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1 | /* |
2 | * arch/v850/kernel/semaphore.c -- Semaphore support | |
3 | * | |
4 | * Copyright (C) 1998-2000 IBM Corporation | |
5 | * Copyright (C) 1999 Linus Torvalds | |
6 | * | |
7 | * This file is subject to the terms and conditions of the GNU General | |
8 | * Public License. See the file COPYING in the main directory of this | |
9 | * archive for more details. | |
10 | * | |
11 | * This file is a copy of the s390 version, arch/s390/kernel/semaphore.c | |
12 | * Author(s): Martin Schwidefsky | |
13 | * which was derived from the i386 version, linux/arch/i386/kernel/semaphore.c | |
14 | */ | |
15 | ||
16 | #include <linux/errno.h> | |
17 | #include <linux/sched.h> | |
18 | #include <linux/init.h> | |
19 | ||
20 | #include <asm/semaphore.h> | |
21 | ||
22 | /* | |
23 | * Semaphores are implemented using a two-way counter: | |
24 | * The "count" variable is decremented for each process | |
25 | * that tries to acquire the semaphore, while the "sleeping" | |
26 | * variable is a count of such acquires. | |
27 | * | |
28 | * Notably, the inline "up()" and "down()" functions can | |
29 | * efficiently test if they need to do any extra work (up | |
30 | * needs to do something only if count was negative before | |
31 | * the increment operation. | |
32 | * | |
33 | * "sleeping" and the contention routine ordering is | |
34 | * protected by the semaphore spinlock. | |
35 | * | |
36 | * Note that these functions are only called when there is | |
37 | * contention on the lock, and as such all this is the | |
38 | * "non-critical" part of the whole semaphore business. The | |
39 | * critical part is the inline stuff in <asm/semaphore.h> | |
40 | * where we want to avoid any extra jumps and calls. | |
41 | */ | |
42 | ||
43 | /* | |
44 | * Logic: | |
45 | * - only on a boundary condition do we need to care. When we go | |
46 | * from a negative count to a non-negative, we wake people up. | |
47 | * - when we go from a non-negative count to a negative do we | |
48 | * (a) synchronize with the "sleeper" count and (b) make sure | |
49 | * that we're on the wakeup list before we synchronize so that | |
50 | * we cannot lose wakeup events. | |
51 | */ | |
52 | ||
53 | void __up(struct semaphore *sem) | |
54 | { | |
55 | wake_up(&sem->wait); | |
56 | } | |
57 | ||
58 | static DEFINE_SPINLOCK(semaphore_lock); | |
59 | ||
60 | void __sched __down(struct semaphore * sem) | |
61 | { | |
62 | struct task_struct *tsk = current; | |
63 | DECLARE_WAITQUEUE(wait, tsk); | |
64 | tsk->state = TASK_UNINTERRUPTIBLE; | |
65 | add_wait_queue_exclusive(&sem->wait, &wait); | |
66 | ||
67 | spin_lock_irq(&semaphore_lock); | |
68 | sem->sleepers++; | |
69 | for (;;) { | |
70 | int sleepers = sem->sleepers; | |
71 | ||
72 | /* | |
73 | * Add "everybody else" into it. They aren't | |
74 | * playing, because we own the spinlock. | |
75 | */ | |
76 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { | |
77 | sem->sleepers = 0; | |
78 | break; | |
79 | } | |
80 | sem->sleepers = 1; /* us - see -1 above */ | |
81 | spin_unlock_irq(&semaphore_lock); | |
82 | ||
83 | schedule(); | |
84 | tsk->state = TASK_UNINTERRUPTIBLE; | |
85 | spin_lock_irq(&semaphore_lock); | |
86 | } | |
87 | spin_unlock_irq(&semaphore_lock); | |
88 | remove_wait_queue(&sem->wait, &wait); | |
89 | tsk->state = TASK_RUNNING; | |
90 | wake_up(&sem->wait); | |
91 | } | |
92 | ||
93 | int __sched __down_interruptible(struct semaphore * sem) | |
94 | { | |
95 | int retval = 0; | |
96 | struct task_struct *tsk = current; | |
97 | DECLARE_WAITQUEUE(wait, tsk); | |
98 | tsk->state = TASK_INTERRUPTIBLE; | |
99 | add_wait_queue_exclusive(&sem->wait, &wait); | |
100 | ||
101 | spin_lock_irq(&semaphore_lock); | |
102 | sem->sleepers ++; | |
103 | for (;;) { | |
104 | int sleepers = sem->sleepers; | |
105 | ||
106 | /* | |
107 | * With signals pending, this turns into | |
108 | * the trylock failure case - we won't be | |
109 | * sleeping, and we* can't get the lock as | |
110 | * it has contention. Just correct the count | |
111 | * and exit. | |
112 | */ | |
113 | if (signal_pending(current)) { | |
114 | retval = -EINTR; | |
115 | sem->sleepers = 0; | |
116 | atomic_add(sleepers, &sem->count); | |
117 | break; | |
118 | } | |
119 | ||
120 | /* | |
121 | * Add "everybody else" into it. They aren't | |
122 | * playing, because we own the spinlock. The | |
123 | * "-1" is because we're still hoping to get | |
124 | * the lock. | |
125 | */ | |
126 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { | |
127 | sem->sleepers = 0; | |
128 | break; | |
129 | } | |
130 | sem->sleepers = 1; /* us - see -1 above */ | |
131 | spin_unlock_irq(&semaphore_lock); | |
132 | ||
133 | schedule(); | |
134 | tsk->state = TASK_INTERRUPTIBLE; | |
135 | spin_lock_irq(&semaphore_lock); | |
136 | } | |
137 | spin_unlock_irq(&semaphore_lock); | |
138 | tsk->state = TASK_RUNNING; | |
139 | remove_wait_queue(&sem->wait, &wait); | |
140 | wake_up(&sem->wait); | |
141 | return retval; | |
142 | } | |
143 | ||
144 | /* | |
145 | * Trylock failed - make sure we correct for | |
146 | * having decremented the count. | |
147 | */ | |
148 | int __down_trylock(struct semaphore * sem) | |
149 | { | |
150 | unsigned long flags; | |
151 | int sleepers; | |
152 | ||
153 | spin_lock_irqsave(&semaphore_lock, flags); | |
154 | sleepers = sem->sleepers + 1; | |
155 | sem->sleepers = 0; | |
156 | ||
157 | /* | |
158 | * Add "everybody else" and us into it. They aren't | |
159 | * playing, because we own the spinlock. | |
160 | */ | |
161 | if (!atomic_add_negative(sleepers, &sem->count)) | |
162 | wake_up(&sem->wait); | |
163 | ||
164 | spin_unlock_irqrestore(&semaphore_lock, flags); | |
165 | return 1; | |
166 | } |