linux-kernel - Re: [PATCH] workqueue: fix rebind bound workers warning

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Message-ID: <20160509170013.GI7110@mtj.duckdns.org>
Date:	Mon, 9 May 2016 13:00:13 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	linux-kernel@...r.kernel.org, Wanpeng Li <wanpeng.li@...mail.com>,
	Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] workqueue: fix rebind bound workers warning

Hello,

On Thu, May 05, 2016 at 09:41:31AM +0800, Wanpeng Li wrote:
> The boot CPU handles housekeeping duty(unbound timers, workqueues, 
> timekeeping, ...) on behalf of full dynticks CPUs. It must remain 
> online when nohz full is enabled. There is a priority set to every
> notifier_blocks:
> 
> workqueue_cpu_up > tick_nohz_cpu_down > workqueue_cpu_down
> 
> So tick_nohz_cpu_down callback failed when down prepare cpu 0, and 
> notifier_blocks behind tick_nohz_cpu_down will not be called any 
> more, which leads to workers are actually not unbound. Then hotplug 
> state machine will fallback to undo and online cpu 0 again. Workers 
> will be rebound unconditionally even if they are not unbound and 
> trigger the warning in this progress.

I'm a bit confused.  Are you saying that the hotplug statemachine may
invoke CPU_DOWN_FAILED w/o preceding CPU_DOWN on the same callback?

Thanks.

-- 
tejun