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

_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 <[email protected]> Acked-by: Paul E. McKenney <[email protected]> Acked-by: Nick Piggin <[email protected]> Cc: Valerie Aurora <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
kyagi · Jun 17, 2009 · 417dcdf · 417dcdf
1 parent a7d932a
commit 417dcdf
Showing 1 changed file with 1 addition and 2 deletions.
diff --git 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))