anon_vma: clone the anon_vma chain in the right order

We want to walk the chain in reverse order when cloning it, so that the
order of the result chain will be the same as the order in the source
chain.  When we add entries to the chain, they go at the head of the
chain, so we want to add the source head last.
Reviewed-by: NRik van Riel <riel@redhat.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Tested-by: Borislav Petkov <bp@alien8.de> [ "No, it still oopses" ]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/rmap.c

@@ -182,7 +182,7 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 {
 	struct anon_vma_chain *avc, *pavc;
 
-	list_for_each_entry(pavc, &src->anon_vma_chain, same_vma) {
+	list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
 		avc = anon_vma_chain_alloc();
 		if (!avc)
 			goto enomem_failure;