linux-kernel - Re: [RFC PATCH 1/2] regmap: add configurable lock class key for lockdep

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Date:	Mon, 29 Jun 2015 08:36:01 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Nicolas Boichat <drinkcat@...omium.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Antti Palosaari <crope@....fi>, Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Bard Liao <bardliao@...ltek.com>,
	Oder Chiou <oder_chiou@...ltek.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	alsa-devel@...a-project.org,
	Anatol Pomozov <anatol.pomozov@...il.com>
Subject: Re: [RFC PATCH 1/2] regmap: add configurable lock class key for lockdep

On 6/29/2015 8:32 AM, Mark Brown wrote:
> On Mon, Jun 29, 2015 at 07:35:20AM -0700, Arjan van de Ven wrote:
>
>> lockdep assumes that there is a known lock hierarchy, at least known
>> to the developer.
>
>> seems like for regmap there isn't
>
> It's not that there's no heirachy of locks, it's that lockdep is unable
> to understand what's going on since it's making simplifying assumptions
> that just aren't true.  If I remember the problem correctly it's
> grouping all locks allocated in the same place into one class which
> doesn't work at all for scenarios where you've got a generic interface
> providing services to many devices which may be stacked on top of each
> other.

but the stacking *IS* a lock hierarchy.

it just seems that the hierarchy is implied rather than explicit.


>> (I would be interested to know how you avoid ABBA deadlocks btw,
>> can you have 2 devices, one with a hierarchy one way, and another
>> with the hierarchy the other way?)
>
> I'm not sure I fully understand what you mean here, sorry - do you mean
> in terms of classes or individual devices?  The relationships between
> devices are all device and system defined, individual regmaps should be
> treated as separate classes.  From this perspective it's basically
> eqivalent to asking how the mutex code avoids misuse of mutexes.

well what I meant is inividual devices/ranges

like device A is on devmap A but then ends up using devmap B underneath
(e.g. the lock nesting case)

what prevents there from being a device B that is on devmap B but that
uses devmap A underneath


>

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