[mptcp-net] mptcp: pm: Defer freeing of MPTCP userspace path manager entries

[Mat Martineau <martineau@kernel.org>]

When path manager entries are deleted from the local address list, they
are first unlinked from the address list using list_del_rcu(). The
entries must not be freed until after the RCU grace period, but the
existing code immediately frees the entry.

Use kfree_rcu_mightsleep() and adjust sk_omem_alloc in open code instead
of using the sock_kfree_s() helper. This code path is only called in a
netlink handler, so the "might sleep" function is preferable to adding
a rarely-used rcu_head member to struct mptcp_pm_addr_entry.

Signed-off-by: Mat Martineau <martineau@kernel.org>
---

My first implementation did add a sock_kfree_rcu_s() function like
Geliang suggested, but kfree_rcu() is a macro so that approach got
complicated. sock_kfree_rcu_s_mightsleep() seemed cumbersome, so I went
ahead and open-coded it. This should be applied after Geliang's v2,
which will delete similar code in a helper function.

---
 net/mptcp/pm_userspace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 7fc19b844384..959af1e42a97 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -337,7 +337,8 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
 
 	release_sock(sk);
 
-	sock_kfree_s(sk, match, sizeof(*match));
+	kfree_rcu_mightsleep(match);
+	atomic_sub(sizeof(*match), &sk->sk_omem_alloc);
 
 	err = 0;
 out:
-- 
2.49.0