Re: [PATCH] drm/i915: Disallow preallocation of requests

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 26 Sep 2012, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> The intention was to allow the caller to avoid a failure to queue a
> request having already written commands to the ring. However, this is a
> moot point as the i915_add_request() can fail for other reasons than a
> mere allocation failure and those failure cases are more likely than
> ENOMEM. So the overlay code already had to handle i915_add_request()
> failures, and due to
>
> commit 3bb73aba1ed5198a2c1dfaac4f3c95459930d84a
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Fri Jul 20 12:40:59 2012 +0100
>
>     drm/i915: Allow late allocation of request for i915_add_request()
>
> the error handling code in intel_overlay.c was subject to causing
> double-frees, as found by coverity.
>
> Rather than further complicate i915_add_request() and callers, realise
> the battle is lost and adapt intel_overlay.c to take advantage of the
> late allocation of requests.
>
> v2: Handle callers passing in a NULL seqno.
> v3: Ditto. This time for sure.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |    2 +-
>  drivers/gpu/drm/i915/i915_gem.c      |   15 +++----
>  drivers/gpu/drm/i915/intel_overlay.c |   72 +++++++---------------------------
>  3 files changed, 24 insertions(+), 65 deletions(-)

Looks good, and I also like the diffstat.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index dddc3dc..d8d4736 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1468,7 +1468,7 @@ int __must_check i915_gpu_idle(struct drm_device *dev);
>  int __must_check i915_gem_idle(struct drm_device *dev);
>  int i915_add_request(struct intel_ring_buffer *ring,
>  		     struct drm_file *file,
> -		     struct drm_i915_gem_request *request);
> +		     u32 *seqno);
>  int __must_check i915_wait_seqno(struct intel_ring_buffer *ring,
>  				 uint32_t seqno);
>  int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index b2effab..014b95e 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2087,11 +2087,12 @@ i915_gem_next_request_seqno(struct intel_ring_buffer *ring)
>  int
>  i915_add_request(struct intel_ring_buffer *ring,
>  		 struct drm_file *file,
> -		 struct drm_i915_gem_request *request)
> +		 u32 *out_seqno)
>  {
>  	drm_i915_private_t *dev_priv = ring->dev->dev_private;
> -	uint32_t seqno;
> +	struct drm_i915_gem_request *request;
>  	u32 request_ring_position;
> +	u32 seqno;
>  	int was_empty;
>  	int ret;
>  
> @@ -2106,11 +2107,9 @@ i915_add_request(struct intel_ring_buffer *ring,
>  	if (ret)
>  		return ret;
>  
> -	if (request == NULL) {
> -		request = kmalloc(sizeof(*request), GFP_KERNEL);
> -		if (request == NULL)
> -			return -ENOMEM;
> -	}
> +	request = kmalloc(sizeof(*request), GFP_KERNEL);
> +	if (request == NULL)
> +		return -ENOMEM;
>  
>  	seqno = i915_gem_next_request_seqno(ring);
>  
> @@ -2162,6 +2161,8 @@ i915_add_request(struct intel_ring_buffer *ring,
>  		}
>  	}
>  
> +	if (out_seqno)
> +		*out_seqno = seqno;
>  	return 0;
>  }
>  
> diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
> index 2fa20a4..ebcbf48 100644
> --- a/drivers/gpu/drm/i915/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/intel_overlay.c
> @@ -210,7 +210,6 @@ static void intel_overlay_unmap_regs(struct intel_overlay *overlay,
>  }
>  
>  static int intel_overlay_do_wait_request(struct intel_overlay *overlay,
> -					 struct drm_i915_gem_request *request,
>  					 void (*tail)(struct intel_overlay *))
>  {
>  	struct drm_device *dev = overlay->dev;
> @@ -219,12 +218,10 @@ static int intel_overlay_do_wait_request(struct intel_overlay *overlay,
>  	int ret;
>  
>  	BUG_ON(overlay->last_flip_req);
> -	ret = i915_add_request(ring, NULL, request);
> -	if (ret) {
> -	    kfree(request);
> -	    return ret;
> -	}
> -	overlay->last_flip_req = request->seqno;
> +	ret = i915_add_request(ring, NULL, &overlay->last_flip_req);
> +	if (ret)
> +		return ret;
> +
>  	overlay->flip_tail = tail;
>  	ret = i915_wait_seqno(ring, overlay->last_flip_req);
>  	if (ret)
> @@ -241,7 +238,6 @@ static int intel_overlay_on(struct intel_overlay *overlay)
>  	struct drm_device *dev = overlay->dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> -	struct drm_i915_gem_request *request;
>  	int ret;
>  
>  	BUG_ON(overlay->active);
> @@ -249,17 +245,9 @@ static int intel_overlay_on(struct intel_overlay *overlay)
>  
>  	WARN_ON(IS_I830(dev) && !(dev_priv->quirks & QUIRK_PIPEA_FORCE));
>  
> -	request = kzalloc(sizeof(*request), GFP_KERNEL);
> -	if (request == NULL) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> -
>  	ret = intel_ring_begin(ring, 4);
> -	if (ret) {
> -		kfree(request);
> -		goto out;
> -	}
> +	if (ret)
> +		return ret;
>  
>  	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_ON);
>  	intel_ring_emit(ring, overlay->flip_addr | OFC_UPDATE);
> @@ -267,9 +255,7 @@ static int intel_overlay_on(struct intel_overlay *overlay)
>  	intel_ring_emit(ring, MI_NOOP);
>  	intel_ring_advance(ring);
>  
> -	ret = intel_overlay_do_wait_request(overlay, request, NULL);
> -out:
> -	return ret;
> +	return intel_overlay_do_wait_request(overlay, NULL);
>  }
>  
>  /* overlay needs to be enabled in OCMD reg */
> @@ -279,17 +265,12 @@ static int intel_overlay_continue(struct intel_overlay *overlay,
>  	struct drm_device *dev = overlay->dev;
>  	drm_i915_private_t *dev_priv = dev->dev_private;
>  	struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> -	struct drm_i915_gem_request *request;
>  	u32 flip_addr = overlay->flip_addr;
>  	u32 tmp;
>  	int ret;
>  
>  	BUG_ON(!overlay->active);
>  
> -	request = kzalloc(sizeof(*request), GFP_KERNEL);
> -	if (request == NULL)
> -		return -ENOMEM;
> -
>  	if (load_polyphase_filter)
>  		flip_addr |= OFC_UPDATE;
>  
> @@ -299,22 +280,14 @@ static int intel_overlay_continue(struct intel_overlay *overlay,
>  		DRM_DEBUG("overlay underrun, DOVSTA: %x\n", tmp);
>  
>  	ret = intel_ring_begin(ring, 2);
> -	if (ret) {
> -		kfree(request);
> +	if (ret)
>  		return ret;
> -	}
> +
>  	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE);
>  	intel_ring_emit(ring, flip_addr);
>  	intel_ring_advance(ring);
>  
> -	ret = i915_add_request(ring, NULL, request);
> -	if (ret) {
> -		kfree(request);
> -		return ret;
> -	}
> -
> -	overlay->last_flip_req = request->seqno;
> -	return 0;
> +	return i915_add_request(ring, NULL, &overlay->last_flip_req);
>  }
>  
>  static void intel_overlay_release_old_vid_tail(struct intel_overlay *overlay)
> @@ -350,15 +323,10 @@ static int intel_overlay_off(struct intel_overlay *overlay)
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
>  	u32 flip_addr = overlay->flip_addr;
> -	struct drm_i915_gem_request *request;
>  	int ret;
>  
>  	BUG_ON(!overlay->active);
>  
> -	request = kzalloc(sizeof(*request), GFP_KERNEL);
> -	if (request == NULL)
> -		return -ENOMEM;
> -
>  	/* According to intel docs the overlay hw may hang (when switching
>  	 * off) without loading the filter coeffs. It is however unclear whether
>  	 * this applies to the disabling of the overlay or to the switching off
> @@ -366,10 +334,9 @@ static int intel_overlay_off(struct intel_overlay *overlay)
>  	flip_addr |= OFC_UPDATE;
>  
>  	ret = intel_ring_begin(ring, 6);
> -	if (ret) {
> -		kfree(request);
> +	if (ret)
>  		return ret;
> -	}
> +
>  	/* wait for overlay to go idle */
>  	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_CONTINUE);
>  	intel_ring_emit(ring, flip_addr);
> @@ -380,8 +347,7 @@ static int intel_overlay_off(struct intel_overlay *overlay)
>  	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
>  	intel_ring_advance(ring);
>  
> -	return intel_overlay_do_wait_request(overlay, request,
> -					     intel_overlay_off_tail);
> +	return intel_overlay_do_wait_request(overlay, intel_overlay_off_tail);
>  }
>  
>  /* recover from an interruption due to a signal
> @@ -426,24 +392,16 @@ static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
>  		return 0;
>  
>  	if (I915_READ(ISR) & I915_OVERLAY_PLANE_FLIP_PENDING_INTERRUPT) {
> -		struct drm_i915_gem_request *request;
> -
>  		/* synchronous slowpath */
> -		request = kzalloc(sizeof(*request), GFP_KERNEL);
> -		if (request == NULL)
> -			return -ENOMEM;
> -
>  		ret = intel_ring_begin(ring, 2);
> -		if (ret) {
> -			kfree(request);
> +		if (ret)
>  			return ret;
> -		}
>  
>  		intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
>  		intel_ring_emit(ring, MI_NOOP);
>  		intel_ring_advance(ring);
>  
> -		ret = intel_overlay_do_wait_request(overlay, request,
> +		ret = intel_overlay_do_wait_request(overlay,
>  						    intel_overlay_release_old_vid_tail);
>  		if (ret)
>  			return ret;
> -- 
> 1.7.10.4
>
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