[CRIU] [PATCH v4 8/9] mount: do remaps for child-overmount of another overmount

[Andrey Vagin]

On Mon, Dec 11, 2017 at 07:07:25PM +0300, Pavel Tikhomirov wrote:
> In case we have mounts:
> 
> 1 /mnt/
> 2 /mnt/a with parent 1
> 3 /mnt/a/b with parent 1
> 4 /mnt/a with parent 2
> 
> We determine 2 as needing remap with does_mnt_overmount() and remap it.

Why do we determine that 2 has to be remmapped? It overmounts nothing.

The test passes without this patch. Could you explain why do we need
this patch? I think we need to improve the test to check the cases what
is fixed by this patch.


> Next we mount 4 on top of 2. Next in fixup_remap_mounts() we want to
> move 2 back to it's parent 1, but instead move 4 there. So in these case
> children-overmounts need to be remapped too.
> 
> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
> ---
>  criu/mount.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/criu/mount.c b/criu/mount.c
> index bacb24222..cdf1c0432 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -630,7 +630,7 @@ static struct mount_info *find_fsroot_mount_for(struct mount_info *bm)
>  	return NULL;
>  }
>  
> -static bool does_mnt_overmount(struct mount_info *m)
> +static bool mnt_needs_remap(struct mount_info *m)
>  {
>  	struct mount_info *t;
>  
> @@ -644,6 +644,14 @@ static bool does_mnt_overmount(struct mount_info *m)
>  			return true;
>  	}
>  
> +	/*
> +	 * If we are children-overmount and parent is remapped, we should be
> +	 * remapped too, else fixup_remap_mounts() won't be able to move parent
> +	 * to it's real place, it will move child instead.
> +	 */
> +	if (!strcmp(m->parent->mountpoint, m->mountpoint))
> +		return mnt_needs_remap(m->parent);
> +
>  	return false;
>  }
>  
> @@ -2488,7 +2496,7 @@ static int try_remap_mount(struct mount_info *m)
>  {
>  	struct mnt_remap_entry *r;
>  
> -	if (!does_mnt_overmount(m))
> +	if (!mnt_needs_remap(m))
>  		return 0;
>  
>  	BUG_ON(!m->parent);
> -- 
> 2.14.3
>