On top of Eric's comments.

On Thu, Sep 22, 2016 at 10:22:45AM +0800, f...@ikuai8.com wrote:
> diff --git a/net/netfilter/nf_conntrack_seqadj.c 
> b/net/netfilter/nf_conntrack_seqadj.c
> index dff0f0c..3bd9c7e 100644
> --- a/net/netfilter/nf_conntrack_seqadj.c
> +++ b/net/netfilter/nf_conntrack_seqadj.c
> @@ -179,30 +179,34 @@ int nf_ct_seq_adjust(struct sk_buff *skb,
>  
>       tcph = (void *)skb->data + protoff;
>       spin_lock_bh(&ct->lock);
> +
>       if (after(ntohl(tcph->seq), this_way->correction_pos))
>               seqoff = this_way->offset_after;
>       else
>               seqoff = this_way->offset_before;
>  
> -     if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
> -               other_way->correction_pos))
> -             ackoff = other_way->offset_after;
> -     else
> -             ackoff = other_way->offset_before;
> -
>       newseq = htonl(ntohl(tcph->seq) + seqoff);
> -     newack = htonl(ntohl(tcph->ack_seq) - ackoff);
> -
>       inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, false);
> -     inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack,
> -                              false);
> -
> -     pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
> -              ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
> -              ntohl(newack));
>  
> +     pr_debug("Adjusting sequence number from %u->%u\n",
> +              ntohl(tcph->seq), ntohl(newseq));
>       tcph->seq = newseq;
> -     tcph->ack_seq = newack;
> +
> +     if (likely(tcph->ack)) {

I'd suggest:

        if (!tcph->ack)
                goto out;

given gcc sets goto branch as unlikely already, then you place an "out"
label...

> +             if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
> +                       other_way->correction_pos))
> +                     ackoff = other_way->offset_after;
> +             else
> +                     ackoff = other_way->offset_before;
> +
> +             newack = htonl(ntohl(tcph->ack_seq) - ackoff);
> +             inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq,
> +                                      newack, false);
> +
> +             pr_debug("Adjusting ack number from %u->%u\n",
> +                      ntohl(tcph->ack_seq), ntohl(newack));
> +             tcph->ack_seq = newack;
> +     }
>  
>       res = nf_ct_sack_adjust(skb, protoff, tcph, ct, ctinfo);

out:    <- here

>       spin_unlock_bh(&ct->lock);

This will get you a smaller patch fix.
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