selftests/namespaces: Wait for thread exit via pidfd in active-ref tests

pthread_join() returns once exit_mm() wakes the CLEARTID futex, but the
exiting thread drops its namespace reference later, in
exit_nsproxy_namespaces(). The joining thread can therefore still see the
namespace as active, making the final open_by_handle_at() check in
thread_ns_inactive_after_exit and thread_ns_fd_keeps_active fail
intermittently.

Have the thread open a PIDFD_THREAD pidfd on itself and poll it before
pthread_join(). A pidfd becomes readable from exit_notify(), which runs
after exit_nsproxy_namespaces().

Fixes: 29f083c49982 ("selftests/namespace: first threaded active reference count test")
Fixes: ee861032381b ("selftests/namespace: second threaded active reference count test")
Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@marliere.net>
Link: https://patch.msgid.link/20261001-selftests-namespaces-nsid_race-v1-1-25f542cf0b9c@marliere.net
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions