netdev - Re: [PATCH] ipv6: fix flow labels when the traffic class is non-0

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Date:   Mon, 30 Jan 2017 15:38:15 -0800
From:   Dimitris Michailidis <dmichail@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Tom Herbert <tom@...bertland.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv6: fix flow labels when the traffic class is non-0

On Mon, Jan 30, 2017 at 2:23 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> On Mon, Jan 30, 2017 at 2:09 PM, Dimitris Michailidis
> <dmichail@...gle.com> wrote:
>> ip6_make_flowlabel() determines the flow label for IPv6 packets. It's
>> supposed to be passed a flow label, which it returns as is if non-0 and
>> in some other cases, otherwise it calculates a new value.
>>
>> The problem is callers often pass a flowi6.flowlabel, which may also
>> contain traffic class bits.
>
> Do you have an idea which commit added this bug Dimitris ?

[Resending reply as text]

I believe it was wrong since cb1ce2ef387b01 ("ipv6: Implement
automatic flow label generation on transmit"), the commit that
introduced ip6_make_flowlabel(). The function was somewhat different
at the time but it was doing

       if (!flowlabel && (autolabel || net->ipv6.sysctl.auto_flowlabels)) {
       ...
       }
       return flowlabel;

 and all the callers were passing flowi6.flowlabel.