linux-kernel - Re: [PATCH 1/5] workqueue: wq_pool_mutex protects the attrs-installation

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Date:	Mon, 11 May 2015 08:23:42 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] workqueue: wq_pool_mutex protects the
 attrs-installation

On Mon, May 11, 2015 at 05:35:48PM +0800, Lai Jiangshan wrote:
> @@ -127,6 +127,12 @@ enum {
>   *
>   * PR: wq_pool_mutex protected for writes.  Sched-RCU protected for reads.
>   *
> + * PW: wq_pool_mutex and wq->mutex protected for writes.  Any one of them
> + *     protected for reads.

	  Either for reads.

> + *
> + * PWR: wq_pool_mutex and wq->mutex protected for writes. Any one of them
> + *      or sched-RCU for reads.

	  Ditto.

> + *
>   * WQ: wq->mutex protected.
>   *
>   * WR: wq->mutex protected for writes.  Sched-RCU protected for reads.
...
> @@ -553,7 +565,7 @@ static int worker_pool_assign_id(struct worker_pool *pool)
>   * @wq: the target workqueue
>   * @node: the node ID
>   *
> - * This must be called either with pwq_lock held or sched RCU read locked.
> + * This must be called either with wq_pool_mutex held or sched RCU read locked.

The comment was outdated before too but the updated one isn't correct
either.

>   * If the pwq needs to be used beyond the locking in effect, the caller is
>   * responsible for guaranteeing that the pwq stays online.
>   *
> @@ -562,7 +574,7 @@ static int worker_pool_assign_id(struct worker_pool *pool)
>  static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq,
>  						  int node)
>  {
> -	assert_rcu_or_wq_mutex(wq);
> +	assert_rcu_or_wq_mutex_or_pool_mutex(wq);
>  	return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
>  }
>  
...
> @@ -3644,10 +3657,9 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
>  	 * pwqs accordingly.
>  	 */
>  	get_online_cpus();
> -
>  	mutex_lock(&wq_pool_mutex);
> +
>  	ctx = apply_wqattrs_prepare(wq, attrs);
> -	mutex_unlock(&wq_pool_mutex);
>  
>  	/* the ctx has been prepared successfully, let's commit it */
>  	if (ctx) {
> @@ -3655,10 +3667,11 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
>  		ret = 0;
>  	}
>  
> -	put_online_cpus();
> -
>  	apply_wqattrs_cleanup(ctx);

Why are we protecting cleanup?

> +	mutex_unlock(&wq_pool_mutex);
> +	put_online_cpus();
> +
>  	return ret;
>  }
>  

Thanks.

-- 
tejun
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