Date: Tue, 22 Mar 2011 18:37:02 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: David Collins <collinsd@codeaurora.org>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>,
        Mark Brown <broonie@opensource.wolfsonmicro.com>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Deadlock scenario in regulator core
Message-ID: <20110322223702.GO14675@home.goodmis.org>
References: <4D891C59.1030009@codeaurora.org>
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On Tue, Mar 22, 2011 at 03:02:01PM -0700, David Collins wrote:
> Assume that A has already called regulator_enable for S1 some time in the
> past.
> 
> Consumer A thread execution:
> 	regulator_disable(S1)
> 	mutex_lock(S1)
> 	_regulator_disable(S1)
> 	_notifier_call_chain(S1)
> 	mutex_lock(L2)
> 
> Consumer B thread execution:
> 	regulator_enable(L2)
> 	mutex_lock(L2)
> 	_regulator_enable(L2)
> 	mutex_lock(S1)
> 
> The locks for S1 and L2 are taken in opposite orders in the two threads;
> therefore, it is possible to achieve deadlock.  I am not sure about the
> best way to resolve this situation.  Is there a correctness requirement
> that regulator_enable holds the child regulator's lock when it attempts to
> enable the parent regulator?  Likewise, is the lock around
> _notifier_call_chain required?

I'm curious, if you had enabled lockdep, do you get a warning? If not,
why not?

Thanks,

-- Steve

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