ioremap: Delay sanity check until after a successful mapping

While tracking down the reason for an ioremap() failure I was
distracted  by the WARN_ONCE() in __ioremap_caller().

Performing a WARN_ONCE() sanity check before the mapping
is successful seems pointless if the caller sends bad values.

A case in point is when the BIOS provides erroneous screen_info
values causing vesafb_probe() to request an outrageuous size.
The WARN_ONCE is then wasted on bogosity. Move the warning to a
point where the mapping has been successfully allocated.

Addresses:

  http://bugs.launchpad.net/bugs/772042

Reviewed-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Link: http://lkml.kernel.org/r/4DB99D2E.9080106@canonical.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/ioremap.c

@@ -90,13 +90,6 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 	if (is_ISA_range(phys_addr, last_addr))
 		return (__force void __iomem *)phys_to_virt(phys_addr);
 
-	/*
-	 * Check if the request spans more than any BAR in the iomem resource
-	 * tree.
-	 */
-	WARN_ONCE(iomem_map_sanity_check(phys_addr, size),
-		  KERN_INFO "Info: mapping multiple BARs. Your kernel is fine.");
-
 	/*
 	 * Don't allow anybody to remap normal RAM that we're using..
 	 */
@@ -170,6 +163,13 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 	ret_addr = (void __iomem *) (vaddr + offset);
 	mmiotrace_ioremap(unaligned_phys_addr, unaligned_size, ret_addr);
 
+	/*
+	 * Check if the request spans more than any BAR in the iomem resource
+	 * tree.
+	 */
+	WARN_ONCE(iomem_map_sanity_check(unaligned_phys_addr, unaligned_size),
+		  KERN_INFO "Info: mapping multiple BARs. Your kernel is fine.");
+
 	return ret_addr;
 err_free_area:
 	free_vm_area(area);