On Thu, Jan 07, 2021 at 01:46:37PM -0800, Eric Biggers wrote:

It looks like that's going to work, and it fixes the XFS bug too.

Note that if __writeback_single_inode() is called from writeback_single_inode()
(rather than writeback_sb_inodes()), then the inode might not be queued for
sync, in which case mark_inode_dirty_sync() will move it to a writeback list.

That's okay because afterwards, writeback_single_inode() will delete the inode
from any writeback list if it's been fully cleaned, right?  So clean inodes
won't get left on a writeback list.

It's confusing because there are comments in writeback_single_inode() and above
__writeback_single_inode() that say that the inode must not be moved between
writeback lists.  I take it that those comments are outdated, as they predate
I_SYNC_QUEUED being introduced by commit 5afced3bf281 ("writeback: Avoid
skipping inode writeback")?

Yes.  I think we need to update the comment as well.