RE: [PATCH] Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

[Dexuan Cui <decui@microsoft.com>]

> -----Original Message-----
> From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On
> Behalf Of Greg Kroah-Hartman
> Sent: Thursday, November 27, 2014 11:03 AM
> To: Vitaly Kuznetsov
> Cc: devel@linuxdriverproject.org; Haiyang Zhang; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH] Drivers: hv: vmbus: prevent cpu offlining on newer
> hypervisors
> 
> On Wed, Nov 26, 2014 at 02:52:22PM +0100, Vitaly Kuznetsov wrote:
> > 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.
> >
> > Tested with WS2008R2 and WS2012R2.
> >
> > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> > ---
> >  drivers/hv/vmbus_drv.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> >
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > index 4d6b269..9a82249 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -32,6 +32,7 @@
> >  #include <linux/completion.h>
> >  #include <linux/hyperv.h>
> >  #include <linux/kernel_stat.h>
> > +#include <linux/cpu.h>
> >  #include <asm/hyperv.h>
> >  #include <asm/hypervisor.h>
> >  #include <asm/mshyperv.h>
> > @@ -671,6 +672,13 @@ static void vmbus_isr(void)
> >  		tasklet_schedule(&msg_dpc);
> >  }
> >
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +static int hyperv_cpu_disable(void)
> > +{
> > +	return -1;
> > +}
> > +#endif
> > +
> >  /*
> >   * vmbus_bus_init -Main vmbus driver initialization routine.
> >   *
> > @@ -711,6 +719,12 @@ static int vmbus_bus_init(int irq)
> >  	if (ret)
> >  		goto err_alloc;
> >
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +	if ((vmbus_proto_version != VERSION_WS2008) &&
> > +	    (vmbus_proto_version != VERSION_WIN7))
> > +		smp_ops.cpu_disable = hyperv_cpu_disable;
> > +#endif
> > +
> >  	vmbus_request_offers();
> >
> >  	return 0;
> > @@ -964,6 +978,11 @@ static void __exit vmbus_exit(void)
> >  	bus_unregister(&hv_bus);
> >  	hv_cleanup();
> >  	acpi_bus_unregister_driver(&vmbus_acpi_driver);
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +	if ((vmbus_proto_version != VERSION_WS2008) &&
> > +	    (vmbus_proto_version != VERSION_WIN7))
> > +		smp_ops.cpu_disable = native_cpu_disable;
> > +#endif
> >  }
> 
> #ifdef in a .c file is not a good idea to do if at all possible, please
> only put this in one place, using a function call to "hide" the mess.
> 
> greg k-h

Hi Vitaly,
The idea of the patch is good to me.

I agree with Greg.
BTW, maybe hv_cpu_hotplug_quirk() is a better name?

Thanks,
-- Dexuan