linux-kernel - Re: [patch 2/2] sched: fix nr_uninterruptible accounting of frozen tasks really

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Date:	Fri, 17 Jul 2009 17:55:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rafael Wysocki <rjw@...k.pl>, Ingo Molnar <mingo@...e.hu>,
	Nathan Lynch <ntl@...ox.com>,
	Nigel Cunningham <nigel@...onice.net>, stable@...nel.org,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org
Subject: Re: [patch 2/2] sched: fix nr_uninterruptible accounting of frozen
 tasks really

On Fri, 2009-07-17 at 08:51 -0700, Matt Helsley wrote:

> So it's not clear to me how adding PF_FREEZING fixes anything. Am I
> missing something?

Yep, PF_FROZEN is only observed going into schedule(), on the way back
out thaw_process() will already have cleared the flag.

So we don't increment in deactivate_task(), but we do decrement in
activate_task(), yielding for some very unbalanced accounting.

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