From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
linux-mm@kvack.org, punit.agrawal@arm.com,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: Bad page state splats on arm64, v4.11-rc{3,4}
Date: Mon, 3 Apr 2017 16:48:15 +0100 [thread overview]
Message-ID: <20170403154815.GE25550@e104818-lin.cambridge.arm.com> (raw)
In-Reply-To: <20170403113751.GD5706@arm.com>
On Mon, Apr 03, 2017 at 12:37:51PM +0100, Will Deacon wrote:
> On Mon, Apr 03, 2017 at 11:56:29AM +0100, Mark Rutland wrote:
> > On Fri, Mar 31, 2017 at 06:58:45PM +0100, Mark Rutland wrote:
> > > Hi,
> > >
> > > I'm seeing intermittent bad page state splats on arm64 with 4.11-rc3 and
> > > v4.11-rc4. I have not tested earlier kernels, or other architectures.
> > >
> > > So far, it looks like the flags are always bad in the same
> > > way:
> > >
> > > bad because of flags: 0x80(waiters)
> > >
> > > ... though I don't know if that's definitely the case for splat 4, the
> > > BUG at mm/page_alloc.c:800.
> > >
> > > I see this in QEMU VMs launched by Syzkaller, triggering once every few
> > > hours. So far, I have not been able to reproduce the issue in any other
> > > way (including using syz-repro).
> >
> > It looks like this may be an issue with the arm64 HUGETLB code.
> >
> > I wasn't able to trigger the issue over the weekend on a kernel with
> > HUGETLBFS disabled. There are known issues with our handling of
> > contiguous entries, and this might be an artefact of that.
>
> After chatting with Punit, it looks like this might be because the GUP
> code doesn't handle huge ptes (which we create using the contiguous hint),
> so follow_page_pte ends up with one of those and goes wrong. In particular,
> the migration code will certainly do the wrong thing.
>
> I'll probably revert the contiguous support (again) if testing indicates
> that it makes this issue disappear.
It might be worth checking with Punit's patches as well:
https://marc.info/?l=linux-arm-kernel&m=149089199018167&w=2
--
Catalin
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next prev parent reply other threads:[~2017-04-03 15:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-31 17:58 Mark Rutland
2017-04-03 10:56 ` Mark Rutland
2017-04-03 11:37 ` Will Deacon
2017-04-03 15:48 ` Catalin Marinas [this message]
2017-04-03 15:51 ` Mark Rutland
2017-04-03 17:43 ` Mark Rutland
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