[PATCH v3 4/7] xprtrdma: Decouple frwr_wp_create from frwr_map

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

frwr_wp_create is the only caller of frwr_map outside the encode
path. It registers a single 4-byte write-pad region from a stack-
local rpcrdma_mr_seg. Inlining the registration logic directly
(sg_init_table + sg_set_page + ib_dma_map_sg + ib_map_mr_sg +
IOVA mangle + reg_wr setup) eliminates the coupling that would
otherwise complicate the removal of rpcrdma_mr_seg from frwr_map's
interface.

The inlined version adds a proper error-unwind ladder: on failure,
the DMA mapping (if established) is released, ep->re_write_pad_mr is
cleared, and the MR is returned to the transport free list. The old
frwr_map-based code relied on rpcrdma_mrs_destroy at teardown to
reclaim partially-initialized MRs.

This is a one-time setup path; duplicating ~20 lines is a reasonable
tradeoff for decoupling the write-pad registration from the data-
path MR registration.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/frwr_ops.c | 57 +++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 7 deletions(-)

diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
index 31434aeb8e29..4331b0b65f4c 100644
--- a/net/sunrpc/xprtrdma/frwr_ops.c
+++ b/net/sunrpc/xprtrdma/frwr_ops.c
@@ -669,9 +669,13 @@ void frwr_unmap_async(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
  */
 int frwr_wp_create(struct rpcrdma_xprt *r_xprt)
 {
+	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
 	struct rpcrdma_ep *ep = r_xprt->rx_ep;
-	struct rpcrdma_mr_seg seg;
+	struct ib_reg_wr *reg_wr;
 	struct rpcrdma_mr *mr;
+	struct ib_mr *ibmr;
+	int dma_nents;
+	int ret;
 
 	mr = rpcrdma_mr_get(r_xprt);
 	if (!mr)
@@ -679,11 +683,39 @@ int frwr_wp_create(struct rpcrdma_xprt *r_xprt)
 	mr->mr_req = NULL;
 	ep->re_write_pad_mr = mr;
 
-	seg.mr_len = XDR_UNIT;
-	seg.mr_page = virt_to_page(ep->re_write_pad);
-	seg.mr_offset = offset_in_page(ep->re_write_pad);
-	if (IS_ERR(frwr_map(r_xprt, &seg, 1, true, xdr_zero, mr)))
-		return -EIO;
+	sg_init_table(mr->mr_sg, 1);
+	sg_set_page(mr->mr_sg, virt_to_page(ep->re_write_pad),
+		    XDR_UNIT, offset_in_page(ep->re_write_pad));
+
+	mr->mr_dir = DMA_FROM_DEVICE;
+	mr->mr_nents = 1;
+	dma_nents = ib_dma_map_sg(ep->re_id->device, mr->mr_sg,
+				  mr->mr_nents, mr->mr_dir);
+	if (!dma_nents) {
+		ret = -EIO;
+		goto out_mr;
+	}
+	mr->mr_device = ep->re_id->device;
+
+	ibmr = mr->mr_ibmr;
+	if (ib_map_mr_sg(ibmr, mr->mr_sg, dma_nents, NULL,
+			 PAGE_SIZE) != dma_nents) {
+		ret = -EIO;
+		goto out_unmap;
+	}
+
+	/* IOVA is not tagged with an XID; the write-pad is not RPC-specific. */
+	ib_update_fast_reg_key(ibmr, ib_inc_rkey(ibmr->rkey));
+
+	reg_wr = &mr->mr_regwr;
+	reg_wr->mr = ibmr;
+	reg_wr->key = ibmr->rkey;
+	reg_wr->access = IB_ACCESS_REMOTE_WRITE | IB_ACCESS_LOCAL_WRITE;
+
+	mr->mr_handle = ibmr->rkey;
+	mr->mr_length = ibmr->length;
+	mr->mr_offset = ibmr->iova;
+
 	trace_xprtrdma_mr_fastreg(mr);
 
 	mr->mr_cqe.done = frwr_wc_fastreg;
@@ -693,5 +725,16 @@ int frwr_wp_create(struct rpcrdma_xprt *r_xprt)
 	mr->mr_regwr.wr.opcode = IB_WR_REG_MR;
 	mr->mr_regwr.wr.send_flags = 0;
 
-	return ib_post_send(ep->re_id->qp, &mr->mr_regwr.wr, NULL);
+	ret = ib_post_send(ep->re_id->qp, &mr->mr_regwr.wr, NULL);
+	if (!ret)
+		return 0;
+
+out_unmap:
+	frwr_mr_unmap(mr);
+out_mr:
+	ep->re_write_pad_mr = NULL;
+	spin_lock(&buf->rb_lock);
+	rpcrdma_mr_push(mr, &buf->rb_mrs);
+	spin_unlock(&buf->rb_lock);
+	return ret;
 }
-- 
2.53.0