Re: [akpm-mm:mm-unstable 179/192] mm/zswap.c:298:24: error: call to undeclared function 'obj_cgroup_memcg'; ISO C99 and later do not support implicit function declarations

[Nhat Pham <nphamcs@gmail.com>]

On Wed, Nov 29, 2023 at 1:34 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 29 Nov 2023 23:42:15 +0800 kernel test robot <lkp@intel.com> wrote:
>
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> > head:   cb1d236cb1038fa1bbae9913803f1c655b86d931
> > commit: 70dd375afcfe1839321ea8a65749404a99f0e773 [179/192] zswap: make shrinking memcg-aware
> > config: s390-randconfig-r071-20231129 (https://download.01.org/0day-ci/archive/20231129/202311292305.43bnw55s-lkp@intel.com/config)
> > compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231129/202311292305.43bnw55s-lkp@intel.com/reproduce)
> >
> > ...
> >
> > >> mm/zswap.c:298:24: error: call to undeclared function 'obj_cgroup_memcg'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >            return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
> >                                  ^
> >    mm/zswap.c:298:24: note: did you mean 'obj_cgroup_put'?
> >    include/linux/memcontrol.h:1352:20: note: 'obj_cgroup_put' declared here
>
> Well I'm going to assume it's this:
>
> --- a/mm/zswap.c~zswap-make-shrinking-memcg-aware-fix
> +++ a/mm/zswap.c
> @@ -29,6 +29,7 @@
>  #include <linux/zpool.h>
>  #include <crypto/acompress.h>
>  #include <linux/zswap.h>
> +#include <linux/memcontrol.h>
>  #include <linux/mm_types.h>
>  #include <linux/page-flags.h>
>  #include <linux/swapops.h>
> _
>
> Can't test because my gcc plugins have gone stupid yet again.
>
> cc1: error: cannot load plugin ./scripts/gcc-plugins/stackleak_plugin.so: ./scripts/gcc-plugins/stackleak_plugin.so: undefined symbol: _ZNK6frange6acceptERK14vrange_visitor
> cc1: error: cannot load plugin ./scripts/gcc-plugins/randomize_layout_plugin.so: ./scripts/gcc-plugins/randomize_layout_plugin.so: undefined symbol: _ZNK6frange6acceptERK14vrange_visitor
>
> help.

Hmm I tried including memcontrol.h, and it still screams at me the
same way with !CONFIG_MEMCG. I think obj_cgroup_memcg() is just not
defined in this case. Let's just return NULL here when !CONFIG_MEMCG.