| From 6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e Mon Sep 17 00:00:00 2001 |
| From: Derek Basehore <dbasehore@chromium.org> |
| Date: Thu, 3 Apr 2014 14:46:22 -0700 |
| Subject: backing_dev: fix hung task on sync |
| |
| From: Derek Basehore <dbasehore@chromium.org> |
| |
| commit 6ca738d60c563d5c6cf6253ee4b8e76fa77b2b9e upstream. |
| |
| 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 commit |
| 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 <dbasehore@chromium.org> |
| Reviewed-by: Jan Kara <jack@suse.cz> |
| Cc: Alexander Viro <viro@zento.linux.org.uk> |
| Reviewed-by: Tejun Heo <tj@kernel.org> |
| Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Cc: "Darrick J. Wong" <darrick.wong@oracle.com> |
| Cc: Derek Basehore <dbasehore@chromium.org> |
| Cc: Kees Cook <keescook@chromium.org> |
| Cc: Benson Leung <bleung@chromium.org> |
| Cc: Sonny Rao <sonnyrao@chromium.org> |
| Cc: Luigi Semenzato <semenzato@chromium.org> |
| Cc: Jens Axboe <axboe@kernel.dk> |
| Cc: Dave Chinner <david@fromorbit.com> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/fs-writeback.c | 8 ++++---- |
| mm/backing-dev.c | 5 ++++- |
| 2 files changed, 8 insertions(+), 5 deletions(-) |
| |
| --- a/fs/fs-writeback.c |
| +++ b/fs/fs-writeback.c |
| @@ -1038,10 +1038,10 @@ 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; |
| } |
| --- a/mm/backing-dev.c |
| +++ b/mm/backing-dev.c |
| @@ -287,13 +287,16 @@ 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); |
| } |
| |
| /* |