fat: fix non-atomic NFS i_pos read

fat_encode_fh() can fetch an invalid i_pos value on systems where 64-bit
accesses are not atomic.  Make it use the same accessor as the rest of the
FAT code.
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fat/inode.c

@@ -738,22 +738,21 @@ static int
 fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
 {
 	int len = *lenp;
-	u32 ipos_h, ipos_m, ipos_l;
+	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+	loff_t i_pos;
 
 	if (len < 5) {
 		*lenp = 5;
 		return 255; /* no room */
 	}
 
-	ipos_h = MSDOS_I(inode)->i_pos >> 8;
-	ipos_m = (MSDOS_I(inode)->i_pos & 0xf0) << 24;
-	ipos_l = (MSDOS_I(inode)->i_pos & 0x0f) << 28;
+	i_pos = fat_i_pos_read(sbi, inode);
 	*lenp = 5;
 	fh[0] = inode->i_ino;
 	fh[1] = inode->i_generation;
-	fh[2] = ipos_h;
-	fh[3] = ipos_m | MSDOS_I(inode)->i_logstart;
-	fh[4] = ipos_l;
+	fh[2] = i_pos >> 8;
+	fh[3] = ((i_pos & 0xf0) << 24) | MSDOS_I(inode)->i_logstart;
+	fh[4] = (i_pos & 0x0f) << 28;
 	if (parent)
 		fh[4] |= MSDOS_I(parent)->i_logstart;
 	return 3;