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Date:   Mon, 17 Oct 2022 15:17:35 +0100
From:   "Russell King (Oracle)" <>
To:     "Guilherme G. Piccoli" <>
Cc:     Marc Zyngier <>,,,
        Mark Rutland <>,,
        Catalin Marinas <>,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Subject: Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs
 shutdown paths

On Mon, Oct 17, 2022 at 11:00:46AM -0300, Guilherme G. Piccoli wrote:
> On 18/09/2022 10:58, Guilherme G. Piccoli wrote:
> > On 19/08/2022 19:17, Guilherme G. Piccoli 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. IRQs are architecturally masked when we
> >> take an interrupt, but FIQs are high priority than IRQs, hence they
> >> aren't masked. With that said, it makes sense to disable FIQs here,
> >> but there's no need for (re-)disabling IRQs.
> >>
> >> More than that: there is an alternative path for disabling CPUs,
> >> in the form of function crash_smp_send_stop(), which is used for
> >> kexec/panic path. This function relies on a SMP call that also
> >> triggers a busy-wait loop [at machine_crash_nonpanic_core()], but
> >> without disabling FIQs. This might lead to odd scenarios, like
> >> early interrupts in the boot of kexec'd kernel or even interrupts
> >> in secondary "disabled" CPUs while the main one still works in the
> >> panic path and assumes all secondary CPUs are (really!) off.
> >>
> >> So, let's disable FIQs in both paths and *not* disable IRQs a second
> >> time, since they are already masked in both paths by the architecture.
> >> This way, we keep both CPU quiesce paths consistent and safe.
> >>
> >> Cc: Marc Zyngier <>
> >> Cc: Michael Kelley <>
> >> Cc: Russell King <>
> >> Signed-off-by: Guilherme G. Piccoli <>
> >>
> Monthly ping - let me know if there's something I should improve in
> order this fix is considered!

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