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

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

On Fri, Apr 21, 2023 at 03:53:30PM -0700, Douglas Anderson wrote:
> From: Colin Cross <ccross@...roid.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.