nfsd: Ensure struct nfs4_client is unhashed before we try to destroy it

When we remove the client_mutex protection, we will need to ensure
that it can't be found by other threads while we're destroying it.
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -1588,12 +1588,23 @@ free_client(struct nfs4_client *clp)
 }
 
 /* must be called under the client_lock */
-static inline void
+static void
 unhash_client_locked(struct nfs4_client *clp)
 {
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 	struct nfsd4_session *ses;
 
-	list_del(&clp->cl_lru);
+	/* Mark the client as expired! */
+	clp->cl_time = 0;
+	/* Make it invisible */
+	if (!list_empty(&clp->cl_idhash)) {
+		list_del_init(&clp->cl_idhash);
+		if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
+			rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
+		else
+			rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
+	}
+	list_del_init(&clp->cl_lru);
 	spin_lock(&clp->cl_lock);
 	list_for_each_entry(ses, &clp->cl_sessions, se_perclnt)
 		list_del_init(&ses->se_hash);
@@ -1601,7 +1612,17 @@ unhash_client_locked(struct nfs4_client *clp)
 }
 
 static void
-destroy_client(struct nfs4_client *clp)
+unhash_client(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	spin_lock(&nn->client_lock);
+	unhash_client_locked(clp);
+	spin_unlock(&nn->client_lock);
+}
+
+static void
+__destroy_client(struct nfs4_client *clp)
 {
 	struct nfs4_openowner *oo;
 	struct nfs4_delegation *dp;
@@ -1634,22 +1655,24 @@ destroy_client(struct nfs4_client *clp)
 	nfsd4_shutdown_callback(clp);
 	if (clp->cl_cb_conn.cb_xprt)
 		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
-	list_del(&clp->cl_idhash);
-	if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
-		rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
-	else
-		rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
 	spin_lock(&nn->client_lock);
-	unhash_client_locked(clp);
 	WARN_ON_ONCE(atomic_read(&clp->cl_refcount));
 	free_client(clp);
 	spin_unlock(&nn->client_lock);
 }
 
+static void
+destroy_client(struct nfs4_client *clp)
+{
+	unhash_client(clp);
+	__destroy_client(clp);
+}
+
 static void expire_client(struct nfs4_client *clp)
 {
+	unhash_client(clp);
 	nfsd4_client_record_remove(clp);
-	destroy_client(clp);
+	__destroy_client(clp);
 }
 
 static void copy_verf(struct nfs4_client *target, nfs4_verifier *source)