2 files changed, 11 insertions, 1 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 1751ec4c47c9..5668ab249af5 100644
--- 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 590f4d048ec7..cecd4ffe2c40 100644
--- 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);