Re: [PATCH] hardlockup: detect hard lockups using secondary (buddy) cpus

From: Daniel Thompson <daniel.thompson@linaro.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Lecopzer Chen <lecopzer.chen@mediatek.com>,
	Stephen Boyd <swboyd@chromium.org>, Chen-Yu Tsai <wens@csie.org>,
	linux-arm-kernel@lists.infradead.org,
	kgdb-bugreport@lists.sourceforge.net,
	Marc Zyngier <maz@kernel.org>,
	linux-perf-users@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>,
	Masayoshi Mizuma <msys.mizuma@gmail.com>,
	Will Deacon <will@kernel.org>,
	ito-yuichi@fujitsu.com, Sumit Garg <sumit.garg@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Colin Cross <ccross@android.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	Guenter Roeck <groeck@chromium.org>,
	Tzung-Bi Shih <tzungbi@chromium.org>,
	Alexander Potapenko <glider@google.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Ingo Molnar <mingo@kernel.org>,
	John Ogness <john.ogness@linutronix.de>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Juergen Gross <jgross@suse.com>,
	Kees Cook <keescook@chromium.org>,
	Laurent Dufour <ldufour@linux.ibm.com>,
	Liam Howlett <liam.howlett@oracle.com>,
	Marco Elver <elver@google.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Miguel Ojeda <ojeda@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Sami Tolvanen <samitolvanen@google.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org
Subject: Re: [PATCH] hardlockup: detect hard lockups using secondary (buddy) cpus
Date: Mon, 24 Apr 2023 13:53:55 +0100	[thread overview]
Message-ID: <20230424125355.GA4054@aspen.lan> (raw)
In-Reply-To: <20230421155255.1.I6bf789d21d0c3d75d382e7e51a804a7a51315f2c@changeid>

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.