netdev - Re: [PATCH] net: ks8851: Drop IRQ threading

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Message-ID: <8605c773-0778-a256-0cc2-7d76eebe3cfe@denx.de>
Date: Wed, 31 May 2023 04:19:55 +0200
From: Marek Vasut <marex@...x.de>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
 "David S. Miller" <davem@...emloft.net>, Geoff Levand <geoff@...radead.org>,
 Jakub Kicinski <kuba@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
 Paolo Abeni <pabeni@...hat.com>, Petr Machata <petrm@...dia.com>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: Re: [PATCH] net: ks8851: Drop IRQ threading

On 12/16/22 23:32, Dmitry Torokhov wrote:
> On Fri, Dec 16, 2022 at 11:19:27PM +0100, Marek Vasut wrote:
>> On 12/16/22 22:54, Dmitry Torokhov wrote:
>>> On Fri, Dec 16, 2022 at 02:23:04PM +0100, Eric Dumazet wrote:
>>>> On Fri, Dec 16, 2022 at 1:47 PM Marek Vasut <marex@...x.de> wrote:
>>>>>
>>>>> Request non-threaded IRQ in the KSZ8851 driver, this fixes the following warning:
>>>>> "
>>>>> NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!
>>>>
>>>> This changelog is a bit terse.
>>>>
>>>> Why can other drivers use request_threaded_irq(), but not this one ?
>>>
>>> This one actually *has* to use threading, as (as far as I can see) the
>>> "lock" that is being taken in ks8851_irq for the SPI variant of the
>>> device is actually a mutex, so we have to be able to sleep in the
>>> interrupt handler...
>>
>> So maybe we should use threaded one for the SPI variant and non-threaded one
>> for the Parallel bus variant ?
> 
> I do not think the threading itself is the issue. I did a quick search
> and "Non-RCU local softirq work is pending" seems to be a somewhat
> common issue in network drivers. I think you should follow for example
> thread in https://lore.kernel.org/all/87y28b9nyn.ffs@tglx/t/ and collect
> the trace data and bug tglx and Paul. I see you are even on CC in that
> thread...

I ran into this again, with Linux 6.1.30, the machine with this MAC just 
flat out freezes when the MAC comes up, if I add this patch the machine 
works as it should. I don't have a good explanation however. Any ideas?