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

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Date:   Tue, 6 Jul 2021 07:23:17 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [irqchip: irq/irqchip-next] irqdomain: Protect the linear revmap
 with RCU

On 7/6/21 2:24 AM, Marc Zyngier wrote:
> 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 ?
> 

Actually they do.

> 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.
> 

Yes, turns out I did not have the necessary debugging options enabled
in my other mips tests.

Thanks,
Guenter