[PATCH 4.14 51/71] net/mlx5e: Fix fixpoint divide exception in mlx5e_am_stats_compare

[Greg Kroah-Hartman]

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

------------------

From: Talat Batheesh <talatb@xxxxxxxxxxxx>


[ Upstream commit e58edaa4863583b54409444f11b4f80dff0af1cd ]

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@xxxxxxxxxx>
Signed-off-by: Talat Batheesh <talatb@xxxxxxxxxxxx>
Signed-off-by: Saeed Mahameed <saeedm@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx_am.c
@@ -197,9 +197,15 @@ static int mlx5e_am_stats_compare(struct
 		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 :