lib: add CONFIG_TEST_SORT to enable self-test of sort()

Along with the addition made to Kconfig.debug, the prior existing but
permanently disabled test function has been slightly refactored.

Patch has been tested using QEMU 2.1.2 with a .config obtained through
'make defconfig' (x86_64) and manually enabling the option.

[arnd@arndb.de: move sort self-test into a separate file]
  Link: http://lkml.kernel.org/r/20170112110657.3123790-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/HE1PR09MB0394B0418D504DCD27167D4FD49B0@HE1PR09MB0394.eurprd09.prod.outlook.com
Signed-off-by: Kostenzer Felix <fkostenzer@live.at>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/sort.c b/lib/sort.c
index fc20df4..975c6ef 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -4,6 +4,8 @@
  * Jan 23 2005  Matt Mackall <mpm@selenic.com>
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/types.h>
 #include <linux/export.h>
 #include <linux/sort.h>
@@ -101,42 +103,3 @@ void sort(void *base, size_t num, size_t size,
 }
 
 EXPORT_SYMBOL(sort);
-
-#if 0
-#include <linux/slab.h>
-/* a simple boot-time regression test */
-
-int cmpint(const void *a, const void *b)
-{
-	return *(int *)a - *(int *)b;
-}
-
-static int sort_test(void)
-{
-	int *a, i, r = 1;
-
-	a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
-	BUG_ON(!a);
-
-	printk("testing sort()\n");
-
-	for (i = 0; i < 1000; i++) {
-		r = (r * 725861) % 6599;
-		a[i] = r;
-	}
-
-	sort(a, 1000, sizeof(int), cmpint, NULL);
-
-	for (i = 0; i < 999; i++)
-		if (a[i] > a[i+1]) {
-			printk("sort() failed!\n");
-			break;
-		}
-
-	kfree(a);
-
-	return 0;
-}
-
-module_init(sort_test);
-#endif