scsi: storvsc: Fix a bug in copy_from_bounce_buffer()

commit 8de58074 upstream.

We may exit this function without properly freeing up the maapings
we may have acquired. Fix the bug.
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>
[bwh: Backported to 3.2:
 - Adjust filename
 - Keep using kmap_atomic()/kunmap_atomic(), not the sg_-prefixed functions]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/staging/hv/storvsc_drv.c

@@ -940,23 +940,24 @@ static unsigned int copy_to_bounce_buffer(struct scatterlist *orig_sgl,
 			if (bounce_sgl[j].length == PAGE_SIZE) {
 				/* full..move to next entry */
 				kunmap_atomic((void *)bounce_addr, KM_IRQ0);
+				bounce_addr = 0;
 				j++;
+			}
 
 			/* if we need to use another bounce buffer */
-				if (srclen || i != orig_sgl_count - 1)
+			if (srclen && bounce_addr == 0)
 				bounce_addr =
 					(unsigned long)kmap_atomic(
 					sg_page((&bounce_sgl[j])), KM_IRQ0);
 
-			} else if (srclen == 0 && i == orig_sgl_count - 1) {
-				/* unmap the last bounce that is < PAGE_SIZE */
-				kunmap_atomic((void *)bounce_addr, KM_IRQ0);
-			}
 		}
 
 		kunmap_atomic((void *)(src_addr - orig_sgl[i].offset), KM_IRQ0);
 	}
 
+	if (bounce_addr)
+		kunmap_atomic((void *)bounce_addr, KM_IRQ0);
+
 	local_irq_restore(flags);
 
 	return total_copied;