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    SubjectRe: [PATCH] bpf: hide cgroup functions for configs without cgroups
    On Fri, Oct 20, 2023 at 6:27 AM Arnd Bergmann <arnd@kernel.org> wrote:
    >
    > From: Arnd Bergmann <arnd@arndb.de>
    >
    > When cgroups are disabled, the newly added functions don't build:
    >
    > kernel/bpf/task_iter.c: In function 'bpf_iter_css_task_new':
    > kernel/bpf/task_iter.c:917:14: error: 'CSS_TASK_ITER_PROCS' undeclared (first use in this function)
    > 917 | case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
    > | ^~~~~~~~~~~~~~~~~~~
    > kernel/bpf/task_iter.c:925:60: error: invalid application of 'sizeof' to incomplete type 'struct css_task_iter'
    > 925 | kit->css_it = bpf_mem_alloc(&bpf_global_ma, sizeof(struct css_task_iter));
    > | ^~~~~~
    >
    > Hide them in an #ifdef section.
    >
    > Fixes: 9c66dc94b62ae ("bpf: Introduce css_task open-coded iterator kfuncs")
    > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    > ---
    > kernel/bpf/task_iter.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
    > index 654601dd6b493..15a184f4f954d 100644
    > --- a/kernel/bpf/task_iter.c
    > +++ b/kernel/bpf/task_iter.c
    > @@ -904,6 +904,7 @@ __diag_push();
    > __diag_ignore_all("-Wmissing-prototypes",
    > "Global functions as their definitions will be in vmlinux BTF");
    >
    > +#ifdef CONFIG_CGROUPS
    > __bpf_kfunc int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
    > struct cgroup_subsys_state *css, unsigned int flags)
    > {
    > @@ -947,6 +948,7 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
    > css_task_iter_end(kit->css_it);
    > bpf_mem_free(&bpf_global_ma, kit->css_it);
    > }
    > +#endif

    Did you actually test build it without cgroups and with bpf+btf?
    I suspect the resolve_btfid step should be failing the build.
    It needs
    #ifdef CONFIG_CGROUPS
    around BTF_ID_FLAGS(func, bpf_iter_css_task*

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