netdev - Re: [bpf PATCH 1/2] bpf, sockmap: fix sk->prot unhash op reset

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Message-ID: <CAM_iQpUdOkbs5MPcfTqNcPV3f0EXU7CQhuV9y2UDrOZ4SawvvA@mail.gmail.com>
Date:   Thu, 25 Mar 2021 11:57:05 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>, bpf <bpf@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [bpf PATCH 1/2] bpf, sockmap: fix sk->prot unhash op reset

On Wed, Mar 24, 2021 at 7:28 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> Cong Wang wrote:
> > On Wed, Mar 24, 2021 at 1:59 PM John Fastabend <john.fastabend@...il.com> wrote:
> > > diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> > > index 47b7c5334c34..ecb5634b4c4a 100644
> > > --- a/net/tls/tls_main.c
> > > +++ b/net/tls/tls_main.c
> > > @@ -754,6 +754,12 @@ static void tls_update(struct sock *sk, struct proto *p,
> > >
> > >         ctx = tls_get_ctx(sk);
> > >         if (likely(ctx)) {
> > > +               /* TLS does not have an unhash proto in SW cases, but we need
> > > +                * to ensure we stop using the sock_map unhash routine because
> > > +                * the associated psock is being removed. So use the original
> > > +                * unhash handler.
> > > +                */
> > > +               WRITE_ONCE(sk->sk_prot->unhash, p->unhash);
> > >                 ctx->sk_write_space = write_space;
> > >                 ctx->sk_proto = p;
> >
> > It looks awkward to update sk->sk_proto inside tls_update(),
> > at least when ctx!=NULL.
>
> hmm. It doesn't strike me as paticularly awkward but OK.

I read tls_update() as "updating ctx when it is initialized", with your
patch, we are updating sk->sk_prot->unhash too when updating ctx,
pretty much like a piggyback, hence it reads odd to me.

Thanks.