[PATCH net] net: avoid an indirect call in ____sys_recvmsg()

From: Eric Dumazet <edumazet@google.com>
To: "David S . Miller" <davem@davemloft.net>
Cc: netdev <netdev@vger.kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Paolo Abeni <pabeni@redhat.com>,
	David Laight <David.Laight@aculab.com>
Subject: [PATCH net] net: avoid an indirect call in ____sys_recvmsg()
Date: Fri,  6 Dec 2019 09:38:36 -0800	[thread overview]
Message-ID: <20191206173836.34294-1-edumazet@google.com> (raw)

CONFIG_RETPOLINE=y made indirect calls expensive.

gcc seems to add an indirect call in ____sys_recvmsg().

Rewriting the code slightly makes sure to avoid this indirection.

Alternative would be to not call sock_recvmsg() and instead
use security_socket_recvmsg() and sock_recvmsg_nosec(),
but this is less readable IMO.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: David Laight <David.Laight@aculab.com>
---
 net/socket.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/socket.c b/net/socket.c
index ea28cbb9e2e7a7180ee63de2d09a81aacb001ab7..5af84d71cbc2f731def460b70aa7f68533a90b16 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2559,7 +2559,12 @@ static int ____sys_recvmsg(struct socket *sock, struct msghdr *msg_sys,
 
 	if (sock->file->f_flags & O_NONBLOCK)
 		flags |= MSG_DONTWAIT;
-	err = (nosec ? sock_recvmsg_nosec : sock_recvmsg)(sock, msg_sys, flags);
+
+	if (unlikely(nosec))
+		err = sock_recvmsg_nosec(sock, msg_sys, flags);
+	else
+		err = sock_recvmsg(sock, msg_sys, flags);
+
 	if (err < 0)
 		goto out;
 	len = err;
-- 
2.24.0.393.g34dc348eaf-goog

