netdev - Re: [PATCH bpf-next v2 1/2] bpf: cpumap: propagate underlying error in cpu_map_update

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Message-ID: <87o6o96ook.fsf@toke.dk>
Date: Mon, 08 Dec 2025 15:19:55 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Kohei Enju <enjuk@...zon.com>, netdev@...r.kernel.org,
 bpf@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>, "David S. Miller" <davem@...emloft.net>, Jakub
 Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>, John
 Fastabend <john.fastabend@...il.com>, Stanislav Fomichev
 <sdf@...ichev.me>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
 <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh
 <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, kohei.enju@...il.com,
 Kohei Enju <enjuk@...zon.com>
Subject: Re: [PATCH bpf-next v2 1/2] bpf: cpumap: propagate underlying error
 in cpu_map_update_elem()

Kohei Enju <enjuk@...zon.com> writes:

> After commit 9216477449f3 ("bpf: cpumap: Add the possibility to attach
> an eBPF program to cpumap"), __cpu_map_entry_alloc() may fail with
> errors other than -ENOMEM, such as -EBADF or -EINVAL.
>
> However, __cpu_map_entry_alloc() returns NULL on all failures, and
> cpu_map_update_elem() unconditionally converts this NULL into -ENOMEM.
> As a result, user space always receives -ENOMEM regardless of the actual
> underlying error.
>
> Examples of unexpected behavior:
>   - Nonexistent fd  : -ENOMEM (should be -EBADF)
>   - Non-BPF fd      : -ENOMEM (should be -EINVAL)
>   - Bad attach type : -ENOMEM (should be -EINVAL)
>
> Change __cpu_map_entry_alloc() to return ERR_PTR(err) instead of NULL
> and have cpu_map_update_elem() propagate this error.
>
> Signed-off-by: Kohei Enju <enjuk@...zon.com>

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>