netdev - Re: [PATCH net] sch_cake: Return __NET_XMIT_STOLEN when consuming enqueued skb

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Message-ID: <87wnao2ha3.fsf@toke.dk>
Date:   Thu, 01 Sep 2022 00:13:24 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, cake@...ts.bufferbloat.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH net] sch_cake: Return __NET_XMIT_STOLEN when consuming
 enqueued skb

patchwork-bot+netdevbpf@...nel.org writes:

> Hello:
>
> This patch was applied to netdev/net.git (master)
> by Jakub Kicinski <kuba@...nel.org>:
>
> On Wed, 31 Aug 2022 11:21:03 +0200 you wrote:
>> When the GSO splitting feature of sch_cake is enabled, GSO superpackets
>> will be broken up and the resulting segments enqueued in place of the
>> original skb. In this case, CAKE calls consume_skb() on the original skb,
>> but still returns NET_XMIT_SUCCESS. This can confuse parent qdiscs into
>> assuming the original skb still exists, when it really has been freed. Fix
>> this by adding the __NET_XMIT_STOLEN flag to the return value in this case.
>> 
>> [...]
>
> Here is the summary with links:
>   - [net] sch_cake: Return __NET_XMIT_STOLEN when consuming enqueued skb
>     https://git.kernel.org/netdev/net/c/90fabae8a2c2

Ah, crossed streams (just sent v2[0]).

Hmm, okay, so as noted in the changelog to v2, just this patch will
break htb+cake (because htb will now skip htb_activate()); do you prefer
that I send a follow-up to fix HTB in this mode, or to revert this and
apply the fix to sfb in v2 instead?

-Toke


[0] https://lore.kernel.org/r/20220831215219.499563-1-toke@toke.dk