linux-kernel - Re: [PATCH 02/12] workqueue: disallow set_cpus_allowed

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Message-ID: <20120926181230.GC12544@google.com>
Date:	Wed, 26 Sep 2012 11:12:30 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, tangchen <tangchen@...fujitsu.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 02/12] workqueue: disallow set_cpus_allowed_ptr() from
 work item

On Thu, Sep 27, 2012 at 01:20:33AM +0800, Lai Jiangshan wrote:
> workers depend on local-wake-up, if a work function change its CPU, it will
> corrupt workqueue, disallow this behavior.
> 
> When set_cpus_allowed_ptr() is called from workqueue.c in worker_thread(),
> we clear the PF_WQ_WORKER before set_cpus_allowed_ptr() and set it back
> after. (rescuer thread has no PF_WQ_WORKER, skip this behavior)
> 
> It prevents other/future BUGs like https://bugzilla.kernel.org/show_bug.cgi?id=47301.

Hmmm... maybe.  We better clear up PF_THREAD_BOUND semantics first
tho.

I think the two possible choices are,

* Don't allow set_cpus_allowed_ptr() at all and make the caller
  responsible for turning it off if it explicitly wants to change
  cpus_allowed.

* Don't allow changing affinity from userland.

Peter, Thomas?

-- 
tejun
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