aboutsummaryrefslogtreecommitdiffstats
path: root/arch/alpha/kernel/semaphore.c
blob: 8c8aaa205eae123f208163749efaabe4ad2df710 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
/*
 * Alpha semaphore implementation.
 *
 * (C) Copyright 1996 Linus Torvalds
 * (C) Copyright 1999, 2000 Richard Henderson
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/init.h>

/*
 * This is basically the PPC semaphore scheme ported to use
 * the Alpha ll/sc sequences, so see the PPC code for
 * credits.
 */

/*
 * Atomically update sem->count.
 * This does the equivalent of the following:
 *
 *	old_count = sem->count;
 *	tmp = MAX(old_count, 0) + incr;
 *	sem->count = tmp;
 *	return old_count;
 */
static inline int __sem_update_count(struct semaphore *sem, int incr)
{
	long old_count, tmp = 0;

	__asm__ __volatile__(
	"1:	ldl_l	%0,%2\n"
	"	cmovgt	%0,%0,%1\n"
	"	addl	%1,%3,%1\n"
	"	stl_c	%1,%2\n"
	"	beq	%1,2f\n"
	"	mb\n"
	".subsection 2\n"
	"2:	br	1b\n"
	".previous"
	: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
	: "Ir" (incr), "1" (tmp), "m" (sem->count));

	return old_count;
}

/*
 * Perform the "down" function.  Return zero for semaphore acquired,
 * return negative for signalled out of the function.
 *
 * If called from down, the return is ignored and the wait loop is
 * not interruptible.  This means that a task waiting on a semaphore
 * using "down()" cannot be killed until someone does an "up()" on
 * the semaphore.
 *
 * If called from down_interruptible, the return value gets checked
 * upon return.  If the return value is negative then the task continues
 * with the negative value in the return register (it can be tested by
 * the caller).
 *
 * Either form may be used in conjunction with "up()".
 */

void __sched
__down_failed(struct semaphore *sem)
{
	struct task_struct *tsk = current;
	DECLARE_WAITQUEUE(wait, tsk);

#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down failed(%p)\n",
	       tsk->comm, tsk->pid, sem);
#endif

	tsk->state = TASK_UNINTERRUPTIBLE;
	wmb();
	add_wait_queue_exclusive(&sem->wait, &wait);

	/*
	 * Try to get the semaphore.  If the count is > 0, then we've
	 * got the semaphore; we decrement count and exit the loop.
	 * If the count is 0 or negative, we set it to -1, indicating
	 * that we are asleep, and then sleep.
	 */
	while (__sem_update_count(sem, -1) <= 0) {
		schedule();
		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
	}
	remove_wait_queue(&sem->wait, &wait);
	tsk->state = TASK_RUNNING;

	/*
	 * If there are any more sleepers, wake one of them up so
	 * that it can either get the semaphore, or set count to -1
	 * indicating that there are still processes sleeping.
	 */
	wake_up(&sem->wait);

#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down acquired(%p)\n",
	       tsk->comm, tsk->pid, sem);
#endif
}

int __sched
__down_failed_interruptible(struct semaphore *sem)
{
	struct task_struct *tsk = current;
	DECLARE_WAITQUEUE(wait, tsk);
	long ret = 0;

#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down failed(%p)\n",
	       tsk->comm, tsk->pid, sem);
#endif

	tsk->state = TASK_INTERRUPTIBLE;
	wmb();
	add_wait_queue_exclusive(&sem->wait, &wait);

	while (__sem_update_count(sem, -1) <= 0) {
		if (signal_pending(current)) {
			/*
			 * A signal is pending - give up trying.
			 * Set sem->count to 0 if it is negative,
			 * since we are no longer sleeping.
			 */
			__sem_update_count(sem, 0);
			ret = -EINTR;
			break;
		}
		schedule();
		set_task_state(tsk, TASK_INTERRUPTIBLE);
	}

	remove_wait_queue(&sem->wait, &wait);
	tsk->state = TASK_RUNNING;
	wake_up(&sem->wait);

#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down %s(%p)\n",
	       current->comm, current->pid,
	       (ret < 0 ? "interrupted" : "acquired"), sem);
#endif
	return ret;
}

void
__up_wakeup(struct semaphore *sem)
{
	/*
	 * Note that we incremented count in up() before we came here,
	 * but that was ineffective since the result was <= 0, and
	 * any negative value of count is equivalent to 0.
	 * This ends up setting count to 1, unless count is now > 0
	 * (i.e. because some other cpu has called up() in the meantime),
	 * in which case we just increment count.
	 */
	__sem_update_count(sem, 1);
	wake_up(&sem->wait);
}

void __sched
down(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
	CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down(%p) <count=%d> from %p\n",
	       current->comm, current->pid, sem,
	       atomic_read(&sem->count), __builtin_return_address(0));
#endif
	__down(sem);
}

int __sched
down_interruptible(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
	CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down(%p) <count=%d> from %p\n",
	       current->comm, current->pid, sem,
	       atomic_read(&sem->count), __builtin_return_address(0));
#endif
	return __down_interruptible(sem);
}

int
down_trylock(struct semaphore *sem)
{
	int ret;

#ifdef WAITQUEUE_DEBUG
	CHECK_MAGIC(sem->__magic);
#endif

	ret = __down_trylock(sem);

#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): down_trylock %s from %p\n",
	       current->comm, current->pid,
	       ret ? "failed" : "acquired",
	       __builtin_return_address(0));
#endif

	return ret;
}

void
up(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
	CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
	printk("%s(%d): up(%p) <count=%d> from %p\n",
	       current->comm, current->pid, sem,
	       atomic_read(&sem->count), __builtin_return_address(0));
#endif
	__up(sem);
}