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

Matthew Wilcox
2025-01-10T16:27:09Z

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.