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From:   Steve Capper <Steve.Capper@arm.com>
To:     Will Deacon <will@kernel.org>
CC:     Qian Cai <cai@lca.pw>, Catalin Marinas <Catalin.Marinas@arm.com>,
        "Andrey Konovalov" <andreyknvl@google.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        nd <nd@arm.com>
Subject: Re: "arm64/for-next/core" causes boot panic
Thread-Topic: "arm64/for-next/core" causes boot panic
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Date:   Tue, 13 Aug 2019 14:41:32 +0000
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On Tue, Aug 13, 2019 at 03:04:52PM +0100, Steve Capper wrote:
> Hi Will,
>=20
> On Tue, Aug 13, 2019 at 01:06:44PM +0100, Will Deacon wrote:
> > [+Steve]
> >=20
> > On Tue, Aug 13, 2019 at 11:58:52AM +0100, Will Deacon wrote:
> > > On Tue, Aug 13, 2019 at 10:02:01AM +0100, Will Deacon wrote:
> > > > On Mon, Aug 12, 2019 at 05:51:35PM -0400, Qian Cai wrote:
> > > > > Booting today's linux-next on an arm64 server triggers a panic wi=
th
> > > > > CONFIG_KASAN_SW_TAGS=3Dy pointing to this line,
> > > >=20
> > > > Is this the only change on top of defconfig? If not, please can you=
 share
> > > > your full .config?
> > > >=20
> > > > > kfree()->virt_to_head_page()->compound_head()
> > > > >=20
> > > > > unsigned long head =3D READ_ONCE(page->compound_head);
> > > > >=20
> > > > > The bisect so far indicates one of those could be bad,
> > > >=20
> > > > I guess that means the issue is reproducible on the arm64 for-next/=
core
> > > > branch. Once I have your .config, I'll give it a go.
> > >=20
> > > FWIW, I've managed to reproduce this using defconfig + SW_TAGS on
> > > for-next/core, so I'll keep investigating.
>=20
> I've installed clang-8 and enabled CONFIG_KASAN_SW_TAGS and was able to
> reproduce the problem quite rapidly. Many apologies for missing this
> before in my testing.
>=20
> >=20
> > Right, hacky diff below seems to resolve this, so I'll split this up in=
to
> > some proper patches as there is more than one bug here.
> >=20
> > Thanks,
> >=20
> > Will
> >=20
> > --->8
> >=20
> > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/m=
emory.h
> FWIW, this fixed the crashes I experienced, I'll run some additional
> tests.
>=20

This works for me with 52-bit VAs + CONFIG_KASAN_SW_TAGS +
CONFIG_DEBUG_VIRTUAL + CONFIG_DEBUG_VM

FWIW:
Tested-by: Steve Capper <steve.capper@arm.com>

Cheers,
--=20
Steve