Commit 417dcdf9 authored Jun 16, 2009 by Jan Blunck Committed by Linus Torvalds Jun 16, 2009

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 <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>

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))

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