netdev - Re: [PATCH net-next] phonet: no longer hold RTNL in route

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Message-ID: <4256876.Znljf6yrvc@basile.remlab.net>
Date: Mon, 06 May 2024 20:23:23 +0300
From: Rémi Denis-Courmont <remi@...lab.net>
To: "David S . Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com,
 Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] phonet: no longer hold RTNL in route_dumpit()

Le maanantaina 6. toukokuuta 2024, 15.11.56 EEST Eric Dumazet a écrit :
> route_dumpit() already relies on RCU, RTNL is not needed.
> 
> Also change return value at the end of a dump.
> This allows NLMSG_DONE to be appended to the current
> skb at the end of a dump, saving a couple of recvmsg()
> system calls.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Remi Denis-Courmont <courmisch@...il.com>

No objections from me, but TBH I am not familiar with the underlying RTNL 
locking so my ack wouldn't be worth anything.

> ---
>  net/phonet/pn_netlink.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
> index
> 59aebe29689077bfa77d37516aea4617fe3b8a50..c11764ff72d6ac86e643123e2c49de6f0
> 758bf97 100644 --- a/net/phonet/pn_netlink.c
> +++ b/net/phonet/pn_netlink.c
> @@ -178,7 +178,7 @@ static int fill_route(struct sk_buff *skb, struct
> net_device *dev, u8 dst, rtm->rtm_type = RTN_UNICAST;
>  	rtm->rtm_flags = 0;
>  	if (nla_put_u8(skb, RTA_DST, dst) ||
> -	    nla_put_u32(skb, RTA_OIF, dev->ifindex))
> +	    nla_put_u32(skb, RTA_OIF, READ_ONCE(dev->ifindex)))
>  		goto nla_put_failure;
>  	nlmsg_end(skb, nlh);
>  	return 0;
> @@ -263,6 +263,7 @@ static int route_doit(struct sk_buff *skb, struct
> nlmsghdr *nlh, static int route_dumpit(struct sk_buff *skb, struct
> netlink_callback *cb) {
>  	struct net *net = sock_net(skb->sk);
> +	int err = 0;
>  	u8 addr;
> 
>  	rcu_read_lock();
> @@ -272,16 +273,16 @@ static int route_dumpit(struct sk_buff *skb, struct
> netlink_callback *cb) if (!dev)
>  			continue;
> 
> -		if (fill_route(skb, dev, addr << 2, NETLINK_CB(cb-
>skb).portid,
> -			       cb->nlh->nlmsg_seq, RTM_NEWROUTE) < 
0)
> -			goto out;
> +		err = fill_route(skb, dev, addr << 2,
> +				 NETLINK_CB(cb->skb).portid,
> +				 cb->nlh->nlmsg_seq, 
RTM_NEWROUTE);
> +		if (err < 0)
> +			break;;
>  	}
> -
> -out:
>  	rcu_read_unlock();
>  	cb->args[0] = addr;
> 
> -	return skb->len;
> +	return err;
>  }
> 
>  int __init phonet_netlink_register(void)
> @@ -301,6 +302,6 @@ int __init phonet_netlink_register(void)
>  	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_DELROUTE,
>  			     route_doit, NULL, 0);
>  	rtnl_register_module(THIS_MODULE, PF_PHONET, RTM_GETROUTE,
> -			     NULL, route_dumpit, 0);
> +			     NULL, route_dumpit, 
RTNL_FLAG_DUMP_UNLOCKED);
>  	return 0;
>  }


-- 
Rémi Denis-Courmont
http://www.remlab.net/