Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

Liam R. Howlett
2025-01-10T19:56:20Z

* David Hildenbrand <david@redhat.com> [250110 11:31]:
> On 10.01.25 17:27, Matthew Wilcox wrote:
> > On Fri, Jan 10, 2025 at 05:19:54PM +0100, David Hildenbrand wrote:
> > > On 10.01.25 17:14, Matthew Wilcox wrote:
> > > > On Fri, Jan 10, 2025 at 04:48:03PM +0100, David Hildenbrand wrote:
> > > > > If I would have to guess, I would assume that we have a refcount issue such
> > > > > that we succeed in splitting a folio while concurrently mapping it.
> > > >
> > > > That would seem hard to accomplish, because both hold the folio lock,
> > > > so it wouldn't be just a refcount bug but also a locking bug. Not sure
> > > > what this is though.
> > >
> > > Yeah, but we also have
> > >
> > > https://lkml.kernel.org/r/6774bf44.050a0220.25abdd.098a.GAE@google.com
> >
> > That one is a UAF on the vma, so it's either a different issue, or the
> > problem is with the VMA refcount/lookup/..., not the folio refcount.
> > cc'ing the relevant maintainers.
>
> Agreed, it's all a bit confusing.
>

This might involve Suren's patch set which changes the locking of the
vmas.

Suren, if you respin and it's not too much trouble can you please make a
git branch with the latest patches for easier review and testing?

Thanks,
Liam