[AF_UNIX]: Remove superfluous reference counting in unix_stream_sendmsg
AF_UNIX stream socket performance on P4 CPUs tends to suffer due to a
lot of pipeline flushes from atomic operations. The patch below
removes the sock_hold() and sock_put() in unix_stream_sendmsg(). This
should be safe as the socket still holds a reference to its peer which
is only released after the file descriptor's final user invokes
unix_release_sock(). The only consideration is that we must add a
memory barrier before setting the peer initially.
Signed-off-by: Benjamin LaHaise <benjamin.c.lahaise@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index acc73ba..1dc3685 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1063,10 +1063,12 @@
/* Set credentials */
sk->sk_peercred = other->sk_peercred;
- sock_hold(newsk);
- unix_peer(sk) = newsk;
sock->state = SS_CONNECTED;
sk->sk_state = TCP_ESTABLISHED;
+ sock_hold(newsk);
+
+ smp_mb__after_atomic_inc(); /* sock_hold() does an atomic_inc() */
+ unix_peer(sk) = newsk;
unix_state_wunlock(sk);
@@ -1414,7 +1416,7 @@
} else {
sunaddr = NULL;
err = -ENOTCONN;
- other = unix_peer_get(sk);
+ other = unix_peer(sk);
if (!other)
goto out_err;
}
@@ -1476,7 +1478,6 @@
other->sk_data_ready(other, size);
sent+=size;
}
- sock_put(other);
scm_destroy(siocb->scm);
siocb->scm = NULL;
@@ -1491,8 +1492,6 @@
send_sig(SIGPIPE,current,0);
err = -EPIPE;
out_err:
- if (other)
- sock_put(other);
scm_destroy(siocb->scm);
siocb->scm = NULL;
return sent ? : err;