linux-kernel - Re: [PATCH] workqueue: Handle race between wake up and rebind

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Message-ID: <20180116173534.GR3460072@devbig577.frc2.facebook.com>
Date:   Tue, 16 Jan 2018 09:35:34 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Neeraj Upadhyay <neeraju@...eaurora.org>
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, prsood@...eaurora.org,
        sramana@...eaurora.org
Subject: Re: [PATCH] workqueue: Handle race between wake up and rebind

Hello, Neeraj.

On Mon, Jan 15, 2018 at 02:08:12PM +0530, Neeraj Upadhyay wrote:
> - kworker/0:0 gets chance to run on cpu1; while processing
>   a work, it goes to sleep. However, it does not decrement
>   pool->nr_running. This is because WORKER_REBOUND (NOT_
>   RUNNING) flag was cleared, when worker entered worker_

Do you mean that because REBOUND was set?

>   thread().
> 
>   Worker 0 runs on cpu1
>     worker_thread()
>       process_one_work()
>         wq_worker_sleeping()
>           if (worker->flags & WORKER_NOT_RUNNING)
>             return NULL;
>           if (WARN_ON_ONCE(pool->cpu != raw_smp_processor_id()))
>             <Does not decrement nr_running>
> 
> - After this, when kworker/0:0 wakes up, this time on its
>   bounded cpu cpu0, it increments pool->nr_running again.
>   So, pool->nr_running becomes 2.

Why is it suddenly 2?  Who made it one on the account of the kworker?

Do you see this happening?  Or better, is there a (semi) reliable
repro for this issue?

Thanks.

-- 
tejun