Revert "xen/p2m: m2p_find_override: use list_for_each_entry_safe"

This reverts commit b960d6c43a63ebd2d8518b328da3816b833ee8cc.

If we have another thread (very likely) touched the list, we
end up hitting a problem "that the next element is wrong because
we should be able to cope with that. The problem is that the
next->next pointer would be set LIST_POISON1. " (Stefano's
comment on the patch).

Reverting for now.

Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/p2m.c

@@ -809,17 +809,21 @@ struct page *m2p_find_override(unsigned long mfn)
 {
 	unsigned long flags;
 	struct list_head *bucket = &m2p_overrides[mfn_hash(mfn)];
-	struct page *p, *t, *ret;
+	struct page *p, *ret;
 
 	ret = NULL;
 
-	list_for_each_entry_safe(p, t, bucket, lru) {
+	spin_lock_irqsave(&m2p_override_lock, flags);
+
+	list_for_each_entry(p, bucket, lru) {
 		if (page_private(p) == mfn) {
 			ret = p;
 			break;
 		}
 	}
 
+	spin_unlock_irqrestore(&m2p_override_lock, flags);
+
 	return ret;
 }