linux-kernel - Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed for kthreadd

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Message-Id: <20131017122344.39d55db97c3923131bdf2831@linux-foundation.org>
Date:	Thu, 17 Oct 2013 12:23:44 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Frysinger <vapier@...too.org>
Subject: Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed for
 kthreadd

On Wed, 16 Oct 2013 22:37:52 +0000 Christoph Lameter <cl@...ux.com> 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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