netdev - Re: [PATCH net] net: fix race between napi kthread mode and busy poll

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Message-ID: <20210224174045.77b970cb@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 24 Feb 2021 17:40:45 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Wei Wang <weiwan@...gle.com>
Cc:     Alexander Duyck <alexanderduyck@...com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Martin Zaharinov <micron10@...il.com>
Subject: Re: [PATCH net] net: fix race between napi kthread mode and busy
 poll

On Wed, 24 Feb 2021 17:06:13 -0800 Wei Wang wrote:
> I really have a hard time reproducing the warning Martin was seeing in
> his setup. The difference between my setup and his is that mine uses
> mlx4 driver, while Martin is using ixgbe driver.
> 
> To keep everyone up to date with Martin's previous email, with this
> patch applied to 5.11.1, the following warning is triggered when
> enabling threaded mode without enabling busy poll:
> echo 1 > /sys/class/net/eth0/threaded
> echo 1 > /sys/class/net/eth1/threaded
> echo 1 > /sys/class/net/eth2/threaded
> echo 1 > /sys/class/net/eth3/threaded
> 
> Warning message:
> [...]
> 
> This is the line in net/core/dev.c:6993
>  WARN_ON(!list_empty(&napi->poll_list));
> in napi_threaded wait()
> 
> Martin, do you think the driver version you are using could be at fault here?

We do kthread_run() meaning the thread gets immediately woken up, even
when sirq is polling the NAPI and owns it. Right?