MPTCP initialize the receive buffer stamp in mptcp_rcv_space_init(),
using the provided subflow stamp. Such helper is invoked in several
places, with a catch-up call in mptcp_rcv_space_adjust().

For passive sockets, MPTCP ends-up accesses the subflow stamp before
its initialization, leading to quite randomic timing for the first
receive buffer auto-tune event.

Fix the issue using a fresh stamp.

Drop the all the mptcp_rcv_space_init() invocations except the catch-up
one: they add unneeded complexity for no good reason.

As a side effect, this avoid using a zero value for imsk->rcvq_space.time,
that made the first receive buffer auto-tune even quite randomic.

This will also make the next patch cleaner.

Fixes: 013e3179dbd2 ("mptcp: fix rcv space initialization")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 40 ++++++++++++++++++++--------------------
 net/mptcp/protocol.h |  6 +++++-
 net/mptcp/subflow.c  |  2 --
 3 files changed, 25 insertions(+), 23 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d16ad1a85411..e17abab7bab6 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2047,6 +2047,21 @@ static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
 	return copied;
 }
 
+static void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
+{
+	const struct tcp_sock *tp = tcp_sk(ssk);
+
+	msk->rcvspace_init = 1;
+	msk->rcvq_space.copied = 0;
+	msk->rcvq_space.rtt_us = 0;
+
+	/* initial rcv_space offering made to peer */
+	msk->rcvq_space.space = min_t(u32, tp->rcv_wnd,
+				      TCP_INIT_CWND * tp->advmss);
+	if (msk->rcvq_space.space == 0)
+		msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;
+}
+
 /* receive buffer autotuning.  See tcp_rcv_space_adjust for more information.
  *
  * Only difference: Use highest rtt estimate of the subflows in use.
@@ -2069,8 +2084,8 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
 
 	msk->rcvq_space.copied += copied;
 
-	mstamp = div_u64(tcp_clock_ns(), NSEC_PER_USEC);
-	time = tcp_stamp_us_delta(mstamp, msk->rcvq_space.time);
+	mstamp = mptcp_stamp();
+	time = tcp_stamp_us_delta(mstamp, READ_ONCE(msk->rcvq_space.time));
 
 	rtt_us = msk->rcvq_space.rtt_us;
 	if (rtt_us && time < (rtt_us >> 3))
@@ -3487,7 +3502,7 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
 	mptcp_copy_inaddrs(nsk, ssk);
 	__mptcp_propagate_sndbuf(nsk, ssk);
 
-	mptcp_rcv_space_init(msk, ssk);
+	msk->rcvq_space.time = mptcp_stamp();
 
 	if (mp_opt->suboptions & OPTION_MPTCP_MPC_ACK)
 		__mptcp_subflow_fully_established(msk, subflow, mp_opt);
@@ -3497,23 +3512,6 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
 	return nsk;
 }
 
-void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
-{
-	const struct tcp_sock *tp = tcp_sk(ssk);
-
-	msk->rcvspace_init = 1;
-	msk->rcvq_space.copied = 0;
-	msk->rcvq_space.rtt_us = 0;
-
-	msk->rcvq_space.time = tp->tcp_mstamp;
-
-	/* initial rcv_space offering made to peer */
-	msk->rcvq_space.space = min_t(u32, tp->rcv_wnd,
-				      TCP_INIT_CWND * tp->advmss);
-	if (msk->rcvq_space.space == 0)
-		msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;
-}
-
 static void mptcp_destroy(struct sock *sk)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
@@ -3703,6 +3701,8 @@ void mptcp_finish_connect(struct sock *ssk)
 	 */
 	WRITE_ONCE(msk->local_key, subflow->local_key);
 
+	WRITE_ONCE(msk->rcvq_space.time, mptcp_stamp());
+
 	mptcp_pm_new_connection(msk, ssk, 0);
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 84f2c51d776c..1f67d8468dfb 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -908,7 +908,11 @@ static inline bool mptcp_is_fully_established(struct sock *sk)
 	       READ_ONCE(mptcp_sk(sk)->fully_established);
 }
 
-void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk);
+static inline u64 mptcp_stamp(void)
+{
+	return div_u64(tcp_clock_ns(), NSEC_PER_USEC);
+}
+
 void mptcp_data_ready(struct sock *sk, struct sock *ssk);
 bool mptcp_finish_join(struct sock *sk);
 bool mptcp_schedule_work(struct sock *sk);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index ac8616e7521e..b64ab7649908 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -462,8 +462,6 @@ void __mptcp_sync_state(struct sock *sk, int state)
 
 	subflow = mptcp_subflow_ctx(ssk);
 	__mptcp_propagate_sndbuf(sk, ssk);
-	if (!msk->rcvspace_init)
-		mptcp_rcv_space_init(msk, ssk);
 
 	if (sk->sk_state == TCP_SYN_SENT) {
 		/* subflow->idsn is always available is TCP_SYN_SENT state,
-- 
2.51.0