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: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 1751ec4c47c9c079aa78b7c7a952e616d0ff6a9c..5668ab249af55c3f24e1f442ea982bb10c6ead29 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -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)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 590f4d048ec7245198bcd1ee2254244a3e768a55..cecd4ffe2c40c20ec554da3e0058dcb355658469 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -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);