Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933608AbZFOS4T (ORCPT ); Mon, 15 Jun 2009 14:56:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751534AbZFOS4G (ORCPT ); Mon, 15 Jun 2009 14:56:06 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:45463 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752035AbZFOS4E (ORCPT ); Mon, 15 Jun 2009 14:56:04 -0400 Date: Mon, 15 Jun 2009 11:56:06 -0700 From: "Paul E. McKenney" To: Valerie Aurora Cc: Nick Piggin , Jan Blunck , linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] atomic: Fix _atomic_dec_and_lock() deadlock on UP Message-ID: <20090615185606.GJ6924@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090615181113.GD352@shell> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090615181113.GD352@shell> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1630 Lines: 45 On Mon, Jun 15, 2009 at 02:11:13PM -0400, Valerie Aurora wrote: > From: Jan Blunck > > _atomic_dec_and_lock() can deadlock on UP with spinlock debugging > enabled. Currently, on UP we unconditionally spin_lock() first, which > calls __spin_lock_debug(), which takes the lock unconditionally even > on UP. This will deadlock in situations in which we call > atomic_dec_and_lock() knowing that the counter won't go to zero > (because we hold another reference) and that we already hold the lock. > Instead, we should use the SMP code path which only takes the lock if > necessary. Reviewed-by: Paul E. McKenney > Signed-off-by: Jan Blunck > Signed-off-by: Valerie Aurora (Henson) > --- > lib/dec_and_lock.c | 3 +-- > 1 files changed, 1 insertions(+), 2 deletions(-) > > 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)) > -- > 1.6.0.6 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/