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Commit d7f6de1e authored by Luca Barbieri's avatar Luca Barbieri Committed by H. Peter Anvin
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x86: Implement atomic[64]_dec_if_positive() 



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: default avatarLuca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267183361-20775-2-git-send-email-luca@luca-barbieri.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 8f4f202b

arch/x86/include/asm/atomic.h

+23 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/include/asm/atomic64_64.h

+23 −0
Original line number Diff line number Diff line
@@ -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 */

lib/atomic64_test.c

+1 −1
Original line number Diff line number Diff line
@@ -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;