netdev - Re: virtio_close() stuck on napi_disable

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Message-ID: <b772e896-5e73-4904-b6c7-8ed913198b02@redhat.com>
Date: Thu, 24 Jul 2025 11:18:13 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Zigit Zo <zuozhijie@...edance.com>, Jakub Kicinski <kuba@...nel.org>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: virtio_close() stuck on napi_disable_locked()

On 7/24/25 10:58 AM, Zigit Zo wrote:
> On 7/23/25 5:55 AM, Jakub Kicinski wrote:
>> On Tue, 22 Jul 2025 13:00:14 +0200 Paolo Abeni wrote:
>>> The NIPA CI is reporting some hung-up in the stats.py test caused by the
>>> virtio_net driver stuck at close time.
>>>
>>> A sample splat is available here:
>>>
>>> https://netdev-3.bots.linux.dev/vmksft-drv-hw-dbg/results/209441/4-stats-py/stderr
>>>
>>> AFAICS the issue happens only on debug builds.
>>>
>>> I'm wild guessing to something similar to the the issue addressed by
>>> commit 4bc12818b363bd30f0f7348dd9ab077290a637ae, possibly for tx_napi,
>>> but I could not spot anything obvious.
>>>
>>> Could you please have a look?
>>
>> It only hits in around 1 in 5 runs. Likely some pre-existing race, but
>> it started popping up for us when be5dcaed694e ("virtio-net: fix
>> recursived rtnl_lock() during probe()") was merged. It never hit before.
>> If we can't find a quick fix I think we should revert be5dcaed694e for
>> now, so that it doesn't end up regressing 6.16 final.
> 
> Just found that there's a new test script `netpoll_basic.py`. Before 209441,
> this test did not exist at all, I randomly picked some test results prior to
> its introduction and did not find any hung logs. Is it relevant?

If I read correctly the nipa configuration, it executes the tests in
sequence. `netpoll_basic.py` runs just before `stats.py`, so it could
cause failure if it leaves some inconsistent state - but not in a
deterministic way, as the issue is sporadic.

Technically possible, IMHO unlikely. Still it would explain why I can't
repro the issue here. With unlimited time available could be worthy
validating if the issue could be reproduced running the 2 tests in sequence.

/P