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

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Date:	Mon, 29 Jun 2015 16:32:56 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
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 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.

> (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.

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