Subject: Re: Deadlock scenario in regulator core
From: Steven Rostedt <rostedt@goodmis.org>
To: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: David Collins <collinsd@codeaurora.org>,
        Liam Girdwood <lrg@slimlogic.co.uk>, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20110323000100.GB2529@opensource.wolfsonmicro.com>
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	 <20110323000100.GB2529@opensource.wolfsonmicro.com>
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Date: Tue, 22 Mar 2011 20:38:54 -0400
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On Wed, 2011-03-23 at 00:01 +0000, Mark Brown wrote:
> On Tue, Mar 22, 2011 at 07:19:58PM -0400, Steven Rostedt wrote:
> 
> > Looks to me that the mutex_lock() in _notifier_call_chain needs to be a
> > mutex_lock_nested().
> 
> > The "_nested()" versions are when you have the same type of mutex taken
> > but belonging to two different instances. Like you have here:
> 
> What's a mutex type?  I have to say this is the first time I've heard of
> mutex types and the documentation in mutex.c and mutex-design.txt isn't
> precisely verbose on what mutex_lock_nested() is for or how one would
> pick subclass.

Sorry, I said "mutex type" as a synonym to "lock class". A lock class is
pretty much how a lock is defined.

struct foo {
	struct mutex	m;
};


struct foo *func(void)
{
	bar = kzalloc(sizeof(*bar));
	mutex_init(&bar->m);
}


bar is an instance of lock class struct foo.m. If you have:

	a = func();
	b = func();

Both a->m and b->m are an instance of struct foo.m lock class.

There's better documentation about this in the lockdep-design.txt.

-- Steve


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