[GFS2] BUG: unable to handle kernel paging request at ffff81002690e000

This patch fixes bugzilla bug bz448866: gfs2: BUG: unable to
handle kernel paging request at ffff81002690e000.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/rgrp.c

@@ -195,7 +195,7 @@ static u32 gfs2_bitfit(const u8 *buffer, unsigned int buflen, u32 goal,
 	   depending on architecture.  I've experimented with several ways
 	   of writing this section such as using an else before the goto
 	   but this one seems to be the fastest. */
-	while ((unsigned char *)plong < end - 1) {
+	while ((unsigned char *)plong < end - sizeof(unsigned long)) {
 		prefetch(plong + 1);
 		if (((*plong) & LBITMASK) != lskipval)
 			break;