linux-kernel - Re: race condition in schedule_on_each

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Date:	Thu, 6 Jun 2013 14:23:03 -0700
From:	Tejun Heo <tj@...nel.org>
To:	韦奇 <weiqi@...inos.com.cn>
Cc:	torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: race condition in schedule_on_each_cpu()

Hello,

On Thu, Jun 06, 2013 at 06:14:46PM +0800, 韦奇 wrote:
> Hello, Tejun Heo
> thanks for your help,
> 1) I've test the two kernel version on this problem:
>     latest 3.10-rc3：(https://www.kernel.org/pub/linux/kernel/v3.x/testing/linux-3.10-rc3.tar.xz)
>      latest 3.0branch - 3.0.80：(https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.0.80.tar.xz
> 
> they all work fine when hot remove raid disk..

Thanks for verifying.

> | preemption                  | machine 1      | machine 2      | kversion    |
> -------------------------------------------------------------------------------
> | Fully Preemptible           |      stuck     |      no stuck  | 3.0.30-rt50 |
> | Low-Latency Desktop         |      no stuck  |      no stuck  | 3.0.30-rt50 |
> | Low-Latency Desktop         |      no stuck  |      --        | 3.0.30      |
> | default                     |      no stuck  |      --        | 3.0.80      |
> | default                     |      no stuck  |      --        | 3.10-rc3    |
> 
> could you tell me some way to debug this problem. for example, how
> to debug workqueue deadlock? I want to find the deadlock point.

I looked through the logs but the only worker depletion related
patches which pop up are around CPU hotplugs, so I don't think they
apply here.  If the problem is relatively easy to reproduce && you
can't move onto a newer kernel, I'm afraid bisection probably is the
best option.

Thanks!

-- 
tejun
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