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workqueue: reject adjusting max_active or applying attrs to ordered w…
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…orkqueues

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: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
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Tejun Heo committed Mar 12, 2013
1 parent 618b01e commit 8719dce
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Showing 2 changed files with 11 additions and 1 deletion.
3 changes: 2 additions & 1 deletion include/linux/workqueue.h
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down Expand Up @@ -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)
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9 changes: 9 additions & 0 deletions kernel/workqueue.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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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