xfs: update atime before I/O in xfs_file_dio_aio_read

After the call to __blkdev_direct_IO the final reference to the file
might have been dropped by aio_complete already, and the call to
file_accessed might cause a use after free.

Instead update the access time before the I/O, similar to how we
update the time stamps before writes.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reported-and-tested-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

fs/xfs/xfs_file.c

@@ -269,6 +269,8 @@ xfs_file_dio_aio_read(
 		return -EINVAL;
 	}
 
+	file_accessed(iocb->ki_filp);
+
 	/*
 	 * Locking is a bit tricky here. If we take an exclusive lock for direct
 	 * IO, we effectively serialise all new concurrent read IO to this file
@@ -323,7 +325,6 @@ xfs_file_dio_aio_read(
 	}
 	xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
 
-	file_accessed(iocb->ki_filp);
 	return ret;
 }