linux-kernel - Re: [PATCH v4 3/3] powerpc/powernv: Introduce sysfs control for fastsleep workaround behavior

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Message-ID: <552DFFC1.6050806@linux.vnet.ibm.com>
Date:	Wed, 15 Apr 2015 11:35:53 +0530
From:	Shreyas B Prabhu <shreyas@...ux.vnet.ibm.com>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>
CC:	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 3/3] powerpc/powernv: Introduce sysfs control for fastsleep
 workaround behavior


> 
> A point that bothers me here is if we can potentially race with cpu
> hotplug ? If cpuX and its siblings are offline and it was interrupted to
> come online:
> 
> cpuX                                     cpuY
> Interrupted to come online
> Undo workaround
> 
>                                 Nop the fastsleep_workaround_exit path
>                                 IPI online cores: apply workaround once
> 
> Set yourself in the online mask
>                                 Nop the fastsleep_workaround_entry path
> 
> 
> This results in cpuX undoing the workaround on its core, never to set it
> back again.
> 
> So should we protect the region between the beginning and end of
> patching instructions with get_online_cpus() and put_online_cpus() ?
> 

Nice catch. I had missed this. Sending out a patch correcting this.

Thanks,
Shreyas

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