RE: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Greg Kroah-Hartman [mailto:gregkh@linuxfoundation.org]
> Sent: Monday, January 26, 2015 2:54 PM
> To: Vitaly Kuznetsov
> Cc: KY Srinivasan; devel@linuxdriverproject.org; Haiyang Zhang; linux-
> kernel@vger.kernel.org; Dexuan Cui
> Subject: Re: [PATCH v3] Drivers: hv: vmbus: prevent cpu offlining on newer
> hypervisors
> 
> On Mon, Jan 26, 2015 at 11:38:54AM +0100, Vitaly Kuznetsov wrote:
> > Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> >
> > > On Mon, Jan 12, 2015 at 05:50:11PM +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>
> > >> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> > >> ---
> > >> Changes since v2:
> > >> - repair the build when vmbus is builded as a module [Greg KH] by
> saving
> > >>   current cpu_disable pointer to previous_cpu_disable and restoring it
> on
> > >>   unload;
> > >> - return -ENOSYS (same as native_cpu_disable when
> !CONFIG_HOTPLUG_CPU) instead
> > >>   of -1 in hyperv_cpu_disable().
> > >>
> > >> Changes since v1:
> > >> - introduce hv_cpu_hotplug_quirk() function to not spread #ifdefs
> > >> [Greg KH];
> > >> - add pr_notice() message "hv_vmbus: CPU offlining is not supported by
> > >>   hypervisor".
> > >> ---
> > >>  drivers/hv/vmbus_drv.c | 36
> ++++++++++++++++++++++++++++++++++++
> > >>  1 file changed, 36 insertions(+)
> > >
> > > Doesn't apply to my char-misc-test branch at all :(
> >
> > Another mid-air collision with K.Y's "Drivers: hv: vmbus: Implement a
> > clockevent device", please use the attached version. No functional
> > changes are required, I just fixed the merge conflict (includes).
> >
> > Othere than that (and sorry for meddling), would it it be better if
> > you switch to 'pull requests' workflow with K.Y? There is a lot of
> > ongoing work in hyperv nowdays and such collisions seem otherwise
> > inevitable ...
> 
> This is a trivial number of patches for this subsystem, so no, a git workflow
> isn't needed.  But if KY would collect the patches up and send them to me for
> all hyperv patches from now on, that would make these types of issues go
> away, KY, can you do that from now on?

Will do.

Thanks,

K. Y
> 
> thanks,
> 
> greg k-h