From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [2.6.36-rc3] Workqueues, XFS, dependencies and deadlocks Date: Tue, 07 Sep 2010 14:26:54 +0200 Message-ID: <4C862F8E.7030507@kernel.org> References: <20100907072954.GM705@dastard> <4C86003B.6090706@kernel.org> <20100907100108.GN705@dastard> <4C861582.6080102@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, xfs@oss.sgi.com, linux-fsdevel@vger.kernel.org To: Dave Chinner Return-path: Received: from hera.kernel.org ([140.211.167.34]:44424 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756256Ab0IGM1E (ORCPT ); Tue, 7 Sep 2010 08:27:04 -0400 In-Reply-To: <4C861582.6080102@kernel.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On 09/07/2010 12:35 PM, Tejun Heo wrote: > Can you please help me a bit more? Are you saying the following? > > Work w0 starts execution on wq0. w0 tries locking but fails. Does > delay(1) and requeues itself on wq0 hoping another work w1 would be > queued on wq0 which will release the lock. The requeueing should make > w0 queued and executed after w1, but instead w1 never gets executed > while w0 hogs the CPU constantly by re-executing itself. Also, how > does delay(1) help with chewing up CPU? Are you talking about > avoiding constant lock/unlock ops starving other lockers? In such > case, wouldn't cpu_relax() make more sense? Ooh, almost forgot. There was nr_active underflow bug in workqueue code which could lead to malfunctioning max_active regulation and problems during queue freezing, so you could be hitting that too. I sent out pull request some time ago but hasn't been pulled into mainline yet. Can you please pull from the following branch and add WQ_HIGHPRI as discussed before and see whether the problem is still reproducible? And if the problem is reproducible, can you please trigger sysrq thread dump and attach it? git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-linus Thanks. -- tejun