--- sys/kern/kern_proc.c.orig
+++ sys/kern/kern_proc.c
@@ -587,8 +587,12 @@
 	    ("enterpgrp: session leader attempted setpgrp"));
 
 	old_pgrp = p->p_pgrp;
-	if (!sx_try_xlock(&old_pgrp->pg_killsx))
+	if (!sx_try_xlock(&old_pgrp->pg_killsx)) {
+		sx_xunlock(&proctree_lock);
+		sx_xlock(&old_pgrp->pg_killsx);
+		sx_xunlock(&old_pgrp->pg_killsx);
 		return (ERESTART);
+	}
 	MPASS(old_pgrp == p->p_pgrp);
 
 	if (sess != NULL) {
@@ -656,11 +660,18 @@
 	    ("%s: p %p belongs to pgrp %p", __func__, p, pgrp));
 
 	old_pgrp = p->p_pgrp;
-	if (!sx_try_xlock(&old_pgrp->pg_killsx))
+	if (!sx_try_xlock(&old_pgrp->pg_killsx)) {
+		sx_xunlock(&proctree_lock);
+		sx_xlock(&old_pgrp->pg_killsx);
+		sx_xunlock(&old_pgrp->pg_killsx);
 		return (ERESTART);
+	}
 	MPASS(old_pgrp == p->p_pgrp);
 	if (!sx_try_xlock(&pgrp->pg_killsx)) {
 		sx_xunlock(&old_pgrp->pg_killsx);
+		sx_xunlock(&proctree_lock);
+		sx_xlock(&pgrp->pg_killsx);
+		sx_xunlock(&pgrp->pg_killsx);
 		return (ERESTART);
 	}
 
--- sys/kern/kern_prot.c.orig
+++ sys/kern/kern_prot.c
@@ -345,10 +345,8 @@
 		error = EPERM;
 	} else {
 		error = enterpgrp(p, p->p_pid, newpgrp, newsess);
-		if (error == ERESTART) {
-			sx_xunlock(&proctree_lock);
+		if (error == ERESTART)
 			goto again;
-		}
 		MPASS(error == 0);
 		td->td_retval[0] = p->p_pid;
 		newpgrp = NULL;
@@ -458,11 +456,11 @@
 		error = enterthispgrp(targp, pgrp);
 	}
 done:
-	sx_xunlock(&proctree_lock);
 	KASSERT(error == 0 || newpgrp != NULL,
 	    ("setpgid failed and newpgrp is NULL"));
 	if (error == ERESTART)
 		goto again;
+	sx_xunlock(&proctree_lock);
 	uma_zfree(pgrp_zone, newpgrp);
 	return (error);
 }