rt_stall tests the ext DL server which was introduced in commit cd959a356205 ("sched_ext: Add a DL server for sched_ext tasks"). On older kernels that lack this feature, the test calls ksft_exit_fail() internally which terminates the entire runner process, preventing subsequent tests from running. Add a guard in setup() that checks for the ext_server field in struct rq via __COMPAT_struct_has_field() and returns SCX_TEST_SKIP if not present. Also print the names of skipped tests in the results summary, mirroring the existing behavior for failed tests. Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com> Signed-off-by: Tejun Heo <tj@kernel.org>