[PATCH mptcp-next v2] mptcp: pm: exit early with ADD_ADDR echo if possible

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

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) <matttbe@kernel.org>
---
Changes in v2:
- Link to v1: https://lore.kernel.org/r/20250224-mptcp-userspace-avoid-worker-v1-1-127325d3e9a4@kernel.org
---
Notes:
- v2:
  - Only modify mptcp_pm_add_addr_echoed().
  - The rest doesn't need to or shouldn't be modified (Geliang).
Cc: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/pm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index 16cacce6c10fe86467aa7ef8e588f9f535b586fb..6c8cadf84f31f4c7dcc38b787beda048d5362dc8 100644
--- a/net/mptcp/pm.c
+++ b/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))

---
base-commit: 1238896935ea03f333a183a32fab666cc0c20e3b
change-id: 20250224-mptcp-userspace-avoid-worker-93f367e39ca6

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>