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Message-ID: <CANn89iJuV1Q3tOJ-UFedQgdfdw=cAWfyE5x=LKE1V-jD5UDf+A@mail.gmail.com> Date: Fri, 11 Aug 2023 09:38:22 +0200 From: Eric Dumazet <edumazet@...gle.com> To: menglong8.dong@...il.com Cc: ncardwell@...gle.com, davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, dsahern@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, flyingpeng@...cent.com, Menglong Dong <imagedong@...cent.com> Subject: Re: [PATCH net-next v4 3/4] net: tcp: fix unexcepted socket die when snd_wnd is 0 On Fri, Aug 11, 2023 at 5:01 AM <menglong8.dong@...il.com> wrote: > > From: Menglong Dong <imagedong@...cent.com> > > In tcp_retransmit_timer(), a window shrunk connection will be regarded > as timeout if 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX'. This is not > right all the time. > > The retransmits will become zero-window probes in tcp_retransmit_timer() > if the 'snd_wnd==0'. Therefore, the icsk->icsk_rto will come up to > TCP_RTO_MAX sooner or later. > > However, the timer can be delayed and be triggered after 122877ms, not > TCP_RTO_MAX, as I tested. > > Therefore, 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX' is always true > once the RTO come up to TCP_RTO_MAX, and the socket will die. > > Fix this by replacing the 'tcp_jiffies32' with '(u32)icsk->icsk_timeout', > which is exact the timestamp of the timeout. > > However, "tp->rcv_tstamp" can restart from idle, then tp->rcv_tstamp > could already be a long time (minutes or hours) in the past even on the > first RTO. So we double check the timeout with the duration of the > retransmission. > > Meanwhile, making "2 * TCP_RTO_MAX" as the timeout to avoid the socket > dying too soon. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Link: https://lore.kernel.org/netdev/CADxym3YyMiO+zMD4zj03YPM3FBi-1LHi6gSD2XT8pyAMM096pg@mail.gmail.com/ > Signed-off-by: Menglong Dong <imagedong@...cent.com> Reviewed-by: Eric Dumazet <edumazet@...gle.com>
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