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Subject: RE: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs
 shutdown path
Thread-Topic: [PATCH 02/30] ARM: kexec: Disable IRQs/FIQs also on crash CPUs
 shutdown path
Thread-Index: AQHYWolciKXO2fn1XUueFH8wz+psXK0HFf6Q
Date:   Fri, 29 Apr 2022 16:26:02 +0000
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References: <20220427224924.592546-1-gpiccoli@igalia.com>
 <20220427224924.592546-3-gpiccoli@igalia.com>
In-Reply-To: <20220427224924.592546-3-gpiccoli@igalia.com>
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From: Guilherme G. Piccoli <gpiccoli@igalia.com> Sent: Wednesday, April 27,=
 2022 3:49 PM
>=20
> 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.
>=20
> 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

s/functions relies in/function relies on/

> 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.
>=20
> 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.
>=20
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Russell King <linux@armlinux.org.uk>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
> ---
>  arch/arm/kernel/machine_kexec.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_ke=
xec.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);
>=20
> +	local_fiq_disable();
> +	local_irq_disable();
> +
>  	while (1) {
>  		cpu_relax();
>  		wfe();
> --
> 2.36.0