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Commit 417dcdf9 authored by Jan Blunck's avatar Jan Blunck Committed by Linus Torvalds
Browse files

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: default avatarJan Blunck <jblunck@suse.de>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarNick Piggin <npiggin@suse.de>
Cc: Valerie Aurora <vaurora@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a7d932af

lib/dec_and_lock.c

+1 −2
Original line number Diff line number Diff line
@@ -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))