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authorMatthew Wilcox <matthew@wil.cx>2008-03-07 21:55:58 -0500
committerMatthew Wilcox <willy@linux.intel.com>2008-04-17 10:42:34 -0400
commit64ac24e738823161693bf791f87adc802cf529ff (patch)
tree19c0b0cf314d4394ca580c05b86cdf874ce0a167 /arch/ppc
parente48b3deee475134585eed03e7afebe4bf9e0dba9 (diff)
Generic semaphore implementation
Semaphores are no longer performance-critical, so a generic C implementation is better for maintainability, debuggability and extensibility. Thanks to Peter Zijlstra for fixing the lockdep warning. Thanks to Harvey Harrison for pointing out that the unlikely() was unnecessary. Signed-off-by: Matthew Wilcox <willy@linux.intel.com> Acked-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/ppc')
-rw-r--r--arch/ppc/kernel/semaphore.c131
1 files changed, 0 insertions, 131 deletions
diff --git a/arch/ppc/kernel/semaphore.c b/arch/ppc/kernel/semaphore.c
deleted file mode 100644
index 2fe429b27c1..00000000000
--- a/arch/ppc/kernel/semaphore.c
+++ /dev/null
@@ -1,131 +0,0 @@
1/*
2 * PowerPC-specific semaphore code.
3 *
4 * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 *
11 * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
12 * to eliminate the SMP races in the old version between the updates
13 * of `count' and `waking'. Now we use negative `count' values to
14 * indicate that some process(es) are waiting for the semaphore.
15 */
16
17#include <linux/sched.h>
18#include <linux/init.h>
19#include <asm/atomic.h>
20#include <asm/semaphore.h>
21#include <asm/errno.h>
22
23/*
24 * Atomically update sem->count.
25 * This does the equivalent of the following:
26 *
27 * old_count = sem->count;
28 * tmp = MAX(old_count, 0) + incr;
29 * sem->count = tmp;
30 * return old_count;
31 */
32static inline int __sem_update_count(struct semaphore *sem, int incr)
33{
34 int old_count, tmp;
35
36 __asm__ __volatile__("\n"
37"1: lwarx %0,0,%3\n"
38" srawi %1,%0,31\n"
39" andc %1,%0,%1\n"
40" add %1,%1,%4\n"
41 PPC405_ERR77(0,%3)
42" stwcx. %1,0,%3\n"
43" bne 1b"
44 : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
45 : "r" (&sem->count), "r" (incr), "m" (sem->count)
46 : "cc");
47
48 return old_count;
49}
50
51void __up(struct semaphore *sem)
52{
53 /*
54 * Note that we incremented count in up() before we came here,
55 * but that was ineffective since the result was <= 0, and
56 * any negative value of count is equivalent to 0.
57 * This ends up setting count to 1, unless count is now > 0
58 * (i.e. because some other cpu has called up() in the meantime),
59 * in which case we just increment count.
60 */
61 __sem_update_count(sem, 1);
62 wake_up(&sem->wait);
63}
64
65/*
66 * Note that when we come in to __down or __down_interruptible,
67 * we have already decremented count, but that decrement was
68 * ineffective since the result was < 0, and any negative value
69 * of count is equivalent to 0.
70 * Thus it is only when we decrement count from some value > 0
71 * that we have actually got the semaphore.
72 */
73void __sched __down(struct semaphore *sem)
74{
75 struct task_struct *tsk = current;
76 DECLARE_WAITQUEUE(wait, tsk);
77
78 tsk->state = TASK_UNINTERRUPTIBLE;
79 add_wait_queue_exclusive(&sem->wait, &wait);
80 smp_wmb();
81
82 /*
83 * Try to get the semaphore. If the count is > 0, then we've
84 * got the semaphore; we decrement count and exit the loop.
85 * If the count is 0 or negative, we set it to -1, indicating
86 * that we are asleep, and then sleep.
87 */
88 while (__sem_update_count(sem, -1) <= 0) {
89 schedule();
90 tsk->state = TASK_UNINTERRUPTIBLE;
91 }
92 remove_wait_queue(&sem->wait, &wait);
93 tsk->state = TASK_RUNNING;
94
95 /*
96 * If there are any more sleepers, wake one of them up so
97 * that it can either get the semaphore, or set count to -1
98 * indicating that there are still processes sleeping.
99 */
100 wake_up(&sem->wait);
101}
102
103int __sched __down_interruptible(struct semaphore * sem)
104{
105 int retval = 0;
106 struct task_struct *tsk = current;
107 DECLARE_WAITQUEUE(wait, tsk);
108
109 tsk->state = TASK_INTERRUPTIBLE;
110 add_wait_queue_exclusive(&sem->wait, &wait);
111 smp_wmb();
112
113 while (__sem_update_count(sem, -1) <= 0) {
114 if (signal_pending(current)) {
115 /*
116 * A signal is pending - give up trying.
117 * Set sem->count to 0 if it is negative,
118 * since we are no longer sleeping.
119 */
120 __sem_update_count(sem, 0);
121 retval = -EINTR;
122 break;
123 }
124 schedule();
125 tsk->state = TASK_INTERRUPTIBLE;
126 }
127 tsk->state = TASK_RUNNING;
128 remove_wait_queue(&sem->wait, &wait);
129 wake_up(&sem->wait);
130 return retval;
131}