linux-kernel - Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity

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Message-ID: <CAJuCfpFSxpps2Vxqb-m-FWbk=O2Lm_yv=Cwg8P-KJXW+uq6tFw@mail.gmail.com>
Date: Fri, 10 Jan 2025 13:24:51 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, Suren Baghdasaryan <surenb@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, 
	syzbot <syzbot+c0673e1f1f054fac28c2@...kaller.appspotmail.com>, 
	akpm@...ux-foundation.org, hdanton@...a.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, David Hildenbrand <david@...hat.com>
Subject: Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

On Fri, Jan 10, 2025 at 11:56 AM Liam R. Howlett
<Liam.Howlett@...cle.com> wrote:
>
> * David Hildenbrand <david@...hat.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.

Possibly... The patchset in linux-next on Jan 1st was somewhat
different from the latest one.

>
> 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?

Ok, I'll see what I can do.
Thanks,
Suren.

>
> Thanks,
> Liam