netdev - Re: [PATCH v3 bpf-next 3/3] bpf: Add cb access in kfree

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Message-ID: <CAEf4BzY6aDYKUGv2D-xy2bQKuH6zeMGvqA5p74xjcUXKq5KDZA@mail.gmail.com>
Date:   Wed, 6 Nov 2019 18:50:02 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 3/3] bpf: Add cb access in kfree_skb test

On Wed, Nov 6, 2019 at 5:47 PM Martin KaFai Lau <kafai@...com> wrote:
>
> Access the skb->cb[] in the kfree_skb test.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  .../selftests/bpf/prog_tests/kfree_skb.c      | 54 +++++++++++++++----
>  tools/testing/selftests/bpf/progs/kfree_skb.c | 25 +++++++--
>  2 files changed, 63 insertions(+), 16 deletions(-)
>

[...]

>
> +       meta.ifindex = _(dev->ifindex);
> +       meta.cb8_0 = cb8[8];
> +       meta.cb32_0 = cb32[2];

Have you tried doing it inside __builtin_preserve_access_index region?
Does it fail because of extra allocations against meta?

> +
>         bpf_probe_read_kernel(&pkt_type, sizeof(pkt_type), _(&skb->__pkt_type_offset));
>         pkt_type &= 7;
>

[...]