Re: [PATCHv2 bpf-next] bpf: fix compilation error without CGROUPS

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	 Andrii Nakryiko <andrii@kernel.org>,
	kernel test robot <lkp@intel.com>,
	bpf@vger.kernel.org,  Martin KaFai Lau <kafai@fb.com>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	 John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	 Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Yafang Shao <laoar.shao@gmail.com>,  Tejun Heo <tj@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	 MPTCP Upstream <mptcp@lists.linux.dev>,
	Matthieu Baerts <matttbe@kernel.org>
Subject: Re: [PATCHv2 bpf-next] bpf: fix compilation error without CGROUPS
Date: Mon, 6 Nov 2023 09:06:15 +0100	[thread overview]
Message-ID: <CAMuHMdUK4iRF7rTrSypEcbGTO0SnBUFDqT_HA9B7Pj62wTbYAw@mail.gmail.com> (raw)
In-Reply-To: <20231101181601.1493271-1-jolsa@kernel.org>

On Wed, Nov 1, 2023 at 7:16 PM Jiri Olsa <jolsa@kernel.org> wrote:
> From: Matthieu Baerts <matttbe@kernel.org>
> Our MPTCP CI complained [1] -- and KBuild too -- that it was no longer
> possible to build the kernel without CONFIG_CGROUPS:
>
>   kernel/bpf/task_iter.c: In function 'bpf_iter_css_task_new':
>   kernel/bpf/task_iter.c:919:14: error: 'CSS_TASK_ITER_PROCS' undeclared (first use in this function)
>     919 |         case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
>         |              ^~~~~~~~~~~~~~~~~~~
>   kernel/bpf/task_iter.c:919:14: note: each undeclared identifier is reported only once for each function it appears in
>   kernel/bpf/task_iter.c:919:36: error: 'CSS_TASK_ITER_THREADED' undeclared (first use in this function)
>     919 |         case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
>         |                                    ^~~~~~~~~~~~~~~~~~~~~~
>   kernel/bpf/task_iter.c:927:60: error: invalid application of 'sizeof' to incomplete type 'struct css_task_iter'
>     927 |         kit->css_it = bpf_mem_alloc(&bpf_global_ma, sizeof(struct css_task_iter));
>         |                                                            ^~~~~~
>   kernel/bpf/task_iter.c:930:9: error: implicit declaration of function 'css_task_iter_start'; did you mean 'task_seq_start'? [-Werror=implicit-function-declaration]
>     930 |         css_task_iter_start(css, flags, kit->css_it);
>         |         ^~~~~~~~~~~~~~~~~~~
>         |         task_seq_start
>   kernel/bpf/task_iter.c: In function 'bpf_iter_css_task_next':
>   kernel/bpf/task_iter.c:940:16: error: implicit declaration of function 'css_task_iter_next'; did you mean 'class_dev_iter_next'? [-Werror=implicit-function-declaration]
>     940 |         return css_task_iter_next(kit->css_it);
>         |                ^~~~~~~~~~~~~~~~~~
>         |                class_dev_iter_next
>   kernel/bpf/task_iter.c:940:16: error: returning 'int' from a function with return type 'struct task_struct *' makes pointer from integer without a cast [-Werror=int-conversion]
>     940 |         return css_task_iter_next(kit->css_it);
>         |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   kernel/bpf/task_iter.c: In function 'bpf_iter_css_task_destroy':
>   kernel/bpf/task_iter.c:949:9: error: implicit declaration of function 'css_task_iter_end' [-Werror=implicit-function-declaration]
>     949 |         css_task_iter_end(kit->css_it);
>         |         ^~~~~~~~~~~~~~~~~
>
> This patch simply surrounds with a #ifdef the new code requiring CGroups
> support. It seems enough for the compiler and this is similar to
> bpf_iter_css_{new,next,destroy}() functions where no other #ifdef have
> been added in kernel/bpf/helpers.c and in the selftests.
>
> Fixes: 9c66dc94b62a ("bpf: Introduce css_task open-coded iterator kfuncs")
> Link: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/6665206927
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310260528.aHWgVFqq-lkp@intel.com/
> Signed-off-by: Matthieu Baerts <matttbe@kernel.org>
> [ added missing ifdefs for BTF_ID cgroup definitions ]
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Thank you, this (finally, reported first on Oct 20!) fixes the build of
e.g. m68k/defconfig.

Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds