[MPTCP] [PATCH mptcp-next 1/1] mptcp: fix stale subflow->writeable caching

[MPTCP] [PATCH mptcp-next 1/1] mptcp: fix stale subflow->writeable caching

[Florian Westphal]

[-- Attachment #1: Type: text/plain, Size: 1237 bytes --]

Even with fixed subflow_write_space(), we may still indicate EPOLLOUT
even if no subflow is writeable.

We need to re-check the last ssk that was used after the final tcp_push().
tcp_push() can allocate new skbs that get charged to the subflow sk
which may bring it above the wmem limit.

Signed-off-by: Florian Westphal <fw(a)strlen.de>
---
 net/mptcp/protocol.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ad91f4588216..4dd5d35a8f39 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1239,7 +1239,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		msk->snd_burst -= ret;
 		copied += ret;
 
-		if (!sk_stream_memory_free(ssk))
+		if (!sk_stream_is_writeable(ssk))
 			WRITE_ONCE(subflow->writable, false);
 
 		tx_ok = msg_data_left(msg);
@@ -1294,6 +1294,9 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		/* start the timer, if it's not pending */
 		if (!mptcp_timer_pending(sk))
 			mptcp_reset_timer(sk);
+
+		if (!sk_stream_is_writeable(ssk))
+			WRITE_ONCE(mptcp_subflow_ctx(ssk)->writable, false);
 	}
 
 	release_sock(ssk);
-- 
2.26.2