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Subject: Re: [tip: locking/core] lockdep: Fix usage_traceoverflow
From:   Chris Wilson <chris@chris-wilson.co.uk>
Cc:     linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        tip-bot2 for Peter Zijlstra <tip-bot2@linutronix.de>,
        Qian Cai <cai@redhat.com>, x86 <x86@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Date:   Tue, 27 Oct 2020 16:34:53 +0000
Message-ID: <160381649396.10461.15013696719989662769@build.alporthouse.com>
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Quoting Peter Zijlstra (2020-10-27 15:45:33)
> On Tue, Oct 27, 2020 at 01:29:10PM +0000, Chris Wilson wrote:
> 
> > <4> [304.908891] hm#2, depth: 6 [6], 3425cfea6ff31f7f != 547d92e9ec2ab9af
> > <4> [304.908897] WARNING: CPU: 0 PID: 5658 at kernel/locking/lockdep.c:3679 check_chain_key+0x1a4/0x1f0
> 
> Urgh, I don't think I've _ever_ seen that warning trigger.
> 
> The comments that go with it suggest memory corruption is the most
> likely trigger of it. Is it easy to trigger?

For the automated CI, yes, the few machines that run that particular HW
test seem to hit it regularly. I have not yet reproduced it for myself.
I thought it looked like something kasan would provide some insight for
and we should get a kasan run through CI over the w/e. I suspect we've
feed in some garbage and called it a lock.
-Chris