net/mlx5e: Fix fixpoint divide exception in mlx5e_am_stats_compare

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@de.ibm.com>
Signed-off-by: Talat Batheesh <talatb@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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 e401d9d245f33e4187c2468f4533df052cdea5ec..b69a705fd787d9a78c19f11e866a866d341b926e 100644 (file)
--- 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 :