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Message-Id: <fba74ffdd78018799c36688b137fe5e00be1d9f5.1637331462.git.pabeni@redhat.com>
Date: Fri, 19 Nov 2021 15:27:55 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: mptcp@...ts.linux.dev, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 2/2] 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 <mathew.j.martineau>@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
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);
--
2.33.1
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