Need to initialize map_bh.b_state to zero.  Otherwise, in case of a faulty
user-buffer its possible to go into dio_zero_block() and submit a page by
mistake - since it checks for buffer_new().

http://marc.info/?l=linux-kernel&m=118551339032528&w=2

akpm: Linus had a (better) patch to just do a kzalloc() in there, but it got
lost.  Probably this version is better for -stable anwyay.
Signed-off-by: NBadari Pulavarty <pbadari@us.ibm.com>
Acked-by: NJoe Jin <joe.jin@oracle.com>
Acked-by: NZach Brown <zach.brown@oracle.com>
Cc: gurudas pai <gurudas.pai@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>