Btrfs: stop refusing the relocation of chunk 0

AFAICT chunk 0 is no longer special, and so it should be restriped just like every other chunk. One reason for this change is us refusing the relocation can lead to filesystems that can only be mounted ro, and never rw -- see the bugzilla [1] for details. The other reason is that device removal code is already doing this: it will happily relocate chunk 0 is part of shrinking the device.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=60594

---
 fs/btrfs/volumes.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

index c9a0977..e8325de 100644
@@ -2991,10 +2991,6 @@ again:
 		if (found_key.objectid != key.objectid)
 			break;
 
-		/* chunk zero is special */
-		if (found_key.offset == 0)
-			break;
-
 		chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
 
 		if (!counting) {

@@ -3030,6 +3026,8 @@ again:
 			spin_unlock(&fs_info->balance_lock);
 		}
 loop:
+		if (found_key.offset == 0)
+			break;
 		key.offset = found_key.offset - 1;
 	}
 

1.7.10.4