From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f169.google.com (mail-wi0-f169.google.com [209.85.212.169]) by kanga.kvack.org (Postfix) with ESMTP id 1A3DC6B0035 for ; Tue, 11 Mar 2014 16:19:07 -0400 (EDT) Received: by mail-wi0-f169.google.com with SMTP id hm4so1336233wib.4 for ; Tue, 11 Mar 2014 13:19:07 -0700 (PDT) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b18si22291329wjb.1.2014.03.11.13.19.04 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 11 Mar 2014 13:19:05 -0700 (PDT) Date: Tue, 11 Mar 2014 21:19:02 +0100 From: Jan Kara Subject: Re: [PATCH] backing_dev: Fix hung task on sync Message-ID: <20140311201902.GA17011@quack.suse.cz> References: <1392437537-27392-1-git-send-email-dbasehore@chromium.org> <20140218225548.GI31892@mtj.dyndns.org> <20140219092731.GA4849@quack.suse.cz> <20140219190139.GQ10134@htj.dyndns.org> <20140311112355.d335295ed62cd480eb5ab33c@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140311112355.d335295ed62cd480eb5ab33c@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Tejun Heo , Jan Kara , Derek Basehore , Alexander Viro , Greg Kroah-Hartman , "Darrick J. Wong" , Kees Cook , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bleung@chromium.org, sonnyrao@chromium.org, semenzato@chromium.org On Tue 11-03-14 11:23:55, Andrew Morton wrote: > On Wed, 19 Feb 2014 14:01:39 -0500 Tejun Heo wrote: > > > Hello, Jan. > > > > On Wed, Feb 19, 2014 at 10:27:31AM +0100, Jan Kara wrote: > > > You are the workqueue expert so you may know better ;) But the way I > > > understand it is that queue_delayed_work() does nothing if the timer is > > > already running. Since we queue flusher work to run either immediately or > > > after dirty_writeback_interval we are safe to run queue_delayed_work() > > > whenever we want it to run after dirty_writeback_interval and > > > mod_delayed_work() whenever we want to run it immediately. > > > > Ah, okay, so it's always mod on immediate and queue on delayed. Yeah, > > that should work. > > > > > But it's subtle and some interface where we could say queue delayed work > > > after no later than X would be easier to grasp. > > > > Yeah, I think it'd be better if we had something like > > mod_delayed_work_if_later(). Hmm... > > The code comments which you asked for were not forthcoming. > > Are you otherwise OK with merging this into 3.14 and -stable? I have actually added the comment when nothing happened and have a patch with Tejun's Reviewed-by. Just noone picked it up. I'll send it your way together with another fix in flush work handling. Honza > From: Derek Basehore > Subject: backing_dev: fix hung task on sync > > bdi_wakeup_thread_delayed() used mod_delayed_work() 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 from the move to the bdi > workqueue design. > > 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. > > For the same reason, this also changes 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. > > Signed-off-by: Derek Basehore > Reviewed-by: Jan Kara > Cc: Alexander Viro > Cc: Tejun Heo > Cc: Greg Kroah-Hartman > Cc: "Darrick J. Wong" > Cc: Derek Basehore > Cc: Kees Cook > Cc: Benson Leung > Cc: Sonny Rao > Cc: Luigi Semenzato > Cc: Jens Axboe > Cc: Dave Chinner > Cc: > Signed-off-by: Andrew Morton > --- > > fs/fs-writeback.c | 5 +++-- > mm/backing-dev.c | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff -puN fs/fs-writeback.c~backing_dev-fix-hung-task-on-sync fs/fs-writeback.c > --- a/fs/fs-writeback.c~backing_dev-fix-hung-task-on-sync > +++ a/fs/fs-writeback.c > @@ -1039,8 +1039,9 @@ void bdi_writeback_workfn(struct work_st > trace_writeback_pages_written(pages_written); > } > > - if (!list_empty(&bdi->work_list) || > - (wb_has_dirty_io(wb) && dirty_writeback_interval)) > + if (!list_empty(&bdi->work_list)) > + mod_delayed_work(bdi_wq, &wb->dwork, 0); > + else if (wb_has_dirty_io(wb) && dirty_writeback_interval) > queue_delayed_work(bdi_wq, &wb->dwork, > msecs_to_jiffies(dirty_writeback_interval * 10)); > > diff -puN mm/backing-dev.c~backing_dev-fix-hung-task-on-sync mm/backing-dev.c > --- a/mm/backing-dev.c~backing_dev-fix-hung-task-on-sync > +++ a/mm/backing-dev.c > @@ -294,7 +294,7 @@ void bdi_wakeup_thread_delayed(struct ba > unsigned long timeout; > > timeout = msecs_to_jiffies(dirty_writeback_interval * 10); > - mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); > + queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); > } > > /* > _ > -- Jan Kara SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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