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

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Date:   Fri, 29 Apr 2022 18:38:19 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Marc Zyngier <maz@...nel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.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,
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        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

Thanks Marc and Michael for the review/discussion.

On 29/04/2022 15:20, Marc Zyngier wrote:
> [...]

> 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.
> 

Marc, I did some investigation in the code (and tried/failed in the ARM
documentation as well heh), but this is still not 100% clear for me.

You're saying IPI calls disable IRQs/FIQs by default in the the target
CPUs? Where does it happen? I'm a bit confused if this a processor
mechanism, or it's in code.

Looking the smp_send_stop() in arch/arm/, it does IPI the CPUs, with the
flag IPI_CPU_STOP, eventually calling ipi_cpu_stop(), and the latter
does disable IRQ/FIQ in code - that's where I stole my code from.

But crash_smp_send_stop() is different, it seems to IPI the other CPUs
with the flag IPI_CALL_FUNC, which leads to calling
generic_smp_call_function_interrupt() - does it disable interrupts/FIQs
as well? I couldn't find it.

Appreciate your clarifications about that, thanks again.
Cheers,


Guilherme