Re: [PATCH 1/6] sched: Unbreak wakeups

Davidlohr Bueso
2021-06-02T19:44:23Z

On Wed, 02 Jun 2021, Peter Zijlstra wrote:

>Remove broken task->state references and let wake_up_process() DTRT.
>
>The anti-pattern in these patches breaks the ordering of ->state vs
>COND as described in the comment near set_current_state() and can lead
>to missed wakeups:
>
> (OoO load, observes RUNNING)<-.
> for (;;) { |
> t->state = UNINTERRUPTIBLE; |
> smp_mb(); ,-----> ,' (OoO load, observed !COND)
> | |
> | | COND = 1;
> | `- if (t->state != RUNNING)
> | wake_up_process(t); // not done
> if (COND) ---------'
> break;
> schedule(); // forever waiting
> }
> t->state = TASK_RUNNING;
>
>Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Davidlohr Bueso <dbueso@suse.de>