Messages in this thread | | | Date | Mon, 29 Jun 2015 17:02:46 +0100 | From | Mark Brown <> | Subject | Re: [RFC PATCH 1/2] regmap: add configurable lock class key for lockdep |
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On Mon, Jun 29, 2015 at 08:36:01AM -0700, Arjan van de Ven wrote: > On 6/29/2015 8:32 AM, Mark Brown wrote: > >On Mon, Jun 29, 2015 at 07:35:20AM -0700, Arjan van de Ven wrote:
> >It's not that there's no heirachy of locks, it's that lockdep is unable > >to understand what's going on since it's making simplifying assumptions > >that just aren't true. If I remember the problem correctly it's > >grouping all locks allocated in the same place into one class which > >doesn't work at all for scenarios where you've got a generic interface > >providing services to many devices which may be stacked on top of each > >other.
> but the stacking *IS* a lock hierarchy.
This is why I said "It's not that there is no heirachy of locks".
> it just seems that the hierarchy is implied rather than explicit.
It's explicit for any given system, like I say it's just that lockdep's simplifying assumptions don't cope. As far as I can tell to do something that robustly works without random magic thrown into individual drivers with no clear logic we need to allocate a lock class per regmap (or at least per regmap config that might be instantiated) which is a problem as they need to be statically allocated.
> >>(I would be interested to know how you avoid ABBA deadlocks btw, > >>can you have 2 devices, one with a hierarchy one way, and another > >>with the hierarchy the other way?)
> >I'm not sure I fully understand what you mean here, sorry - do you mean > >in terms of classes or individual devices? The relationships between > >devices are all device and system defined, individual regmaps should be > >treated as separate classes. From this perspective it's basically > >eqivalent to asking how the mutex code avoids misuse of mutexes.
> well what I meant is inividual devices/ranges
> like device A is on devmap A but then ends up using devmap B underneath > (e.g. the lock nesting case)
I'm not entirely sure what you mean by a "devmap" here - is that just a regmap or do you mean something else?
> what prevents there from being a device B that is on devmap B but that > uses devmap A underneath
Assuming you mean regmap nothing prevents that and we should be able to detect if something messes up there. It's a problem for the users, not for regmap itself. [unhandled content-type:application/pgp-signature] | |