Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed forkthreadd

From: Andrew Morton
Date: Thu Oct 17 2013 - 15:23:50 EST


On Wed, 16 Oct 2013 22:37:52 +0000 Christoph Lameter <cl@xxxxxxxxx> wrote:

> > > - /* We can run anywhere, unlike our parent keventd(). */
> > > - set_cpus_allowed_ptr(current, cpu_all_mask);
> > > + /* We can run anywhere kthreadd can run */
> >
> > This is a poor comment - it explains "what" (which was utterly obvious)
> > but doesn't explain "why". The reader will want to know *why*
> > call_usermodehelper() only runs on kthreadd CPUs, but we didn't tell
> > him.
>
> We'd like to have the ability to avoid running usermodehelper on certain
> cpus to avoid cpu holdoff situations? Would that we an acceptable
> explanation?
>
> Or restricting kthreadd will also restrict usermodehelper spawning to
> allow control for all spawned kernel threads?

Both, please ;)
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