Index: head/sys/kern/tty_info.c
===================================================================
--- head/sys/kern/tty_info.c
+++ head/sys/kern/tty_info.c
@@ -49,11 +49,14 @@
 #include <sys/cons.h>
 #include <sys/kdb.h>
 #include <sys/lock.h>
+#include <sys/malloc.h>
 #include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/resourcevar.h>
 #include <sys/sbuf.h>
 #include <sys/sched.h>
+#include <sys/stack.h>
+#include <sys/sysctl.h>
 #include <sys/systm.h>
 #include <sys/tty.h>
 
@@ -233,6 +236,11 @@
 	return (-ENXIO);
 }
 
+static bool tty_info_kstacks = false;
+SYSCTL_BOOL(_kern, OID_AUTO, tty_info_kstacks, CTLFLAG_RWTUN,
+    &tty_info_kstacks, 0,
+    "Enable printing kernel stack(9) traces on ^T (tty info)");
+
 /*
  * Report on state of foreground process group.
  */
@@ -240,12 +248,13 @@
 tty_info(struct tty *tp)
 {
 	struct timeval rtime, utime, stime;
+	struct stack stack;
 	struct proc *p, *ppick;
 	struct thread *td, *tdpick;
 	const char *stateprefix, *state;
 	struct sbuf sb;
 	long rss;
-	int load, pctcpu;
+	int load, pctcpu, sterr;
 	pid_t pid;
 	char comm[MAXCOMLEN + 1];
 	struct rusage ru;
@@ -320,6 +329,15 @@
 	else
 		state = "unknown";
 	pctcpu = (sched_pctcpu(td) * 10000 + FSCALE / 2) >> FSHIFT;
+	if (tty_info_kstacks) {
+		stack_zero(&stack);
+		if (TD_IS_SWAPPED(td) || TD_IS_RUNNING(td))
+			sterr = stack_save_td_running(&stack, td);
+		else {
+			stack_save_td(&stack, td);
+			sterr = 0;
+		}
+	}
 	thread_unlock(td);
 	if (p->p_state == PRS_NEW || p->p_state == PRS_ZOMBIE)
 		rss = 0;
@@ -340,6 +358,9 @@
 	    (long)utime.tv_sec, utime.tv_usec / 10000,
 	    (long)stime.tv_sec, stime.tv_usec / 10000,
 	    pctcpu / 100, rss);
+
+	if (tty_info_kstacks && sterr == 0)
+		stack_sbuf_print_flags(&sb, &stack, M_NOWAIT);
 
 out:
 	sbuf_finish(&sb);