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SubjectRe: 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

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