Previously, it would be possible for prev->next to point to &free_slob_pages,
and thus we would try to move a list onto itself, and bad things would
happen.

It seems a bit hairy to be doing list operations with the list marker as an
entry, rather than a head, but...

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
Index: linux-2.6/mm/slob.c
===================================================================
--- linux-2.6.orig/mm/slob.c
+++ linux-2.6/mm/slob.c
@@ -321,7 +321,8 @@ static void *slob_alloc(size_t size, gfp
 		/* Improve fragment distribution and reduce our average
 		 * search time by starting our next search here. (see
 		 * Knuth vol 1, sec 2.5, pg 449) */
-		if (free_slob_pages.next != prev->next)
+		if (prev != free_slob_pages.prev &&
+				free_slob_pages.next != prev->next)
 			list_move_tail(&free_slob_pages, prev->next);
 		break;
 	}