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1da177e4 LT |
1 | /* |
2 | * Just taken from alpha implementation. | |
3 | * This can't work well, perhaps. | |
4 | */ | |
5 | /* | |
6 | * Generic semaphore code. Buyer beware. Do your own | |
7 | * specific changes in <asm/semaphore-helper.h> | |
8 | */ | |
9 | ||
10 | #include <linux/errno.h> | |
11 | #include <linux/sched.h> | |
12 | #include <linux/wait.h> | |
13 | #include <linux/init.h> | |
14 | #include <asm/semaphore.h> | |
15 | #include <asm/semaphore-helper.h> | |
16 | ||
765ae317 | 17 | DEFINE_SPINLOCK(semaphore_wake_lock); |
1da177e4 LT |
18 | |
19 | /* | |
20 | * Semaphores are implemented using a two-way counter: | |
21 | * The "count" variable is decremented for each process | |
22 | * that tries to sleep, while the "waking" variable is | |
23 | * incremented when the "up()" code goes to wake up waiting | |
24 | * processes. | |
25 | * | |
26 | * Notably, the inline "up()" and "down()" functions can | |
27 | * efficiently test if they need to do any extra work (up | |
28 | * needs to do something only if count was negative before | |
29 | * the increment operation. | |
30 | * | |
31 | * waking_non_zero() (from asm/semaphore.h) must execute | |
32 | * atomically. | |
33 | * | |
34 | * When __up() is called, the count was negative before | |
35 | * incrementing it, and we need to wake up somebody. | |
36 | * | |
37 | * This routine adds one to the count of processes that need to | |
38 | * wake up and exit. ALL waiting processes actually wake up but | |
39 | * only the one that gets to the "waking" field first will gate | |
40 | * through and acquire the semaphore. The others will go back | |
41 | * to sleep. | |
42 | * | |
43 | * Note that these functions are only called when there is | |
44 | * contention on the lock, and as such all this is the | |
45 | * "non-critical" part of the whole semaphore business. The | |
46 | * critical part is the inline stuff in <asm/semaphore.h> | |
47 | * where we want to avoid any extra jumps and calls. | |
48 | */ | |
49 | void __up(struct semaphore *sem) | |
50 | { | |
51 | wake_one_more(sem); | |
52 | wake_up(&sem->wait); | |
53 | } | |
54 | ||
55 | /* | |
56 | * Perform the "down" function. Return zero for semaphore acquired, | |
57 | * return negative for signalled out of the function. | |
58 | * | |
59 | * If called from __down, the return is ignored and the wait loop is | |
60 | * not interruptible. This means that a task waiting on a semaphore | |
61 | * using "down()" cannot be killed until someone does an "up()" on | |
62 | * the semaphore. | |
63 | * | |
64 | * If called from __down_interruptible, the return value gets checked | |
65 | * upon return. If the return value is negative then the task continues | |
66 | * with the negative value in the return register (it can be tested by | |
67 | * the caller). | |
68 | * | |
69 | * Either form may be used in conjunction with "up()". | |
70 | * | |
71 | */ | |
72 | ||
73 | #define DOWN_VAR \ | |
74 | struct task_struct *tsk = current; \ | |
75 | wait_queue_t wait; \ | |
76 | init_waitqueue_entry(&wait, tsk); | |
77 | ||
78 | #define DOWN_HEAD(task_state) \ | |
79 | \ | |
80 | \ | |
81 | tsk->state = (task_state); \ | |
82 | add_wait_queue(&sem->wait, &wait); \ | |
83 | \ | |
84 | /* \ | |
85 | * Ok, we're set up. sem->count is known to be less than zero \ | |
86 | * so we must wait. \ | |
87 | * \ | |
88 | * We can let go the lock for purposes of waiting. \ | |
89 | * We re-acquire it after awaking so as to protect \ | |
90 | * all semaphore operations. \ | |
91 | * \ | |
92 | * If "up()" is called before we call waking_non_zero() then \ | |
93 | * we will catch it right away. If it is called later then \ | |
94 | * we will have to go through a wakeup cycle to catch it. \ | |
95 | * \ | |
96 | * Multiple waiters contend for the semaphore lock to see \ | |
97 | * who gets to gate through and who has to wait some more. \ | |
98 | */ \ | |
99 | for (;;) { | |
100 | ||
101 | #define DOWN_TAIL(task_state) \ | |
102 | tsk->state = (task_state); \ | |
103 | } \ | |
104 | tsk->state = TASK_RUNNING; \ | |
105 | remove_wait_queue(&sem->wait, &wait); | |
106 | ||
107 | void __sched __down(struct semaphore * sem) | |
108 | { | |
109 | DOWN_VAR | |
110 | DOWN_HEAD(TASK_UNINTERRUPTIBLE) | |
111 | if (waking_non_zero(sem)) | |
112 | break; | |
113 | schedule(); | |
114 | DOWN_TAIL(TASK_UNINTERRUPTIBLE) | |
115 | } | |
116 | ||
117 | int __sched __down_interruptible(struct semaphore * sem) | |
118 | { | |
119 | int ret = 0; | |
120 | DOWN_VAR | |
121 | DOWN_HEAD(TASK_INTERRUPTIBLE) | |
122 | ||
123 | ret = waking_non_zero_interruptible(sem, tsk); | |
124 | if (ret) | |
125 | { | |
126 | if (ret == 1) | |
127 | /* ret != 0 only if we get interrupted -arca */ | |
128 | ret = 0; | |
129 | break; | |
130 | } | |
131 | schedule(); | |
132 | DOWN_TAIL(TASK_INTERRUPTIBLE) | |
133 | return ret; | |
134 | } | |
135 | ||
136 | int __down_trylock(struct semaphore * sem) | |
137 | { | |
138 | return waking_non_zero_trylock(sem); | |
139 | } |