linux-kernel - Re: [irqchip: irq/irqchip-next] irqdomain: Protect the linear revmap with RCU

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Message-ID: <87eecb94mq.wl-maz@kernel.org>
Date:   Tue, 06 Jul 2021 10:24:29 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [irqchip: irq/irqchip-next] irqdomain: Protect the linear revmap with RCU

On Mon, 05 Jul 2021 21:36:36 +0100,
Guenter Roeck <linux@...ck-us.net> wrote:
> 
> On 7/5/21 11:43 AM, Marc Zyngier wrote:

> > It definitely helps, and confirms my hunch. With the patch below, I'm
> > not getting the warnings anymore. I'm pretty sure a number of other
> > MIPS systems suffer from similar issues, which I'll address similarly.
> > 
> > Please let me know if that addresses the issue on your end.
> > 
> 
> Yes, it does. Feel free to add
> 
> Tested-by: Guenter Roeck <linux@...ck-us.net>
> 
> to the real patch.

Thanks.

> Now the big question: Why does this only affect 32-bit little endian
> mips images, but not the matching big endian images, nor 64-bit images ?

Are you sure these images are using the exact same HW? A bunch (most?)
of MIPS systems do not use irqdomains in their root interrupt
handling, so this issue wouldn't be visible (irq_enter() will already
have been done for the chained interrupt handling).

FWIW, I can reproduce the problem by switching your mipsel config to
BE, and adding this patch fixes it.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.