netdev - Re: Linux kernel error stack

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Message-ID: <CAPgF-fq7pa3Ai0iOCWnJqHCrFWdyfiGBmBo5JDDCHjzypYHLFA@mail.gmail.com>
Date:   Sun, 5 Aug 2018 08:43:31 -0400
From:   Satish Patel <satish.txt@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org
Subject: Re: Linux kernel error stack

Thanks Florian,

FYI, I don't have any CHECKSUM configure in my iptables, i have
following rules, also do you think this kernel WARNNING is just
warning and not impacting my performance, based on that i have to
decided criticality of this issue.

[root@...ack-infra-02 ~]# iptables -L -n
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:53
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:53
ACCEPT     tcp  --  0.0.0.0/0            0.0.0.0/0            tcp dpt:67
ACCEPT     udp  --  0.0.0.0/0            0.0.0.0/0            udp dpt:67

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0
ACCEPT     all  --  0.0.0.0/0            0.0.0.0/0

On Sun, Aug 5, 2018 at 5:48 AM, Florian Westphal <fw@...len.de> wrote:
> Satish Patel <satish.txt@...il.com> wrote:
>> I am installing openstack and as you know i have lots of bridges and
>> vlan interface on my Linux CentOS 7.5
>>
>> I was getting following error stack on 3.10 kernel and found this is
>> kernel bug which required kernel upgrade so now i have upgraded my
>> kernel to 4.17.12 but i am still seeing same kernel stack error on my
>> dmesg
>>
>> I have disable TSO, LRO, SG & GSO on my NIC but still getting error
>> just wanted to understand what is this and why it popping up
>
> Get rid of CHECKSUM target in the iptables rules.
> This thing was added 8 years ago to work around dhcp bugs, I don't
> think its use is needed anymore.
> Try removing it and see that all VMs can still retrieve IP address
> via DHCP.
>
> I'm curious as to the rules, normally CHECKSUM target should be
> limited to -p udp --dport bootp; its bad idea to feed it normal
> packets, its expensive to do this in software rather than have device
> do the checksumming.
>
> As for fix, I'm tempted to send patch to make checksum target
> eval a no-op & add deprecation warning on init...
>
> Other "fix" is to
>
> diff --git a/net/netfilter/xt_CHECKSUM.c b/net/netfilter/xt_CHECKSUM.c
> index 9f4151ec3e06..23a17dda604d 100644
> --- a/net/netfilter/xt_CHECKSUM.c
> +++ b/net/netfilter/xt_CHECKSUM.c
> @@ -25,8 +25,12 @@ MODULE_ALIAS("ip6t_CHECKSUM");
>  static unsigned int
>  checksum_tg(struct sk_buff *skb, const struct xt_action_param *par)
>  {
> -       if (skb->ip_summed == CHECKSUM_PARTIAL)
> -               skb_checksum_help(skb);
> +       if (skb->ip_summed == CHECKSUM_PARTIAL) {
> +               if (skb_shinfo(skb)->gso_size)
> +                       skb->ip_summed = CHECKSUM_NONE;
> +               else
> +                       skb_checksum_help(skb);
> +       }
>
>         return XT_CONTINUE;
>  }
>
> (unfortunately, the target isn't restricted to POSTROUTING, sigh).