From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Subject: Re: [PATCH review  16/19] mnt: Track which mounts use a dentry as
	root.
Date: Fri, 3 Apr 2015 06:54:50 +0100
Message-ID: <20150403055449.GE889@ZenIV.linux.org.uk>
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To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Andrey Vagin <avagin-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>, Richard Weinberger <richard-/L3Ra7n9ekc@public.gmane.org>, Linux Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jann Horn <jann-XZ1E9jl8jIdeoWH0uzbU5w@public.gmane.org>, Willy Tarreau <w@1wt.eu>
List-Id: containers.vger.kernel.org

On Thu, Apr 02, 2015 at 08:56:20PM -0500, Eric W. Biederman wrote:

One general note - I'd probably put a pointer to that sucker into struct
mount.  For one thing, root-preserving clone_mnt() is a fairly common
case.  For another, searching for that thing in mnt_put_root() looks
wrong.  Matter of taste, but...

Another thing is that IMO it's better to preallocate that thing in
vfs_kern_mount() and free if it turns out to be unused.  Simpler cleanup
path that way...


> -	mnt->mnt.mnt_root = root;
> +	err = mnt_set_root(mnt, root);
> +	if (err) {
> +		dput(mnt->mnt.mnt_root);

	Unless I'm misreading your code, mnt_set_root() does *not* set it
on failure, so what's going on here?

>  #define DCACHE_FALLTHRU			0x01000000 /* Fall through to lower layer */
						^^^^^^^^^^
> +#define DCACHE_MOUNTROOT		0x01000000 /* is root of a vfsmount */
					^^^^^^^^^^

	Er...