[PATCH net-next] net/dim: Fix fixpoint divide exception in net_dim_stats_compare

[PATCH net-next] net/dim: Fix fixpoint divide exception in net_dim_stats_compare

[Tal Gilboa]

From: Talat Batheesh <talatb@mellanox.com>

Helmut reported a bug about devision 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 devision by zero.

This patch prevent this division for both ppms and epms.

Fixes: c3164d2fc48f ("net/mlx5e: Added BW check for DIM decision mechanism")
Fixes: 4c4dbb4a7363 ("net/mlx5e: Move dynamic interrupt coalescing code to include/linux")
Reported-by: Helmut Grauer <helmut.grauer@de.ibm.com>
Signed-off-by: Talat Batheesh <talatb@mellanox.com>
Signed-off-by: Tal Gilboa <talgi@mellanox.com>
---
 include/linux/net_dim.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/linux/net_dim.h b/include/linux/net_dim.h
index 1c7e450..bebeaad 100644
--- a/include/linux/net_dim.h
+++ b/include/linux/net_dim.h
@@ -244,10 +244,17 @@ static inline int net_dim_stats_compare(struct net_dim_stats *curr,
 		return (curr->bpms > prev->bpms) ? NET_DIM_STATS_BETTER :
 						   NET_DIM_STATS_WORSE;
 
+	if (!prev->ppms)
+		return curr->ppms ? NET_DIM_STATS_BETTER :
+				    NET_DIM_STATS_SAME;
+
 	if (IS_SIGNIFICANT_DIFF(curr->ppms, prev->ppms))
 		return (curr->ppms > prev->ppms) ? NET_DIM_STATS_BETTER :
 						   NET_DIM_STATS_WORSE;
 
+	if (!prev->epms)
+		return NET_DIM_STATS_SAME;
+
 	if (IS_SIGNIFICANT_DIFF(curr->epms, prev->epms))
 		return (curr->epms < prev->epms) ? NET_DIM_STATS_BETTER :
 						   NET_DIM_STATS_WORSE;
-- 
1.8.3.1

Re: [PATCH net-next] net/dim: Fix fixpoint divide exception in net_dim_stats_compare

[David Miller]

From: Tal Gilboa <talgi@mellanox.com>
Date: Wed, 17 Jan 2018 23:13:16 +0200

> From: Talat Batheesh <talatb@mellanox.com>
> 
> Helmut reported a bug about devision 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 devision by zero.
> 
> This patch prevent this division for both ppms and epms.
> 
> Fixes: c3164d2fc48f ("net/mlx5e: Added BW check for DIM decision mechanism")
> Fixes: 4c4dbb4a7363 ("net/mlx5e: Move dynamic interrupt coalescing code to include/linux")
> Reported-by: Helmut Grauer <helmut.grauer@de.ibm.com>
> Signed-off-by: Talat Batheesh <talatb@mellanox.com>
> Signed-off-by: Tal Gilboa <talgi@mellanox.com>

Applied, thanks.