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

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Message-ID: <5FF5EDEE-FF34-43E0-9DFA-6CBDB206360D@fb.com>
Date:   Wed, 1 Nov 2017 13:47:17 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
CC:     Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tcp_nv: fix division by zero in tcpnv_acked()

Thank you for finding and fixing this.

On 11/1/17, 6:32 AM, "Konstantin Khlebnikov" <khlebnikov@...dex-team.ru> wrote:

    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
Acked-by: Lawrence Brakmo <Brakmo@...com>
    ---
     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