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

[David Hildenbrand (Arm)]

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