From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753612AbaBYWni (ORCPT ); Tue, 25 Feb 2014 17:43:38 -0500 Received: from mail-qa0-f49.google.com ([209.85.216.49]:57817 "EHLO mail-qa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752550AbaBYWne (ORCPT ); Tue, 25 Feb 2014 17:43:34 -0500 Date: Tue, 25 Feb 2014 17:43:30 -0500 From: Tejun Heo To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, LKML , Jens Axboe , Derek Basehore , stable@vger.kernel.org Subject: Re: [PATCH 1/2] bdi: Fix hung task on sync Message-ID: <20140225224330.GB8568@mtj.dyndns.org> References: <1393367354-5172-1-git-send-email-jack@suse.cz> <1393367354-5172-2-git-send-email-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1393367354-5172-2-git-send-email-jack@suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 25, 2014 at 11:29:13PM +0100, Jan Kara wrote: > From: Derek Basehore > > bdi_wakeup_thread_delayed() used the mod_delayed_work() function to > schedule work to writeback dirty inodes. The problem with this is that > it can delay work that is scheduled for immediate execution, such as the > work from sync_inodes_sb(). This can happen since mod_delayed_work() > can now steal work from a work_queue. This fixes the problem by using > queue_delayed_work() instead. This is a regression caused by > 839a8e8660b6 "writeback: replace custom worker pool implementation with > unbound workqueue". > > The reason that this causes a problem is that laptop-mode will change > the delay, dirty_writeback_centisecs, to 60000 (10 minutes) by default. > In the case that bdi_wakeup_thread_delayed() races with > sync_inodes_sb(), sync will be stopped for 10 minutes and trigger a hung > task. Even if dirty_writeback_centisecs is not long enough to cause a > hung task, we still don't want to delay sync for that long. > > We fix the problem by using queue_delayed_work() when we want to > schedule writeback sometime in future. This function doesn't change the > timer if it is already armed. > > For the same reason, we also change bdi_writeback_workfn() to > immediately queue the work again in the case that the work_list is not > empty. The same problem can happen if the sync work is run on the rescue > worker. > > Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 > CC: stable@vger.kernel.org > Signed-off-by: Derek Basehore > Signed-off-by: Jan Kara Reviewed-by: Tejun Heo Thanks. -- tejun