linux-kernel - Re: [PATCH] workqueue: Fix pool->nr

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Date: Tue, 6 Feb 2024 06:52:41 -1000
From: Tejun Heo <tj@...nel.org>
To: Yunlong Xing <yunlong.xing@...soc.com>
Cc: jiangshanlai@...il.com, yunlong.xing23@...il.com,
	linux-kernel@...r.kernel.org, hongyu.jin@...soc.com,
	zhiguo.niu@...soc.com, zhengxu.zhang@...soc.com
Subject: Re: [PATCH] workqueue: Fix pool->nr_running type back to atomic

Hello,

On Tue, Feb 06, 2024 at 04:00:24PM +0800, Yunlong Xing wrote:
> In CPU-hotplug test, when plug the core, set_cpus_allowed_ptr() restoring
> the cpus_mask of the per-cpu worker may fail, the cpus_mask of the worker
> remain wq_unbound_cpumask until the core hotpluged next time. so, workers
> in the same per-cpu pool can run concurrently and change nr_running at the
>  same time, atomic problem occur.

How would set_cpus_allowed_ptr() fail? That should trigger WARN_ON, right?
If set_cpus_allowed_ptr() fails, nr_running getting desynchronized is only a
part of the problem. We will end up running per-cpu work items which must
execute on the same CPU on foreign CPUs.

Thanks.

-- 
tejun