From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [merged] backing_dev-fix-hung-task-on-sync.patch removed from -mm tree Date: Fri, 04 Apr 2014 12:29:18 -0700 Message-ID: <533f080e.7zUrfCzO2VYMfvIv%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:42608 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753882AbaDDT3T (ORCPT ); Fri, 4 Apr 2014 15:29:19 -0400 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: mm-commits@vger.kernel.org, viro@zento.linux.org.uk, tj@kernel.org, stable@vger.kernel.org, sonnyrao@chromium.org, semenzato@chromium.org, keescook@chromium.org, jack@suse.cz, gregkh@linuxfoundation.org, david@fromorbit.com, darrick.wong@oracle.com, bleung@chromium.org, axboe@kernel.dk, dbasehore@chromium.org Subject: [merged] backing_dev-fix-hung-task-on-sync.patch removed from -mm tree To: dbasehore@chromium.org,axboe@kernel.dk,bleung@chromium.org,darrick.wong@oracle.com,david@fromorbit.com,gregkh@linuxfoundation.org,jack@suse.cz,keescook@chromium.org,semenzato@chromium.org,sonnyrao@chromium.org,stable@vger.kernel.org,tj@kernel.org,viro@zento.linux.org.uk,mm-commits@vger.kernel.org From: akpm@linux-foundation.org Date: Fri, 04 Apr 2014 12:29:18 -0700 The patch titled Subject: backing_dev: fix hung task on sync has been removed from the -mm tree. Its filename was backing_dev-fix-hung-task-on-sync.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Derek Basehore Subject: backing_dev: fix hung task on sync 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. [jack@suse.cz: update changelog, add comment, use bdi_wakeup_thread_delayed()] Signed-off-by: Derek Basehore Reviewed-by: Jan Kara Cc: Alexander Viro Reviewed-by: 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 | 8 ++++---- mm/backing-dev.c | 5 ++++- 2 files changed, 8 insertions(+), 5 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 @@ -1039,10 +1039,10 @@ 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)) - 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 -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 @@ -288,13 +288,16 @@ int bdi_has_dirty_io(struct backing_dev_ * 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); } /* _ Patches currently in -mm which might be from dbasehore@chromium.org are origin.patch