drm/msm: Implement .gem_free_object_unlocked

We use a llist and a worker to delay the object cleanup. This avoids
taking mmap_sem and struct_mutex in the wrong order when calling
drm_gem_object_put_unlocked() from drm_gem_mmap().

Fixes lockdep problem with copy_from_user() in msm_ioctl_gem_submit().
Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_drv.c

@@ -458,6 +458,9 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
 
 	priv->wq = alloc_ordered_workqueue("msm", 0);
 
+	INIT_WORK(&priv->free_work, msm_gem_free_work);
+	init_llist_head(&priv->free_list);
+
 	INIT_LIST_HEAD(&priv->inactive_list);
 
 	drm_mode_config_init(ddev);
@@ -1026,7 +1029,7 @@ static struct drm_driver msm_driver = {
 	.irq_uninstall      = msm_irq_uninstall,
 	.enable_vblank      = msm_enable_vblank,
 	.disable_vblank     = msm_disable_vblank,
-	.gem_free_object    = msm_gem_free_object,
+	.gem_free_object_unlocked = msm_gem_free_object,
 	.gem_vm_ops         = &vm_ops,
 	.dumb_create        = msm_gem_dumb_create,
 	.dumb_map_offset    = msm_gem_dumb_map_offset,

drivers/gpu/drm/msm/msm_drv.h

@@ -185,6 +185,10 @@ struct msm_drm_private {
 	/* list of GEM objects: */
 	struct list_head inactive_list;
 
+	/* worker for delayed free of objects: */
+	struct work_struct free_work;
+	struct llist_head free_list;
+
 	struct workqueue_struct *wq;
 
 	unsigned int num_planes;
@@ -325,6 +329,7 @@ void msm_gem_kernel_put(struct drm_gem_object *bo,
 		struct msm_gem_address_space *aspace, bool locked);
 struct drm_gem_object *msm_gem_import(struct drm_device *dev,
 		struct dma_buf *dmabuf, struct sg_table *sgt);
+void msm_gem_free_work(struct work_struct *work);
 
 __printf(2, 3)
 void msm_gem_object_set_name(struct drm_gem_object *bo, const char *fmt, ...);

drivers/gpu/drm/msm/msm_gem.c

@@ -853,8 +853,18 @@ void msm_gem_describe_objects(struct list_head *list, struct seq_file *m)
 /* don't call directly!  Use drm_gem_object_put() and friends */
 void msm_gem_free_object(struct drm_gem_object *obj)
 {
-	struct drm_device *dev = obj->dev;
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+	struct drm_device *dev = obj->dev;
+	struct msm_drm_private *priv = dev->dev_private;
+
+	if (llist_add(&msm_obj->freed, &priv->free_list))
+		queue_work(priv->wq, &priv->free_work);
+}
+
+static void free_object(struct msm_gem_object *msm_obj)
+{
+	struct drm_gem_object *obj = &msm_obj->base;
+	struct drm_device *dev = obj->dev;
 
 	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 
@@ -892,6 +902,29 @@ void msm_gem_free_object(struct drm_gem_object *obj)
 	kfree(msm_obj);
 }
 
+void msm_gem_free_work(struct work_struct *work)
+{
+	struct msm_drm_private *priv =
+		container_of(work, struct msm_drm_private, free_work);
+	struct drm_device *dev = priv->dev;
+	struct llist_node *freed;
+	struct msm_gem_object *msm_obj, *next;
+
+	while ((freed = llist_del_all(&priv->free_list))) {
+
+		mutex_lock(&dev->struct_mutex);
+
+		llist_for_each_entry_safe(msm_obj, next,
+					  freed, freed)
+			free_object(msm_obj);
+
+		mutex_unlock(&dev->struct_mutex);
+
+		if (need_resched())
+			break;
+	}
+}
+
 /* convenience method to construct a GEM buffer object, and userspace handle */
 int msm_gem_new_handle(struct drm_device *dev, struct drm_file *file,
 		uint32_t size, uint32_t flags, uint32_t *handle,

drivers/gpu/drm/msm/msm_gem.h

@@ -84,6 +84,8 @@ struct msm_gem_object {
 
 	struct list_head vmas;    /* list of msm_gem_vma */
 
+	struct llist_node freed;
+
 	/* normally (resv == &_resv) except for imported bo's */
 	struct reservation_object *resv;
 	struct reservation_object _resv;
@@ -133,6 +135,7 @@ enum msm_gem_lock {
 
 void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass);
 void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass);
+void msm_gem_free_work(struct work_struct *work);
 
 /* Created per submit-ioctl, to track bo's and cmdstream bufs, etc,
  * associated with the cmdstream submission for synchronization (and