turnstile_lookup
ts = turnstile_lookup(&invl_gen_ts);
ts = turnstile_lookup(&m->lock_object);
ts = turnstile_lookup(&rm->lock_object);
ts = turnstile_lookup(&rw->lock_object);
ts = turnstile_lookup(&rw->lock_object);
ts = turnstile_lookup(&rw->lock_object);
struct turnstile *turnstile_lookup(struct lock_object *);