nfsd4: nfsd4_destroy_session must set callback client under the state lock

nfsd4_set_callback_client must be called under the state lock to atomically
set or unset the callback client and shutting down the previous one.
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4callback.c

@@ -718,6 +718,7 @@ void nfsd4_destroy_callback_queue(void)
 	destroy_workqueue(callback_wq);
 }
 
+/* must be called under the state lock */
 void nfsd4_set_callback_client(struct nfs4_client *clp, struct rpc_clnt *new)
 {
 	struct rpc_clnt *old = clp->cl_cb_client;

fs/nfsd/nfs4state.c

@@ -1427,8 +1427,10 @@ nfsd4_destroy_session(struct svc_rqst *r,
 	unhash_session(ses);
 	spin_unlock(&client_lock);
 
+	nfs4_lock_state();
 	/* wait for callbacks */
 	nfsd4_set_callback_client(ses->se_client, NULL);
+	nfs4_unlock_state();
 	nfsd4_put_session(ses);
 	status = nfs_ok;
 out: