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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/sh/kernel/semaphore.c
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/sh/kernel/semaphore.c')
-rw-r--r--arch/sh/kernel/semaphore.c139
1 files changed, 139 insertions, 0 deletions
diff --git a/arch/sh/kernel/semaphore.c b/arch/sh/kernel/semaphore.c
new file mode 100644
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+++ b/arch/sh/kernel/semaphore.c
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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
17spinlock_t semaphore_wake_lock;
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 */
49void __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
107void __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
117int __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
136int __down_trylock(struct semaphore * sem)
137{
138 return waking_non_zero_trylock(sem);
139}