linux-kernel - Re: system hung up when offlining CPUs

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Date:   Mon, 2 Oct 2017 12:36:52 -0400
From:   YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kashyap Desai <kashyap.desai@...adcom.com>,
        Hannes Reinecke <hare@...e.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        mpe@...erman.id.au, keith.busch@...el.com, peterz@...radead.org,
        LKML <linux-kernel@...r.kernel.org>, linux-scsi@...r.kernel.org,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan Srikanteshwara 
        <shivasharan.srikanteshwara@...adcom.com>
Subject: Re: system hung up when offlining CPUs



On 09/16/2017 11:02 AM, Thomas Gleixner wrote:
> On Sat, 16 Sep 2017, Thomas Gleixner wrote:
>> On Thu, 14 Sep 2017, YASUAKI ISHIMATSU wrote:
>>> Here are one irq's info of megasas:
>>>
>>> - Before offline CPU
>>> /proc/irq/70/smp_affinity_list
>>> 24-29
>>>
>>> /proc/irq/70/effective_affinity
>>> 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,3f000000
>>>
>>> /sys/kernel/debug/irq/irqs/70
>>> handler:  handle_edge_irq
>>> status:   0x00004000
>>> istate:   0x00000000
>>> ddepth:   0
>>> wdepth:   0
>>> dstate:   0x00609200
>>>             IRQD_ACTIVATED
>>>             IRQD_IRQ_STARTED
>>>             IRQD_MOVE_PCNTXT
>>>             IRQD_AFFINITY_SET
>>>             IRQD_AFFINITY_MANAGED
>>
>> So this uses managed affinity, which means that once the last CPU in the
>> affinity mask goes offline, the interrupt is shut down by the irq core
>> code, which is the case:
>>
>>> dstate:   0x00a39000
>>>             IRQD_IRQ_DISABLED
>>>             IRQD_IRQ_MASKED
>>>             IRQD_MOVE_PCNTXT
>>>             IRQD_AFFINITY_SET
>>>             IRQD_AFFINITY_MANAGED
>>>             IRQD_MANAGED_SHUTDOWN  <---------------
>>
>> So the irq core code works as expected, but something in the
>> driver/scsi/block stack seems to fiddle with that shut down queue.
>>
>> I only can tell about the inner workings of the irq code, but I have no
>> clue about the rest.
> 
> Though there is something wrong here:
> 
>> affinity: 24-29
>> effectiv: 24-29
> 
> and after offlining:
> 
>> affinity: 29
>> effectiv: 29
> 
> But that should be:
> 
> affinity: 24-29
> effectiv: 29
> 
> because the irq core code preserves 'affinity'. It merily updates
> 'effective', which is where your interrupts are routed to.
> 
> Is the driver issuing any set_affinity() calls? If so, that's wrong.
> 
> Which driver are we talking about?

We are talking about megasas driver.
So I added linux-scsi and maintainers of megasas into the thread.

Thanks,
Yasuaki Ishimatsu

> 
> Thanks,
> 
> 	tglx
>