Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753026AbZDNGwz (ORCPT ); Tue, 14 Apr 2009 02:52:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750812AbZDNGwo (ORCPT ); Tue, 14 Apr 2009 02:52:44 -0400 Received: from cantor2.suse.de ([195.135.220.15]:43904 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751649AbZDNGwn (ORCPT ); Tue, 14 Apr 2009 02:52:43 -0400 Date: Tue, 14 Apr 2009 08:52:39 +0200 From: Nick Piggin To: Jan Blunck Cc: "Paul E. McKenney" , Linux-Kernel Mailinglist Subject: Re: [PATCH] atomic: Only take lock when the counter drops to zero on UP as well Message-ID: <20090414065239.GA20951@wotan.suse.de> References: <20090411141754.45F7B16080@e179.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090411141754.45F7B16080@e179.suse.de> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1433 Lines: 43 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. 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/