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

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Date:   Thu, 18 Aug 2022 22:39:21 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Petr Mladek <pmladek@...e.com>, Michal Hocko <mhocko@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [RFC PATCH 1/8] workqueue: Unconditionally set cpumask in worker_attach_to_pool()

On Wed, Aug 17, 2022 at 5:18 AM Tejun Heo <tj@...nel.org> wrote:
>
> cc'ing Waiman.
>
> 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.
> >
> > Do unconditionally affinity binding in worker_attach_to_pool() to fix
> > the problem.
> >
> > Prepare for moving worker_attach_to_pool() from create_worker() to the
> > starting of worker_thread() which will really cause the said interval
> > even without spurious wakeup.
>
> So, this looks fine but I think the whole thing can be simplified if we
> integrate this with the persistent user cpumask change that Waiman is
> working on. We can just set the cpumask once during init and let the
> scheduler core figure out what the current effective mask is as CPU
> availability changes.
>
>  http://lkml.kernel.org/r/20220816192734.67115-4-longman@redhat.com
>

I like this approach.