Re: [PATCH 0/4] KVM: arm64: vgic: Locking fixes

From: Marc Zyngier <maz@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.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 09:46:45 +0100	[thread overview]
Message-ID: <86cz2wlnd6.wl-maz@kernel.org> (raw)
In-Reply-To: <20230518100914.2837292-1-jean-philippe@linaro.org>

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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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