Re: [PATCH 3/5] mm, notifier: Catch sleeping/blocking for !blockable

[Daniel Vetter]

On Wed, Aug 14, 2019 at 09:00:29PM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 14, 2019 at 10:20:25PM +0200, Daniel Vetter wrote:
> > We need to make sure implementations don't cheat and don't have a
> > possible schedule/blocking point deeply burried where review can't
> > catch it.
> > 
> > I'm not sure whether this is the best way to make sure all the
> > might_sleep() callsites trigger, and it's a bit ugly in the code flow.
> > But it gets the job done.
> > 
> > Inspired by an i915 patch series which did exactly that, because the
> > rules haven't been entirely clear to us.
> 
> I thought lockdep already was able to detect:
> 
>  spin_lock()
>  might_sleep();
>  spin_unlock()
> 
> Am I mistaken? If yes, couldn't this patch just inject a dummy lockdep
> spinlock?

Hm ... assuming I didn't get lost in the maze I think might_sleep (well
___might_sleep) doesn't do any lockdep checking at all. And we want
might_sleep, since that catches a lot more than lockdep.

Maybe you mixed it up with the hard/softirq context stuff that lockdep
tracks and complains about if you get it wrong?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch