On Fri 14-02-14 20:12:17, Derek Basehore wrote: > 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 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. The patch looks good. You can add: Reviewed-by: Jan Kara <jack@xxxxxxx> I'd also suggest to push this to stable kernels. Honza > > Signed-off-by: Derek Basehore <dbasehore@xxxxxxxxxxxx> > --- > fs/fs-writeback.c | 5 +++-- > mm/backing-dev.c | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index e0259a1..95b7b8c 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -1047,8 +1047,9 @@ 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)) > + 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 --git a/mm/backing-dev.c b/mm/backing-dev.c > index ce682f7..3fde024 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -294,7 +294,7 @@ 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); > } > > /* > -- > 1.9.0.rc1.175.g0b1dcb5 > -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>