Re: [PATCH] drm/i915: Track old framebuffer instead of object

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Feb 02, 2015 at 03:44:15PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> Daniel Vetter spotted a bug while reviewing some of my refactoring in this
> are of the code. I'll quote:
> 
> """
> > @@ -9764,6 +9768,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
> >  	work->event = event;
> >  	work->crtc = crtc;
> >  	work->old_fb_obj = intel_fb_obj(old_fb);
> > +	work->old_tiling_mode = to_intel_framebuffer(old_fb)->tiling_mode;
> 
> Hm, that's actually an interesting bugfix - currently userspace could be
> sneaky and destroy the old fb immediately after the flip completes and the
> change the tiling of the underlying object before the unpin work had a
> chance to run (needs some fudgin with rt prios to starve workers to make
> this work though).
> 
> Imo the right fix is to hold a reference onto the fb and not the
> underlying gem object. With that tiling is guaranteed not to change.
> """
> 
> This patch tries to implement the above proposed change.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 14 +++++++-------
>  drivers/gpu/drm/i915/intel_drv.h     |  2 +-
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 1a689b3..24904cc 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9111,9 +9111,9 @@ static void intel_unpin_work_fn(struct work_struct *__work)
>  	enum pipe pipe = to_intel_crtc(work->crtc)->pipe;
>  
>  	mutex_lock(&dev->struct_mutex);
> -	intel_unpin_fb_obj(work->old_fb_obj);
> +	intel_unpin_fb_obj(intel_fb_obj(work->old_fb));
>  	drm_gem_object_unreference(&work->pending_flip_obj->base);
> -	drm_gem_object_unreference(&work->old_fb_obj->base);
> +	drm_framebuffer_unreference(work->old_fb);
>  
>  	intel_fbc_update(dev);
>  
> @@ -9816,7 +9816,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  
>  	work->event = event;
>  	work->crtc = crtc;
> -	work->old_fb_obj = intel_fb_obj(old_fb);
> +	work->old_fb = old_fb;
>  	INIT_WORK(&work->work, intel_unpin_work_fn);
>  
>  	ret = drm_crtc_vblank_get(crtc);
> @@ -9852,7 +9852,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  		goto cleanup;
>  
>  	/* Reference the objects for the scheduled work. */
> -	drm_gem_object_reference(&work->old_fb_obj->base);
> +	drm_framebuffer_reference(work->old_fb);
>  	drm_gem_object_reference(&obj->base);
>  
>  	crtc->primary->fb = fb;
> @@ -9867,7 +9867,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  
>  	if (IS_VALLEYVIEW(dev)) {
>  		ring = &dev_priv->ring[BCS];
> -		if (obj->tiling_mode != work->old_fb_obj->tiling_mode)
> +		if (obj->tiling_mode != intel_fb_obj(work->old_fb)->tiling_mode)
>  			/* vlv: DISPLAY_FLIP fails to change tiling */
>  			ring = NULL;
>  	} else if (IS_IVYBRIDGE(dev) || IS_HASWELL(dev)) {
> @@ -9908,7 +9908,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  	work->flip_queued_vblank = drm_vblank_count(dev, intel_crtc->pipe);
>  	work->enable_stall_check = true;
>  
> -	i915_gem_track_fb(work->old_fb_obj, obj,
> +	i915_gem_track_fb(intel_fb_obj(work->old_fb), obj,
>  			  INTEL_FRONTBUFFER_PRIMARY(pipe));
>  
>  	intel_fbc_disable(dev);
> @@ -9924,7 +9924,7 @@ cleanup_unpin:
>  cleanup_pending:
>  	atomic_dec(&intel_crtc->unpin_work_count);
>  	crtc->primary->fb = old_fb;
> -	drm_gem_object_unreference(&work->old_fb_obj->base);
> +	drm_framebuffer_unreference(work->old_fb);
>  	drm_gem_object_unreference(&obj->base);
>  	mutex_unlock(&dev->struct_mutex);
>  
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index de513ec..a8f895f 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -712,7 +712,7 @@ intel_get_crtc_for_plane(struct drm_device *dev, int plane)
>  struct intel_unpin_work {
>  	struct work_struct work;
>  	struct drm_crtc *crtc;
> -	struct drm_i915_gem_object *old_fb_obj;
> +	struct drm_framebuffer *old_fb;
>  	struct drm_i915_gem_object *pending_flip_obj;
>  	struct drm_pending_vblank_event *event;
>  	atomic_t pending;

Random style comment: For internal structs/funcs we're slowing trying to
move over to intel_ structs/pointers. And somehow I now find intel_fb_obj
a misleading function. Anway queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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