This patch fixes the race condition

  |      fat_free                |    fat_get_cluster
  +------------------------------+-----------------------
                                     fat_cache_lookup()
                                     (get the copy of cache)
   fat_cache_inval_inode()
(invalidate caches on inode)
                                     fat_cache_add()
                                     (update/add the getted cache)

The above race has possible that invalidated cache is added.

This patch fixes the race condition by adding the cache-id to copy of cache.
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>