3.10-stable review patch. If anyone has any objections, please let me know.
------------------ From: Derek Basehore <[email protected]> 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. [[email protected]: update changelog, add comment, use bdi_wakeup_thread_delayed()] Signed-off-by: Derek Basehore <[email protected]> Reviewed-by: Jan Kara <[email protected]> Cc: Alexander Viro <[email protected]> Reviewed-by: Tejun Heo <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: "Darrick J. Wong" <[email protected]> Cc: Derek Basehore <[email protected]> Cc: Kees Cook <[email protected]> Cc: Benson Leung <[email protected]> Cc: Sonny Rao <[email protected]> Cc: Luigi Semenzato <[email protected]> Cc: Jens Axboe <[email protected]> Cc: Dave Chinner <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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); } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
