xprtrdma: Don't invalidate FRMRs if registration fails

If FRMR registration fails, it's likely to transition the QP to the
error state. Or, registration may have failed because the QP is
_already_ in ERROR.

Thus calling rpcrdma_deregister_external() in
rpcrdma_create_chunks() is useless in FRMR mode: the LOCAL_INVs just
get flushed.

It is safe to leave existing registrations: when FRMR registration
is tried again, rpcrdma_register_frmr_external() checks if each FRMR
is already/still VALID, and knocks it down first if it is.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Tested-by: Shirley Ma <shirley.ma@oracle.com>
Tested-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -271,9 +271,11 @@ rpcrdma_create_chunks(struct rpc_rqst *rqst, struct xdr_buf *target,
 	return (unsigned char *)iptr - (unsigned char *)headerp;
 
 out:
-	for (pos = 0; nchunks--;)
-		pos += rpcrdma_deregister_external(
-				&req->rl_segments[pos], r_xprt);
+	if (r_xprt->rx_ia.ri_memreg_strategy != RPCRDMA_FRMR) {
+		for (pos = 0; nchunks--;)
+			pos += rpcrdma_deregister_external(
+					&req->rl_segments[pos], r_xprt);
+	}
 	return n;
 }