Btrfs: fix a regression in balance usage filter

Commit 3fed40cc ("Btrfs: cleanup duplicated division functions"), which
was merged into 3.8-rc1, has introduced a regression by removing logic
that was guarding us against bad user input.  Bring it back.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 9c84dbe64f18..469609838913 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2614,7 +2614,14 @@ static int chunk_usage_filter(struct btrfs_fs_info *fs_info, u64 chunk_offset,
         cache = btrfs_lookup_block_group(fs_info, chunk_offset);
         chunk_used = btrfs_block_group_used(&cache->item);
 
-        user_thresh = div_factor_fine(cache->key.offset, bargs->usage);
+        if (bargs->usage == 0)
+                user_thresh = 0;
+        else if (bargs->usage > 100)
+                user_thresh = cache->key.offset;
+        else
+                user_thresh = div_factor_fine(cache->key.offset,
+                                              bargs->usage);
+
         if (chunk_used < user_thresh)
                 ret = 0;