Commit 8719dcea authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: reject adjusting max_active or applying attrs to ordered workqueues 



Adjusting max_active of or applying new workqueue_attrs to an ordered
workqueue breaks its ordering guarantee.  The former is obvious.  The
latter is because applying attrs creates a new pwq (pool_workqueue)
and there is no ordering constraint between the old and new pwqs.

Make apply_workqueue_attrs() and workqueue_set_max_active() trigger
WARN_ON() if those operations are requested on an ordered workqueue
and fail / ignore respectively.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent 618b01eb

include/linux/workqueue.h

+2 −1
Original line number Diff line number Diff line
@@ -295,6 +295,7 @@ enum { 
	WQ_CPU_INTENSIVE	= 1 << 5, /* cpu instensive workqueue */



	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */

	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */



	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */

	WQ_MAX_UNBOUND_PER_CPU	= 4,	  /* 4 * #cpus for unbound wq */
@@ -397,7 +398,7 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active, 
 * Pointer to the allocated workqueue on success, %NULL on failure.

 */

#define alloc_ordered_workqueue(fmt, flags, args...)			\

	alloc_workqueue(fmt, WQ_UNBOUND | (flags), 1, ##args)

	alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)



#define create_workqueue(name)						\

	alloc_workqueue((name), WQ_MEM_RECLAIM, 1)

kernel/workqueue.c

+9 −0
Original line number Diff line number Diff line
@@ -3494,9 +3494,14 @@ int apply_workqueue_attrs(struct workqueue_struct *wq, 
	struct pool_workqueue *pwq, *last_pwq;

	struct worker_pool *pool;



	/* only unbound workqueues can change attributes */

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

		return -EINVAL;



	/* creating multiple pwqs breaks ordering guarantee */

	if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))

		return -EINVAL;



	pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);

	if (!pwq)

		return -ENOMEM;
@@ -3752,6 +3757,10 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active) 
{

	struct pool_workqueue *pwq;



	/* disallow meddling with max_active for ordered workqueues */

	if (WARN_ON(wq->flags & __WQ_ORDERED))

		return;



	max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);



	spin_lock_irq(&workqueue_lock);

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