[PATCH 5.15 358/917] mptcp: do not shrink snd_nxt when recovering

Greg Kroah-Hartman
2021-11-15T23:37:56Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit 0d199e4363b482badcedba764e2aceab53a4a10a ]

When recovering after a link failure, snd_nxt should not be set to a
lower value. Else, update of snd_nxt is broken because:

msk->snd_nxt += ret; (where ret is number of bytes sent)

assumes that snd_nxt always moves forward.
After reduction, its possible that snd_nxt update gets out of sync:
dfrag we just sent might have had a data sequence number even past
recovery_snd_nxt.

This change factors the common msk state update to a helper
and updates snd_nxt based on the current dfrag data sequence number.

The conditional is required for the recovery phase where we may
re-transmit old dfrags that are before current snd_nxt.

After this change, snd_nxt only moves forward and covers all in-sequence
data that was transmitted.

recovery_snd_nxt is retained to detect when recovery has completed.

Fixes: 1e1d9d6f119c5 ("mptcp: handle pending data on closed subflow")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/mptcp/options.c | 8 +++-----
net/mptcp/protocol.c | 43 +++++++++++++++++++++++++++++++------------
2 files changed, 34 insertions(+), 17 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index f0f22eb4fd5f7..350348f070700 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1019,11 +1019,9 @@ static void ack_update_msk(struct mptcp_sock *msk,
old_snd_una = msk->snd_una;
new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);

- /* ACK for data not even sent yet and even above recovery bound? Ignore.*/
- if (unlikely(after64(new_snd_una, snd_nxt))) {
- if (!msk->recovery || after64(new_snd_una, msk->recovery_snd_nxt))
- new_snd_una = old_snd_una;
- }
+ /* ACK for data not even sent yet? Ignore.*/
+ if (unlikely(after64(new_snd_una, snd_nxt)))
+ new_snd_una = old_snd_una;

new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d073b21113828..4379d69aead7e 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1505,6 +1505,32 @@ static void mptcp_push_release(struct sock *sk, struct sock *ssk,
release_sock(ssk);
}

+static void mptcp_update_post_push(struct mptcp_sock *msk,
+ struct mptcp_data_frag *dfrag,
+ u32 sent)
+{
+ u64 snd_nxt_new = dfrag->data_seq;
+
+ dfrag->already_sent += sent;
+
+ msk->snd_burst -= sent;
+ msk->tx_pending_data -= sent;
+
+ snd_nxt_new += dfrag->already_sent;
+
+ /* snd_nxt_new can be smaller than snd_nxt in case mptcp
+ * is recovering after a failover. In that event, this re-sends
+ * old segments.
+ *
+ * Thus compute snd_nxt_new candidate based on
+ * the dfrag->data_seq that was sent and the data
+ * that has been handed to the subflow for transmission
+ * and skip update in case it was old dfrag.
+ */
+ if (likely(after64(snd_nxt_new, msk->snd_nxt)))
+ msk->snd_nxt = snd_nxt_new;
+}
+
void __mptcp_push_pending(struct sock *sk, unsigned int flags)
{
struct sock *prev_ssk = NULL, *ssk = NULL;
@@ -1548,12 +1574,10 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
}

info.sent += ret;
- dfrag->already_sent += ret;
- msk->snd_nxt += ret;
- msk->snd_burst -= ret;
- msk->tx_pending_data -= ret;
copied += ret;
len -= ret;
+
+ mptcp_update_post_push(msk, dfrag, ret);
}
WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
}
@@ -1606,13 +1630,11 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
goto out;

info.sent += ret;
- dfrag->already_sent += ret;
- msk->snd_nxt += ret;
- msk->snd_burst -= ret;
- msk->tx_pending_data -= ret;
copied += ret;
len -= ret;
first = false;
+
+ mptcp_update_post_push(msk, dfrag, ret);
}
WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
}
@@ -2183,15 +2205,12 @@ bool __mptcp_retransmit_pending_data(struct sock *sk)
return false;
}

- /* will accept ack for reijected data before re-sending them */
- if (!msk->recovery || after64(msk->snd_nxt, msk->recovery_snd_nxt))
- msk->recovery_snd_nxt = msk->snd_nxt;
+ msk->recovery_snd_nxt = msk->snd_nxt;
msk->recovery = true;
mptcp_data_unlock(sk);

msk->first_pending = rtx_head;
msk->tx_pending_data += msk->snd_nxt - rtx_head->data_seq;
- msk->snd_nxt = rtx_head->data_seq;
msk->snd_burst = 0;

/* be sure to clear the "sent status" on all re-injected fragments */
--
2.33.0