hammer_rel_interlock
int hammer_rel_interlock(struct hammer_lock *lock, int locked);
if (hammer_rel_interlock(&buffer->io.lock, locked) == 0)
if (hammer_rel_interlock(&node->lock, locked) == 0)
if (hammer_rel_interlock(&volume->io.lock, locked)) {
if (hammer_rel_interlock(&buffer->io.lock, 1)) /* safety */