xprtrdma: Fix max_send_wr computation

For FRWR, the computation of max_send_wr is split between
frwr_op_open and rpcrdma_ep_create, which makes it difficult to tell
that the max_send_wr result is currently incorrect if frwr_op_open
has to reduce the credit limit to accommodate a small max_qp_wr.
This is a problem now that extra WRs are needed for backchannel
operations and a drain CQE.

So, refactor the computation so that it is all done in ->ro_open,
and fix the FRWR version of this computation so that it
accommodates HCAs with small max_qp_wr correctly.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

3 files changed, 52 insertions, 24 deletions

diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
index 5cc68a824f45..592d1e8e27c3 100644
--- a/net/sunrpc/xprtrdma/fmr_ops.c
+++ b/net/sunrpc/xprtrdma/fmr_ops.c
@@ -159,10 +159,32 @@ out_release:
         fmr_op_release_mr(mr);
 }
 
+/* On success, sets:
+ *      ep->rep_attr.cap.max_send_wr
+ *      ep->rep_attr.cap.max_recv_wr
+ *      cdata->max_requests
+ *      ia->ri_max_segs
+ */
 static int
 fmr_op_open(struct rpcrdma_ia *ia, struct rpcrdma_ep *ep,
             struct rpcrdma_create_data_internal *cdata)
 {
+        int max_qp_wr;
+
+        max_qp_wr = ia->ri_device->attrs.max_qp_wr;
+        max_qp_wr -= RPCRDMA_BACKWARD_WRS;
+        max_qp_wr -= 1;
+        if (max_qp_wr < RPCRDMA_MIN_SLOT_TABLE)
+                return -ENOMEM;
+        if (cdata->max_requests > max_qp_wr)
+                cdata->max_requests = max_qp_wr;
+        ep->rep_attr.cap.max_send_wr = cdata->max_requests;
+        ep->rep_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;
+        ep->rep_attr.cap.max_send_wr += 1; /* for ib_drain_sq */
+        ep->rep_attr.cap.max_recv_wr = cdata->max_requests;
+        ep->rep_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
+        ep->rep_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */
+
         ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
                                 RPCRDMA_MAX_FMR_SGES);
         return 0;
diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
index c5743a0960be..0f2e108d387e 100644
--- a/net/sunrpc/xprtrdma/frwr_ops.c
+++ b/net/sunrpc/xprtrdma/frwr_ops.c
@@ -205,12 +205,22 @@ out_release:
         frwr_op_release_mr(mr);
 }
 
+/* On success, sets:
+ *      ep->rep_attr.cap.max_send_wr
+ *      ep->rep_attr.cap.max_recv_wr
+ *      cdata->max_requests
+ *      ia->ri_max_segs
+ *
+ * And these FRWR-related fields:
+ *      ia->ri_max_frwr_depth
+ *      ia->ri_mrtype
+ */
 static int
 frwr_op_open(struct rpcrdma_ia *ia, struct rpcrdma_ep *ep,
              struct rpcrdma_create_data_internal *cdata)
 {
         struct ib_device_attr *attrs = &ia->ri_device->attrs;
-        int depth, delta;
+        int max_qp_wr, depth, delta;
 
         ia->ri_mrtype = IB_MR_TYPE_MEM_REG;
         if (attrs->device_cap_flags & IB_DEVICE_SG_GAPS_REG)
@@ -244,14 +254,26 @@ frwr_op_open(struct rpcrdma_ia *ia, struct rpcrdma_ep *ep,
                 } while (delta > 0);
         }
 
-        ep->rep_attr.cap.max_send_wr *= depth;
-        if (ep->rep_attr.cap.max_send_wr > attrs->max_qp_wr) {
-                cdata->max_requests = attrs->max_qp_wr / depth;
+        max_qp_wr = ia->ri_device->attrs.max_qp_wr;
+        max_qp_wr -= RPCRDMA_BACKWARD_WRS;
+        max_qp_wr -= 1;
+        if (max_qp_wr < RPCRDMA_MIN_SLOT_TABLE)
+                return -ENOMEM;
+        if (cdata->max_requests > max_qp_wr)
+                cdata->max_requests = max_qp_wr;
+        ep->rep_attr.cap.max_send_wr = cdata->max_requests * depth;
+        if (ep->rep_attr.cap.max_send_wr > max_qp_wr) {
+                cdata->max_requests = max_qp_wr / depth;
                 if (!cdata->max_requests)
                         return -EINVAL;
                 ep->rep_attr.cap.max_send_wr = cdata->max_requests *
                                                depth;
         }
+        ep->rep_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;
+        ep->rep_attr.cap.max_send_wr += 1; /* for ib_drain_sq */
+        ep->rep_attr.cap.max_recv_wr = cdata->max_requests;
+        ep->rep_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
+        ep->rep_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */
 
         ia->ri_max_segs = max_t(unsigned int, 1, RPCRDMA_MAX_DATA_SEGS /
                                 ia->ri_max_frwr_depth);
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 07529ef8e33e..62baddefced3 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -501,8 +501,8 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
                   struct rpcrdma_create_data_internal *cdata)
 {
         struct rpcrdma_connect_private *pmsg = &ep->rep_cm_private;
-        unsigned int max_qp_wr, max_sge;
         struct ib_cq *sendcq, *recvcq;
+        unsigned int max_sge;
         int rc;
 
         max_sge = min_t(unsigned int, ia->ri_device->attrs.max_sge,
@@ -513,29 +513,13 @@ rpcrdma_ep_create(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia,
         }
         ia->ri_max_send_sges = max_sge;
 
-        if (ia->ri_device->attrs.max_qp_wr <= RPCRDMA_BACKWARD_WRS) {
-                dprintk("RPC:       %s: insufficient wqe's available\n",
-                        __func__);
-                return -ENOMEM;
-        }
-        max_qp_wr = ia->ri_device->attrs.max_qp_wr - RPCRDMA_BACKWARD_WRS - 1;
-
-        /* check provider's send/recv wr limits */
-        if (cdata->max_requests > max_qp_wr)
-                cdata->max_requests = max_qp_wr;
+        rc = ia->ri_ops->ro_open(ia, ep, cdata);
+        if (rc)
+                return rc;
 
         ep->rep_attr.event_handler = rpcrdma_qp_async_error_upcall;
         ep->rep_attr.qp_context = ep;
         ep->rep_attr.srq = NULL;
-        ep->rep_attr.cap.max_send_wr = cdata->max_requests;
-        ep->rep_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;
-        ep->rep_attr.cap.max_send_wr += 1;      /* drain cqe */
-        rc = ia->ri_ops->ro_open(ia, ep, cdata);
-        if (rc)
-                return rc;
-        ep->rep_attr.cap.max_recv_wr = cdata->max_requests;
-        ep->rep_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
-        ep->rep_attr.cap.max_recv_wr += 1;      /* drain cqe */
         ep->rep_attr.cap.max_send_sge = max_sge;
         ep->rep_attr.cap.max_recv_sge = 1;
         ep->rep_attr.cap.max_inline_data = 0;