Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | /* $Id: semaphore.c,v 1.7 2001/04/18 21:06:05 davem Exp $ */ |
2 | ||
3 | /* sparc32 semaphore implementation, based on i386 version */ | |
4 | ||
5 | #include <linux/sched.h> | |
6 | #include <linux/errno.h> | |
7 | #include <linux/init.h> | |
8 | ||
9 | #include <asm/semaphore.h> | |
10 | ||
11 | /* | |
12 | * Semaphores are implemented using a two-way counter: | |
13 | * The "count" variable is decremented for each process | |
14 | * that tries to acquire the semaphore, while the "sleeping" | |
15 | * variable is a count of such acquires. | |
16 | * | |
17 | * Notably, the inline "up()" and "down()" functions can | |
18 | * efficiently test if they need to do any extra work (up | |
19 | * needs to do something only if count was negative before | |
20 | * the increment operation. | |
21 | * | |
22 | * "sleeping" and the contention routine ordering is | |
23 | * protected by the semaphore spinlock. | |
24 | * | |
25 | * Note that these functions are only called when there is | |
26 | * contention on the lock, and as such all this is the | |
27 | * "non-critical" part of the whole semaphore business. The | |
28 | * critical part is the inline stuff in <asm/semaphore.h> | |
29 | * where we want to avoid any extra jumps and calls. | |
30 | */ | |
31 | ||
32 | /* | |
33 | * Logic: | |
34 | * - only on a boundary condition do we need to care. When we go | |
35 | * from a negative count to a non-negative, we wake people up. | |
36 | * - when we go from a non-negative count to a negative do we | |
37 | * (a) synchronize with the "sleeper" count and (b) make sure | |
38 | * that we're on the wakeup list before we synchronize so that | |
39 | * we cannot lose wakeup events. | |
40 | */ | |
41 | ||
42 | void __up(struct semaphore *sem) | |
43 | { | |
44 | wake_up(&sem->wait); | |
45 | } | |
46 | ||
47 | static DEFINE_SPINLOCK(semaphore_lock); | |
48 | ||
49 | void __sched __down(struct semaphore * sem) | |
50 | { | |
51 | struct task_struct *tsk = current; | |
52 | DECLARE_WAITQUEUE(wait, tsk); | |
53 | tsk->state = TASK_UNINTERRUPTIBLE; | |
54 | add_wait_queue_exclusive(&sem->wait, &wait); | |
55 | ||
56 | spin_lock_irq(&semaphore_lock); | |
57 | sem->sleepers++; | |
58 | for (;;) { | |
59 | int sleepers = sem->sleepers; | |
60 | ||
61 | /* | |
62 | * Add "everybody else" into it. They aren't | |
63 | * playing, because we own the spinlock. | |
64 | */ | |
65 | if (!atomic24_add_negative(sleepers - 1, &sem->count)) { | |
66 | sem->sleepers = 0; | |
67 | break; | |
68 | } | |
69 | sem->sleepers = 1; /* us - see -1 above */ | |
70 | spin_unlock_irq(&semaphore_lock); | |
71 | ||
72 | schedule(); | |
73 | tsk->state = TASK_UNINTERRUPTIBLE; | |
74 | spin_lock_irq(&semaphore_lock); | |
75 | } | |
76 | spin_unlock_irq(&semaphore_lock); | |
77 | remove_wait_queue(&sem->wait, &wait); | |
78 | tsk->state = TASK_RUNNING; | |
79 | wake_up(&sem->wait); | |
80 | } | |
81 | ||
82 | int __sched __down_interruptible(struct semaphore * sem) | |
83 | { | |
84 | int retval = 0; | |
85 | struct task_struct *tsk = current; | |
86 | DECLARE_WAITQUEUE(wait, tsk); | |
87 | tsk->state = TASK_INTERRUPTIBLE; | |
88 | add_wait_queue_exclusive(&sem->wait, &wait); | |
89 | ||
90 | spin_lock_irq(&semaphore_lock); | |
91 | sem->sleepers ++; | |
92 | for (;;) { | |
93 | int sleepers = sem->sleepers; | |
94 | ||
95 | /* | |
96 | * With signals pending, this turns into | |
97 | * the trylock failure case - we won't be | |
98 | * sleeping, and we* can't get the lock as | |
99 | * it has contention. Just correct the count | |
100 | * and exit. | |
101 | */ | |
102 | if (signal_pending(current)) { | |
103 | retval = -EINTR; | |
104 | sem->sleepers = 0; | |
105 | atomic24_add(sleepers, &sem->count); | |
106 | break; | |
107 | } | |
108 | ||
109 | /* | |
110 | * Add "everybody else" into it. They aren't | |
111 | * playing, because we own the spinlock. The | |
112 | * "-1" is because we're still hoping to get | |
113 | * the lock. | |
114 | */ | |
115 | if (!atomic24_add_negative(sleepers - 1, &sem->count)) { | |
116 | sem->sleepers = 0; | |
117 | break; | |
118 | } | |
119 | sem->sleepers = 1; /* us - see -1 above */ | |
120 | spin_unlock_irq(&semaphore_lock); | |
121 | ||
122 | schedule(); | |
123 | tsk->state = TASK_INTERRUPTIBLE; | |
124 | spin_lock_irq(&semaphore_lock); | |
125 | } | |
126 | spin_unlock_irq(&semaphore_lock); | |
127 | tsk->state = TASK_RUNNING; | |
128 | remove_wait_queue(&sem->wait, &wait); | |
129 | wake_up(&sem->wait); | |
130 | return retval; | |
131 | } | |
132 | ||
133 | /* | |
134 | * Trylock failed - make sure we correct for | |
135 | * having decremented the count. | |
136 | */ | |
137 | int __down_trylock(struct semaphore * sem) | |
138 | { | |
139 | int sleepers; | |
140 | unsigned long flags; | |
141 | ||
142 | spin_lock_irqsave(&semaphore_lock, flags); | |
143 | sleepers = sem->sleepers + 1; | |
144 | sem->sleepers = 0; | |
145 | ||
146 | /* | |
147 | * Add "everybody else" and us into it. They aren't | |
148 | * playing, because we own the spinlock. | |
149 | */ | |
150 | if (!atomic24_add_negative(sleepers, &sem->count)) | |
151 | wake_up(&sem->wait); | |
152 | ||
153 | spin_unlock_irqrestore(&semaphore_lock, flags); | |
154 | return 1; | |
155 | } |