Re: [PATCH] workqueue: Protects wq_unbound_cpumask with wq_pool_attach_mutex

[Tejun Heo]

Hello,

On Thu, Aug 18, 2022 at 10:33:48PM +0800, Lai Jiangshan wrote:
> @@ -5342,6 +5344,11 @@ static int workqueue_apply_unbound_cpumask(void)
>  		apply_wqattrs_cleanup(ctx);
>  	}
>  
> +	if (!ret) {
> +		mutex_lock(&wq_pool_attach_mutex);
> +		cpumask_copy(wq_unbound_cpumask, unbound_cpumask);
> +		mutex_unlock(&wq_pool_attach_mutex);

Is this enough? Shouldn't the lock be protecting a wider scope? If there's
someone reading the flag with just pool_attach_mutex, what prevents them
reading it right before the new value is committed and keeps using the stale
value?

Thanks.

-- 
tejun