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Subject: Re: [PATCH v1 bpf-next 1/4] bpf: Fix btf_get_field_type to fail for
 multiple bpf_refcount fields
Content-Language: en-GB
To: Dave Marchevsky <davemarchevsky@fb.com>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
 Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>,
 Martin KaFai Lau <martin.lau@kernel.org>, Kernel Team <kernel-team@fb.com>
References: <20231023220030.2556229-1-davemarchevsky@fb.com>
 <20231023220030.2556229-2-davemarchevsky@fb.com>
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From: Yonghong Song <yonghong.song@linux.dev>
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On 10/23/23 3:00 PM, Dave Marchevsky wrote:
> If a struct has a bpf_refcount field, the refcount controls lifetime of
> the entire struct. Currently there's no usecase or support for multiple
> bpf_refcount fields in a struct.
>
> bpf_spin_lock and bpf_timer fields don't support multiples either, but
> with better error behavior. Parsing BTF w/ a struct containing multiple
> {bpf_spin_lock, bpf_timer} fields fails in btf_get_field_type, while
> multiple bpf_refcount fields doesn't fail BTF parsing at all, instead
> triggering a WARN_ON_ONCE in btf_parse_fields, with the verifier using
> the last bpf_refcount field to actually do refcounting.
>
> This patch changes bpf_refcount handling in btf_get_field_type to use
> same error logic as bpf_spin_lock and bpf_timer. Since it's being used
> 3x and is boilerplatey, the logic is shoved into
> field_mask_test_name_check_seen helper macro.
>
> Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
> Fixes: d54730b50bae ("bpf: Introduce opaque bpf_refcount struct and add btf_record plumbing")

Acked-by: Yonghong Song <yonghong.song@linux.dev>