Re: [PATCH] abort secondary CPU bring-up gracefully if do_boot_cpu timed out on cpu_callin_mask

[Ingo Molnar <mingo@kernel.org>]

* Igor Mammedov <imammedo@redhat.com> wrote:

> On Thu, 6 Mar 2014 08:08:32 +0100
> Ingo Molnar <mingo@kernel.org> wrote:
> 
> > 
> > * Igor Mammedov <imammedo@redhat.com> wrote:
> > 
> > > Master CPU may timeout before cpu_callin_mask is set and cancel
> > > booting CPU, but being onlined CPU still continues to boot, sets
> > > cpu_active_mask (CPU_STARTING notifiers) and spins in
> > > check_tsc_sync_target() for master cpu to arrive. Following attempt
> > > to online another cpu hangs in stop_machine, initiated from here:
> > 
> > The changelog needs to prominently contain a description of the 
> > practical relevance of this patch: has the hang triggered on any 
> > system and under what circumstances, and did the patch resolve the 
> > hang, etc.?
> 
> Hang is observed on virtual machines during CPU hotplug, especially 
> in big guests with many CPUs. (It happens more often if host is 
> over-committed).
> 
> Similar patch is carried in RHEL6 since 2012 and it fixes issue 
> there, when applied to upstream kernel it also fixes issue.

Okay, cool - please update the patch description with that and 
resubmit.

Thanks,

	Ingo