Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

[Rafael J. Wysocki]

On Saturday 12 December 2009, Alan Stern wrote:
> On Sat, 12 Dec 2009, Rafael J. Wysocki wrote:
> 
> > Below is a patch I've just tested, but there's a lockdep problem in it I don't
> > know how to solve.  Namely, lockdep is apparently unhappy with us not releasing
> > the lock taken in device_suspend() and it complains we take it twice in a row
> > (which we do, but for another device).  I need to use down_read_non_owner()
> > to make it shut up and then I also need to use up_read_non_owner() in
> > __device_suspend(), although there's the comment in include/linux/rwsem.h
> > saying exatly this about that:
> > 
> > /*
> >  * Take/release a lock when not the owner will release it.
> >  *
> >  * [ This API should be avoided as much as possible - the
> >  *   proper abstraction for this case is completions. ]
> >  */
> > 
> > (I'd like to know your opinion about that).  Yet, that's not all, because next
> > it complains during resume that __device_resume() releases a lock it didn't
> > acquire, which it clearly does, but that is intentional.  Unfortunately,
> > there's no up_write_non_owner() ...
> 
> Hah!  I knew it!
> 
> How come lockdep didn't complain earlier?  What's different about this 
> patch?  Only the nesting annotations?  Why should adding annotations 
> make lockdep less happy?

I'm not sure.  Perhaps I made a mistake during the previous tests.

Rafael
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