linux-kernel - [PATCH] tcp_nv: fix division by zero in tcpnv

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Date:   Wed, 01 Nov 2017 16:32:15 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:     Lawrence Brakmo <brakmo@...com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

Average RTT could become zero. This happened in real life at least twice.
This patch treats zero as 1us.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
---
 net/ipv4/tcp_nv.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
index 1ff73982e28c..125fc1450b01 100644
--- a/net/ipv4/tcp_nv.c
+++ b/net/ipv4/tcp_nv.c
@@ -252,7 +252,7 @@ static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
 
 	/* rate in 100's bits per second */
 	rate64 = ((u64)sample->in_flight) * 8000000;
-	rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100));
+	rate = (u32)div64_u64(rate64, (u64)(avg_rtt ?: 1) * 100);
 
 	/* Remember the maximum rate seen during this RTT
 	 * Note: It may be more than one RTT. This function should be