In a normal scenario when sys-admin replaces a disk, the
expeted is btrfs will release the disk completely.

However the below test case gives a wrong impression that
replaced disk is still is in use.

$ btrfs rep start /dev/sde /dev/sdg4 /btrfs
$ mkfs.btrfs /dev/sde
/dev/sde appears to contain an existing filesystem (btrfs).
Error: Use the -f option to force overwrite.

Signed-off-by: Anand Jain <anand.j...@oracle.com>
---
v1->v2: add missing signed-off

 fs/btrfs/volumes.c | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 7243196..1567439 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6311,16 +6311,33 @@ int btrfs_scratch_superblock(struct btrfs_device 
*device)
 {
        struct buffer_head *bh;
        struct btrfs_super_block *disk_super;
+       int i;
+       u64 bytenr;
 
-       bh = btrfs_read_dev_super(device->bdev);
-       if (!bh)
-               return -EINVAL;
-       disk_super = (struct btrfs_super_block *)bh->b_data;
+       for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+               bytenr = btrfs_sb_offset(i);
+               if (bytenr + BTRFS_SUPER_INFO_SIZE >=
+                               i_size_read(device->bdev->bd_inode))
+                       break;
 
-       memset(&disk_super->magic, 0, sizeof(disk_super->magic));
-       set_buffer_dirty(bh);
-       sync_dirty_buffer(bh);
-       brelse(bh);
+               bh = __bread(device->bdev, bytenr / 4096,
+                                       BTRFS_SUPER_INFO_SIZE);
+               if (!bh)
+                       continue;
+
+               disk_super = (struct btrfs_super_block *)bh->b_data;
+               if (btrfs_super_bytenr(disk_super) != bytenr ||
+                               btrfs_super_magic(disk_super) != BTRFS_MAGIC) {
+                       brelse(bh);
+                       continue;
+               }
+
+               memset(&disk_super->magic, 0, sizeof(disk_super->magic));
+
+               set_buffer_dirty(bh);
+               sync_dirty_buffer(bh);
+               brelse(bh);
+       }
 
        return 0;
 }
-- 
1.8.5.3

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