[PATCH] Fix swiotlb pci_map_sg error handling

The overflow checking condition in lib/swiotlb.c was wrong.
It would first run a NULL pointer through virt_to_phys before
testing it. Since pci_map_sg overflow is not that uncommon
and causes data corruption (including broken file systems) when not
properly detected I think it's better to fix it in 2.6.15.

This affects x86-64 and IA64.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

lib/swiotlb.c

@@ -704,8 +704,9 @@ swiotlb_map_sg(struct device *hwdev, struct scatterlist *sg, int nelems,
 		addr = SG_ENT_VIRT_ADDRESS(sg);
 		dev_addr = virt_to_phys(addr);
 		if (swiotlb_force || address_needs_mapping(hwdev, dev_addr)) {
-			sg->dma_address = (dma_addr_t) virt_to_phys(map_single(hwdev, addr, sg->length, dir));
-			if (!sg->dma_address) {
+			void *map = map_single(hwdev, addr, sg->length, dir);
+			sg->dma_address = virt_to_bus(map);
+			if (!map) {
 				/* Don't panic here, we expect map_sg users
 				   to do proper error handling. */
 				swiotlb_full(hwdev, sg->length, dir, 0);