netdev - Re: [PATCH] tcp: fix TCP socks unreleased in BBR mode

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Date:   Tue, 2 Jun 2020 06:05:44 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     kerneljasonxing@...il.com
Cc:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, liweishi@...ishou.com,
        lishujin@...ishou.com
Subject: Re: [PATCH] tcp: fix TCP socks unreleased in BBR mode

On Tue, Jun 2, 2020 at 1:05 AM <kerneljasonxing@...il.com> wrote:
>
> From: Jason Xing <kerneljasonxing@...il.com>
>
> TCP socks cannot be released because of the sock_hold() increasing the
> sk_refcnt in the manner of tcp_internal_pacing() when RTO happens.
> Therefore, this situation could increase the slab memory and then trigger
> the OOM if the machine has beening running for a long time. This issue,
> however, can happen on some machine only running a few days.
>
> We add one exception case to avoid unneeded use of sock_hold if the
> pacing_timer is enqueued.
>
> 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 in the dev to simulate the busy 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.
>
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> Signed-off-by: liweishi <liweishi@...ishou.com>
> Signed-off-by: Shujin Li <lishujin@...ishou.com>
> ---
>  net/ipv4/tcp_output.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index cc4ba42..5cf63d9 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -969,7 +969,8 @@ static void tcp_internal_pacing(struct sock *sk, const struct sk_buff *skb)
>         u64 len_ns;
>         u32 rate;
>
> -       if (!tcp_needs_internal_pacing(sk))
> +       if (!tcp_needs_internal_pacing(sk) ||
> +           hrtimer_is_queued(&tcp_sk(sk)->pacing_timer))
>                 return;
>         rate = sk->sk_pacing_rate;
>         if (!rate || rate == ~0U)
> --
> 1.8.3.1
>

Hi Jason.

Please do not send patches that do not apply to current upstream trees.

Instead, backport to your kernels the needed fixes.

I suspect that you are not using a pristine linux kernel, but some
heavily modified one and something went wrong in your backports.
Do not ask us to spend time finding what went wrong.

Thank you.