FLR doesn't hold layout lock (LL) during IO (OST_READ) operations, but verify layout at the beginning of IO and at the end of IO.
the problem is that pages get Uptodate flag from brw_interpret context while the layout is checked for changes later. the pages are still marked uptodate till that point.
three processes:

• 1st modifying the file
• 2nd initiated OST_READ and going to repeat OST_READ due to layout change
• 3rd which finds result of OST_READ (stale data) in ll_do_fast_read()