linux-kernel - Re: [PATCH v4 4/4] workqueue: Unbind workers before sending them to exit()

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Message-ID: <xhsmh7d1e2qp2.mognet@vschneid.remote.csb>
Date:   Wed, 05 Oct 2022 17:14:17 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v4 4/4] workqueue: Unbind workers before sending them to
 exit()

On 05/10/22 22:50, Hillf Danton wrote:
> On 05 Oct 2022 12:13:17 +0100 Valentin Schneider <vschneid@...hat.com>
>
> Bound kworkers can be destroyed by the idle timer on a housekeeping CPU.
>
> Diff is only for thoughts.
>
> +++ b/kernel/workqueue.c
> @@ -1985,6 +1985,7 @@ fail:
>  static void destroy_worker(struct worker *worker)
>  {
>       struct worker_pool *pool = worker->pool;
> +	int cpu = smp_processor_id();
>
>       lockdep_assert_held(&pool->lock);
>
> @@ -1999,6 +2000,12 @@ static void destroy_worker(struct worker
>
>       list_del_init(&worker->entry);
>       worker->flags |= WORKER_DIE;
> +
> +	if (!(pool->flags & POOL_DISASSOCIATED) && pool->cpu != cpu) {
> +		/* send worker to die on a housekeeping cpu */
> +		cpumask_clear(&worker->task->cpus_mask);
> +		cpumask_set_cpu(cpu, &worker->task->cpus_mask);
> +	}
>       wake_up_process(worker->task);
>  }
>

The proper interface to play with that cpumask is set_cpus_allowed_ptr(),
which requires a sleepable context, hence the whole series.