linux-kernel - [PATCH AUTOSEL 4.4 11/14] RDMA/core/sa

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Date:   Thu,  9 Sep 2021 20:24:00 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Håkon Bugge <haakon.bugge@...cle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Sasha Levin <sashal@...nel.org>, linux-rdma@...r.kernel.org
Subject: [PATCH AUTOSEL 4.4 11/14] RDMA/core/sa_query: Retry SA queries

From: Håkon Bugge <haakon.bugge@...cle.com>

[ Upstream commit 5f5a650999d5718af766fc70a120230b04235a6f ]

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@...cle.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/infiniband/core/cma.c      | 3 +++
 drivers/infiniband/core/sa_query.c | 9 ++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index b5e7bd23857e..88a59557cabd 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -2390,6 +2390,9 @@ int rdma_resolve_route(struct rdma_cm_id *id, int timeout_ms)
 	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;
diff --git a/drivers/infiniband/core/sa_query.c b/drivers/infiniband/core/sa_query.c
index d3b7ecd106f7..070b1ab80674 100644
--- a/drivers/infiniband/core/sa_query.c
+++ b/drivers/infiniband/core/sa_query.c
@@ -1091,6 +1091,7 @@ static int send_mad(struct ib_sa_query *query, int timeout_ms, gfp_t gfp_mask)
 	bool preload = gfpflags_allow_blocking(gfp_mask);
 	unsigned long flags;
 	int ret, id;
+	const int nmbr_sa_query_retries = 10;
 
 	if (preload)
 		idr_preload(gfp_mask);
@@ -1104,7 +1105,13 @@ static int send_mad(struct ib_sa_query *query, int timeout_ms, gfp_t gfp_mask)
 	if (id < 0)
 		return id;
 
-	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;
 
-- 
2.30.2