Re: [PATCH] drm/i915: Unpin last_context at reset

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jun 23, 2014 at 01:07:50PM +0300, Ville Syrjälä wrote:
> On Wed, Jun 18, 2014 at 10:04:48PM +0300, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > We're forgetting to unpin the last_context from the ggtt at GPU reset
> > time. This leads to the vma pin_count leaking at every reset if the
> > last context wasn't the ring default context. Further use of the same
> > context will trigger the pin_count check in i915_gem_object_pin() and
> > userspace will be faced with EBUSY as a result.
> > 
> > This plaques kms_flip rather badly since it performs lots of resets,
> > and every fd has its own default context these days.
> > 
> > Fix the problem by properly unpinning the last context at reset.
> > 
> > Testcase: igt/gem_ctx_exec/reset-pin-leak
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> I pushed the igt, and also kms_flip hits this easily.
> 
> It looks to me that the bug has been there since the introduction of
> i915_gem_context_reset() in [1], so I think we may want this patch
> merged with cc: stable. Afterwards people can work on killing
> i915_gem_context_reset() if they so wish.
> 
> [1]
>  commit acce9ffa4807027965ebd948456fa8385bbee32e
>  Author: Ben Widawsky <ben@bwidawsk.net>
>  Date:   Fri Dec 6 14:11:03 2013 -0800
> 
>     drm/i915: Better reset handling for contexts

I've added this regression marker but forgone the cc: stable - haven't
heard anyone complain about this loud enough yet ... So just merged to
dinq.

We can do the proper fix of unifying the paths here a bit more later on.

Thanks for the patch.
-Daniel
> 
> > ---
> >  drivers/gpu/drm/i915/i915_gem_context.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> > index 3ffe308..e362c96 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> > @@ -382,6 +382,9 @@ void i915_gem_context_reset(struct drm_device *dev)
> >  			dctx->obj->active = 0;
> >  		}
> >  
> > +		if (ring->last_context->obj && i == RCS)
> > +			i915_gem_object_ggtt_unpin(ring->last_context->obj);
> > +
> >  		i915_gem_context_unreference(ring->last_context);
> >  		i915_gem_context_reference(dctx);
> >  		ring->last_context = dctx;
> > -- 
> > 1.8.5.5
> 
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch