Re: [RFC PATCH bpf-next v2 2/2] selftests/bpf: add tests for selective kmod BTF loading

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The tracking counter `obj->kmod_btfs->nr_loaded` is never updated, rendering the early termination optimization for BTF loading completely ineffective.
--

--- Patch [2]: [RFC PATCH bpf-next v2 2/2] selftests/bpf: add tests for selective kmod BTF loading ---
commit 506359525a106f517e013e060ee2c6feb17720c8
Author: Fuyu Zhao <zhaofuyu@vivo.com>

selftests/bpf: add tests for selective kmod BTF loading

Add test cases to verify the new ".kmod_btfs" section logic in libbpf.
The added test cases cover three main scenarios: valid module, non-existent
module, and duplicates/unneeded modules.

> diff --git a/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c b/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
> index 0000000000000..d875fcce6681d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/kmod_btfs.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include "kmod_btfs.skel.h"
> +#include "kmod_btfs_nonexist.skel.h"
> +#include "kmod_btfs_mix.skel.h"
> +

[ ... ]

[Severity: Medium]
While reviewing these tests, I noticed a potential regression in the libbpf
code they exercise. In load_module_btfs():

tools/lib/bpf/libbpf.c:load_module_btfs() {
...
		if (obj->kmod_btfs &&
		    obj->kmod_btfs->nr_names == obj->kmod_btfs->nr_loaded)
			break;
...
}

Is obj->kmod_btfs->nr_loaded ever incremented when a module BTF is
successfully loaded?

If it is not incremented, will this early termination condition ever be
met? It appears this might unnecessarily iterate over all remaining
system BTFs, which would bypass the intended performance optimization
of the .kmod_btfs section.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260813032613.2755-1-zhaofuyu@vivo.com?part=2