bcachefs: Ensure we flush btree updates in evacuate path

This fixes a possible race where we fail to remove a device because of
btree nodes still on it, that are being deleted by in flight btree
updates.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
This commit is contained in:
Kent Overstreet 2021-10-24 17:00:33 -04:00 • committed by Kent Overstreet
commit 23af498cc4