linux-kernel - Re: "arm64/for-next/core" causes boot panic

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Message-ID: <20190813140451.GA24579@capper-ampere.manchester.arm.com>
Date:   Tue, 13 Aug 2019 14:04:54 +0000
From:   Steve Capper <Steve.Capper@....com>
To:     Will Deacon <will@...nel.org>
CC:     Qian Cai <cai@....pw>, Catalin Marinas <Catalin.Marinas@....com>,
        "Andrey Konovalov" <andreyknvl@...gle.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        nd <nd@....com>
Subject: Re: "arm64/for-next/core" causes boot panic

Hi Will,

On Tue, Aug 13, 2019 at 01:06:44PM +0100, Will Deacon wrote:
> [+Steve]
> 
> 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 with
> > > > CONFIG_KASAN_SW_TAGS=y pointing to this line,
> > > 
> > > Is this the only change on top of defconfig? If not, please can you share
> > > your full .config?
> > > 
> > > > kfree()->virt_to_head_page()->compound_head()
> > > > 
> > > > unsigned long head = READ_ONCE(page->compound_head);
> > > > 
> > > > The bisect so far indicates one of those could be bad,
> > > 
> > > 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.
> > 
> > FWIW, I've managed to reproduce this using defconfig + SW_TAGS on
> > for-next/core, so I'll keep investigating.

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.

> 
> Right, hacky diff below seems to resolve this, so I'll split this up into
> some proper patches as there is more than one bug here.
> 
> Thanks,
> 
> Will
> 
> --->8
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
FWIW, this fixed the crashes I experienced, I'll run some additional
tests.

Cheers,
-- 
Steve