On Mon, May 14, 2018 at 04:45:51PM +0100, Al Viro wrote: > 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. We could separate the two--add a flag to export_operations, if necessary. I haven't formulated a strong argument, but exporting those filesystems makes me *really* uncomfortable. Poking around.... Looks like this was added by aa8188253474 "kernfs: add exportfs operations", and they really do claim a use case for lookup by filehandle. > > > 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(). Oh, got it. Could move the bottom fh_update to just above the nfsd_create_setattr(), though? > > > 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 ;-/ Thanks, makes sense. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
