aboutsummaryrefslogtreecommitdiffstats
path: root/include/asm-x86_64/spinlock.h
blob: be7a9e629fb262ebecef04fe3bd454752816c7ae (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
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H

#include <asm/atomic.h>
#include <asm/rwlock.h>
#include <asm/page.h>

/*
 * Your basic SMP spinlocks, allowing only a single CPU anywhere
 *
 * Simple spin lock operations.  There are two variants, one clears IRQ's
 * on the local processor, one does not.
 *
 * We make no fairness assumptions. They have a cost.
 *
 * (the type definitions are in asm/spinlock_types.h)
 */

static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
{
	return *(volatile signed int *)(&(lock)->slock) <= 0;
}

static inline void __raw_spin_lock(raw_spinlock_t *lock)
{
	asm volatile(
		"\n1:\t"
		LOCK_PREFIX " ; decl %0\n\t"
		"jns 2f\n"
		"3:\n"
		"rep;nop\n\t"
		"cmpl $0,%0\n\t"
		"jle 3b\n\t"
		"jmp 1b\n"
		"2:\t" : "=m" (lock->slock) : : "memory");
}

#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)

static inline int __raw_spin_trylock(raw_spinlock_t *lock)
{
	int oldval;

	asm volatile(
		"xchgl %0,%1"
		:"=q" (oldval), "=m" (lock->slock)
		:"0" (0) : "memory");

	return oldval > 0;
}

static inline void __raw_spin_unlock(raw_spinlock_t *lock)
{
	asm volatile("movl $1,%0" :"=m" (lock->slock) :: "memory");
}

static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
{
	while (__raw_spin_is_locked(lock))
		cpu_relax();
}

/*
 * Read-write spinlocks, allowing multiple readers
 * but only one writer.
 *
 * NOTE! it is quite common to have readers in interrupts
 * but no interrupt writers. For those circumstances we
 * can "mix" irq-safe locks - any writer needs to get a
 * irq-safe write-lock, but readers can get non-irqsafe
 * read-locks.
 *
 * On x86, we implement read-write locks as a 32-bit counter
 * with the high bit (sign) being the "contended" bit.
 */

static inline int __raw_read_can_lock(raw_rwlock_t *lock)
{
	return (int)(lock)->lock > 0;
}

static inline int __raw_write_can_lock(raw_rwlock_t *lock)
{
	return (lock)->lock == RW_LOCK_BIAS;
}

static inline void __raw_read_lock(raw_rwlock_t *rw)
{
	asm volatile(LOCK_PREFIX "subl $1,(%0)\n\t"
		     "jns 1f\n"
		     "call __read_lock_failed\n"
		     "1:\n"
		     ::"D" (rw), "i" (RW_LOCK_BIAS) : "memory");
}

static inline void __raw_write_lock(raw_rwlock_t *rw)
{
	asm volatile(LOCK_PREFIX "subl %1,(%0)\n\t"
		     "jz 1f\n"
		     "\tcall __write_lock_failed\n\t"
		     "1:\n"
		     ::"D" (rw), "i" (RW_LOCK_BIAS) : "memory");
}

static inline int __raw_read_trylock(raw_rwlock_t *lock)
{
	atomic_t *count = (atomic_t *)lock;
	atomic_dec(count);
	if (atomic_read(count) >= 0)
		return 1;
	atomic_inc(count);
	return 0;
}

static inline int __raw_write_trylock(raw_rwlock_t *lock)
{
	atomic_t *count = (atomic_t *)lock;
	if (atomic_sub_and_test(RW_LOCK_BIAS, count))
		return 1;
	atomic_add(RW_LOCK_BIAS, count);
	return 0;
}

static inline void __raw_read_unlock(raw_rwlock_t *rw)
{
	asm volatile(LOCK_PREFIX " ; incl %0" :"=m" (rw->lock) : : "memory");
}

static inline void __raw_write_unlock(raw_rwlock_t *rw)
{
	asm volatile(LOCK_PREFIX " ; addl $" RW_LOCK_BIAS_STR ",%0"
				: "=m" (rw->lock) : : "memory");
}

#endif /* __ASM_SPINLOCK_H */