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A BPF > > scheduler kicks the next CPU in the ring with SCX_KICK_WAIT on every > > enqueue while userspace workers generate continuous scheduling churn via > > sched_yield(). Without the preceding fix, this hangs the machine within seconds. > > I think it would be better to skip this test on older, unpatched kernels. > Sometimes I use my local kernel for testing before the stable patches are > fully integrated, so skipping the test would be a safer approach. > > Otherwise, this test can stall the machine and make it impossible to > exit the test runner. Actually, I disagree. The whole point of the kselftests is to expose kernel issues, including bugs in older kernels that may need fixes. So, I think we shouldn't skip the test. -Andrea > > Log: > > $ sudo ./runner -t cyclic_kick_wait # on v6.14 > ===== START ===== > TEST: cyclic_kick_wait > DESCRIPTION: Verify SCX_KICK_WAIT forward progress under a 3-CPU wait cycle > OUTPUT: > libbpf: struct_ops cyclic_kick_wait_ops: member cgroup_set_bandwidth not found in kernel, skipping it as it's set to zero > libbpf: struct_ops cyclic_kick_wait_ops: member cgroup_set_idle not found in kernel, skipping it as it's set to zero > libbpf: struct_ops cyclic_kick_wait_ops: member priv not found in kernel, skipping it as it's set to zero > ERR: cyclic_kick_wait.c:169 > Failed to join worker thread 0 (-110) > > Thanks, > Cheng-Yang > > From 6f09d2298e547aa7a519d4bff262fc6851a969ea Mon Sep 17 00:00:00 2001 > From: Cheng-Yang Chou > Date: Sun, 29 Mar 2026 16:07:05 +0800 > Subject: [PATCH] selftests/sched_ext: Skip cyclic_kick_wait on kernels without > deadlock fix > > 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 > --- > 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 >