netdev - Re: [PATCH v2 bpf-next 2/9] bpf: Add bpf helper bpf_tcp_enter

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Date:   Sat, 23 Feb 2019 17:32:14 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>
Cc:     Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 2/9] bpf: Add bpf helper bpf_tcp_enter_cwr



On 02/22/2019 05:06 PM, brakmo wrote:
> From: Martin KaFai Lau <kafai@...com>
> 
> This patch adds a new bpf helper BPF_FUNC_tcp_enter_cwr
> "int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)".
> It is added to BPF_PROG_TYPE_CGROUP_SKB which can be attached
> to the egress path where the bpf prog is called by
> ip_finish_output() or ip6_finish_output().  The verifier
> ensures that the parameter must be a tcp_sock.
> 
> This helper makes a tcp_sock enter CWR state.  It can be used
> by a bpf_prog to manage egress network bandwidth limit per
> cgroupv2.  A later patch will have a sample program to
> show how it can be used to limit bandwidth usage per cgroupv2.
> 
> To ensure it is only called from BPF_CGROUP_INET_EGRESS, the
> attr->expected_attach_type must be specified as BPF_CGROUP_INET_EGRESS
> during load time if the prog uses this new helper.
> The newly added prog->enforce_expected_attach_type bit will also be set
> if this new helper is used.  This bit is for backward compatibility reason
> because currently prog->expected_attach_type has been ignored in
> BPF_PROG_TYPE_CGROUP_SKB.  During attach time,
> prog->expected_attach_type is only enforced if the
> prog->enforce_expected_attach_type bit is set.
> i.e. prog->expected_attach_type is only enforced if this new helper
> is used by the prog.
> 

BTW, it seems to me that BPF_CGROUP_INET_EGRESS can be used while the socket lock is not held.

Maybe we should fix :/