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

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Message-ID: <x4nbsrscpdv4vmnwprsjdrwgxjr2wrwwq5ygaa4yq52gmicqg6@yuf6xqcchcdh>
Date: Fri, 10 Jan 2025 23:29:47 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: 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)

* Suren Baghdasaryan <surenb@...gle.com> [250110 16:25]:
> 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.

Yeah, I asked the bot to retest the latest unstable (which is still
somewhat out of date..).  I suspect it'll be okay now.  We'll see what
it comes back with.

> 
> >
> > 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, I appreciate it.

Regards,
Liam