Re: [PATCH 0/4] KVM: arm64: vgic: Locking fixes - Jean-Philippe Brucker

From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Marc Zyngier <maz@kernel.org>
Cc: oliver.upton@linux.dev, james.morse@arm.com,
	suzuki.poulose@arm.com, yuzenghui@huawei.com,
	catalin.marinas@arm.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH 0/4] KVM: arm64: vgic: Locking fixes
Date: Fri, 19 May 2023 14:22:51 +0100	[thread overview]
Message-ID: <20230519132251.GA2976986@myrica> (raw)
In-Reply-To: <86cz2wlnd6.wl-maz@kernel.org>

On Fri, May 19, 2023 at 09:46:45AM +0100, Marc Zyngier wrote:
> On Thu, 18 May 2023 11:09:14 +0100,
> Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:
> > 
> > Another fun locking puzzle, between the new config_lock and srcu.
> > Patch 1 attempts to fix it, and the other patches fix simpler issues.
> 
> Thanks for that and for your excellent description of the problems.
> 
> > I got these lockdep reports while running KVM QEMU on a TCG QEMU, but it
> > can also be triggered by running the vgic_irq kselftest on TCG QEMU.
> > Now, with the fix and lockdep enabled, vgic_irq hangs but I believe it's
> > an unrelated weirdness: if I introduce a separate lockdep warning for
> > some made up locks, then the test passes again. So I'm sending this out
> > now for discussion, and will investigate that one later.
> 
> I've taken these patches for a spin, and I cannot reproduce this hang,
> though I'm running on actual HW and not QEMU. It would be really
> annoying if lockdep actively introduced issues... :-/
> 
> Any chance you could dig into this as you have a good reproducer? I'll
> try to setup a TGC environment on my end as well.

Sure, I'll investigate this. All I know so far is that it is stuck
somewhere in the first test_inject_preemption()

Thanks,
Jean

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