Re: [ANNOUNCE] v5.14-rc5-rt8

[Mike Galbraith <efault@gmx.de>]

On Sun, 2021-08-15 at 11:35 +0200, Vlastimil Babka wrote:
> On 8/15/21 6:17 AM, Mike Galbraith wrote:
> > On Sat, 2021-08-14 at 21:08 +0200, Vlastimil Babka wrote:
> > >
> > > Aha! That's helpful. Hopefully it's just a small issue where we
> > > opportunistically test flags on a page that's protected by the local
> > > lock we didn't take yet, and I didn't realize there's the VM_BUG_ON
> > > which can trigger if our page went away (which we would have realized
> > > after taking the lock).
> >
> > Speaking of optimistic peeking perhaps going badly, why is the below
> > not true?  There's protection against ->partial going disappearing
> > during a preemption... but can't it just as easily appear, so where is
> > that protection?
>
> If it appears, it appears, we don't care, we just leave it there and
> won't use it.
>
> > If the other side of that window is safe, it could use a comment so
> > dummies reading this code don't end up asking mm folks why the heck
> > they don't just take the darn lock and be done with it instead of tap
> > dancing all around thething :)
>
> Well, with your patch, ->partial might appear just after the unlock, so
> does that really change anything?

Viewed from pov consumption is optional, it makes sense.

	-Mike