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

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Date:	Sat, 20 Jun 2015 00:09:45 +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()



On 2015/6/19 20:21, Thomas Gleixner wrote:
> On Fri, 19 Jun 2015, Thomas Gleixner wrote:
>> On Fri, 19 Jun 2015, Sergey Senozhatsky wrote:
>>> [    0.412291] WARNING: CPU: 0 PID: 0 at kernel/irq/migration.c:21 irq_move_masked_irq+0x57/0xc4()
>>> [    0.412371] Can't balance irq 0 [edge]
>>
>> Yuck.
>>
>>> Do you guys want to replace WAN_ON() with WARN_ONCE(), perhaps? This, of course,
>>> doesn't fix anything; but at least one can boot the system. (not really a patch,
>>> just an idea).
>>
>> Indeed. We really want to clear the move pending bit before the can
>> balance check. Patch below. But that does not explain why this happens
>> in the first place.
>>
>> Can you please send me a full dmesg, kernel config and output of
>> /proc/interrupts ? (Private mail is fine, or upload it to some place)
> 
> Thanks for providing the data. I think I know what happens.
> 
> 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.
---------------------------------------------------------------
static int hpet_setup_irq(struct hpet_dev *dev)
{

        if (request_irq(dev->irq, hpet_interrupt_handler,
                        IRQF_TIMER | IRQF_NOBALANCING,
                        dev->name, dev))
                return -1;

        disable_irq(dev->irq);
        irq_set_affinity(dev->irq, cpumask_of(dev->cpu));
        enable_irq(dev->irq);

        printk(KERN_DEBUG "hpet: %s irq %d for MSI\n",
                         dev->name, dev->irq);

        return 0;
}
-------------------------------------------------------------
Thanks!
Gerry

> 
> Thanks,
> 
> 	tglx
> 
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