Re: Crashes with 874bbfe600a6 in 3.18.25

[Mike Galbraith]

On Tue, 2016-02-09 at 12:54 -0500, Tejun Heo wrote:
> Hello, Mike.
> 
> On Tue, Feb 09, 2016 at 06:04:04PM +0100, Mike Galbraith wrote:
> > workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask
> > CPUs
> > 
> > WORK_CPU_UNBOUND work items queued to a bound workqueue always run
> > locally.  This is a good thing normally, but not when the user has
> > asked us to keep unbound work away from certain CPUs.  Round robin
> > these to wq_unbound_cpumask CPUs instead, as perturbation avoidance
> > trumps performance.
> 
> I don't think doing this by default for everyone is a good idea.  A
> lot of workqueue usages tend to touch whatever the scheduler was
> touching after all.  Doing things per-cpu is generally a pretty good
> thing.

It doesn't do anything unless the user twiddles the mask to exclude
certain (think no_hz_full) CPUs, so there are no clueless victims.

	-Mike