linux-kernel - Re: [-next] !irqd_can_balance() WARNINGs at irq_move_masked

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Message-ID: <alpine.DEB.2.11.1506191829260.4107@nanos>
Date:	Fri, 19 Jun 2015 18:30:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [-next] !irqd_can_balance() WARNINGs at irq_move_masked_irq()

On Sat, 20 Jun 2015, Jiang Liu wrote:
> On 2015/6/20 0:15, Thomas Gleixner wrote:
> > On Sat, 20 Jun 2015, Jiang Liu wrote:
> > 
> >> [...]
> >>>> Something in the kernel (not yet clear what) tries to move the hpet
> >>>> irq 0 by calling irq_set_affinity(). That's an kernel internal
> >>>> interface which does not check whether the NO BALANCE flag is set for
> >>>> the irq. So the call runs and triggers the move from next interrupt
> >>>> machinery which ends up calling irq_move_masked_irq() and that trips
> >>>> over the flag and yells.
> >>>>
> >>>> That's why I changed the WARN to a pr_warn() because we already know
> >>>> the call stack.
> >>>>
> >>>> So the core behaviour is inconsistent. We let the caller of
> >>>> irq_set_affinity() succeed and yell later because we think it's wrong.
> >>>>
> >>>> I'm pretty sure that we must drop the check for NO BALANCE in
> >>>> irq_move_masked_irq() and only check for the per_cpu bit, but at the
> >>>> same time I really want to know where that call to irq_set_affinity(irq0)
> >>>> is coming from.
> >>>>
> >>>> Can you please collect the output of /proc/timer_list for the previous
> >>>> patch and then replace the previous patch with the one below and
> >>>> gather all the data again?
> >>>
> >>> Hi Thomas,
> >>> 	Maybe it's caused by the hpet driver itself?
> >>> irq_set_affinity() may set the IRQD_SETAFFINITY_PENDING flag,
> >>> thus triggering the warning.
> >> And the usage pattern seems reasonable, the IRQF_NOBALANCING flag
> >> means nobody may change the affinity except myself:)
> > 
> > Right, that's why I removed the restriction. I just wonder why we have
> > not seen that before ...
> I suspected it's caused by the hierarchy irqdomain at first glance
> because the multiple irq_datas issue, but seems it's not after checking
> the code. It will only be triggered if HPET works in MSI mode instead of
> legacy IRQ mode, but still need more investigation here.

Right. And what confuses me is that this happens on irq0, which is
ioapic edge.

Thanks,

	tglx

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