linux-kernel - Re: [PATCH bpf-next] bpf: fix compilation error without CGROUPS

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Message-ID: <9aad3bb9-daca-405a-93c3-dccea3c0a07a@kernel.org>
Date:   Wed, 1 Nov 2023 09:25:34 +0100
From:   Matthieu Baerts <matttbe@...nel.org>
To:     Jiri Olsa <olsajiri@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Yonghong Song <yonghong.song@...ux.dev>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        Chuyi Zhou <zhouchuyi@...edance.com>,
        Tejun Heo <tj@...nel.org>, bpf <bpf@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        MPTCP Upstream <mptcp@...ts.linux.dev>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH bpf-next] bpf: fix compilation error without CGROUPS

Hi Jirka, Alexei,

On 01/11/2023 08:25, Jiri Olsa wrote:
> On Tue, Oct 31, 2023 at 08:54:56PM -0700, Alexei Starovoitov wrote:
>> On Tue, Oct 31, 2023 at 10:05 AM Jiri Olsa <olsajiri@...il.com> wrote:
>>>
>>> On Tue, Oct 31, 2023 at 04:49:34PM +0100, Matthieu Baerts wrote:
>>>> 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@...el.com>
>>>> Closes: https://lore.kernel.org/oe-kbuild-all/202310260528.aHWgVFqq-lkp@intel.com/
>>>> Signed-off-by: Matthieu Baerts <matttbe@...nel.org>
>>>
>>> Acked/Tested-by: Jiri Olsa <jolsa@...nel.org>
>>
>> I believe this patch has the same issue as Arnd's patch:
>> https://lore.kernel.org/all/CAADnVQL-zoFPPOVu3nM981gKxRu7Q3G3LTRsKstJEeahpoR1RQ@mail.gmail.com/

@Alexei: Arf, sorry, I didn't find this patch when searching for
"9c66dc94b62a" on lore. I don't know why I didn't search for the commit
title as usual...

>> I'd like to merge the fix asap. Please make it a complete fix.
> 
> ugh, it won't fail the build, it just warns.. I think we should
> fail the build in that case, I'll check

@Jirka: Thank you for checking that! Please tell me if you want me to
send a v2 or if you prefer to do that. I don't mind if you prefer to
send your own patches, as long as there is a fix for that at the end :)

Note that if a warning is emitted for these new bpf_iter_css_task_*()
functions, I guess you will have the same issue with bpf_iter_css_*()
and probably others as mentioned in my commit message.

Cheers,
Matt