workqueue: factor out start_flush_work()

Factor out start_flush_work() from flush_work().  start_flush_work()
has @wait_executing argument which controls whether the barrier is
queued only if the work is pending or also if executing.  As
flush_work() needs to wait for execution too, it uses %true.

This commit doesn't cause any behavior difference.  start_flush_work()
will be used to implement flush_work_sync().

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1240b9d..33d31d7 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2326,35 +2326,17 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(flush_workqueue);
 
-/**
- * flush_work - wait for a work to finish executing the last queueing instance
- * @work: the work to flush
- *
- * Wait until @work has finished execution.  This function considers
- * only the last queueing instance of @work.  If @work has been
- * enqueued across different CPUs on a non-reentrant workqueue or on
- * multiple workqueues, @work might still be executing on return on
- * some of the CPUs from earlier queueing.
- *
- * If @work was queued only on a non-reentrant, ordered or unbound
- * workqueue, @work is guaranteed to be idle on return if it hasn't
- * been requeued since flush started.
- *
- * RETURNS:
- * %true if flush_work() waited for the work to finish execution,
- * %false if it was already idle.
- */
-bool flush_work(struct work_struct *work)
+static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
+                            bool wait_executing)
 {
        struct worker *worker = NULL;
        struct global_cwq *gcwq;
        struct cpu_workqueue_struct *cwq;
-       struct wq_barrier barr;
 
        might_sleep();
        gcwq = get_work_gcwq(work);
        if (!gcwq)
-               return 0;
+               return false;
 
        spin_lock_irq(&gcwq->lock);
        if (!list_empty(&work->entry)) {
@@ -2367,26 +2349,54 @@ bool flush_work(struct work_struct *work)
                cwq = get_work_cwq(work);
                if (unlikely(!cwq || gcwq != cwq->gcwq))
                        goto already_gone;
-       } else {
+       } else if (wait_executing) {
                worker = find_worker_executing_work(gcwq, work);
                if (!worker)
                        goto already_gone;
                cwq = worker->current_cwq;
-       }
+       } else
+               goto already_gone;
 
-       insert_wq_barrier(cwq, &barr, work, worker);
+       insert_wq_barrier(cwq, barr, work, worker);
        spin_unlock_irq(&gcwq->lock);
 
        lock_map_acquire(&cwq->wq->lockdep_map);
        lock_map_release(&cwq->wq->lockdep_map);
-
-       wait_for_completion(&barr.done);
-       destroy_work_on_stack(&barr.work);
        return true;
 already_gone:
        spin_unlock_irq(&gcwq->lock);
        return false;
 }
+
+/**
+ * flush_work - wait for a work to finish executing the last queueing instance
+ * @work: the work to flush
+ *
+ * Wait until @work has finished execution.  This function considers
+ * only the last queueing instance of @work.  If @work has been
+ * enqueued across different CPUs on a non-reentrant workqueue or on
+ * multiple workqueues, @work might still be executing on return on
+ * some of the CPUs from earlier queueing.
+ *
+ * If @work was queued only on a non-reentrant, ordered or unbound
+ * workqueue, @work is guaranteed to be idle on return if it hasn't
+ * been requeued since flush started.
+ *
+ * RETURNS:
+ * %true if flush_work() waited for the work to finish execution,
+ * %false if it was already idle.
+ */
+bool flush_work(struct work_struct *work)
+{
+       struct wq_barrier barr;
+
+       if (start_flush_work(work, &barr, true)) {
+               wait_for_completion(&barr.done);
+               destroy_work_on_stack(&barr.work);
+               return true;
+       } else
+               return false;
+}
 EXPORT_SYMBOL_GPL(flush_work);
 
 static bool wait_on_cpu_work(struct global_cwq *gcwq, struct work_struct *work)