linux-kernel - Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different contexts

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Message-ID: <20130523143137.GH2412@sirena.org.uk>
Date:	Thu, 23 May 2013 09:31:37 -0500
From:	Mark Brown <broonie@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Davide Ciminaghi <ciminaghi@...dd.com>,
	Stephen Warren <swarren@...dotorg.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different
 contexts

On Thu, May 23, 2013 at 04:20:27PM +0200, Lars-Peter Clausen wrote:
> On 05/23/2013 04:05 PM, Mark Brown wrote:

> > This seems really invasive, why not just have the lock that gets passed
> > in point to a struct which has both the lock and the flags?  As far as
> > the core is concerned the lock is just whatever data is required to do
> > the locking, the fact that it's actually two values is an implementation
> > detail of this locking implementation.

> I think that won't work. spin_lock_irqsave() will write to the flags
> parameter before it has successfully taken the look. So if a process running
> on another CPU tries to acquire the the lock while it is already held we'll
> end up overwriting the flags. E.g:

So you'd have to allocate a struct on the stack with a pointer and the
flags in it and initialise the pointer.  Not awesome but not the end of
the world.

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