On Tue, Aug 24, 2021 at 01:05:22PM +0800, Anand Jain wrote:

There were few lock dep warnings because btrfs_show_devname() was using
device_list_mutex as recorded in the commits
  ccd05285e7f (btrfs: fix a possible umount deadlock)

Commit ccd05285e7f does not exist in my tree, but the subject matches
0ccd05285e7f. Please format the references like it's done for the Fixes:
tag with HASH ("Subject"). Nobody types that by hand, a simple git alias
does that for free:

.gitconfig:
[alias]
	one = show -s --pretty='format:%h (\"%s\")'