Re: [PATCH 03/34] teach move_mount(2) to work with OPEN_TREE_CLONE [ver #12]

[Alan Jenkins]

On 10/10/2018 14:02, David Howells wrote:
> The attached change seems to fix the lazy-umount problem.
>
> David
> ---
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 5adeeea2a4d9..d43f0fa152e9 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2472,7 +2472,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path)
>   	if (old->mnt_ns && !attached)
>   		goto out1;
>   
> -	if (old->mnt.mnt_flags & MNT_LOCKED)
> +	if (old->mnt.mnt_flags & (MNT_LOCKED | MNT_UMOUNT))
>   		goto out1;
>   
>   	if (old_path->dentry != old_path->mnt->mnt_root)


I can't test any more at the moment, as my laptop died today :). But I 
have no objection to this.

It would be more fun if there was a way to support it :), but I don't 
have a genuine reason to want it. And you couldn't use it for fully 
general purposes anyway, because umount2( , MNT_DETACH) is defined as 
separating all the child mounts.

P.S. Regarding the issue with the namespace loop. My strawman solution 
would be for graft_tree() to silently detach any NS file mounts that 
have a sequence number less than or equal to the namespace they are 
being mounted into.