f2fs: add f2fs_bug_on in __remove_discard_cmd

Recently, discard related codes have changed a lot, so add f2fs_bug_on to
detect potential bug.

Signed-off-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 0fa717a..86a0c109 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -739,6 +739,8 @@ static void __remove_discard_cmd(struct f2fs_sb_info *sbi,
 {
 	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
 
+	f2fs_bug_on(sbi, dc->ref);
+
 	if (dc->error == -EOPNOTSUPP)
 		dc->error = 0;