Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
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
References: <cover.1597089543.git.mirq-linux@rere.qmqm.pl>
 <9a5c8ca6-2027-4d89-e290-6db564b99962@gmail.com>
 <20200810201846.GA12091@qmqm.qmqm.pl>
 <d9c3f307-e124-ea5e-c036-71138f9232f4@gmail.com>
Message-ID: <81e490af-d1da-873a-51b4-130ca82fd1f6@gmail.com>
Date:   Mon, 10 Aug 2020 23:56:13 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <d9c3f307-e124-ea5e-c036-71138f9232f4@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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?