[Intel-gfx] [PATCH] drm: Release driver tracking before making the object available again

[Daniel Vetter]

On Sat, Aug 19, 2017 at 01:05:58PM +0100, Chris Wilson wrote:
> This is the same bug as we fixed in commit f6cd7daecff5 ("drm: Release
> driver references to handle before making it available again"), but now
> the exposure is via the PRIME lookup tables. If we remove the
> object/handle from the PRIME lut, then a new request for the same
> object/fd will generate a new handle, thus for a short window that
> object is known to userspace by two different handles. Fix this by
> releasing the driver tracking before PRIME.
> 
> Fixes: 0ff926c7d4f0 ("drm/prime: add exported buffers to current fprivs
> imported buffer list (v2)")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: David Airlie <airlied at linux.ie>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Thierry Reding <treding at nvidia.com>
> Cc: stable at vger.kernel.org

Do we have an evil igt for this? I guess since the old one didn't have
one, this new race is also hard to reproduce ...

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/drm_gem.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index ad4e9cfe48a2..88c6d78ee2d5 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -255,13 +255,13 @@ drm_gem_object_release_handle(int id, void *ptr, void *data)
>  	struct drm_gem_object *obj = ptr;
>  	struct drm_device *dev = obj->dev;
>  
> +	if (dev->driver->gem_close_object)
> +		dev->driver->gem_close_object(obj, file_priv);
> +
>  	if (drm_core_check_feature(dev, DRIVER_PRIME))
>  		drm_gem_remove_prime_handles(obj, file_priv);
>  	drm_vma_node_revoke(&obj->vma_node, file_priv);
>  
> -	if (dev->driver->gem_close_object)
> -		dev->driver->gem_close_object(obj, file_priv);
> -
>  	drm_gem_object_handle_put_unlocked(obj);
>  
>  	return 0;
> -- 
> 2.14.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch