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Date:   Mon, 24 Apr 2023 13:53:55 +0100
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Douglas Anderson <dianders@chromium.org>
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Subject: Re: [PATCH] hardlockup: detect hard lockups using secondary (buddy)
 cpus
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On Fri, Apr 21, 2023 at 03:53:30PM -0700, Douglas Anderson wrote:
> From: Colin Cross <ccross@android.com>
>
> Implement a hardlockup detector that can be enabled on SMP systems
> that don't have an arch provided one or one implemented atop perf by
> using interrupts on other cpus. Each cpu will use its softlockup
> hrtimer to check that the next cpu is processing hrtimer interrupts by
> verifying that a counter is increasing.
>
> NOTE: unlike the other hard lockup detectors, the buddy one can't
> easily provide a backtrace on the CPU that locked up. It relies on
> some other mechanism in the system to get information about the locked
> up CPUs. This could be support for NMI backtraces like [1], it could
> be a mechanism for printing the PC of locked CPUs like [2], or it
> could be something else.
>
> This style of hardlockup detector originated in some downstream
> Android trees and has been rebased on / carried in ChromeOS trees for
> quite a long time for use on arm and arm64 boards. Historically on
> these boards we've leveraged mechanism [2] to get information about
> hung CPUs, but we could move to [1].

On the Arm platforms is this code able to leverage the existing
infrastructure to extract status from stuck CPUs:
https://docs.kernel.org/trace/coresight/coresight-cpu-debug.html


Daniel.