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Subject[PATCH] atomic: Only take lock when the counter drops to zero on UP as well (v2)
_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>
---
diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c
index a65c314..e73822a 100644
--- a/lib/dec_and_lock.c
+++ b/lib/dec_and_lock.c
@@ -19,11 +19,10 @@
*/
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) */
if (atomic_add_unless(atomic, -1, 1))
return 0;
-#endif
+
/* Otherwise do it the slow way */
spin_lock(lock);
if (atomic_dec_and_test(atomic))

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