On Mon, May 14, 2018 at 11:32:16AM -0400, J. Bruce Fields wrote: > On Fri, May 11, 2018 at 10:13:39PM +0100, Al Viro wrote: > > [-stable fodder; as it is, one can e.g. add > > /mnt/cgroup localhost(rw,no_root_squash,fsid=4242) > > to /etc/exports, > > mount -t cgroup none /mnt/cgroup > > mkdir /tmp/a > > mount -t nfs localhost://mnt/cgroup /tmp/a > > mkdir /tmp/a/foo > > How is the cgroup filesystem exportable? That sounds like a bug in > itself. We don't want people using NFS as some kind of weird remote > configuration protocol. You can't have open-by-fhandle without exportability. And it's not the only fs like that. > > and have knfsd oops; the patch below deals with that. > > > > Questions: > > 1) is fh_update() use below legitimate, or should we > > do fh_put/fh_compose instead? > > fh_update looks OK to me, but do we need it here? There's already a > > if (!err) > err = fh_update(reshp); > > at the end of nfsd_create_locked. Might be too late for that, though - the trouble hits when we hit nfsd_create_setattr(). > > 2) is nfserr_serverfail valid for situation when > > directory created by such vfs_mkdir() manages to disappear > > under us immediately afterwards? Or should we return nfserr_stale > > instead? > > We just got a successful result on the create and the parent's still > locked, so if somebody hits this I think we want them reporting a bug, > not wasting time trying to find a mistake in their own logic. No. Suppose it's NFS-over-NFS (and yes, I agree that it's a bad idea; somebody *has* done that). Lookup after successful mkdir can legitimately fail if it's been removed server-side. And we *will* need to allow nfs_mkdir() to return that way in some cases (== success with dentry passed to it left unhashed negative), I'm afraid ;-/
