Re: [net-next PATCH] net: reduce cycles spend on ICMP replies that gets rate limited

[David Miller]

From: Eric Dumazet <eric.duma...@gmail.com>
Date: Fri, 06 Jan 2017 14:08:06 -0800

> On Fri, 2017-01-06 at 11:40 -0800, Eric Dumazet wrote:
>> On Fri, 2017-01-06 at 18:39 +0100, Jesper Dangaard Brouer wrote:
>> 
>> 
>> > @@ -648,13 +668,17 @@ void icmp_send(struct sk_buff *skb_in, int type, int 
>> > code, __be32 info)
>> >            }
>> >    }
>> >  
>> > -  icmp_param = kmalloc(sizeof(*icmp_param), GFP_ATOMIC);
>> > -  if (!icmp_param)
>> > -          return;
>> > -
>> >    sk = icmp_xmit_lock(net);
>> >    if (!sk)
>> > -          goto out_free;
>> > +          goto out;
>> > +
>> > +  /* Check global sysctl_icmp_msgs_per_sec ratelimit */
>> > +  if (!icmpv4_global_allow(net, type, code))
>> > +          goto out_unlock;
>> > +
>> > +  icmp_param = kmalloc(sizeof(*icmp_param), GFP_ATOMIC);
>> > +  if (!icmp_param)
>> > +          goto out_unlock;
>> 
> 
> You could call icmp_xmit_lock() _after_ checking global limit perhaps. 

BTW Eric, you asked about kmalloc() allocation, you were CC:'d in the
patch which did this :-)

commit 9a99d4a50cb8ce516adf0f2436138d4c8e6e4535
Author: Cong Wang <amw...@redhat.com>
Date:   Sun Jun 2 15:00:52 2013 +0000

    icmp: avoid allocating large struct on stack
    
    struct icmp_bxm is a large struct, reduce stack usage
    by allocating it on heap.
    
    Cc: Eric Dumazet <eric.duma...@gmail.com>
    Cc: Joe Perches <j...@perches.com>
    Cc: David S. Miller <da...@davemloft.net>
    Signed-off-by: Cong Wang <amw...@redhat.com>
    Signed-off-by: David S. Miller <da...@davemloft.net>

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 2864ca3..5f7d11a 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -482,7 +482,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, 
__be32 info)
 {
        struct iphdr *iph;
        int room;
-       struct icmp_bxm icmp_param;
+       struct icmp_bxm *icmp_param;
        struct rtable *rt = skb_rtable(skb_in);
        struct ipcm_cookie ipc;
        struct flowi4 fl4;
@@ -558,9 +558,13 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, 
__be32 info)
                }
        }
 
+       icmp_param = kmalloc(sizeof(*icmp_param), GFP_ATOMIC);
+       if (!icmp_param)
+               return;
+
        sk = icmp_xmit_lock(net);
        if (sk == NULL)
-               return;
+               goto out_free;
 
        /*
         *      Construct source address and options.
@@ -586,7 +590,7 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, 
__be32 info)
                                           IPTOS_PREC_INTERNETCONTROL) :
                                          iph->tos;
 
-       if (ip_options_echo(&icmp_param.replyopts.opt.opt, skb_in))
+       if (ip_options_echo(&icmp_param->replyopts.opt.opt, skb_in))
                goto out_unlock;
 
 
@@ -594,19 +598,19 @@ void icmp_send(struct sk_buff *skb_in, int type, int 
code, __be32 info)
         *      Prepare data for ICMP header.
         */
 
-       icmp_param.data.icmph.type       = type;
-       icmp_param.data.icmph.code       = code;
-       icmp_param.data.icmph.un.gateway = info;
-       icmp_param.data.icmph.checksum   = 0;
-       icmp_param.skb    = skb_in;
-       icmp_param.offset = skb_network_offset(skb_in);
+       icmp_param->data.icmph.type      = type;
+       icmp_param->data.icmph.code      = code;
+       icmp_param->data.icmph.un.gateway = info;
+       icmp_param->data.icmph.checksum  = 0;
+       icmp_param->skb   = skb_in;
+       icmp_param->offset = skb_network_offset(skb_in);
        inet_sk(sk)->tos = tos;
        ipc.addr = iph->saddr;
-       ipc.opt = &icmp_param.replyopts.opt;
+       ipc.opt = &icmp_param->replyopts.opt;
        ipc.tx_flags = 0;
 
        rt = icmp_route_lookup(net, &fl4, skb_in, iph, saddr, tos,
-                              type, code, &icmp_param);
+                              type, code, icmp_param);
        if (IS_ERR(rt))
                goto out_unlock;
 
@@ -618,19 +622,21 @@ void icmp_send(struct sk_buff *skb_in, int type, int 
code, __be32 info)
        room = dst_mtu(&rt->dst);
        if (room > 576)
                room = 576;
-       room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
+       room -= sizeof(struct iphdr) + icmp_param->replyopts.opt.opt.optlen;
        room -= sizeof(struct icmphdr);
 
-       icmp_param.data_len = skb_in->len - icmp_param.offset;
-       if (icmp_param.data_len > room)
-               icmp_param.data_len = room;
-       icmp_param.head_len = sizeof(struct icmphdr);
+       icmp_param->data_len = skb_in->len - icmp_param->offset;
+       if (icmp_param->data_len > room)
+               icmp_param->data_len = room;
+       icmp_param->head_len = sizeof(struct icmphdr);
 
-       icmp_push_reply(&icmp_param, &fl4, &ipc, &rt);
+       icmp_push_reply(icmp_param, &fl4, &ipc, &rt);
 ende:
        ip_rt_put(rt);
 out_unlock:
        icmp_xmit_unlock(sk);
+out_free:
+       kfree(icmp_param);
 out:;
 }
 EXPORT_SYMBOL(icmp_send);