rpcrdma: Fix SQ size calculation when memreg is FRMR

This patch updates the computation to include the worst case situation
where three FRMR are required to map a single RPC REQ.
Signed-off-by: Tom Tucker <tom@ogc.us>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xprtrdma/rpc_rdma.c

@@ -249,6 +249,8 @@ rpcrdma_create_chunks(struct rpc_rqst *rqst, struct xdr_buf *target,
 	req->rl_nchunks = nchunks;
 
 	BUG_ON(nchunks == 0);
+	BUG_ON((r_xprt->rx_ia.ri_memreg_strategy == RPCRDMA_FRMR)
+	       && (nchunks > 3));
 
 	/*
 	 * finish off header. If write, marshal discrim and nchunks.

net/sunrpc/xprtrdma/verbs.c

@@ -650,10 +650,22 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
 	ep->rep_attr.cap.max_send_wr = cdata->max_requests;
 	switch (ia->ri_memreg_strategy) {
 	case RPCRDMA_FRMR:
-		/* Add room for frmr register and invalidate WRs */
-		ep->rep_attr.cap.max_send_wr *= 3;
-		if (ep->rep_attr.cap.max_send_wr > devattr.max_qp_wr)
-			return -EINVAL;
+		/* Add room for frmr register and invalidate WRs.
+		 * 1. FRMR reg WR for head
+		 * 2. FRMR invalidate WR for head
+		 * 3. FRMR reg WR for pagelist
+		 * 4. FRMR invalidate WR for pagelist
+		 * 5. FRMR reg WR for tail
+		 * 6. FRMR invalidate WR for tail
+		 * 7. The RDMA_SEND WR
+		 */
+		ep->rep_attr.cap.max_send_wr *= 7;
+		if (ep->rep_attr.cap.max_send_wr > devattr.max_qp_wr) {
+			cdata->max_requests = devattr.max_qp_wr / 7;
+			if (!cdata->max_requests)
+				return -EINVAL;
+			ep->rep_attr.cap.max_send_wr = cdata->max_requests * 7;
+		}
 		break;
 	case RPCRDMA_MEMWINDOWS_ASYNC:
 	case RPCRDMA_MEMWINDOWS: