dma-debug: warn of unmapping an invalid dma address

Impact: extend DMA-debug checks

Calling dma_unmap families against an invalid dma address should be a
bug.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Joerg Roedel <joerg.roedel@amd.com>
LKML-Reference: <20090319103743N.fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

lib/dma-debug.c

@@ -531,8 +531,11 @@ static void check_unmap(struct dma_debug_entry *ref)
 	struct hash_bucket *bucket;
 	unsigned long flags;
 
-	if (dma_mapping_error(ref->dev, ref->dev_addr))
+	if (dma_mapping_error(ref->dev, ref->dev_addr)) {
+		err_printk(ref->dev, NULL, "DMA-API: device driver tries "
+			   "to free an invalid DMA memory address\n");
 		return;
+	}
 
 	bucket = get_hash_bucket(ref, &flags);
 	entry = hash_bucket_find(bucket, ref);