Messages in this thread | | | Date | Tue, 14 Jul 2015 19:32:02 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down |
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On Tue, 14 Jul 2015, Boris Ostrovsky wrote: > 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()
Sigh.
> > > > > > Any chance this locking can be moved into arch code? > > No.
The issue here is that all architectures need that protection and just Xen does irq allocations in cpu_up.
So moving that protection into architecture code is not really an option.
> > > Otherwise we will need to have something like arch_post_cpu_up() > > > after the lock is released.
I'm not sure, that this will work. You probably want to do this in the cpu prepare stage, i.e. before calling __cpu_up().
I have to walk the dogs now. Will look into it later tonight.
> > > (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()
Right, that's outside the lock held region.
Thanks,
tglx
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