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

[Jiri Olsa <olsajiri@gmail.com>]

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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202310260528.aHWgVFqq-lkp@intel.com/
> Signed-off-by: Matthieu Baerts <matttbe@kernel.org>

Acked/Tested-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>  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@kernel.org>
>