Commit 006a0973 authored Aug 25, 2015 by Tejun Heo Committed by Jens Axboe Aug 25, 2015

writeback: sync_inodes_sb() must write out I_DIRTY_TIME inodes and always call wait_sb_inodes()



e7972912 ("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@kernel.org>
Fixes: e7972912 ("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@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.com>
Cc: Ted Ts'o <tytso@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent c13dcf9f

fs/fs-writeback.c

+13 −9

Original line number	Diff line number	Diff line
		@@ -844,14 +844,15 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
		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 backing_dev_info *bdi,
		{
		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 *sb)
		};
		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));

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