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Date: Wed, 1 Nov 2017 15:13:51 +0100 From: Stephen Hemminger <stephen@...workplumber.org> To: Lawrence Brakmo <brakmo@...com> Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, 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() On Wed, 1 Nov 2017 13:47:17 +0000 Lawrence Brakmo <brakmo@...com> wrote: > 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); Why is this code using expensive 64 bit by 64 bit divide when avg_rtt should never be bigger than 32 bits?
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