netdev - Re: [PATCH net-next] bpf, skb_do_redirect: clear sender

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Date:	Fri, 9 Oct 2015 20:19:39 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Daniel Borkmann <daniel@...earbox.net>,
	"Devon H. O'Dell" <dho@...tly.com>
Cc:	davem@...emloft.net, edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf, skb_do_redirect: clear sender_cpu before
 xmit

On 10/9/15 10:33 AM, Daniel Borkmann wrote:
>> I was thinking may be we can use sign bit to distinguish between
>> napi_id and sender_cpu.
>> Like:
>>          if ((int)skb->sender_cpu >= 0)
>>                  skb->sender_cpu = - (raw_smp_processor_id() + 1);
>> and inside get_xps_queue() use it only if it's negative.
>> Then we can remove skb_sender_cpu_clear() from everywhere.
>> Adding a check to napi_hash_add() to make sure that napi_id is not
>> negative is probably ok too.
>> Thoughts?
>
> I think this doesn't make it any more maintainable.
>
> skb_sender_cpu_clear(), one can at least git-grep to easily find
> out and review call-sites in the code. There are various members
> already used differently depending on the context.

since this bug wasn't fixed at once in all places, it means
that it is hard to review _all_ needed call-sites.
There are 7 places that call skb_sender_cpu_clear() in net-next.
Plus 2 more in net.
How many such paths from rx to tx left?
On the first glance ovs is missing one and who knows what else.

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