From: Alexei Starovoitov <ast@plumgrid•com>
To: David Miller <davem@davemloft•net>
Cc: daniel@iogearbox•net, jiri@resnulli•us, jhs@mojatatu•com,
netdev@vger•kernel.org
Subject: Re: [PATCH v2 net-next 2/2] tc: make ingress and egress qdiscs consistent
Date: Tue, 07 Apr 2015 20:22:34 -0700 [thread overview]
Message-ID: <55249EFA.5040405@plumgrid.com> (raw)
In-Reply-To: <20150407.223549.335906307265617841.davem@davemloft.net>
On 4/7/15 7:35 PM, David Miller wrote:
> From: Alexei Starovoitov <ast@plumgrid•com>
> Date: Tue, 7 Apr 2015 18:03:45 -0700
>
>> +
>> + /* don't recompute skb->csum back and forth while pushing/pulling L2 */
>> + __skb_push(skb, hard_header_len);
>> result = tc_classify(skb, fl, &res);
>> + __skb_pull(skb, hard_header_len);
>
> This is not legal.
>
> This SKB can be referenced by other entities, such as AF_PACKET
> sockets and other network taps on input. You absolutely do not
> have private access to this SKB object, and any modification you
> make to it will be seen by others.
>
> Therefore you cannot push and pull the headers, because that
> modification will be seen by the other entities referencing this SKB.
ohh, yes. Spent too much time looking at TC that forgot the obvious.
Was modeling this one by skb_defer_rx_timestamp() which is called before
taps. My v1 patch was obviously broken too :(
> And you do not want to add this expensive operation here.
>
> That would be really stupid overhead just to accomodate BPF things.
skb_share_check is only expensive if taps are active and
not only cls_bpf, but ematch and bunch of other cls/acts assume L2,
but it seems no one cares about using them with ingress, so I'll go back
to cls_bpf specific skb_share_check and push.
Other classifiers that care about attaching to ingress would need
to do the same thing or play nicely with offsets. Fair enough.
next prev parent reply other threads:[~2015-04-08 3:22 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-08 1:03 [PATCH v2 net-next 1/2] net: introduce skb_postpush_rcsum() helper Alexei Starovoitov
2015-04-08 1:03 ` [PATCH v2 net-next 2/2] tc: make ingress and egress qdiscs consistent Alexei Starovoitov
2015-04-08 2:35 ` David Miller
2015-04-08 3:22 ` Alexei Starovoitov [this message]
2015-04-08 4:48 ` Alexei Starovoitov
2015-04-08 8:36 ` Daniel Borkmann
2015-04-08 9:05 ` Jiri Pirko
2015-04-08 10:54 ` Daniel Borkmann
2015-04-08 11:14 ` Daniel Borkmann
2015-04-08 11:47 ` Jamal Hadi Salim
2015-04-08 12:31 ` Daniel Borkmann
2015-04-08 12:58 ` Jamal Hadi Salim
2015-04-08 13:14 ` Thomas Graf
2015-04-08 13:27 ` Daniel Borkmann
2015-04-08 13:34 ` Jiri Pirko
2015-04-08 13:41 ` Daniel Borkmann
2015-04-08 13:47 ` Thomas Graf
2015-04-08 13:52 ` Jamal Hadi Salim
2015-04-08 14:53 ` Daniel Borkmann
2015-04-08 16:26 ` Alexei Starovoitov
2015-04-08 16:32 ` David Miller
2015-04-08 16:44 ` Alexei Starovoitov
2015-04-08 16:54 ` Daniel Borkmann
2015-04-08 11:43 ` Jamal Hadi Salim
2015-04-08 7:25 ` [PATCH v2 net-next 1/2] net: introduce skb_postpush_rcsum() helper Daniel Borkmann
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