Revision 161d898ac974818156afe48d755578bfd0d6e7c0 authored by Guenter Roeck on 19 December 2012, 21:17:01 UTC, committed by Jean Delvare on 19 December 2012, 21:17:01 UTC
Signed-off-by: Guenter Roeck <linux@roeck-us.net> Signed-off-by: Jean Delvare <khali@linux-fr.org>
1 parent 2cece01
dec_and_lock.c
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
/*
* This is an implementation of the notion of "decrement a
* reference count, and return locked if it decremented to zero".
*
* NOTE NOTE NOTE! This is _not_ equivalent to
*
* if (atomic_dec_and_test(&atomic)) {
* spin_lock(&lock);
* return 1;
* }
* return 0;
*
* because the spin-lock and the decrement must be
* "atomic".
*/
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{
/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
if (atomic_add_unless(atomic, -1, 1))
return 0;
/* Otherwise do it the slow way */
spin_lock(lock);
if (atomic_dec_and_test(atomic))
return 1;
spin_unlock(lock);
return 0;
}
EXPORT_SYMBOL(_atomic_dec_and_lock);
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