[PATCH mptcp-net v4 4/5] mptcp: fix the dead_loack in mptcp_data_ready

[Gang Yan <gang.yan@linux.dev>]

From: Gang Yan <yangang@kylinos.cn>

This patch defers mptcp_check_data_fin from __mptcp_move_skbs to avoid
deadlock.

When processing backlogged data in softirq context, __mptcp_move_skbs
directly calls mptcp_check_data_fin, which can lead to a deadlock if
the msk socket is in TCP_FIN_WAIT2 state. In that case,
mptcp_check_data_fin calls mptcp_shutdown_subflows, which attempts to
lock the subflow socket with lock_sock_fast() - a sleeping function
that cannot be called in atomic context (softirq).

The correct pattern is already used in move_skbs_to_msk: if a data fin
is pending, schedule the work to be processed later in process context
rather than handling it directly.

Reported-by: Geliang Tang <geliang@kernel.org>
Co-developed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 net/mptcp/protocol.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 16c5dcab8982..872022f4796b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2247,8 +2247,12 @@ static bool __mptcp_move_skbs(struct sock *sk, struct list_head *skbs, u32 *delt
 	}
 
 	__mptcp_ofo_queue(msk);
-	if (moved)
-		mptcp_check_data_fin((struct sock *)msk);
+	if (moved) {
+		if (mptcp_pending_data_fin(sk, NULL))
+			mptcp_schedule_work(sk);
+		else
+			mptcp_check_data_fin(sk);
+	}
 	return moved;
 }
 
-- 
2.43.0