Re: Deadlock scenario in regulator core

[Steven Rostedt <rostedt@goodmis.org>]

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