[PATCH mptcp-next v2 4/5] Squash to "mptcp: pm: init and release mptcp_pm_ops"

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

From: Gang Yan <yangang@kylinos.cn>

This commit introduces the mptcp_pm_ops lifetime handling on sockets
(mptcp_pm_ops_init/release taking a module reference), and would then
be the first one whose per-net path managers can be unloaded while a
pernet still stores them. Extend the same reference handling to the
pernet level:

  - mptcp_pernet_set_defaults() pins &mptcp_pm_kernel;
  - mptcp_set_path_manager() takes a reference on the new ops and
    releases the one held on the ops it replaces;
  - mptcp_net_exit() releases the last reference.

Depends on the sysctl patches earlier in this series.

Assisted-by: Claude:GLM5.2
Co-developed-by: Tao Cui <cuitao@kylinos.cn>
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 net/mptcp/ctrl.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 733706f06f1b..32268aa26097 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -124,7 +124,9 @@ static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet)
 	pernet->pm_type = MPTCP_PM_TYPE_KERNEL;
 
 	RCU_INIT_POINTER(pernet->scheduler, &mptcp_sched_default);
-	RCU_INIT_POINTER(pernet->path_manager, &mptcp_pm_kernel);
+
+	if (bpf_try_module_get(&mptcp_pm_kernel, mptcp_pm_kernel.owner))
+		RCU_INIT_POINTER(pernet->path_manager, &mptcp_pm_kernel);
 
 	pernet->add_addr_v6_port_drop_ts = 1;
 }
@@ -208,15 +210,22 @@ static int proc_blackhole_detect_timeout(const struct ctl_table *table,
 
 static int mptcp_set_path_manager(struct mptcp_pernet *pernet, const char *name)
 {
-	struct mptcp_pm_ops *pm_ops;
+	struct mptcp_pm_ops *pm_ops, *prev;
 	int ret = 0;
 
 	rcu_read_lock();
 	pm_ops = mptcp_pm_find(name);
-	if (pm_ops)
-		xchg(&pernet->path_manager, pm_ops);
-	else
+	if (pm_ops) {
+		if (bpf_try_module_get(pm_ops, pm_ops->owner)) {
+			prev = xchg(&pernet->path_manager, pm_ops);
+			if (prev)
+				bpf_module_put(prev, prev->owner);
+		} else {
+			ret = -EBUSY;
+		}
+	} else {
 		ret = -ENOENT;
+	}
 	rcu_read_unlock();
 
 	return ret;
@@ -594,8 +603,13 @@ static int __net_init mptcp_net_init(struct net *net)
 static void __net_exit mptcp_net_exit(struct net *net)
 {
 	struct mptcp_pernet *pernet = mptcp_get_pernet(net);
+	struct mptcp_pm_ops *pm;
 
 	mptcp_pernet_del_table(pernet);
+
+	pm = rcu_dereference_protected(pernet->path_manager, true);
+	if (pm)
+		bpf_module_put(pm, pm->owner);
 }
 
 static struct pernet_operations mptcp_pernet_ops = {
-- 
2.43.0