[Intel-gfx] [PATCH] drm/i915: Unpin last_context at reset

[Ville Syrjälä]

On Wed, Jun 18, 2014 at 10:04:48PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at 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 at 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 at bwidawsk.net>
 Date:   Fri Dec 6 14:11:03 2013 -0800

    drm/i915: Better reset handling for contexts

> ---
>  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