linux-kernel - Re: [PATCH] nohz: Make tick_nohz_irq

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Date:	Thu, 21 Feb 2013 17:46:16 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org
Subject: Re: [PATCH] nohz: Make tick_nohz_irq_exit() irq safe

On Thu, 21 Feb 2013, Frederic Weisbecker wrote:
> 2013/2/21 Thomas Gleixner <tglx@...utronix.de>:
> > On Wed, 20 Feb 2013, Frederic Weisbecker wrote:
> >> 2013/2/20 Thomas Gleixner <tglx@...utronix.de>:
> >> > That's not a fix. That's an hack.
> >>
> >> I know it looks that way. That's because it's a pure regression fix,
> >> minimal for backportability.
> >>
> >> I'm distinguishing two different things here: the fact that some archs
> >> can call irq_exit() with interrupts enabled which is a global design
> >> problem, and the fact that tick_nohz_irq_exit() was safe against that
> >> until 3.2 when I broke it with a commit of mine.
> >>
> >> My goal was basically to restore that protection in a minimal commit
> >> such that we can backport the regression fix, then deal with
> >> __ARCH_IRQ_EXIT_IRQS_DISABLED afterward, since it requires some more
> >> invasive changes.
> >>
> >> >> A saner long term solution will be to remove
> >> >> __ARCH_IRQ_EXIT_IRQS_DISABLED.
> >> >
> >> > We really want to enforce that interrupt disabled condition for
> >> > calling irq_exit(). So why make this exclusive to tick_nohz_irq_exit()?
> >>
> >> I need a fix that I can backport. Is the below fine with a stable tag?
> >> It looks a bit too invasive for the single regression involved.
> >
> > I think that's fine as it's obviously correct and not diluting the
> > real underlying issue of the __ARCH_IRQ_EXIT_IRQS_DISABLED insanity.
> 
> Ok fine. Do you plan to commit your proposed change then?

Second thoughts. I probably go for your minimal fix for stable and
then push my version on top of it to Linus only.

Thanks,

	tglx
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