linux-kernel - Re: cpusets and kthreads, inconsistent behaviour

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Message-ID: <alpine.DEB.1.10.0806101350110.29422@chino.kir.corp.google.com>
Date:	Tue, 10 Jun 2008 13:54:50 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Max Krasnyansky <maxk@...lcomm.com>
cc:	Paul Jackson <pj@....com>, mingo@...e.hu,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, menage@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: cpusets and kthreads, inconsistent behaviour

On Tue, 10 Jun 2008, Max Krasnyansky wrote:

> Hmm, technically you are correct of course. But we do not have any other
> kernel tasks besides kthreads. All the kernel tasks I have on my machines have
> kthreadd as their parent.
> And I'm not aware of any kernel code that changes affinity mask of a
> user-space task without paying attention to the cpuset the task belongs to. If
> you know of any we should fix it because it'd clearly be a bug.
> 

This is why it shouldn't belong in the sched or kthread code; the 
discrepency that you point out between p->cpus_allowed and 
task_cs(p)->cpus_allowed is a cpuset created one.

So to avoid having tasks with a cpus_allowed mask that is not a subset of 
its cpuset's set of allowable cpus, the solution would probably be to add 
a flavor of cpuset_update_task_memory_state() for a cpus generation value.
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