From bcd97734318d1d87bb237dbc0a60c81237b0ac50 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Fri, 19 Nov 2021 15:27:55 +0100 Subject: [PATCH] mptcp: use delegate action to schedule 3rd ack retrans Scheduling a delack in mptcp_established_options_mp() is not a good idea: such function is called by tcp_send_ack() and the pending delayed ack will be cleared shortly after by the tcp_event_ack_sent() call in __tcp_transmit_skb(). Instead use the mptcp delegated action infrastructure to schedule the delayed ack after the current bh processing completes. Additionally moves the schedule_3rdack_retransmission() helper into protocol.c to avoid making it visible in a different compilation unit. Fixes: ec3edaa7ca6ce02f ("mptcp: Add handling of outgoing MP_JOIN requests") Reviewed-by: Mat Martineau @linux.intel.com> Signed-off-by: Paolo Abeni Signed-off-by: David S. Miller --- net/mptcp/options.c | 33 ++++++++-------------------- net/mptcp/protocol.c | 51 ++++++++++++++++++++++++++++++++++++-------- net/mptcp/protocol.h | 17 ++++++++------- 3 files changed, 60 insertions(+), 41 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 2e9b73eeeeb5..fe98e4f475ba 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -422,29 +422,6 @@ bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb, return false; } -/* MP_JOIN client subflow must wait for 4th ack before sending any data: - * TCP can't schedule delack timer before the subflow is fully established. - * MPTCP uses the delack timer to do 3rd ack retransmissions - */ -static void schedule_3rdack_retransmission(struct sock *sk) -{ - struct inet_connection_sock *icsk = inet_csk(sk); - struct tcp_sock *tp = tcp_sk(sk); - unsigned long timeout; - - /* reschedule with a timeout above RTT, as we must look only for drop */ - if (tp->srtt_us) - timeout = usecs_to_jiffies(tp->srtt_us >> (3 - 1)); - else - timeout = TCP_TIMEOUT_INIT; - timeout += jiffies; - - WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER); - icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; - icsk->icsk_ack.timeout = timeout; - sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); -} - static void clear_3rdack_retransmission(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); @@ -527,7 +504,15 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb, *size = TCPOLEN_MPTCP_MPJ_ACK; pr_debug("subflow=%p", subflow); - schedule_3rdack_retransmission(sk); + /* we can use the full delegate action helper only from BH context + * If we are in process context - sk is flushing the backlog at + * socket lock release time - just set the appropriate flag, will + * be handled by the release callback + */ + if (sock_owned_by_user(sk)) + set_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status); + else + mptcp_subflow_delegate(subflow, MPTCP_DELEGATE_ACK); return true; } return false; diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index b7e32e316738..c82a76d2d0bf 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1596,7 +1596,8 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk) if (!xmit_ssk) goto out; if (xmit_ssk != ssk) { - mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk)); + mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk), + MPTCP_DELEGATE_SEND); goto out; } @@ -2943,7 +2944,7 @@ void __mptcp_check_push(struct sock *sk, struct sock *ssk) if (xmit_ssk == ssk) __mptcp_subflow_push_pending(sk, ssk); else if (xmit_ssk) - mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk)); + mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk), MPTCP_DELEGATE_SEND); } else { set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags); } @@ -2993,18 +2994,50 @@ static void mptcp_release_cb(struct sock *sk) __mptcp_update_rmem(sk); } +/* MP_JOIN client subflow must wait for 4th ack before sending any data: + * TCP can't schedule delack timer before the subflow is fully established. + * MPTCP uses the delack timer to do 3rd ack retransmissions + */ +static void schedule_3rdack_retransmission(struct sock *ssk) +{ + struct inet_connection_sock *icsk = inet_csk(ssk); + struct tcp_sock *tp = tcp_sk(ssk); + unsigned long timeout; + + if (mptcp_subflow_ctx(ssk)->fully_established) + return; + + /* reschedule with a timeout above RTT, as we must look only for drop */ + if (tp->srtt_us) + timeout = usecs_to_jiffies(tp->srtt_us >> (3 - 1)); + else + timeout = TCP_TIMEOUT_INIT; + timeout += jiffies; + + WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER); + icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; + icsk->icsk_ack.timeout = timeout; + sk_reset_timer(ssk, &icsk->icsk_delack_timer, timeout); +} + void mptcp_subflow_process_delegated(struct sock *ssk) { struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk); struct sock *sk = subflow->conn; - mptcp_data_lock(sk); - if (!sock_owned_by_user(sk)) - __mptcp_subflow_push_pending(sk, ssk); - else - set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags); - mptcp_data_unlock(sk); - mptcp_subflow_delegated_done(subflow); + if (test_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status)) { + mptcp_data_lock(sk); + if (!sock_owned_by_user(sk)) + __mptcp_subflow_push_pending(sk, ssk); + else + set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags); + mptcp_data_unlock(sk); + mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SEND); + } + if (test_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status)) { + schedule_3rdack_retransmission(ssk); + mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_ACK); + } } static int mptcp_hash(struct sock *sk) diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 67a61ac48b20..d87cc040352e 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -387,6 +387,7 @@ struct mptcp_delegated_action { DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions); #define MPTCP_DELEGATE_SEND 0 +#define MPTCP_DELEGATE_ACK 1 /* MPTCP subflow context */ struct mptcp_subflow_context { @@ -492,23 +493,23 @@ static inline void mptcp_add_pending_subflow(struct mptcp_sock *msk, void mptcp_subflow_process_delegated(struct sock *ssk); -static inline void mptcp_subflow_delegate(struct mptcp_subflow_context *subflow) +static inline void mptcp_subflow_delegate(struct mptcp_subflow_context *subflow, int action) { struct mptcp_delegated_action *delegated; bool schedule; + /* the caller held the subflow bh socket lock */ + lockdep_assert_in_softirq(); + /* The implied barrier pairs with mptcp_subflow_delegated_done(), and * ensures the below list check sees list updates done prior to status * bit changes */ - if (!test_and_set_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status)) { + if (!test_and_set_bit(action, &subflow->delegated_status)) { /* still on delegated list from previous scheduling */ if (!list_empty(&subflow->delegated_node)) return; - /* the caller held the subflow bh socket lock */ - lockdep_assert_in_softirq(); - delegated = this_cpu_ptr(&mptcp_delegated_actions); schedule = list_empty(&delegated->head); list_add_tail(&subflow->delegated_node, &delegated->head); @@ -533,16 +534,16 @@ mptcp_subflow_delegated_next(struct mptcp_delegated_action *delegated) static inline bool mptcp_subflow_has_delegated_action(const struct mptcp_subflow_context *subflow) { - return test_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status); + return !!READ_ONCE(subflow->delegated_status); } -static inline void mptcp_subflow_delegated_done(struct mptcp_subflow_context *subflow) +static inline void mptcp_subflow_delegated_done(struct mptcp_subflow_context *subflow, int action) { /* pairs with mptcp_subflow_delegate, ensures delegate_node is updated before * touching the status bit */ smp_wmb(); - clear_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status); + clear_bit(action, &subflow->delegated_status); } int mptcp_is_enabled(const struct net *net); -- 2.20.1