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

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Message-ID: <20140306133211.GA2220@gmail.com>
Date:	Thu, 6 Mar 2014 14:32:11 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, drjones@...hat.com,
	toshi.kani@...com, prarit@...hat.com,
	kirill.shutemov@...ux.intel.com, JBeulich@...e.com,
	peterz@...radead.org, paul.gortmaker@...driver.com,
	seiji.aguchi@....com, bp@...e.de, hpa@...or.com, mingo@...hat.com,
	x86@...nel.org, tglx@...utronix.de, riel@...hat.com
Subject: Re: [PATCH] abort secondary CPU bring-up gracefully if do_boot_cpu
 timed out on cpu_callin_mask


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

> On Thu, 6 Mar 2014 08:08:32 +0100
> Ingo Molnar <mingo@...nel.org> wrote:
> 
> > 
> > * Igor Mammedov <imammedo@...hat.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
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