Re: [PATCH v2] arm64: kexec: Check if IRQ is already masked before masking

From: Thomas Gleixner <tglx@linutronix.de>
To: Eliav Farber <farbere@amazon.com>,
	linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org,
	mpe@ellerman.id.au, npiggin@gmail.com,
	christophe.leroy@csgroup.eu, naveen@kernel.org,
	maddy@linux.ibm.com, paul.walmsley@sifive.com,
	palmer@dabbelt.com, aou@eecs.berkeley.edu,
	akpm@linux-foundation.org, bhe@redhat.com, farbere@amazon.com,
	hbathini@linux.ibm.com, adityag@linux.ibm.com,
	songshuaishuai@tinylab.org, takakura@valinux.co.jp,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-riscv@lists.infradead.org
Cc: jonnyc@amazon.com
Subject: Re: [PATCH v2] arm64: kexec: Check if IRQ is already masked before masking
Date: Thu, 28 Nov 2024 11:39:11 +0100	[thread overview]
Message-ID: <87o71zy75c.ffs@tglx> (raw)
In-Reply-To: <20241127152236.26122-1-farbere@amazon.com>

On Wed, Nov 27 2024 at 15:22, Eliav Farber wrote:
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index 80ceb5bd2680..54d0bd1bd449 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -142,11 +142,8 @@ static void machine_kexec_mask_interrupts(void)
>  		if (chip->irq_eoi && irqd_irq_inprogress(&desc->irq_data))
>  			chip->irq_eoi(&desc->irq_data);
>  
> -		if (chip->irq_mask)
> -			chip->irq_mask(&desc->irq_data);
> -
> -		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
> -			chip->irq_disable(&desc->irq_data);
> +		irq_set_status_flags(i, IRQ_DISABLE_UNLAZY);
> +		irq_disable(desc);

This is just wrong. If the interrupt was torn down, then its state is
deactivated and it was masked already. So the EOI handling and the
mask/disable dance are neither required nor make sense.

So this whole thing should be:

		chip = irq_desc_get_chip(desc);
-		if (!chip)
+		if (!chip || !irqd_is_started(&desc->irq_data))
                	continue;

But what's worse is that we have 4 almost identical variants of the same
code.

So instead of exposing core functionality and "fixing" up four variants,
can we please have a consolidated version of this function in the core
code:
                struct irq_chip *chip;
                int check_eoi = 1;

		chip = irq_desc_get_chip(desc);
		if (!chip || !irqd_is_started(&desc->irq_data))
                	continue;

                if (IS_ENABLED(CONFIG_.....)) {
                        /*
                         * Add a sensible comment which explains this.
                         */
                	check_eoi = irq_set_irqchip_state(....);
                }

		if (check_eoi && ....)
                	chip->irq_eoi(&desc->irq_data);

		irq_shutdown(desc);

No?

Thanks,

        tglx