NFSv4.1: fix handling NFS4ERR_DELAY when testing for session trunking

Currently when client sends an EXCHANGE_ID for a possible trunked
connection, for any error that happened, the trunk will be thrown
out. However, an NFS4ERR_DELAY is a transient error that should be
retried instead.

Fixes: e818bd08 ("NFSv4.1 remove xprt from xprt_switch if session trunking test fails")
Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/nfs4proc.c

@@ -8959,6 +8959,7 @@ void nfs4_test_session_trunk(struct rpc_clnt *clnt, struct rpc_xprt *xprt,
 
 	sp4_how = (adata->clp->cl_sp4_flags == 0 ? SP4_NONE : SP4_MACH_CRED);
 
+try_again:
 	/* Test connection for session trunking. Async exchange_id call */
 	task = nfs4_run_exchange_id(adata->clp, adata->cred, sp4_how, xprt);
 	if (IS_ERR(task))
@@ -8971,11 +8972,15 @@ void nfs4_test_session_trunk(struct rpc_clnt *clnt, struct rpc_xprt *xprt,
 
 	if (status == 0)
 		rpc_clnt_xprt_switch_add_xprt(clnt, xprt);
-	else if (rpc_clnt_xprt_switch_has_addr(clnt,
+	else if (status != -NFS4ERR_DELAY && rpc_clnt_xprt_switch_has_addr(clnt,
 				(struct sockaddr *)&xprt->addr))
 		rpc_clnt_xprt_switch_remove_xprt(clnt, xprt);
 
 	rpc_put_task(task);
+	if (status == -NFS4ERR_DELAY) {
+		ssleep(1);
+		goto try_again;
+	}
 }
 EXPORT_SYMBOL_GPL(nfs4_test_session_trunk);