workqueue: implement several utility APIs

Implement the following utility APIs.

 workqueue_set_max_active()	: adjust max_active of a wq
 workqueue_congested()		: test whether a wq is contested
 work_cpu()			: determine the last / current cpu of a work
 work_busy()			: query whether a work is busy

* Anton Blanchard fixed missing ret initialization in work_busy().
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Anton Blanchard <anton@samba.org>

include/linux/workqueue.h

@@ -61,6 +61,10 @@ enum {
 	WORK_STRUCT_FLAG_MASK	= (1UL << WORK_STRUCT_FLAG_BITS) - 1,
 	WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
 	WORK_STRUCT_NO_CPU	= NR_CPUS << WORK_STRUCT_FLAG_BITS,
+
+	/* bit mask for work_busy() return values */
+	WORK_BUSY_PENDING	= 1 << 0,
+	WORK_BUSY_RUNNING	= 1 << 1,
 };
 
 struct work_struct {
@@ -307,9 +311,14 @@ extern void init_workqueues(void);
 int execute_in_process_context(work_func_t fn, struct execute_work *);
 
 extern int flush_work(struct work_struct *work);
-
 extern int cancel_work_sync(struct work_struct *work);
 
+extern void workqueue_set_max_active(struct workqueue_struct *wq,
+				     int max_active);
+extern bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq);
+extern unsigned int work_cpu(struct work_struct *work);
+extern unsigned int work_busy(struct work_struct *work);
+
 /*
  * Kill off a pending schedule_delayed_work().  Note that the work callback
  * function may still be running on return from cancel_delayed_work(), unless

kernel/workqueue.c

@@ -203,7 +203,7 @@ struct workqueue_struct {
 	cpumask_var_t		mayday_mask;	/* cpus requesting rescue */
 	struct worker		*rescuer;	/* I: rescue worker */
 
-	int			saved_max_active; /* I: saved cwq max_active */
+	int			saved_max_active; /* W: saved cwq max_active */
 	const char		*name;		/* I: workqueue name */
 #ifdef CONFIG_LOCKDEP
 	struct lockdep_map	lockdep_map;
@@ -2675,6 +2675,112 @@ void destroy_workqueue(struct workqueue_struct *wq)
 }
 EXPORT_SYMBOL_GPL(destroy_workqueue);
 
+/**
+ * workqueue_set_max_active - adjust max_active of a workqueue
+ * @wq: target workqueue
+ * @max_active: new max_active value.
+ *
+ * Set max_active of @wq to @max_active.
+ *
+ * CONTEXT:
+ * Don't call from IRQ context.
+ */
+void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
+{
+	unsigned int cpu;
+
+	max_active = wq_clamp_max_active(max_active, wq->name);
+
+	spin_lock(&workqueue_lock);
+
+	wq->saved_max_active = max_active;
+
+	for_each_possible_cpu(cpu) {
+		struct global_cwq *gcwq = get_gcwq(cpu);
+
+		spin_lock_irq(&gcwq->lock);
+
+		if (!(wq->flags & WQ_FREEZEABLE) ||
+		    !(gcwq->flags & GCWQ_FREEZING))
+			get_cwq(gcwq->cpu, wq)->max_active = max_active;
+
+		spin_unlock_irq(&gcwq->lock);
+	}
+
+	spin_unlock(&workqueue_lock);
+}
+EXPORT_SYMBOL_GPL(workqueue_set_max_active);
+
+/**
+ * workqueue_congested - test whether a workqueue is congested
+ * @cpu: CPU in question
+ * @wq: target workqueue
+ *
+ * Test whether @wq's cpu workqueue for @cpu is congested.  There is
+ * no synchronization around this function and the test result is
+ * unreliable and only useful as advisory hints or for debugging.
+ *
+ * RETURNS:
+ * %true if congested, %false otherwise.
+ */
+bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq)
+{
+	struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+	return !list_empty(&cwq->delayed_works);
+}
+EXPORT_SYMBOL_GPL(workqueue_congested);
+
+/**
+ * work_cpu - return the last known associated cpu for @work
+ * @work: the work of interest
+ *
+ * RETURNS:
+ * CPU number if @work was ever queued.  NR_CPUS otherwise.
+ */
+unsigned int work_cpu(struct work_struct *work)
+{
+	struct global_cwq *gcwq = get_work_gcwq(work);
+
+	return gcwq ? gcwq->cpu : NR_CPUS;
+}
+EXPORT_SYMBOL_GPL(work_cpu);
+
+/**
+ * work_busy - test whether a work is currently pending or running
+ * @work: the work to be tested
+ *
+ * Test whether @work is currently pending or running.  There is no
+ * synchronization around this function and the test result is
+ * unreliable and only useful as advisory hints or for debugging.
+ * Especially for reentrant wqs, the pending state might hide the
+ * running state.
+ *
+ * RETURNS:
+ * OR'd bitmask of WORK_BUSY_* bits.
+ */
+unsigned int work_busy(struct work_struct *work)
+{
+	struct global_cwq *gcwq = get_work_gcwq(work);
+	unsigned long flags;
+	unsigned int ret = 0;
+
+	if (!gcwq)
+		return false;
+
+	spin_lock_irqsave(&gcwq->lock, flags);
+
+	if (work_pending(work))
+		ret |= WORK_BUSY_PENDING;
+	if (find_worker_executing_work(gcwq, work))
+		ret |= WORK_BUSY_RUNNING;
+
+	spin_unlock_irqrestore(&gcwq->lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(work_busy);
+
 /*
  * CPU hotplug.
  *