Re: [PATCHv6 net-next 03/14] ipvs: some service readers can use RCU

[Dust Li <dust.li@linux.alibaba.com>]

On 2025-10-19 18:57:00, Julian Anastasov wrote:
>Some places walk the services under mutex but they can just use RCU:
>
>* ip_vs_dst_event() uses ip_vs_forget_dev() which uses its own lock
>  to modify dest
>* ip_vs_genl_dump_services(): ip_vs_genl_fill_service() just fills skb
>* ip_vs_genl_parse_service(): move RCU lock to callers
>  ip_vs_genl_set_cmd(), ip_vs_genl_dump_dests() and ip_vs_genl_get_cmd()
>* ip_vs_genl_dump_dests(): just fill skb
>
>Signed-off-by: Julian Anastasov <ja@ssi.bg>

Reviewed-by: Dust Li <dust.li@linux.alibaba.com>

Best regards,
Dust


>---
> net/netfilter/ipvs/ip_vs_ctl.c | 47 +++++++++++++++++-----------------
> 1 file changed, 23 insertions(+), 24 deletions(-)
>
>diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
>index 2fb9034b4f53..b18d08d79bcb 100644
>--- a/net/netfilter/ipvs/ip_vs_ctl.c
>+++ b/net/netfilter/ipvs/ip_vs_ctl.c
>@@ -1759,23 +1759,21 @@ static int ip_vs_dst_event(struct notifier_block *this, unsigned long event,
> 	if (event != NETDEV_DOWN || !ipvs)
> 		return NOTIFY_DONE;
> 	IP_VS_DBG(3, "%s() dev=%s\n", __func__, dev->name);
>-	mutex_lock(&ipvs->service_mutex);
>+	rcu_read_lock();
> 	for (idx = 0; idx < IP_VS_SVC_TAB_SIZE; idx++) {
>-		hlist_for_each_entry(svc, &ipvs->svc_table[idx], s_list) {
>-			list_for_each_entry(dest, &svc->destinations,
>-					    n_list) {
>+		hlist_for_each_entry_rcu(svc, &ipvs->svc_table[idx], s_list)
>+			list_for_each_entry_rcu(dest, &svc->destinations,
>+						n_list)
> 				ip_vs_forget_dev(dest, dev);
>-			}
>-		}
> 
>-		hlist_for_each_entry(svc, &ipvs->svc_fwm_table[idx], f_list) {
>-			list_for_each_entry(dest, &svc->destinations,
>-					    n_list) {
>+		hlist_for_each_entry_rcu(svc, &ipvs->svc_fwm_table[idx], f_list)
>+			list_for_each_entry_rcu(dest, &svc->destinations,
>+						n_list)
> 				ip_vs_forget_dev(dest, dev);
>-			}
>-		}
> 	}
>+	rcu_read_unlock();
> 
>+	mutex_lock(&ipvs->service_mutex);
> 	spin_lock_bh(&ipvs->dest_trash_lock);
> 	list_for_each_entry(dest, &ipvs->dest_trash, t_list) {
> 		ip_vs_forget_dev(dest, dev);
>@@ -3318,9 +3316,9 @@ static int ip_vs_genl_fill_service(struct sk_buff *skb,
> 			goto nla_put_failure;
> 	}
> 
>-	sched = rcu_dereference_protected(svc->scheduler, 1);
>+	sched = rcu_dereference(svc->scheduler);
> 	sched_name = sched ? sched->name : "none";
>-	pe = rcu_dereference_protected(svc->pe, 1);
>+	pe = rcu_dereference(svc->pe);
> 	if (nla_put_string(skb, IPVS_SVC_ATTR_SCHED_NAME, sched_name) ||
> 	    (pe && nla_put_string(skb, IPVS_SVC_ATTR_PE_NAME, pe->name)) ||
> 	    nla_put(skb, IPVS_SVC_ATTR_FLAGS, sizeof(flags), &flags) ||
>@@ -3374,9 +3372,9 @@ static int ip_vs_genl_dump_services(struct sk_buff *skb,
> 	struct net *net = sock_net(skb->sk);
> 	struct netns_ipvs *ipvs = net_ipvs(net);
> 
>-	mutex_lock(&ipvs->service_mutex);
>+	rcu_read_lock();
> 	for (i = 0; i < IP_VS_SVC_TAB_SIZE; i++) {
>-		hlist_for_each_entry(svc, &ipvs->svc_table[i], s_list) {
>+		hlist_for_each_entry_rcu(svc, &ipvs->svc_table[i], s_list) {
> 			if (++idx <= start)
> 				continue;
> 			if (ip_vs_genl_dump_service(skb, svc, cb) < 0) {
>@@ -3387,7 +3385,7 @@ static int ip_vs_genl_dump_services(struct sk_buff *skb,
> 	}
> 
> 	for (i = 0; i < IP_VS_SVC_TAB_SIZE; i++) {
>-		hlist_for_each_entry(svc, &ipvs->svc_fwm_table[i], f_list) {
>+		hlist_for_each_entry_rcu(svc, &ipvs->svc_fwm_table[i], f_list) {
> 			if (++idx <= start)
> 				continue;
> 			if (ip_vs_genl_dump_service(skb, svc, cb) < 0) {
>@@ -3398,7 +3396,7 @@ static int ip_vs_genl_dump_services(struct sk_buff *skb,
> 	}
> 
> nla_put_failure:
>-	mutex_unlock(&ipvs->service_mutex);
>+	rcu_read_unlock();
> 	cb->args[0] = idx;
> 
> 	return skb->len;
>@@ -3454,13 +3452,11 @@ static int ip_vs_genl_parse_service(struct netns_ipvs *ipvs,
> 		usvc->fwmark = 0;
> 	}
> 
>-	rcu_read_lock();
> 	if (usvc->fwmark)
> 		svc = __ip_vs_svc_fwm_find(ipvs, usvc->af, usvc->fwmark);
> 	else
> 		svc = __ip_vs_service_find(ipvs, usvc->af, usvc->protocol,
> 					   &usvc->addr, usvc->port);
>-	rcu_read_unlock();
> 	*ret_svc = svc;
> 
> 	/* If a full entry was requested, check for the additional fields */
>@@ -3587,7 +3583,7 @@ static int ip_vs_genl_dump_dests(struct sk_buff *skb,
> 	struct net *net = sock_net(skb->sk);
> 	struct netns_ipvs *ipvs = net_ipvs(net);
> 
>-	mutex_lock(&ipvs->service_mutex);
>+	rcu_read_lock();
> 
> 	/* Try to find the service for which to dump destinations */
> 	if (nlmsg_parse_deprecated(cb->nlh, GENL_HDRLEN, attrs, IPVS_CMD_ATTR_MAX, ip_vs_cmd_policy, cb->extack))
>@@ -3599,7 +3595,7 @@ static int ip_vs_genl_dump_dests(struct sk_buff *skb,
> 		goto out_err;
> 
> 	/* Dump the destinations */
>-	list_for_each_entry(dest, &svc->destinations, n_list) {
>+	list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
> 		if (++idx <= start)
> 			continue;
> 		if (ip_vs_genl_dump_dest(skb, dest, cb) < 0) {
>@@ -3612,7 +3608,7 @@ static int ip_vs_genl_dump_dests(struct sk_buff *skb,
> 	cb->args[0] = idx;
> 
> out_err:
>-	mutex_unlock(&ipvs->service_mutex);
>+	rcu_read_unlock();
> 
> 	return skb->len;
> }
>@@ -3915,9 +3911,12 @@ static int ip_vs_genl_set_cmd(struct sk_buff *skb, struct genl_info *info)
> 	if (cmd == IPVS_CMD_NEW_SERVICE || cmd == IPVS_CMD_SET_SERVICE)
> 		need_full_svc = true;
> 
>+	/* We use function that requires RCU lock */
>+	rcu_read_lock();
> 	ret = ip_vs_genl_parse_service(ipvs, &usvc,
> 				       info->attrs[IPVS_CMD_ATTR_SERVICE],
> 				       need_full_svc, &svc);
>+	rcu_read_unlock();
> 	if (ret)
> 		goto out;
> 
>@@ -4037,7 +4036,7 @@ static int ip_vs_genl_get_cmd(struct sk_buff *skb, struct genl_info *info)
> 	if (!msg)
> 		return -ENOMEM;
> 
>-	mutex_lock(&ipvs->service_mutex);
>+	rcu_read_lock();
> 
> 	reply = genlmsg_put_reply(msg, info, &ip_vs_genl_family, 0, reply_cmd);
> 	if (reply == NULL)
>@@ -4105,7 +4104,7 @@ static int ip_vs_genl_get_cmd(struct sk_buff *skb, struct genl_info *info)
> out_err:
> 	nlmsg_free(msg);
> out:
>-	mutex_unlock(&ipvs->service_mutex);
>+	rcu_read_unlock();
> 
> 	return ret;
> }
>-- 
>2.51.0
>