Christian Brauner <brauner@kernel.org>:
> Also fix the argument passed to nullfs_userspace_init() in
> switch_fs_struct(): pass the old fs_struct itself rather than the
> conditional return value which is NULL when other users still hold
> a reference, ensuring the PID 1 unshare detection actually works.

This description doesn't match actual patch.

Your patch doesn't change what is passed to nullfs_userspace_init in
switch_fs_struct. Code before this patch already passed fs.

-- 
Askar Safin