From bad2520a2b8d970d8623c199d0d57e667ca40069 Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sun, 5 Oct 2014 07:21:41 +0000
Subject: [PATCH] Avoid unnecessary ppeers_lock acquisition in exit1.

MFC after:	1 week
---
 sys/kern/kern_exit.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 1dbb9974bdb..1e4c0956474 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -265,8 +265,8 @@ exit1(struct thread *td, int rv)
 	AUDIT_SYSCALL_EXIT(0, td);
 #endif
 
-	/* Are we a task leader? */
-	if (p == p->p_leader) {
+	/* Are we a task leader with peers? */
+	if (p->p_peers != NULL && p == p->p_leader) {
 		mtx_lock(&ppeers_lock);
 		q = p->p_peers;
 		while (q != NULL) {
@@ -337,15 +337,17 @@ exit1(struct thread *td, int rv)
 	/*
 	 * Remove ourself from our leader's peer list and wake our leader.
 	 */
-	mtx_lock(&ppeers_lock);
-	if (p->p_leader->p_peers) {
-		q = p->p_leader;
-		while (q->p_peers != p)
-			q = q->p_peers;
-		q->p_peers = p->p_peers;
-		wakeup(p->p_leader);
+	if (p->p_leader->p_peers != NULL) {
+		mtx_lock(&ppeers_lock);
+		if (p->p_leader->p_peers != NULL) {
+			q = p->p_leader;
+			while (q->p_peers != p)
+				q = q->p_peers;
+			q->p_peers = p->p_peers;
+			wakeup(p->p_leader);
+		}
+		mtx_unlock(&ppeers_lock);
 	}
-	mtx_unlock(&ppeers_lock);
 
 	vmspace_exit(td);