netdev - Re: net/sched: latent livelock in dev_deactivate

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Message-ID: <20170405173105.7f41d7fc@plumbers-lap.home.lan>
Date:   Wed, 5 Apr 2017 17:31:05 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Mike Galbraith <efault@....de>
Cc:     netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: net/sched: latent livelock in dev_deactivate_many() due to
 yield() usage

On Sun, 02 Apr 2017 06:28:41 +0200
Mike Galbraith <efault@....de> wrote:

> Livelock can be triggered by setting kworkers to SCHED_FIFO, then
> suspend/resume.. you come back from sleepy-land with a spinning
> kworker.  For whatever reason, I can only do that with an enterprise
> like config, my standard config refuses to play, but no matter, it's
> "Typical broken usage".
> 
> (yield() should be rendered dead)

The kernel is not normally built to have kworkers run at SCHED_FIFO.
The user has do some action to alter the process priorities.

I classify this as user error. We don't support killing kworker threads
either.