Index: subr_autoconf.c
===================================================================
RCS file: /cvs/src/sys/kern/subr_autoconf.c,v
retrieving revision 1.85
diff -u -p -r1.85 subr_autoconf.c
--- subr_autoconf.c	9 Feb 2015 12:37:18 -0000	1.85
+++ subr_autoconf.c	9 Feb 2015 12:58:16 -0000
@@ -51,6 +51,7 @@
 #include <sys/systm.h>
 #include <sys/queue.h>
 #include <sys/mutex.h>
+#include <sys/task.h>
 
 #include "hotplug.h"
 #include "mpath.h"
@@ -80,6 +81,7 @@ struct matchinfo {
 int autoconf_verbose = AUTOCONF_VERBOSE;	/* trace probe calls */
 
 static void mapply(struct matchinfo *, struct cfdata *);
+void device_free(void *);
 
 struct deferred_config {
 	TAILQ_ENTRY(deferred_config) dc_queue;
@@ -932,13 +934,31 @@ device_ref(struct device *dv)
  *
  * Context: process or interrupt
  */
+struct device_free_mem {
+	struct task	task;
+	size_t		size;
+};
+
 void
 device_unref(struct device *dv)
 {
+	struct device_free_mem *mem;
 	struct cfattach *ca;
 
 	if (atomic_dec_int_nv(&dv->dv_ref) == 0) {
 		ca = dv->dv_cfdata->cf_attach;
-		free(dv, M_DEVBUF, ca->ca_devsize);
+
+		mem = (struct device_free_mem *)dv;
+		/* arc4random_buf? */
+		task_set(&mem->task, device_free, mem);
+		task_add(systq, &mem->task);
 	}
+}
+
+void
+device_free(void *memp)
+{
+	struct device_free_mem *mem = memp;
+
+	free(mem, M_DEVBUF, mem->size);
 }