selftests/bpf: move trampoline_count to dedicated bpf_testmod target

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>
Link: https://lore.kernel.org/r/20260324044949.869801-1-sun.jian.kdev@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 297b02372fa6..061356f10093 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;
@@ -1902,6 +1909,16 @@ 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[] = {
@@ -1918,6 +1935,7 @@ 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);