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

From: Marc Zyngier
Date: Tue Jul 06 2021 - 05:24:34 EST

On Mon, 05 Jul 2021 21:36:36 +0100,
Guenter Roeck <linux@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> to the real patch.


> 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.



Without deviation from the norm, progress is not possible.