linux-kernel - Re: [PATCH] workqueue: Protects wq_unbound_cpumask with wq_pool_attach

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Message-ID: <Ywlmb1ADhHnfFUI8@slm.duckdns.org>
Date:   Fri, 26 Aug 2022 14:33:51 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Phil Auld <pauld@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Zqiang <qiang1.zhang@...el.com>
Subject: Re: [PATCH] workqueue: Protects wq_unbound_cpumask with
 wq_pool_attach_mutex

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