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1 | /* MN10300 Semaphore implementation | |
2 | * | |
3 | * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved. | |
4 | * Written by David Howells (dhowells@redhat.com) | |
5 | * | |
6 | * This program is free software; you can redistribute it and/or | |
7 | * modify it under the terms of the GNU General Public Licence | |
8 | * as published by the Free Software Foundation; either version | |
9 | * 2 of the Licence, or (at your option) any later version. | |
10 | */ | |
11 | #include <linux/sched.h> | |
12 | #include <linux/module.h> | |
13 | #include <asm/semaphore.h> | |
14 | ||
15 | struct sem_waiter { | |
16 | struct list_head list; | |
17 | struct task_struct *task; | |
18 | }; | |
19 | ||
20 | #if SEMAPHORE_DEBUG | |
21 | void semtrace(struct semaphore *sem, const char *str) | |
22 | { | |
23 | if (sem->debug) | |
24 | printk(KERN_DEBUG "[%d] %s({%d,%d})\n", | |
25 | current->pid, | |
26 | str, | |
27 | atomic_read(&sem->count), | |
28 | list_empty(&sem->wait_list) ? 0 : 1); | |
29 | } | |
30 | #else | |
31 | #define semtrace(SEM, STR) do { } while (0) | |
32 | #endif | |
33 | ||
34 | /* | |
35 | * wait for a token to be granted from a semaphore | |
36 | * - entered with lock held and interrupts disabled | |
37 | */ | |
38 | void __down(struct semaphore *sem, unsigned long flags) | |
39 | { | |
40 | struct task_struct *tsk = current; | |
41 | struct sem_waiter waiter; | |
42 | ||
43 | semtrace(sem, "Entering __down"); | |
44 | ||
45 | /* set up my own style of waitqueue */ | |
46 | waiter.task = tsk; | |
47 | get_task_struct(tsk); | |
48 | ||
49 | list_add_tail(&waiter.list, &sem->wait_list); | |
50 | ||
51 | /* we don't need to touch the semaphore struct anymore */ | |
52 | spin_unlock_irqrestore(&sem->wait_lock, flags); | |
53 | ||
54 | /* wait to be given the semaphore */ | |
55 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); | |
56 | ||
57 | for (;;) { | |
58 | if (!waiter.task) | |
59 | break; | |
60 | schedule(); | |
61 | set_task_state(tsk, TASK_UNINTERRUPTIBLE); | |
62 | } | |
63 | ||
64 | tsk->state = TASK_RUNNING; | |
65 | semtrace(sem, "Leaving __down"); | |
66 | } | |
67 | EXPORT_SYMBOL(__down); | |
68 | ||
69 | /* | |
70 | * interruptibly wait for a token to be granted from a semaphore | |
71 | * - entered with lock held and interrupts disabled | |
72 | */ | |
73 | int __down_interruptible(struct semaphore *sem, unsigned long flags) | |
74 | { | |
75 | struct task_struct *tsk = current; | |
76 | struct sem_waiter waiter; | |
77 | int ret; | |
78 | ||
79 | semtrace(sem, "Entering __down_interruptible"); | |
80 | ||
81 | /* set up my own style of waitqueue */ | |
82 | waiter.task = tsk; | |
83 | get_task_struct(tsk); | |
84 | ||
85 | list_add_tail(&waiter.list, &sem->wait_list); | |
86 | ||
87 | /* we don't need to touch the semaphore struct anymore */ | |
88 | set_task_state(tsk, TASK_INTERRUPTIBLE); | |
89 | ||
90 | spin_unlock_irqrestore(&sem->wait_lock, flags); | |
91 | ||
92 | /* wait to be given the semaphore */ | |
93 | ret = 0; | |
94 | for (;;) { | |
95 | if (!waiter.task) | |
96 | break; | |
97 | if (unlikely(signal_pending(current))) | |
98 | goto interrupted; | |
99 | schedule(); | |
100 | set_task_state(tsk, TASK_INTERRUPTIBLE); | |
101 | } | |
102 | ||
103 | out: | |
104 | tsk->state = TASK_RUNNING; | |
105 | semtrace(sem, "Leaving __down_interruptible"); | |
106 | return ret; | |
107 | ||
108 | interrupted: | |
109 | spin_lock_irqsave(&sem->wait_lock, flags); | |
110 | list_del(&waiter.list); | |
111 | spin_unlock_irqrestore(&sem->wait_lock, flags); | |
112 | ||
113 | ret = 0; | |
114 | if (!waiter.task) { | |
115 | put_task_struct(current); | |
116 | ret = -EINTR; | |
117 | } | |
118 | goto out; | |
119 | } | |
120 | EXPORT_SYMBOL(__down_interruptible); | |
121 | ||
122 | /* | |
123 | * release a single token back to a semaphore | |
124 | * - entered with lock held and interrupts disabled | |
125 | */ | |
126 | void __up(struct semaphore *sem) | |
127 | { | |
128 | struct task_struct *tsk; | |
129 | struct sem_waiter *waiter; | |
130 | ||
131 | semtrace(sem, "Entering __up"); | |
132 | ||
133 | /* grant the token to the process at the front of the queue */ | |
134 | waiter = list_entry(sem->wait_list.next, struct sem_waiter, list); | |
135 | ||
136 | /* We must be careful not to touch 'waiter' after we set ->task = NULL. | |
137 | * It is an allocated on the waiter's stack and may become invalid at | |
138 | * any time after that point (due to a wakeup from another source). | |
139 | */ | |
140 | list_del_init(&waiter->list); | |
141 | tsk = waiter->task; | |
142 | smp_mb(); | |
143 | waiter->task = NULL; | |
144 | wake_up_process(tsk); | |
145 | put_task_struct(tsk); | |
146 | ||
147 | semtrace(sem, "Leaving __up"); | |
148 | } | |
149 | EXPORT_SYMBOL(__up); |