netdev - [PATCH net V2] net/mlx5e: Fix fixpoint divide exception in mlx5e_am_stats

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Message-Id: <20180121033042.9091-1-saeedm@mellanox.com>
Date:   Sun, 21 Jan 2018 05:30:42 +0200
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Talat Batheesh <talatb@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: [PATCH net V2] net/mlx5e: Fix fixpoint divide exception in mlx5e_am_stats_compare

From: Talat Batheesh <talatb@...lanox.com>

Helmut reported a bug about division by zero while
running traffic and doing physical cable pull test.

When the cable unplugged the ppms become zero, so when
dividing the current ppms by the previous ppms in the
next dim iteration there is division by zero.

This patch prevent this division for both ppms and epms.

Fixes: c3164d2fc48f ("net/mlx5e: Added BW check for DIM decision mechanism")
Reported-by: Helmut Grauer <helmut.grauer@...ibm.com>
Signed-off-by: Talat Batheesh <talatb@...lanox.com>
Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
---
v2:
    - Fix spelling in commit message.

This patch is the equivalent of:
("net/dim: Fix fixpoint divide exception in net_dim_stats_compare")
which was already submitted to net-next. Since mlx5 irq moderation code
got moved in net-next, this patch should only go to net and skip net-next.

for -stable: 4.12.y and later.

 drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
index e401d9d245f3..b69a705fd787 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
@@ -201,9 +201,15 @@ static int mlx5e_am_stats_compare(struct mlx5e_rx_am_stats *curr,
 		return (curr->bpms > prev->bpms) ? MLX5E_AM_STATS_BETTER :
 						   MLX5E_AM_STATS_WORSE;
 
+	if (!prev->ppms)
+		return curr->ppms ? MLX5E_AM_STATS_BETTER :
+				    MLX5E_AM_STATS_SAME;
+
 	if (IS_SIGNIFICANT_DIFF(curr->ppms, prev->ppms))
 		return (curr->ppms > prev->ppms) ? MLX5E_AM_STATS_BETTER :
 						   MLX5E_AM_STATS_WORSE;
+	if (!prev->epms)
+		return MLX5E_AM_STATS_SAME;
 
 	if (IS_SIGNIFICANT_DIFF(curr->epms, prev->epms))
 		return (curr->epms < prev->epms) ? MLX5E_AM_STATS_BETTER :
-- 
2.13.0