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atomic: only take lock when the counter drops to zero on UP as well

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_atomic_dec_and_lock() should not unconditionally take the lock before
calling atomic_dec_and_test() in the UP case.  For consistency reasons it
should behave exactly like in the SMP case.

Besides that this works around the problem that with CONFIG_DEBUG_SPINLOCK
this spins in __spin_lock_debug() if the lock is already taken even if the
counter doesn't drop to 0.

Signed-off-by: Jan Blunck <jblunck@suse.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Cc: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Blunck 2009-06-16 15:33:33 -07:00 committed by Linus Torvalds
parent a7d932af06
commit 417dcdf99e
1 changed files with 1 additions and 2 deletions
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3
lib/dec_and_lock.c
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@ -19,11 +19,10 @@
*/ */
int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
{ {
#ifdef CONFIG_SMP
/* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
if (atomic_add_unless(atomic, -1, 1)) if (atomic_add_unless(atomic, -1, 1))
return 0; return 0;
#endif
/* Otherwise do it the slow way */ /* Otherwise do it the slow way */
spin_lock(lock); spin_lock(lock);
if (atomic_dec_and_test(atomic)) if (atomic_dec_and_test(atomic))