linux-kernel - [PATCH] ntb_transport: fix qp count bug

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Message-Id: <20171209000106.18259-2-logang@deltatee.com>
Date:   Fri,  8 Dec 2017 17:01:05 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-ntb@...glegroups.com, linux-kernel@...r.kernel.org
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <Allen.Hubbe@....com>
Subject: [PATCH] ntb_transport: fix qp count bug

In cases where there are more mw's than spads/2-2, the mw count gets
reduced to match the limitation. ntb_transport also tries to ensure that
there are fewer qps than mws but uses the full mw count instead of
the reduced one. When this happens, the math in
'ntb_transport_setup_qp_mw' will get confused and result in a kernel
paging request bug.

This patch fixes the bug by reducing qp_count to the reduced mw count
instead of the full mw count.

Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Cc: Jon Mason <jdmason@...zu.us>
Cc: Dave Jiang <dave.jiang@...el.com>
Cc: Allen Hubbe <Allen.Hubbe@....com>
---
 drivers/ntb/ntb_transport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index 02ca45fdd892..0a778d2cab94 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -1128,8 +1128,8 @@ static int ntb_transport_probe(struct ntb_client *self, struct ntb_dev *ndev)
 	qp_count = ilog2(qp_bitmap);
 	if (max_num_clients && max_num_clients < qp_count)
 		qp_count = max_num_clients;
-	else if (mw_count < qp_count)
-		qp_count = mw_count;
+	else if (nt->mw_count < qp_count)
+		qp_count = nt->mw_count;
 
 	qp_bitmap &= BIT_ULL(qp_count) - 1;
 
-- 
2.11.0