linux-kernel - Re: [PATCHv3 3/6] arm64: irq: rework root IRQ handler registration

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Date:   Wed, 24 Mar 2021 16:49:22 +0000
From:   Will Deacon <will@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, james.morse@....com, marcan@...can.st,
        maz@...nel.org, tglx@...utronix.de
Subject: Re: [PATCHv3 3/6] arm64: irq: rework root IRQ handler registration

On Mon, Mar 15, 2021 at 11:56:26AM +0000, Mark Rutland wrote:
> If we accidentally unmask IRQs before we've registered a root IRQ
> handler, handle_arch_irq will be NULL, and the IRQ exception handler
> will branch to a bogus address.
> 
> To make this easier to debug, this patch initialises handle_arch_irq to
> a default handler which will panic(), making such problems easier to
> debug. When we add support for FIQ handlers, we can follow the same
> approach.
> 
> When we add support for a root FIQ handler, it's possible to have root
> IRQ handler without an root FIQ handler, and in theory the inverse is
> also possible. To permit this, and to keep the IRQ/FIQ registration
> logic similar, this patch removes the panic in the absence of a root IRQ
> controller. Instead, set_handle_irq() logs when a handler is registered,
> which is sufficient for debug purposes.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Tested-by: Hector Martin <marcan@...can.st>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Will Deacon <will@...nel.org>
> ---
>  arch/arm64/kernel/irq.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)

Acked-by: Will Deacon <will@...nel.org>

Will