[PATCH 2/2] btrfs: don't double brelse on device rm

[Zach Brown <zab@redhat.com>]

Device removal currently causes bdev removal to try to double free a bh
in the bdev:

[   55.714833] WARNING: at fs/buffer.c:1160 __brelse+0x36/0x40()
[   55.714833] VFS: brelse: Trying to free free buffer

Commit 7e3d9ebb1 added a double release of the bh for a device being
removed when all the supers don't fit in the device.  In that case it
releases the bh assuming that it's going to read a new one, finds that
it won't read, and goes to a label that releases the bh again.

All it needed to do was only brelse() right before overwriting the
current bh with __bread().

Signed-off-by: Zach Brown <zab@redhat.com>
---
 fs/btrfs/volumes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 090f57c..adb0bca 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1656,11 +1656,12 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		 * the below would take of the rest
 		 */
 		for (i = 1; i < BTRFS_SUPER_MIRROR_MAX; i++) {
-			brelse(bh);
 			bytenr = btrfs_sb_offset(i);
 			if (bytenr + BTRFS_SUPER_INFO_SIZE >=
 					i_size_read(bdev->bd_inode))
 				break;
+
+			brelse(bh);
 			bh = __bread(bdev, bytenr / 4096,
 					BTRFS_SUPER_INFO_SIZE);
 			if (!bh)
-- 
1.7.11.7