btrfs: Fix early enospc because 'unused' calculated with wrong sign.

'unused' calculated with wrong sign in reserve_metadata_bytes().
This might have lead to unwanted over-reservations.

Signed-off-by: Arne Jansen <sensille@gmx.net>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a541bc87f04c..ddaf6340fe7f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3413,7 +3413,7 @@ again:
          * our reservation.
          */
         if (unused <= space_info->total_bytes) {
-                unused -= space_info->total_bytes;
+                unused = space_info->total_bytes - unused;
                 if (unused >= num_bytes) {
                         if (!reserved)
                                 space_info->bytes_reserved += orig_bytes;