Re: [PATCH bpf-next 2/2] selftests/bpf: Don't stack a bpffs in cgroup_hierarchical_stats

[Qiliang Yuan]

On Thu, Oct 8, 2026 at 7:11 AM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> Seems like both of these tests do not mount bpffs, but rely on its
> existence. If it's generally expected that bpffs is mounted when the
> tests are run, should we drop the mounting code here instead?
>
> Alternatively, should we have a common helper for creating directories
> in bpffs that mounts it if it isn't already there?

Thanks for the review. Looking further, the bpffs is mounted in the
wrong place: setup_bpffs() runs before setup_cgroups() moves the test
into a private mount namespace, so the bpffs lands in the namespace
shared with the other tests, and cleanup_bpffs() can't unmount it from
the private one. The BPF CI bot pointed that out as well.

v2 sets up the cgroups first, so that the bpffs is mounted in the
private mount namespace. The test keeps working where no bpffs is
mounted, and it no longer affects any other test, so neither dropping
the mount nor a common helper is needed for this. I kept your
Reviewed-by on the unmount fix, whose code didn't change.

v2: https://lore.kernel.org/r/20261009-selftests-bpf-cgroup-stats-bpffs-v2-0-f93a111da992@xxxxxxxxx

Thanks,
Qiliang