This allows invoking an additional callback under the
socket spin lock.

Will be used by the next patches to avoid additional
spin lock contention

Signed-off-by: Paolo Abeni <pabeni(a)redhat.com>
---
 net/core/sock.c      |  2 +-
 net/mptcp/protocol.h | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 727ea1cc633c..89ee8582bf01 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2486,7 +2486,7 @@ bool sk_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
 }
 EXPORT_SYMBOL(sk_page_frag_refill);
 
-static void __lock_sock(struct sock *sk)
+void __lock_sock(struct sock *sk)
 	__releases(&sk->sk_lock.slock)
 	__acquires(&sk->sk_lock.slock)
 {
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 82d5626323b1..e9f553993322 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -253,6 +253,21 @@ struct mptcp_sock {
 	} rcvq_space;
 };
 
+void __lock_sock(struct sock *sk);
+
+#define mptcp_lock_sock(___sk, cb) do {					\
+	struct sock *__sk = (___sk); /* silence macro reuse warning */	\
+	might_sleep();							\
+	spin_lock_bh(&__sk->sk_lock.slock);				\
+	if (__sk->sk_lock.owned)					\
+		__lock_sock(__sk);					\
+	cb;								\
+	__sk->sk_lock.owned = 1;					\
+	spin_unlock(&__sk->sk_lock.slock);				\
+	mutex_acquire(&__sk->sk_lock.dep_map, 0, 0, _RET_IP_);		\
+	local_bh_enable();						\
+} while (0)
+
 #define mptcp_for_each_subflow(__msk, __subflow)			\
 	list_for_each_entry(__subflow, &((__msk)->conn_list), node)
 
-- 
2.26.2