From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758289AbZC0UHK (ORCPT ); Fri, 27 Mar 2009 16:07:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760921AbZC0UGf (ORCPT ); Fri, 27 Mar 2009 16:06:35 -0400 Received: from mx2.redhat.com ([66.187.237.31]:55305 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760489AbZC0UGc (ORCPT ); Fri, 27 Mar 2009 16:06:32 -0400 From: Eric Paris Subject: [PATCH -V2 01/13] mutex: add atomic_dec_and_mutex_lock To: linux-kernel@vger.kernel.org Cc: viro@zeniv.linux.org.uk, hch@infradead.org, alan@lxorguk.ukuu.org.uk, sfr@canb.auug.org.au, john@johnmccutchan.com, rlove@rlove.org, akpm@linux-foundation.org Date: Fri, 27 Mar 2009 16:05:08 -0400 Message-ID: <20090327200508.32007.63278.stgit@paris.rdu.redhat.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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; +} + #endif