netdev - Re: regression: tethering fails in 3.5 with iwlwifi

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Date:	Thu, 20 Sep 2012 14:46:52 +0200
From:	Eric Dumazet <edumazet@...gle.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	artem.bityutskiy@...ux.intel.com, linux-wireless@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: regression: tethering fails in 3.5 with iwlwifi

Or its the lines with CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS ?

What arch is it ?


On Thu, Sep 20, 2012 at 2:45 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> I guess you only need to make sure 14 bytes of ethernet header are
> available before eth_type_trans(skb, dev);
>
> diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
> index 61c621e..ffe5f84 100644
> --- a/net/mac80211/rx.c
> +++ b/net/mac80211/rx.c
> @@ -1795,9 +1795,13 @@ ieee80211_deliver_skb(struct ieee80211_rx_data *rx)
>
>                 if (skb) {
>                         /* deliver to local stack */
> -                       skb->protocol = eth_type_trans(skb, dev);
> -                       memset(skb->cb, 0, sizeof(skb->cb));
> -                       netif_receive_skb(skb);
> +                       if (pskb_may_pull(skb, sizeof(struct ethhdr))) {
> +                               skb->protocol = eth_type_trans(skb, dev);
> +                               memset(skb->cb, 0, sizeof(skb->cb));
> +                               netif_receive_skb(skb);
> +                       } else {
> +                               kfree_skb(skb);
> +                       }
>                 }
>         }
>
>
> On Thu, Sep 20, 2012 at 2:40 PM, Eric Dumazet <edumazet@...gle.com> wrote:
>> OK, but which netif_receive_skb(), as I count 5 occurrences in
>> net/mac80211/rx.c ?
>>
>> Instead of skb_linearize() calls
>>
>> you could try several values of XXX in
>>
>> pskb_may_pull(skb, XXX)
>>
>> So that you make sure XXX bytes are available in skb->head, and not
>> the whole frame.
>>
>> One you know the limit for XXX, it might give a clue where a
>> pskb_may_pull(skb, XXX) is missing.
>>
>> On Thu, Sep 20, 2012 at 2:35 PM, Johannes Berg
>> <johannes@...solutions.net> wrote:
>>> Hi,
>>>
>>>> >             56138f5 iwlwifi: dont pull too much payload in skb head
>>>> >             3edaf3e mac80211: manage AP netdev carrier state
>>>>
>>>> The second patch (AP carrier state) actually exposed a connman issue
>>>> which I fixed and submitted a connman patch:
>>>> http://lists.connman.net/pipermail/connman/2012-September/011232.html
>>>>
>>>> However, Eric's patch still causes tethering problems to me.
>>>
>>>
>>> Let me recap a bit. Artem is using connman, which sets up the wifi
>>> interface as part of a bridge. It runs wpa_supplicant to create an AP
>>> (only AP and mesh mode interfaces can be bridged anyway).
>>>
>>>
>>> Eric, you said:
>>>
>>>> I would say some part of the stack assumes a header (I dont know wich
>>>> one ?) is pulled in skb->head/data, and thats a bug.
>>>>
>>>> Always use pskb_may_pull(skb, XXX) to make sure you can access XXX
>>>> bytes in skb->data
>>>
>>> I thought we'd figure out which part of the stack assumes a header, so I
>>> asked Artem to test a one-line patch which adds "skb_linearize()" before
>>> "netif_receive_skb()" in mac80211. This makes it work, but I'm not sure
>>> where after that the bad assumption might be.
>>>
>>> johannes
>>>
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