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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/mips
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/mips')
-rw-r--r--arch/mips/kernel/Makefile2
-rw-r--r--arch/mips/kernel/semaphore.c168
2 files changed, 1 insertions, 169 deletions
diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 9e78e1a4ca17..6fcdb6fda2e2 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -5,7 +5,7 @@
5extra-y := head.o init_task.o vmlinux.lds 5extra-y := head.o init_task.o vmlinux.lds
6 6
7obj-y += cpu-probe.o branch.o entry.o genex.o irq.o process.o \ 7obj-y += cpu-probe.o branch.o entry.o genex.o irq.o process.o \
8 ptrace.o reset.o semaphore.o setup.o signal.o syscall.o \ 8 ptrace.o reset.o setup.o signal.o syscall.o \
9 time.o topology.o traps.o unaligned.o 9 time.o topology.o traps.o unaligned.o
10 10
11obj-$(CONFIG_CEVT_BCM1480) += cevt-bcm1480.o 11obj-$(CONFIG_CEVT_BCM1480) += cevt-bcm1480.o
diff --git a/arch/mips/kernel/semaphore.c b/arch/mips/kernel/semaphore.c
deleted file mode 100644
index 1265358cdca1..000000000000
--- a/arch/mips/kernel/semaphore.c
+++ /dev/null
@@ -1,168 +0,0 @@
1/*
2 * MIPS-specific semaphore code.
3 *
4 * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
5 * Copyright (C) 2004 Ralf Baechle <ralf@linux-mips.org>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version
10 * 2 of the License, or (at your option) any later version.
11 *
12 * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
13 * to eliminate the SMP races in the old version between the updates
14 * of `count' and `waking'. Now we use negative `count' values to
15 * indicate that some process(es) are waiting for the semaphore.
16 */
17
18#include <linux/module.h>
19#include <linux/sched.h>
20#include <linux/init.h>
21#include <asm/atomic.h>
22#include <asm/cpu-features.h>
23#include <asm/errno.h>
24#include <asm/semaphore.h>
25#include <asm/war.h>
26/*
27 * Atomically update sem->count.
28 * This does the equivalent of the following:
29 *
30 * old_count = sem->count;
31 * tmp = MAX(old_count, 0) + incr;
32 * sem->count = tmp;
33 * return old_count;
34 *
35 * On machines without lld/scd we need a spinlock to make the manipulation of
36 * sem->count and sem->waking atomic. Scalability isn't an issue because
37 * this lock is used on UP only so it's just an empty variable.
38 */
39static inline int __sem_update_count(struct semaphore *sem, int incr)
40{
41 int old_count, tmp;
42
43 if (cpu_has_llsc && R10000_LLSC_WAR) {
44 __asm__ __volatile__(
45 " .set mips3 \n"
46 "1: ll %0, %2 # __sem_update_count \n"
47 " sra %1, %0, 31 \n"
48 " not %1 \n"
49 " and %1, %0, %1 \n"
50 " addu %1, %1, %3 \n"
51 " sc %1, %2 \n"
52 " beqzl %1, 1b \n"
53 " .set mips0 \n"
54 : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
55 : "r" (incr), "m" (sem->count));
56 } else if (cpu_has_llsc) {
57 __asm__ __volatile__(
58 " .set mips3 \n"
59 "1: ll %0, %2 # __sem_update_count \n"
60 " sra %1, %0, 31 \n"
61 " not %1 \n"
62 " and %1, %0, %1 \n"
63 " addu %1, %1, %3 \n"
64 " sc %1, %2 \n"
65 " beqz %1, 1b \n"
66 " .set mips0 \n"
67 : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
68 : "r" (incr), "m" (sem->count));
69 } else {
70 static DEFINE_SPINLOCK(semaphore_lock);
71 unsigned long flags;
72
73 spin_lock_irqsave(&semaphore_lock, flags);
74 old_count = atomic_read(&sem->count);
75 tmp = max_t(int, old_count, 0) + incr;
76 atomic_set(&sem->count, tmp);
77 spin_unlock_irqrestore(&semaphore_lock, flags);
78 }
79
80 return old_count;
81}
82
83void __up(struct semaphore *sem)
84{
85 /*
86 * Note that we incremented count in up() before we came here,
87 * but that was ineffective since the result was <= 0, and
88 * any negative value of count is equivalent to 0.
89 * This ends up setting count to 1, unless count is now > 0
90 * (i.e. because some other cpu has called up() in the meantime),
91 * in which case we just increment count.
92 */
93 __sem_update_count(sem, 1);
94 wake_up(&sem->wait);
95}
96
97EXPORT_SYMBOL(__up);
98
99/*
100 * Note that when we come in to __down or __down_interruptible,
101 * we have already decremented count, but that decrement was
102 * ineffective since the result was < 0, and any negative value
103 * of count is equivalent to 0.
104 * Thus it is only when we decrement count from some value > 0
105 * that we have actually got the semaphore.
106 */
107void __sched __down(struct semaphore *sem)
108{
109 struct task_struct *tsk = current;
110 DECLARE_WAITQUEUE(wait, tsk);
111
112 __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
113 add_wait_queue_exclusive(&sem->wait, &wait);
114
115 /*
116 * Try to get the semaphore. If the count is > 0, then we've
117 * got the semaphore; we decrement count and exit the loop.
118 * If the count is 0 or negative, we set it to -1, indicating
119 * that we are asleep, and then sleep.
120 */
121 while (__sem_update_count(sem, -1) <= 0) {
122 schedule();
123 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
124 }
125 remove_wait_queue(&sem->wait, &wait);
126 __set_task_state(tsk, TASK_RUNNING);
127
128 /*
129 * If there are any more sleepers, wake one of them up so
130 * that it can either get the semaphore, or set count to -1
131 * indicating that there are still processes sleeping.
132 */
133 wake_up(&sem->wait);
134}
135
136EXPORT_SYMBOL(__down);
137
138int __sched __down_interruptible(struct semaphore * sem)
139{
140 int retval = 0;
141 struct task_struct *tsk = current;
142 DECLARE_WAITQUEUE(wait, tsk);
143
144 __set_task_state(tsk, TASK_INTERRUPTIBLE);
145 add_wait_queue_exclusive(&sem->wait, &wait);
146
147 while (__sem_update_count(sem, -1) <= 0) {
148 if (signal_pending(current)) {
149 /*
150 * A signal is pending - give up trying.
151 * Set sem->count to 0 if it is negative,
152 * since we are no longer sleeping.
153 */
154 __sem_update_count(sem, 0);
155 retval = -EINTR;
156 break;
157 }
158 schedule();
159 set_task_state(tsk, TASK_INTERRUPTIBLE);
160 }
161 remove_wait_queue(&sem->wait, &wait);
162 __set_task_state(tsk, TASK_RUNNING);
163
164 wake_up(&sem->wait);
165 return retval;
166}
167
168EXPORT_SYMBOL(__down_interruptible);
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