Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756206AbZDNQtU (ORCPT ); Tue, 14 Apr 2009 12:49:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757325AbZDNQsl (ORCPT ); Tue, 14 Apr 2009 12:48:41 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:41616 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757391AbZDNQsk (ORCPT ); Tue, 14 Apr 2009 12:48:40 -0400 Date: Tue, 14 Apr 2009 09:48:39 -0700 From: "Paul E. McKenney" To: Nick Piggin Cc: Jan Blunck , Linux-Kernel Mailinglist Subject: Re: [PATCH] atomic: Only take lock when the counter drops to zero on UP as well Message-ID: <20090414164839.GI6753@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090411141754.45F7B16080@e179.suse.de> <20090414065239.GA20951@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090414065239.GA20951@wotan.suse.de> 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: 1655 Lines: 48 On Tue, Apr 14, 2009 at 08:52:39AM +0200, Nick Piggin wrote: > On Fri, Apr 10, 2009 at 06:13:57PM +0200, Jan Blunck wrote: > > I think it is wrong to unconditionally take the lock before calling > > atomic_dec_and_test() in _atomic_dec_and_lock(). This will deadlock in > > situation where it is known that the counter will not reach zero (e.g. holding > > another reference to the same object) but the lock is already taken. > > > > Signed-off-by: Jan Blunck > > Paul's worry about callers aside, I think it is probably a good idea > to reduce ifdefs and share more code. I am also OK with this patch. Acked-by: Paul E. McKenney > So for this patch, > > Acked-by: Nick Piggin > > > --- > > 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)) > > -- > > 1.6.0.2 -- 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/