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

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Message-Id: <20231031-bpf-compil-err-css-v1-1-e2244c637835@kernel.org>
Date:   Tue, 31 Oct 2023 16:49:34 +0100
From:   Matthieu Baerts <matttbe@...nel.org>
To:     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>, Jiri Olsa <jolsa@...nel.org>,
        Chuyi Zhou <zhouchuyi@...edance.com>, Tejun Heo <tj@...nel.org>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        mptcp@...ts.linux.dev, kernel test robot <lkp@...el.com>,
        Matthieu Baerts <matttbe@...nel.org>
Subject: [PATCH bpf-next] bpf: fix compilation error without CGROUPS

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>
---
 kernel/bpf/task_iter.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 59e747938bdb..e0d313114a5b 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -894,6 +894,8 @@ __bpf_kfunc void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it)
 
 __diag_pop();
 
+#ifdef CONFIG_CGROUPS
+
 struct bpf_iter_css_task {
 	__u64 __opaque[1];
 } __attribute__((aligned(8)));
@@ -952,6 +954,8 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
 
 __diag_pop();
 
+#endif /* CONFIG_CGROUPS */
+
 struct bpf_iter_task {
 	__u64 __opaque[3];
 } __attribute__((aligned(8)));

---
base-commit: f1c73396133cb3d913e2075298005644ee8dfade
change-id: 20231031-bpf-compil-err-css-056f3db04860

Best regards,
-- 
Matthieu Baerts <matttbe@...nel.org>