Btrfs: fix infinite loop in btrfs_shrink_device()

If relocate of block group 0 fails with ENOSPC we end up infinitely
looping because key.offset -= 1 statement in that case brings us back to
where we started.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index bcc0acda8691..be2d4e0e6cfb 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2987,7 +2987,7 @@ again:
         key.offset = (u64)-1;
         key.type = BTRFS_DEV_EXTENT_KEY;
 
-        while (1) {
+        do {
                 ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
                 if (ret < 0)
                         goto done;
@@ -3029,8 +3029,7 @@ again:
                         goto done;
                 if (ret == -ENOSPC)
                         failed++;
-                key.offset -= 1;
-        }
+        } while (key.offset-- > 0);
 
         if (failed && !retried) {
                 failed = 0;