1 files changed, 18 insertions, 6 deletions

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index d67add91c9b90..7e637f468065c 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -334,6 +334,10 @@ struct mptcp_sock {
 	u32		subflow_id;
 	u32		setsockopt_seq;
 	char		ca_name[TCP_CA_NAME_MAX];
+
+	spinlock_t	fallback_lock;	/* protects fallback and
+					 * allow_infinite_fallback
+					 */
 };
 
 #define mptcp_data_lock(sk) spin_lock_bh(&(sk)->sk_lock.slock)
@@ -1097,25 +1101,32 @@ static inline bool mptcp_check_fallback(const struct sock *sk)
 	return __mptcp_check_fallback(msk);
 }
 
-static inline void __mptcp_do_fallback(struct mptcp_sock *msk)
+static inline bool __mptcp_try_fallback(struct mptcp_sock *msk)
 {
 	if (test_bit(MPTCP_FALLBACK_DONE, &msk->flags)) {
 		pr_debug("TCP fallback already done (msk=%p)\n", msk);
-		return;
+		return true;
 	}
-	if (WARN_ON_ONCE(!READ_ONCE(msk->allow_infinite_fallback)))
-		return;
+	spin_lock_bh(&msk->fallback_lock);
+	if (!msk->allow_infinite_fallback) {
+		spin_unlock_bh(&msk->fallback_lock);
+		return false;
+	}
+
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
+	spin_unlock_bh(&msk->fallback_lock);
+	return true;
 }
 
-static inline void mptcp_do_fallback(struct sock *ssk)
+static inline bool mptcp_try_fallback(struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	struct sock *sk = subflow->conn;
 	struct mptcp_sock *msk;
 
 	msk = mptcp_sk(sk);
-	__mptcp_do_fallback(msk);
+	if (!__mptcp_try_fallback(msk))
+		return false;
 	if (READ_ONCE(msk->snd_data_fin_enable) && !(ssk->sk_shutdown & SEND_SHUTDOWN)) {
 		gfp_t saved_allocation = ssk->sk_allocation;
 
@@ -1127,6 +1138,7 @@ static inline void mptcp_do_fallback(struct sock *ssk)
 		tcp_shutdown(ssk, SEND_SHUTDOWN);
 		ssk->sk_allocation = saved_allocation;
 	}
+	return true;
 }
 
 #define pr_fallback(a) pr_debug("%s:fallback to TCP (msk=%p)\n", __func__, a)