From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030397Ab2GKWMy (ORCPT ); Wed, 11 Jul 2012 18:12:54 -0400 Received: from www.linutronix.de ([62.245.132.108]:35589 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933361Ab2GKWMv (ORCPT ); Wed, 11 Jul 2012 18:12:51 -0400 Date: Thu, 12 Jul 2012 00:12:44 +0200 (CEST) From: Thomas Gleixner To: Jan Kara cc: Jeff Moyer , LKML , linux-fsdevel@vger.kernel.org, Tejun Heo , Jens Axboe , mgalbraith@suse.com Subject: Re: Deadlocks due to per-process plugging In-Reply-To: <20120711201601.GB9779@quack.suse.cz> Message-ID: References: <20120711133735.GA8122@quack.suse.cz> <20120711201601.GB9779@quack.suse.cz> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 11 Jul 2012, Jan Kara wrote: > On Wed 11-07-12 12:05:51, Jeff Moyer wrote: > > This eventually ends in a call to blk_run_queue_async(q) after > > submitting the I/O from the plug list. Right? So is the question > > really why doesn't the kblockd workqueue get scheduled? > Ah, I didn't know this. Thanks for the hint. So in the kdump I have I can > see requests queued in tsk->plug despite the process is sleeping in > TASK_UNINTERRUPTIBLE state. So the only way how unplug could have been > omitted is if tsk_is_pi_blocked() was true. Rummaging through the dump... > indeed task has pi_blocked_on = 0xffff8802717d79c8. The dump is from an -rt > kernel (I just didn't originally thought that makes any difference) so > actually any mutex is rtmutex and thus tsk_is_pi_blocked() is true whenever > we are sleeping on a mutex. So this seems like a bug in rtmutex code. > Thomas, you seemed to have added that condition... Any idea how to avoid > the deadlock? Mike has sent out a fix related to the plug stuff, which I just posted for the rt stable series. Can you verify against that ? Thanks, tglx