Index: subr_hints.c
===================================================================
--- subr_hints.c	(revision 240251)
+++ subr_hints.c	(working copy)
@@ -28,12 +28,12 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/bus.h>
 #include <sys/lock.h>
 #include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/sysctl.h>
-#include <sys/systm.h>
-#include <sys/bus.h>
 
 /*
  * Access functions for device resources.
@@ -45,7 +45,7 @@ static char *hintp;
 
 /*
  * Define kern.hintmode sysctl, which only accept value 2, that cause to
- * switch from Static KENV mode to Dynamic KENV. So systems that have hints
+ * switch from Static KENV mode to Dynamic KENV.  So systems that have hints
  * compiled into kernel will be able to see/modify KENV (and hints too).
  */
 
@@ -60,21 +60,20 @@ sysctl_hintmode(SYSCTL_HANDLER_ARGS)
 	cp = kern_envp;
 	value = hintmode;
 
-	/* Fetch candidate for new hintmode value */
+	/* Fetch candidate for new hintmode value. */
 	error = sysctl_handle_int(oidp, &value, 0, req);
-	if (error || req->newptr == NULL)
+	if (error != 0 || req->newptr == NULL)
 		return (error);
 
-	if (value != 2)
-		/* Only accept swithing to hintmode 2 */
+	if (value != 2) /* Only accept swithing to hintmode 2 */
 		return (EINVAL);
 
-	/* Migrate from static to dynamic hints */
+	/* Migrate from static to dynamic hints. */
 	switch (hintmode) {
 	case 0:
 		if (dynamic_kenv) {
 			/*
-			 * Already here. But assign hintmode to 2, to not
+			 * Already here.  But assign hintmode to 2, to not
 			 * check it in the future.
 			 */
 			hintmode = 2;
@@ -87,22 +86,30 @@ sysctl_hintmode(SYSCTL_HANDLER_ARGS)
 		cp = static_hints;
 		break;
 	case 2:
-		/* Nothing to do, hintmode already 2 */
+		/* Nothing to do, if hintmode already 2. */
 		return (0);
 	}
 
-	while (cp) {
+	/*
+	 * We have no source to copy from, so just update hintmode/use_kenv
+	 * and return.
+	 */
+	if (cp == NULL) {
+		hintmode = value;
+		use_kenv = 1;
+		return (0);
+	}
+
+	/* While next line is not empty. */
+	while (*cp != '\0') {
 		i = strlen(cp);
-		if (i == 0)
-			break;
 		if (from_kenv) {
 			if (strncmp(cp, "hint.", 5) != 0)
-				/* kenv can have not only hints */
+				/* kenv can have not only hints. */
 				continue;
 		}
 		eq = strchr(cp, '=');
-		if (eq == NULL)
-			/* Bad hint value */
+		if (eq == NULL) /* Bad hint value */
 			continue;
 		eqidx = eq - cp;