Date: Sat, 6 Jan 2018 11:38:35 -0500
From: Alexandru Chirvasitu <achirvasub@gmail.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        intel-gfx@lists.freedesktop.org,
        kernel list <linux-kernel@vger.kernel.org>
Subject: Re: PROBLEM: i915 causes complete desktop freezes in 4.15-rc5
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On Sat, Jan 06, 2018 at 08:24:43AM -0500, Alexandru Chirvasitu wrote:
> Thank you!
> 
> I'll apply that more elaborate patch you sent in the longer message to
> my clone of the repo and see if it still freezes.
>

I'm on it now with no freezes yet, despite trying my best :).

I have a question though:

> On Sat, Jan 06, 2018 at 10:43:20AM +0000, Chris Wilson wrote:
> > Quoting Alexandru Chirvasitu (2018-01-05 22:05:18)
> > > Here we go.
> > > 
> > > I have
> > > 
> > > CONFIG_PAGE_POISONING not set
> > > CONFIG_SLUB_STATS=y
> > > CONFIG_SLUB_DEBUG not set
> > > CONFIG_KASAN=y
> > > 
> > > .config attached along as well for verification, in case I missed
> > > anything.
> > > 
> > > Again crashed by an attempt to open a terminal window.
> > 
> > Gotcha,
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index b21322b50419..96cf46a10b4e 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -472,7 +472,7 @@ static void __fence_set_priority(struct dma_fence *fence, int prio)
> >         struct drm_i915_gem_request *rq;
> >         struct intel_engine_cs *engine;
> >  
> > -       if (!dma_fence_is_i915(fence))
> > +       if (dma_fence_is_signaled(fence) || !dma_fence_is_i915(fence))
> >                 return;
> >  
> >         rq = to_request(fence);

I went back to Linus' tree and compared the respective i915_gem.c
files in the 4.14 and 4.15-rc6 commits. The offending piece of code
seems to be in both, so I am wondering why I was not getting freezes before 4.15-rc.

Is the other change (in drivers/gpu/drm/i915/intel_lrc.c) crucial too? The line

GEM_BUG_ON(prio == I915_PRIORITY_INVALID);

is caught by the diff, so that region of *that* file differs between
4.14 and 4.15-rc.

I suppose it might also be that my distro's maintainers modify the
4.14 code in some fashion; I have not checked.