drm: Switch blobs to the new generic modeset obj refcounting

Need to move the free function around a bit, but otherwise mostly
just removing code.

Specifically we can nuke all the _locked variants since the weak idr
reference is now protected by the idr_mutex, which we never hold
anywhere expect in the lookup/reg/unreg functions. And those never
call anything else.

Another benefit of this is that this patch switches the weak reference
logic from kref_put_mutex to kref_get_unless_zero. And the later is in
general more flexible wrt accomodating multiple weak references
protected by different locks, which might or might not come handy
eventually.

But one consequence of that switch is that we need to acquire the
blob_lock from the free function for the list_del calls. That's a bit
tricky to pull off, but works well if we pick the exact same scheme as
is already used for framebuffers. Most important changes:

- filp list is maintainer by create/destroy_blob ioctls directly
(already the case, so we can just remove the redundant list_del from
the free function).

- filp close handler walks the filp-private list lockless - works
because we know no one else can access it. I copied the same comment
from the fb code over to explain this.

- Otherwise we need to sufficiently restrict blob_lock critical
sections to avoid all the unreference calls. Easy to do once the
blob_lock only protects the list, and no longer the weak reference.

Cc: Dave Airlie <[e-mail]>
Cc: Daniel Stone <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/drm_crtc.c

···
 		obj = NULL;
 	if (obj && obj->id != id)
 		obj = NULL;
-	/* don't leak out unref'd fb's */
-	if (obj &&
-	    obj->type == DRM_MODE_OBJECT_BLOB)
-		obj = NULL;
 
 	if (obj && obj->free_cb) {
 		if (!kref_get_unless_zero(&obj->refcount))
···
 {
 	struct drm_mode_object *obj = NULL;
 
-	WARN_ON(type == DRM_MODE_OBJECT_BLOB);
 	obj = _object_find(dev, id, type);
 	return obj;
 }
···
 	return ret;
 }
 
+static void drm_property_free_blob(struct kref *kref)
+{
+	struct drm_property_blob *blob =
+		container_of(kref, struct drm_property_blob, base.refcount);
+
+	mutex_lock(&blob->dev->mode_config.blob_lock);
+	list_del(&blob->head_global);
+	mutex_unlock(&blob->dev->mode_config.blob_lock);
+
+	drm_mode_object_unregister(blob->dev, &blob->base);
+
+	kfree(blob);
+}
+
 /**
  * drm_property_create_blob - Create new blob property
  *
···
 	if (data)
 		memcpy(blob->data, data, length);
 
-	mutex_lock(&dev->mode_config.blob_lock);
-
-	ret = drm_mode_object_get(dev, &blob->base, DRM_MODE_OBJECT_BLOB);
+	ret = drm_mode_object_get_reg(dev, &blob->base, DRM_MODE_OBJECT_BLOB,
+				      true, drm_property_free_blob);
 	if (ret) {
 		kfree(blob);
-		mutex_unlock(&dev->mode_config.blob_lock);
 		return ERR_PTR(-EINVAL);
 	}
 
-	kref_init(&blob->refcount);
-
+	mutex_lock(&dev->mode_config.blob_lock);
 	list_add_tail(&blob->head_global,
 	              &dev->mode_config.property_blob_list);
-
 	mutex_unlock(&dev->mode_config.blob_lock);
 
 	return blob;
 }
 EXPORT_SYMBOL(drm_property_create_blob);
-
-/**
- * drm_property_free_blob - Blob property destructor
- *
- * Internal free function for blob properties; must not be used directly.
- *
- * @kref: Reference
- */
-static void drm_property_free_blob(struct kref *kref)
-{
-	struct drm_property_blob *blob =
-		container_of(kref, struct drm_property_blob, refcount);
-
-	WARN_ON(!mutex_is_locked(&blob->dev->mode_config.blob_lock));
-
-	list_del(&blob->head_global);
-	list_del(&blob->head_file);
-	drm_mode_object_unregister(blob->dev, &blob->base);
-
-	kfree(blob);
-}
 
 /**
  * drm_property_unreference_blob - Unreference a blob property
···
  */
 void drm_property_unreference_blob(struct drm_property_blob *blob)
 {
-	struct drm_device *dev;
-
 	if (!blob)
 		return;
 
-	dev = blob->dev;
-
-	DRM_DEBUG("%p: blob ID: %d (%d)\n", blob, blob->base.id, atomic_read(&blob->refcount.refcount));
-
-	if (kref_put_mutex(&blob->refcount, drm_property_free_blob,
-			   &dev->mode_config.blob_lock))
-		mutex_unlock(&dev->mode_config.blob_lock);
-	else
-		might_lock(&dev->mode_config.blob_lock);
+	drm_mode_object_unreference(&blob->base);
 }
 EXPORT_SYMBOL(drm_property_unreference_blob);
-
-/**
- * drm_property_unreference_blob_locked - Unreference a blob property with blob_lock held
- *
- * Drop a reference on a blob property. May free the object. This must be
- * called with blob_lock held.
- *
- * @blob: Pointer to blob property
- */
-static void drm_property_unreference_blob_locked(struct drm_property_blob *blob)
-{
-	if (!blob)
-		return;
-
-	DRM_DEBUG("%p: blob ID: %d (%d)\n", blob, blob->base.id, atomic_read(&blob->refcount.refcount));
-
-	kref_put(&blob->refcount, drm_property_free_blob);
-}
 
 /**
  * drm_property_destroy_user_blobs - destroy all blobs created by this client
···
 {
 	struct drm_property_blob *blob, *bt;
 
-	mutex_lock(&dev->mode_config.blob_lock);
-
+	/*
+	 * When the file gets released that means no one else can access the
+	 * blob list any more, so no need to grab dev->blob_lock.
+	 */
 	list_for_each_entry_safe(blob, bt, &file_priv->blobs, head_file) {
 		list_del_init(&blob->head_file);
-		drm_property_unreference_blob_locked(blob);
+		drm_property_unreference_blob(blob);
 	}
-
-	mutex_unlock(&dev->mode_config.blob_lock);
 }
 
 /**
···
  */
 struct drm_property_blob *drm_property_reference_blob(struct drm_property_blob *blob)
 {
-	DRM_DEBUG("%p: blob ID: %d (%d)\n", blob, blob->base.id, atomic_read(&blob->refcount.refcount));
-	kref_get(&blob->refcount);
+	drm_mode_object_reference(&blob->base);
 	return blob;
 }
 EXPORT_SYMBOL(drm_property_reference_blob);
-
-/*
- * Like drm_property_lookup_blob, but does not return an additional reference.
- * Must be called with blob_lock held.
- */
-static struct drm_property_blob *__drm_property_lookup_blob(struct drm_device *dev,
-							    uint32_t id)
-{
-	struct drm_mode_object *obj = NULL;
-	struct drm_property_blob *blob;
-
-	WARN_ON(!mutex_is_locked(&dev->mode_config.blob_lock));
-
-	mutex_lock(&dev->mode_config.idr_mutex);
-	obj = idr_find(&dev->mode_config.crtc_idr, id);
-	if (!obj || (obj->type != DRM_MODE_OBJECT_BLOB) || (obj->id != id))
-		blob = NULL;
-	else
-		blob = obj_to_blob(obj);
-	mutex_unlock(&dev->mode_config.idr_mutex);
-
-	return blob;
-}
 
 /**
  * drm_property_lookup_blob - look up a blob property and take a reference
···
 struct drm_property_blob *drm_property_lookup_blob(struct drm_device *dev,
 					           uint32_t id)
 {
-	struct drm_property_blob *blob;
+	struct drm_mode_object *obj;
+	struct drm_property_blob *blob = NULL;
 
-	mutex_lock(&dev->mode_config.blob_lock);
-	blob = __drm_property_lookup_blob(dev, id);
-	if (blob) {
-		if (!kref_get_unless_zero(&blob->refcount))
-			blob = NULL;
-	}
-	mutex_unlock(&dev->mode_config.blob_lock);
-
+	obj = _object_find(dev, id, DRM_MODE_OBJECT_BLOB);
+	if (obj)
+		blob = obj_to_blob(obj);
 	return blob;
 }
 EXPORT_SYMBOL(drm_property_lookup_blob);
···
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;
 
-	drm_modeset_lock_all(dev);
-	mutex_lock(&dev->mode_config.blob_lock);
-	blob = __drm_property_lookup_blob(dev, out_resp->blob_id);
-	if (!blob) {
-		ret = -ENOENT;
-		goto done;
-	}
+	blob = drm_property_lookup_blob(dev, out_resp->blob_id);
+	if (!blob)
+		return -ENOENT;
 
 	if (out_resp->length == blob->length) {
 		blob_ptr = (void __user *)(unsigned long)out_resp->data;
 		if (copy_to_user(blob_ptr, blob->data, blob->length)) {
 			ret = -EFAULT;
-			goto done;
+			goto unref;
 		}
 	}
 	out_resp->length = blob->length;
+unref:
+	drm_property_unreference_blob(blob);
 
-done:
-	mutex_unlock(&dev->mode_config.blob_lock);
-	drm_modeset_unlock_all(dev);
 	return ret;
 }
 
···
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;
 
-	mutex_lock(&dev->mode_config.blob_lock);
-	blob = __drm_property_lookup_blob(dev, out_resp->blob_id);
-	if (!blob) {
-		ret = -ENOENT;
-		goto err;
-	}
+	blob = drm_property_lookup_blob(dev, out_resp->blob_id);
+	if (!blob)
+		return -ENOENT;
 
+	mutex_lock(&dev->mode_config.blob_lock);
 	/* Ensure the property was actually created by this user. */
 	list_for_each_entry(bt, &file_priv->blobs, head_file) {
 		if (bt == blob) {
···
 	/* We must drop head_file here, because we may not be the last
 	 * reference on the blob. */
 	list_del_init(&blob->head_file);
-	drm_property_unreference_blob_locked(blob);
 	mutex_unlock(&dev->mode_config.blob_lock);
+
+	/* One reference from lookup, and one from the filp. */
+	drm_property_unreference_blob(blob);
+	drm_property_unreference_blob(blob);
 
 	return 0;
 
 err:
 	mutex_unlock(&dev->mode_config.blob_lock);
+	drm_property_unreference_blob(blob);
+
 	return ret;
 }
 

include/drm/drm_crtc.h

···
 struct drm_property_blob {
 	struct drm_mode_object base;
 	struct drm_device *dev;
-	struct kref refcount;
 	struct list_head head_global;
 	struct list_head head_file;
 	size_t length;