From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758641AbZCTPTl (ORCPT ); Fri, 20 Mar 2009 11:19:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758120AbZCTPSv (ORCPT ); Fri, 20 Mar 2009 11:18:51 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:59801 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757422AbZCTPSu (ORCPT ); Fri, 20 Mar 2009 11:18:50 -0400 Message-Id: <20090320151734.909016733@chello.nl> References: <20090320151547.937040269@chello.nl> User-Agent: quilt/0.46-1 Date: Fri, 20 Mar 2009 16:15:49 +0100 From: Peter Zijlstra To: Ingo Molnar , linux-kernel@vger.kernel.org Cc: Paul Mackerras , Peter Zijlstra , Eric Paris Subject: [RFC][PATCH 2/3] mutex: add atomic_dec_and_mutex_lock] Content-Disposition: inline; filename=eparis-mutex-add_atomic_dec_and_mutex_lock.patch X-Bad-Reply: References but no 'Re:' in Subject. Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Paris 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 --- include/linux/mutex.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) Index: linux-2.6/include/linux/mutex.h =================================================================== --- linux-2.6.orig/include/linux/mutex.h +++ linux-2.6/include/linux/mutex.h @@ -151,4 +151,27 @@ extern int __must_check mutex_lock_killa 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 --