nfsd: Ensure that nfs4_open_delegation() references the delegation stateid

Ensure that nfs4_open_delegation() keeps a reference to the delegation
stateid until it is done working with it. Necessary step toward
client_mutex removal.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -674,6 +674,7 @@ hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
 	lockdep_assert_held(&state_lock);
 	lockdep_assert_held(&fp->fi_lock);
 
+	atomic_inc(&dp->dl_stid.sc_count);
 	dp->dl_stid.sc_type = NFS4_DELEG_STID;
 	list_add(&dp->dl_perfile, &fp->fi_delegations);
 	list_add(&dp->dl_perclnt, &dp->dl_stid.sc_client->cl_delegations);
@@ -3704,6 +3705,7 @@ nfs4_open_delegation(struct svc_fh *fh, struct nfsd4_open *open,
 	dprintk("NFSD: delegation stateid=" STATEID_FMT "\n",
 		STATEID_VAL(&dp->dl_stid.sc_stateid));
 	open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
+	nfs4_put_stid(&dp->dl_stid);
 	return;
 out_no_deleg:
 	open->op_delegate_type = NFS4_OPEN_DELEGATE_NONE;