Re: [PATCH v2 02/21] drm/i915: Remove stallcheck special handling, v3.

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On Tue, May 17, 2016 at 03:07:45PM +0200, Maarten Lankhorst wrote:
> Both intel_unpin_work.pending and intel_unpin_work.enable_stall_check
> were used to see if work should be enabled. By only using pending
> some special cases are gone, and access to unpin_work can be simplified.
> 
> A flip could previously be queued before
> stallcheck was active. With the addition of the pending member
> enable_stall_check became obsolete and can thus be removed.
> 
> Use this to only access work members untilintel_mark_page_flip_active
> is called, or intel_queue_mmio_flip is used. This will prevent
> use-after-free, and makes it easier to verify accesses.
> 
> Changes since v1:
> - Reword commit message.
> - Do not access unpin_work after intel_mark_page_flip_active.
> - Add the right memory barriers.
> Changes since v2:
> - atomic_read() needs a full smp_rmb.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>

Reviewed-by: Patrik Jakobsson <patrik.jakobsson@xxxxxxxxxxxxxxx>

> ---
>  drivers/gpu/drm/i915/i915_debugfs.c  | 11 +++---
>  drivers/gpu/drm/i915/intel_display.c | 71 ++++++++++++++----------------------
>  drivers/gpu/drm/i915/intel_drv.h     |  1 -
>  3 files changed, 34 insertions(+), 49 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 24f4105b910f..f23b119a365d 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -615,9 +615,14 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
>  			seq_printf(m, "No flip due on pipe %c (plane %c)\n",
>  				   pipe, plane);
>  		} else {
> +			u32 pending;
>  			u32 addr;
>  
> -			if (atomic_read(&work->pending) < INTEL_FLIP_COMPLETE) {
> +			pending = atomic_read(&work->pending);
> +			if (pending == INTEL_FLIP_INACTIVE) {
> +				seq_printf(m, "Flip ioctl preparing on pipe %c (plane %c)\n",
> +					   pipe, plane);
> +			} else if (pending >= INTEL_FLIP_COMPLETE) {
>  				seq_printf(m, "Flip queued on pipe %c (plane %c)\n",
>  					   pipe, plane);
>  			} else {
> @@ -639,10 +644,6 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
>  				   work->flip_queued_vblank,
>  				   work->flip_ready_vblank,
>  				   drm_crtc_vblank_count(&crtc->base));
> -			if (work->enable_stall_check)
> -				seq_puts(m, "Stall check enabled, ");
> -			else
> -				seq_puts(m, "Stall check waiting for page flip ioctl, ");
>  			seq_printf(m, "%d prepares\n", atomic_read(&work->pending));
>  
>  			if (INTEL_INFO(dev)->gen >= 4)
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 4777087326f6..3bcab21e67d3 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3813,8 +3813,6 @@ static void page_flip_completed(struct intel_crtc *intel_crtc)
>  	struct drm_i915_private *dev_priv = to_i915(intel_crtc->base.dev);
>  	struct intel_unpin_work *work = intel_crtc->unpin_work;
>  
> -	/* ensure that the unpin work is consistent wrt ->pending. */
> -	smp_rmb();
>  	intel_crtc->unpin_work = NULL;
>  
>  	if (work->event)
> @@ -10890,16 +10888,13 @@ static void do_intel_finish_page_flip(struct drm_i915_private *dev_priv,
>  	spin_lock_irqsave(&dev->event_lock, flags);
>  	work = intel_crtc->unpin_work;
>  
> -	/* Ensure we don't miss a work->pending update ... */
> -	smp_rmb();
> +	if (work && atomic_read(&work->pending) >= INTEL_FLIP_COMPLETE) {
> +		/* ensure that the unpin work is consistent wrt ->pending. */
> +		smp_rmb();
>  
> -	if (work == NULL || atomic_read(&work->pending) < INTEL_FLIP_COMPLETE) {
> -		spin_unlock_irqrestore(&dev->event_lock, flags);
> -		return;
> +		page_flip_completed(intel_crtc);
>  	}
>  
> -	page_flip_completed(intel_crtc);
> -
>  	spin_unlock_irqrestore(&dev->event_lock, flags);
>  }
>  
> @@ -10995,10 +10990,8 @@ void intel_prepare_page_flip(struct drm_i915_private *dev_priv, int plane)
>  static inline void intel_mark_page_flip_active(struct intel_unpin_work *work)
>  {
>  	/* Ensure that the work item is consistent when activating it ... */
> -	smp_wmb();
> +	smp_mb__before_atomic();
>  	atomic_set(&work->pending, INTEL_FLIP_PENDING);
> -	/* and that it is marked active as soon as the irq could fire. */
> -	smp_wmb();
>  }
>  
>  static int intel_gen2_queue_flip(struct drm_device *dev,
> @@ -11032,7 +11025,6 @@ static int intel_gen2_queue_flip(struct drm_device *dev,
>  	intel_ring_emit(engine, intel_crtc->unpin_work->gtt_offset);
>  	intel_ring_emit(engine, 0); /* aux display base address, unused */
>  
> -	intel_mark_page_flip_active(intel_crtc->unpin_work);
>  	return 0;
>  }
>  
> @@ -11064,7 +11056,6 @@ static int intel_gen3_queue_flip(struct drm_device *dev,
>  	intel_ring_emit(engine, intel_crtc->unpin_work->gtt_offset);
>  	intel_ring_emit(engine, MI_NOOP);
>  
> -	intel_mark_page_flip_active(intel_crtc->unpin_work);
>  	return 0;
>  }
>  
> @@ -11103,7 +11094,6 @@ static int intel_gen4_queue_flip(struct drm_device *dev,
>  	pipesrc = I915_READ(PIPESRC(intel_crtc->pipe)) & 0x0fff0fff;
>  	intel_ring_emit(engine, pf | pipesrc);
>  
> -	intel_mark_page_flip_active(intel_crtc->unpin_work);
>  	return 0;
>  }
>  
> @@ -11139,7 +11129,6 @@ static int intel_gen6_queue_flip(struct drm_device *dev,
>  	pipesrc = I915_READ(PIPESRC(intel_crtc->pipe)) & 0x0fff0fff;
>  	intel_ring_emit(engine, pf | pipesrc);
>  
> -	intel_mark_page_flip_active(intel_crtc->unpin_work);
>  	return 0;
>  }
>  
> @@ -11234,7 +11223,6 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
>  	intel_ring_emit(engine, intel_crtc->unpin_work->gtt_offset);
>  	intel_ring_emit(engine, (MI_NOOP));
>  
> -	intel_mark_page_flip_active(intel_crtc->unpin_work);
>  	return 0;
>  }
>  
> @@ -11361,8 +11349,6 @@ static void intel_do_mmio_flip(struct intel_mmio_flip *mmio_flip)
>  	if (work == NULL)
>  		return;
>  
> -	intel_mark_page_flip_active(work);
> -
>  	intel_pipe_update_start(crtc);
>  
>  	if (INTEL_INFO(mmio_flip->i915)->gen >= 9)
> @@ -11372,6 +11358,8 @@ static void intel_do_mmio_flip(struct intel_mmio_flip *mmio_flip)
>  		ilk_do_mmio_flip(crtc, work);
>  
>  	intel_pipe_update_end(crtc);
> +
> +	intel_mark_page_flip_active(work);
>  }
>  
>  static void intel_mmio_flip_work_func(struct work_struct *work)
> @@ -11437,15 +11425,14 @@ static bool __intel_pageflip_stall_check(struct drm_device *dev,
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	struct intel_unpin_work *work = intel_crtc->unpin_work;
>  	u32 addr;
> +	u32 pending;
>  
> -	if (atomic_read(&work->pending) >= INTEL_FLIP_COMPLETE)
> -		return true;
> -
> -	if (atomic_read(&work->pending) < INTEL_FLIP_PENDING)
> -		return false;
> +	pending = atomic_read(&work->pending);
> +	/* ensure that the unpin work is consistent wrt ->pending. */
> +	smp_rmb();
>  
> -	if (!work->enable_stall_check)
> -		return false;
> +	if (pending != INTEL_FLIP_PENDING)
> +		return pending == INTEL_FLIP_COMPLETE;
>  
>  	if (work->flip_ready_vblank == 0) {
>  		if (work->flip_queued_req &&
> @@ -11626,6 +11613,11 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  	 */
>  	if (!mmio_flip) {
>  		ret = i915_gem_object_sync(obj, engine, &request);
> +		if (!ret && !request) {
> +			request = i915_gem_request_alloc(engine, NULL);
> +			ret = PTR_ERR_OR_ZERO(request);
> +		}
> +
>  		if (ret)
>  			goto cleanup_pending;
>  	}
> @@ -11639,36 +11631,29 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  	work->gtt_offset += intel_crtc->dspaddr_offset;
>  
>  	if (mmio_flip) {
> -		ret = intel_queue_mmio_flip(dev, crtc, obj);
> -		if (ret)
> -			goto cleanup_unpin;
> +		work->flip_queued_vblank = drm_crtc_vblank_count(crtc);
>  
>  		i915_gem_request_assign(&work->flip_queued_req,
>  					obj->last_write_req);
> -	} else {
> -		if (!request) {
> -			request = i915_gem_request_alloc(engine, NULL);
> -			if (IS_ERR(request)) {
> -				ret = PTR_ERR(request);
> -				goto cleanup_unpin;
> -			}
> -		}
>  
> +		ret = intel_queue_mmio_flip(dev, crtc, obj);
> +		if (ret)
> +			goto cleanup_unpin;
> +	} else {
>  		ret = dev_priv->display.queue_flip(dev, crtc, fb, obj, request,
>  						   page_flip_flags);
>  		if (ret)
>  			goto cleanup_unpin;
>  
>  		i915_gem_request_assign(&work->flip_queued_req, request);
> -	}
>  
> -	if (request)
> -		i915_add_request_no_flush(request);
> +		work->flip_queued_vblank = drm_crtc_vblank_count(crtc);
> +		intel_mark_page_flip_active(work);
>  
> -	work->flip_queued_vblank = drm_crtc_vblank_count(crtc);
> -	work->enable_stall_check = true;
> +		i915_add_request_no_flush(request);
> +	}
>  
> -	i915_gem_track_fb(intel_fb_obj(work->old_fb), obj,
> +	i915_gem_track_fb(intel_fb_obj(old_fb), obj,
>  			  to_intel_plane(primary)->frontbuffer_bit);
>  	mutex_unlock(&dev->struct_mutex);
>  
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 0dc2bc9c65cf..f19e755bb16f 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -992,7 +992,6 @@ struct intel_unpin_work {
>  	struct drm_i915_gem_request *flip_queued_req;
>  	u32 flip_queued_vblank;
>  	u32 flip_ready_vblank;
> -	bool enable_stall_check;
>  };
>  
>  struct intel_load_detect_pipe {
> -- 
> 2.5.5
> 
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