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Commit 9e8cd2f5 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: implement apply_workqueue_attrs() 



Implement apply_workqueue_attrs() which applies workqueue_attrs to the
specified unbound workqueue by creating a new pwq (pool_workqueue)
linked to worker_pool with the specified attributes.

A new pwq is linked at the head of wq->pwqs instead of tail and
__queue_work() verifies that the first unbound pwq has positive refcnt
before choosing it for the actual queueing.  This is to cover the case
where creation of a new pwq races with queueing.  As base ref on a pwq
won't be dropped without making another pwq the first one,
__queue_work() is guaranteed to make progress and not add work item to
a dead pwq.

init_and_link_pwq() is updated to return the last first pwq the new
pwq replaced, which is put by apply_workqueue_attrs().

Note that apply_workqueue_attrs() is almost identical to unbound pwq
part of alloc_and_link_pwqs().  The only difference is that there is
no previous first pwq.  apply_workqueue_attrs() is implemented to
handle such cases and replaces unbound pwq handling in
alloc_and_link_pwqs().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent c9178087

include/linux/workqueue.h

+2 −0
Original line number Diff line number Diff line
@@ -410,6 +410,8 @@ extern void destroy_workqueue(struct workqueue_struct *wq); 


struct workqueue_attrs *alloc_workqueue_attrs(gfp_t gfp_mask);

void free_workqueue_attrs(struct workqueue_attrs *attrs);

int apply_workqueue_attrs(struct workqueue_struct *wq,

			  const struct workqueue_attrs *attrs);



extern bool queue_work_on(int cpu, struct workqueue_struct *wq,

			struct work_struct *work);

kernel/workqueue.c

+71 −20
Original line number Diff line number Diff line
@@ -1228,7 +1228,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
	if (unlikely(wq->flags & WQ_DRAINING) &&

	    WARN_ON_ONCE(!is_chained_work(wq)))

		return;



retry:

	/* pwq which will be used unless @work is executing elsewhere */

	if (!(wq->flags & WQ_UNBOUND)) {

		if (cpu == WORK_CPU_UNBOUND)
@@ -1262,6 +1262,25 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
		spin_lock(&pwq->pool->lock);

	}



	/*

	 * pwq is determined and locked.  For unbound pools, we could have

	 * raced with pwq release and it could already be dead.  If its

	 * refcnt is zero, repeat pwq selection.  Note that pwqs never die

	 * without another pwq replacing it as the first pwq or while a

	 * work item is executing on it, so the retying is guaranteed to

	 * make forward-progress.

	 */

	if (unlikely(!pwq->refcnt)) {

		if (wq->flags & WQ_UNBOUND) {

			spin_unlock(&pwq->pool->lock);

			cpu_relax();

			goto retry;

		}

		/* oops */

		WARN_ONCE(true, "workqueue: per-cpu pwq for %s on cpu%d has 0 refcnt",

			  wq->name, cpu);

	}



	/* pwq determined, queue */

	trace_workqueue_queue_work(req_cpu, pwq, work);
@@ -3425,7 +3444,8 @@ static void pwq_unbound_release_workfn(struct work_struct *work) 


static void init_and_link_pwq(struct pool_workqueue *pwq,

			      struct workqueue_struct *wq,

			      struct worker_pool *pool)

			      struct worker_pool *pool,

			      struct pool_workqueue **p_last_pwq)

{

	BUG_ON((unsigned long)pwq & WORK_STRUCT_FLAG_MASK);
@@ -3445,13 +3465,58 @@ static void init_and_link_pwq(struct pool_workqueue *pwq, 
	mutex_lock(&wq->flush_mutex);

	spin_lock_irq(&workqueue_lock);



	if (p_last_pwq)

		*p_last_pwq = first_pwq(wq);

	pwq->work_color = wq->work_color;

	list_add_tail_rcu(&pwq->pwqs_node, &wq->pwqs);

	list_add_rcu(&pwq->pwqs_node, &wq->pwqs);



	spin_unlock_irq(&workqueue_lock);

	mutex_unlock(&wq->flush_mutex);

}



/**

 * apply_workqueue_attrs - apply new workqueue_attrs to an unbound workqueue

 * @wq: the target workqueue

 * @attrs: the workqueue_attrs to apply, allocated with alloc_workqueue_attrs()

 *

 * Apply @attrs to an unbound workqueue @wq.  If @attrs doesn't match the

 * current attributes, a new pwq is created and made the first pwq which

 * will serve all new work items.  Older pwqs are released as in-flight

 * work items finish.  Note that a work item which repeatedly requeues

 * itself back-to-back will stay on its current pwq.

 *

 * Performs GFP_KERNEL allocations.  Returns 0 on success and -errno on

 * failure.

 */

int apply_workqueue_attrs(struct workqueue_struct *wq,

			  const struct workqueue_attrs *attrs)

{

	struct pool_workqueue *pwq, *last_pwq;

	struct worker_pool *pool;



	if (WARN_ON(!(wq->flags & WQ_UNBOUND)))

		return -EINVAL;



	pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);

	if (!pwq)

		return -ENOMEM;



	pool = get_unbound_pool(attrs);

	if (!pool) {

		kmem_cache_free(pwq_cache, pwq);

		return -ENOMEM;

	}



	init_and_link_pwq(pwq, wq, pool, &last_pwq);

	if (last_pwq) {

		spin_lock_irq(&last_pwq->pool->lock);

		put_pwq(last_pwq);

		spin_unlock_irq(&last_pwq->pool->lock);

	}



	return 0;

}



static int alloc_and_link_pwqs(struct workqueue_struct *wq)

{

	bool highpri = wq->flags & WQ_HIGHPRI;
@@ -3468,26 +3533,12 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq) 
			struct worker_pool *cpu_pools =

				per_cpu(cpu_worker_pools, cpu);



			init_and_link_pwq(pwq, wq, &cpu_pools[highpri]);

			init_and_link_pwq(pwq, wq, &cpu_pools[highpri], NULL);

		}

		return 0;

	} else {

		struct pool_workqueue *pwq;

		struct worker_pool *pool;



		pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);

		if (!pwq)

			return -ENOMEM;



		pool = get_unbound_pool(unbound_std_wq_attrs[highpri]);

		if (!pool) {

			kmem_cache_free(pwq_cache, pwq);

			return -ENOMEM;

		}



		init_and_link_pwq(pwq, wq, pool);

		return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);

	}



	return 0;

}



static int wq_clamp_max_active(int max_active, unsigned int flags,