Re: [RESEND PATCH bpf-next v9 5/5] selftests/bpf: add a selftest for cgroup hierarchical stats collection

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Wed, Aug 24, 2022 at 7:41 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> On Wed, Aug 24, 2022 at 7:09 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Aug 24, 2022 at 4:31 PM Hao Luo <haoluo@google.com> wrote:
> > > +
> > > +       for (i = 0; i < N_CGROUPS; i++) {
> > > +               fd = create_and_get_cgroup(cgroups[i].path);
> > > +               if (!ASSERT_GE(fd, 0, "create_and_get_cgroup"))
> > > +                       return fd;
> > > +
> > > +               cgroups[i].fd = fd;
> > > +               cgroups[i].id = get_cgroup_id(cgroups[i].path);
> > > +
> > > +               /*
> > > +                * Enable memcg controller for the entire hierarchy.
> > > +                * Note that stats are collected for all cgroups in a hierarchy
> > > +                * with memcg enabled anyway, but are only exposed for cgroups
> > > +                * that have memcg enabled.
> > > +                */
> > > +               if (i < N_NON_LEAF_CGROUPS) {
> > > +                       err = enable_controllers(cgroups[i].path, "memory");
> > > +                       if (!ASSERT_OK(err, "enable_controllers"))
> > > +                               return err;
> > > +               }
> > > +       }
> >
> > It passes BPF CI, but fails in my setup with:
> >
> > # ./test_progs -t cgroup_hier -vv
> > bpf_testmod.ko is already unloaded.
> > Loading bpf_testmod.ko...
> > Successfully loaded bpf_testmod.ko.
> > setup_bpffs:PASS:mount 0 nsec
> > setup_cgroups:PASS:setup_cgroup_environment 0 nsec
> > setup_cgroups:PASS:get_root_cgroup 0 nsec
> > setup_cgroups:PASS:create_and_get_cgroup 0 nsec
> > (cgroup_helpers.c:92: errno: No such file or directory) Enabling
> > controller memory:
> > /mnt/cgroup-test-work-dir6526//test/cgroup.subtree_control
> > setup_cgroups:FAIL:enable_controllers unexpected error: 1 (errno 2)
> > cleanup_bpffs:FAIL:rmdir /sys/fs/bpf/vmscan/ unexpected error: -1 (errno 2)
> > #36      cgroup_hierarchical_stats:FAIL
> > Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
> >
> > How do I debug it?
>
> The failure with ENOENT happens when we try to write "+memory" to
> /mnt/cgroup-test-work-dir6526//test/cgroup.subtree_control, not when
> we try to open it. So the file is there. AFAICT, ENOENT can be
> returned from this write if the memory controller is not enabled on
> this cgroup.
>
> In setup_cgroup_environment(), we should be enabling all available
> controllers on /mnt and /mnt/cgroup-test-work-dir6526 by this line:
>
>         if (__enable_controllers(CGROUP_MOUNT_PATH, NULL) ||
>               __enable_controllers(cgroup_workdir, NULL))
>                   return 1;
>
> The first thing that comes to mind is that maybe the memory controller
> is not enabled on your setup at all? Can you check
> /sys/fs/cgroup/cgroup.controllers (or wherever your global cgroup
> mount is)?

Indeed. I didn't have a memory controller in cgroup2.
My system booted with cgroup v1 and it had cgroup1 memory
controller enabled which prevented cgroup2 to enable it.
Without Tejun's help I would have been able to figure this out.

Anyway, pushed the set to bpf-next. Thanks everyone.