MFC r261242:

Decrease lock contention within the TCP accept case by removing
the INP_INFO lock from tcp_usr_accept.  As the PR/patch states
this was following the advice already in the code.
See the PR below for a full discussion of this change and its
measured effects.

PR:		183659
Submitted by:	Julien Charbon
Reviewed by:	jhb

2 files changed, 3 insertions, 10 deletions

diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
index 0398b03..03e8c72 100644
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -683,7 +683,7 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
 	 * connection when the SYN arrived.  If we can't create
 	 * the connection, abort it.
 	 */
-	so = sonewconn(lso, SS_ISCONNECTED);
+	so = sonewconn(lso, 0);
 	if (so == NULL) {
 		/*
 		 * Drop the connection; we will either send a RST or
@@ -922,6 +922,8 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
 
 	INP_WUNLOCK(inp);
 
+	soisconnected(so);
+
 	TCPSTAT_INC(tcps_accepts);
 	return (so);
 
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index 1ccbf9a..8d7e9a0 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -643,13 +643,6 @@ out:
 /*
  * Accept a connection.  Essentially all the work is done at higher levels;
  * just return the address of the peer, storing through addr.
- *
- * The rationale for acquiring the tcbinfo lock here is somewhat complicated,
- * and is described in detail in the commit log entry for r175612.  Acquiring
- * it delays an accept(2) racing with sonewconn(), which inserts the socket
- * before the inpcb address/port fields are initialized.  A better fix would
- * prevent the socket from being placed in the listen queue until all fields
- * are fully initialized.
  */
 static int
 tcp_usr_accept(struct socket *so, struct sockaddr **nam)
@@ -666,7 +659,6 @@ tcp_usr_accept(struct socket *so, struct sockaddr **nam)
 
 	inp = sotoinpcb(so);
 	KASSERT(inp != NULL, ("tcp_usr_accept: inp == NULL"));
-	INP_INFO_RLOCK(&V_tcbinfo);
 	INP_WLOCK(inp);
 	if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 		error = ECONNABORTED;
@@ -686,7 +678,6 @@ tcp_usr_accept(struct socket *so, struct sockaddr **nam)
 out:
 	TCPDEBUG2(PRU_ACCEPT);
 	INP_WUNLOCK(inp);
-	INP_INFO_RUNLOCK(&V_tcbinfo);
 	if (error == 0)
 		*nam = in_sockaddr(port, &addr);
 	return error;