Re: [PATCH net-next v2 4/8] net: ipv4: Convert inet_rtm_getroute to rcu versions of route lookup

[David Ahern]

On 5/31/17 2:11 PM, John Fastabend wrote:
>> @@ -2721,14 +2724,14 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, 
>> struct nlmsghdr *nlh,
>>              skb->protocol   = htons(ETH_P_IP);
>>              skb->dev        = dev;
>>              skb->mark       = mark;
>> -            err = ip_route_input(skb, dst, src, rtm->rtm_tos, dev);
>> +            err = ip_route_input_rcu(skb, dst, src, rtm->rtm_tos,
>> +                                     dev, &res);
>>  
>>              rt = skb_rtable(skb);
>>              if (err == 0 && rt->dst.error)
>>                      err = -rt->dst.error;
>>      } else {
>> -            rt = ip_route_output_key(net, &fl4);
>> -
>> +            rt = ip_route_output_key_hash_rcu(net, &fl4, &res, skb);
>>              err = 0;
>>              if (IS_ERR(rt))
>>                      err = PTR_ERR(rt);
>> @@ -2737,7 +2740,6 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, 
>> struct nlmsghdr *nlh,
>>      if (err)
>>              goto errout_free;
>>  
>> -    skb_dst_set(skb, &rt->dst);
> 
> 
> Why did you remove this? Neither ip_route_input() or ip_route_output_key()
> seem to justify this with a quick scan on my side. Feel free to correct me
> here.
> 

original patch was done in January. I forget why I took it out. It is
clearly needed to release the dst. Might as well undo the argument
change to rt_fill_info since it is attached to the skb. Something like
this (whitespace damaged on paste - stupid Mac):

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f1f2e5aaa2d6..93cca12a8319 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2547,8 +2547,9 @@ EXPORT_SYMBOL_GPL(ip_route_output_flow);
 /* called with rcu_read_lock held */
 static int rt_fill_info(struct net *net,  __be32 dst, __be32 src, u32
table_id,
                        struct flowi4 *fl4, struct sk_buff *skb, u32 portid,
-                       u32 seq, struct rtable *rt)
+                       u32 seq)
 {
+       struct rtable *rt = skb_rtable(skb);
        struct rtmsg *r;
        struct nlmsghdr *nlh;
        unsigned long expires = 0;
@@ -2750,6 +2751,8 @@ static int inet_rtm_getroute(struct sk_buff
*in_skb, struct nlmsghdr *nlh,
        if (err)
                goto errout_free;

+       skb_dst_set(skb, &rt->dst);
+
        if (rtm->rtm_flags & RTM_F_NOTIFY)
                rt->rt_flags |= RTCF_NOTIFY;

@@ -2763,8 +2766,7 @@ static int inet_rtm_getroute(struct sk_buff
*in_skb, struct nlmsghdr *nlh,
                                    fl4.flowi4_tos, res.fi, 0);
        else
                err = rt_fill_info(net, dst, src, table_id, &fl4, skb,
-                                  NETLINK_CB(in_skb).portid,
nlh->nlmsg_seq,
-                                  rt);
+                                  NETLINK_CB(in_skb).portid,
nlh->nlmsg_seq);
        if (err < 0)
                goto errout_free;


Seems to work for me.