mptcp: pm: lockless list traversal to dump endp

To return an endpoint to the userspace via Netlink, and to dump all of
them, the endpoint list was iterated while holding the pernet->lock, but
only to read the content of the list.

In these cases, the spin locks can be replaced by RCU read ones, and use
the _rcu variants to iterate over the entries list in a lockless way.

Note that the __lookup_addr_by_id() helper has been modified to use the
_rcu variants of list_for_each_entry(), but with an extra conditions, so
it can be called either while the RCU read lock is held, or when the
associated pernet->lock is held.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20241115-net-next-mptcp-pm-lockless-dump-v1-1-f4a1bcb4ca2c@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 758a0db..2b005dd 100644 (file)
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -512,7 +512,8 @@ __lookup_addr_by_id(struct pm_nl_pernet *pernet, unsigned int id)
 {
        struct mptcp_pm_addr_entry *entry;
 
-       list_for_each_entry(entry, &pernet->local_addr_list, list) {
+       list_for_each_entry_rcu(entry, &pernet->local_addr_list, list,
+                               lockdep_is_held(&pernet->lock)) {
                if (entry->addr.id == id)
                        return entry;
        }
@@ -1824,7 +1825,7 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
                goto fail;
        }
 
-       spin_lock_bh(&pernet->lock);
+       rcu_read_lock();
        entry = __lookup_addr_by_id(pernet, addr.addr.id);
        if (!entry) {
                GENL_SET_ERR_MSG(info, "address not found");
@@ -1838,11 +1839,11 @@ int mptcp_pm_nl_get_addr(struct sk_buff *skb, struct genl_info *info)
 
        genlmsg_end(msg, reply);
        ret = genlmsg_reply(msg, info);
-       spin_unlock_bh(&pernet->lock);
+       rcu_read_unlock();
        return ret;
 
 unlock_fail:
-       spin_unlock_bh(&pernet->lock);
+       rcu_read_unlock();
 
 fail:
        nlmsg_free(msg);
@@ -1866,7 +1867,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
 
        pernet = pm_nl_get_pernet(net);
 
-       spin_lock_bh(&pernet->lock);
+       rcu_read_lock();
        for (i = id; i < MPTCP_PM_MAX_ADDR_ID + 1; i++) {
                if (test_bit(i, pernet->id_bitmap)) {
                        entry = __lookup_addr_by_id(pernet, i);
@@ -1891,7 +1892,7 @@ int mptcp_pm_nl_dump_addr(struct sk_buff *msg,
                        genlmsg_end(msg, hdr);
                }
        }
-       spin_unlock_bh(&pernet->lock);
+       rcu_read_unlock();
 
        cb->args[0] = id;
        return msg->len;