[PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Paolo Abeni]

This an attempt to fix the data transfer stall reported by Geliang and
Gang more carefully enforcing memory constraints at the MPTCP level.

Patch 1/10 moves the bound check before entering the TCP socket.
Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
TCP helpers on MPTCP skbs.
Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
makes use of them. Patch 8 addresses an edge scenario that could still
lead to transfer stall under memory pressure.
Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
make recovery from memory pressure significanly faster.

Note that the diffstat is biases by the quite large patch 4/9, which
contains mechanical transformation of existing code; "real" changes are
noticiable smaller.

Tested successfully vs the test cases proposed by Geliang and Gang and
vs the selftests.
---
Some notes on each patch WRT ignored or false positive issues noticed
by sashiko so far.

Paolo Abeni (10):
  mptcp: move checks vs rcvbuf size earlier in the RX path
  mptcp: drop the mptcp_ooo_try_coalesce() helper
  mptcp: drop the cant_coalesce CB field
  mptcp: remove CB offset field
  mptcp: sync mptcp skb cb layout with tcp one
  tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too
  mptcp: implemented OoO queue pruning
  mptcp: track prune recovery status
  mptcp: move the retrans loop to a separate helper
  mptcp: let the retrans scheduler do its job.

 include/net/tcp.h    |   8 +
 net/ipv4/tcp_input.c |  55 +++---
 net/mptcp/fastopen.c |  17 +-
 net/mptcp/mib.c      |   3 +
 net/mptcp/mib.h      |   3 +
 net/mptcp/options.c  |  64 ++++++-
 net/mptcp/protocol.c | 399 ++++++++++++++++++++++++++++---------------
 net/mptcp/protocol.h |  24 ++-
 net/mptcp/subflow.c  |  11 ++
 9 files changed, 414 insertions(+), 170 deletions(-)

-- 
2.54.0

[PATCH v3 mptcp-next 01/10] mptcp: move checks vs rcvbuf size earlier in the RX path

[Paolo Abeni]

Currently the enforcement of the rcvbuf constraint is implemented
when moving the skbs into the msk receive or OoO queue.

Under significant memory pressure the above can cause permanent data
transfer stalls. Move the checks early on, before landing even in
the subflow queues.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v1 -> v2:
 - deal correctly with tcp fin and zero win probe

RFC -> v1:
 - limit vs actual buffer size
 - use CB info instead of skb->len

Note that:
 - this needs the follow-up patches to really fix the stall
 - sashiko can assume ZWP carries unacked data and may be silently dropped.
   AFAIK that is false.
 - the memory comparison is intentionally very rough, as
   the msk socket lock is not currently held where the condition is
   now enforced. This should require some refinement, shared as-is
   to avoid more latency on my side
---
 net/mptcp/options.c  | 25 +++++++++++++++++++++++--
 net/mptcp/protocol.c | 10 ++--------
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 4cc583fdc7a9..ad4bb6fd86e1 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1158,8 +1158,23 @@ static bool add_addr_hmac_valid(struct mptcp_sock *msk,
 	return hmac == mp_opt->ahmac;
 }
 
-/* Return false in case of error (or subflow has been reset),
- * else return true.
+static bool mptcp_over_limit(struct sock *sk, const struct sock *ssk,
+			     const struct sk_buff *skb)
+{
+	if (likely(sk_rmem_alloc_get(sk) <= READ_ONCE(sk->sk_rcvbuf)))
+		return false;
+
+	/* Avoid silently dropping pure acks, fin or zero win probes. */
+	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq ||
+	    TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN ||
+	    !after(TCP_SKB_CB(skb)->end_seq, tcp_sk(ssk)->rcv_nxt))
+		return false;
+
+	return true;
+}
+
+/* Return false when the caller must drop the packet, i.e. in case of error,
+ * subflow has been reset, or over memory limits.
  */
 bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 {
@@ -1185,6 +1200,9 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 		__mptcp_data_acked(subflow->conn);
 		mptcp_data_unlock(subflow->conn);
+
+		if (mptcp_over_limit(subflow->conn, sk, skb))
+			return false;
 		return true;
 	}
 
@@ -1263,6 +1281,9 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 		return true;
 	}
 
+	if (mptcp_over_limit(subflow->conn, sk, skb))
+		return false;
+
 	mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
 	if (!mpext)
 		return false;
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 17b9a8c13ebf..81a9b8077d6b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -739,7 +739,7 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 
 			mptcp_init_skb(ssk, skb, offset, len);
 
-			if (own_msk && sk_rmem_alloc_get(sk) < sk->sk_rcvbuf) {
+			if (own_msk) {
 				mptcp_subflow_lend_fwdmem(subflow, skb);
 				ret |= __mptcp_move_skb(sk, skb);
 			} else {
@@ -2197,10 +2197,6 @@ static bool __mptcp_move_skbs(struct sock *sk, struct list_head *skbs, u32 *delt
 
 	*delta = 0;
 	while (1) {
-		/* If the msk recvbuf is full stop, don't drop */
-		if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
-			break;
-
 		prefetch(skb->next);
 		list_del(&skb->list);
 		*delta += skb->truesize;
@@ -2228,9 +2224,7 @@ static bool mptcp_can_spool_backlog(struct sock *sk, struct list_head *skbs)
 	DEBUG_NET_WARN_ON_ONCE(msk->backlog_unaccounted && sk->sk_socket &&
 			       mem_cgroup_from_sk(sk));
 
-	/* Don't spool the backlog if the rcvbuf is full. */
-	if (list_empty(&msk->backlog_list) ||
-	    sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
+	if (list_empty(&msk->backlog_list))
 		return false;
 
 	INIT_LIST_HEAD(skbs);
-- 
2.54.0

[PATCH v3 mptcp-next 02/10] mptcp: drop the mptcp_ooo_try_coalesce() helper

[Paolo Abeni]

It's used to save an additional comparison for in-order skbs, but is
also a barrier to remove CB offset. Remove the helper, let
__mptcp_try_coalesce() always perform the sequence check and remove
duplicate checks from the callers.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 81a9b8077d6b..ad0a289b544b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -159,7 +159,8 @@ static bool __mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
 {
 	int limit = READ_ONCE(sk->sk_rcvbuf);
 
-	if (unlikely(MPTCP_SKB_CB(to)->cant_coalesce) ||
+	if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq ||
+	    unlikely(MPTCP_SKB_CB(to)->cant_coalesce) ||
 	    MPTCP_SKB_CB(from)->offset ||
 	    ((to->len + from->len) > (limit >> 3)) ||
 	    !skb_try_coalesce(to, from, fragstolen, delta))
@@ -192,15 +193,6 @@ static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
 	return true;
 }
 
-static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
-				   struct sk_buff *from)
-{
-	if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq)
-		return false;
-
-	return mptcp_try_coalesce((struct sock *)msk, to, from);
-}
-
 /* "inspired" by tcp_rcvbuf_grow(), main difference:
  * - mptcp does not maintain a msk-level window clamp
  * - returns true when  the receive buffer is actually updated
@@ -275,7 +267,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	/* with 2 subflows, adding at end of ooo queue is quite likely
 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
 	 */
-	if (mptcp_ooo_try_coalesce(msk, msk->ooo_last_skb, skb)) {
+	if (mptcp_try_coalesce(sk, msk->ooo_last_skb, skb)) {
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
 		return;
@@ -321,7 +313,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
 				goto merge_right;
 			}
-		} else if (mptcp_ooo_try_coalesce(msk, skb1, skb)) {
+		} else if (mptcp_try_coalesce(sk, skb1, skb)) {
 			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
 			return;
 		}
@@ -672,8 +664,7 @@ static void __mptcp_add_backlog(struct sock *sk,
 	if (!list_empty(&msk->backlog_list))
 		tail = list_last_entry(&msk->backlog_list, struct sk_buff, list);
 
-	if (tail && MPTCP_SKB_CB(skb)->map_seq == MPTCP_SKB_CB(tail)->end_seq &&
-	    ssk == tail->sk &&
+	if (tail && ssk == tail->sk &&
 	    __mptcp_try_coalesce(sk, tail, skb, &fragstolen, &delta)) {
 		skb->truesize -= delta;
 		kfree_skb_partial(skb, fragstolen);
@@ -797,7 +788,7 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
 
 		end_seq = MPTCP_SKB_CB(skb)->end_seq;
 		tail = skb_peek_tail(&sk->sk_receive_queue);
-		if (!tail || !mptcp_ooo_try_coalesce(msk, tail, skb)) {
+		if (!tail || !mptcp_try_coalesce(sk, tail, skb)) {
 			int delta = msk->ack_seq - MPTCP_SKB_CB(skb)->map_seq;
 
 			/* skip overlapping data, if any */
-- 
2.54.0

[PATCH v3 mptcp-next 03/10] mptcp: drop the cant_coalesce CB field

[Paolo Abeni]

Such field is used to ensure in-sequence processing in case of fastopen.
Instead let's perform synchronization of the fastopen skb sequence
when the IASN becomes available with the 3rd ack.

When the `cant_coalesce` field has been introduced, commit f03afb3aeb9d
("mptcp: drop __mptcp_fastopen_gen_msk_ackseq()") noted that updating the
already queued skb for passive fastopen socket at 3rd ack time would be
difficult and race prone. The main point is that such update don't need
to be synchronously performed at 3rd ack time, but is sufficient to
perform it before the next segment is introduced into the msk.

To such extent, add an explicit test in __mptcp_move_skb(). Performance
wise this trades a conditional in the fast path - in __mptcp_try_coalesce()
- with a similar one in __mptcp_move_skb() and a couple more in slow paths.

After this change the user-space will always observe consistent sequence
numbers in the receive queue, even in the TFO dummy mapping case.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/fastopen.c |  2 +-
 net/mptcp/protocol.c | 28 ++++++++++++++++++++++++++--
 net/mptcp/protocol.h |  4 +++-
 net/mptcp/subflow.c  |  7 +++++++
 4 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index 082c46c0f50e..c7d5bee8088e 100644
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -48,11 +48,11 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
 	MPTCP_SKB_CB(skb)->end_seq = 0;
 	MPTCP_SKB_CB(skb)->offset = 0;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
-	MPTCP_SKB_CB(skb)->cant_coalesce = 1;
 
 	mptcp_data_lock(sk);
 	DEBUG_NET_WARN_ON_ONCE(sock_owned_by_user_nocheck(sk));
 
+	mptcp_sk(sk)->rcvd_dummy_seq = true;
 	mptcp_borrow_fwdmem(sk, skb);
 	skb_set_owner_r(skb, sk);
 	__skb_queue_tail(&sk->sk_receive_queue, skb);
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ad0a289b544b..fd88a81f1821 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -160,7 +160,6 @@ static bool __mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
 	int limit = READ_ONCE(sk->sk_rcvbuf);
 
 	if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq ||
-	    unlikely(MPTCP_SKB_CB(to)->cant_coalesce) ||
 	    MPTCP_SKB_CB(from)->offset ||
 	    ((to->len + from->len) > (limit >> 3)) ||
 	    !skb_try_coalesce(to, from, fragstolen, delta))
@@ -357,7 +356,6 @@ static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
 	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + copy_len;
 	MPTCP_SKB_CB(skb)->offset = offset;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
-	MPTCP_SKB_CB(skb)->cant_coalesce = 0;
 
 	__skb_unlink(skb, &ssk->sk_receive_queue);
 
@@ -365,6 +363,24 @@ static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
 	skb_dst_drop(skb);
 }
 
+void __mptcp_sync_rcv_sequence(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct sk_buff *skb;
+
+	if (likely(!msk->rcvd_dummy_seq))
+		return;
+
+	/* User space can have already received the TFO skb. */
+	msk->rcvd_dummy_seq = false;
+	skb = skb_peek_tail(&sk->sk_receive_queue);
+	if (!skb)
+		return;
+
+	MPTCP_SKB_CB(skb)->map_seq = msk->ack_seq - skb->len;
+	MPTCP_SKB_CB(skb)->end_seq = msk->ack_seq;
+}
+
 static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 {
 	u64 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
@@ -373,6 +389,12 @@ static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 
 	mptcp_borrow_fwdmem(sk, skb);
 
+	/* Be sure to sync the eventual fastopen dummy mapping before any other
+	 * skb lands into the msk.
+	 */
+	if (unlikely(msk->rcvd_dummy_seq))
+		__mptcp_sync_rcv_sequence(sk);
+
 	if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
 		/* in sequence */
 		msk->bytes_received += copy_len;
@@ -3682,6 +3704,8 @@ static void mptcp_release_cb(struct sock *sk)
 			__mptcp_error_report(sk);
 		if (__test_and_clear_bit(MPTCP_SYNC_SNDBUF, &msk->cb_flags))
 			__mptcp_sync_sndbuf(sk);
+		if (__test_and_clear_bit(MPTCP_SYNC_SEQ, &msk->cb_flags))
+			__mptcp_sync_rcv_sequence(sk);
 	}
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 661600f8b573..16a1f4531dad 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -124,13 +124,13 @@
 #define MPTCP_FLUSH_JOIN_LIST	5
 #define MPTCP_SYNC_STATE	6
 #define MPTCP_SYNC_SNDBUF	7
+#define MPTCP_SYNC_SEQ		8
 
 struct mptcp_skb_cb {
 	u64 map_seq;
 	u64 end_seq;
 	u32 offset;
 	u8  has_rxtstamp;
-	u8  cant_coalesce;
 };
 
 #define MPTCP_SKB_CB(__skb)	((struct mptcp_skb_cb *)&((__skb)->cb[0]))
@@ -310,6 +310,7 @@ struct mptcp_sock {
 	u32		token;
 	unsigned long	flags;
 	unsigned long	cb_flags;
+	bool		rcvd_dummy_seq;
 	bool		recovery;		/* closing subflow write queue reinjected */
 	bool		can_ack;
 	bool		fully_established;
@@ -1172,6 +1173,7 @@ void mptcp_event_pm_listener(const struct sock *ssk,
 			     enum mptcp_event_type event);
 bool mptcp_userspace_pm_active(const struct mptcp_sock *msk);
 
+void __mptcp_sync_rcv_sequence(struct sock *sk);
 void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subflow,
 					      struct request_sock *req);
 int mptcp_pm_genl_fill_addr(struct sk_buff *msg,
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index c57ed27a5fb0..b226c7cd1b79 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -478,6 +478,8 @@ static void subflow_set_remote_key(struct mptcp_sock *msk,
 				   struct mptcp_subflow_context *subflow,
 				   const struct mptcp_options_received *mp_opt)
 {
+	struct sock *sk = (struct sock *)msk;
+
 	/* active MPC subflow will reach here multiple times:
 	 * at subflow_finish_connect() time and at 4th ack time
 	 */
@@ -496,6 +498,11 @@ static void subflow_set_remote_key(struct mptcp_sock *msk,
 	WRITE_ONCE(msk->ack_seq, subflow->iasn);
 	WRITE_ONCE(msk->can_ack, true);
 	atomic64_set(&msk->rcv_wnd_sent, subflow->iasn);
+
+	if (!sock_owned_by_user(sk))
+		__mptcp_sync_rcv_sequence(sk);
+	else
+		__set_bit(MPTCP_SYNC_SEQ, &msk->cb_flags);
 }
 
 static void mptcp_propagate_state(struct sock *sk, struct sock *ssk,
-- 
2.54.0

[PATCH v3 mptcp-next 04/10] mptcp: remove CB offset field

[Paolo Abeni]

Instead, use a new msk-level field to track the bytes already consumed
inside each skb, carrying the amount of bytes already copied to
user-space, alike what TCP is already doing.

`copied_seq` is always accessed under the msk socket lock, delegating the
synchronization with IASN to the msk release cb, when the socket is owned
by the user-space at remote key reception time. Such synchronization
preserves any partial progress (copy) made on the TFO packet.

Prior to this patch, the TFO skb dummy mapping was always ignored, now it
affects the `copied_seq` initial update: be sure to extends the sign
correctly of such mapping initialization time.

Overall this simplify a bit the __mptcp_recvmsg_mskq() and mptcp_inq_hint()
code and will also make possible the next patch.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3:
  - do not use msk->first in release_cb to deal with MPTCP_SYNC_SEQ:
    subflow->iasn access is (data) racy and msk->first can be null, instead
    recompute iasn from msk bytes_received and TFO skb len
  - when updating copied_seq after remote key reception, add iasn to it
    instead of overwriting, to avoid deleting any partial progress.

v1 -> v2:
  - deal correctly with peek, as usally "inspired" from the correspondent
    tcp code
  - update mptcp_inq_hint(), too

Notes:
- this explicitly relays on "mptcp: do not drop partial packets" to
avoid dropping partially consumed packets
- sashiko may confuse the 'offset' in mptcp_init_skb for an MPTCP-level
  one, but it refers to the TCP sequence space. Conclusion out of the
  that assumptions are wrong.
- the data race in mptcp_inq_hint() is real, but pre-existing and can
  impact only sockopt() output - the other call-sites are race free, as
  ack_seq updates are serialized by the RX path.
  Fixing the race for good without sashiko tripping on other similar
  minor races would require another largish series. Postponed.
- sashiko may see a race vs `copied_seq` access in mptcp_recv_skb(), but
  that is not possible: `copied_seq` is maintained in sync with the TFO
  skb via __mptcp_sync_rcv_sequence
---
 net/mptcp/fastopen.c | 15 +++++---
 net/mptcp/protocol.c | 89 ++++++++++++++++++--------------------------
 net/mptcp/protocol.h |  8 +++-
 net/mptcp/subflow.c  |  7 +++-
 4 files changed, 59 insertions(+), 60 deletions(-)

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index c7d5bee8088e..2ace3a73f24e 100644
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -9,6 +9,7 @@
 void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subflow,
 					      struct request_sock *req)
 {
+	struct mptcp_sock *msk;
 	struct sock *sk, *ssk;
 	struct sk_buff *skb;
 	struct tcp_sock *tp;
@@ -43,20 +44,24 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
 	subflow->ssn_offset += skb->len;
 	has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
-	/* Only the sequence delta is relevant */
-	MPTCP_SKB_CB(skb)->map_seq = -skb->len;
+	/* The TFO segment data sits before the IASN; before receiving
+	 * the remove key, IASN is assumed being 0.
+	 */
+	MPTCP_SKB_CB(skb)->map_seq = -(u64)skb->len;
 	MPTCP_SKB_CB(skb)->end_seq = 0;
-	MPTCP_SKB_CB(skb)->offset = 0;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
 
 	mptcp_data_lock(sk);
 	DEBUG_NET_WARN_ON_ONCE(sock_owned_by_user_nocheck(sk));
 
-	mptcp_sk(sk)->rcvd_dummy_seq = true;
+	msk = mptcp_sk(sk);
+	msk->rcvd_dummy_seq = true;
+	msk->copied_seq = MPTCP_SKB_CB(skb)->map_seq;
+	msk->tfo_skb_len = skb->len;
 	mptcp_borrow_fwdmem(sk, skb);
 	skb_set_owner_r(skb, sk);
 	__skb_queue_tail(&sk->sk_receive_queue, skb);
-	mptcp_sk(sk)->bytes_received += skb->len;
+	msk->bytes_received += skb->len;
 
 	sk->sk_data_ready(sk);
 
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index fd88a81f1821..d57544681b7e 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -160,7 +160,6 @@ static bool __mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
 	int limit = READ_ONCE(sk->sk_rcvbuf);
 
 	if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq ||
-	    MPTCP_SKB_CB(from)->offset ||
 	    ((to->len + from->len) > (limit >> 3)) ||
 	    !skb_try_coalesce(to, from, fragstolen, delta))
 		return false;
@@ -342,8 +341,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	skb_set_owner_r(skb, sk);
 }
 
-static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
-			   int copy_len)
+static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	bool has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
@@ -352,9 +350,9 @@ static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
 	 * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
 	 * value
 	 */
-	MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow);
-	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + copy_len;
-	MPTCP_SKB_CB(skb)->offset = offset;
+	MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow) -
+				     offset;
+	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
 
 	__skb_unlink(skb, &ssk->sk_receive_queue);
@@ -377,8 +375,8 @@ void __mptcp_sync_rcv_sequence(struct sock *sk)
 	if (!skb)
 		return;
 
-	MPTCP_SKB_CB(skb)->map_seq = msk->ack_seq - skb->len;
-	MPTCP_SKB_CB(skb)->end_seq = msk->ack_seq;
+	MPTCP_SKB_CB(skb)->map_seq = mptcp_iasn(msk) - skb->len;
+	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
 }
 
 static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
@@ -750,7 +748,7 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 		if (offset < skb->len) {
 			size_t len = skb->len - offset;
 
-			mptcp_init_skb(ssk, skb, offset, len);
+			mptcp_init_skb(ssk, skb, offset);
 
 			if (own_msk) {
 				mptcp_subflow_lend_fwdmem(subflow, skb);
@@ -817,8 +815,6 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
 			pr_debug("uncoalesced seq=%llx ack seq=%llx delta=%d\n",
 				 MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq,
 				 delta);
-			MPTCP_SKB_CB(skb)->offset += delta;
-			MPTCP_SKB_CB(skb)->map_seq += delta;
 			__skb_queue_tail(&sk->sk_receive_queue, skb);
 		}
 		msk->bytes_received += end_seq - msk->ack_seq;
@@ -2062,34 +2058,22 @@ static void mptcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb)
 }
 
 static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
-				size_t len, int flags, int copied_total,
+				size_t len, int flags, u64 *seq,
 				struct scm_timestamping_internal *tss,
 				int *cmsg_flags, struct sk_buff **last)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct sk_buff *skb, *tmp;
-	int total_data_len = 0;
 	int copied = 0;
 
 	skb_queue_walk_safe(&sk->sk_receive_queue, skb, tmp) {
-		u32 delta, offset = MPTCP_SKB_CB(skb)->offset;
-		u32 data_len = skb->len - offset;
-		u32 count;
+		u64 offset = *seq - MPTCP_SKB_CB(skb)->map_seq;
+		u32 count, data_len = skb->len - offset;
 		int err;
 
-		if (flags & MSG_PEEK) {
-			/* skip already peeked skbs */
-			if (total_data_len + data_len <= copied_total) {
-				total_data_len += data_len;
-				*last = skb;
-				continue;
-			}
-
-			/* skip the already peeked data in the current skb */
-			delta = copied_total - total_data_len;
-			offset += delta;
-			data_len -= delta;
-		}
+		/* Skip the already peeked data. */
+		if (offset >= skb->len)
+			continue;
 
 		count = min_t(size_t, len - copied, data_len);
 		if (!(flags & MSG_TRUNC)) {
@@ -2107,14 +2091,12 @@ static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
 		}
 
 		copied += count;
+		*seq += count;
 
 		if (!(flags & MSG_PEEK)) {
 			msk->bytes_consumed += count;
-			if (count < data_len) {
-				MPTCP_SKB_CB(skb)->offset += count;
-				MPTCP_SKB_CB(skb)->map_seq += count;
+			if (count < data_len)
 				break;
-			}
 
 			mptcp_eat_recv_skb(sk, skb);
 		} else {
@@ -2275,22 +2257,17 @@ static bool mptcp_move_skbs(struct sock *sk)
 static unsigned int mptcp_inq_hint(const struct sock *sk)
 {
 	const struct mptcp_sock *msk = mptcp_sk(sk);
-	const struct sk_buff *skb;
+	u64 hint_val;
 
-	skb = skb_peek(&sk->sk_receive_queue);
-	if (skb) {
-		u64 hint_val = READ_ONCE(msk->ack_seq) - MPTCP_SKB_CB(skb)->map_seq;
+	hint_val = READ_ONCE(msk->ack_seq) - msk->copied_seq;
+	if (hint_val >= INT_MAX)
+		return INT_MAX;
 
-		if (hint_val >= INT_MAX)
-			return INT_MAX;
-
-		return (unsigned int)hint_val;
-	}
-
-	if (sk->sk_state == TCP_CLOSE || (sk->sk_shutdown & RCV_SHUTDOWN))
+	if (!hint_val &&
+	    (sk->sk_state == TCP_CLOSE || (sk->sk_shutdown & RCV_SHUTDOWN)))
 		return 1;
 
-	return 0;
+	return (unsigned int)hint_val;
 }
 
 static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
@@ -2299,6 +2276,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct scm_timestamping_internal tss;
 	int copied = 0, cmsg_flags = 0;
+	u64 peek_seq, *seq;
 	int target;
 	long timeo;
 
@@ -2318,6 +2296,11 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 	len = min_t(size_t, len, INT_MAX);
 	target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
+	seq = &msk->copied_seq;
+	if (flags & MSG_PEEK) {
+		peek_seq = msk->copied_seq;
+		seq = &peek_seq;
+	}
 
 	if (unlikely(msk->recvmsg_inq))
 		cmsg_flags = MPTCP_CMSG_INQ;
@@ -2327,7 +2310,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		int err, bytes_read;
 
 		bytes_read = __mptcp_recvmsg_mskq(sk, msg, len - copied, flags,
-						  copied, &tss, &cmsg_flags,
+						  seq, &tss, &cmsg_flags,
 						  &last);
 		if (unlikely(bytes_read < 0)) {
 			if (!copied)
@@ -3475,10 +3458,12 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	msk->bytes_retrans = 0;
 	msk->rcvspace_init = 0;
 	msk->fastclosing = 0;
+	msk->tfo_skb_len = 0;
 	mptcp_init_rtt_est(msk);
 
 	/* for fallback's sake */
 	WRITE_ONCE(msk->ack_seq, 0);
+	msk->copied_seq = 0;
 
 	WRITE_ONCE(sk->sk_shutdown, 0);
 	sk_error_report(sk);
@@ -3704,8 +3689,10 @@ static void mptcp_release_cb(struct sock *sk)
 			__mptcp_error_report(sk);
 		if (__test_and_clear_bit(MPTCP_SYNC_SNDBUF, &msk->cb_flags))
 			__mptcp_sync_sndbuf(sk);
-		if (__test_and_clear_bit(MPTCP_SYNC_SEQ, &msk->cb_flags))
+		if (__test_and_clear_bit(MPTCP_SYNC_SEQ, &msk->cb_flags)) {
+			msk->copied_seq += mptcp_iasn(msk);
 			__mptcp_sync_rcv_sequence(sk);
+		}
 	}
 }
 
@@ -4364,7 +4351,7 @@ static struct sk_buff *mptcp_recv_skb(struct sock *sk, u32 *off)
 		mptcp_move_skbs(sk);
 
 	while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
-		offset = MPTCP_SKB_CB(skb)->offset;
+		offset = msk->copied_seq - MPTCP_SKB_CB(skb)->map_seq;
 		if (offset < skb->len) {
 			*off = offset;
 			return skb;
@@ -4406,11 +4393,9 @@ static int __mptcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 		copied += count;
 
 		msk->bytes_consumed += count;
-		if (count < data_len) {
-			MPTCP_SKB_CB(skb)->offset += count;
-			MPTCP_SKB_CB(skb)->map_seq += count;
+		msk->copied_seq += count;
+		if (count < data_len)
 			break;
-		}
 
 		mptcp_eat_recv_skb(sk, skb);
 	}
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 16a1f4531dad..f3d852e52982 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -129,7 +129,6 @@
 struct mptcp_skb_cb {
 	u64 map_seq;
 	u64 end_seq;
-	u32 offset;
 	u8  has_rxtstamp;
 };
 
@@ -289,6 +288,7 @@ struct mptcp_sock {
 	u64		bytes_sent;
 	u64		snd_nxt;
 	u64		bytes_received;
+	u64		copied_seq;
 	u64		ack_seq;
 	atomic64_t	rcv_wnd_sent;
 	u64		rcv_data_fin_seq;
@@ -308,6 +308,7 @@ struct mptcp_sock {
 	u32		last_ack_recv;
 	unsigned long	timer_ival;
 	u32		token;
+	u32		tfo_skb_len;
 	unsigned long	flags;
 	unsigned long	cb_flags;
 	bool		rcvd_dummy_seq;
@@ -859,6 +860,11 @@ struct sock *mptcp_subflow_get_retrans(struct mptcp_sock *msk);
 int mptcp_sched_get_send(struct mptcp_sock *msk);
 int mptcp_sched_get_retrans(struct mptcp_sock *msk);
 
+static inline u64 mptcp_iasn(const struct mptcp_sock *msk)
+{
+	return msk->ack_seq - msk->bytes_received + msk->tfo_skb_len;
+}
+
 static inline u64 mptcp_data_avail(const struct mptcp_sock *msk)
 {
 	return READ_ONCE(msk->bytes_received) - READ_ONCE(msk->bytes_consumed);
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index b226c7cd1b79..130f9ed7d809 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -499,10 +499,13 @@ static void subflow_set_remote_key(struct mptcp_sock *msk,
 	WRITE_ONCE(msk->can_ack, true);
 	atomic64_set(&msk->rcv_wnd_sent, subflow->iasn);
 
-	if (!sock_owned_by_user(sk))
+	if (!sock_owned_by_user(sk)) {
+		/* User space could have already read partially the TFO skb */
+		msk->copied_seq += subflow->iasn;
 		__mptcp_sync_rcv_sequence(sk);
-	else
+	} else {
 		__set_bit(MPTCP_SYNC_SEQ, &msk->cb_flags);
+	}
 }
 
 static void mptcp_propagate_state(struct sock *sk, struct sock *ssk,
-- 
2.54.0

[PATCH v3 mptcp-next 05/10] mptcp: sync mptcp skb cb layout with tcp one

[Paolo Abeni]

The MPTCP protocol uses a significantly different CB layout WRT TCP, as it
includes different information and use 64 bits for the sequence numbers.

As the msk-level rcvbuf buffer size is limited by the core socket code the
INT_MAX; after validating the incoming skb vs the current receive window,
we can safely use 32 bits for MPTCP-level sequence number. This allow
updating the MPTCP CB layout so that fields with a corresponding TCP-level
data use the same area inside the CB itself.

Add build time check to ensure the latter invariant.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v1 -> v2:
  - use u64 for admission checks

rfc -> v1:
  - keep `ack_seq` up2date
---
 net/mptcp/fastopen.c |  6 ++--
 net/mptcp/protocol.c | 78 ++++++++++++++++++++++++++++----------------
 net/mptcp/protocol.h |  7 ++--
 3 files changed, 58 insertions(+), 33 deletions(-)

diff --git a/net/mptcp/fastopen.c b/net/mptcp/fastopen.c
index 2ace3a73f24e..8e6f70399f7d 100644
--- a/net/mptcp/fastopen.c
+++ b/net/mptcp/fastopen.c
@@ -47,8 +47,10 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
 	/* The TFO segment data sits before the IASN; before receiving
 	 * the remove key, IASN is assumed being 0.
 	 */
-	MPTCP_SKB_CB(skb)->map_seq = -(u64)skb->len;
+	MPTCP_SKB_CB(skb)->map_seq64 = -(u64)skb->len;
+	MPTCP_SKB_CB(skb)->map_seq = MPTCP_SKB_CB(skb)->map_seq64;
 	MPTCP_SKB_CB(skb)->end_seq = 0;
+	MPTCP_SKB_CB(skb)->flags = 0;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
 
 	mptcp_data_lock(sk);
@@ -56,7 +58,7 @@ void mptcp_fastopen_subflow_synack_set_params(struct mptcp_subflow_context *subf
 
 	msk = mptcp_sk(sk);
 	msk->rcvd_dummy_seq = true;
-	msk->copied_seq = MPTCP_SKB_CB(skb)->map_seq;
+	msk->copied_seq = MPTCP_SKB_CB(skb)->map_seq64;
 	msk->tfo_skb_len = skb->len;
 	mptcp_borrow_fwdmem(sk, skb);
 	skb_set_owner_r(skb, sk);
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d57544681b7e..048d556d75e1 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -164,7 +164,7 @@ static bool __mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
 	    !skb_try_coalesce(to, from, fragstolen, delta))
 		return false;
 
-	pr_debug("colesced seq %llx into %llx new len %d new end seq %llx\n",
+	pr_debug("colesced seq %x into %x new len %d new end seq %x\n",
 		 MPTCP_SKB_CB(from)->map_seq, MPTCP_SKB_CB(to)->map_seq,
 		 to->len, MPTCP_SKB_CB(from)->end_seq);
 	MPTCP_SKB_CB(to)->end_seq = MPTCP_SKB_CB(from)->end_seq;
@@ -234,14 +234,18 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 {
 	struct sock *sk = (struct sock *)msk;
 	struct rb_node **p, *parent;
-	u64 seq, end_seq, max_seq;
+	u64 end_seq, max_seq;
 	struct sk_buff *skb1;
+	u32 seq;
 
 	seq = MPTCP_SKB_CB(skb)->map_seq;
-	end_seq = MPTCP_SKB_CB(skb)->end_seq;
+	end_seq = MPTCP_SKB_CB(skb)->map_seq64 + skb->len;
 	max_seq = atomic64_read(&msk->rcv_wnd_sent);
 
-	pr_debug("msk=%p seq=%llx limit=%llx empty=%d\n", msk, seq, max_seq,
+	/* Use the full sequence space to perform the admission checks, to
+	 * protect vs possible wrap-arounds.
+	 */
+	pr_debug("msk=%p seq=%x limit=%llx empty=%d\n", msk, seq, max_seq,
 		 RB_EMPTY_ROOT(&msk->out_of_order_queue));
 	if (after64(end_seq, max_seq)) {
 		/* out of window */
@@ -272,7 +276,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	}
 
 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
-	if (!before64(seq, MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq)) {
+	if (!before(seq, MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq)) {
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
 		parent = &msk->ooo_last_skb->rbnode;
 		p = &parent->rb_right;
@@ -284,18 +288,18 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 	while (*p) {
 		parent = *p;
 		skb1 = rb_to_skb(parent);
-		if (before64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
+		if (before(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
 			p = &parent->rb_left;
 			continue;
 		}
-		if (before64(seq, MPTCP_SKB_CB(skb1)->end_seq)) {
-			if (!after64(end_seq, MPTCP_SKB_CB(skb1)->end_seq)) {
+		if (before(seq, MPTCP_SKB_CB(skb1)->end_seq)) {
+			if (!after(end_seq, MPTCP_SKB_CB(skb1)->end_seq)) {
 				/* All the bits are present. Drop. */
 				mptcp_drop(sk, skb);
 				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
 				return;
 			}
-			if (after64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
+			if (after(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
 				/* partial overlap:
 				 *     |     skb      |
 				 *  |     skb1    |
@@ -326,7 +330,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
 merge_right:
 	/* Remove other segments covered by skb. */
 	while ((skb1 = skb_rb_next(skb)) != NULL) {
-		if (before64(end_seq, MPTCP_SKB_CB(skb1)->end_seq))
+		if (before((u32)end_seq, MPTCP_SKB_CB(skb1)->end_seq))
 			break;
 		rb_erase(&skb1->rbnode, &msk->out_of_order_queue);
 		mptcp_drop(sk, skb1);
@@ -346,13 +350,15 @@ static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset)
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	bool has_rxtstamp = TCP_SKB_CB(skb)->has_rxtstamp;
 
-	/* the skb map_seq accounts for the skb offset:
+	/* The skb map_seq accounts for the skb offset:
 	 * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
-	 * value
+	 * value; note that end seq number is only available in 32bits format.
 	 */
-	MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow) -
-				     offset;
+	MPTCP_SKB_CB(skb)->map_seq64 = mptcp_subflow_get_mapped_dsn(subflow) -
+				       offset;
+	MPTCP_SKB_CB(skb)->map_seq = (u32)MPTCP_SKB_CB(skb)->map_seq64;
 	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
+	MPTCP_SKB_CB(skb)->flags = 0;
 	MPTCP_SKB_CB(skb)->has_rxtstamp = has_rxtstamp;
 
 	__skb_unlink(skb, &ssk->sk_receive_queue);
@@ -375,13 +381,14 @@ void __mptcp_sync_rcv_sequence(struct sock *sk)
 	if (!skb)
 		return;
 
-	MPTCP_SKB_CB(skb)->map_seq = mptcp_iasn(msk) - skb->len;
+	MPTCP_SKB_CB(skb)->map_seq64 = mptcp_iasn(msk) - skb->len;
+	MPTCP_SKB_CB(skb)->map_seq = (u32)MPTCP_SKB_CB(skb)->map_seq64;
 	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
 }
 
 static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 {
-	u64 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
+	u32 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct sk_buff *tail;
 
@@ -393,7 +400,7 @@ static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 	if (unlikely(msk->rcvd_dummy_seq))
 		__mptcp_sync_rcv_sequence(sk);
 
-	if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
+	if (MPTCP_SKB_CB(skb)->map_seq64 == msk->ack_seq) {
 		/* in sequence */
 		msk->bytes_received += copy_len;
 		WRITE_ONCE(msk->ack_seq, msk->ack_seq + copy_len);
@@ -404,7 +411,8 @@ static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 		skb_set_owner_r(skb, sk);
 		__skb_queue_tail(&sk->sk_receive_queue, skb);
 		return true;
-	} else if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq)) {
+	} else if (after64(MPTCP_SKB_CB(skb)->map_seq64 + skb->len,
+			   msk->ack_seq)) {
 		mptcp_data_queue_ofo(msk, skb);
 		return false;
 	}
@@ -785,40 +793,40 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
 {
 	struct sock *sk = (struct sock *)msk;
 	struct sk_buff *skb, *tail;
+	u32 seq_delta, ack_seq;
 	bool moved = false;
 	struct rb_node *p;
-	u64 end_seq;
 
 	p = rb_first(&msk->out_of_order_queue);
 	pr_debug("msk=%p empty=%d\n", msk, RB_EMPTY_ROOT(&msk->out_of_order_queue));
 	while (p) {
+		ack_seq = msk->ack_seq;
 		skb = rb_to_skb(p);
-		if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq))
+		if (after(MPTCP_SKB_CB(skb)->map_seq, ack_seq))
 			break;
 
 		p = rb_next(p);
 		rb_erase(&skb->rbnode, &msk->out_of_order_queue);
 
-		if (unlikely(!after64(MPTCP_SKB_CB(skb)->end_seq,
-				      msk->ack_seq))) {
+		if (unlikely(!after(MPTCP_SKB_CB(skb)->end_seq, ack_seq))) {
 			mptcp_drop(sk, skb);
 			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
 			continue;
 		}
 
-		end_seq = MPTCP_SKB_CB(skb)->end_seq;
+		seq_delta = MPTCP_SKB_CB(skb)->end_seq - ack_seq;
 		tail = skb_peek_tail(&sk->sk_receive_queue);
 		if (!tail || !mptcp_try_coalesce(sk, tail, skb)) {
-			int delta = msk->ack_seq - MPTCP_SKB_CB(skb)->map_seq;
+			int delta = ack_seq - MPTCP_SKB_CB(skb)->map_seq;
 
 			/* skip overlapping data, if any */
-			pr_debug("uncoalesced seq=%llx ack seq=%llx delta=%d\n",
-				 MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq,
+			pr_debug("uncoalesced seq=%x ack seq=%x delta=%d\n",
+				 MPTCP_SKB_CB(skb)->map_seq, ack_seq,
 				 delta);
 			__skb_queue_tail(&sk->sk_receive_queue, skb);
 		}
-		msk->bytes_received += end_seq - msk->ack_seq;
-		WRITE_ONCE(msk->ack_seq, end_seq);
+		msk->bytes_received += seq_delta;
+		WRITE_ONCE(msk->ack_seq, msk->ack_seq + seq_delta);
 		moved = true;
 	}
 	return moved;
@@ -2067,7 +2075,7 @@ static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg,
 	int copied = 0;
 
 	skb_queue_walk_safe(&sk->sk_receive_queue, skb, tmp) {
-		u64 offset = *seq - MPTCP_SKB_CB(skb)->map_seq;
+		u32 offset = (u32)(*seq) - MPTCP_SKB_CB(skb)->map_seq;
 		u32 count, data_len = skb->len - offset;
 		int err;
 
@@ -4600,11 +4608,23 @@ static int mptcp_napi_poll(struct napi_struct *napi, int budget)
 	return work_done;
 }
 
+#define CHK_CB_FIELD(mptcp_field, tcp_field)	\
+	({					\
+		BUILD_BUG_ON(offsetof(struct mptcp_skb_cb, mptcp_field) !=    \
+			     offsetof(struct tcp_skb_cb, tcp_field));	      \
+		BUILD_BUG_ON(offsetofend(struct mptcp_skb_cb, mptcp_field) != \
+			     offsetofend(struct tcp_skb_cb, tcp_field));      \
+	})
+
 void __init mptcp_proto_init(void)
 {
 	struct mptcp_delegated_action *delegated;
 	int cpu;
 
+	CHK_CB_FIELD(map_seq, seq);
+	CHK_CB_FIELD(end_seq, end_seq);
+	CHK_CB_FIELD(flags, tcp_flags);
+
 	mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;
 
 	if (percpu_counter_init(&mptcp_sockets_allocated, 0, GFP_KERNEL))
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f3d852e52982..6786da97bbc8 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -127,9 +127,12 @@
 #define MPTCP_SYNC_SEQ		8
 
 struct mptcp_skb_cb {
-	u64 map_seq;
-	u64 end_seq;
+	u32 map_seq;
+	u32 end_seq;
+	u32 unused;
+	u16 flags;
 	u8  has_rxtstamp;
+	u64 map_seq64;
 };
 
 #define MPTCP_SKB_CB(__skb)	((struct mptcp_skb_cb *)&((__skb)->cb[0]))
-- 
2.54.0

[PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Paolo Abeni]

The end goal is to avoid duplicating the quite untrivial strategy at MPTCP
level.

After the previous patch, the mentioned helpers could process skbs standing
in MPTCP-level queues without any CB-related adaptation.

The only additional adjustment needed is explicitly providing the OoO queue
reference, to cope with different sk layout.

Additionally rename the helper to clearly document its hybrid nature and
let it return the number of collapsed skbs, to allow proper accounting from
the future MPTCP caller.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
rfc -> v1:
 - fix arg typo

Note:
 - this will need a significant amount of testing at the TCP level and
   explicit approval from Eric, which I can't guess if we can hope.
---
 include/net/tcp.h    |  8 +++++++
 net/ipv4/tcp_input.c | 55 ++++++++++++++++++++++++++++----------------
 2 files changed, 43 insertions(+), 20 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6156d1d068e1..34a96f0bcf0a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1828,6 +1828,14 @@ extern void tcp_openreq_init_rwin(struct request_sock *req,
 
 void tcp_enter_memory_pressure(struct sock *sk);
 void tcp_leave_memory_pressure(struct sock *sk);
+unsigned int xtcp_collapse(struct sock *sk, struct sk_buff_head *list,
+			   struct rb_root *root, struct sk_buff *head,
+			   struct sk_buff *tail, u32 start, u32 end,
+			   u8 scaling_ratio);
+unsigned int xtcp_collapse_ofo_queue(struct sock *sk,
+				     struct rb_root *out_of_order_queue,
+				     struct sk_buff **ooo_last_skb,
+				     u8 scaling_ratio);
 
 static inline int keepalive_intvl_when(const struct tcp_sock *tp)
 {
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7171442c3ed7..8417785fa48f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5725,16 +5725,22 @@ static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
 /* Collapse contiguous sequence of skbs head..tail with
  * sequence numbers start..end.
  *
+ * sk can be either a TCP or an MPTCP socket.
+ *
  * If tail is NULL, this means until the end of the queue.
  *
  * Segments with FIN/SYN are not collapsed (only because this
  * simplifies code)
+ *
+ * Returns the number of collapsed skbs.
  */
-static void
-tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
-	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
+unsigned int
+xtcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
+	      struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end,
+	      u8 scaling_ratio)
 {
 	struct sk_buff *skb = head, *n;
+	unsigned int collapsed = 0;
 	struct sk_buff_head tmp;
 	bool end_of_skbs;
 
@@ -5750,6 +5756,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 
 		/* No new bits? It is possible on ofo queue. */
 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+			collapsed++;
 			skb = tcp_collapse_one(sk, skb, list, root);
 			if (!skb)
 				break;
@@ -5762,7 +5769,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 		 *   overlaps to the next one and mptcp allow collapsing.
 		 */
 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
-		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
+		    (__tcp_win_from_space(scaling_ratio, skb->truesize) > skb->len ||
 		     before(TCP_SKB_CB(skb)->seq, start))) {
 			end_of_skbs = false;
 			break;
@@ -5782,7 +5789,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 	if (end_of_skbs ||
 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
 	    !skb_frags_readable(skb))
-		return;
+		return collapsed;
 
 	__skb_queue_head_init(&tmp);
 
@@ -5819,6 +5826,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 				start += size;
 			}
 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+				collapsed++;
 				skb = tcp_collapse_one(sk, skb, list, root);
 				if (!skb ||
 				    skb == tail ||
@@ -5832,23 +5840,26 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
 end:
 	skb_queue_walk_safe(&tmp, skb, n)
 		tcp_rbtree_insert(root, skb);
+	return collapsed;
 }
 
 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
- * and tcp_collapse() them until all the queue is collapsed.
+ * and xtcp_collapse() them until all the queue is collapsed.
  */
-static void tcp_collapse_ofo_queue(struct sock *sk)
+unsigned int xtcp_collapse_ofo_queue(struct sock *sk,
+				     struct rb_root *ooo_queue,
+				     struct sk_buff **ooo_last_skb,
+				     u8 scaling_ratio)
 {
-	struct tcp_sock *tp = tcp_sk(sk);
-	u32 range_truesize, sum_tiny = 0;
+	u32 range_truesize, sum_tiny = 0, collapsed = 0;
 	struct sk_buff *skb, *head;
 	u32 start, end;
 
-	skb = skb_rb_first(&tp->out_of_order_queue);
+	skb = skb_rb_first(ooo_queue);
 new_range:
 	if (!skb) {
-		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
-		return;
+		*ooo_last_skb = skb_rb_last(ooo_queue);
+		return collapsed;
 	}
 	start = TCP_SKB_CB(skb)->seq;
 	end = TCP_SKB_CB(skb)->end_seq;
@@ -5866,12 +5877,13 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
 			/* Do not attempt collapsing tiny skbs */
 			if (range_truesize != head->truesize ||
 			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
-				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
-					     head, skb, start, end);
+				collapsed += xtcp_collapse(sk, NULL, ooo_queue,
+					      head, skb, start, end,
+					      scaling_ratio);
 			} else {
 				sum_tiny += range_truesize;
 				if (sum_tiny > sk->sk_rcvbuf >> 3)
-					return;
+					return collapsed;
 			}
 			goto new_range;
 		}
@@ -5882,6 +5894,7 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
 		if (after(TCP_SKB_CB(skb)->end_seq, end))
 			end = TCP_SKB_CB(skb)->end_seq;
 	}
+	return collapsed;
 }
 
 /*
@@ -5969,12 +5982,14 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
 	if (tcp_can_ingest(sk, in_skb))
 		return 0;
 
-	tcp_collapse_ofo_queue(sk);
+	xtcp_collapse_ofo_queue(sk, &tp->out_of_order_queue,
+				&tp->ooo_last_skb, tp->scaling_ratio);
 	if (!skb_queue_empty(&sk->sk_receive_queue))
-		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
-			     skb_peek(&sk->sk_receive_queue),
-			     NULL,
-			     tp->copied_seq, tp->rcv_nxt);
+		xtcp_collapse(sk, &sk->sk_receive_queue, NULL,
+			      skb_peek(&sk->sk_receive_queue),
+			      NULL,
+			      tp->copied_seq, tp->rcv_nxt,
+			      tp->scaling_ratio);
 
 	if (tcp_can_ingest(sk, in_skb))
 		return 0;
-- 
2.54.0

Re: [PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Paolo Abeni]

Hi Eric,

I'd like to re-use some existing TCP helpers (tcp_collapse_ofo_queue()
and tcp_collapse()) in the MPTCP code, to avoid duplicating the non
trivial logic there.

The idea is that the 'struct sock *' in such helpers could be either a
tcp_sock* or an mptcp_sock *, and the processed skbs could be sitting in
TCP level queues or MPTCP ones.

That poses some hard constraints on the sk fields that the helpers can
access. To make them clear I'm renaming such helpers using an 'xtcp_'
prefix.

The full patch touching the TCP code is below. For completeness,  the
whole series is available here:

https://lore.kernel.org/mptcp/cover.1777908248.git.pabeni@redhat.com/T/#me6eda13ec2c70fbb400b6223aa2d07a4fd3bf865

but I guess most of it is not interesting for you/from TCP perspective.

The MPTCP bits are not yet finalized, but I'd like to know it you would
consider this approach doable or a complete no-go.

Thanks,

Paolo
---
On 5/4/26 5:40 PM, Paolo Abeni wrote:
> The end goal is to avoid duplicating the quite untrivial strategy at MPTCP
> level.
> 
> After the previous patch, the mentioned helpers could process skbs standing
> in MPTCP-level queues without any CB-related adaptation.
> 
> The only additional adjustment needed is explicitly providing the OoO queue
> reference, to cope with different sk layout.
> 
> Additionally rename the helper to clearly document its hybrid nature and
> let it return the number of collapsed skbs, to allow proper accounting from
> the future MPTCP caller.
> 
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> rfc -> v1:
>  - fix arg typo
> 
> Note:
>  - this will need a significant amount of testing at the TCP level and
>    explicit approval from Eric, which I can't guess if we can hope.
> ---
>  include/net/tcp.h    |  8 +++++++
>  net/ipv4/tcp_input.c | 55 ++++++++++++++++++++++++++++----------------
>  2 files changed, 43 insertions(+), 20 deletions(-)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 6156d1d068e1..34a96f0bcf0a 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1828,6 +1828,14 @@ extern void tcp_openreq_init_rwin(struct request_sock *req,
>  
>  void tcp_enter_memory_pressure(struct sock *sk);
>  void tcp_leave_memory_pressure(struct sock *sk);
> +unsigned int xtcp_collapse(struct sock *sk, struct sk_buff_head *list,
> +			   struct rb_root *root, struct sk_buff *head,
> +			   struct sk_buff *tail, u32 start, u32 end,
> +			   u8 scaling_ratio);
> +unsigned int xtcp_collapse_ofo_queue(struct sock *sk,
> +				     struct rb_root *out_of_order_queue,
> +				     struct sk_buff **ooo_last_skb,
> +				     u8 scaling_ratio);
>  
>  static inline int keepalive_intvl_when(const struct tcp_sock *tp)
>  {
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 7171442c3ed7..8417785fa48f 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5725,16 +5725,22 @@ static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
>  /* Collapse contiguous sequence of skbs head..tail with
>   * sequence numbers start..end.
>   *
> + * sk can be either a TCP or an MPTCP socket.
> + *
>   * If tail is NULL, this means until the end of the queue.
>   *
>   * Segments with FIN/SYN are not collapsed (only because this
>   * simplifies code)
> + *
> + * Returns the number of collapsed skbs.
>   */
> -static void
> -tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
> -	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
> +unsigned int
> +xtcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
> +	      struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end,
> +	      u8 scaling_ratio)
>  {
>  	struct sk_buff *skb = head, *n;
> +	unsigned int collapsed = 0;
>  	struct sk_buff_head tmp;
>  	bool end_of_skbs;
>  
> @@ -5750,6 +5756,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
>  
>  		/* No new bits? It is possible on ofo queue. */
>  		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
> +			collapsed++;
>  			skb = tcp_collapse_one(sk, skb, list, root);
>  			if (!skb)
>  				break;
> @@ -5762,7 +5769,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
>  		 *   overlaps to the next one and mptcp allow collapsing.
>  		 */
>  		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
> -		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
> +		    (__tcp_win_from_space(scaling_ratio, skb->truesize) > skb->len ||
>  		     before(TCP_SKB_CB(skb)->seq, start))) {
>  			end_of_skbs = false;
>  			break;
> @@ -5782,7 +5789,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
>  	if (end_of_skbs ||
>  	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
>  	    !skb_frags_readable(skb))
> -		return;
> +		return collapsed;
>  
>  	__skb_queue_head_init(&tmp);
>  
> @@ -5819,6 +5826,7 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
>  				start += size;
>  			}
>  			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
> +				collapsed++;
>  				skb = tcp_collapse_one(sk, skb, list, root);
>  				if (!skb ||
>  				    skb == tail ||
> @@ -5832,23 +5840,26 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
>  end:
>  	skb_queue_walk_safe(&tmp, skb, n)
>  		tcp_rbtree_insert(root, skb);
> +	return collapsed;
>  }
>  
>  /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
> - * and tcp_collapse() them until all the queue is collapsed.
> + * and xtcp_collapse() them until all the queue is collapsed.
>   */
> -static void tcp_collapse_ofo_queue(struct sock *sk)
> +unsigned int xtcp_collapse_ofo_queue(struct sock *sk,
> +				     struct rb_root *ooo_queue,
> +				     struct sk_buff **ooo_last_skb,
> +				     u8 scaling_ratio)
>  {
> -	struct tcp_sock *tp = tcp_sk(sk);
> -	u32 range_truesize, sum_tiny = 0;
> +	u32 range_truesize, sum_tiny = 0, collapsed = 0;
>  	struct sk_buff *skb, *head;
>  	u32 start, end;
>  
> -	skb = skb_rb_first(&tp->out_of_order_queue);
> +	skb = skb_rb_first(ooo_queue);
>  new_range:
>  	if (!skb) {
> -		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
> -		return;
> +		*ooo_last_skb = skb_rb_last(ooo_queue);
> +		return collapsed;
>  	}
>  	start = TCP_SKB_CB(skb)->seq;
>  	end = TCP_SKB_CB(skb)->end_seq;
> @@ -5866,12 +5877,13 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
>  			/* Do not attempt collapsing tiny skbs */
>  			if (range_truesize != head->truesize ||
>  			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
> -				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
> -					     head, skb, start, end);
> +				collapsed += xtcp_collapse(sk, NULL, ooo_queue,
> +					      head, skb, start, end,
> +					      scaling_ratio);
>  			} else {
>  				sum_tiny += range_truesize;
>  				if (sum_tiny > sk->sk_rcvbuf >> 3)
> -					return;
> +					return collapsed;
>  			}
>  			goto new_range;
>  		}
> @@ -5882,6 +5894,7 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
>  		if (after(TCP_SKB_CB(skb)->end_seq, end))
>  			end = TCP_SKB_CB(skb)->end_seq;
>  	}
> +	return collapsed;
>  }
>  
>  /*
> @@ -5969,12 +5982,14 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
>  	if (tcp_can_ingest(sk, in_skb))
>  		return 0;
>  
> -	tcp_collapse_ofo_queue(sk);
> +	xtcp_collapse_ofo_queue(sk, &tp->out_of_order_queue,
> +				&tp->ooo_last_skb, tp->scaling_ratio);
>  	if (!skb_queue_empty(&sk->sk_receive_queue))
> -		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
> -			     skb_peek(&sk->sk_receive_queue),
> -			     NULL,
> -			     tp->copied_seq, tp->rcv_nxt);
> +		xtcp_collapse(sk, &sk->sk_receive_queue, NULL,
> +			      skb_peek(&sk->sk_receive_queue),
> +			      NULL,
> +			      tp->copied_seq, tp->rcv_nxt,
> +			      tp->scaling_ratio);
>  
>  	if (tcp_can_ingest(sk, in_skb))
>  		return 0;

Re: [PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Eric Dumazet]

On Mon, May 4, 2026 at 9:39 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> Hi Eric,
>
> I'd like to re-use some existing TCP helpers (tcp_collapse_ofo_queue()
> and tcp_collapse()) in the MPTCP code, to avoid duplicating the non
> trivial logic there.
>
> The idea is that the 'struct sock *' in such helpers could be either a
> tcp_sock* or an mptcp_sock *, and the processed skbs could be sitting in
> TCP level queues or MPTCP ones.
>
> That poses some hard constraints on the sk fields that the helpers can
> access. To make them clear I'm renaming such helpers using an 'xtcp_'
> prefix.
>
> The full patch touching the TCP code is below. For completeness,  the
> whole series is available here:
>
> https://lore.kernel.org/mptcp/cover.1777908248.git.pabeni@redhat.com/T/#me6eda13ec2c70fbb400b6223aa2d07a4fd3bf865
>
> but I guess most of it is not interesting for you/from TCP perspective.
>
> The MPTCP bits are not yet finalized, but I'd like to know it you would
> consider this approach doable or a complete no-go.

No concerns from my side, if we except the fact that TCP collapses are
a high risk, we might
remove them completely (or at least guard them under a sysctl)

Re: [PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Paolo Abeni]

On 5/4/26 9:07 PM, Eric Dumazet wrote:
> On Mon, May 4, 2026 at 9:39 AM Paolo Abeni <pabeni@redhat.com> wrote:
>> I'd like to re-use some existing TCP helpers (tcp_collapse_ofo_queue()
>> and tcp_collapse()) in the MPTCP code, to avoid duplicating the non
>> trivial logic there.
>>
>> The idea is that the 'struct sock *' in such helpers could be either a
>> tcp_sock* or an mptcp_sock *, and the processed skbs could be sitting in
>> TCP level queues or MPTCP ones.
>>
>> That poses some hard constraints on the sk fields that the helpers can
>> access. To make them clear I'm renaming such helpers using an 'xtcp_'
>> prefix.
>>
>> The full patch touching the TCP code is below. For completeness,  the
>> whole series is available here:
>>
>> https://lore.kernel.org/mptcp/cover.1777908248.git.pabeni@redhat.com/T/#me6eda13ec2c70fbb400b6223aa2d07a4fd3bf865
>>
>> but I guess most of it is not interesting for you/from TCP perspective.
>>
>> The MPTCP bits are not yet finalized, but I'd like to know it you would
>> consider this approach doable or a complete no-go.
> 
> No concerns from my side, if we except the fact that TCP collapses are
> a high risk, we might
> remove them completely (or at least guard them under a sysctl)

I'm sorry I can't follow the above suggestion, could you please rephrase?

The patch should not add bugs to TCP collapses for TCP sockets or MPTCP
subflows (still tcp_sock). Collapses for MPTCP sockets could become
buggy if the tcp_collapse_ofo_queue()/tcp_collapse() implementation will
be modified in the future without care.

Thanks,

Paolo

Re: [PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Eric Dumazet]

On Tue, May 5, 2026 at 8:57 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On 5/4/26 9:07 PM, Eric Dumazet wrote:
> > On Mon, May 4, 2026 at 9:39 AM Paolo Abeni <pabeni@redhat.com> wrote:
> >> I'd like to re-use some existing TCP helpers (tcp_collapse_ofo_queue()
> >> and tcp_collapse()) in the MPTCP code, to avoid duplicating the non
> >> trivial logic there.
> >>
> >> The idea is that the 'struct sock *' in such helpers could be either a
> >> tcp_sock* or an mptcp_sock *, and the processed skbs could be sitting in
> >> TCP level queues or MPTCP ones.
> >>
> >> That poses some hard constraints on the sk fields that the helpers can
> >> access. To make them clear I'm renaming such helpers using an 'xtcp_'
> >> prefix.
> >>
> >> The full patch touching the TCP code is below. For completeness,  the
> >> whole series is available here:
> >>
> >> https://lore.kernel.org/mptcp/cover.1777908248.git.pabeni@redhat.com/T/#me6eda13ec2c70fbb400b6223aa2d07a4fd3bf865
> >>
> >> but I guess most of it is not interesting for you/from TCP perspective.
> >>
> >> The MPTCP bits are not yet finalized, but I'd like to know it you would
> >> consider this approach doable or a complete no-go.
> >
> > No concerns from my side, if we except the fact that TCP collapses are
> > a high risk, we might
> > remove them completely (or at least guard them under a sysctl)
>
> I'm sorry I can't follow the above suggestion, could you please rephrase?
>
> The patch should not add bugs to TCP collapses for TCP sockets or MPTCP
> subflows (still tcp_sock). Collapses for MPTCP sockets could become
> buggy if the tcp_collapse_ofo_queue()/tcp_collapse() implementation will
> be modified in the future without care.

I think TCP collapses should be avoided like the plague.

They were ok 20 years ago, when 'line rate' was 64Kbit :0)

Re: [PATCH v3 mptcp-next 06/10] tcp: expose the tcp_collapse_ofo_queue() helper to mptcp usage, too

[Paolo Abeni]

On 5/5/26 6:35 PM, Eric Dumazet wrote:
> On Tue, May 5, 2026 at 8:57 AM Paolo Abeni <pabeni@redhat.com> wrote:
>>
>> On 5/4/26 9:07 PM, Eric Dumazet wrote:
>>> On Mon, May 4, 2026 at 9:39 AM Paolo Abeni <pabeni@redhat.com> wrote:
>>>> I'd like to re-use some existing TCP helpers (tcp_collapse_ofo_queue()
>>>> and tcp_collapse()) in the MPTCP code, to avoid duplicating the non
>>>> trivial logic there.
>>>>
>>>> The idea is that the 'struct sock *' in such helpers could be either a
>>>> tcp_sock* or an mptcp_sock *, and the processed skbs could be sitting in
>>>> TCP level queues or MPTCP ones.
>>>>
>>>> That poses some hard constraints on the sk fields that the helpers can
>>>> access. To make them clear I'm renaming such helpers using an 'xtcp_'
>>>> prefix.
>>>>
>>>> The full patch touching the TCP code is below. For completeness,  the
>>>> whole series is available here:
>>>>
>>>> https://lore.kernel.org/mptcp/cover.1777908248.git.pabeni@redhat.com/T/#me6eda13ec2c70fbb400b6223aa2d07a4fd3bf865
>>>>
>>>> but I guess most of it is not interesting for you/from TCP perspective.
>>>>
>>>> The MPTCP bits are not yet finalized, but I'd like to know it you would
>>>> consider this approach doable or a complete no-go.
>>>
>>> No concerns from my side, if we except the fact that TCP collapses are
>>> a high risk, we might
>>> remove them completely (or at least guard them under a sysctl)
>>
>> I'm sorry I can't follow the above suggestion, could you please rephrase?
>>
>> The patch should not add bugs to TCP collapses for TCP sockets or MPTCP
>> subflows (still tcp_sock). Collapses for MPTCP sockets could become
>> buggy if the tcp_collapse_ofo_queue()/tcp_collapse() implementation will
>> be modified in the future without care.
> 
> I think TCP collapses should be avoided like the plague.
> 
> They were ok 20 years ago, when 'line rate' was 64Kbit :0)

Understood, thanks! It looks like the sysctl is a bit hortogonal to this
patch.

FYI, this work sparked from some TLS-derived self-tests (sending data 1
byte segments with OoO) hitting the collapse condition with MPTCP. I
think a similar test would call for collapses even with plain TCP - the
main difference is that with MPTCP and multiple subflows OoO are
physiological/frequent events.

Thanks,

Paolo

[PATCH v3 mptcp-next 07/10] mptcp: implemented OoO queue pruning

[Paolo Abeni]

Leverage the hybrid helpers to implement the receive queue and OoO queue
collapsing at ingress time when reaching memory bounds.

If the msk is owned by the user-space at incoming skb time, perform the
pruning in the release_cb. The prune check is additionally performed
when the skb reaches the msk-level queues.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3:
 - deal with unsynced TFO skb at prune time - only possible when pruning
   in mptcp_over_limit()

v1 -> v2:
 - collapse rcv queue, too
 - deal with MPC map, too
 - drop left-over sentence in the commit message

RFC -> v1:
 - use data_seq only when available
 - avoid ack_seq lockless access
 - drop limit on fallback
 - collapse rcvqueue, too
 - drop only when pruning is not possible and over rcvbuf * 2
---
 net/mptcp/mib.c      |  3 ++
 net/mptcp/mib.h      |  3 ++
 net/mptcp/options.c  | 42 ++++++++++++++++++++++++---
 net/mptcp/protocol.c | 69 ++++++++++++++++++++++++++++++++++++++++++++
 net/mptcp/protocol.h |  2 ++
 5 files changed, 115 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index f23fda0c55a7..5128feec942c 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -85,6 +85,9 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
 	SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),
 	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
+	SNMP_MIB_ITEM("OfoPruned", MPTCP_MIB_OFO_PRUNED),
+	SNMP_MIB_ITEM("RcvPruned", MPTCP_MIB_RCVPRUNED),
+	SNMP_MIB_ITEM("RcvCollapsed", MPTCP_MIB_RCVCOLLAPSED),
 };
 
 /* mptcp_mib_alloc - allocate percpu mib counters
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 812218b5ed2b..2f8f68e33ac5 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -88,6 +88,9 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_SIMULTCONNFALLBACK,	/* Simultaneous connect */
 	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
 	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
+	MPTCP_MIB_OFO_PRUNED,		/* MPTCP-level OoO queue pruned */
+	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constrains */
+	MPTCP_MIB_RCVCOLLAPSED,		/* Collapsed due to memory pressure */
 	__MPTCP_MIB_MAX
 };
 
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index ad4bb6fd86e1..607451166d77 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1159,8 +1159,12 @@ static bool add_addr_hmac_valid(struct mptcp_sock *msk,
 }
 
 static bool mptcp_over_limit(struct sock *sk, const struct sock *ssk,
-			     const struct sk_buff *skb)
+			     const struct sk_buff *skb,
+			     const struct mptcp_options_received *mp_opt)
 {
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	bool ret;
+
 	if (likely(sk_rmem_alloc_get(sk) <= READ_ONCE(sk->sk_rcvbuf)))
 		return false;
 
@@ -1170,7 +1174,33 @@ static bool mptcp_over_limit(struct sock *sk, const struct sock *ssk,
 	    !after(TCP_SKB_CB(skb)->end_seq, tcp_sk(ssk)->rcv_nxt))
 		return false;
 
-	return true;
+	mptcp_data_lock(sk);
+	if (!sock_owned_by_user(sk)) {
+		/* When the data sequence is not (yet) available for the
+		 * incoming skb, allow pruning the whole OoO queue.
+		 */
+		u32 seq = !mp_opt->use_map || mp_opt->mpc_map ? msk->ack_seq :
+			  mp_opt->data_seq;
+
+		/* Be sure TFO skb sequence number is in-sync, as the
+		 * TCP pruning helper will be badly fouled otherwise.
+		 */
+		if (unlikely(msk->rcvd_dummy_seq))
+			__mptcp_sync_rcv_sequence(sk);
+
+		__mptcp_check_prune(sk, seq);
+		ret = sk_rmem_alloc_get(sk) > READ_ONCE(sk->sk_rcvbuf);
+	} else {
+		u64 limit = ((u64)READ_ONCE(sk->sk_rcvbuf)) << 1;
+
+		/* Pruning will take place later in the RX path, allow
+		 * some extra slack.
+		 */
+		ret = sk_rmem_alloc_get(sk) > limit;
+		__set_bit(MPTCP_PRUNE, &msk->cb_flags);
+	}
+	mptcp_data_unlock(sk);
+	return ret;
 }
 
 /* Return false when the caller must drop the packet, i.e. in case of error,
@@ -1201,7 +1231,11 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 		__mptcp_data_acked(subflow->conn);
 		mptcp_data_unlock(subflow->conn);
 
-		if (mptcp_over_limit(subflow->conn, sk, skb))
+		/* Will use ack_seq as limit for OoO pruning; any value would do
+		 * as OoO queue must be empty.
+		 */
+		mp_opt.use_map = 0;
+		if (mptcp_over_limit(subflow->conn, sk, skb, &mp_opt))
 			return false;
 		return true;
 	}
@@ -1281,7 +1315,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 		return true;
 	}
 
-	if (mptcp_over_limit(subflow->conn, sk, skb))
+	if (mptcp_over_limit(subflow->conn, sk, skb, &mp_opt))
 		return false;
 
 	mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 048d556d75e1..f4015a949f6f 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -386,6 +386,67 @@ void __mptcp_sync_rcv_sequence(struct sock *sk)
 	MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + skb->len;
 }
 
+/* "Inspired" from the TCP version */
+static void mptcp_prune_ofo_queue(struct sock *sk, u32 seq)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct rb_node *node, *prev;
+	bool pruned = false;
+
+	if (RB_EMPTY_ROOT(&msk->out_of_order_queue))
+		return;
+
+	node = &msk->ooo_last_skb->rbnode;
+
+	do {
+		struct sk_buff *skb = rb_to_skb(node);
+
+		/* Stop pruning if the incoming skb would land in OoO tail. */
+		if (after(seq, MPTCP_SKB_CB(skb)->map_seq))
+			break;
+
+		pruned = true;
+		prev = rb_prev(node);
+		rb_erase(node, &msk->out_of_order_queue);
+		mptcp_drop(sk, skb);
+		msk->ooo_last_skb = rb_to_skb(prev);
+		if (atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf)
+			break;
+
+		node = prev;
+	} while (node);
+
+	if (pruned)
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFO_PRUNED);
+}
+
+bool __mptcp_check_prune(struct sock *sk, u32 seq)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	unsigned int dropped;
+
+	if (likely(atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf))
+		return false;
+
+	dropped = xtcp_collapse_ofo_queue(sk, &msk->out_of_order_queue,
+					  &msk->ooo_last_skb,
+					  msk->scaling_ratio);
+	if (!skb_queue_empty(&sk->sk_receive_queue))
+		dropped += xtcp_collapse(sk, &sk->sk_receive_queue, NULL,
+					 skb_peek(&sk->sk_receive_queue),
+					 NULL,
+					 msk->copied_seq, msk->ack_seq,
+					 msk->scaling_ratio);
+
+	if (dropped)
+		MPTCP_ADD_STATS(sock_net(sk), MPTCP_MIB_RCVCOLLAPSED, dropped);
+	if (likely(atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf))
+		return false;
+
+	mptcp_prune_ofo_queue(sk, seq);
+	return atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf;
+}
+
 static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 {
 	u32 copy_len = MPTCP_SKB_CB(skb)->end_seq - MPTCP_SKB_CB(skb)->map_seq;
@@ -400,6 +461,12 @@ static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 	if (unlikely(msk->rcvd_dummy_seq))
 		__mptcp_sync_rcv_sequence(sk);
 
+	if (__mptcp_check_prune(sk, MPTCP_SKB_CB(skb)->map_seq)) {
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
+		mptcp_drop(sk, skb);
+		return false;
+	}
+
 	if (MPTCP_SKB_CB(skb)->map_seq64 == msk->ack_seq) {
 		/* in sequence */
 		msk->bytes_received += copy_len;
@@ -3701,6 +3768,8 @@ static void mptcp_release_cb(struct sock *sk)
 			msk->copied_seq += mptcp_iasn(msk);
 			__mptcp_sync_rcv_sequence(sk);
 		}
+		if (__test_and_clear_bit(MPTCP_PRUNE, &msk->cb_flags))
+			__mptcp_check_prune(sk, msk->ack_seq - 1);
 	}
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 6786da97bbc8..ae019a10e1c8 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -125,6 +125,7 @@
 #define MPTCP_SYNC_STATE	6
 #define MPTCP_SYNC_SNDBUF	7
 #define MPTCP_SYNC_SEQ		8
+#define MPTCP_PRUNE		9
 
 struct mptcp_skb_cb {
 	u32 map_seq;
@@ -832,6 +833,7 @@ bool __mptcp_close(struct sock *sk, long timeout);
 void mptcp_cancel_work(struct sock *sk);
 void __mptcp_unaccepted_force_close(struct sock *sk);
 void mptcp_set_state(struct sock *sk, int state);
+bool __mptcp_check_prune(struct sock *sk, u32 seq);
 
 bool mptcp_addresses_equal(const struct mptcp_addr_info *a,
 			   const struct mptcp_addr_info *b, bool use_port);
-- 
2.54.0

[PATCH v3 mptcp-next 08/10] mptcp: track prune recovery status

[Paolo Abeni]

After dropping any data already acked at the TCP level, the MPTCP must
avoid inducing TCP-level retransmission until the pruned data has been
successfully acked at MPTCP level. Otherwise the subflows could keep
retransmitting skbs carring OoO MPTCP data, preventing reinjections and
stalling completely the data transfer.

Explicitly keep track of the highest pruned MPTCP-level seq number and
stop dropping at TCP level until such sequence has been acked.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/options.c  |  7 ++++++-
 net/mptcp/protocol.c | 14 +++++++++++++-
 net/mptcp/protocol.h |  3 +++
 net/mptcp/subflow.c  |  1 +
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 607451166d77..061116babeff 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1200,7 +1200,12 @@ static bool mptcp_over_limit(struct sock *sk, const struct sock *ssk,
 		__set_bit(MPTCP_PRUNE, &msk->cb_flags);
 	}
 	mptcp_data_unlock(sk);
-	return ret;
+
+	/* After pruning any packets ensure that MPTCP-driven drops do not
+	 * cause TCP-level retransmission
+	 */
+	return ret &&
+	       !before(READ_ONCE(msk->ack_seq), READ_ONCE(msk->pruned_seq));
 }
 
 /* Return false when the caller must drop the packet, i.e. in case of error,
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index f4015a949f6f..2db6d076ce48 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -392,12 +392,14 @@ static void mptcp_prune_ofo_queue(struct sock *sk, u32 seq)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct rb_node *node, *prev;
 	bool pruned = false;
+	u32 pruned_seq;
 
 	if (RB_EMPTY_ROOT(&msk->out_of_order_queue))
 		return;
 
 	node = &msk->ooo_last_skb->rbnode;
 
+	pruned_seq = msk->pruned_seq;
 	do {
 		struct sk_buff *skb = rb_to_skb(node);
 
@@ -408,16 +410,21 @@ static void mptcp_prune_ofo_queue(struct sock *sk, u32 seq)
 		pruned = true;
 		prev = rb_prev(node);
 		rb_erase(node, &msk->out_of_order_queue);
+		if (after(MPTCP_SKB_CB(skb)->end_seq, pruned_seq))
+			pruned_seq = MPTCP_SKB_CB(skb)->end_seq;
 		mptcp_drop(sk, skb);
 		msk->ooo_last_skb = rb_to_skb(prev);
+
 		if (atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf)
 			break;
 
 		node = prev;
 	} while (node);
 
-	if (pruned)
+	if (pruned) {
+		WRITE_ONCE(msk->pruned_seq, pruned_seq);
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFO_PRUNED);
+	}
 }
 
 bool __mptcp_check_prune(struct sock *sk, u32 seq)
@@ -462,6 +469,8 @@ static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb)
 		__mptcp_sync_rcv_sequence(sk);
 
 	if (__mptcp_check_prune(sk, MPTCP_SKB_CB(skb)->map_seq)) {
+		if (after(MPTCP_SKB_CB(skb)->end_seq, msk->pruned_seq))
+			WRITE_ONCE(msk->pruned_seq, MPTCP_SKB_CB(skb)->end_seq);
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RCVPRUNED);
 		mptcp_drop(sk, skb);
 		return false;
@@ -896,6 +905,8 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
 		WRITE_ONCE(msk->ack_seq, msk->ack_seq + seq_delta);
 		moved = true;
 	}
+	if (after(msk->ack_seq, msk->pruned_seq))
+		WRITE_ONCE(msk->pruned_seq, (u32)msk->ack_seq);
 	return moved;
 }
 
@@ -3539,6 +3550,7 @@ static int mptcp_disconnect(struct sock *sk, int flags)
 	/* for fallback's sake */
 	WRITE_ONCE(msk->ack_seq, 0);
 	msk->copied_seq = 0;
+	WRITE_ONCE(msk->pruned_seq, 0);
 
 	WRITE_ONCE(sk->sk_shutdown, 0);
 	sk_error_report(sk);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index ae019a10e1c8..37e3f4c95163 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -307,6 +307,9 @@ struct mptcp_sock {
 	u64		bytes_acked;
 	u64		snd_una;
 	u64		wnd_end;
+	u32		pruned_seq;		/* If above ack_seq, highest
+						 * seq pruned.
+						 */
 	u32		last_data_sent;
 	u32		last_data_recv;
 	u32		last_ack_recv;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 130f9ed7d809..cb55d8808d49 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -496,6 +496,7 @@ static void subflow_set_remote_key(struct mptcp_sock *msk,
 
 	WRITE_ONCE(msk->remote_key, subflow->remote_key);
 	WRITE_ONCE(msk->ack_seq, subflow->iasn);
+	WRITE_ONCE(msk->pruned_seq, subflow->iasn);
 	WRITE_ONCE(msk->can_ack, true);
 	atomic64_set(&msk->rcv_wnd_sent, subflow->iasn);
 
-- 
2.54.0

[PATCH v3 mptcp-next 09/10] mptcp: move the retrans loop to a separate helper

[Paolo Abeni]

This is a cleanup in order to make the next patch simpler.
No functional change intended.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 74 +++++++++++++++++++++++++-------------------
 1 file changed, 43 insertions(+), 31 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 2db6d076ce48..47ad0d776a12 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2838,41 +2838,14 @@ static void mptcp_check_fastclose(struct mptcp_sock *msk)
 	sk_error_report(sk);
 }
 
-static void __mptcp_retrans(struct sock *sk)
+/* Retransmit the specified data fragment on all the selected subflows. */
+static int __mptcp_push_retrans(struct sock *sk, struct mptcp_data_frag *dfrag)
 {
 	struct mptcp_sendmsg_info info = { .data_lock_held = true, };
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct mptcp_subflow_context *subflow;
-	struct mptcp_data_frag *dfrag;
 	struct sock *ssk;
-	int ret, err;
-	u16 len = 0;
-
-	mptcp_clean_una_wakeup(sk);
-
-	/* first check ssk: need to kick "stale" logic */
-	err = mptcp_sched_get_retrans(msk);
-	dfrag = mptcp_rtx_head(sk);
-	if (!dfrag) {
-		if (mptcp_data_fin_enabled(msk)) {
-			struct inet_connection_sock *icsk = inet_csk(sk);
-
-			WRITE_ONCE(icsk->icsk_retransmits,
-				   icsk->icsk_retransmits + 1);
-			mptcp_set_datafin_timeout(sk);
-			mptcp_send_ack(msk);
-
-			goto reset_timer;
-		}
-
-		if (!mptcp_send_head(sk))
-			goto clear_scheduled;
-
-		goto reset_timer;
-	}
-
-	if (err)
-		goto reset_timer;
+	int ret, len = 0;
 
 	mptcp_for_each_subflow(msk, subflow) {
 		if (READ_ONCE(subflow->scheduled)) {
@@ -2900,7 +2873,7 @@ static void __mptcp_retrans(struct sock *sk)
 			    !msk->allow_subflows) {
 				spin_unlock_bh(&msk->fallback_lock);
 				release_sock(ssk);
-				goto clear_scheduled;
+				return -1;
 			}
 
 			while (info.sent < info.limit) {
@@ -2923,6 +2896,45 @@ static void __mptcp_retrans(struct sock *sk)
 			release_sock(ssk);
 		}
 	}
+	return len;
+}
+
+static void __mptcp_retrans(struct sock *sk)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct mptcp_subflow_context *subflow;
+	struct mptcp_data_frag *dfrag;
+	int err, len;
+
+	mptcp_clean_una_wakeup(sk);
+
+	/* first check ssk: need to kick "stale" logic */
+	err = mptcp_sched_get_retrans(msk);
+	dfrag = mptcp_rtx_head(sk);
+	if (!dfrag) {
+		if (mptcp_data_fin_enabled(msk)) {
+			struct inet_connection_sock *icsk = inet_csk(sk);
+
+			WRITE_ONCE(icsk->icsk_retransmits,
+				   icsk->icsk_retransmits + 1);
+			mptcp_set_datafin_timeout(sk);
+			mptcp_send_ack(msk);
+
+			goto reset_timer;
+		}
+
+		if (!mptcp_send_head(sk))
+			goto clear_scheduled;
+
+		goto reset_timer;
+	}
+
+	if (err)
+		goto reset_timer;
+
+	len = __mptcp_push_retrans(sk, dfrag);
+	if (len < 0)
+		goto clear_scheduled;
 
 	msk->bytes_retrans += len;
 	dfrag->already_sent = max(dfrag->already_sent, len);
-- 
2.54.0

[PATCH v3 mptcp-next 10/10] mptcp: let the retrans scheduler do its job.

[Paolo Abeni]

Currently the MPTCP core enforces that when MPTCP-level retrans timer
fires, at most a single dfrag is retransmitted. If some corner-cases it
may be necessary retransmit multiple dfrags, and the MPTCP socket will
need to wait multiple retrans timeout to accomplish that.

Remove the mentioned constraint, allowing to transmit multiple dfrags per
retrans period, as long as the scheduler keeps selecting subflows for
retransmissions and pending data is available in the rtx queue.
The default scheduler will transmit a dfrag per available subflow.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v2 -> v3:
  - fix infinite loop issue (should address tls tests failures)

v1 -> v2:
  - fix retrans sequence update (sashiko)
---
 net/mptcp/protocol.c | 82 ++++++++++++++++++++++++++------------------
 1 file changed, 48 insertions(+), 34 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 47ad0d776a12..032711f9b9dc 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1217,13 +1217,6 @@ static void __mptcp_clean_una_wakeup(struct sock *sk)
 	mptcp_write_space(sk);
 }
 
-static void mptcp_clean_una_wakeup(struct sock *sk)
-{
-	mptcp_data_lock(sk);
-	__mptcp_clean_una_wakeup(sk);
-	mptcp_data_unlock(sk);
-}
-
 static void mptcp_enter_memory_pressure(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow;
@@ -2838,7 +2831,10 @@ static void mptcp_check_fastclose(struct mptcp_sock *msk)
 	sk_error_report(sk);
 }
 
-/* Retransmit the specified data fragment on all the selected subflows. */
+/*
+ * Retransmit the specified data fragment on all the selected subflows,
+ * starting from the specified sequence
+ */
 static int __mptcp_push_retrans(struct sock *sk, struct mptcp_data_frag *dfrag)
 {
 	struct mptcp_sendmsg_info info = { .data_lock_held = true, };
@@ -2904,42 +2900,60 @@ static void __mptcp_retrans(struct sock *sk)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct mptcp_subflow_context *subflow;
 	struct mptcp_data_frag *dfrag;
+	u64 retrans_seq;
 	int err, len;
 
-	mptcp_clean_una_wakeup(sk);
-
-	/* first check ssk: need to kick "stale" logic */
-	err = mptcp_sched_get_retrans(msk);
-	dfrag = mptcp_rtx_head(sk);
-	if (!dfrag) {
-		if (mptcp_data_fin_enabled(msk)) {
-			struct inet_connection_sock *icsk = inet_csk(sk);
+	mptcp_data_lock(sk);
+	__mptcp_clean_una_wakeup(sk);
+	retrans_seq = msk->snd_una;
+	mptcp_data_unlock(sk);
 
-			WRITE_ONCE(icsk->icsk_retransmits,
-				   icsk->icsk_retransmits + 1);
-			mptcp_set_datafin_timeout(sk);
-			mptcp_send_ack(msk);
+	for (;;) {
+		/* first check ssk: need to kick "stale" logic */
+		err = mptcp_sched_get_retrans(msk);
+		dfrag = mptcp_rtx_head(sk);
+		if (!dfrag) {
+			if (mptcp_data_fin_enabled(msk)) {
+				struct inet_connection_sock *icsk;
+
+				icsk = inet_csk(sk);
+				WRITE_ONCE(icsk->icsk_retransmits,
+					   icsk->icsk_retransmits + 1);
+				mptcp_set_datafin_timeout(sk);
+				mptcp_send_ack(msk);
+				break;
+			}
 
-			goto reset_timer;
+			if (!mptcp_send_head(sk))
+				goto clear_scheduled;
+			break;
 		}
 
-		if (!mptcp_send_head(sk))
-			goto clear_scheduled;
-
-		goto reset_timer;
-	}
+		if (err)
+			break;
 
-	if (err)
-		goto reset_timer;
+		/* Skip the data already retransmitted in this run */
+		while (dfrag && !before64(retrans_seq, dfrag->data_seq +
+					  dfrag->data_len))
+			dfrag = list_is_last(&dfrag->list, &msk->rtx_queue) ?
+				NULL : list_next_entry(dfrag, list);
+		if (!dfrag || !dfrag->already_sent)
+			break;
 
-	len = __mptcp_push_retrans(sk, dfrag);
-	if (len < 0)
-		goto clear_scheduled;
+		len = __mptcp_push_retrans(sk, dfrag);
+		if (len < 0)
+			goto clear_scheduled;
 
-	msk->bytes_retrans += len;
-	dfrag->already_sent = max(dfrag->already_sent, len);
+		retrans_seq += len;
+		msk->bytes_retrans += len;
+		dfrag->already_sent = max(dfrag->already_sent, len);
 
-reset_timer:
+		/* Attempt the next fragment only if the current one is
+		 * completely retransmitted.
+		 */
+		if (len < dfrag->data_len)
+			break;
+	}
 	mptcp_check_and_set_pending(sk);
 
 	if (!mptcp_rtx_timer_pending(sk))
-- 
2.54.0

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[MPTCP CI]

Hi Paolo,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal (except selftest_mptcp_join): Success! ✅
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Unstable: 1 failed test(s): packetdrill_sockopts ⚠️ 
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/25329194631

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/4ee2213ed212
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1089374


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Matthieu Baerts]

Hi Geliang, Gang,

On 04/05/2026 17:39, Paolo Abeni wrote:
> This an attempt to fix the data transfer stall reported by Geliang and
> Gang more carefully enforcing memory constraints at the MPTCP level.
> 
> Patch 1/10 moves the bound check before entering the TCP socket.
> Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
> TCP helpers on MPTCP skbs.
> Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
> makes use of them. Patch 8 addresses an edge scenario that could still
> lead to transfer stall under memory pressure.
> Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
> make recovery from memory pressure significanly faster.
> 
> Note that the diffstat is biases by the quite large patch 4/9, which
> contains mechanical transformation of existing code; "real" changes are
> noticiable smaller.
> 
> Tested successfully vs the test cases proposed by Geliang and Gang and
> vs the selftests.

At the last meeting on Wednesday, Geliang mentioned he validated this
series. Just to be sure, was it the v2 -- from last week -- or the v3 --
from this week, while you were in EU -- that you validated? Because
Paolo couldn't reproduce the issue you mentioned on the v3 on his side.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[gang.yan]

May 8, 2026 at 6:49 PM, "Matthieu Baerts" <matttbe@kernel.org mailto:matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel.org%3E > wrote:


> 
> Hi Geliang, Gang,
> 
> On 04/05/2026 17:39, Paolo Abeni wrote:
> 
> > 
> > This an attempt to fix the data transfer stall reported by Geliang and
> >  Gang more carefully enforcing memory constraints at the MPTCP level.
> >  
> >  Patch 1/10 moves the bound check before entering the TCP socket.
> >  Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
> >  TCP helpers on MPTCP skbs.
> >  Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
> >  makes use of them. Patch 8 addresses an edge scenario that could still
> >  lead to transfer stall under memory pressure.
> >  Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
> >  make recovery from memory pressure significanly faster.
> >  
> >  Note that the diffstat is biases by the quite large patch 4/9, which
> >  contains mechanical transformation of existing code; "real" changes are
> >  noticiable smaller.
> >  
> >  Tested successfully vs the test cases proposed by Geliang and Gang and
> >  vs the selftests.
> > 
> At the last meeting on Wednesday, Geliang mentioned he validated this
> series. Just to be sure, was it the v2 -- from last week -- or the v3 --
> from this week, while you were in EU -- that you validated? Because
> Paolo couldn't reproduce the issue you mentioned on the v3 on his side.
> 
Hi, Matt

The issue can also be reproduced on v3. I reproduced it using Docker's
auto-debug mode with the mptcp_data.sh selftest:

‘’‘
	Not running all tests but:

-------- 8< --------
run_loop run_selftest_one mptcp_data.sh
-------- 8< --------




	=== Attempt: 1 (Sat, 09 May 2026 06:55:44 +0000) ===


Selftest Test: ./mptcp_data.sh
TAP version 13
1..1
# add_addr_accepted 4 subflows 4 
# id 1 flags signal 127.0.0.1 10001
# id 2 flags signal 127.0.0.1 10002
# id 3 flags signal 127.0.0.1 10003
# id 4 flags signal 127.0.0.1 10004
# TAP version 13
# 1..48
# # Starting 48 tests from 2 test cases.
# #  RUN           global.mptcp_v6 ...
# #            OK  global.mptcp_v6
# ok 1 global.mptcp_v6
# #  RUN           mptcp.shutdown_reuse ...
# #            OK  mptcp.shutdown_reuse
# ok 2 mptcp.shutdown_reuse
...
# ok 48 mptcp.sendfile
# # FAILED: 41 / 48 tests passed.
# # Totals: pass:41 fail:7 xfail:0 xpass:0 skip:0 error:0
not ok 1 test: selftest_mptcp_data # FAIL
# time=33
’‘’

As Geliang mentioned in the weekly meeting, we will continue
to debug and locate the problem based on Paolo's v3 patches.

We will post any updates to the mailing list once we make
some progess.

Thanks
Gang
> Cheers,
> Matt
> -- 
> Sponsored by the NGI0 Core fund.
>

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Paolo Abeni]

On 5/9/26 9:07 AM, gang.yan@linux.dev wrote:
> May 8, 2026 at 6:49 PM, "Matthieu Baerts" <matttbe@kernel.org mailto:matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel.org%3E > wrote:
>>
>> Hi Geliang, Gang,
>>
>> On 04/05/2026 17:39, Paolo Abeni wrote:
>>
>>>
>>> This an attempt to fix the data transfer stall reported by Geliang and
>>>  Gang more carefully enforcing memory constraints at the MPTCP level.
>>>  
>>>  Patch 1/10 moves the bound check before entering the TCP socket.
>>>  Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely re-using
>>>  TCP helpers on MPTCP skbs.
>>>  Patch 6 makes TCP pruning related helpers available to MPTCP and patch 7
>>>  makes use of them. Patch 8 addresses an edge scenario that could still
>>>  lead to transfer stall under memory pressure.
>>>  Finally patch 9 and 10 improve the MPTCP-level retransmission schema to
>>>  make recovery from memory pressure significanly faster.
>>>  
>>>  Note that the diffstat is biases by the quite large patch 4/9, which
>>>  contains mechanical transformation of existing code; "real" changes are
>>>  noticiable smaller.
>>>  
>>>  Tested successfully vs the test cases proposed by Geliang and Gang and
>>>  vs the selftests.
>>>
>> At the last meeting on Wednesday, Geliang mentioned he validated this
>> series. Just to be sure, was it the v2 -- from last week -- or the v3 --
>> from this week, while you were in EU -- that you validated? Because
>> Paolo couldn't reproduce the issue you mentioned on the v3 on his side.
>>
> Hi, Matt
> 
> The issue can also be reproduced on v3. I reproduced it using Docker's
> auto-debug mode with the mptcp_data.sh selftest:
> 
> ‘’‘
> 	Not running all tests but:
> 
> -------- 8< --------
> run_loop run_selftest_one mptcp_data.sh
> -------- 8< --------
> 
> 
> 
> 
> 	=== Attempt: 1 (Sat, 09 May 2026 06:55:44 +0000) ===
> 
> 
> Selftest Test: ./mptcp_data.sh
> TAP version 13
> 1..1
> # add_addr_accepted 4 subflows 4 
> # id 1 flags signal 127.0.0.1 10001
> # id 2 flags signal 127.0.0.1 10002
> # id 3 flags signal 127.0.0.1 10003
> # id 4 flags signal 127.0.0.1 10004
> # TAP version 13
> # 1..48
> # # Starting 48 tests from 2 test cases.
> # #  RUN           global.mptcp_v6 ...
> # #            OK  global.mptcp_v6
> # ok 1 global.mptcp_v6
> # #  RUN           mptcp.shutdown_reuse ...
> # #            OK  mptcp.shutdown_reuse
> # ok 2 mptcp.shutdown_reuse
> ...
> # ok 48 mptcp.sendfile
> # # FAILED: 41 / 48 tests passed.
> # # Totals: pass:41 fail:7 xfail:0 xpass:0 skip:0 error:0
> not ok 1 test: selftest_mptcp_data # FAIL
> # time=33
> ’‘’
> 
> As Geliang mentioned in the weekly meeting, we will continue
> to debug and locate the problem based on Paolo's v3 patches.

Thanks for testing. I went over a couple more revisions. I run more than
100 iterations successfully on a local build on top of v5 (no failures,
I stop due to time constraints):

https://lore.kernel.org/mptcp/f00bdac0-b544-87b8-2ef4-ca4de0f045de@gmail.com/T/#t

please have a spin as such later version.

Thanks,

Paolo

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Geliang Tang]

Hi Paolo,

On Mon, 2026-05-11 at 10:29 +0200, Paolo Abeni wrote:
> On 5/9/26 9:07 AM, gang.yan@linux.dev wrote:
> > May 8, 2026 at 6:49 PM, "Matthieu Baerts"
> > <matttbe@kernel.org mailto:
> > matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel
> > .org%3E > wrote:
> > > 
> > > Hi Geliang, Gang,
> > > 
> > > On 04/05/2026 17:39, Paolo Abeni wrote:
> > > 
> > > > 
> > > > This an attempt to fix the data transfer stall reported by
> > > > Geliang and
> > > >  Gang more carefully enforcing memory constraints at the MPTCP
> > > > level.
> > > >  
> > > >  Patch 1/10 moves the bound check before entering the TCP
> > > > socket.
> > > >  Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely
> > > > re-using
> > > >  TCP helpers on MPTCP skbs.
> > > >  Patch 6 makes TCP pruning related helpers available to MPTCP
> > > > and patch 7
> > > >  makes use of them. Patch 8 addresses an edge scenario that
> > > > could still
> > > >  lead to transfer stall under memory pressure.
> > > >  Finally patch 9 and 10 improve the MPTCP-level retransmission
> > > > schema to
> > > >  make recovery from memory pressure significanly faster.
> > > >  
> > > >  Note that the diffstat is biases by the quite large patch 4/9,
> > > > which
> > > >  contains mechanical transformation of existing code; "real"
> > > > changes are
> > > >  noticiable smaller.
> > > >  
> > > >  Tested successfully vs the test cases proposed by Geliang and
> > > > Gang and
> > > >  vs the selftests.
> > > > 
> > > At the last meeting on Wednesday, Geliang mentioned he validated
> > > this
> > > series. Just to be sure, was it the v2 -- from last week -- or
> > > the v3 --
> > > from this week, while you were in EU -- that you validated?
> > > Because
> > > Paolo couldn't reproduce the issue you mentioned on the v3 on his
> > > side.
> > > 
> > Hi, Matt
> > 
> > The issue can also be reproduced on v3. I reproduced it using
> > Docker's
> > auto-debug mode with the mptcp_data.sh selftest:
> > 
> > ‘’‘
> > 	Not running all tests but:
> > 
> > -------- 8< --------
> > run_loop run_selftest_one mptcp_data.sh
> > -------- 8< --------
> > 
> > 
> > 
> > 
> > 	=== Attempt: 1 (Sat, 09 May 2026 06:55:44 +0000) ===
> > 
> > 
> > Selftest Test: ./mptcp_data.sh
> > TAP version 13
> > 1..1
> > # add_addr_accepted 4 subflows 4 
> > # id 1 flags signal 127.0.0.1 10001
> > # id 2 flags signal 127.0.0.1 10002
> > # id 3 flags signal 127.0.0.1 10003
> > # id 4 flags signal 127.0.0.1 10004
> > # TAP version 13
> > # 1..48
> > # # Starting 48 tests from 2 test cases.
> > # #  RUN           global.mptcp_v6 ...
> > # #            OK  global.mptcp_v6
> > # ok 1 global.mptcp_v6
> > # #  RUN           mptcp.shutdown_reuse ...
> > # #            OK  mptcp.shutdown_reuse
> > # ok 2 mptcp.shutdown_reuse
> > ...
> > # ok 48 mptcp.sendfile
> > # # FAILED: 41 / 48 tests passed.
> > # # Totals: pass:41 fail:7 xfail:0 xpass:0 skip:0 error:0
> > not ok 1 test: selftest_mptcp_data # FAIL
> > # time=33
> > ’‘’
> > 
> > As Geliang mentioned in the weekly meeting, we will continue
> > to debug and locate the problem based on Paolo's v3 patches.
> 
> Thanks for testing. I went over a couple more revisions. I run more
> than
> 100 iterations successfully on a local build on top of v5 (no
> failures,
> I stop due to time constraints):
> 
> https://lore.kernel.org/mptcp/f00bdac0-b544-87b8-2ef4-ca4de0f045de@gmail.com/T/#t
> 
> please have a spin as such later version.

On v5, mptcp_data.sh works fine in normal mode with the virtme docker
image, but in debug mode it's still unstable - failing after several
loop iterations.

Thanks,
-Geliang

> 
> Thanks,
> 
> Paolo
> 

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Paolo Abeni]

On 5/11/26 1:11 PM, Geliang Tang wrote:
> On Mon, 2026-05-11 at 10:29 +0200, Paolo Abeni wrote:
>> On 5/9/26 9:07 AM, gang.yan@linux.dev wrote:
>>> May 8, 2026 at 6:49 PM, "Matthieu Baerts"
>>> <matttbe@kernel.org mailto:
>>> matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel
>>> .org%3E > wrote:
>>>>
>>>> Hi Geliang, Gang,
>>>>
>>>> On 04/05/2026 17:39, Paolo Abeni wrote:
>>>>
>>>>>
>>>>> This an attempt to fix the data transfer stall reported by
>>>>> Geliang and
>>>>>  Gang more carefully enforcing memory constraints at the MPTCP
>>>>> level.
>>>>>  
>>>>>  Patch 1/10 moves the bound check before entering the TCP
>>>>> socket.
>>>>>  Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely
>>>>> re-using
>>>>>  TCP helpers on MPTCP skbs.
>>>>>  Patch 6 makes TCP pruning related helpers available to MPTCP
>>>>> and patch 7
>>>>>  makes use of them. Patch 8 addresses an edge scenario that
>>>>> could still
>>>>>  lead to transfer stall under memory pressure.
>>>>>  Finally patch 9 and 10 improve the MPTCP-level retransmission
>>>>> schema to
>>>>>  make recovery from memory pressure significanly faster.
>>>>>  
>>>>>  Note that the diffstat is biases by the quite large patch 4/9,
>>>>> which
>>>>>  contains mechanical transformation of existing code; "real"
>>>>> changes are
>>>>>  noticiable smaller.
>>>>>  
>>>>>  Tested successfully vs the test cases proposed by Geliang and
>>>>> Gang and
>>>>>  vs the selftests.
>>>>>
>>>> At the last meeting on Wednesday, Geliang mentioned he validated
>>>> this
>>>> series. Just to be sure, was it the v2 -- from last week -- or
>>>> the v3 --
>>>> from this week, while you were in EU -- that you validated?
>>>> Because
>>>> Paolo couldn't reproduce the issue you mentioned on the v3 on his
>>>> side.
>>>>
>>> Hi, Matt
>>>
>>> The issue can also be reproduced on v3. I reproduced it using
>>> Docker's
>>> auto-debug mode with the mptcp_data.sh selftest:
>>>
>>> ‘’‘
>>> 	Not running all tests but:
>>>
>>> -------- 8< --------
>>> run_loop run_selftest_one mptcp_data.sh
>>> -------- 8< --------
>>>
>>>
>>>
>>>
>>> 	=== Attempt: 1 (Sat, 09 May 2026 06:55:44 +0000) ===
>>>
>>>
>>> Selftest Test: ./mptcp_data.sh
>>> TAP version 13
>>> 1..1
>>> # add_addr_accepted 4 subflows 4 
>>> # id 1 flags signal 127.0.0.1 10001
>>> # id 2 flags signal 127.0.0.1 10002
>>> # id 3 flags signal 127.0.0.1 10003
>>> # id 4 flags signal 127.0.0.1 10004
>>> # TAP version 13
>>> # 1..48
>>> # # Starting 48 tests from 2 test cases.
>>> # #  RUN           global.mptcp_v6 ...
>>> # #            OK  global.mptcp_v6
>>> # ok 1 global.mptcp_v6
>>> # #  RUN           mptcp.shutdown_reuse ...
>>> # #            OK  mptcp.shutdown_reuse
>>> # ok 2 mptcp.shutdown_reuse
>>> ...
>>> # ok 48 mptcp.sendfile
>>> # # FAILED: 41 / 48 tests passed.
>>> # # Totals: pass:41 fail:7 xfail:0 xpass:0 skip:0 error:0
>>> not ok 1 test: selftest_mptcp_data # FAIL
>>> # time=33
>>> ’‘’
>>>
>>> As Geliang mentioned in the weekly meeting, we will continue
>>> to debug and locate the problem based on Paolo's v3 patches.
>>
>> Thanks for testing. I went over a couple more revisions. I run more
>> than
>> 100 iterations successfully on a local build on top of v5 (no
>> failures,
>> I stop due to time constraints):
>>
>> https://lore.kernel.org/mptcp/f00bdac0-b544-87b8-2ef4-ca4de0f045de@gmail.com/T/#t
>>
>> please have a spin as such later version.
> 
> On v5, mptcp_data.sh works fine in normal mode with the virtme docker
> image, but in debug mode it's still unstable - failing after several
> loop iterations.

How many interactions? Can you please provide a sample of such failure?
does the failure always happen in the same way/on the same test case?

Thanks!

Paolo

Re: [PATCH v3 mptcp-next 00/10] mptcp: address stall under memory pressure

[Paolo Abeni]

On 5/11/26 6:35 PM, Paolo Abeni wrote:
> On 5/11/26 1:11 PM, Geliang Tang wrote:
>> On Mon, 2026-05-11 at 10:29 +0200, Paolo Abeni wrote:
>>> On 5/9/26 9:07 AM, gang.yan@linux.dev wrote:
>>>> May 8, 2026 at 6:49 PM, "Matthieu Baerts"
>>>> <matttbe@kernel.org mailto:
>>>> matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel
>>>> .org%3E > wrote:
>>>>>
>>>>> Hi Geliang, Gang,
>>>>>
>>>>> On 04/05/2026 17:39, Paolo Abeni wrote:
>>>>>
>>>>>>
>>>>>> This an attempt to fix the data transfer stall reported by
>>>>>> Geliang and
>>>>>>  Gang more carefully enforcing memory constraints at the MPTCP
>>>>>> level.
>>>>>>  
>>>>>>  Patch 1/10 moves the bound check before entering the TCP
>>>>>> socket.
>>>>>>  Patch 2, 3, 4 and 5 are cleanups/refactors finalized to safely
>>>>>> re-using
>>>>>>  TCP helpers on MPTCP skbs.
>>>>>>  Patch 6 makes TCP pruning related helpers available to MPTCP
>>>>>> and patch 7
>>>>>>  makes use of them. Patch 8 addresses an edge scenario that
>>>>>> could still
>>>>>>  lead to transfer stall under memory pressure.
>>>>>>  Finally patch 9 and 10 improve the MPTCP-level retransmission
>>>>>> schema to
>>>>>>  make recovery from memory pressure significanly faster.
>>>>>>  
>>>>>>  Note that the diffstat is biases by the quite large patch 4/9,
>>>>>> which
>>>>>>  contains mechanical transformation of existing code; "real"
>>>>>> changes are
>>>>>>  noticiable smaller.
>>>>>>  
>>>>>>  Tested successfully vs the test cases proposed by Geliang and
>>>>>> Gang and
>>>>>>  vs the selftests.
>>>>>>
>>>>> At the last meeting on Wednesday, Geliang mentioned he validated
>>>>> this
>>>>> series. Just to be sure, was it the v2 -- from last week -- or
>>>>> the v3 --
>>>>> from this week, while you were in EU -- that you validated?
>>>>> Because
>>>>> Paolo couldn't reproduce the issue you mentioned on the v3 on his
>>>>> side.
>>>>>
>>>> Hi, Matt
>>>>
>>>> The issue can also be reproduced on v3. I reproduced it using
>>>> Docker's
>>>> auto-debug mode with the mptcp_data.sh selftest:
>>>>
>>>> ‘’‘
>>>> 	Not running all tests but:
>>>>
>>>> -------- 8< --------
>>>> run_loop run_selftest_one mptcp_data.sh
>>>> -------- 8< --------
>>>>
>>>>
>>>>
>>>>
>>>> 	=== Attempt: 1 (Sat, 09 May 2026 06:55:44 +0000) ===
>>>>
>>>>
>>>> Selftest Test: ./mptcp_data.sh
>>>> TAP version 13
>>>> 1..1
>>>> # add_addr_accepted 4 subflows 4 
>>>> # id 1 flags signal 127.0.0.1 10001
>>>> # id 2 flags signal 127.0.0.1 10002
>>>> # id 3 flags signal 127.0.0.1 10003
>>>> # id 4 flags signal 127.0.0.1 10004
>>>> # TAP version 13
>>>> # 1..48
>>>> # # Starting 48 tests from 2 test cases.
>>>> # #  RUN           global.mptcp_v6 ...
>>>> # #            OK  global.mptcp_v6
>>>> # ok 1 global.mptcp_v6
>>>> # #  RUN           mptcp.shutdown_reuse ...
>>>> # #            OK  mptcp.shutdown_reuse
>>>> # ok 2 mptcp.shutdown_reuse
>>>> ...
>>>> # ok 48 mptcp.sendfile
>>>> # # FAILED: 41 / 48 tests passed.
>>>> # # Totals: pass:41 fail:7 xfail:0 xpass:0 skip:0 error:0
>>>> not ok 1 test: selftest_mptcp_data # FAIL
>>>> # time=33
>>>> ’‘’
>>>>
>>>> As Geliang mentioned in the weekly meeting, we will continue
>>>> to debug and locate the problem based on Paolo's v3 patches.
>>>
>>> Thanks for testing. I went over a couple more revisions. I run more
>>> than
>>> 100 iterations successfully on a local build on top of v5 (no
>>> failures,
>>> I stop due to time constraints):
>>>
>>> https://lore.kernel.org/mptcp/f00bdac0-b544-87b8-2ef4-ca4de0f045de@gmail.com/T/#t
>>>
>>> please have a spin as such later version.
>>
>> On v5, mptcp_data.sh works fine in normal mode with the virtme docker
>> image, but in debug mode it's still unstable - failing after several
>> loop iterations.
> 
> How many interactions? Can you please provide a sample of such failure?
> does the failure always happen in the same way/on the same test case?

I could reproduce some failures with several iteration in debug build.
Interesting they pointed out to:
- a pre-existing issue (missing wake-up) that deserves a separate patch [1].
- an intrinsic problem with queue collapsing: it's (very) slow and can
slow down the received a lot. I had to raise the timeout (replacing
TEST_F with TEST_F_TIMEOUT) above 300 seconds to complete 600 mptcp_data
runs without errors.

A working alternative to the latter change is avoid entirely the
xtcp_*collapse() stuff. The trade off here is that such option will make
./mptcp_join.sh -R slower (as more mptcp-level retransmissions will be
needed)

I'll try to share somewhat soonish the fix [1].

/P