block: rescan partitions on invalidated devices on -ENOMEDIA too

__blkdev_get() doesn't rescan partitions if disk->fops->open() fails,
which leads to ghost partition devices lingering after medimum removal
is known to both the kernel and userland.  The behavior also creates a
subtle inconsistency where O_NONBLOCK open, which doesn't fail even if
there's no medium, clears the ghots partitions, which is exploited to
work around the problem from userland.

Fix it by updating __blkdev_get() to issue partition rescan after
-ENOMEDIA too.

This was reported in the following bz.

 https://bugzilla.kernel.org/show_bug.cgi?id=13029

Note for stable: 2.6.38 and later only

Cc: stable@kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: David Zeuthen <zeuthen@gmail.com>
Reported-by: Martin Pitt <martin.pitt@ubuntu.com>
Reported-by: Kay Sievers <kay.sievers@vrfy.org>
Tested-by: Kay Sievers <kay.sievers@vrfy.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/block_dev.c

@@ -1102,6 +1102,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			if (!bdev->bd_part)
 				goto out_clear;
 
+			ret = 0;
 			if (disk->fops->open) {
 				ret = disk->fops->open(bdev, mode);
 				if (ret == -ERESTARTSYS) {
@@ -1118,9 +1119,18 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 					put_disk(disk);
 					goto restart;
 				}
+			}
+			/*
+			 * If the device is invalidated, rescan partition
+			 * if open succeeded or failed with -ENOMEDIUM.
+			 * The latter is necessary to prevent ghost
+			 * partitions on a removed medium.
+			 */
+			if (bdev->bd_invalidated && (!ret || ret == -ENOMEDIUM))
+				rescan_partitions(disk, bdev);
 			if (ret)
 				goto out_clear;
-			}
+
 			if (!bdev->bd_openers) {
 				bd_set_size(bdev,(loff_t)get_capacity(disk)<<9);
 				bdi = blk_get_backing_dev_info(bdev);
@@ -1128,8 +1138,6 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 					bdi = &default_backing_dev_info;
 				bdev_inode_switch_bdi(bdev->bd_inode, bdi);
 			}
-			if (bdev->bd_invalidated)
-				rescan_partitions(disk, bdev);
 		} else {
 			struct block_device *whole;
 			whole = bdget_disk(disk, 0);
@@ -1153,14 +1161,15 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 		}
 	} else {
 		if (bdev->bd_contains == bdev) {
-			if (bdev->bd_disk->fops->open) {
+			ret = 0;
+			if (bdev->bd_disk->fops->open)
 				ret = bdev->bd_disk->fops->open(bdev, mode);
+			/* the same as first opener case, read comment there */
+			if (bdev->bd_invalidated && (!ret || ret == -ENOMEDIUM))
+				rescan_partitions(bdev->bd_disk, bdev);
 			if (ret)
 				goto out_unlock_bdev;
 		}
-			if (bdev->bd_invalidated)
-				rescan_partitions(bdev->bd_disk, bdev);
-		}
 		/* only one opener holds refs to the module and disk */
 		module_put(disk->fops->owner);
 		put_disk(disk);