netdev - Re: [PATCH 2/2] net: ks8851: Handle softirqs at the end of IRQ thread to fix hang

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Message-ID: <001769c4-02de-4114-ab64-46530f36838e@raritan.com>
Date: Mon, 29 Apr 2024 15:50:50 +0200
From: Ronald Wahl <ronald.wahl@...itan.com>
To: Marek Vasut <marex@...x.de>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Mark Brown <broonie@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>
Subject: Re: [PATCH 2/2] net: ks8851: Handle softirqs at the end of IRQ thread
 to fix hang

On 29.04.24 15:23, Marek Vasut wrote:
> On 4/29/24 1:46 PM, Ronald Wahl wrote:
>> Hi,
>
> Hi,
>
>> for the spi version of the chip this change now leads to
>>
>> [   23.793000] BUG: sleeping function called from invalid context at
>> kernel/locking/mutex.c:283
>> [   23.801915] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid:
>> 857, name: irq/52-eth-link
>> [   23.810895] preempt_count: 200, expected: 0
>> [   23.815288] CPU: 0 PID: 857 Comm: irq/52-eth-link Not tainted
>> 6.6.28-sama5 #1
>> [   23.822790] Hardware name: Atmel SAMA5
>> [   23.826717]  unwind_backtrace from show_stack+0xb/0xc
>> [   23.831992]  show_stack from dump_stack_lvl+0x19/0x1e
>> [   23.837433]  dump_stack_lvl from __might_resched+0xb7/0xec
>> [   23.843122]  __might_resched from mutex_lock+0xf/0x2c
>> [   23.848540]  mutex_lock from ks8851_irq+0x1f/0x164
>> [   23.853525]  ks8851_irq from irq_thread_fn+0xf/0x28
>> [   23.858776]  irq_thread_fn from irq_thread+0x93/0x130
>> [   23.864037]  irq_thread from kthread+0x7f/0x90
>> [   23.868699]  kthread from ret_from_fork+0x11/0x1c
>>
>> Actually the spi driver variant does not suffer from the issue as it has
>> different locking so we probably should do the
>> local_bh_disable/local_bh_enable only for the "par" version. What do
>> you think?
>
> Ah sigh, sorry for the breakage. Indeed, the locking is not great here.
>
> I am not entirely sure about the local_bh_disable/enable being par only.
>
> I will try to prepare some sort of a patch, would you be willing to test
> it on the SPI variant ?

Yes, I can help here, thanks. Meanwhile I also have some good understanding
at least on the TX path because we had some issues here in the past.

I will come up myself with another fix in the interrupt handler later. We
currently reset the ISR status flags too late risking a TX queue stall with
the SPI chip variant. They must be reset immediately after reading them.
Need
to wait a bit for field feedback as I was not able to reproduce this
mysqelf.

- ron

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