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-rw-r--r--arch/arm26/kernel/semaphore.c223
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diff --git a/arch/arm26/kernel/semaphore.c b/arch/arm26/kernel/semaphore.c
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1/*
2 * ARM semaphore implementation, taken from
3 *
4 * i386 semaphore implementation.
5 *
6 * (C) Copyright 1999 Linus Torvalds
7 * (C) Copyright 2003 Ian Molton (ARM26 mods)
8 *
9 * Modified for ARM by Russell King
10 *
11 * This program is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU General Public License version 2 as
13 * published by the Free Software Foundation.
14 */
15#include <linux/module.h>
16#include <linux/config.h>
17#include <linux/sched.h>
18#include <linux/errno.h>
19#include <linux/init.h>
20
21#include <asm/semaphore.h>
22
23/*
24 * Semaphores are implemented using a two-way counter:
25 * The "count" variable is decremented for each process
26 * that tries to acquire the semaphore, while the "sleeping"
27 * variable is a count of such acquires.
28 *
29 * Notably, the inline "up()" and "down()" functions can
30 * efficiently test if they need to do any extra work (up
31 * needs to do something only if count was negative before
32 * the increment operation.
33 *
34 * "sleeping" and the contention routine ordering is
35 * protected by the semaphore spinlock.
36 *
37 * Note that these functions are only called when there is
38 * contention on the lock, and as such all this is the
39 * "non-critical" part of the whole semaphore business. The
40 * critical part is the inline stuff in <asm/semaphore.h>
41 * where we want to avoid any extra jumps and calls.
42 */
43
44/*
45 * Logic:
46 * - only on a boundary condition do we need to care. When we go
47 * from a negative count to a non-negative, we wake people up.
48 * - when we go from a non-negative count to a negative do we
49 * (a) synchronize with the "sleeper" count and (b) make sure
50 * that we're on the wakeup list before we synchronize so that
51 * we cannot lose wakeup events.
52 */
53
54void __up(struct semaphore *sem)
55{
56 wake_up(&sem->wait);
57}
58
59static DEFINE_SPINLOCK(semaphore_lock);
60
61void __sched __down(struct semaphore * sem)
62{
63 struct task_struct *tsk = current;
64 DECLARE_WAITQUEUE(wait, tsk);
65 tsk->state = TASK_UNINTERRUPTIBLE;
66 add_wait_queue_exclusive(&sem->wait, &wait);
67
68 spin_lock_irq(&semaphore_lock);
69 sem->sleepers++;
70 for (;;) {
71 int sleepers = sem->sleepers;
72
73 /*
74 * Add "everybody else" into it. They aren't
75 * playing, because we own the spinlock.
76 */
77 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
78 sem->sleepers = 0;
79 break;
80 }
81 sem->sleepers = 1; /* us - see -1 above */
82 spin_unlock_irq(&semaphore_lock);
83
84 schedule();
85 tsk->state = TASK_UNINTERRUPTIBLE;
86 spin_lock_irq(&semaphore_lock);
87 }
88 spin_unlock_irq(&semaphore_lock);
89 remove_wait_queue(&sem->wait, &wait);
90 tsk->state = TASK_RUNNING;
91 wake_up(&sem->wait);
92}
93
94int __sched __down_interruptible(struct semaphore * sem)
95{
96 int retval = 0;
97 struct task_struct *tsk = current;
98 DECLARE_WAITQUEUE(wait, tsk);
99 tsk->state = TASK_INTERRUPTIBLE;
100 add_wait_queue_exclusive(&sem->wait, &wait);
101
102 spin_lock_irq(&semaphore_lock);
103 sem->sleepers ++;
104 for (;;) {
105 int sleepers = sem->sleepers;
106
107 /*
108 * With signals pending, this turns into
109 * the trylock failure case - we won't be
110 * sleeping, and we* can't get the lock as
111 * it has contention. Just correct the count
112 * and exit.
113 */
114 if (signal_pending(current)) {
115 retval = -EINTR;
116 sem->sleepers = 0;
117 atomic_add(sleepers, &sem->count);
118 break;
119 }
120
121 /*
122 * Add "everybody else" into it. They aren't
123 * playing, because we own the spinlock. The
124 * "-1" is because we're still hoping to get
125 * the lock.
126 */
127 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
128 sem->sleepers = 0;
129 break;
130 }
131 sem->sleepers = 1; /* us - see -1 above */
132 spin_unlock_irq(&semaphore_lock);
133
134 schedule();
135 tsk->state = TASK_INTERRUPTIBLE;
136 spin_lock_irq(&semaphore_lock);
137 }
138 spin_unlock_irq(&semaphore_lock);
139 tsk->state = TASK_RUNNING;
140 remove_wait_queue(&sem->wait, &wait);
141 wake_up(&sem->wait);
142 return retval;
143}
144
145/*
146 * Trylock failed - make sure we correct for
147 * having decremented the count.
148 *
149 * We could have done the trylock with a
150 * single "cmpxchg" without failure cases,
151 * but then it wouldn't work on a 386.
152 */
153int __down_trylock(struct semaphore * sem)
154{
155 int sleepers;
156 unsigned long flags;
157
158 spin_lock_irqsave(&semaphore_lock, flags);
159 sleepers = sem->sleepers + 1;
160 sem->sleepers = 0;
161
162 /*
163 * Add "everybody else" and us into it. They aren't
164 * playing, because we own the spinlock.
165 */
166 if (!atomic_add_negative(sleepers, &sem->count))
167 wake_up(&sem->wait);
168
169 spin_unlock_irqrestore(&semaphore_lock, flags);
170 return 1;
171}
172
173/*
174 * The semaphore operations have a special calling sequence that
175 * allow us to do a simpler in-line version of them. These routines
176 * need to convert that sequence back into the C sequence when
177 * there is contention on the semaphore.
178 *
179 * ip contains the semaphore pointer on entry. Save the C-clobbered
180 * registers (r0 to r3 and lr), but not ip, as we use it as a return
181 * value in some cases..
182 */
183asm(" .section .sched.text , #alloc, #execinstr \n\
184 .align 5 \n\
185 .globl __down_failed \n\
186__down_failed: \n\
187 stmfd sp!, {r0 - r3, lr} \n\
188 mov r0, ip \n\
189 bl __down \n\
190 ldmfd sp!, {r0 - r3, pc}^ \n\
191 \n\
192 .align 5 \n\
193 .globl __down_interruptible_failed \n\
194__down_interruptible_failed: \n\
195 stmfd sp!, {r0 - r3, lr} \n\
196 mov r0, ip \n\
197 bl __down_interruptible \n\
198 mov ip, r0 \n\
199 ldmfd sp!, {r0 - r3, pc}^ \n\
200 \n\
201 .align 5 \n\
202 .globl __down_trylock_failed \n\
203__down_trylock_failed: \n\
204 stmfd sp!, {r0 - r3, lr} \n\
205 mov r0, ip \n\
206 bl __down_trylock \n\
207 mov ip, r0 \n\
208 ldmfd sp!, {r0 - r3, pc}^ \n\
209 \n\
210 .align 5 \n\
211 .globl __up_wakeup \n\
212__up_wakeup: \n\
213 stmfd sp!, {r0 - r3, lr} \n\
214 mov r0, ip \n\
215 bl __up \n\
216 ldmfd sp!, {r0 - r3, pc}^ \n\
217 ");
218
219EXPORT_SYMBOL(__down_failed);
220EXPORT_SYMBOL(__down_interruptible_failed);
221EXPORT_SYMBOL(__down_trylock_failed);
222EXPORT_SYMBOL(__up_wakeup);
223
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