netdev - Re: [PATCH net-next v2] Add Mellanox BlueField Gigabit Ethernet driver

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Message-ID: <20200820230439.5duakpmsg7jysdwq@skbuf>
Date:   Fri, 21 Aug 2020 02:04:39 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Thompson <dthompson@...lanox.com>, netdev@...r.kernel.org,
        davem@...emloft.net, jiri@...lanox.com,
        Asmaa Mnebhi <asmaa@...lanox.com>
Subject: Re: [PATCH net-next v2] Add Mellanox BlueField Gigabit Ethernet
 driver

On Thu, Jul 30, 2020 at 05:30:59PM -0700, Jakub Kicinski wrote:
> On Thu, 30 Jul 2020 18:53:58 -0400 David Thompson wrote:
> > +
> > +	/* Tell networking subsystem to poll GigE driver */
> > +	napi_schedule(&priv->napi);
> 
> _irqoff

Hmm, I wouldn't be so sure about this particular advice. With
PREEMPT_RT, interrupt handlers are force-threaded and run in process
context, therefore with hardirqs enabled. This driver doesn't call
request_irq with IRQF_NO_THREAD, so calling napi_schedule_irqoff would
create a bug that is very, very difficult to find.

Thanks,
-Vladimir