md: fix mddev->kobj lifetime

Once a kobject is initialized, the containing object should not be
directly freed.  So delay initialization until it is added.  Also
remove the kobject_del call as the last put will remove the kobject as
well.  The explicitly delete isn't needed here, and dropping it will
simplify further fixes.

With this md_free now does not need to check that ->gendisk is non-NULL
as it is always set by the time that kobject_init is called on
mddev->kobj.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/md.c

@@ -678,7 +678,6 @@ static void md_safemode_timeout(struct timer_list *t);
 
 void mddev_init(struct mddev *mddev)
 {
-	kobject_init(&mddev->kobj, &md_ktype);
 	mutex_init(&mddev->open_mutex);
 	mutex_init(&mddev->reconfig_mutex);
 	mutex_init(&mddev->bitmap_info.mutex);
@@ -5590,10 +5589,9 @@ static void md_free(struct kobject *ko)
 	if (mddev->sysfs_level)
 		sysfs_put(mddev->sysfs_level);
 
-	if (mddev->gendisk) {
 	del_gendisk(mddev->gendisk);
 	put_disk(mddev->gendisk);
-	}
+
 	percpu_ref_exit(&mddev->writes_pending);
 
 	bioset_exit(&mddev->bio_set);
@@ -5617,7 +5615,6 @@ static void mddev_delayed_delete(struct work_struct *ws)
 {
 	struct mddev *mddev = container_of(ws, struct mddev, del_work);
 
-	kobject_del(&mddev->kobj);
 	kobject_put(&mddev->kobj);
 }
 
@@ -5719,6 +5716,7 @@ int md_alloc(dev_t dev, char *name)
 	if (error)
 		goto out_cleanup_disk;
 
+	kobject_init(&mddev->kobj, &md_ktype);
 	error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md");
 	if (error)
 		goto out_del_gendisk;