The patch titled
atomic: only take lock when the counter drops to zero on UP as well
has been added to the -mm tree. Its filename is
atomic-only-take-lock-when-the-counter-drops-to-zero-on-up-as-well.patch
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------------------------------------------------------
Subject: atomic: only take lock when the counter drops to zero on UP as well
From: Jan Blunck <jblunck@xxxxxxx>
_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@xxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/dec_and_lock.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff -puN lib/dec_and_lock.c~atomic-only-take-lock-when-the-counter-drops-to-zero-on-up-as-well lib/dec_and_lock.c
--- a/lib/dec_and_lock.c~atomic-only-take-lock-when-the-counter-drops-to-zero-on-up-as-well
+++ a/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))
_
Patches currently in -mm which might be from jblunck@xxxxxxx are
atomic-only-take-lock-when-the-counter-drops-to-zero-on-up-as-well.patch
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