Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/14/2015 11:44 AM, Thomas Gleixner wrote:
> On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
> > > Prevent allocation and freeing of interrupt descriptors accross cpu
> > > hotplug.
> > This breaks Xen guests that allocate interrupt descriptors in .cpu_up().
> And where exactly does XEN allocate those descriptors?
xen_cpu_up()
    xen_setup_timer()
        bind_virq_to_irqhandler()
            bind_virq_to_irq()
                xen_allocate_irq_dynamic()
                    xen_allocate_irqs_dynamic()
                        irq_alloc_descs()


There is also a similar pass via xen_cpu_up() -> xen_smp_intr_init()


>   
> > Any chance this locking can be moved into arch code?
> No.
>
> > (The patch doesn't appear to have any side effects for the down path since Xen
> > guests deallocate descriptors in __cpu_die()).
>   
> Exact place please.
Whose place? Where descriptors are deallocated?

__cpu_die()
    xen_cpu_die()
        xen_teardown_timer()
            unbind_from_irqhandler()
                unbind_from_irq()
                    __unbind_from_irq()
                        xen_free_irq()
                            irq_free_descs()
                                free_desc()

-boris


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