linux-kernel - Re: [PATCH v5 4/4] x86: initialize secondary CPU only if master CPU will wait for it

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Date:	Mon, 05 May 2014 15:35:10 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Igor Mammedov <imammedo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, bp@...e.de,
	paul.gortmaker@...driver.com, JBeulich@...e.com, prarit@...hat.com,
	drjones@...hat.com, riel@...hat.com, gong.chen@...ux.intel.com,
	andi@...stfloor.org, lenb@...nel.org, rjw@...ysocki.net,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v5 4/4] x86: initialize secondary CPU only if master CPU
 will wait for it

On Mon, 2014-05-05 at 22:49 +0200, Igor Mammedov wrote:
> Hang is observed on virtual machines during CPU hotplug,
> especially in big guests with many CPUs. (It reproducible
> more often if host is over-committed).
> 
> It happens because master CPU gives up waiting on
> secondary CPU and allows it to run wild. As result
> AP causes locking or crashing system. For example
> as described here: https://lkml.org/lkml/2014/3/6/257
> 
> If master CPU have sent STARTUP IPI successfully,
> and AP signalled to master CPU that it's ready
> to start initialization, make master CPU wait
> indefinitely till AP is onlined.
> To ensure that AP won't ever run wild, make it
> wait at early startup till master CPU confirms its
> intention to wait for AP. If AP doesn't respond in 10
> seconds, the master CPU will timeout and cancel
> AP onlining.
> 
> Signed-off-by: Igor Mammedov <imammedo@...hat.com>

Thanks for the update.

Acked-by: Toshi Kani <toshi.kani@...com>

-Toshi

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