[PATCH UPDATED 28/31] workqueue: reject adjusting max_active or applying attrs to ordered workqueues

Tejun Heo
2013-03-04T18:30:10Z

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>
---
include/linux/workqueue.h | 3 ++-
kernel/workqueue.c | 9 +++++++++
2 files changed, 11 insertions(+), 1 deletion(-)

--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -294,6 +294,7 @@ 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 */
@@ -396,7 +397,7 @@ __alloc_workqueue_key(const char *fmt, u
* 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)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3487,9 +3487,14 @@ int apply_workqueue_attrs(struct workque
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;
@@ -3745,6 +3750,10 @@ void workqueue_set_max_active(struct wor
{
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);