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
modify_return and get_func_ip_test. When those 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.

Add a dedicated bpf_trampoline_count_test target and switch
trampoline_count to use it. This keeps the test semantics unchanged
while isolating it from other modify_return-based 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 -t modify_return -vv
  ./test_progs -t get_func_ip_test -vv
  ./test_progs -j$(nproc) -t trampoline_count -vv
  ./test_progs -j$(nproc) -t
    trampoline_count,modify_return,get_func_ip_test -vv

Tested-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Sun Jian <sun.jian.kdev@gmail.com>
---

v2:
- add Paul's Tested-by

 net/bpf/test_run.c                                        | 7 +++++++
 tools/testing/selftests/bpf/prog_tests/trampoline_count.c | 3 +--
 tools/testing/selftests/bpf/progs/test_trampoline_count.c | 6 +++---
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 178c4738e63b..b41147a29f16 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -580,6 +580,12 @@ __bpf_kfunc int bpf_modify_return_test2(int a, int *b, short c, int d,
 	return a + *b + c + d + (long)e + f + g;
 }
 
+__bpf_kfunc int bpf_trampoline_count_test(int a, int *b)
+{
+	*b += 1;
+	return a + *b;
+}
+
 __bpf_kfunc int bpf_modify_return_test_tp(int nonce)
 {
 	trace_bpf_trigger_tp(nonce);
@@ -635,6 +641,7 @@ BTF_KFUNCS_START(bpf_test_modify_return_ids)
 BTF_ID_FLAGS(func, bpf_modify_return_test)
 BTF_ID_FLAGS(func, bpf_modify_return_test2)
 BTF_ID_FLAGS(func, bpf_modify_return_test_tp)
+BTF_ID_FLAGS(func, bpf_trampoline_count_test)
 BTF_ID_FLAGS(func, bpf_fentry_test1, KF_SLEEPABLE)
 BTF_KFUNCS_END(bpf_test_modify_return_ids)
 
diff --git a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
index 6cd7349d4a2b..b19358aed126 100644
--- a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
+++ b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
@@ -30,8 +30,7 @@ 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" };
diff --git a/tools/testing/selftests/bpf/progs/test_trampoline_count.c b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
index 7765720da7d5..911d282fd423 100644
--- a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
+++ b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
@@ -3,19 +3,19 @@
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 
-SEC("fentry/bpf_modify_return_test")
+SEC("fentry/bpf_trampoline_count_test")
 int BPF_PROG(fentry_test, int a, int *b)
 {
 	return 0;
 }
 
-SEC("fmod_ret/bpf_modify_return_test")
+SEC("fmod_ret/bpf_trampoline_count_test")
 int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
 {
 	return 0;
 }
 
-SEC("fexit/bpf_modify_return_test")
+SEC("fexit/bpf_trampoline_count_test")
 int BPF_PROG(fexit_test, int a, int *b, int ret)
 {
 	return 0;

base-commit: 267594792a71018788af69e836c52e34bb8054af
-- 
2.43.0