Revision e501f29c727dea74e2124c584cbab5fa805d489b authored by Linus Torvalds on 20 July 2011, 04:50:21 UTC, committed by Linus Torvalds on 20 July 2011, 04:50:21 UTC
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: vfs: fix race in rcu lookup of pruned dentry Fix cifs_get_root() [ Edited the last commit to get rid of a 'unused variable "seq"' warning due to Al editing the patch. - Linus ]
dec_and_lock.c
#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/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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