drm/i915: Introduce a vma.kref

Start introducing a kref on i915_vma in order to protect the vma unbind
(i915_gem_object_unbind) from a parallel destruction (i915_vma_parked).
Later, we will use the refcount to manage all access and turn i915_vma
into a first class container.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Acked-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191222210256.2066451-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -194,7 +194,7 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 				GEM_BUG_ON(vma->obj != obj);
 				spin_unlock(&obj->vma.lock);
 
-				i915_vma_destroy(vma);
+				__i915_vma_put(vma);
 
 				spin_lock(&obj->vma.lock);
 			}

drivers/gpu/drm/i915/gem/selftests/huge_pages.c

@@ -1110,8 +1110,7 @@ static int __igt_write_huge(struct intel_context *ce,
 out_vma_unpin:
 	i915_vma_unpin(vma);
 out_vma_close:
-	i915_vma_destroy(vma);
-
+	__i915_vma_put(vma);
 	return err;
 }
 

drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c

@@ -163,7 +163,7 @@ static int check_partial_mapping(struct drm_i915_gem_object *obj,
 	kunmap(p);
 
 out:
-	i915_vma_destroy(vma);
+	__i915_vma_put(vma);
 	return err;
 }
 
@@ -257,7 +257,7 @@ static int check_partial_mappings(struct drm_i915_gem_object *obj,
 		if (err)
 			return err;
 
-		i915_vma_destroy(vma);
+		__i915_vma_put(vma);
 
 		if (igt_timeout(end_time,
 				"%s: timed out after tiling=%d stride=%d\n",

drivers/gpu/drm/i915/i915_gem.c

@@ -136,7 +136,6 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
 						       struct i915_vma,
 						       obj_link))) {
 		struct i915_address_space *vm = vma->vm;
-		bool awake = false;
 
 		list_move_tail(&vma->obj_link, &still_in_list);
 		if (!i915_vma_is_bound(vma, I915_VMA_BIND_MASK))
@@ -147,26 +146,18 @@ int i915_gem_object_unbind(struct drm_i915_gem_object *obj,
 			break;
 
 		/* Prevent vma being freed by i915_vma_parked as we unbind */
-		if (intel_gt_pm_get_if_awake(vm->gt)) {
-			awake = true;
-		} else {
-			if (i915_vma_is_closed(vma)) {
-				spin_unlock(&obj->vma.lock);
-				i915_vma_parked(vm->gt);
-				goto err_vm;
-			}
-		}
-
+		vma = __i915_vma_get(vma);
 		spin_unlock(&obj->vma.lock);
 
-		ret = -EBUSY;
-		if (flags & I915_GEM_OBJECT_UNBIND_ACTIVE ||
-		    !i915_vma_is_active(vma))
-			ret = i915_vma_unbind(vma);
+		if (vma) {
+			ret = -EBUSY;
+			if (flags & I915_GEM_OBJECT_UNBIND_ACTIVE ||
+			    !i915_vma_is_active(vma))
+				ret = i915_vma_unbind(vma);
+
+			__i915_vma_put(vma);
+		}
 
-		if (awake)
-			intel_gt_pm_put(vm->gt);
-err_vm:
 		i915_vm_close(vm);
 		spin_lock(&obj->vma.lock);
 	}

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -534,7 +534,7 @@ void __i915_vm_close(struct i915_address_space *vm)
 
 		atomic_and(~I915_VMA_PIN_MASK, &vma->flags);
 		WARN_ON(__i915_vma_unbind(vma));
-		i915_vma_destroy(vma);
+		__i915_vma_put(vma);
 
 		i915_gem_object_put(obj);
 	}
@@ -1812,7 +1812,7 @@ static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
 {
 	struct gen6_ppgtt *ppgtt = to_gen6_ppgtt(i915_vm_to_ppgtt(vm));
 
-	i915_vma_destroy(ppgtt->vma);
+	__i915_vma_put(ppgtt->vma);
 
 	gen6_ppgtt_free_pd(ppgtt);
 	free_scratch(vm);
@@ -1895,6 +1895,7 @@ static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 
 	i915_active_init(&vma->active, NULL, NULL);
 
+	kref_init(&vma->ref);
 	mutex_init(&vma->pages_mutex);
 	vma->vm = i915_vm_get(&ggtt->vm);
 	vma->ops = &pd_vma_ops;

drivers/gpu/drm/i915/i915_vma.c

@@ -114,6 +114,7 @@ vma_create(struct drm_i915_gem_object *obj,
 	if (vma == NULL)
 		return ERR_PTR(-ENOMEM);
 
+	kref_init(&vma->ref);
 	mutex_init(&vma->pages_mutex);
 	vma->vm = i915_vm_get(vm);
 	vma->ops = &vm->vma_ops;
@@ -1021,8 +1022,10 @@ void i915_vma_reopen(struct i915_vma *vma)
 		__i915_vma_remove_closed(vma);
 }
 
-void i915_vma_destroy(struct i915_vma *vma)
+void i915_vma_release(struct kref *ref)
 {
+	struct i915_vma *vma = container_of(ref, typeof(*vma), ref);
+
 	if (drm_mm_node_allocated(&vma->node)) {
 		mutex_lock(&vma->vm->mutex);
 		atomic_and(~I915_VMA_PIN_MASK, &vma->flags);
@@ -1072,7 +1075,7 @@ void i915_vma_parked(struct intel_gt *gt)
 		spin_unlock_irq(&gt->closed_lock);
 
 		if (obj) {
-			i915_vma_destroy(vma);
+			__i915_vma_put(vma);
 			i915_gem_object_put(obj);
 		}
 
@@ -1236,7 +1239,7 @@ int __i915_vma_unbind(struct i915_vma *vma)
 	i915_vma_detach(vma);
 	vma_unbind_pages(vma);
 
-	drm_mm_remove_node(&vma->node); /* pairs with i915_vma_destroy() */
+	drm_mm_remove_node(&vma->node); /* pairs with i915_vma_release() */
 	return 0;
 }
 

drivers/gpu/drm/i915/i915_vma.h

@@ -51,14 +51,19 @@ enum i915_cache_level;
  */
 struct i915_vma {
 	struct drm_mm_node node;
-	struct drm_i915_gem_object *obj;
+
 	struct i915_address_space *vm;
 	const struct i915_vma_ops *ops;
-	struct i915_fence_reg *fence;
+
+	struct drm_i915_gem_object *obj;
 	struct dma_resv *resv; /** Alias of obj->resv */
+
 	struct sg_table *pages;
 	void __iomem *iomap;
 	void *private; /* owned by creator */
+
+	struct i915_fence_reg *fence;
+
 	u64 size;
 	u64 display_alignment;
 	struct i915_page_sizes page_sizes;
@@ -74,6 +79,7 @@ struct i915_vma {
 	 * handles (but same file) for execbuf, i.e. the number of aliases
 	 * that exist in the ctx->handle_vmas LUT for this vma.
 	 */
+	struct kref ref;
 	atomic_t open_count;
 	atomic_t flags;
 	/**
@@ -336,7 +342,20 @@ int __must_check i915_vma_unbind(struct i915_vma *vma);
 void i915_vma_unlink_ctx(struct i915_vma *vma);
 void i915_vma_close(struct i915_vma *vma);
 void i915_vma_reopen(struct i915_vma *vma);
-void i915_vma_destroy(struct i915_vma *vma);
+
+static inline struct i915_vma *__i915_vma_get(struct i915_vma *vma)
+{
+	if (kref_get_unless_zero(&vma->ref))
+		return vma;
+
+	return NULL;
+}
+
+void i915_vma_release(struct kref *ref);
+static inline void __i915_vma_put(struct i915_vma *vma)
+{
+	kref_put(&vma->ref, i915_vma_release);
+}
 
 #define assert_vma_held(vma) dma_resv_assert_held((vma)->resv)