md: simplify md_open

Now that devices are on the all_mddevs list until the gendisk is freed,
there can't be any duplicates.  Remove the global list lookup and just
grab a reference.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/md.c

@@ -7783,44 +7783,32 @@ static int md_set_read_only(struct block_device *bdev, bool ro)
 
 static int md_open(struct block_device *bdev, fmode_t mode)
 {
-	/*
-	 * Succeed if we can lock the mddev, which confirms that
-	 * it isn't being stopped right now.
-	 */
-	struct mddev *mddev = mddev_find(bdev->bd_dev);
+	struct mddev *mddev;
 	int err;
 
+	spin_lock(&all_mddevs_lock);
+	mddev = mddev_get(bdev->bd_disk->private_data);
+	spin_unlock(&all_mddevs_lock);
 	if (!mddev)
 		return -ENODEV;
 
-	if (mddev->gendisk != bdev->bd_disk) {
-		/* we are racing with mddev_put which is discarding this
-		 * bd_disk.
-		 */
-		mddev_put(mddev);
-		/* Wait until bdev->bd_disk is definitely gone */
-		if (work_pending(&mddev->del_work))
-			flush_workqueue(md_misc_wq);
-		return -EBUSY;
-	}
-	BUG_ON(mddev != bdev->bd_disk->private_data);
-
-	if ((err = mutex_lock_interruptible(&mddev->open_mutex)))
+	err = mutex_lock_interruptible(&mddev->open_mutex);
+	if (err)
 		goto out;
 
-	if (test_bit(MD_CLOSING, &mddev->flags)) {
-		mutex_unlock(&mddev->open_mutex);
 	err = -ENODEV;
-		goto out;
-	}
+	if (test_bit(MD_CLOSING, &mddev->flags))
+		goto out_unlock;
 
-	err = 0;
 	atomic_inc(&mddev->openers);
 	mutex_unlock(&mddev->open_mutex);
 
 	bdev_check_media_change(bdev);
- out:
-	if (err)
+	return 0;
+
+out_unlock:
+	mutex_unlock(&mddev->open_mutex);
+out:
 	mddev_put(mddev);
 	return err;
 }