netdev - Re: [PATCH net 1/1] tcp: check skb is non-NULL in tcp_rto_delta

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Message-ID: <CAL+tcoB=wdX7-O7x_xOzpBgfxKLvYwjvLo-dve=+bRAfgL4OrA@mail.gmail.com>
Date: Fri, 23 Aug 2024 15:36:13 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Josh Hunt <johunt@...mai.com>, Neal Cardwell <ncardwell@...gle.com>, davem@...emloft.net, 
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/1] tcp: check skb is non-NULL in tcp_rto_delta_us()

On Fri, Aug 23, 2024 at 2:44 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Aug 23, 2024 at 4:14 AM Josh Hunt <johunt@...mai.com> wrote:
> >
> > There have been multiple occassions where we have crashed in this path
> > because packets_out suggested there were packets on the write or retransmit
> > queues, but in fact there weren't leading to a NULL skb being dereferenced.
> > While we should fix that root cause we should also just make sure the skb
> > is not NULL before dereferencing it. Also add a warn once here to capture
> > some information if/when the problem case is hit again.
> >
> > Signed-off-by: Josh Hunt <johunt@...mai.com>
> > ---
> >  include/net/tcp.h | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/net/tcp.h b/include/net/tcp.h
> > index 2aac11e7e1cc..19ea6ed87880 100644
> > --- a/include/net/tcp.h
> > +++ b/include/net/tcp.h
> > @@ -2433,10 +2433,19 @@ void tcp_plb_update_state_upon_rto(struct sock *sk, struct tcp_plb_state *plb);
> >  static inline s64 tcp_rto_delta_us(const struct sock *sk)
> >  {
> >         const struct sk_buff *skb = tcp_rtx_queue_head(sk);
> > -       u32 rto = inet_csk(sk)->icsk_rto;
> > -       u64 rto_time_stamp_us = tcp_skb_timestamp_us(skb) + jiffies_to_usecs(rto);
> > +       u32 rto = jiffies_to_usecs(inet_csk(sk)->icsk_rto);
> > +
> > +       if (likely(skb)) {
> > +               u64 rto_time_stamp_us = tcp_skb_timestamp_us(skb) + rto;
> > +
> > +               return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;
> > +       } else {
> > +               WARN_ONCE(1,
> > +                       "rtx queue emtpy: inflight %u tlp_high_seq %u state %u\n",
> > +                       tcp_sk(sk)->packets_out, tcp_sk(sk)->tlp_high_seq, sk->sk_state);
> > +               return rto;
> > +       }
> >
> > -       return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;
> >  }
> >
> >  /*
> > --
> > 2.34.1
> >
>
> Are you using a recent linux kernel version ?

I'm afraid that he doesn't. What that link shows to me is the
5.4.0-174-generic ubuntu kernel.