linux-kernel - Re: [BUG] ixgbe: Detected Tx Unit Hang (XDP)

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Message-ID: <b06ede77-541b-453f-9e7a-79f3e5591f66@hetzner-cloud.de>
Date: Wed, 23 Apr 2025 16:20:07 +0200
From: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
 Michal Kubiak <michal.kubiak@...el.com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>, Jay Vosburgh
 <jv@...sburgh.net>, Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, intel-wired-lan@...ts.osuosl.org,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 sdn@...zner-cloud.de
Subject: Re: [BUG] ixgbe: Detected Tx Unit Hang (XDP)

Am 17.04.25 um 16:47 schrieb Maciej Fijalkowski:
> On Fri, Apr 11, 2025 at 10:14:57AM +0200, Michal Kubiak wrote:
>> On Thu, Apr 10, 2025 at 04:54:35PM +0200, Marcus Wichelmann wrote:
>>> Am 10.04.25 um 16:30 schrieb Michal Kubiak:
>>>> On Wed, Apr 09, 2025 at 05:17:49PM +0200, Marcus Wichelmann wrote:
>>>>> Hi,
>>>>>
>>>>> in a setup where I use native XDP to redirect packets to a bonding interface
>>>>> that's backed by two ixgbe slaves, I noticed that the ixgbe driver constantly
>>>>> resets the NIC with the following kernel output:
>>>>>
>>>>>   ixgbe 0000:01:00.1 ixgbe-x520-2: Detected Tx Unit Hang (XDP)
>>>>>     Tx Queue             <4>
>>>>>     TDH, TDT             <17e>, <17e>
>>>>>     next_to_use          <181>
>>>>>     next_to_clean        <17e>
>>>>>   tx_buffer_info[next_to_clean]
>>>>>     time_stamp           <0>
>>>>>     jiffies              <10025c380>
>>>>>   ixgbe 0000:01:00.1 ixgbe-x520-2: tx hang 19 detected on queue 4, resetting adapter
>>>>>   ixgbe 0000:01:00.1 ixgbe-x520-2: initiating reset due to tx timeout
>>>>>   ixgbe 0000:01:00.1 ixgbe-x520-2: Reset adapter
>>>>>
>>>>> This only occurs in combination with a bonding interface and XDP, so I don't
>>>>> know if this is an issue with ixgbe or the bonding driver.
>>>>> I first discovered this with Linux 6.8.0-57, but kernel 6.14.0 and 6.15.0-rc1
>>>>> show the same issue.
>>>>>
>>>>>
>>>>> I managed to reproduce this bug in a lab environment. Here are some details
>>>>> about my setup and the steps to reproduce the bug:
>>>>>
>>>>> [...]
>>>>>
>>>>> Do you have any ideas what may be causing this issue or what I can do to
>>>>> diagnose this further?
>>>>>
>>>>> Please let me know when I should provide any more information.
>>>>>
>>>>>
>>>>> Thanks!
>>>>> Marcus
>>>>>
>>>>
>> [...]
>>
>> Hi Marcus,
>>
>>> thank you for looking into it. And not even 24 hours after my report, I'm
>>> very impressed! ;)
>>
>> Thanks! :-)
>>
>>> Interesting. I just tried again but had no luck yet with reproducing it
>>> without a bonding interface. May I ask how your setup looks like?
>>
>> For now, I've just grabbed the first available system with the HW
>> controlled by the "ixgbe" driver. In my case it was:
>>
>>   Ethernet controller: Intel Corporation Ethernet Controller X550
>>
>> Also, for my first attempt, I didn't use the upstream kernel - I just tried
>> the kernel installed on that system. It was the Fedora kernel:
>>
>>   6.12.8-200.fc41.x86_64
>>
>>
>> I think that may be the "beauty" of timing issues - sometimes you can change
>> just one piece in your system and get a completely different replication ratio.
>> Anyway, the higher the repro probability, the easier it is to debug
>> the timing problem. :-)
> 
> Hi Marcus, to break the silence could you try to apply the diff below on
> your side?

Hi, thank you for the patch. We've tried it and with your changes we can no
longer trigger the error and the NIC is no longer being reset.

> We see several issues around XDP queues in ixgbe, but before we
> proceed let's this small change on your side.

How confident are you that this patch is sufficient to make things stable enough
for production use? Was it just the Tx hang detection that was misbehaving for
the XDP case, or is there an underlying issue with the XDP queues that is not
solved by disabling the detection for it?

With our current setup we cannot verify accurately, that we have no packet loss 
or stuck queues. We can do additional tests to verify that. 

> Additional question, do you have enabled pause frames on your setup?

Pause frames were enabled, but we can also reproduce it after disabling them,
without your patch.

Thanks!
Marcus