linux-kernel - Re: [RT] Question about i40e threaded irq

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Date:   Tue, 11 May 2021 09:46:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-rt-users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, sassmann@...hat.com
Subject: Re: [RT] Question about i40e threaded irq

On Tue, May 11 2021 at 08:09, Juri Lelli wrote:
> My understanding is that rps_trigger_softirq() sneaked in while
> i40e_msix_clean_rings() threaded irq was running and, since the latter is
> using napi_schedule_irqoff(), the softnet_data poll_list got eventually
> corrupted.
>
> Now, doing s/napi_schedule_irqoff/napi_schedule/ in the i40e driver seem
> to cure the problem. I'm not sure that there isn't a more general
> solution, though. Is it expected that napi_schedule_irqoff users in RT
> know what they are doing or do we want/need to fix this in a more
> general way?

The straight forward fix it to map napi_schedule_irqoff() to
napi_schedule() on RT. Fixing this at the driver level is a whack-a-mole
game.

Thanks,

        tglx