drm/i915: Rework clflush to work correctly without obj->mm.lock.

Pin in the caller, not in the work itself. This should also
work better for dma-fence annotations.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-22-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_clflush.c

@@ -27,15 +27,8 @@ static void __do_clflush(struct drm_i915_gem_object *obj)
 static int clflush_work(struct dma_fence_work *base)
 {
 	struct clflush *clflush = container_of(base, typeof(*clflush), base);
-	struct drm_i915_gem_object *obj = clflush->obj;
-	int err;
 
-	err = i915_gem_object_pin_pages(obj);
-	if (err)
-		return err;
-
-	__do_clflush(obj);
-	i915_gem_object_unpin_pages(obj);
+	__do_clflush(clflush->obj);
 
 	return 0;
 }
@@ -44,6 +37,7 @@ static void clflush_release(struct dma_fence_work *base)
 {
 	struct clflush *clflush = container_of(base, typeof(*clflush), base);
 
+	i915_gem_object_unpin_pages(clflush->obj);
 	i915_gem_object_put(clflush->obj);
 }
 
@@ -63,6 +57,11 @@ static struct clflush *clflush_work_create(struct drm_i915_gem_object *obj)
 	if (!clflush)
 		return NULL;
 
+	if (__i915_gem_object_get_pages(obj) < 0) {
+		kfree(clflush);
+		return NULL;
+	}
+
 	dma_fence_work_init(&clflush->base, &clflush_ops);
 	clflush->obj = i915_gem_object_get(obj); /* obj <-> clflush cycle */