From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756252AbYEKNBz (ORCPT ); Sun, 11 May 2008 09:01:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752348AbYEKNBp (ORCPT ); Sun, 11 May 2008 09:01:45 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:56211 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751986AbYEKNBo (ORCPT ); Sun, 11 May 2008 09:01:44 -0400 Date: Sun, 11 May 2008 15:01:27 +0200 From: Ingo Molnar To: Matthew Wilcox Cc: Sven Wegener , Linus Torvalds , "Zhang, Yanmin" , Andi Kleen , LKML , Alexander Viro , Andrew Morton , Thomas Gleixner , "H. Peter Anvin" Subject: Re: [git pull] scheduler fixes Message-ID: <20080511130127.GA30685@elte.hu> References: <1210214696.3453.87.camel@ymzhang> <1210219729.3453.97.camel@ymzhang> <20080508120130.GA2860@elte.hu> <20080508122802.GA4880@elte.hu> <20080508144316.GA9869@elte.hu> <20080508151028.GA12109@elte.hu> <20080511110306.GP19219@parisc-linux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080511110306.GP19219@parisc-linux.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matthew Wilcox wrote: > + /* It's possible we need to wake up the next task on the list too */ > + if (unlikely(sem->count > 1) && !list_empty(&sem->wait_list)) > + __up(sem); this needs to check for ret != 0 as well, otherwise we can be woken but a timeout can also trigger => we lose a wakeup. I.e. like the patch below. Hm? Ingo -----------------------------> Subject: semaphore: fix #3 From: Ingo Molnar Date: Sun May 11 09:51:07 CEST 2008 Signed-off-by: Ingo Molnar --- kernel/semaphore.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) Index: linux/kernel/semaphore.c =================================================================== --- linux.orig/kernel/semaphore.c +++ linux/kernel/semaphore.c @@ -194,6 +194,13 @@ struct semaphore_waiter { struct task_struct *task; }; +static noinline void __sched __up(struct semaphore *sem) +{ + struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, + struct semaphore_waiter, list); + wake_up_process(waiter->task); +} + /* * Because this function is inlined, the 'state' parameter will be * constant, and thus optimised away by the compiler. Likewise the @@ -231,6 +238,10 @@ static inline int __sched __down_common( } list_del(&waiter.list); + if (unlikely(!list_empty(&sem->wait_list)) && + ((sem->count > 1) || ret)) + __up(sem); + return ret; } @@ -254,9 +265,10 @@ static noinline int __sched __down_timeo return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies); } -static noinline void __sched __up(struct semaphore *sem) -{ - struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list, - struct semaphore_waiter, list); - wake_up_process(waiter->task); -} + + /* + * Rotate sleepers - to make sure all of them get woken in case + * of parallel up()s: + */ + list_move_tail(&waiter->list, &sem->wait_list); +