Re: [PATCH v4] selftests/bpf: move trampoline_count to dedicated bpf_testmod target

Jiri Olsa
2026-03-24T09:08:14Z

On Tue, Mar 24, 2026 at 12:49:49PM +0800, Sun Jian wrote:
> trampoline_count fills all trampoline attachment slots for a single
> target function and verifies that one extra attach fails with -E2BIG.
>
> It currently targets bpf_modify_return_test, which is also used by
> other selftests such as modify_return, get_func_ip_test, and
> get_func_args_test. When such tests run in parallel, they can contend
> for the same per-function trampoline quota and cause unexpected attach
> failures. This issue is currently masked by harness serialization.
>
> Move trampoline_count to a dedicated bpf_testmod target and register it
> for fmod_ret attachment. Also route the final trigger through
> trigger_module_test_read(), so the execution path exercises the same
> dedicated target.
>
> This keeps the test semantics unchanged while isolating it from other
> selftests, so it no longer needs to run in serial mode. Remove the
> TODO comment as well.
>
> Tested:
> ./test_progs -t trampoline_count -vv
> ./test_progs -j$(nproc) -t trampoline_count -vv
> ./test_progs -j$(nproc) -t \
> trampoline_count,modify_return,get_func_ip_test,get_func_args_test -vv
> 20 runs of:
> ./test_progs -j$(nproc) -t \
> trampoline_count,modify_return,get_func_ip_test,get_func_args_test
>
> Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
>
> Link: https://lore.kernel.org/bpf/20260320074150.628094-1-sun.jian.kdev@gmail.com/
>
> v4:
> - simplify the dedicated trampoline_count target and its trigger path
> - simplify the associated fentry/fmod_ret/fexit test program signatures
> - reduce the final trigger to a plain ASSERT_OK()
> - drop Suggested-by per Jiri
>
> v3:
> - route the final trigger through trigger_module_test_read() and make
> bpf_testmod_test_read() call the dedicated trampoline_count target
>
> v2:
> - rewrite the subject to describe the change
> - resend with the correct patch content
>
> .../bpf/prog_tests/trampoline_count.c | 17 +++--------------
> .../bpf/progs/test_trampoline_count.c | 12 ++++++------
> .../selftests/bpf/test_kmods/bpf_testmod.c | 18 ++++++++++++++++++
> 3 files changed, 27 insertions(+), 20 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> index 6cd7349d4a2b..7321850db75f 100644
> --- a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> +++ b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> @@ -30,16 +30,14 @@ static struct bpf_program *load_prog(char *file, char *name, struct inst *inst)
> return prog;
> }
>
> -/* TODO: use different target function to run in concurrent mode */
> -void serial_test_trampoline_count(void)
> +void test_trampoline_count(void)
> {
> char *file = "test_trampoline_count.bpf.o";
> char *const progs[] = { "fentry_test", "fmod_ret_test", "fexit_test" };
> - int bpf_max_tramp_links, err, i, prog_fd;
> + int bpf_max_tramp_links, i;
> struct bpf_program *prog;
> struct bpf_link *link;
> struct inst *inst;
> - LIBBPF_OPTS(bpf_test_run_opts, opts);
>
> bpf_max_tramp_links = get_bpf_max_tramp_links();
> if (!ASSERT_GE(bpf_max_tramp_links, 1, "bpf_max_tramp_links"))
> @@ -80,16 +78,7 @@ void serial_test_trampoline_count(void)
> goto cleanup;
>
> /* and finally execute the probe */
> - prog_fd = bpf_program__fd(prog);
> - if (!ASSERT_GE(prog_fd, 0, "bpf_program__fd"))
> - goto cleanup;
> -
> - err = bpf_prog_test_run_opts(prog_fd, &opts);
> - if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
> - goto cleanup;
> -
> - ASSERT_EQ(opts.retval & 0xffff, 33, "bpf_modify_return_test.result");
> - ASSERT_EQ(opts.retval >> 16, 2, "bpf_modify_return_test.side_effect");
> + ASSERT_OK(trigger_module_test_read(256), "trigger_module_test_read");
>
> cleanup:
> for (; i >= 0; i--) {
> diff --git a/tools/testing/selftests/bpf/progs/test_trampoline_count.c b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> index 7765720da7d5..02f52806b1b2 100644
> --- a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> +++ b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> @@ -3,20 +3,20 @@
> #include <bpf/bpf_helpers.h>
> #include <bpf/bpf_tracing.h>
>
> -SEC("fentry/bpf_modify_return_test")
> -int BPF_PROG(fentry_test, int a, int *b)
> +SEC("fentry/bpf_testmod_trampoline_count_test")
> +int BPF_PROG(fentry_test)
> {
> return 0;
> }
>
> -SEC("fmod_ret/bpf_modify_return_test")
> -int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
> +SEC("fmod_ret/bpf_testmod_trampoline_count_test")
> +int BPF_PROG(fmod_ret_test, int ret)
> {
> return 0;
> }
>
> -SEC("fexit/bpf_modify_return_test")
> -int BPF_PROG(fexit_test, int a, int *b, int ret)
> +SEC("fexit/bpf_testmod_trampoline_count_test")
> +int BPF_PROG(fexit_test, int ret)
> {
> return 0;
> }
> diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> index e62c6b78657f..9caf9ffa1bb0 100644
> --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> @@ -470,6 +470,11 @@ noinline void bpf_testmod_stacktrace_test_1(void)
>
> int bpf_testmod_fentry_ok;
>
> +noinline int bpf_testmod_trampoline_count_test(void)
> +{
> + return 0;
> +}
> +
> noinline ssize_t
> bpf_testmod_test_read(struct file *file, struct kobject *kobj,
> const struct bin_attribute *bin_attr,
> @@ -548,6 +553,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
> 21, 22, 23, 24, 25, 26) != 231)
> goto out;
>
> + bpf_testmod_trampoline_count_test();
> +
> bpf_testmod_stacktrace_test_1();
>
> bpf_testmod_fentry_ok = 1;
> @@ -1843,6 +1850,16 @@ struct bpf_struct_ops testmod_multi_st_ops = {
>
> extern int bpf_fentry_test1(int a);
>
> +BTF_KFUNCS_START(bpf_testmod_trampoline_count_ids)
> +BTF_ID_FLAGS(func, bpf_testmod_trampoline_count_test)
> +BTF_KFUNCS_END(bpf_testmod_trampoline_count_ids)
> +
> +static const struct
> +btf_kfunc_id_set bpf_testmod_trampoline_count_fmodret_set = {
> + .owner = THIS_MODULE,
> + .set = &bpf_testmod_trampoline_count_ids,
> +};
> +
> static int bpf_testmod_init(void)
> {
> const struct btf_id_dtor_kfunc bpf_testmod_dtors[] = {
> @@ -1859,6 +1876,7 @@ static int bpf_testmod_init(void)
> ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_testmod_kfunc_set);
> ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_testmod_kfunc_set);
> ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_testmod_kfunc_set);
> + ret = ret ?: register_btf_fmodret_id_set(&bpf_testmod_trampoline_count_fmodret_set);
> ret = ret ?: register_bpf_struct_ops(&bpf_bpf_testmod_ops, bpf_testmod_ops);
> ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops2, bpf_testmod_ops2);
> ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops3, bpf_testmod_ops3);
>
> base-commit: 8a30aeb0d1b4e4aaf7f7bae72f20f2ae75385ccb
> --
> 2.43.0
>