From: Hongfu Li <lihongfu@kylinos.cn>

cg_run_in_subcgroups() discards its arg and always passes NULL to cg_run(),
turning the (void *)100 from test_kmem_dead_cgroups() into NULL so no
allocation occurs.

This makes test_kmem_dead_cgroups() falsely pass without exercising the
"dying cgroup with charged slab" scenario it intends to test.

Pass the arg through to cg_run() to fix this.

Fixes: 933dc80ec262 ("kselftests: cgroup: add kernel memory accounting tests")
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
---
 tools/testing/selftests/cgroup/test_kmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
index 1db0ba1226b9..98e9f9f45ab9 100644
--- a/tools/testing/selftests/cgroup/test_kmem.c
+++ b/tools/testing/selftests/cgroup/test_kmem.c
@@ -145,7 +145,7 @@ static int cg_run_in_subcgroups(const char *parent,
 			return -1;
 		}
 
-		if (cg_run(child, fn, NULL)) {
+		if (cg_run(child, fn, arg)) {
 			cg_destroy(child);
 			free(child);
 			return -1;
-- 
2.54.0

Applied to cgroup/for-7.3-fixes with Michal's Reviewed-by added.

Thanks.

--
tejun

On Thu, Aug 20, 2026 at 03:09:44PM +0800, Hongfu Li <hongfu.li@linux.dev> wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
> 
> cg_run_in_subcgroups() discards its arg and always passes NULL to cg_run(),
> turning the (void *)100 from test_kmem_dead_cgroups() into NULL so no
> allocation occurs.
> 
> This makes test_kmem_dead_cgroups() falsely pass without exercising the
> "dying cgroup with charged slab" scenario it intends to test.
> 
> Pass the arg through to cg_run() to fix this.
> 
> Fixes: 933dc80ec262 ("kselftests: cgroup: add kernel memory accounting tests")
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---
>  tools/testing/selftests/cgroup/test_kmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Good catch,

Reviewed-by: Michal Koutný <mkoutny@suse.com>