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

[Jiri Olsa]

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@xxxxxxxxx> 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@xxxxxxxxx>
> > > Closes: https://lore.kernel.org/oe-kbuild-all/202310260528.aHWgVFqq-lkp@xxxxxxxxx/
> > > Signed-off-by: Matthieu Baerts <matttbe@xxxxxxxxxx>
> >
> > Acked/Tested-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> 
> I believe this patch has the same issue as Arnd's patch:
> https://lore.kernel.org/all/CAADnVQL-zoFPPOVu3nM981gKxRu7Q3G3LTRsKstJEeahpoR1RQ@xxxxxxxxxxxxxx/
> 
> 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