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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/arm/kernel
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/arm/kernel')
-rw-r--r--arch/arm/kernel/Makefile2
-rw-r--r--arch/arm/kernel/semaphore.c221
2 files changed, 1 insertions, 222 deletions
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 00d44c6fbfe9..6235f72a14f0 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -7,7 +7,7 @@ AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
7# Object file lists. 7# Object file lists.
8 8
9obj-y := compat.o entry-armv.o entry-common.o irq.o \ 9obj-y := compat.o entry-armv.o entry-common.o irq.o \
10 process.o ptrace.o semaphore.o setup.o signal.o \ 10 process.o ptrace.o setup.o signal.o \
11 sys_arm.o stacktrace.o time.o traps.o 11 sys_arm.o stacktrace.o time.o traps.o
12 12
13obj-$(CONFIG_ISA_DMA_API) += dma.o 13obj-$(CONFIG_ISA_DMA_API) += dma.o
diff --git a/arch/arm/kernel/semaphore.c b/arch/arm/kernel/semaphore.c
deleted file mode 100644
index 981fe5c6ccbe..000000000000
--- a/arch/arm/kernel/semaphore.c
+++ /dev/null
@@ -1,221 +0,0 @@
1/*
2 * ARM semaphore implementation, taken from
3 *
4 * i386 semaphore implementation.
5 *
6 * (C) Copyright 1999 Linus Torvalds
7 *
8 * Modified for ARM by Russell King
9 *
10 * This program is free software; you can redistribute it and/or modify
11 * it under the terms of the GNU General Public License version 2 as
12 * published by the Free Software Foundation.
13 */
14#include <linux/module.h>
15#include <linux/sched.h>
16#include <linux/errno.h>
17#include <linux/init.h>
18
19#include <asm/semaphore.h>
20
21/*
22 * Semaphores are implemented using a two-way counter:
23 * The "count" variable is decremented for each process
24 * that tries to acquire the semaphore, while the "sleeping"
25 * variable is a count of such acquires.
26 *
27 * Notably, the inline "up()" and "down()" functions can
28 * efficiently test if they need to do any extra work (up
29 * needs to do something only if count was negative before
30 * the increment operation.
31 *
32 * "sleeping" and the contention routine ordering is
33 * protected by the semaphore spinlock.
34 *
35 * Note that these functions are only called when there is
36 * contention on the lock, and as such all this is the
37 * "non-critical" part of the whole semaphore business. The
38 * critical part is the inline stuff in <asm/semaphore.h>
39 * where we want to avoid any extra jumps and calls.
40 */
41
42/*
43 * Logic:
44 * - only on a boundary condition do we need to care. When we go
45 * from a negative count to a non-negative, we wake people up.
46 * - when we go from a non-negative count to a negative do we
47 * (a) synchronize with the "sleeper" count and (b) make sure
48 * that we're on the wakeup list before we synchronize so that
49 * we cannot lose wakeup events.
50 */
51
52void __up(struct semaphore *sem)
53{
54 wake_up(&sem->wait);
55}
56
57static DEFINE_SPINLOCK(semaphore_lock);
58
59void __sched __down(struct semaphore * sem)
60{
61 struct task_struct *tsk = current;
62 DECLARE_WAITQUEUE(wait, tsk);
63 tsk->state = TASK_UNINTERRUPTIBLE;
64 add_wait_queue_exclusive(&sem->wait, &wait);
65
66 spin_lock_irq(&semaphore_lock);
67 sem->sleepers++;
68 for (;;) {
69 int sleepers = sem->sleepers;
70
71 /*
72 * Add "everybody else" into it. They aren't
73 * playing, because we own the spinlock.
74 */
75 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
76 sem->sleepers = 0;
77 break;
78 }
79 sem->sleepers = 1; /* us - see -1 above */
80 spin_unlock_irq(&semaphore_lock);
81
82 schedule();
83 tsk->state = TASK_UNINTERRUPTIBLE;
84 spin_lock_irq(&semaphore_lock);
85 }
86 spin_unlock_irq(&semaphore_lock);
87 remove_wait_queue(&sem->wait, &wait);
88 tsk->state = TASK_RUNNING;
89 wake_up(&sem->wait);
90}
91
92int __sched __down_interruptible(struct semaphore * sem)
93{
94 int retval = 0;
95 struct task_struct *tsk = current;
96 DECLARE_WAITQUEUE(wait, tsk);
97 tsk->state = TASK_INTERRUPTIBLE;
98 add_wait_queue_exclusive(&sem->wait, &wait);
99
100 spin_lock_irq(&semaphore_lock);
101 sem->sleepers ++;
102 for (;;) {
103 int sleepers = sem->sleepers;
104
105 /*
106 * With signals pending, this turns into
107 * the trylock failure case - we won't be
108 * sleeping, and we* can't get the lock as
109 * it has contention. Just correct the count
110 * and exit.
111 */
112 if (signal_pending(current)) {
113 retval = -EINTR;
114 sem->sleepers = 0;
115 atomic_add(sleepers, &sem->count);
116 break;
117 }
118
119 /*
120 * Add "everybody else" into it. They aren't
121 * playing, because we own the spinlock. The
122 * "-1" is because we're still hoping to get
123 * the lock.
124 */
125 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
126 sem->sleepers = 0;
127 break;
128 }
129 sem->sleepers = 1; /* us - see -1 above */
130 spin_unlock_irq(&semaphore_lock);
131
132 schedule();
133 tsk->state = TASK_INTERRUPTIBLE;
134 spin_lock_irq(&semaphore_lock);
135 }
136 spin_unlock_irq(&semaphore_lock);
137 tsk->state = TASK_RUNNING;
138 remove_wait_queue(&sem->wait, &wait);
139 wake_up(&sem->wait);
140 return retval;
141}
142
143/*
144 * Trylock failed - make sure we correct for
145 * having decremented the count.
146 *
147 * We could have done the trylock with a
148 * single "cmpxchg" without failure cases,
149 * but then it wouldn't work on a 386.
150 */
151int __down_trylock(struct semaphore * sem)
152{
153 int sleepers;
154 unsigned long flags;
155
156 spin_lock_irqsave(&semaphore_lock, flags);
157 sleepers = sem->sleepers + 1;
158 sem->sleepers = 0;
159
160 /*
161 * Add "everybody else" and us into it. They aren't
162 * playing, because we own the spinlock.
163 */
164 if (!atomic_add_negative(sleepers, &sem->count))
165 wake_up(&sem->wait);
166
167 spin_unlock_irqrestore(&semaphore_lock, flags);
168 return 1;
169}
170
171/*
172 * The semaphore operations have a special calling sequence that
173 * allow us to do a simpler in-line version of them. These routines
174 * need to convert that sequence back into the C sequence when
175 * there is contention on the semaphore.
176 *
177 * ip contains the semaphore pointer on entry. Save the C-clobbered
178 * registers (r0 to r3 and lr), but not ip, as we use it as a return
179 * value in some cases..
180 * To remain AAPCS compliant (64-bit stack align) we save r4 as well.
181 */
182asm(" .section .sched.text,\"ax\",%progbits \n\
183 .align 5 \n\
184 .globl __down_failed \n\
185__down_failed: \n\
186 stmfd sp!, {r0 - r4, lr} \n\
187 mov r0, ip \n\
188 bl __down \n\
189 ldmfd sp!, {r0 - r4, pc} \n\
190 \n\
191 .align 5 \n\
192 .globl __down_interruptible_failed \n\
193__down_interruptible_failed: \n\
194 stmfd sp!, {r0 - r4, lr} \n\
195 mov r0, ip \n\
196 bl __down_interruptible \n\
197 mov ip, r0 \n\
198 ldmfd sp!, {r0 - r4, pc} \n\
199 \n\
200 .align 5 \n\
201 .globl __down_trylock_failed \n\
202__down_trylock_failed: \n\
203 stmfd sp!, {r0 - r4, lr} \n\
204 mov r0, ip \n\
205 bl __down_trylock \n\
206 mov ip, r0 \n\
207 ldmfd sp!, {r0 - r4, pc} \n\
208 \n\
209 .align 5 \n\
210 .globl __up_wakeup \n\
211__up_wakeup: \n\
212 stmfd sp!, {r0 - r4, lr} \n\
213 mov r0, ip \n\
214 bl __up \n\
215 ldmfd sp!, {r0 - r4, pc} \n\
216 ");
217
218EXPORT_SYMBOL(__down_failed);
219EXPORT_SYMBOL(__down_interruptible_failed);
220EXPORT_SYMBOL(__down_trylock_failed);
221EXPORT_SYMBOL(__up_wakeup);
generated by cgit v1.2.2 (git 2.25.0) at 2024-10-04 14:27:47 -0400