From 382172be686cf55d308e38daef0bb219fb9abe10 Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Wed, 10 Aug 2016 15:24:15 +0000
Subject: [PATCH] sigio: do a lockless check in funsetownlist

There is no need to grab the lock first to see if sigio is used, and it
typically is not.
---
 sys/kern/kern_descrip.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 1005830df41..f3959acfbd5 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -942,6 +942,8 @@ funsetown(struct sigio **sigiop)
 {
 	struct sigio *sigio;
 
+	if (*sigiop == NULL)
+		return;
 	SIGIO_LOCK();
 	sigio = *sigiop;
 	if (sigio == NULL) {