[PATCH v2 block/for-linus] writeback: sync_inodes_sb() must write out I_DIRTY_TIME inodes and always call wait_sb_inodes()

[Jens Axboe]

On 08/25/2015 12:11 PM, 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 at kernel.org>
> Fixes: e79729123f63 ("writeback: don't issue wb_writeback_work if clean")
> Link: http://lkml.kernel.org/g/20150812101204.GE17933@dhcp-13-216.nay.redhat.com
> Reported-and-bisected-by: Eryu Guan <eguan at redhat.com>
> Cc: Dave Chinner <david at fromorbit.com>
> Cc: Jan Kara <jack at suse.com>
> Cc: Ted Ts'o <tytso at google.com>

Added for 4.2.

-- 
Jens Axboe