 | } | |
159 | } |