On Tue, Jul 04, 2023 at 02:56:48PM +0200, Jan Kara wrote:

Hello!

This is second version of the patches to add config option to not allow writing
to mounted block devices. For motivation why this is interesting see patch 1/6.
I've been testing the patches more extensively this time and I've found couple
of things that get broken by disallowing writes to mounted block devices:
1) Bind mounts get broken because get_tree_bdev() / mount_bdev() first try to
   claim the bdev before searching whether it is already mounted. Patch 6
   reworks the mount code to avoid this problem.
2) btrfs mounting is likely having the same problem as 1). It should be fixable

It likely would. Note that I've got a series to port btrfs to the new
mount api that I sent out which changes btrfs mounting quite
significantly.