Index: sys/kern/tty.c
===================================================================
RCS file: /cvsroot/src/sys/kern/tty.c,v
retrieving revision 1.283
diff -u -p -r1.283 tty.c
--- sys/kern/tty.c	2 Jan 2020 16:52:55 -0000	1.283
+++ sys/kern/tty.c	2 Jan 2020 16:55:14 -0000
@@ -2551,27 +2551,35 @@ ttygetinfo(struct tty *tp, int fromsig, 
 
 			if (pick == NULL) {
 				pick = p;
+				mutex_enter(p->p_lock);
 				continue;
 			}
-			if (pick->p_lock < p->p_lock) {
-				mutex_enter(pick->p_lock);
-				mutex_enter(p->p_lock);
-			} else if (pick->p_lock > p->p_lock) {
-				mutex_enter(p->p_lock);
-				mutex_enter(pick->p_lock);
-			} else
+
+			if (p->p_lock < pick->p_lock) {
+				if (!mutex_tryenter(p->p_lock)) {
+					mutex_exit(pick->p_lock);
+					mutex_enter(p->p_lock);
+					mutex_enter(pick->p_lock);
+				}
+			} else if (p->p_lock > pick->p_lock) {
 				mutex_enter(p->p_lock);
+			}
+
 			oldpick = pick;
-			if (proc_compare_wrapper(pick, p))
+			if (proc_compare_wrapper(pick, p)) {
 				pick = p;
-			mutex_exit(p->p_lock);
-			if (p->p_lock != oldpick->p_lock)
 				mutex_exit(oldpick->p_lock);
+			} else {
+				mutex_exit(p->p_lock);
+			}
 		}
+
 		if (fromsig &&
 		    (SIGACTION_PS(pick->p_sigacts, SIGINFO).sa_flags &
-		    SA_NOKERNINFO))
+		    SA_NOKERNINFO)) {
+			mutex_exit(pick->p_lock);
 			return;
+		}
 		msg = NULL;
 	}
 
@@ -2589,7 +2597,7 @@ ttygetinfo(struct tty *tp, int fromsig, 
 	    pick->p_pid);
 	strlcat(buf, lmsg, bufsz);
 
-	mutex_enter(pick->p_lock);
+	KASSERT(mutex_owned(pick->p_lock));
 	LIST_FOREACH(l, &pick->p_lwps, l_sibling) {
 		const char *lp;
 		lwp_lock(l);
@@ -2679,11 +2687,8 @@ proc_compare_wrapper(struct proc *p1, st
 	KASSERT(mutex_owned(p1->p_lock));
 	KASSERT(mutex_owned(p2->p_lock));
 
-	if ((l1 = LIST_FIRST(&p1->p_lwps)) == NULL)
-		return 1;
-
-	if ((l2 = LIST_FIRST(&p2->p_lwps)) == NULL)
-		return 0;
+	l1 = LIST_FIRST(&p1->p_lwps);
+	l2 = LIST_FIRST(&p2->p_lwps);
 
 	return proc_compare(p1, l1, p2, l2);
 }
Index: common/lib/libutil/proc_compare.c
===================================================================
RCS file: /cvsroot/src/common/lib/libutil/proc_compare.c,v
retrieving revision 1.1
diff -u -p -r1.1 proc_compare.c
--- common/lib/libutil/proc_compare.c	21 Oct 2011 02:09:00 -0000	1.1
+++ common/lib/libutil/proc_compare.c	2 Jan 2020 16:55:14 -0000
@@ -89,6 +89,17 @@ int
 proc_compare(const PROC *p1, const LWP *l1, const PROC *p2, const LWP *l2)
 {
 	/*
+ 	 * weed out zombies
+	 */
+	switch (TESTAB(P_ZOMBIE(p1), P_ZOMBIE(p2))) {
+	case ONLYA:
+		return 1;
+	case ONLYB:
+		return 0;
+	case BOTH:
+		goto out;
+	}
+	/*
 	 * see if at least one of them is runnable
 	 */
 	switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
@@ -105,17 +116,6 @@ proc_compare(const PROC *p1, const LWP *
 		goto out;
 	}
 	/*
- 	 * weed out zombies
-	 */
-	switch (TESTAB(P_ZOMBIE(p1), P_ZOMBIE(p2))) {
-	case ONLYA:
-		return 1;
-	case ONLYB:
-		return 0;
-	case BOTH:
-		goto out;
-	}
-	/*
 	 * pick the one with the smallest sleep time
 	 */
 	if (l1->l_slptime < l2->l_slptime)