There's a few places that use incorrect exclusion for the cramfs raw
data access buffers.  The proper lock is "read_mutex" (and BKL does
nothing).

 - fix mount-time read and block number initialization without the mutex
   held. 
 - cramfs_readdir() needs to copy the name and inode information into a
   separate buffer since it can't hold the semaphore over the
   (potentially blocking) user mode access
 - cramfs_lookup() needs to hold the access lock over the whole
   function, not just the read itself
 - use generic_file_llseek on directories to get i_sem exclusion on
   readdir/lseek