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Source at commit b05a5adf03613de371c77c3235f7d970d7cd0c71 created 13 years 1 month ago. By Lars-Peter Clausen, NAND: Optimize reading the eec data for the JZ4740 (evil hack) | |
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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 |
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. |
26 | */ |
27 | |
28 | #include <linux/compiler.h> |
29 | #include <linux/kernel.h> |
30 | #include <linux/module.h> |
31 | #include <linux/sched.h> |
32 | #include <linux/semaphore.h> |
33 | #include <linux/spinlock.h> |
34 | #include <linux/ftrace.h> |
35 | |
36 | static noinline void __down(struct semaphore *sem); |
37 | static noinline int __down_interruptible(struct semaphore *sem); |
38 | static noinline int __down_killable(struct semaphore *sem); |
39 | static noinline int __down_timeout(struct semaphore *sem, long jiffies); |
40 | static noinline void __up(struct semaphore *sem); |
41 | |
42 | /** |
43 | * down - acquire the semaphore |
44 | * @sem: the semaphore to be acquired |
45 | * |
46 | * Acquires the semaphore. If no more tasks are allowed to acquire the |
47 | * semaphore, calling this function will put the task to sleep until the |
48 | * semaphore is released. |
49 | * |
50 | * Use of this function is deprecated, please use down_interruptible() or |
51 | * down_killable() instead. |
52 | */ |
53 | void down(struct semaphore *sem) |
54 | { |
55 | unsigned long flags; |
56 | |
57 | spin_lock_irqsave(&sem->lock, flags); |
58 | if (likely(sem->count > 0)) |
59 | sem->count--; |
60 | else |
61 | __down(sem); |
62 | spin_unlock_irqrestore(&sem->lock, flags); |
63 | } |
64 | EXPORT_SYMBOL(down); |
65 | |
66 | /** |
67 | * down_interruptible - acquire the semaphore unless interrupted |
68 | * @sem: the semaphore to be acquired |
69 | * |
70 | * Attempts to acquire the semaphore. If no more tasks are allowed to |
71 | * acquire the semaphore, calling this function will put the task to sleep. |
72 | * If the sleep is interrupted by a signal, this function will return -EINTR. |
73 | * If the semaphore is successfully acquired, this function returns 0. |
74 | */ |
75 | int down_interruptible(struct semaphore *sem) |
76 | { |
77 | unsigned long flags; |
78 | int result = 0; |
79 | |
80 | spin_lock_irqsave(&sem->lock, flags); |
81 | if (likely(sem->count > 0)) |
82 | sem->count--; |
83 | else |
84 | result = __down_interruptible(sem); |
85 | spin_unlock_irqrestore(&sem->lock, flags); |
86 | |
87 | return result; |
88 | } |
89 | EXPORT_SYMBOL(down_interruptible); |
90 | |
91 | /** |
92 | * down_killable - acquire the semaphore unless killed |
93 | * @sem: the semaphore to be acquired |
94 | * |
95 | * Attempts to acquire the semaphore. If no more tasks are allowed to |
96 | * acquire the semaphore, calling this function will put the task to sleep. |
97 | * If the sleep is interrupted by a fatal signal, this function will return |
98 | * -EINTR. If the semaphore is successfully acquired, this function returns |
99 | * 0. |
100 | */ |
101 | int down_killable(struct semaphore *sem) |
102 | { |
103 | unsigned long flags; |
104 | int result = 0; |
105 | |
106 | spin_lock_irqsave(&sem->lock, flags); |
107 | if (likely(sem->count > 0)) |
108 | sem->count--; |
109 | else |
110 | result = __down_killable(sem); |
111 | spin_unlock_irqrestore(&sem->lock, flags); |
112 | |
113 | return result; |
114 | } |
115 | EXPORT_SYMBOL(down_killable); |
116 | |
117 | /** |
118 | * down_trylock - try to acquire the semaphore, without waiting |
119 | * @sem: the semaphore to be acquired |
120 | * |
121 | * Try to acquire the semaphore atomically. Returns 0 if the mutex has |
122 | * been acquired successfully or 1 if it it cannot be acquired. |
123 | * |
124 | * NOTE: This return value is inverted from both spin_trylock and |
125 | * mutex_trylock! Be careful about this when converting code. |
126 | * |
127 | * Unlike mutex_trylock, this function can be used from interrupt context, |
128 | * and the semaphore can be released by any task or interrupt. |
129 | */ |
130 | int down_trylock(struct semaphore *sem) |
131 | { |
132 | unsigned long flags; |
133 | int count; |
134 | |
135 | spin_lock_irqsave(&sem->lock, flags); |
136 | count = sem->count - 1; |
137 | if (likely(count >= 0)) |
138 | sem->count = count; |
139 | spin_unlock_irqrestore(&sem->lock, flags); |
140 | |
141 | return (count < 0); |
142 | } |
143 | EXPORT_SYMBOL(down_trylock); |
144 | |
145 | /** |
146 | * down_timeout - acquire the semaphore within a specified time |
147 | * @sem: the semaphore to be acquired |
148 | * @jiffies: how long to wait before failing |
149 | * |
150 | * Attempts to acquire the semaphore. If no more tasks are allowed to |
151 | * acquire the semaphore, calling this function will put the task to sleep. |
152 | * If the semaphore is not released within the specified number of jiffies, |
153 | * this function returns -ETIME. It returns 0 if the semaphore was acquired. |
154 | */ |
155 | int down_timeout(struct semaphore *sem, long jiffies) |
156 | { |
157 | unsigned long flags; |
158 | int result = 0; |
159 | |
160 | spin_lock_irqsave(&sem->lock, flags); |
161 | if (likely(sem->count > 0)) |
162 | sem->count--; |
163 | else |
164 | result = __down_timeout(sem, jiffies); |
165 | spin_unlock_irqrestore(&sem->lock, flags); |
166 | |
167 | return result; |
168 | } |
169 | EXPORT_SYMBOL(down_timeout); |
170 | |
171 | /** |
172 | * up - release the semaphore |
173 | * @sem: the semaphore to release |
174 | * |
175 | * Release the semaphore. Unlike mutexes, up() may be called from any |
176 | * context and even by tasks which have never called down(). |
177 | */ |
178 | void up(struct semaphore *sem) |
179 | { |
180 | unsigned long flags; |
181 | |
182 | spin_lock_irqsave(&sem->lock, flags); |
183 | if (likely(list_empty(&sem->wait_list))) |
184 | sem->count++; |
185 | else |
186 | __up(sem); |
187 | spin_unlock_irqrestore(&sem->lock, flags); |
188 | } |
189 | EXPORT_SYMBOL(up); |
190 | |
191 | /* Functions for the contended case */ |
192 | |
193 | struct semaphore_waiter { |
194 | struct list_head list; |
195 | struct task_struct *task; |
196 | int up; |
197 | }; |
198 | |
199 | /* |
200 | * Because this function is inlined, the 'state' parameter will be |
201 | * constant, and thus optimised away by the compiler. Likewise the |
202 | * 'timeout' parameter for the cases without timeouts. |
203 | */ |
204 | static inline int __sched __down_common(struct semaphore *sem, long state, |
205 | long timeout) |
206 | { |
207 | struct task_struct *task = current; |
208 | struct semaphore_waiter waiter; |
209 | |
210 | list_add_tail(&waiter.list, &sem->wait_list); |
211 | waiter.task = task; |
212 | waiter.up = 0; |
213 | |
214 | for (;;) { |
215 | if (signal_pending_state(state, task)) |
216 | goto interrupted; |
217 | if (timeout <= 0) |
218 | goto timed_out; |
219 | __set_task_state(task, state); |
220 | spin_unlock_irq(&sem->lock); |
221 | timeout = schedule_timeout(timeout); |
222 | spin_lock_irq(&sem->lock); |
223 | if (waiter.up) |
224 | return 0; |
225 | } |
226 | |
227 | timed_out: |
228 | list_del(&waiter.list); |
229 | return -ETIME; |
230 | |
231 | interrupted: |
232 | list_del(&waiter.list); |
233 | return -EINTR; |
234 | } |
235 | |
236 | static noinline void __sched __down(struct semaphore *sem) |
237 | { |
238 | __down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); |
239 | } |
240 | |
241 | static noinline int __sched __down_interruptible(struct semaphore *sem) |
242 | { |
243 | return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); |
244 | } |
245 | |
246 | static noinline int __sched __down_killable(struct semaphore *sem) |
247 | { |
248 | return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT); |
249 | } |
250 | |
251 | static noinline int __sched __down_timeout(struct semaphore *sem, long jiffies) |
252 | { |
253 | return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies); |
254 | } |
255 | |
256 | static noinline void __sched __up(struct semaphore *sem) |
257 | { |
258 | struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, |
259 | struct semaphore_waiter, list); |
260 | list_del(&waiter->list); |
261 | waiter->up = 1; |
262 | wake_up_process(waiter->task); |
263 | } |
264 |
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Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
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v3.9