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Subject: Re: [PATCH] set_cpus_allowed() atomicity fix
From: Robert Love <rml@tech9.net>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
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Date: 09 Oct 2002 21:05:17 -0400
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On Wed, 2002-10-09 at 19:17, Linus Torvalds wrote:

> On 9 Oct 2002, Robert Love wrote:
> > 
> > Anyhow, attached patch fixes the atomicity debugging error.
> 
> I don't think this is right. You have to be preempt safe over the whole 
> time you're holding the "rq" pointer, I think. Otherwise you might move to 
> another CPU, at which point the rq state isn't valid any more. Or maybe I 
> misunderstood.

I agree.  But aren't we?

We are preempt-safe through the entire function (starting at the top
with task_rq_lock()) until the preempt_disable().  The only instruction
outside of the critical section is the wait_for_completion() which
sleeps anyhow.

Or maybe _I_ misunderstood?

	Robert Love