hfs: atomically read inode size

See i_size_read() comments in include/linux/fs.h

Link: http://lkml.kernel.org/r/20170123175245.3272-1-fabf@skynet.be
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfs/mdb.c

@@ -38,7 +38,7 @@ static int hfs_get_last_session(struct super_block *sb,
 
 	/* default values */
 	*start = 0;
-	*size = sb->s_bdev->bd_inode->i_size >> 9;
+	*size = i_size_read(sb->s_bdev->bd_inode) >> 9;
 
 	if (HFS_SB(sb)->session >= 0) {
 		te.cdte_track = HFS_SB(sb)->session;