Fix iommu address space allocation

This fixes kernel.org bug #13584. The IOVA code attempted to optimise
the insertion of new ranges into the rbtree, with the unfortunate result
that some ranges just didn't get inserted into the tree at all. Then
those ranges would be handed out more than once, and things kind of go
downhill from there.

Introduced after 2.6.25 by ddf02886
("PCI: iova RB tree setup tweak").
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: mark gross <mgross@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pci/iova.c

 /*
- * Copyright (c) 2006, Intel Corporation.
+ * Copyright © 2006-2009, Intel Corporation.
  *
- * This file is released under the GPLv2.
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+ * Place - Suite 330, Boston, MA 02111-1307 USA.
  *
- * Copyright (C) 2006-2008 Intel Corporation
  * Author: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
  */
 
@@ -123,7 +133,15 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 	/* Insert the new_iova into domain rbtree by holding writer lock */
 	/* Add new node and rebalance tree. */
 	{
-		struct rb_node **entry = &((prev)), *parent = NULL;
+		struct rb_node **entry, *parent = NULL;
+
+		/* If we have 'prev', it's a valid place to start the
+		   insertion. Otherwise, start from the root. */
+		if (prev)
+			entry = &prev;
+		else
+			entry = &iovad->rbroot.rb_node;
+
 		/* Figure out where to put new node */
 		while (*entry) {
 			struct iova *this = container_of(*entry,