linux-kernel - Re: [PATCH v8 07/10] kgdb: Expose default CPUs roundup fallback mechanism

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Date:   Fri, 12 May 2023 14:48:53 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>, ito-yuichi@...itsu.com,
        kgdb-bugreport@...ts.sourceforge.net, Chen-Yu Tsai <wens@...e.org>,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        linux-arm-kernel@...ts.infradead.org,
        Stephen Boyd <swboyd@...omium.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-perf-users@...r.kernel.org,
        Jason Wessel <jason.wessel@...driver.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 07/10] kgdb: Expose default CPUs roundup fallback
 mechanism

On Wed, Apr 19, 2023 at 03:56:01PM -0700, Douglas Anderson wrote:
> From: Sumit Garg <sumit.garg@...aro.org>
>
> Add a new API kgdb_smp_call_nmi_hook() to expose default CPUs roundup
> mechanism to a particular archichecture as a runtime fallback if it
> detects to not support NMI roundup.
>
> Currently such an architecture example is arm64 supporting pseudo NMIs
> feature which is only available on platforms which have support for GICv3
> or later version.
>
> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
> Tested-by: Chen-Yu Tsai <wens@...e.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
> (no changes since v1)
>
>  include/linux/kgdb.h      | 12 ++++++++++++
>  kernel/debug/debug_core.c |  8 +++++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index 258cdde8d356..87713bd390f3 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -199,6 +199,18 @@ kgdb_arch_handle_qxfer_pkt(char *remcom_in_buffer,
>
>  extern void kgdb_call_nmi_hook(void *ignored);
>
> +/**
> + *	kgdb_smp_call_nmi_hook - Provide default fallback mechanism to
> + *				 round-up CPUs
> + *
> + *	If you're using the default implementation of kgdb_roundup_cpus()
> + *	this function will be called.  And if an arch detects at runtime to
> + *	not support NMI based roundup then it can fallback to default
> + *	mechanism using this API.
> + */
> +
> +extern void kgdb_smp_call_nmi_hook(void);

Concept looks sensible but this is a terrible name for aa command to
round up the CPUs using smp_call... functions. Whilst it is true it that
kgdb_roundup_cpus() does use kgdb_call_nmi_hook() internally that
doesn't mean we should name functions after it. They should be named
after what they are do, not how they do it.

Something more like kgdb_roundup_cpus_with_smp_call() would be a much
better name.


Daniel.