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x86: Implement atomic[64]_dec_if_positive()

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Add support for atomic_dec_if_positive(), and
atomic64_dec_if_positive() for x86-64.

atomic64_dec_if_positive() for x86-32 was already implemented in a previous patch.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267183361-20775-2-git-send-email-luca@luca-barbieri.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Luca Barbieri 2010-02-26 12:22:41 +01:00 committed by H. Peter Anvin
parent 8f4f202b33
commit d7f6de1e9c
3 changed files with 47 additions and 1 deletions
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23
arch/x86/include/asm/atomic.h
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@ -246,6 +246,29 @@ static inline int atomic_add_unless(atomic_t *v, int a, int u)
#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)
/*
* atomic_dec_if_positive - decrement by 1 if old value positive
* @v: pointer of type atomic_t
*
* The function returns the old value of *v minus 1, even if
* the atomic variable, v, was not decremented.
*/
static inline int atomic_dec_if_positive(atomic_t *v)
{
int c, old, dec;
c = atomic_read(v);
for (;;) {
dec = c - 1;
if (unlikely(dec < 0))
break;
old = atomic_cmpxchg((v), c, dec);
if (likely(old == c))
break;
c = old;
}
return dec;
}
/**
* atomic_inc_short - increment of a short integer
* @v: pointer to type int

23
arch/x86/include/asm/atomic64_64.h
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@ -221,4 +221,27 @@ static inline int atomic64_add_unless(atomic64_t *v, long a, long u)
#define atomic64_inc_not_zero(v) atomic64_add_unless((v), 1, 0)
/*
* atomic64_dec_if_positive - decrement by 1 if old value positive
* @v: pointer of type atomic_t
*
* The function returns the old value of *v minus 1, even if
* the atomic variable, v, was not decremented.
*/
static inline long atomic64_dec_if_positive(atomic64_t *v)
{
long c, old, dec;
c = atomic64_read(v);
for (;;) {
dec = c - 1;
if (unlikely(dec < 0))
break;
old = atomic64_cmpxchg((v), c, dec);
if (likely(old == c))
break;
c = old;
}
return dec;
}
#endif /* _ASM_X86_ATOMIC64_64_H */

2
lib/atomic64_test.c
View File

@ -112,7 +112,7 @@ static __init int test_atomic64(void)
r += one;
BUG_ON(v.counter != r);
#if defined(CONFIG_X86_32) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
#if defined(CONFIG_X86) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
INIT(onestwos);
BUG_ON(atomic64_dec_if_positive(&v) != (onestwos - 1));
r -= one;