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

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Date:   Sat, 16 Sep 2017 17:02:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
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 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?

Thanks,

	tglx