From: =?UTF-8?q?H=C3=A5kon=20Bugge?= <haakon.bugge@oracle.com>
Date: Thu, 12 Aug 2021 18:12:35 +0200
Subject: RDMA/core/sa_query: Retry SA queries
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v5.15-rc1
Git-commit: 5f5a650999d5718af766fc70a120230b04235a6f
References: jsc#SLE-19249

A MAD packet is sent as an unreliable datagram (UD). SA requests are sent
as MAD packets. As such, SA requests or responses may be silently dropped.

IB Core's MAD layer has a timeout and retry mechanism, which amongst
other, is used by RDMA CM. But it is not used by SA queries. The lack of
retries of SA queries leads to long specified timeout, and error being
returned in case of packet loss. The ULP or user-land process has to
perform the retry.

Fix this by taking advantage of the MAD layer's retry mechanism.

First, a check against a zero timeout is added in rdma_resolve_route(). In
send_mad(), we set the MAD layer timeout to one tenth of the specified
timeout and the number of retries to 10. The special case when timeout is
less than 10 is handled.

With this fix:

 # ucmatose -c 1000 -S 1024 -C 1

runs stable on an Infiniband fabric. Without this fix, we see an
intermittent behavior and it errors out with:

cmatose: event: RDMA_CM_EVENT_ROUTE_ERROR, error: -110

(110 is ETIMEDOUT)

Link: https://lore.kernel.org/r/1628784755-28316-1-git-send-email-haakon.bugge@oracle.com
Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/infiniband/core/cma.c      |    3 +++
 drivers/infiniband/core/sa_query.c |    9 ++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -3132,6 +3132,9 @@ int rdma_resolve_route(struct rdma_cm_id
 	struct rdma_id_private *id_priv;
 	int ret;
 
+	if (!timeout_ms)
+		return -EINVAL;
+
 	id_priv = container_of(id, struct rdma_id_private, id);
 	if (!cma_comp_exch(id_priv, RDMA_CM_ADDR_RESOLVED, RDMA_CM_ROUTE_QUERY))
 		return -EINVAL;
--- a/drivers/infiniband/core/sa_query.c
+++ b/drivers/infiniband/core/sa_query.c
@@ -1304,6 +1304,7 @@ static int send_mad(struct ib_sa_query *
 {
 	unsigned long flags;
 	int ret, id;
+	const int nmbr_sa_query_retries = 10;
 
 	xa_lock_irqsave(&queries, flags);
 	ret = __xa_alloc(&queries, &id, query, xa_limit_32b, gfp_mask);
@@ -1311,7 +1312,13 @@ static int send_mad(struct ib_sa_query *
 	if (ret < 0)
 		return ret;
 
-	query->mad_buf->timeout_ms  = timeout_ms;
+	query->mad_buf->timeout_ms  = timeout_ms / nmbr_sa_query_retries;
+	query->mad_buf->retries = nmbr_sa_query_retries;
+	if (!query->mad_buf->timeout_ms) {
+		/* Special case, very small timeout_ms */
+		query->mad_buf->timeout_ms = 1;
+		query->mad_buf->retries = timeout_ms;
+	}
 	query->mad_buf->context[0] = query;
 	query->id = id;