block: reopen the device in blkdev_reread_part

Historically the BLKRRPART ioctls called into the now defunct ->revalidate
method, which caused the sd driver to check if any media is present.
When the ->revalidate method was removed this revalidation was lost,
leading to lots of I/O errors when using the eject command.  Fix this by
reopening the device to rescan the partitions, and thus calling the
revalidation logic in the sd driver.

Fixes: 471bd0af ("sd: use bdev_check_media_change")
Reported--by: Tom Seewald <tseewald@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Tom Seewald <tseewald@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/ioctl.c

@@ -81,20 +81,27 @@ static int compat_blkpg_ioctl(struct block_device *bdev,
 }
 #endif
 
-static int blkdev_reread_part(struct block_device *bdev)
+static int blkdev_reread_part(struct block_device *bdev, fmode_t mode)
 {
-	int ret;
+	struct block_device *tmp;
 
 	if (!disk_part_scan_enabled(bdev->bd_disk) || bdev_is_partition(bdev))
 		return -EINVAL;
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
-	mutex_lock(&bdev->bd_mutex);
-	ret = bdev_disk_changed(bdev, false);
-	mutex_unlock(&bdev->bd_mutex);
+	/*
+	 * Reopen the device to revalidate the driver state and force a
+	 * partition rescan.
+	 */
+	mode &= ~FMODE_EXCL;
+	set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
 
-	return ret;
+	tmp = blkdev_get_by_dev(bdev->bd_dev, mode, NULL);
+	if (IS_ERR(tmp))
+		return PTR_ERR(tmp);
+	blkdev_put(tmp, mode);
+	return 0;
 }
 
 static int blk_ioctl_discard(struct block_device *bdev, fmode_t mode,
@@ -498,7 +505,7 @@ static int blkdev_common_ioctl(struct block_device *bdev, fmode_t mode,
 		bdev->bd_bdi->ra_pages = (arg * 512) / PAGE_SIZE;
 		return 0;
 	case BLKRRPART:
-		return blkdev_reread_part(bdev);
+		return blkdev_reread_part(bdev, mode);
 	case BLKTRACESTART:
 	case BLKTRACESTOP:
 	case BLKTRACETEARDOWN: