linux-kernel - Re: [Xen-devel] [PATCH v7] x86: initialize secondary CPU only if master CPU will wait for it

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Date:	Tue, 24 Jun 2014 13:25:25 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Igor Mammedov <imammedo@...hat.com>
CC:	linux-kernel@...r.kernel.org, toshi.kani@...com, x86@...nel.org,
	mingo@...hat.com, hpa@...or.com, xen-devel@...ts.xenproject.org,
	tglx@...utronix.de
Subject: Re: [Xen-devel] [PATCH v7] x86: initialize secondary CPU only if
 master CPU will wait for it

On 06/20/2014 08:23 AM, 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>

On Xen:

Tested-by: Boris Ostrovsky <boris.ostrovsky@...ce.com>

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