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Message-ID: <CAL+tcoBhdqVs0ZMzifriVf+3gpLeA72HByB5TW4vJyUn+KntMA@mail.gmail.com>
Date: Fri, 5 Apr 2024 22:29:01 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] tcp: annotate data-races around tp->window_clamp
On Thu, Apr 4, 2024 at 7:53 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> tp->window_clamp can be read locklessly, add READ_ONCE()
> and WRITE_ONCE() annotations.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
> net/ipv4/syncookies.c | 3 ++-
> net/ipv4/tcp.c | 8 ++++----
> net/ipv4/tcp_input.c | 17 ++++++++++-------
> net/ipv4/tcp_output.c | 18 ++++++++++--------
> net/ipv6/syncookies.c | 2 +-
> net/mptcp/protocol.c | 2 +-
> net/mptcp/sockopt.c | 2 +-
> 7 files changed, 29 insertions(+), 23 deletions(-)
>
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 500f665f98cbce4a3d681f8e39ecd368fe4013b1..b61d36810fe3fd62b1e5c5885bbaf20185f1abf0 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -462,7 +462,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
> }
>
> /* Try to redo what tcp_v4_send_synack did. */
> - req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
> + req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :
> + dst_metric(&rt->dst, RTAX_WINDOW);
> /* limit the window selection if the user enforce a smaller rx buffer */
> full_space = tcp_full_space(sk);
> if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index e767721b3a588b5d56567ae7badf5dffcd35a76a..92ee60492314a1483cfbfa2f73d32fcad5632773 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1721,7 +1721,7 @@ int tcp_set_rcvlowat(struct sock *sk, int val)
> space = tcp_space_from_win(sk, val);
> if (space > sk->sk_rcvbuf) {
> WRITE_ONCE(sk->sk_rcvbuf, space);
> - tcp_sk(sk)->window_clamp = val;
> + WRITE_ONCE(tcp_sk(sk)->window_clamp, val);
> }
> return 0;
> }
> @@ -3379,7 +3379,7 @@ int tcp_set_window_clamp(struct sock *sk, int val)
> if (!val) {
> if (sk->sk_state != TCP_CLOSE)
> return -EINVAL;
> - tp->window_clamp = 0;
> + WRITE_ONCE(tp->window_clamp, 0);
> } else {
> u32 new_rcv_ssthresh, old_window_clamp = tp->window_clamp;
> u32 new_window_clamp = val < SOCK_MIN_RCVBUF / 2 ?
> @@ -3388,7 +3388,7 @@ int tcp_set_window_clamp(struct sock *sk, int val)
> if (new_window_clamp == old_window_clamp)
> return 0;
>
> - tp->window_clamp = new_window_clamp;
> + WRITE_ONCE(tp->window_clamp, new_window_clamp);
> if (new_window_clamp < old_window_clamp) {
> /* need to apply the reserved mem provisioning only
> * when shrinking the window clamp
> @@ -4057,7 +4057,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
> TCP_RTO_MAX / HZ);
> break;
> case TCP_WINDOW_CLAMP:
> - val = tp->window_clamp;
> + val = READ_ONCE(tp->window_clamp);
> break;
> case TCP_INFO: {
> struct tcp_info info;
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 1b6cd384001202df5f8e8e8c73adff0db89ece63..8d44ab5671eacd4bc06647c7cca387a79e346618 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -563,19 +563,20 @@ static void tcp_init_buffer_space(struct sock *sk)
> maxwin = tcp_full_space(sk);
>
> if (tp->window_clamp >= maxwin) {
I wonder if it is necessary to locklessly protect the above line with
READ_ONCE() because I saw the full reader protection in the
tcp_select_initial_window()? There are some other places like this.
Any special reason?
Thanks,
Jason
> - tp->window_clamp = maxwin;
> + WRITE_ONCE(tp->window_clamp, maxwin);
>
> if (tcp_app_win && maxwin > 4 * tp->advmss)
> - tp->window_clamp = max(maxwin -
> - (maxwin >> tcp_app_win),
> - 4 * tp->advmss);
> + WRITE_ONCE(tp->window_clamp,
> + max(maxwin - (maxwin >> tcp_app_win),
> + 4 * tp->advmss));
> }
>
> /* Force reservation of one segment. */
> if (tcp_app_win &&
> tp->window_clamp > 2 * tp->advmss &&
> tp->window_clamp + tp->advmss > maxwin)
> - tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
> + WRITE_ONCE(tp->window_clamp,
> + max(2 * tp->advmss, maxwin - tp->advmss));
>
> tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
> tp->snd_cwnd_stamp = tcp_jiffies32;
> @@ -773,7 +774,8 @@ void tcp_rcv_space_adjust(struct sock *sk)
> WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
>
> /* Make the window clamp follow along. */
> - tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
> + WRITE_ONCE(tp->window_clamp,
> + tcp_win_from_space(sk, rcvbuf));
> }
> }
> tp->rcvq_space.space = copied;
> @@ -6426,7 +6428,8 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
>
> if (!tp->rx_opt.wscale_ok) {
> tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
> - tp->window_clamp = min(tp->window_clamp, 65535U);
> + WRITE_ONCE(tp->window_clamp,
> + min(tp->window_clamp, 65535U));
> }
>
> if (tp->rx_opt.saw_tstamp) {
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index e3167ad965676facaacd8f82848c52cf966f97c3..9282fafc0e6109f3ac86d1641740f24588b2d75d 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -203,16 +203,17 @@ static inline void tcp_event_ack_sent(struct sock *sk, u32 rcv_nxt)
> * This MUST be enforced by all callers.
> */
> void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
> - __u32 *rcv_wnd, __u32 *window_clamp,
> + __u32 *rcv_wnd, __u32 *__window_clamp,
> int wscale_ok, __u8 *rcv_wscale,
> __u32 init_rcv_wnd)
> {
> unsigned int space = (__space < 0 ? 0 : __space);
> + u32 window_clamp = READ_ONCE(*__window_clamp);
>
> /* If no clamp set the clamp to the max possible scaled window */
> - if (*window_clamp == 0)
> - (*window_clamp) = (U16_MAX << TCP_MAX_WSCALE);
> - space = min(*window_clamp, space);
> + if (window_clamp == 0)
> + window_clamp = (U16_MAX << TCP_MAX_WSCALE);
> + space = min(window_clamp, space);
>
> /* Quantize space offering to a multiple of mss if possible. */
> if (space > mss)
> @@ -239,12 +240,13 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
> /* Set window scaling on max possible window */
> space = max_t(u32, space, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
> space = max_t(u32, space, READ_ONCE(sysctl_rmem_max));
> - space = min_t(u32, space, *window_clamp);
> + space = min_t(u32, space, window_clamp);
> *rcv_wscale = clamp_t(int, ilog2(space) - 15,
> 0, TCP_MAX_WSCALE);
> }
> /* Set the clamp no higher than max representable value */
> - (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp);
> + WRITE_ONCE(*__window_clamp,
> + min_t(__u32, U16_MAX << (*rcv_wscale), window_clamp));
> }
> EXPORT_SYMBOL(tcp_select_initial_window);
>
> @@ -3855,7 +3857,7 @@ static void tcp_connect_init(struct sock *sk)
> tcp_ca_dst_init(sk, dst);
>
> if (!tp->window_clamp)
> - tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
> + WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW));
> tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
>
> tcp_initialize_rcv_mss(sk);
> @@ -3863,7 +3865,7 @@ static void tcp_connect_init(struct sock *sk)
> /* limit the window selection if the user enforce a smaller rx buffer */
> if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
> (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
> - tp->window_clamp = tcp_full_space(sk);
> + WRITE_ONCE(tp->window_clamp, tcp_full_space(sk));
>
> rcv_wnd = tcp_rwnd_init_bpf(sk);
> if (rcv_wnd == 0)
> diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
> index 6d8286c299c9d139938ef6751d9958c80d3031e9..bfad1e89b6a6bb99c28b9ef14c142a6c4aeae54b 100644
> --- a/net/ipv6/syncookies.c
> +++ b/net/ipv6/syncookies.c
> @@ -246,7 +246,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
> }
> }
>
> - req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
> + req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? :dst_metric(dst, RTAX_WINDOW);
> /* limit the window selection if the user enforce a smaller rx buffer */
> full_space = tcp_full_space(sk);
> if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 3a1967bc7bad63d5a8a628b3f3b868e3a27baaca..3897a03bb8cb88f7869180b5ec261158e8e5d027 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -2056,7 +2056,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
> ssk = mptcp_subflow_tcp_sock(subflow);
> slow = lock_sock_fast(ssk);
> WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
> - tcp_sk(ssk)->window_clamp = window_clamp;
> + WRITE_ONCE(tcp_sk(ssk)->window_clamp, window_clamp);
> tcp_cleanup_rbuf(ssk, 1);
> unlock_sock_fast(ssk, slow);
> }
> diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
> index dcd1c76d2a3ba1ccc31a3e9279f725cd6d433782..b702e994633788183ad95b2e12859ee6b60bf208 100644
> --- a/net/mptcp/sockopt.c
> +++ b/net/mptcp/sockopt.c
> @@ -1519,7 +1519,7 @@ int mptcp_set_rcvlowat(struct sock *sk, int val)
>
> slow = lock_sock_fast(ssk);
> WRITE_ONCE(ssk->sk_rcvbuf, space);
> - tcp_sk(ssk)->window_clamp = val;
> + WRITE_ONCE(tcp_sk(ssk)->window_clamp, val);
> unlock_sock_fast(ssk, slow);
> }
> return 0;
> --
> 2.44.0.478.gd926399ef9-goog
>
>
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