linux-kernel - Re: [RFC PATCH 1/8] workqueue: Unconditionally set cpumask in worker_attach_to

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Message-ID: <Yx7luoAJpenWO5zK@hirez.programming.kicks-ass.net>
Date:   Mon, 12 Sep 2022 09:54:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Tejun Heo <tj@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Michal Hocko <mhocko@...e.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>
Subject: Re: [RFC PATCH 1/8] workqueue: Unconditionally set cpumask in
 worker_attach_to_pool()

On Thu, Aug 04, 2022 at 04:41:28PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> If a worker is spuriously woken up after kthread_bind_mask() but before
> worker_attach_to_pool(), and there are some cpu-hot-[un]plug happening
> during the same interval, the worker task might be pushed away from its
> bound CPU with its affinity changed by the scheduler and worker_attach_to_pool()
> doesn't rebind it properly.

Can you *please* be more explicit. The above doesn't give me enough clue
to reconstruct the actual scenario you're fixing.

Draw a picture or something.