Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

From: Peter Zijlstra
Date: Tue Feb 19 2019 - 04:15:38 EST

On Mon, Feb 18, 2019 at 04:24:30PM -0800, Linus Torvalds wrote:
> On Mon, Feb 18, 2019 at 2:31 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> >
> > The question is what "fix it" means. I'm really concerned about AC escapes,
> > and everyone else should be, too.
> I do think that it might be the right thing to do to add some kind of
> WARN_ON_ONCE() for AC being set in various can-reschedule situations.

So I disagree.

Either we set AC with preempt disabled, and then we don't need an extra
warning, because we already have a warning about scheduling with
preemption disabled, or we accept that the fault handler can run.