linux-kernel - Re: [PATCH] w1: Introduce a slave mutex for serializing IO.

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Message-ID: <20120501213958.GA15560@ioremap.net>
Date:	Wed, 2 May 2012 01:39:58 +0400
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] w1: Introduce a slave mutex for serializing IO.

On Wed, Apr 25, 2012 at 12:49:14PM +1000, NeilBrown (neilb@...e.de) wrote:
> w1 devices need a mutex to serial IO.
> Most use master->mutex.
> 
> However that is used for other purposes and they can conflict.
> 
> In particular master->mutex is held while w1_attach_slave_device is
> called.
> 
> For bq27000, this registers a 'powersupply' device which tries to
> read the current status.  The attempt to read will cause a deadlock on
> master->mutex.
> 
> So create a new per-slave mutex and use that for serializing IO for
> bq27000.

How will this protect against master doing search for example?
It performs a number of read/write operations which are not allowed to
be interrupted by outside read.

-- 
	Evgeniy Polyakov
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