]>
Commit | Line | Data |
---|---|---|
64ac24e7 MW |
1 | /* |
2 | * Copyright (c) 2008 Intel Corporation | |
3 | * Author: Matthew Wilcox <willy@linux.intel.com> | |
4 | * | |
5 | * Distributed under the terms of the GNU GPL, version 2 | |
714493cd MW |
6 | * |
7 | * This file implements counting semaphores. | |
8 | * A counting semaphore may be acquired 'n' times before sleeping. | |
9 | * See mutex.c for single-acquisition sleeping locks which enforce | |
10 | * rules which allow code to be debugged more easily. | |
11 | */ | |
12 | ||
13 | /* | |
14 | * Some notes on the implementation: | |
15 | * | |
16 | * The spinlock controls access to the other members of the semaphore. | |
17 | * down_trylock() and up() can be called from interrupt context, so we | |
18 | * have to disable interrupts when taking the lock. It turns out various | |
19 | * parts of the kernel expect to be able to use down() on a semaphore in | |
20 | * interrupt context when they know it will succeed, so we have to use | |
21 | * irqsave variants for down(), down_interruptible() and down_killable() | |
22 | * too. | |
23 | * | |
24 | * The ->count variable represents how many more tasks can acquire this | |
25 | * semaphore. If it's zero, there may be tasks waiting on the wait_list. | |
64ac24e7 MW |
26 | */ |
27 | ||
28 | #include <linux/compiler.h> | |
29 | #include <linux/kernel.h> | |
9984de1a | 30 | #include <linux/export.h> |
64ac24e7 | 31 | #include <linux/sched.h> |
b17b0153 | 32 | #include <linux/sched/debug.h> |
64ac24e7 MW |
33 | #include <linux/semaphore.h> |
34 | #include <linux/spinlock.h> | |
74f4e369 | 35 | #include <linux/ftrace.h> |
64ac24e7 | 36 | |
64ac24e7 MW |
37 | static noinline void __down(struct semaphore *sem); |
38 | static noinline int __down_interruptible(struct semaphore *sem); | |
f06d9686 | 39 | static noinline int __down_killable(struct semaphore *sem); |
31542769 | 40 | static noinline int __down_timeout(struct semaphore *sem, long timeout); |
64ac24e7 MW |
41 | static noinline void __up(struct semaphore *sem); |
42 | ||
714493cd MW |
43 | /** |
44 | * down - acquire the semaphore | |
45 | * @sem: the semaphore to be acquired | |
46 | * | |
47 | * Acquires the semaphore. If no more tasks are allowed to acquire the | |
48 | * semaphore, calling this function will put the task to sleep until the | |
49 | * semaphore is released. | |
50 | * | |
51 | * Use of this function is deprecated, please use down_interruptible() or | |
52 | * down_killable() instead. | |
53 | */ | |
64ac24e7 MW |
54 | void down(struct semaphore *sem) |
55 | { | |
56 | unsigned long flags; | |
57 | ||
8292c9e1 | 58 | raw_spin_lock_irqsave(&sem->lock, flags); |
00b41ec2 LT |
59 | if (likely(sem->count > 0)) |
60 | sem->count--; | |
61 | else | |
64ac24e7 | 62 | __down(sem); |
8292c9e1 | 63 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
64ac24e7 MW |
64 | } |
65 | EXPORT_SYMBOL(down); | |
66 | ||
714493cd MW |
67 | /** |
68 | * down_interruptible - acquire the semaphore unless interrupted | |
69 | * @sem: the semaphore to be acquired | |
70 | * | |
71 | * Attempts to acquire the semaphore. If no more tasks are allowed to | |
72 | * acquire the semaphore, calling this function will put the task to sleep. | |
73 | * If the sleep is interrupted by a signal, this function will return -EINTR. | |
74 | * If the semaphore is successfully acquired, this function returns 0. | |
75 | */ | |
64ac24e7 MW |
76 | int down_interruptible(struct semaphore *sem) |
77 | { | |
78 | unsigned long flags; | |
79 | int result = 0; | |
80 | ||
8292c9e1 | 81 | raw_spin_lock_irqsave(&sem->lock, flags); |
00b41ec2 | 82 | if (likely(sem->count > 0)) |
bf726eab | 83 | sem->count--; |
00b41ec2 LT |
84 | else |
85 | result = __down_interruptible(sem); | |
8292c9e1 | 86 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
64ac24e7 MW |
87 | |
88 | return result; | |
89 | } | |
90 | EXPORT_SYMBOL(down_interruptible); | |
91 | ||
714493cd MW |
92 | /** |
93 | * down_killable - acquire the semaphore unless killed | |
94 | * @sem: the semaphore to be acquired | |
95 | * | |
96 | * Attempts to acquire the semaphore. If no more tasks are allowed to | |
97 | * acquire the semaphore, calling this function will put the task to sleep. | |
98 | * If the sleep is interrupted by a fatal signal, this function will return | |
99 | * -EINTR. If the semaphore is successfully acquired, this function returns | |
100 | * 0. | |
101 | */ | |
f06d9686 MW |
102 | int down_killable(struct semaphore *sem) |
103 | { | |
104 | unsigned long flags; | |
105 | int result = 0; | |
106 | ||
8292c9e1 | 107 | raw_spin_lock_irqsave(&sem->lock, flags); |
00b41ec2 | 108 | if (likely(sem->count > 0)) |
bf726eab | 109 | sem->count--; |
00b41ec2 LT |
110 | else |
111 | result = __down_killable(sem); | |
8292c9e1 | 112 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
f06d9686 MW |
113 | |
114 | return result; | |
115 | } | |
116 | EXPORT_SYMBOL(down_killable); | |
117 | ||
64ac24e7 MW |
118 | /** |
119 | * down_trylock - try to acquire the semaphore, without waiting | |
120 | * @sem: the semaphore to be acquired | |
121 | * | |
f7232f08 | 122 | * Try to acquire the semaphore atomically. Returns 0 if the semaphore has |
714493cd | 123 | * been acquired successfully or 1 if it it cannot be acquired. |
64ac24e7 MW |
124 | * |
125 | * NOTE: This return value is inverted from both spin_trylock and | |
126 | * mutex_trylock! Be careful about this when converting code. | |
127 | * | |
128 | * Unlike mutex_trylock, this function can be used from interrupt context, | |
129 | * and the semaphore can be released by any task or interrupt. | |
130 | */ | |
131 | int down_trylock(struct semaphore *sem) | |
132 | { | |
133 | unsigned long flags; | |
134 | int count; | |
135 | ||
8292c9e1 | 136 | raw_spin_lock_irqsave(&sem->lock, flags); |
64ac24e7 MW |
137 | count = sem->count - 1; |
138 | if (likely(count >= 0)) | |
139 | sem->count = count; | |
8292c9e1 | 140 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
64ac24e7 MW |
141 | |
142 | return (count < 0); | |
143 | } | |
144 | EXPORT_SYMBOL(down_trylock); | |
145 | ||
714493cd MW |
146 | /** |
147 | * down_timeout - acquire the semaphore within a specified time | |
148 | * @sem: the semaphore to be acquired | |
31542769 | 149 | * @timeout: how long to wait before failing |
714493cd MW |
150 | * |
151 | * Attempts to acquire the semaphore. If no more tasks are allowed to | |
152 | * acquire the semaphore, calling this function will put the task to sleep. | |
153 | * If the semaphore is not released within the specified number of jiffies, | |
154 | * this function returns -ETIME. It returns 0 if the semaphore was acquired. | |
155 | */ | |
31542769 | 156 | int down_timeout(struct semaphore *sem, long timeout) |
f1241c87 MW |
157 | { |
158 | unsigned long flags; | |
159 | int result = 0; | |
160 | ||
8292c9e1 | 161 | raw_spin_lock_irqsave(&sem->lock, flags); |
00b41ec2 | 162 | if (likely(sem->count > 0)) |
bf726eab | 163 | sem->count--; |
00b41ec2 | 164 | else |
31542769 | 165 | result = __down_timeout(sem, timeout); |
8292c9e1 | 166 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
f1241c87 MW |
167 | |
168 | return result; | |
169 | } | |
170 | EXPORT_SYMBOL(down_timeout); | |
171 | ||
714493cd MW |
172 | /** |
173 | * up - release the semaphore | |
174 | * @sem: the semaphore to release | |
175 | * | |
176 | * Release the semaphore. Unlike mutexes, up() may be called from any | |
177 | * context and even by tasks which have never called down(). | |
178 | */ | |
64ac24e7 MW |
179 | void up(struct semaphore *sem) |
180 | { | |
181 | unsigned long flags; | |
182 | ||
8292c9e1 | 183 | raw_spin_lock_irqsave(&sem->lock, flags); |
00b41ec2 LT |
184 | if (likely(list_empty(&sem->wait_list))) |
185 | sem->count++; | |
186 | else | |
64ac24e7 | 187 | __up(sem); |
8292c9e1 | 188 | raw_spin_unlock_irqrestore(&sem->lock, flags); |
64ac24e7 MW |
189 | } |
190 | EXPORT_SYMBOL(up); | |
191 | ||
192 | /* Functions for the contended case */ | |
193 | ||
194 | struct semaphore_waiter { | |
195 | struct list_head list; | |
196 | struct task_struct *task; | |
06a6ea37 | 197 | bool up; |
64ac24e7 MW |
198 | }; |
199 | ||
64ac24e7 | 200 | /* |
f1241c87 MW |
201 | * Because this function is inlined, the 'state' parameter will be |
202 | * constant, and thus optimised away by the compiler. Likewise the | |
203 | * 'timeout' parameter for the cases without timeouts. | |
64ac24e7 | 204 | */ |
f1241c87 MW |
205 | static inline int __sched __down_common(struct semaphore *sem, long state, |
206 | long timeout) | |
64ac24e7 | 207 | { |
64ac24e7 MW |
208 | struct semaphore_waiter waiter; |
209 | ||
bf726eab | 210 | list_add_tail(&waiter.list, &sem->wait_list); |
d269a8b8 | 211 | waiter.task = current; |
06a6ea37 | 212 | waiter.up = false; |
64ac24e7 MW |
213 | |
214 | for (;;) { | |
d269a8b8 | 215 | if (signal_pending_state(state, current)) |
00b41ec2 | 216 | goto interrupted; |
c74f66ce | 217 | if (unlikely(timeout <= 0)) |
00b41ec2 | 218 | goto timed_out; |
642fa448 | 219 | __set_current_state(state); |
8292c9e1 | 220 | raw_spin_unlock_irq(&sem->lock); |
f1241c87 | 221 | timeout = schedule_timeout(timeout); |
8292c9e1 | 222 | raw_spin_lock_irq(&sem->lock); |
00b41ec2 LT |
223 | if (waiter.up) |
224 | return 0; | |
64ac24e7 MW |
225 | } |
226 | ||
00b41ec2 LT |
227 | timed_out: |
228 | list_del(&waiter.list); | |
229 | return -ETIME; | |
230 | ||
231 | interrupted: | |
64ac24e7 | 232 | list_del(&waiter.list); |
00b41ec2 | 233 | return -EINTR; |
64ac24e7 MW |
234 | } |
235 | ||
236 | static noinline void __sched __down(struct semaphore *sem) | |
237 | { | |
f1241c87 | 238 | __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); |
64ac24e7 MW |
239 | } |
240 | ||
241 | static noinline int __sched __down_interruptible(struct semaphore *sem) | |
242 | { | |
f1241c87 | 243 | return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); |
64ac24e7 MW |
244 | } |
245 | ||
f06d9686 MW |
246 | static noinline int __sched __down_killable(struct semaphore *sem) |
247 | { | |
f1241c87 MW |
248 | return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT); |
249 | } | |
250 | ||
31542769 | 251 | static noinline int __sched __down_timeout(struct semaphore *sem, long timeout) |
f1241c87 | 252 | { |
31542769 | 253 | return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout); |
f06d9686 MW |
254 | } |
255 | ||
64ac24e7 MW |
256 | static noinline void __sched __up(struct semaphore *sem) |
257 | { | |
b17170b2 MW |
258 | struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, |
259 | struct semaphore_waiter, list); | |
00b41ec2 | 260 | list_del(&waiter->list); |
06a6ea37 | 261 | waiter->up = true; |
b17170b2 | 262 | wake_up_process(waiter->task); |
64ac24e7 | 263 | } |