kernel: process: livelock in thread_free()

# Issue

We are sometimes encountering a livelock situation when freeing the thread structure in thread free,
due to  kfree() being called in a non-preemptible scope. The kfree() function tries to acquire
the underlying slab's lock, which may currently be held by another process. Since the current process
cannot be rescheduled we end up stuck here, forever. 