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

[Jason Xing <kerneljasonxing@gmail.com>]

Hi Eric,

I'm sorry that I didn't write enough clearly. We're running the
pristine 4.19.125 linux kernel (the latest LTS version) and have been
haunted by such an issue. This patch is high-important, I think. So
I'm going to resend this email with the [patch 4.19] on the headline
and cc Greg.

Thanks,
Jason

On Tue, Jun 2, 2020 at 9:05 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Tue, Jun 2, 2020 at 1:05 AM <kerneljasonxing@gmail.com> wrote:
> >
> > From: Jason Xing <kerneljasonxing@gmail.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@gmail.com>
> > Signed-off-by: liweishi <liweishi@kuaishou.com>
> > Signed-off-by: Shujin Li <lishujin@kuaishou.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.