From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id D01EFB7CF7 for ; Sat, 17 Apr 2010 08:02:40 +1000 (EST) Subject: Re: Possible bug with mutex adaptative spinning From: Benjamin Herrenschmidt To: Peter Zijlstra In-Reply-To: <1271453251.1674.485.camel@laptop> References: <1271212509.13059.135.camel@pasglop> <1271213767.13059.137.camel@pasglop> <1271453251.1674.485.camel@laptop> Content-Type: text/plain; charset="UTF-8" Date: Sat, 17 Apr 2010 08:01:32 +1000 Message-ID: <1271455292.13059.198.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev , "linux-kernel@vger.kernel.org" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 2010-04-16 at 23:27 +0200, Peter Zijlstra wrote: > > If the owner is actually running, it may do so for a very long time. It > > looks to me that everybody trying to take the mutex will thus spin and > > never get out of the spin loop until the owner stops running. > > The inner-most spin loop breaks out on need_resched(): > > if (task_thread_info(rq->curr) != owner || need_resched()) > return 0; You are right, this was only a problem in conjunction with the other bug returning 1 all the time, causing us to ignore need_resched(). With that fixed, it looks fine now. Thanks ! Cheers, Ben.