[PATCH] selftests/sched_ext: Skip cyclic_kick_wait on kernels without deadlock fix

[Cheng-Yang Chou]

The cyclic_kick_wait test triggers a deadlock on kernels lacking the
SCX_KICK_WAIT fix, causing the machine to hang or worker threads to
timeout (-110).

Use __COMPAT_struct_has_field() to probe vmlinux BTF for
rq_scx.kick_sync_pending, a field introduced by the SCX_KICK_WAIT
deadlock fix. Skip the test on older kernels that lack the fix rather
than hanging the machine.

Example failure on unpatched kernels:
  ERR: cyclic_kick_wait.c:169
  Failed to join worker thread 0 (-110)

Fixes: e9b990b76922 ("selftests/sched_ext: Add cyclic SCX_KICK_WAIT stress test")
Signed-off-by: Cheng-Yang Chou <yphbchou0911@xxxxxxxxx>
---
 tools/testing/selftests/sched_ext/cyclic_kick_wait.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/sched_ext/cyclic_kick_wait.c b/tools/testing/selftests/sched_ext/cyclic_kick_wait.c
index c2e5aa9de715..b060ffe63ba3 100644
--- a/tools/testing/selftests/sched_ext/cyclic_kick_wait.c
+++ b/tools/testing/selftests/sched_ext/cyclic_kick_wait.c
@@ -88,6 +88,11 @@ static enum scx_test_status setup(void **ctx)
 {
 	struct cyclic_kick_wait *skel;
 
+	if (!__COMPAT_struct_has_field("rq_scx", "kick_sync_pending")) {
+		fprintf(stderr, "Skipping test: kernel lacks SCX_KICK_WAIT deadlock fix\n");
+		return SCX_TEST_SKIP;
+	}
+
 	skel = cyclic_kick_wait__open();
 	SCX_FAIL_IF(!skel, "Failed to open skel");
 	SCX_ENUM_INIT(skel);
-- 
2.43.0


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