Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops

[Michael S. Tsirkin]

On Wed, Jul 08, 2026 at 02:03:21PM +0200, David Hildenbrand (Arm) wrote:
> On 7/7/26 22:27, Michael S. Tsirkin wrote:
> > On Wed, Jul 01, 2026 at 10:36:31AM +0200, David Hildenbrand (Arm) wrote:
> >> On 7/1/26 10:33, Michael S. Tsirkin wrote:
> >>>
> >>> what do you think ;) post it?
> >>
> >> As RFC please :) [and if it's AI generated, obviously properly reviewed and
> >> reworked by you]
> > 
> > I spent a bit poking at it, and it's hairy.
> 
> What I thought ...
> 
> > The issue is that we have calls to both set and clear bits.
> > When we record them in a side side structure so they can be retried,
> > we have to carefully record both sets and clears and their order and make sure
> > they do not bypass each other. So if there's set already in the
> > structure, we need to take it out of structure and only then add a clear.
> > 
> > It gets very hairy because we want to set from NMI.  So now we can have
> > clear in the data structure and set from NMI bypasses that. Now what?
> > And set from NMI can't be 100% safe anyway as we discussed ...  Kinda
> > reduced my motivation to try and make this reliable at all.
> 
> Maybe we should just really keep it as broken as it currently is. It's not
> really worth our time fixing basic design flaws ... given that we didn't have
> any report about these races so far :/
> 
> I mean, sure, if it's easy, ... but it sounds like getting more and more complex.
> 
> -- 
> Cheers,
> 
> David

Right. Either we do the RCU thing or let it be. But then I'm uninclined
to even bother with fixing other weird behaviour I see there.

-- 
MST