On 5/15/23 19:40, David Ahern wrote:
On 5/15/23 12:14 PM, Eric Dumazet wrote:
On Mon, May 15, 2023 at 7:29 PM David Ahern <dsahern@xxxxxxxxxx> wrote:
On 5/15/23 10:06 AM, Pavel Begunkov wrote:
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 40f591f7fce1..3d18e295bb2f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1231,7 +1231,6 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
if ((flags & MSG_ZEROCOPY) && 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)) {
skb = tcp_write_queue_tail(sk);
@@ -1458,7 +1457,9 @@ 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);
+ /* msg->msg_ubuf is pinned by the caller so we don't take extra refs */
+ if (uarg && !msg->msg_ubuf)
+ net_zcopy_put(uarg);
return copied + copied_syn;
do_error:
@@ -1467,7 +1468,9 @@ 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);
+ /* msg->msg_ubuf is pinned by the caller so we don't take extra refs */
+ 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)) {
Both net_zcopy_put_abort and net_zcopy_put have an `if (uarg)` check.
Right, but here this might avoid a read of msg->msg_ubuf, which might
be more expensive to fetch.
agreed.
I put it there to avoid one extra check in the non-zerocopy path.
msg->msg_ubuf is null there, the conditional will pass and it'll
still have to test uarg.
Compiler will probably remove the second test (uarg) from net_zcopy_put()
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Thank you for reviews!
The one in net_zcopy_put can be removed with the above change. It's
other caller is net_zcopy_put_abort which has already checked uarg is set.
Ah yes, do you want me to fold it in?
--
Pavel Begunkov
