linux-kernel - Re: [PATCH 01/34] VFS: Make clone_mnt() and copy

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Message-ID: <AANLkTin0k-Sz8Y6dwm9s6isKgDPgcqpg0NON5kuiOcJ3@mail.gmail.com>
Date:	Fri, 1 Oct 2010 11:12:48 +0200
From:	Szeredi Miklos <miklos@...redi.hu>
To:	Ram Pai <linuxram@...ibm.com>
Cc:	mszeredi2@...il.com, Valerie Aurora <vaurora@...hat.com>,
	viro@...iv.linux.org.uk, hch@...radead.org, agruen@...e.de,
	npiggin@...nel.dk, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 01/34] VFS: Make clone_mnt() and copy_tree() return error codes

On Fri, Oct 1, 2010 at 3:58 AM, Ram Pai <linuxram@...ibm.com> wrote:
> > > > > @@ -1212,11 +1216,12 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
> > > > >         struct path path;
> > > > >
> > > > >         if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
> > > > > -               return NULL;
> > > > > +               return ERR_PTR(-EINVAL);
> > >
> > > Ram, do you remember how this worked?
> >
> > Oops. That should be a OR condition. there is one other check in that
> > function that should also be a OR condition.
>
> I may be wrong here. Can't exactly recollect what CL_COPY_ALL flag means. Al Viro
> might remember?  If CL_COPY_ALL means, to clone everything irrespective of any other
> flags, then the above code seems right.

CL_COPY_ALL means clone the mount despite MNT_UNBINDABLE.  It is used
for cloning the whole namespace and for collect_mounts(), both of
which ignore MNT_UNBINDABLE.

Of the two remaining callers of copy_tree() do_loopback already checks
MNT_UNBINDABLE on the root of the tree to be copied.

So that leaves the one in pnode.c.   That one will be called when
attaching a new mount or mount tree.  If the root of that tree is
unbindable then the propagation will fail with -ENOMEM which is wrong,
it should simply skip the whole tree and not try to propagate.   Calls
which result in propagation are  do_loopback, do_move_mount and
do_add_mount.  Of this do_loopback and do_move_mount already check for
MNT_UNBINDABLE, do_add_mount doesn't check, but should probably just
mask out MNT_UNBINDABLE.

So in the end that check in copy_tree() should never actually trigger
and can be turned into a WARN_ON

Additionally the propagation code should perhaps be more defensive and
skip MNT_UNBINDABLE source mounts.

Thanks,
Miklos
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