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

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Message-ID: <00000141c7a80d07-b74ad917-06d0-419a-aac6-ec643e2ccbe2-000000@email.amazonses.com>
Date:	Thu, 17 Oct 2013 18:23:01 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	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>,
	Andrew Morton <akpm@...ux-foundation.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 Thu, 17 Oct 2013, Frederic Weisbecker wrote:

> > The invocation is coming from keventd so the affinity seems to be set to
> > a different cpu before we get the thread moved.
>
> Looking at alloc_singlethread_workqueue(), it seems to create a kthread by using
> kthread_create(). So I guess the resulting works have the affinity of that kthread.
> And thus call_usermodehelper() initially has that affinity, until it spreads it explicitly
> to all CPUs.
>
> Couldn't we instead make kthread children (those created with kthread_create()) to inherit
> kthread initial affinity? Currently kthread's children have cpu_all_mask. We could change
> that behaviour. This way the initial kthread affinity could be inherited all along.

Some of the code relies on being able to set the affinities separately.
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