linux-kernel - [RFC net-next v3 12/29] tcp: kill extra io

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Date:   Tue, 28 Jun 2022 19:56:34 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     io-uring@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jens Axboe <axboe@...nel.dk>, kernel-team@...com,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC net-next v3 12/29] tcp: kill extra io_uring's uarg refcounting

io_uring guarantees that passed in uarg stays alive until we return from
sendmsg, so no need to temporarily refcount-pin it in
tcp_sendmsg_locked().

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 net/ipv4/tcp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 832c1afcdbe7..3482c934eec8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1207,7 +1207,6 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 		if (msg->msg_ubuf) {
 			uarg = msg->msg_ubuf;
-			net_zcopy_get(uarg);
 			zc = sk->sk_route_caps & NETIF_F_SG;
 		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
 			uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
@@ -1437,7 +1436,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 		tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
 	}
 out_nopush:
-	net_zcopy_put(uarg);
+	if (uarg && !msg->msg_ubuf)
+		net_zcopy_put(uarg);
 	return copied + copied_syn;
 
 do_error:
@@ -1446,7 +1446,8 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 	if (copied + copied_syn)
 		goto out;
 out_err:
-	net_zcopy_put_abort(uarg, true);
+	if (uarg && !msg->msg_ubuf)
+		net_zcopy_put_abort(uarg, true);
 	err = sk_stream_error(sk, flags, err);
 	/* make sure we wake any epoll edge trigger waiter */
 	if (unlikely(tcp_rtx_and_write_queues_empty(sk) && err == -EAGAIN)) {
-- 
2.36.1