From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754302AbZD1UOV (ORCPT ); Tue, 28 Apr 2009 16:14:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752255AbZD1UOJ (ORCPT ); Tue, 28 Apr 2009 16:14:09 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:42152 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750905AbZD1UOH (ORCPT ); Tue, 28 Apr 2009 16:14:07 -0400 Date: Tue, 28 Apr 2009 13:08:47 -0700 From: Andrew Morton To: eparis@redhat.com, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, hch@infradead.org, alan@lxorguk.ukuu.org.uk, sfr@canb.auug.org.au, john@johnmccutchan.com, rlove@rlove.org Subject: Re: [PATCH -V2 01/13] mutex: add atomic_dec_and_mutex_lock Message-Id: <20090428130847.849478bd.akpm@linux-foundation.org> In-Reply-To: <20090407160601.a824da99.akpm@linux-foundation.org> References: <20090327200508.32007.63278.stgit@paris.rdu.redhat.com> <20090407160601.a824da99.akpm@linux-foundation.org> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 7 Apr 2009 16:06:01 -0700 Andrew Morton wrote: > On Fri, 27 Mar 2009 16:05:08 -0400 > Eric Paris wrote: > > > Much like the atomic_dec_and_lock() function in which we take an hold a > > spin_lock if we drop the atomic to 0 this function takes and holds the > > mutex if we dec the atomic to 0. > > > > Signed-off-by: Eric Paris > > Signed-off-by: Peter Zijlstra > > Cc: Paul Mackerras > > LKML-Reference: <20090323172417.410913479@chello.nl> > > Signed-off-by: Ingo Molnar > > --- > > > > include/linux/mutex.h | 23 +++++++++++++++++++++++ > > 1 files changed, 23 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/mutex.h b/include/linux/mutex.h > > index 3069ec7..93054fc 100644 > > --- a/include/linux/mutex.h > > +++ b/include/linux/mutex.h > > @@ -151,4 +151,27 @@ extern int __must_check mutex_lock_killable(struct mutex *lock); > > extern int mutex_trylock(struct mutex *lock); > > extern void mutex_unlock(struct mutex *lock); > > > > +/** > > + * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 > > + * @cnt: the atomic which we are to dec > > + * @lock: the mutex to return holding if we dec to 0 > > + * > > + * return true and hold lock if we dec to 0, return false otherwise > > + */ > > +static inline int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) > > +{ > > + /* dec if we can't possibly hit 0 */ > > + if (atomic_add_unless(cnt, -1, 1)) > > + return 0; > > + /* we might hit 0, so take the lock */ > > + mutex_lock(lock); > > + if (!atomic_dec_and_test(cnt)) { > > + /* when we actually did the dec, we didn't hit 0 */ > > + mutex_unlock(lock); > > + return 0; > > + } > > + /* we hit 0, and we hold the lock */ > > + return 1; > > +} > > + > > This looks too large to be inlined? It still looks too large to be inlined. Take a look at atomic_add_unless(), and split your sides laughing. Once you factor in all the lockdep and other debug goop, the code generation here is pretty bewildering, but it won't be small.