vfio/mdev: Use the driver core to create the 'remove' file

The device creator is supposed to use the dev.groups value to add sysfs
files before device_add is called, not call sysfs_create_files() after
device_add() returns. This creates a race with uevent delivery where the
extra attribute will not be visible.

This was being done because the groups had been co-opted by the mdev
driver, now that prior patches have moved the driver's groups to the
struct device_driver the dev.group is properly free for use here.
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20220411141403.86980-34-hch@lst.deReviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>

drivers/vfio/mdev/mdev_core.c

@@ -269,6 +269,7 @@ int mdev_device_create(struct mdev_type *type, const guid_t *uuid)
 	mdev->dev.parent  = parent->dev;
 	mdev->dev.bus = &mdev_bus_type;
 	mdev->dev.release = mdev_device_release;
+	mdev->dev.groups = mdev_device_groups;
 	mdev->type = type;
 	/* Pairs with the put in mdev_device_release() */
 	kobject_get(&type->kobj);

drivers/vfio/mdev/mdev_private.h

@@ -32,6 +32,8 @@ struct mdev_type {
 	unsigned int type_group_id;
 };
 
+extern const struct attribute_group *mdev_device_groups[];
+
 #define to_mdev_type_attr(_attr)	\
 	container_of(_attr, struct mdev_type_attribute, attr)
 #define to_mdev_type(_kobj)		\

drivers/vfio/mdev/mdev_sysfs.c

@@ -244,11 +244,20 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr,
 
 static DEVICE_ATTR_WO(remove);
 
-static const struct attribute *mdev_device_attrs[] = {
+static struct attribute *mdev_device_attrs[] = {
 	&dev_attr_remove.attr,
 	NULL,
 };
 
+static const struct attribute_group mdev_device_group = {
+	.attrs = mdev_device_attrs,
+};
+
+const struct attribute_group *mdev_device_groups[] = {
+	&mdev_device_group,
+	NULL
+};
+
 int mdev_create_sysfs_files(struct mdev_device *mdev)
 {
 	struct mdev_type *type = mdev->type;
@@ -262,15 +271,8 @@ int mdev_create_sysfs_files(struct mdev_device *mdev)
 	ret = sysfs_create_link(kobj, &type->kobj, "mdev_type");
 	if (ret)
 		goto type_link_failed;
-
-	ret = sysfs_create_files(kobj, mdev_device_attrs);
-	if (ret)
-		goto create_files_failed;
-
 	return ret;
 
-create_files_failed:
-	sysfs_remove_link(kobj, "mdev_type");
 type_link_failed:
 	sysfs_remove_link(mdev->type->devices_kobj, dev_name(&mdev->dev));
 	return ret;
@@ -280,7 +282,6 @@ void mdev_remove_sysfs_files(struct mdev_device *mdev)
 {
 	struct kobject *kobj = &mdev->dev.kobj;
 
-	sysfs_remove_files(kobj, mdev_device_attrs);
 	sysfs_remove_link(kobj, "mdev_type");
 	sysfs_remove_link(mdev->type->devices_kobj, dev_name(&mdev->dev));
 }