Re: [PATCH 1/2] drm/i915: fix possible RPM ref leaking during RPS disabling

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, May 13, 2014 at 04:46:10PM +0300, Imre Deak wrote:
> On Mon, 2014-05-12 at 19:51 +0200, Daniel Vetter wrote:
> > On Mon, May 12, 2014 at 06:35:04PM +0300, Imre Deak wrote:
> > > In
> > > 
> > > commit c6df39b5ea6342323a42edfbeeca0a28c643d7ae
> > > Author: Imre Deak <imre.deak@intel.com>
> > > Date:   Mon Apr 14 20:24:29 2014 +0300
> > > 
> > >     drm/i915: get a runtime PM ref for the deferred GT powersave enabling
> > > 
> > > I added an RPM get-ref when enabling RPS from a deferred work, but forgot
> > > to add the corresponding put-ref when canceling the work. This may leave
> > > RPM disabled.
> > > 
> > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > 
> > Could we intentionally hit this by e.g. racing a suspend/resume against
> > runtime pm? E.g.
> > 1. disable all outputs, make sure we've entered runtime pm
> > 2. set runtime autosuspend delay to 0
> > 3. suspend/resume
> > 4. autosuspend (hopefully, my understanding is a bit unclear)
> > 
> > ->Boom
> > 
> > Would look nice as an igt subtest if it works ;-)
> 
> Yep, works consistently as expected both before and after the fix. I
> pushed the new subtest, please add here:
> Testcase: igt/pm_pc8/system-suspend

Now I'm confused: I expected this to blow up without your fix here, and
not work with or without it?! Please unconfuse ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch