linux-kernel - Re: [PATCH v8 09/10] arm64: kgdb: Roundup cpus using IPI as NMI

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Message-ID: <20230512140051.GA217273@aspen.lan>
Date:   Fri, 12 May 2023 15:00:51 +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,
        Alexandru Elisei <alexandru.elisei@....com>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 09/10] arm64: kgdb: Roundup cpus using IPI as NMI

On Wed, Apr 19, 2023 at 03:56:03PM -0700, Douglas Anderson wrote:
> From: Sumit Garg <sumit.garg@...aro.org>
>
> arm64 platforms with GICv3 or later supports pseudo NMIs which can be
> leveraged to roundup CPUs which are stuck in hard lockup state with
> interrupts disabled that wouldn't be possible with a normal IPI.
>
> So instead switch to roundup CPUs using IPI turned as NMI. And in
> case a particular arm64 platform doesn't supports pseudo NMIs,
> it will switch back to default kgdb CPUs roundup mechanism.
>
> 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)
>
>  arch/arm64/kernel/ipi_nmi.c |  5 +++++
>  arch/arm64/kernel/kgdb.c    | 18 ++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
> index c592e92b8cbf..2adaaf1519e5 100644
> --- a/arch/arm64/kernel/ipi_nmi.c
> +++ b/arch/arm64/kernel/ipi_nmi.c
> @@ -8,6 +8,7 @@
>
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
> +#include <linux/kgdb.h>
>  #include <linux/nmi.h>
>  #include <linux/smp.h>
>
> @@ -45,10 +46,14 @@ bool arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
>  static irqreturn_t ipi_nmi_handler(int irq, void *data)
>  {
>  	irqreturn_t ret = IRQ_NONE;
> +	unsigned int cpu = smp_processor_id();

Does this play nice with CONFIG_DEBUG_PREEMPT? I may have missed
something about the NMI entry but a quick scan of the arm64
arch_irq_disabled() suggests that debug_smp_processor_id() will issue
warnings at this point...

Other than I didn't see anything I don't like here.


Daniel.