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

  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>
---
 kernel/bpf/helpers.c   | 8 +++++---
 kernel/bpf/task_iter.c | 4 ++++
 kernel/bpf/verifier.c  | 8 ++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)
  

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Wed,  1 Nov 2023 19:16:01 +0100 you 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);
>         |         ^~~~~~~~~~~~~~~~~
> 
> [...]

Here is the summary with links:
  - [PATCHv2,bpf-next] bpf: fix compilation error without CGROUPS
    https://git.kernel.org/bpf/bpf/c/05670f81d128

You are awesome, thank you!
  

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