From b7b7769e947a139f7ab610561b4d427bc2b9e035 Mon Sep 17 00:00:00 2001
From: markj <markj@FreeBSD.org>
Date: Mon, 3 Feb 2020 22:49:05 +0000
Subject: [PATCH] Fix the !SMP case in sched_add() after r355779.

If the thread's lock is already that of the runqueue, don't recurse on
the queue lock.

Reviewed by:	jeff, kib
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D23492
---
 sys/kern/sched_ule.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index e2adf98ec6fd..62e19678c8f7 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -2605,15 +2605,17 @@ sched_add(struct thread *td, int flags)
 		sched_setpreempt(td);
 #else
 	tdq = TDQ_SELF();
-	TDQ_LOCK(tdq);
 	/*
 	 * Now that the thread is moving to the run-queue, set the lock
 	 * to the scheduler's lock.
 	 */
-	if ((flags & SRQ_HOLD) != 0)
-		td->td_lock = TDQ_LOCKPTR(tdq);
-	else
-		thread_lock_set(td, TDQ_LOCKPTR(tdq));
+	if (td->td_lock != TDQ_LOCKPTR(tdq)) {
+		TDQ_LOCK(tdq);
+		if ((flags & SRQ_HOLD) != 0)
+			td->td_lock = TDQ_LOCKPTR(tdq);
+		else
+			thread_lock_set(td, TDQ_LOCKPTR(tdq));
+	}
 	tdq_add(tdq, td, flags);
 	if (!(flags & SRQ_YIELDING))
 		sched_setpreempt(td);