drm/i915: Disallow preallocation of requests

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 3bb73aba
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>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1427,7 +1427,7 @@ 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);

drivers/gpu/drm/i915/i915_gem.c

@@ -1956,11 +1956,12 @@ 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;
 
@@ -1975,11 +1976,9 @@ 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);
 
@@ -2031,6 +2030,8 @@ i915_add_request(struct intel_ring_buffer *ring,
 		}
 	}
 
+	if (out_seqno)
+		*out_seqno = seqno;
 	return 0;
 }
 

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;