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SubjectRe: [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The comment was outdated before too but the updated one isn't correct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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