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Subject: Re: regulator: deadlock vs memory reclaim
From:   Dmitry Osipenko <digetx@gmail.com>
To:     =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>,
        Mark Brown <broonie@kernel.org>
Cc:     Liam Girdwood <lgirdwood@gmail.com>, linux-kernel@vger.kernel.org
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Date:   Tue, 11 Aug 2020 00:23:37 +0300
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10.08.2020 23:56, Dmitry Osipenko пишет:
> 10.08.2020 23:21, Dmitry Osipenko пишет:
>> 10.08.2020 23:18, Michał Mirosław пишет:
>>> On Mon, Aug 10, 2020 at 11:15:28PM +0300, Dmitry Osipenko wrote:
>>>> 10.08.2020 23:09, Michał Mirosław пишет:
>>>>> At first I also thought so, but there's more. Below is a lockdep
>>>>> complaint with your patch applied. I did a similar patch and then two more
>>>>> (following) and that is still not enough (sysfs/debugfs do allocations,
>>>>> too).
>>>> Then it should be good to move the locking for init_coupling() like I
>>>> suggested and use GFP_NOWAIT for the two other cases. It all could be a
>>>> single small patch. Could you please check whether GFP_NOWAIT helps?
>>>
>>> This would be equivalent to my patches. Problem with sysfs and debugfs
>>> remains as they don't have the option of GFP_NOWAIT. This needs to be
>>> moved outside of the locks.
>>
>> Ah okay, you meant the debugfs core. I see now, thanks.
>>
> 
> This indeed needs a capital solution.
> 
> It's not obvious how to fix it.. we can probably remove taking the
> list_mutex from lock_dependent(), but this still won't help the case of
> memory reclaiming because reclaim may cause touching the already locked
> regulator. IIUC, the case of memory reclaiming under regulator lock was
> always dangerous and happened to work by chance before, correct?
> 

And like Mark mentioned before, this situation also potentially may
happen from other paths.