This is a note to let you know that I've just added the patch titled
tcp: remove poll() flakes with FastOpen
to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: tcp-remove-poll-flakes-with-fastopen.patch and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Mar 22 14:57:32 CET 2018
From: Eric Dumazet edumazet@google.com Date: Tue, 18 Apr 2017 09:45:52 -0700 Subject: tcp: remove poll() flakes with FastOpen
From: Eric Dumazet edumazet@google.com
[ 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: Eric Dumazet edumazet@google.com Acked-by: Yuchung Cheng ycheng@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/tcp_input.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)
--- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5464,10 +5464,6 @@ void tcp_finish_connect(struct sock *sk, 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, @@ -5531,6 +5527,7 @@ static int tcp_rcv_synsent_state_process 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) @@ -5633,10 +5630,15 @@ static int tcp_rcv_synsent_state_process
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) {
Patches currently in stable-queue which might be from edumazet@google.com are
queue-4.4/tcp-remove-poll-flakes-with-fastopen.patch