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

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Message-ID: <b7df0abb-8bdd-6348-a60a-75a66d6a9d91@candelatech.com>
Date:   Wed, 29 Sep 2021 17:04:09 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: 5.15-rc3+ crash in fq-codel?

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.

Thanks,
Ben