Re: [PATCH] selftests/bpf: modify_return: isolate fmod_ret hooks by pid

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Mar 12, 2026 at 06:42:19PM +0800, Sun Jian wrote:

SNIP

> diff --git a/tools/testing/selftests/bpf/progs/modify_return.c b/tools/testing/selftests/bpf/progs/modify_return.c
> index 3376d4849f58..5ff18ddb3050 100644
> --- a/tools/testing/selftests/bpf/progs/modify_return.c
> +++ b/tools/testing/selftests/bpf/progs/modify_return.c
> @@ -7,16 +7,29 @@
>  #include <linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
> +#include <stdbool.h>
>  
>  char _license[] SEC("license") = "GPL";
>  
>  static int sequence = 0;
>  __s32 input_retval = 0;
> +__u32 test_pid = 0;
> +
> +static __always_inline bool match_pid(void)
> +{
> +	__u64 pid_tgid = bpf_get_current_pid_tgid();
> +
> +	if (!test_pid)
> +		return false;
> +	return (__u32)(pid_tgid >> 32) == test_pid;
> +}
>  
>  __u64 fentry_result = 0;
>  SEC("fentry/bpf_modify_return_test")
>  int BPF_PROG(fentry_test, int a, __u64 b)
>  {
> +	if (!match_pid())
> +		return 0;

I think just simple pid check like we do in other places
should be enough:

	if (bpf_get_current_pid_tgid() >> 32 != test_pid)
		return 0;

jirka


>  	sequence++;
>  	fentry_result = (sequence == 1);
>  	return 0;
> @@ -26,6 +39,8 @@ __u64 fmod_ret_result = 0;
>  SEC("fmod_ret/bpf_modify_return_test")
>  int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
>  {
> +	if (!match_pid())
> +		return ret;
>  	sequence++;
>  	/* This is the first fmod_ret program, the ret passed should be 0 */
>  	fmod_ret_result = (sequence == 2 && ret == 0);
> @@ -36,6 +51,8 @@ __u64 fexit_result = 0;
>  SEC("fexit/bpf_modify_return_test")
>  int BPF_PROG(fexit_test, int a, __u64 b, int ret)
>  {
> +	if (!match_pid())
> +		return 0;
>  	sequence++;
>  	/* If the input_reval is non-zero a successful modification should have
>  	 * occurred.
> @@ -55,6 +72,8 @@ SEC("fentry/bpf_modify_return_test2")
>  int BPF_PROG(fentry_test2, int a, int *b, short c, int d, void *e, char f,
>  	     int g)
>  {
> +	if (!match_pid())
> +		return 0;
>  	sequence2++;
>  	fentry_result2 = (sequence2 == 1);
>  	return 0;
> @@ -65,6 +84,8 @@ SEC("fmod_ret/bpf_modify_return_test2")
>  int BPF_PROG(fmod_ret_test2, int a, int *b, short c, int d, void *e, char f,
>  	     int g, int ret)
>  {
> +	if (!match_pid())
> +		return ret;
>  	sequence2++;
>  	/* This is the first fmod_ret program, the ret passed should be 0 */
>  	fmod_ret_result2 = (sequence2 == 2 && ret == 0);
> @@ -76,6 +97,8 @@ SEC("fexit/bpf_modify_return_test2")
>  int BPF_PROG(fexit_test2, int a, int *b, short c, int d, void *e, char f,
>  	     int g, int ret)
>  {
> +	if (!match_pid())
> +		return 0;
>  	sequence2++;
>  	/* If the input_reval is non-zero a successful modification should have
>  	 * occurred.
> 
> base-commit: 80234b5ab240f52fa45d201e899e207b9265ef91
> -- 
> 2.43.0
> 
>