linux-kernel - Re: console_cpu_notify can cause scheduling BUG during CPU hotplug

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Message-ID: <4DB894C3.2040300@codeaurora.org>
Date:	Wed, 27 Apr 2011 15:12:19 -0700
From:	Michael Bohan <mbohan@...eaurora.org>
To:	Borislav Petkov <bp@...en8.de>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Cernekee <cernekee@...il.com>, mingo@...e.hu,
	akpm@...ux-foundation.org, simon.kagstrom@...insight.net,
	David.Woodhouse@...el.com, lethal@...ux-sh.org, tj@...nel.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Conny Seidel <conny.seidel@....com>,
	Borislav Petkov <borislav.petkov@....com>
Subject: Re: console_cpu_notify can cause scheduling BUG during CPU hotplug

On 4/27/2011 12:38 AM, Borislav Petkov wrote:
> Great, whatever you guys come up with, we'd like to give it a run too.
> We (AMD) hit the same issue in one of our tests but in our case we end
> up in an endless loop of the state machine at stop_machine_cpu_stop()
> since the core being offlined cannot ack the state transition to
> STOPMACHINE_EXIT due to a similar reason.
>
> One possible fix is dropping CPU_DYING from console_cpu_notify()
> since it is called into by the offlining path in
> kernel/cpu.c::take_cpu_down().

This seems to be a different problem. Could you elaborate about why 
removing CPU_DYING from console_cpu_notify resolves your problem? What 
are other possible fixes?

In the failure case I witnessed, we're attempting to sleep in atomic 
mode, which is a clear violation caused by the addition of CPU_DYING. I 
haven't thoroughly investigated whether other actions in 
console_cpu_notify (eg. ONLINE, DEAD, DOWN_FAILED, UP_CANCELED) are in 
atomic mode violation as well.

Thanks,
Mike

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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