Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230613-so-reuseport-v4-6-4ece76708bba@isovalent.com> <20230628185352.76923-1-kuniyu@amazon.com>
In-Reply-To: <20230628185352.76923-1-kuniyu@amazon.com>
From:   Lorenz Bauer <lmb@isovalent.com>
Date:   Mon, 3 Jul 2023 10:57:23 +0100
Message-ID: <CAN+4W8hLXYZuNFG+=J-FWLXWhbwT5TrHjMg5VzjQhv2NBo5VaA@mail.gmail.com>
Subject: Re: [PATCH bpf-next v4 6/7] bpf, net: Support SO_REUSEPORT sockets
 with bpf_sk_assign
To:     Kuniyuki Iwashima <kuniyu@amazon.com>
Cc:     andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, davem@davemloft.net, dsahern@kernel.org,
        edumazet@google.com, haoluo@google.com, hemanthmalla@gmail.com,
        joe@cilium.io, joe@wand.net.nz, john.fastabend@gmail.com,
        jolsa@kernel.org, kpsingh@kernel.org, kuba@kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        martin.lau@linux.dev, mykolal@fb.com, netdev@vger.kernel.org,
        pabeni@redhat.com, sdf@google.com, shuah@kernel.org,
        song@kernel.org, willemdebruijn.kernel@gmail.com, yhs@fb.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Wed, Jun 28, 2023 at 7:54=E2=80=AFPM Kuniyuki Iwashima <kuniyu@amazon.co=
m> wrote:

> > +     reuse_sk =3D inet6_lookup_reuseport(net, sk, skb, doff,
> > +                                       saddr, sport, daddr, ntohs(dpor=
t),
> > +                                       ehashfn);
> > +     if (!reuse_sk || reuse_sk =3D=3D sk)
> > +             return sk;
> > +
> > +     /* We've chosen a new reuseport sock which is never refcounted. T=
his
> > +      * implies that sk also isn't refcounted.
> > +      */
> > +     WARN_ON_ONCE(*refcounted);
>
> One more nit.
>
> WARN_ON_ONCE() should be tested before inet6?_lookup_reuseport() not to
> miss the !reuse_sk case.

I was just pondering that as well, but I came to the opposite
conclusion. In the !reuse_sk case we don't really know anything about
sk, except that it isn't part of a reuseport group. How can we be sure
that it's not refcounted?