From e372699677c4a92077e82b46c28e146d4bfeb087 Mon Sep 17 00:00:00 2001
From: mjg <mjg@FreeBSD.org>
Date: Sat, 31 Dec 2016 12:49:20 +0000
Subject: MFC r303921:

    ktrace: do a lockless check on fork to see if tracing is enabled

    This saves 2 lock acquisitions in the common case.
---
 sys/kern/kern_ktrace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c
index 0e30fc9..676cd43 100644
--- a/sys/kern/kern_ktrace.c
+++ b/sys/kern/kern_ktrace.c
@@ -572,9 +572,14 @@ void
 ktrprocfork(struct proc *p1, struct proc *p2)
 {
 
+	MPASS(p2->p_tracevp == NULL);
+	MPASS(p2->p_traceflag == 0);
+
+	if (p1->p_traceflag == 0)
+		return;
+
 	PROC_LOCK(p1);
 	mtx_lock(&ktrace_mtx);
-	KASSERT(p2->p_tracevp == NULL, ("new process has a ktrace vnode"));
 	if (p1->p_traceflag & KTRFAC_INHERIT) {
 		p2->p_traceflag = p1->p_traceflag;
 		if ((p2->p_tracevp = p1->p_tracevp) != NULL) {
-- 
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