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

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Message-ID: <alpine.DEB.2.11.1506191815110.4107@nanos>
Date:	Fri, 19 Jun 2015 18:15:46 +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:

> [...]
> >> 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 ...

Thanks,

	tglx
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