fs/direct-io.c: fix possible use-after-free with AIO

fs/direct-io.c: fix possible use-after-free with AIO

Running AIO is pinning inode in memory using file reference.  Once AIO is
completed using aio_complete(), file reference is put and inode can be
freed from memory.  So we have to be sure that calling aio_complete() is
the last thing we do with the inode.

Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>