mptcp: pm: exit early with ADD_ADDR echo if possible

When the userspace PM is used, or when the in-kernel limits are reached,
there will be no need to schedule the PM worker to signal new addresses.
That corresponds to pm->work_pending set to 0.

In this case, an early exit can be done in mptcp_pm_add_addr_echoed()
not to hold the PM lock, and iterate over the announced addresses list,
not to schedule the worker anyway in this case. This is similar to what
is done when a connection or a subflow has been established.

Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

Author: matttbe

net/mptcp/pm.c

@@ -251,6 +251,9 @@ void mptcp_pm_add_addr_echoed(struct mptcp_sock *msk,
 
 	pr_debug("msk=%p\n", msk);
 
+	if (!READ_ONCE(pm->work_pending))
+		return;
+
 	spin_lock_bh(&pm->lock);
 
 	if (mptcp_lookup_anno_list_by_saddr(msk, addr) && READ_ONCE(pm->work_pending))