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Date: Tue, 20 Sep 2011 11:05:15 -0500 (CDT)
From: Christoph Lameter <cl@gentwo.org>
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To: Peter Zijlstra <peterz@infradead.org>
cc: Thomas Gleixner <tglx@linutronix.de>, Steven Rostedt <rostedt@goodmis.org>,
        Andi Kleen <andi@firstfloor.org>, LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, Tejun Heo <htejun@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for
 this_cpu_read/write()
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On Tue, 20 Sep 2011, Peter Zijlstra wrote:

> On Tue, 2011-09-20 at 10:03 -0500, Christoph Lameter wrote:
> >
> > Well yes the misunderstanding of per cpu operations was one reason why I
> > proposed the discussion on the subject of esoteric kernel synchronization.
> > I do not think that it was accepted.
>
> I don't think anybody here misunderstands it, we're just all very angry
> that its causing so much problems.

What problems? RT does not work with it? The memcg confusion?

> __this_cpu doesn't have preempt debug checks, and there's a lot of
> this_cpu usage that really should have been __this_cpu.

That only works if preemption is disabled when the this_cpu op is being
invoked.