Re: Deadlock scenario in regulator core

From: David Collins
Date: Tue Mar 22 2011 - 19:41:34 EST

On 03/22/2011 04:19 PM, 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:
> blocking_notifier_call_chain(&rdev->notifier, event, NULL);
> /* now notify regulator we supply */
> list_for_each_entry(_rdev, &rdev->supply_list, slist) {
> mutex_lock(&_rdev->mutex);
> _notifier_call_chain(_rdev, event, data);
> mutex_unlock(&_rdev->mutex);
> }
> The rdev->mutex is already held, so we don't need to take it to call the
> blocking_notifier_call_chain() with the rdev->notifier. But then the
> list of rdev's in the rdev->supply_list are different instances but we
> are still taking the same type of lock. lockdep treats all instances of
> the same lock the same, so to lockdep this looks like a deadlock. To
> teach lockdep that this is a different instance, simply use
> mutex_lock_nested() instead.
> -- Steve

There seem to be very few uses of mutex_lock_nested() in the kernel. Most
of them use subclass = SINGLE_DEPTH_NESTING. Would this be sufficient for
usage in the regulator core in _notifier_call_chain (and perhaps other
places) or should some other subclass be used?


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