[CRIU] [PATCH] mount: Umount nested temporary mount pathes in do_bind_mount()

[Andrew Vagin]

On Thu, Feb 25, 2016 at 04:54:27PM +0300, Kirill Tkhai wrote:
> When a parent directory of restored mount is bound to itself,
> a temporary mount is cloned, so we need to umount it twice:
> 
> # mkdir -p parent/child /tmp/cr-XXX
> # mount --bind parent parent
> # mount --bind parent/child /tmp/cr-XXX/
> # mount --bind /tmp/cr-XXX/ parent/child
> # umount /tmp/cr-XXX/
> # mount | grep "/tmp/cr-XXX"
> /dev/sda3 on /tmp/cr-XXX type ext4 (rw,noatime,nodiratime,data=ordered)
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/mount.c |   27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/criu/mount.c b/criu/mount.c
> index 1a6b034..bce2465 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -301,6 +301,26 @@ static bool mounts_equal(struct mount_info *a, struct mount_info *b)
>  }
>  
>  /*
> + * Successively umount all file systems mounted on @path
> + */
> +static int umount2_nested(const char *path, int flags)
> +{
> +	bool once = true;
> +	int ret;
> +
> +	while (1) {
> +		ret = umount2(path, flags);
> +		if (ret)
> +			break;
> +		once = false;
> +	}
> +
> +	if (once || errno != EINVAL)
> +		return -1;
> +	return 0;
> +}
> +
> +/*
>   * mnt_roots is a temporary directory for restoring sub-trees of
>   * non-root namespaces.
>   */
> @@ -2397,7 +2417,12 @@ static int do_bind_mount(struct mount_info *mi)
 if (mount(NULL, mnt_path, NULL, MS_PRIVATE, NULL)) {

I think we don't need to make it private ^^^^, because it may be
propagated to somewhere. Kirll, could you try to remove your changes and
this mount and check that everythink works as expected in this case.

Thanks,
Andrew

>  			pr_perror("Unable to make %s private", mnt_path);
>  			return -1;
>  		}
> -		if (umount2(mnt_path, MNT_DETACH)) {
> +		/*
> +		 * If mi and mi->bind have the same mountpoint, and
> +		 * a parent dir of the mountpoint is bound to itself,
> +		 * then we have several mounts on mnt_path.
> +		 */
> +		if (umount2_nested(mnt_path, MNT_DETACH)) {
>  			pr_perror("Unable to umount %s", mnt_path);
>  			return -1;
>  		}
> 
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