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

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Date:	Thu, 21 Feb 2013 17:13:18 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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

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?
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