Re: [PATCH bpf-next 2/2] selftests/bpf: Test fentry link after tracing_multi link

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Test Flakiness due to Missing PID Filtering in BPF `fentry` Program
--

--- Patch [2]: [PATCH bpf-next 2/2] selftests/bpf: Test fentry link after tracing_multi link ---
commit 7dc95a7a3d3a0ca96e45e5ad2ebebe5157ae17ed
Author: Leon Hwang <leon.hwang@linux.dev>

selftests/bpf: Test fentry link after tracing_multi link

This commit adds a selftest to verify that an fentry link can be attached
safely after a tracing_multi link. It introduces a new fentry BPF program
and a corresponding user-space test case.

> diff --git a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
> index cd5be0bb6ffdd..5ebbe3b602a4f 100644
> --- a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
> +++ b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c

[ ... ]

> @@ -11,6 +11,14 @@ __u64 test_result_fentry_1 = 0;
>  __u64 test_result_fentry_2 = 0;
>  __u64 test_result_fexit_1 = 0;
>  __u64 test_result_fexit_2 = 0;
> +__u64 test_result_fentry = 0;
> +
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(fentry, int a)
> +{
> +	test_result_fentry += a == 1;

[Severity: Medium]
Can this cause test flakiness during parallel selftest runs?

Because bpf_fentry_test1 is a global kernel function widely used across
various BPF selftests, parallel test executions might trigger this program.
Since the counter is incremented blindly without filtering by the executing
process PID, could parallel executions increase test_result_fentry above 1
and cause the userland assertion ASSERT_EQ(skel->bss->test_result_fentry, 1)
to sporadically fail?

> +	return 0;
> +}
>  
>  SEC("fentry.multi")
>  int BPF_PROG(fentry_1)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260710144734.78203-1-leon.hwang@linux.dev?part=2