Merge branch 'for-5.6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq
Pull workqueue fixes from Tejun Heo:
"Workqueue has been incorrectly round-robining per-cpu work items.
Hillf's patch fixes that.
The other patch documents memory-ordering properties of workqueue
operations"
* 'for-5.6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
workqueue: don't use wq_select_unbound_cpu() for bound works
workqueue: Document (some) memory-ordering properties of {queue,schedule}_work()
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 4261d1c..e48554e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -487,6 +487,19 @@
*
* We queue the work to the CPU on which it was submitted, but if the CPU dies
* it can be processed by another CPU.
+ *
+ * Memory-ordering properties: If it returns %true, guarantees that all stores
+ * preceding the call to queue_work() in the program order will be visible from
+ * the CPU which will execute @work by the time such work executes, e.g.,
+ *
+ * { x is initially 0 }
+ *
+ * CPU0 CPU1
+ *
+ * WRITE_ONCE(x, 1); [ @work is being executed ]
+ * r0 = queue_work(wq, work); r1 = READ_ONCE(x);
+ *
+ * Forbids: r0 == true && r1 == 0
*/
static inline bool queue_work(struct workqueue_struct *wq,
struct work_struct *work)
@@ -546,6 +559,9 @@
* This puts a job in the kernel-global workqueue if it was not already
* queued and leaves it in the same position on the kernel-global
* workqueue otherwise.
+ *
+ * Shares the same memory-ordering properties of queue_work(), cf. the
+ * DocBook header of queue_work().
*/
static inline bool schedule_work(struct work_struct *work)
{
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 301db44..4e01c44 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1411,14 +1411,16 @@
return;
rcu_read_lock();
retry:
- if (req_cpu == WORK_CPU_UNBOUND)
- cpu = wq_select_unbound_cpu(raw_smp_processor_id());
-
/* pwq which will be used unless @work is executing elsewhere */
- if (!(wq->flags & WQ_UNBOUND))
- pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
- else
+ if (wq->flags & WQ_UNBOUND) {
+ if (req_cpu == WORK_CPU_UNBOUND)
+ cpu = wq_select_unbound_cpu(raw_smp_processor_id());
pwq = unbound_pwq_by_node(wq, cpu_to_node(cpu));
+ } else {
+ if (req_cpu == WORK_CPU_UNBOUND)
+ cpu = raw_smp_processor_id();
+ pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
+ }
/*
* If @work was previously on a different pool, it might still be
