Merge remote-tracking branch 'workqueues/for-next'

2 files changed, 17 insertions, 3 deletions

diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst
index ffdec94fbca1..3943b5bfa8cf 100644
--- a/Documentation/core-api/workqueue.rst
+++ b/Documentation/core-api/workqueue.rst
@@ -243,11 +243,15 @@ throttling the number of active work items, specifying '0' is
 recommended.
 
 Some users depend on the strict execution ordering of ST wq.  The
-combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` is used to
-achieve this behavior.  Work items on such wq are always queued to the
-unbound worker-pools and only one work item can be active at any given
+combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` used to
+achieve this behavior.  Work items on such wq were always queued to the
+unbound worker-pools and only one work item could be active at any given
 time thus achieving the same ordering property as ST wq.
 
+In the current implementation the above configuration only guarantees
+ST behavior within a given NUMA node. Instead alloc_ordered_queue should
+be used to achieve system wide ST behavior.
+
 
 Example Execution Scenarios
 ===========================
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a86688fabc55..abe4a4971c24 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3929,6 +3929,16 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
 	struct workqueue_struct *wq;
 	struct pool_workqueue *pwq;
 
+	/*
+	 * Unbound && max_active == 1 used to imply ordered, which is no
+	 * longer the case on NUMA machines due to per-node pools.  While
+	 * alloc_ordered_workqueue() is the right way to create an ordered
+	 * workqueue, keep the previous behavior to avoid subtle breakages
+	 * on NUMA.
+	 */
+	if ((flags & WQ_UNBOUND) && max_active == 1)
+		flags |= __WQ_ORDERED;
+
 	/* see the comment above the definition of WQ_POWER_EFFICIENT */
 	if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
 		flags |= WQ_UNBOUND;