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Commit 3a5294f0 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman
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tcp: remove poll() flakes with FastOpen 




[ Upstream commit 0f9fa831aecfc297b7b45d4f046759bcefcf87f0 ]

When using TCP FastOpen for an active session, we send one wakeup event
from tcp_finish_connect(), right before the data eventually contained in
the received SYNACK is queued to sk->sk_receive_queue.

This means that depending on machine load or luck, poll() users
might receive POLLOUT events instead of POLLIN|POLLOUT

To fix this, we need to move the call to sk->sk_state_change()
after the (optional) call to tcp_rcv_fastopen_synack()

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarSasha Levin <alexander.levin@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0a4063b0

net/ipv4/tcp_input.c

+9 −7
Original line number Diff line number Diff line
@@ -5322,10 +5322,6 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb) 
	else

		tp->pred_flags = 0;



	if (!sock_flag(sk, SOCK_DEAD)) {

		sk->sk_state_change(sk);

		sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);

	}

}



static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
@@ -5380,6 +5376,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 
	struct tcp_sock *tp = tcp_sk(sk);

	struct tcp_fastopen_cookie foc = { .len = -1 };

	int saved_clamp = tp->rx_opt.mss_clamp;

	bool fastopen_fail;



	tcp_parse_options(skb, &tp->rx_opt, 0, &foc);

	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
@@ -5482,10 +5479,15 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 


		tcp_finish_connect(sk, skb);



		if ((tp->syn_fastopen || tp->syn_data) &&

		    tcp_rcv_fastopen_synack(sk, skb, &foc))

			return -1;

		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&

				tcp_rcv_fastopen_synack(sk, skb, &foc);



		if (!sock_flag(sk, SOCK_DEAD)) {

			sk->sk_state_change(sk);

			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);

		}

		if (fastopen_fail)

			return -1;

		if (sk->sk_write_pending ||

		    icsk->icsk_accept_queue.rskq_defer_accept ||

		    icsk->icsk_ack.pingpong) {