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

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Date:	Thu, 21 Feb 2013 00:15:55 +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 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.

Thanks,

	tglx
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