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

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Date:	Sat, 20 Jun 2015 00:12:41 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
CC:	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()

[...]
>> 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:)

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