linux-kernel - Re: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs shutdown path

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Date:   Fri, 29 Apr 2022 19:20:29 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com, coresight@...ts.linaro.org,
        linuxppc-dev@...ts.ozlabs.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-edac@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
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        xen-devel@...ts.xenproject.org, x86@...nel.org,
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        fabiomirmar@...il.com, alejandro.j.jimenez@...cle.com,
        andriy.shevchenko@...ux.intel.com, arnd@...db.de, bp@...en8.de,
        corbet@....net, d.hatayama@...fujitsu.com,
        dave.hansen@...ux.intel.com, dyoung@...hat.com,
        feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs shutdown path

On Wed, 27 Apr 2022 23:48:56 +0100,
"Guilherme G. Piccoli" <gpiccoli@...lia.com> wrote:
> 
> Currently the regular CPU shutdown path for ARM disables IRQs/FIQs
> in the secondary CPUs - smp_send_stop() calls ipi_cpu_stop(), which
> is responsible for that. This makes sense, since we're turning off
> such CPUs, putting them in an endless busy-wait loop.
> 
> Problem is that there is an alternative path for disabling CPUs,
> in the form of function crash_smp_send_stop(), used for kexec/panic
> paths. This functions relies in a SMP call that also triggers a
> busy-wait loop [at machine_crash_nonpanic_core()], but *without*
> disabling interrupts. This might lead to odd scenarios, like early
> interrupts in the boot of kexec'd kernel or even interrupts in
> other CPUs while the main one still works in the panic path and
> assumes all secondary CPUs are (really!) off.
> 
> This patch mimics the ipi_cpu_stop() interrupt disable mechanism
> in the crash CPU shutdown path, hence disabling IRQs/FIQs in all
> secondary CPUs in the kexec/panic path as well.
> 
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> ---
>  arch/arm/kernel/machine_kexec.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index f567032a09c0..ef788ee00519 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -86,6 +86,9 @@ void machine_crash_nonpanic_core(void *unused)
>  	set_cpu_online(smp_processor_id(), false);
>  	atomic_dec(&waiting_for_crash_ipi);
>  
> +	local_fiq_disable();
> +	local_irq_disable();
> +

My expectations would be that, since we're getting here using an IPI,
interrupts are already masked. So what reenabled them the first place?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.