On Tue 25-08-15 14:11:52, Tejun Heo wrote:
> e79729123f63 ("writeback: don't issue wb_writeback_work if clean")
> updated writeback path to avoid kicking writeback work items if there
> are no inodes to be written out; unfortunately, the avoidance logic
> was too aggressive and broke sync_inodes_sb().
>
> * sync_inodes_sb() must write out I_DIRTY_TIME inodes but I_DIRTY_TIME
> inodes dont't contribute to bdi/wb_has_dirty_io() tests and were
> being skipped over.
>
> * inodes are taken off wb->b_dirty/io/more_io lists after writeback
> starts on them. sync_inodes_sb() skipping wait_sb_inodes() when
> bdi_has_dirty_io() breaks it by making it return while writebacks
> are in-flight.
>
> This patch fixes the breakages by
>
> * Removing bdi_has_dirty_io() shortcut from bdi_split_work_to_wbs().
> The callers are already testing the condition.
>
> * Removing bdi_has_dirty_io() shortcut from sync_inodes_sb() so that
> it always calls into bdi_split_work_to_wbs() and wait_sb_inodes().
>
> * Making bdi_split_work_to_wbs() consider the b_dirty_time list for
> WB_SYNC_ALL writebacks.
>
> Kudos to Eryu, Dave and Jan for tracking down the issue.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Fixes: e79729123f63 ("writeback: don't issue wb_writeback_work if clean")
> Link: http://lkml.kernel.org/g/20150812101204.GE17933@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-and-bisected-by: Eryu Guan <eguan@xxxxxxxxxx>
> Cc: Dave Chinner <david@xxxxxxxxxxxxx>
> Cc: Jan Kara <jack@xxxxxxxx>
> Cc: Ted Ts'o <tytso@xxxxxxxxxx>
> ---
> fs/fs-writeback.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxxx>
Honza
>
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -844,14 +844,15 @@ static void bdi_split_work_to_wbs(struct
> struct wb_iter iter;
>
> might_sleep();
> -
> - if (!bdi_has_dirty_io(bdi))
> - return;
> restart:
> rcu_read_lock();
> bdi_for_each_wb(wb, bdi, &iter, next_blkcg_id) {
> - if (!wb_has_dirty_io(wb) ||
> - (skip_if_busy && writeback_in_progress(wb)))
> + /* SYNC_ALL writes out I_DIRTY_TIME too */
> + if (!wb_has_dirty_io(wb) &&
> + (base_work->sync_mode == WB_SYNC_NONE ||
> + list_empty(&wb->b_dirty_time)))
> + continue;
> + if (skip_if_busy && writeback_in_progress(wb))
> continue;
>
> base_work->nr_pages = wb_split_bdi_pages(wb, nr_pages);
> @@ -899,8 +900,7 @@ static void bdi_split_work_to_wbs(struct
> {
> might_sleep();
>
> - if (bdi_has_dirty_io(bdi) &&
> - (!skip_if_busy || !writeback_in_progress(&bdi->wb))) {
> + if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
> base_work->auto_free = 0;
> base_work->single_wait = 0;
> base_work->single_done = 0;
> @@ -2275,8 +2275,12 @@ void sync_inodes_sb(struct super_block *
> };
> struct backing_dev_info *bdi = sb->s_bdi;
>
> - /* Nothing to do? */
> - if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
> + /*
> + * Can't skip on !bdi_has_dirty() because we should wait for !dirty
> + * inodes under writeback and I_DIRTY_TIME inodes ignored by
> + * bdi_has_dirty() need to be written out too.
> + */
> + if (bdi == &noop_backing_dev_info)
> return;
> WARN_ON(!rwsem_is_locked(&sb->s_umount));
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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