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Date:	Thu, 6 Mar 2014 10:10:09 +0100
From:	Igor Mammedov <>
To:	Ingo Molnar <>
Subject: Re: [PATCH] abort secondary CPU bring-up gracefully if do_boot_cpu
 timed out on cpu_callin_mask

On Thu, 6 Mar 2014 08:08:32 +0100
Ingo Molnar <> wrote:

> * Igor Mammedov <> 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

> Thanks,
> 	Ingo

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