[PATCH v2] RDMA/rtrs-clt: Fix recv repost to satisfy ib_drain_rq

[Quanye Yang via B4 Relay]

From: Quanye Yang <quanyeyang@xxxxxxxxx>

On disconnect the client error recovery path calls ib_drain_qp(), which
requires one free RQ slot and that no recv WQEs are posted while the
queue is being drained.

When the server is loaded with always_invalidate=N, the path does not
advertise RTRS_MSG_NEW_RKEY_F.  A client-requested invalidation is then
a standalone SEND_WITH_INV.  The recv completion path did not repost
that WQE; it posted two empty recv WQEs later, when the RDMA-with-IMM
response carried RTRS_IO_RSP_W_INV_IMM.  If the invalidate receive
never arrived, each such response increased RQ occupancy by one until
ib_post_recv() started returning -ENOMEM and __ib_drain_rq() failed
with:

  failed to drain recv queue: -12

Repost one empty recv WQE for every receive completion, including
SEND_WITH_INV completions on the always_invalidate=N path, and only
while the path is still connected so CQ polling cannot race with
ib_drain_qp().  Size IO connection RQs to 2 * queue_depth + 1 to match
the posted recv count and leave the drain slot.

Tested with a synthetic RTRS client flooding unpaired
RTRS_IO_RSP_W_INV_IMM messages; error recovery no longer triggers
__ib_drain_rq() warnings.

Fixes: 6a98d71daea1 ("RDMA/rtrs: client: main functionality")
Signed-off-by: Quanye Yang <quanyeyang@xxxxxxxxx>
Tested-by: Quanye Yang <quanyeyang@xxxxxxxxx>
Reported-by: Farhad Alemi <farhad.alemi@xxxxxxxxxxxx>
Link: https://lore.kernel.org/linux-rdma/CA+0ovCihE2_pxLimjmmR8NMz4g-ie8dvvq1jmAj-Om33y3Vzfg@xxxxxxxxxxxxxx
Acked-by: Jack Wang <jinpu.wang@xxxxxxxxxxxxxxx>
---
Changes in v2:
- Clarify that the broken recv-repost path is always_invalidate=N
  (no RTRS_MSG_NEW_RKEY_F).
- Collect Acked-by from Jack Wang.
- Link to v1: https://patch.msgid.link/20260921-rtrs-fix-ib-drain-rq-v1-1-11b1637958ba@xxxxxxxxx
---
 drivers/infiniband/ulp/rtrs/rtrs-clt.c | 45 ++++++++++++----------------------
 1 file changed, 15 insertions(+), 30 deletions(-)

diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
index eac38b57b00d..ee6d5c3de16c 100644
--- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
+++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
@@ -577,25 +577,21 @@ static struct ib_cqe io_comp_cqe = {
 	.done = rtrs_clt_rdma_done
 };
 
-/*
- * Post x2 empty WRs: first is for this RDMA with IMM,
- * second is for RECV with INV, which happened earlier.
- */
-static int rtrs_post_recv_empty_x2(struct rtrs_con *con, struct ib_cqe *cqe)
+static int rtrs_clt_repost_recv(struct rtrs_clt_con *con)
 {
-	struct ib_recv_wr wr_arr[2], *wr;
-	int i;
+	struct rtrs_clt_path *clt_path = to_clt_path(con->c.path);
+	int err;
 
-	memset(wr_arr, 0, sizeof(wr_arr));
-	for (i = 0; i < ARRAY_SIZE(wr_arr); i++) {
-		wr = &wr_arr[i];
-		wr->wr_cqe  = cqe;
-		if (i)
-			/* Chain backwards */
-			wr->next = &wr_arr[i - 1];
-	}
+	if (READ_ONCE(clt_path->state) != RTRS_CLT_CONNECTED)
+		return 0;
 
-	return ib_post_recv(con->qp, wr, NULL);
+	err = rtrs_post_recv_empty(&con->c, &io_comp_cqe);
+	if (err) {
+		rtrs_err(con->c.path, "rtrs_post_recv_empty(): %pe\n",
+			 ERR_PTR(err));
+		rtrs_rdma_error_recovery(con);
+	}
+	return err;
 }
 
 static void rtrs_clt_rdma_done(struct ib_cq *cq, struct ib_wc *wc)
@@ -650,19 +646,7 @@ static void rtrs_clt_rdma_done(struct ib_cq *cq, struct ib_wc *wc)
 			rtrs_wrn(con->c.path, "Unknown IMM type %u\n",
 				  imm_type);
 		}
-		if (w_inval)
-			/*
-			 * Post x2 empty WRs: first is for this RDMA with IMM,
-			 * second is for RECV with INV, which happened earlier.
-			 */
-			err = rtrs_post_recv_empty_x2(&con->c, &io_comp_cqe);
-		else
-			err = rtrs_post_recv_empty(&con->c, &io_comp_cqe);
-		if (err) {
-			rtrs_err(con->c.path, "rtrs_post_recv_empty(): %pe\n",
-				 ERR_PTR(err));
-			rtrs_rdma_error_recovery(con);
-		}
+		rtrs_clt_repost_recv(con);
 		break;
 	case IB_WC_RECV:
 		/*
@@ -678,6 +662,7 @@ static void rtrs_clt_rdma_done(struct ib_cq *cq, struct ib_wc *wc)
 
 			return  rtrs_clt_rkey_rsp_done(con, wc);
 		}
+		rtrs_clt_repost_recv(con);
 		break;
 	case IB_WC_RDMA_WRITE:
 		/*
@@ -1693,7 +1678,7 @@ static int create_con_cq_qp(struct rtrs_clt_con *con)
 		clt_path->s.dev_ref++;
 		/* QD * (REQ + RSP + FR REGS or INVS) + drain */
 		max_send_wr = min(wr_limit, clt_path->queue_depth * 4 + 1);
-		max_recv_wr = min(wr_limit, clt_path->queue_depth * 3 + 1);
+		max_recv_wr = min(wr_limit, clt_path->queue_depth * 2 + 1);
 		max_send_sge = 2;
 	}
 	atomic_set(&con->c.sq_wr_avail, max_send_wr);

---
base-commit: 93f51579e7df248780214094418f205253383cc5
change-id: 20260921-rtrs-fix-ib-drain-rq-61dc85d0d759

Best regards,
--  
Quanye Yang <quanyeyang@xxxxxxxxx>