Re: net/sched: latent livelock in dev_deactivate_many() due to yield() usage

[Peter Zijlstra]

On Wed, Apr 05, 2017 at 05:31:05PM -0700, Stephen Hemminger wrote:
> On Sun, 02 Apr 2017 06:28:41 +0200
> Mike Galbraith <efault@xxxxxx> 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.

PI can boost anybody to FIFO, all you need is to be holding a lock.