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From:   Jason Xing <kerneljasonxing@gmail.com>
Date:   Thu, 4 Jun 2020 21:47:36 +0800
Message-ID: <CAL+tcoCU157eGmMMabT5icdFJTMEWymNUNxHBbxY1OTir0=0FQ@mail.gmail.com>
Subject: Re: [PATCH v2 4.19] tcp: fix TCP socks unreleased in BBR mode
To:     Eric Dumazet <edumazet@google.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Neal Cardwell <ncardwell@google.com>,
        David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        liweishi <liweishi@kuaishou.com>,
        Shujin Li <lishujin@kuaishou.com>
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On Thu, Jun 4, 2020 at 9:10 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Thu, Jun 4, 2020 at 2:01 AM <kerneljasonxing@gmail.com> wrote:
> >
> > From: Jason Xing <kerneljasonxing@gmail.com>
> >
> > When using BBR mode, too many tcp socks cannot be released because of
> > duplicate use of the sock_hold() in the manner of tcp_internal_pacing()
> > when RTO happens. Therefore, this situation maddly increases the slab
> > memory and then constantly triggers the OOM until crash.
> >
> > Besides, in addition to BBR mode, if some mode applies pacing function,
> > it could trigger what we've discussed above,
> >
> > Reproduce procedure:
> > 0) cat /proc/slabinfo | grep TCP
> > 1) switch net.ipv4.tcp_congestion_control to bbr
> > 2) using wrk tool something like that to send packages
> > 3) using tc to increase the delay and loss to simulate the RTO case.
> > 4) cat /proc/slabinfo | grep TCP
> > 5) kill the wrk command and observe the number of objects and slabs in
> > TCP.
> > 6) at last, you could notice that the number would not decrease.
> >
> > v2: extend the timer which could cover all those related potential risks
> > (suggested by Eric Dumazet and Neal Cardwell)
> >
> > Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
> > Signed-off-by: liweishi <liweishi@kuaishou.com>
> > Signed-off-by: Shujin Li <lishujin@kuaishou.com>
>
> That is not how things work really.
>
> I will submit this properly so that stable teams do not have to guess
> how to backport this to various kernels.
>
> Changelog is misleading, this has nothing to do with BBR, we need to be precise.
>

Thanks for your help. I can finally apply this patch into my kernel.

Looking forward to your patchset :)

Jason

> Thank you.