[PATCH] mmput() might sleep

exit_aio() and exit_mmap() can sleep.  But it's easy to accidentally call
mmput() from inside locks.

Cc: Dave Peterson <dsp@llnl.gov>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>