Re: Fundamental race condition in wait_event_interruptible_exclusive() ?

[Linus Torvalds]

On Mon, Dec 9, 2019 at 9:38 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> > because we've added ourselves as an exclusive writer to the
> > queue. So it _says_ it was interrupted, not woken up, and the wait got
> > cancelled, but because we were an exclusive waiter, we might be the
> > _only_ thing that got woken up,
>
> And that is why ___wait_event() always checks the condition after
> prepare_to_wait_event(), whatever it returns.

Ack. I misread the code, and you're right - if we've been woken up,
the condition is supposed to be true, and we never actually return
-ERESTARTSYS.

So the situation of "got woken but returned error, and lost wakeup"
won't actually ever happen.

Good.

So yeah, I can do what I wanted to do, and it should all work.

I never even tested it, because I was getting fairly anal about
possible races in the pipe code by then.

               Linus