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Date: Fri, 16 Jun 2017 15:58:55 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Lawrence Brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>
CC: Kernel Team <kernel-team@...com>, Blake Matheny <bmatheny@...com>,
Alexei Starovoitov <ast@...com>,
David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [RFC PATCH net-next v2 10/15] bpf: Add support for changing congestion
control
On 06/15/2017 10:08 PM, Lawrence Brakmo wrote:
> Added support for changing congestion control for SOCKET_OPS bps
> programs through the setsockopt bpf helper function. It also adds
> a new SOCKET_OPS op, BPF_SOCKET_OPS_NEEDS_ECN, that is needed for
> congestion controls, like dctcp, that need to enable ECN in the
> SYN packets.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
I like the use-case! ;)
> ---
> include/net/tcp.h | 9 ++++++++-
> include/uapi/linux/bpf.h | 3 +++
> net/core/filter.c | 11 +++++++++--
> net/ipv4/tcp.c | 2 +-
> net/ipv4/tcp_cong.c | 15 ++++++++++-----
> net/ipv4/tcp_input.c | 3 ++-
> net/ipv4/tcp_output.c | 8 +++++---
> 7 files changed, 38 insertions(+), 13 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 29c27dc..371b1bd 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1001,7 +1001,9 @@ void tcp_get_default_congestion_control(char *name);
> void tcp_get_available_congestion_control(char *buf, size_t len);
> void tcp_get_allowed_congestion_control(char *buf, size_t len);
> int tcp_set_allowed_congestion_control(char *allowed);
> -int tcp_set_congestion_control(struct sock *sk, const char *name);
> +int tcp_set_congestion_control(struct sock *sk, const char *name, bool load);
> +void tcp_reinit_congestion_control(struct sock *sk,
> + const struct tcp_congestion_ops *ca);
> u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
> void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
>
> @@ -2039,4 +2041,9 @@ static inline u32 tcp_rwnd_init_bpf(struct sock *sk, bool is_req_sock)
> rwnd = 0;
> return rwnd;
> }
> +
> +static inline bool tcp_bpf_ca_needs_ecn(struct sock *sk)
> +{
> + return (tcp_call_bpf(sk, true, BPF_SOCKET_OPS_NEEDS_ECN) == 1);
> +}
> #endif /* _TCP_H */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c3490d3..8d1d2b7 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -776,6 +776,9 @@ enum {
> * passive connection is
> * established
> */
> + BPF_SOCKET_OPS_NEEDS_ECN, /* If connection's congestion control
> + * needs ECN
> + */
> };
>
> #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 9ff567c..4325aba 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2716,8 +2716,15 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_socket_ops_kern *, bpf_socket,
> }
> } else if (level == SOL_TCP &&
> bpf_socket->sk->sk_prot->setsockopt == tcp_setsockopt) {
> - /* Place holder */
> - ret = -EINVAL;
> + if (optname == TCP_CONGESTION) {
> + ret = tcp_set_congestion_control(sk, optval, false);
> + if (!ret && bpf_socket->op > BPF_SOCKET_OPS_NEEDS_ECN)
> + /* replacing an existing ca */
> + tcp_reinit_congestion_control(sk,
> + inet_csk(sk)->icsk_ca_ops);
Can you elaborate on the sematics of BPF_SOCKET_OPS_NEEDS_ECN?
It's called from tcp_bpf_ca_needs_ecn(), so if someone sets a cong ctl
from that callback, or any other bpf_socket->op > BPF_SOCKET_OPS_NEEDS_ECN
then we call tcp_reinit_congestion_control()? Why 'bpf_socket->op > ..'?
Could the needs_ecn implementation detail be hidden altogether from the
BPF prog?
> + } else {
> + ret = -EINVAL;
> + }
> } else {
> ret = -EINVAL;
> }
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index cc8fd8b..07984ea 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2478,7 +2478,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
> name[val] = 0;
>
> lock_sock(sk);
> - err = tcp_set_congestion_control(sk, name);
> + err = tcp_set_congestion_control(sk, name, true);
> release_sock(sk);
> return err;
> }
> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> index 324c9bc..e6f3717 100644
> --- a/net/ipv4/tcp_cong.c
> +++ b/net/ipv4/tcp_cong.c
> @@ -189,8 +189,8 @@ void tcp_init_congestion_control(struct sock *sk)
> INET_ECN_dontxmit(sk);
> }
>
> -static void tcp_reinit_congestion_control(struct sock *sk,
> - const struct tcp_congestion_ops *ca)
> +void tcp_reinit_congestion_control(struct sock *sk,
> + const struct tcp_congestion_ops *ca)
> {
> struct inet_connection_sock *icsk = inet_csk(sk);
>
> @@ -334,7 +334,7 @@ int tcp_set_allowed_congestion_control(char *val)
> }
>
> /* Change congestion control for socket */
> -int tcp_set_congestion_control(struct sock *sk, const char *name)
> +int tcp_set_congestion_control(struct sock *sk, const char *name, bool load)
> {
> struct inet_connection_sock *icsk = inet_csk(sk);
> const struct tcp_congestion_ops *ca;
> @@ -344,7 +344,10 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
> return -EPERM;
>
> rcu_read_lock();
> - ca = __tcp_ca_find_autoload(name);
> + if (!load)
> + ca = tcp_ca_find(name);
> + else
> + ca = __tcp_ca_find_autoload(name);
From BPF program side, we call with !load since we're not allowed
to sleep under RCU, that's correct ...
> /* No change asking for existing value */
> if (ca == icsk->icsk_ca_ops) {
> icsk->icsk_ca_setsockopt = 1;
> @@ -352,8 +355,10 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
> }
> if (!ca)
> err = -ENOENT;
> + else if (!load)
> + icsk->icsk_ca_ops = ca;
... but don't we also need to hold a module ref in this case as done
below?
Meaning, tcp_ca_find() could return a ca that was previously loaded
to the tcp_cong_list as module, then resulting in ref count imbalance
when set from BPF?
> else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
> - ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
> + ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
Nit: slipped in?
> err = -EPERM;
> else if (!try_module_get(ca->owner))
> err = -EBUSY;
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index e0d688a..14c889f 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -6192,7 +6192,8 @@ static void tcp_ecn_create_request(struct request_sock *req,
> ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
>
> if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
> - (ecn_ok_dst & DST_FEATURE_ECN_CA))
> + (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
> + tcp_bpf_ca_needs_ecn((struct sock *)req))
> inet_rsk(req)->ecn_ok = 1;
> }
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 9124d3d..30660ee 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -316,7 +316,8 @@ static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
> TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
> if (!(tp->ecn_flags & TCP_ECN_OK))
> TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
> - else if (tcp_ca_needs_ecn(sk))
> + else if (tcp_ca_needs_ecn(sk) ||
> + tcp_bpf_ca_needs_ecn(sk))
> INET_ECN_xmit(sk);
> }
>
> @@ -324,8 +325,9 @@ static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
> static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
> {
> struct tcp_sock *tp = tcp_sk(sk);
> + bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk);
> bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
> - tcp_ca_needs_ecn(sk);
> + tcp_ca_needs_ecn(sk) || bpf_needs_ecn;
>
> if (!use_ecn) {
> const struct dst_entry *dst = __sk_dst_get(sk);
> @@ -339,7 +341,7 @@ static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
> if (use_ecn) {
> TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
> tp->ecn_flags = TCP_ECN_OK;
> - if (tcp_ca_needs_ecn(sk))
> + if (tcp_ca_needs_ecn(sk) || bpf_needs_ecn)
> INET_ECN_xmit(sk);
> }
> }
>
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