Index: sys/ddb/db_command.c
===================================================================
--- sys/ddb/db_command.c
+++ sys/ddb/db_command.c
@@ -72,6 +72,7 @@
 static db_cmdfcn_t	db_kill;
 static db_cmdfcn_t	db_reset;
 static db_cmdfcn_t	db_stack_trace;
+static db_cmdfcn_t	db_stack_trace_active;
 static db_cmdfcn_t	db_stack_trace_all;
 static db_cmdfcn_t	db_watchdog;
 
@@ -79,6 +80,12 @@
  * 'show' commands
  */
 
+static struct command db_show_active_cmds[] = {
+	{ "trace",	db_stack_trace_active,	0,	NULL },
+};
+struct command_table db_show_active_table =
+    LIST_HEAD_INITIALIZER(db_show_active_table);
+
 static struct command db_show_all_cmds[] = {
 	{ "trace",	db_stack_trace_all,	0,	NULL },
 };
@@ -86,6 +93,7 @@
     LIST_HEAD_INITIALIZER(db_show_all_table);
 
 static struct command db_show_cmds[] = {
+	{ "active",	0,			0,	&db_show_active_table },
 	{ "all",	0,			0,	&db_show_all_table },
 	{ "registers",	db_show_regs,		0,	NULL },
 	{ "breaks",	db_listbreak_cmd, 	0,	NULL },
@@ -120,6 +128,8 @@
 	{ "match",	db_trace_until_matching_cmd,0,	NULL },
 	{ "trace",	db_stack_trace,		CS_OWN,	NULL },
 	{ "t",		db_stack_trace,		CS_OWN,	NULL },
+	/* XXX alias for active trace */
+	{ "acttrace",	db_stack_trace_active,	0,	NULL },
 	/* XXX alias for all trace */
 	{ "alltrace",	db_stack_trace_all,	0,	NULL },
 	{ "where",	db_stack_trace,		CS_OWN,	NULL },
@@ -195,6 +205,9 @@
 		db_command_register(&db_cmd_table, &db_cmds[i]);
 	for (i = 0; i < N(db_show_cmds); i++)
 		db_command_register(&db_show_table, &db_show_cmds[i]);
+	for (i = 0; i < N(db_show_active_cmds); i++)
+		db_command_register(&db_show_active_table,
+		    &db_show_active_cmds[i]);
 	for (i = 0; i < N(db_show_all_cmds); i++)
 		db_command_register(&db_show_all_table, &db_show_all_cmds[i]);
 #undef N
@@ -799,6 +812,35 @@
 }
 
 static void
+db_stack_trace_active(db_expr_t dummy, bool dummy2, db_expr_t dummy3,
+    char *dummy4)
+{
+	struct proc *p;
+	struct thread *td;
+	jmp_buf jb;
+	void *prev_jb;
+
+	FOREACH_PROC_IN_SYSTEM(p) {
+		prev_jb = kdb_jmpbuf(jb);
+		if (setjmp(jb) == 0) {
+			FOREACH_THREAD_IN_PROC(p, td) {
+				if (td->td_state != TDS_RUNNING)
+					continue;
+				db_printf("\nTracing command %s pid %d tid %ld"
+				    " td %p (CPU %d)\n", p->p_comm, p->p_pid,
+				    (long)td->td_tid, td, td->td_oncpu);
+				db_trace_thread(td, -1);
+				if (db_pager_quit) {
+					kdb_jmpbuf(prev_jb);
+					return;
+				}
+			}
+		}
+		kdb_jmpbuf(prev_jb);
+	}
+}
+
+static void
 db_stack_trace_all(db_expr_t dummy, bool dummy2, db_expr_t dummy3,
     char *dummy4)
 {