netdev - Re: [PATCH net-next 2/2] tcp: factorize logic into tcp_epollin

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Message-ID: <CANn89iK7U69XKZVFS2PXUSZhck5xaRE-hkxVe7Q1pbaE8m1cZw@mail.gmail.com>
Date:   Sat, 13 Feb 2021 09:04:55 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Wei Wang <weiwan@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>, Arjun Roy <arjunroy@...gle.com>
Subject: Re: [PATCH net-next 2/2] tcp: factorize logic into tcp_epollin_ready()

On Sat, Feb 13, 2021 at 8:50 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Sat, Feb 13, 2021 at 1:30 AM Wei Wang <weiwan@...gle.com> wrote:
> >
>
> > >  void tcp_data_ready(struct sock *sk)
> > >  {
> > > -       const struct tcp_sock *tp = tcp_sk(sk);
> > > -       int avail = tp->rcv_nxt - tp->copied_seq;
> > > -
> > > -       if (avail < sk->sk_rcvlowat && !tcp_rmem_pressure(sk) &&
> > > -           !sock_flag(sk, SOCK_DONE) &&
> >
> > Seems "!sock_flag(sk, SOCK_DONE)" is not checked in
> > tcp_epollin_read(). Does it matter?
> >
>
>
> Yes, probably, good catch.
>
> Not sure where tcp_poll() gets this, I have to double check.

It gets the info from sk->sk_hutdown & RCV_SHUTDOWN

tcp_find() sets both sk->sk_shutdown |= RCV_SHUTDOWN and
sock_set_flag(sk, SOCK_DONE);

This seems to suggest tcp_fin() could call sk->sk_data_ready() so that
we do not have to test for this unlikely condition in tcp_data_ready()