netdev - Re: 5.15-rc3+ crash in fq-codel?

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Message-ID: <c4000c2a-8894-c3f5-9497-82bce4615be1@gmail.com>
Date:   Wed, 29 Sep 2021 17:29:42 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ben Greear <greearb@...delatech.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: 5.15-rc3+ crash in fq-codel?



On 9/29/21 5:04 PM, Ben Greear wrote:
> On 9/29/21 4:48 PM, Ben Greear wrote:
>> On 9/29/21 4:42 PM, Eric Dumazet wrote:
>>>
>>>
>>> On 9/29/21 4:28 PM, Eric Dumazet wrote:
>>>>
>>>
>>>>
>>>> Actually the bug seems to be in pktgen, vs NET_XMIT_CN
>>>>
>>>> You probably would hit the same issues with other qdisc also using NET_XMIT_CN
>>>>
>>>
>>> I would try the following patch :
>>>
>>> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
>>> index a3d74e2704c42e3bec1aa502b911c1b952a56cf1..0a2d9534f8d08d1da5dfc68c631f3a07f95c6f77 100644
>>> --- a/net/core/pktgen.c
>>> +++ b/net/core/pktgen.c
>>> @@ -3567,6 +3567,7 @@ static void pktgen_xmit(struct pktgen_dev *pkt_dev)
>>>          case NET_XMIT_DROP:
>>>          case NET_XMIT_CN:
>>>                  /* skb has been consumed */
>>> +               pkt_dev->last_ok = 1;
>>>                  pkt_dev->errors++;
>>>                  break;
>>>          default: /* Drivers are not supposed to return other values! */
> 
> While patching my variant of pktgen, I took a look at the 'default' case.  I think
> it should probably go above NET_XMIT_DROP and fallthrough into the consumed pkt path?
> 
> Although, probably not a big deal since only bugs elsewhere would hit that path, and
> we don't really know if skb would be consumed in that case or not.
> 

This is probably dead code after commit

commit f466dba1832f05006cf6caa9be41fb98d11cb848    pktgen: ndo_start_xmit can return NET_XMIT_xxx values

So this does not really matter anymore.