linux-kernel - [PATCH 3.12 22/66] ib_isert: Add max_send_sge=2 minimum for control PDU responses

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Message-Id: <bad84a260c714cb8f5ded73c9d24aeee0b153199.1417878427.git.jslaby@suse.cz>
Date:	Sat,  6 Dec 2014 16:07:14 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Or Gerlitz <ogerlitz@...lanox.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 22/66] ib_isert: Add max_send_sge=2 minimum for control PDU responses

From: Or Gerlitz <ogerlitz@...lanox.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit f57915cfa5b2b14c1cffa2e83c034f55e3f0e70d upstream.

This patch adds a max_send_sge=2 minimum in isert_conn_setup_qp()
to ensure outgoing control PDU responses with tx_desc->num_sge=2
are able to function correctly.

This addresses a bug with RDMA hardware using dev_attr.max_sge=3,
that in the original code with the ConnectX-2 work-around would
result in isert_conn->max_sge=1 being negotiated.

Originally reported by Chris with ocrdma driver.

Reported-by: Chris Moore <Chris.Moore@...lex.com>
Tested-by: Chris Moore <Chris.Moore@...lex.com>
Signed-off-by: Or Gerlitz <ogerlitz@...lanox.com>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/infiniband/ulp/isert/ib_isert.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
index 7db40f85eeff..2c14232447e4 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.c
+++ b/drivers/infiniband/ulp/isert/ib_isert.c
@@ -111,9 +111,12 @@ isert_conn_setup_qp(struct isert_conn *isert_conn, struct rdma_cm_id *cma_id)
 	attr.cap.max_recv_wr = ISERT_QP_MAX_RECV_DTOS;
 	/*
 	 * FIXME: Use devattr.max_sge - 2 for max_send_sge as
-	 * work-around for RDMA_READ..
+	 * work-around for RDMA_READs with ConnectX-2.
+	 *
+	 * Also, still make sure to have at least two SGEs for
+	 * outgoing control PDU responses.
 	 */
-	attr.cap.max_send_sge = device->dev_attr.max_sge - 2;
+	attr.cap.max_send_sge = max(2, device->dev_attr.max_sge - 2);
 	isert_conn->max_sge = attr.cap.max_send_sge;
 
 	attr.cap.max_recv_sge = 1;
-- 
2.1.3

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