From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753416AbaBYW33 (ORCPT ); Tue, 25 Feb 2014 17:29:29 -0500 Received: from cantor2.suse.de ([195.135.220.15]:59850 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752875AbaBYW31 (ORCPT ); Tue, 25 Feb 2014 17:29:27 -0500 From: Jan Kara To: linux-fsdevel@vger.kernel.org Cc: LKML , Jens Axboe , Tejun Heo , Derek Basehore , stable@vger.kernel.org, Jan Kara Subject: [PATCH 1/2] bdi: Fix hung task on sync Date: Tue, 25 Feb 2014 23:29:13 +0100 Message-Id: <1393367354-5172-2-git-send-email-jack@suse.cz> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1393367354-5172-1-git-send-email-jack@suse.cz> References: <1393367354-5172-1-git-send-email-jack@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- fs/fs-writeback.c | 8 ++++---- mm/backing-dev.c | 5 ++++- 2 files changed, 8 insertions(+), 5 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index e0259a163f98..8277b76be983 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1047,10 +1047,10 @@ void bdi_writeback_workfn(struct work_struct *work) trace_writeback_pages_written(pages_written); } - if (!list_empty(&bdi->work_list) || - (wb_has_dirty_io(wb) && dirty_writeback_interval)) - queue_delayed_work(bdi_wq, &wb->dwork, - msecs_to_jiffies(dirty_writeback_interval * 10)); + if (!list_empty(&bdi->work_list)) + mod_delayed_work(bdi_wq, &wb->dwork, 0); + else if (wb_has_dirty_io(wb) && dirty_writeback_interval) + bdi_wakeup_thread_delayed(bdi); current->flags &= ~PF_SWAPWRITE; } diff --git a/mm/backing-dev.c b/mm/backing-dev.c index ce682f7a4f29..fab8401fc54e 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -288,13 +288,16 @@ int bdi_has_dirty_io(struct backing_dev_info *bdi) * Note, we wouldn't bother setting up the timer, but this function is on the * fast-path (used by '__mark_inode_dirty()'), so we save few context switches * by delaying the wake-up. + * + * We have to be careful not to postpone flush work if it is scheduled for + * earlier. Thus we use queue_delayed_work(). */ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) { 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); } /* -- 1.8.1.4