On Tue, 2016-04-12 at 19:08 +0100, Luis Henriques wrote:
> 3.16.7-ckt27 -stable review patch. If anyone has any objections, please let me know.
>
> ---8<------------------------------------------------------------
>
> From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
>
> commit e513229b4c386e6c9f66298c13fde92f73e6e1ac upstream.
>
> When an SMP Hyper-V guest is running on top of 2012R2 Server and secondary
> cpus are sent offline (with echo 0 > /sys/devices/system/cpu/cpu$cpu/online)
> the system freeze is observed. This happens due to the fact that on newer
> hypervisors (Win8, WS2012R2, ...) vmbus channel handlers are distributed
> across all cpus (see init_vp_index() function in drivers/hv/channel_mgmt.c)
> and on cpu offlining nobody reassigns them to CPU0. Prevent cpu offlining
> when vmbus is loaded until the issue is fixed host-side.
>
> This patch also disables hibernation but it is OK as it is also broken (MCE
> error is hit on resume). Suspend still works.
[...]
> +static void hv_cpu_hotplug_quirk(bool vmbus_loaded)
> +{
> + static void *previous_cpu_disable;
> +
> + /*
> + * Offlining a CPU when running on newer hypervisors (WS2012R2, Win8,
> + * ...) is not supported at this moment as channel interrupts are
> + * distributed across all of them.
> + */
> +
> + if ((vmbus_proto_version == VERSION_WS2008) ||
> + (vmbus_proto_version == VERSION_WIN7))
> + return;
> +
> + if (vmbus_loaded) {
> + previous_cpu_disable = smp_ops.cpu_disable;
> + smp_ops.cpu_disable = hyperv_cpu_disable;
> + pr_notice("CPU offlining is not supported by hypervisor\n");
> + } else if (previous_cpu_disable)
> + smp_ops.cpu_disable = previous_cpu_disable;
[...]
This is a really bad hack. What if two different drivers patched
smp_ops and got unloaded in a different order? Perhaps the core
support code for Hyper-V should define its own smp_ops.
I don't want to stop this going into stable, but seriously, please
clean this up.
Ben.
--
Ben Hutchings
In a hierarchy, every employee tends to rise to his level of incompetence.Attachment:
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