linux-kernel - Re: [PATCH REPOST v3.9-rc1] sched: replace PF_THREAD_BOUND with PF_NO

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Message-ID: <20130318094140.GB25045@gmail.com>
Date:	Mon, 18 Mar 2013 10:41:40 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH REPOST v3.9-rc1] sched: replace PF_THREAD_BOUND with
 PF_NO_SETAFFINITY


* Tejun Heo <tj@...nel.org> wrote:

> PF_THREAD_BOUND was originally used to mark kernel threads which were
> bound to a specific CPU using kthread_bind() and a task with the flag
> set allows cpus_allowed modifications only to itself.  Workqueue is
> currently abusing it to prevent userland from meddling with
> cpus_allowed of workqueue workers.
> 
> What we need is a flag to prevent userland from messing with
> cpus_allowed of certain kernel tasks.  In kernel, anyone can
> (incorrectly) squash the flag, and, for worker-type usages,
> restricting cpus_allowed modification to the task itself doesn't
> provide meaningful extra proection as other tasks can inject work
> items to the task anyway.
> 
> This patch replaces PF_THREAD_BOUND with PF_NO_SETAFFINITY.
> sched_setaffinity() checks the flag and return -EINVAL if set.
> set_cpus_allowed_ptr() is no longer affected by the flag.
> 
> This will allow simplifying workqueue worker CPU affinity management.

Acked-by: Ingo Molnar <mingo@...nel.org>

I suspect you want to carry this in the workqueue tree, to enable those 
extra simplifications?

Thanks,

	Ingo
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