On 10/09, Peter Zijlstra wrote:

One thing you might need to consider is the memory ordering, will the
list_empty -- either careful or not -- observe the right list pointer,
or could it -- when racing with wait_event()/prepare_to_wait() --
observe a stale value. Or.. is that all already covered in on the use
site.

I agree.

Without spin_lock(q->lock) (or some other barriers) wait_event-like
code can miss an event.

wait_event:

	prepare_to_wait(wq)	// takes wq->lock

	if (!CONDITION)
		schedule();

Now,

	CONDITION = 1;
	wake_up(wq);

at least need the full mb() before lits_empty().

Oleg.