linux-kernel - Re: [PATCH v2] i2c: rk3x: fix potential spinlock recursion on poll

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Date:   Thu, 7 Dec 2023 19:00:42 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Dragan Simic <dsimic@...jaro.org>,
        Jensen Huang <jensenhuang@...endlyarm.com>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        Andi Shyti <andi.shyti@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chris Morgan <macroalpha82@...il.com>,
        Benjamin Bara <bbara93@...il.com>
Subject: Re: [PATCH v2] i2c: rk3x: fix potential spinlock recursion on poll

On 12/7/23 17:10, Dragan Simic wrote:
> On 2023-12-07 10:25, Jensen Huang wrote:
>> On Thu, Dec 7, 2023 at 4:37 PM Dragan Simic <dsimic@...jaro.org> wrote:
>>>
>>> On 2023-12-07 09:21, Jensen Huang wrote:
>>> > Possible deadlock scenario (on reboot):
>>> > rk3x_i2c_xfer_common(polling)
>>> >     -> rk3x_i2c_wait_xfer_poll()
>>> >         -> rk3x_i2c_irq(0, i2c);
>>> >             --> spin_lock(&i2c->lock);
>>> >             ...
>>> >         <rk3x i2c interrupt>
>>> >         -> rk3x_i2c_irq(0, i2c);
>>> >             --> spin_lock(&i2c->lock); (deadlock here)
>>> >
>>> > Store the IRQ number and disable/enable it around the polling
>>> transfer.
>>> > This patch has been tested on NanoPC-T4.
>>>
>>> In case you haven't already seen the related discussion linked below,
>>> please have a look.  I also added more people to the list of recipients,
>>> in an attempt to make everyone aware of the different approaches to
>>> solving this issue.
>>>
>>> https://lore.kernel.org/all/655177f4.050a0220.d85c9.3ba0@mx.google.com/T/#m6fc9c214452fec6681843e7f455978c35c6f6c8b
>>
>> Thank you for providing the information. I hadn't seen this link before.
>> After carefully looking into the related discussion, it appears that
>> Dmitry Osipenko is already working on a suitable patch. To avoid
>> duplication
>> or conflicts, my patch can be discarded.
> 
> Thank you for responding so quickly.  Perhaps it would be best to hear
> from Dmitry as well, before discarding anything.  It's been a while
> since Dmitry wrote about working on the patch, so he might have
> abandoned it.

This patch is okay. In general, will be better to have IRQ disabled by
default like I did in my variant, it should allow to remove the spinlock
entirely. Of course this also can be done later on in a follow up
patches. Jensen, feel free to use my variant of the patch, add my
s-o-b+co-developed tags to the commit msg if you'll do. Otherwise I'll
be able to send my patch next week.

-- 
Best regards,
Dmitry