[Patch bpf-next v2 3/9] udp: implement ->sendmsg_locked()

[Cong Wang <xiyou.wangcong@xxxxxxxxx>]

From: Cong Wang <cong.wang@xxxxxxxxxxxxx>

UDP already has udp_sendmsg() which takes lock_sock() inside.
We have to build ->sendmsg_locked() on top of it, by adding
a new parameter for whether the sock has been locked.

Cc: John Fastabend <john.fastabend@xxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Cc: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
Cc: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
---
 include/net/udp.h  |  1 +
 net/ipv4/af_inet.c |  1 +
 net/ipv4/udp.c     | 30 +++++++++++++++++++++++-------
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index df7cc1edc200..5264ba1439f9 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -292,6 +292,7 @@ int udp_get_port(struct sock *sk, unsigned short snum,
 int udp_err(struct sk_buff *, u32);
 int udp_abort(struct sock *sk, int err);
 int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len);
+int udp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t len);
 int udp_push_pending_frames(struct sock *sk);
 void udp_flush_pending_frames(struct sock *sk);
 int udp_cmsg_send(struct sock *sk, struct msghdr *msg, u16 *gso_size);
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index a02ce89b56b5..d8c73a848c53 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1071,6 +1071,7 @@ const struct proto_ops inet_dgram_ops = {
 	.setsockopt	   = sock_common_setsockopt,
 	.getsockopt	   = sock_common_getsockopt,
 	.sendmsg	   = inet_sendmsg,
+	.sendmsg_locked    = udp_sendmsg_locked,
 	.recvmsg	   = inet_recvmsg,
 	.mmap		   = sock_no_mmap,
 	.sendpage	   = inet_sendpage,
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index dbd25b59ce0e..93db853601d7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1024,7 +1024,7 @@ int udp_cmsg_send(struct sock *sk, struct msghdr *msg, u16 *gso_size)
 }
 EXPORT_SYMBOL_GPL(udp_cmsg_send);
 
-int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
+static int __udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len, bool locked)
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct udp_sock *up = udp_sk(sk);
@@ -1063,15 +1063,18 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		 * There are pending frames.
 		 * The socket lock must be held while it's corked.
 		 */
-		lock_sock(sk);
+		if (!locked)
+			lock_sock(sk);
 		if (likely(up->pending)) {
 			if (unlikely(up->pending != AF_INET)) {
-				release_sock(sk);
+				if (!locked)
+					release_sock(sk);
 				return -EINVAL;
 			}
 			goto do_append_data;
 		}
-		release_sock(sk);
+		if (!locked)
+			release_sock(sk);
 	}
 	ulen += sizeof(struct udphdr);
 
@@ -1241,11 +1244,13 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		goto out;
 	}
 
-	lock_sock(sk);
+	if (!locked)
+		lock_sock(sk);
 	if (unlikely(up->pending)) {
 		/* The socket is already corked while preparing it. */
 		/* ... which is an evident application bug. --ANK */
-		release_sock(sk);
+		if (!locked)
+			release_sock(sk);
 
 		net_dbg_ratelimited("socket already corked\n");
 		err = -EINVAL;
@@ -1272,7 +1277,8 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		err = udp_push_pending_frames(sk);
 	else if (unlikely(skb_queue_empty(&sk->sk_write_queue)))
 		up->pending = 0;
-	release_sock(sk);
+	if (!locked)
+		release_sock(sk);
 
 out:
 	ip_rt_put(rt);
@@ -1302,8 +1308,18 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	err = 0;
 	goto out;
 }
+
+int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
+{
+	return __udp_sendmsg(sk, msg, len, false);
+}
 EXPORT_SYMBOL(udp_sendmsg);
 
+int udp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t len)
+{
+	return __udp_sendmsg(sk, msg, len, true);
+}
+
 int udp_sendpage(struct sock *sk, struct page *page, int offset,
 		 size_t size, int flags)
 {
-- 
2.25.1