Commit 3fbb27b7 authored by Matthieu Baerts (NGI0)'s avatar Matthieu Baerts (NGI0) Committed by Jakub Kicinski
Browse files

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: default avatarGeliang Tang <geliang@kernel.org>
Signed-off-by: default avatarMatthieu 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: default avatarJakub Kicinski <kuba@kernel.org>
parent cc84d89a

net/mptcp/pm_netlink.c

+7 −6
Original line number Diff line number Diff line
@@ -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;