[PATCH bpf-next v2 1/2] selftests/bpf: Keep the bpffs of cgroup_hierarchical_stats private

[Qiliang Yuan]

setup_hierarchy() mounts a bpffs on /sys/fs/bpf with setup_bpffs(), and
then sets up the cgroups with setup_cgroups(), which moves the test into
a private mount namespace.

The bpffs thus lands in the mount namespace that test_progs shares with
the tests running in parallel, on top of the bpffs already there, and
hides what they pin. cleanup_bpffs() later runs in the private mount
namespace and can't unmount it, so it stays there for good.
bpftool_maps_access then fails to pin an iterator because
/sys/fs/bpf/test_bpftool_map doesn't exist anymore, and bpftool_metadata
can't find the program it pinned in /sys/fs/bpf/test_metadata.

Set up the cgroups first, so that the bpffs is mounted in the private
mount namespace.

Fixes: 88886309d2e8 ("selftests/bpf: add a selftest for cgroup hierarchical stats collection")
Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
index 3bd27d2ea668c..ad19d6d41918a 100644
--- a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
+++ b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
@@ -151,7 +151,7 @@ static void cleanup_cgroups(void)
 /* Sets up cgroup hiearchary, returns 0 on success. */
 static int setup_hierarchy(void)
 {
-	return setup_bpffs() || setup_cgroups();
+	return setup_cgroups() || setup_bpffs();
 }
 
 static void destroy_hierarchy(void)

-- 
2.43.0