Re: [PATCH v2 27/52] x86, pci, amd-bus: Fix CPU hotplug callback registration

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On Fri, Feb 14, 2014 at 12:55 AM, Srivatsa S. Bhat
<srivatsa.bhat@xxxxxxxxxxxxxxxxxx> wrote:
> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
>
>         get_online_cpus();
>
>         for_each_online_cpu(cpu)
>                 init_cpu(cpu);
>
>         register_cpu_notifier(&foobar_cpu_notifier);
>
>         put_online_cpus();
>
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).
>
> Instead, the correct and race-free way of performing the callback
> registration is:
>
>         cpu_notifier_register_begin();
>
>         for_each_online_cpu(cpu)
>                 init_cpu(cpu);
>
>         /* Note the use of the double underscored version of the API */
>         __register_cpu_notifier(&foobar_cpu_notifier);
>
>         cpu_notifier_register_done();
>
>
> Fix the amd-bus code in x86 by using this latter form of callback
> registration.
>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>

This looks fine to me.

Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

I think it makes sense for you to merge it along with all your other
similar changes.  I don't foresee any conflicts with things in my PCI
tree.

> ---
>
>  arch/x86/pci/amd_bus.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/pci/amd_bus.c b/arch/x86/pci/amd_bus.c
> index a48be98..f05cbf0 100644
> --- a/arch/x86/pci/amd_bus.c
> +++ b/arch/x86/pci/amd_bus.c
> @@ -380,10 +380,13 @@ static int __init pci_io_ecs_init(void)
>         if (early_pci_allowed())
>                 pci_enable_pci_io_ecs();
>
> -       register_cpu_notifier(&amd_cpu_notifier);
> +       cpu_notifier_register_begin();
>         for_each_online_cpu(cpu)
>                 amd_cpu_notify(&amd_cpu_notifier, (unsigned long)CPU_ONLINE,
>                                (void *)(long)cpu);
> +       __register_cpu_notifier(&amd_cpu_notifier);
> +       cpu_notifier_register_done();
> +
>         pci_probe |= PCI_HAS_IO_ECS;
>
>         return 0;
>
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