workqueue: Introduce show_one_worker_pool and show_one_workqueue.

Currently show_workqueue_state shows the state of all workqueues and of
all worker pools. In certain cases we may need to dump state of only a
specific workqueue or worker pool. For example in destroy_workqueue we
only need to show state of the workqueue which is getting destroyed.

So rename show_workqueue_state to show_all_workqueues(to signify it
dumps state of all busy workqueues) and divide it into more granular
functions (show_one_workqueue and show_one_worker_pool), that would show
states of individual workqueues and worker pools and can be used in
cases such as the one mentioned above.

Also, as mentioned earlier, make destroy_workqueue dump data pertaining
to only the workqueue that is being destroyed and make user(s) of
earlier interface(show_workqueue_state), use new interface
(show_all_workqueues).

Signed-off-by: Imran Khan <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

drivers/tty/sysrq.c

···
 static void sysrq_handle_showstate(int key)
 {
 	show_state();
-	show_workqueue_state();
+	show_all_workqueues();
 }
 static const struct sysrq_key_op sysrq_showstate_op = {
 	.handler	= sysrq_handle_showstate,

include/linux/workqueue.h

···
 extern unsigned int work_busy(struct work_struct *work);
 extern __printf(1, 2) void set_worker_desc(const char *fmt, ...);
 extern void print_worker_info(const char *log_lvl, struct task_struct *task);
-extern void show_workqueue_state(void);
+extern void show_all_workqueues(void);
+extern void show_one_workqueue(struct workqueue_struct *wq);
 extern void wq_worker_comm(char *buf, size_t size, struct task_struct *task);
 
 /**

kernel/power/process.c

···
 		       todo - wq_busy, wq_busy);
 
 		if (wq_busy)
-			show_workqueue_state();
+			show_all_workqueues();
 
 		if (!wakeup || pm_debug_messages_on) {
 			read_lock(&tasklist_lock);

kernel/workqueue.c

···
 static int worker_thread(void *__worker);
 static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 static void show_pwq(struct pool_workqueue *pwq);
+static void show_one_worker_pool(struct worker_pool *pool);
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/workqueue.h>
···
 			raw_spin_unlock_irq(&pwq->pool->lock);
 			mutex_unlock(&wq->mutex);
 			mutex_unlock(&wq_pool_mutex);
-			show_workqueue_state();
+			show_one_workqueue(wq);
 			return;
 		}
 		raw_spin_unlock_irq(&pwq->pool->lock);
···
 }
 
 /**
- * show_workqueue_state - dump workqueue state
+ * show_one_workqueue - dump state of specified workqueue
+ * @wq: workqueue whose state will be printed
+ */
+void show_one_workqueue(struct workqueue_struct *wq)
+{
+	struct pool_workqueue *pwq;
+	bool idle = true;
+	unsigned long flags;
+
+	for_each_pwq(pwq, wq) {
+		if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
+			idle = false;
+			break;
+		}
+	}
+	if (idle) /* Nothing to print for idle workqueue */
+		return;
+
+	pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
+
+	for_each_pwq(pwq, wq) {
+		raw_spin_lock_irqsave(&pwq->pool->lock, flags);
+		if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
+			/*
+			 * Defer printing to avoid deadlocks in console
+			 * drivers that queue work while holding locks
+			 * also taken in their write paths.
+			 */
+			printk_deferred_enter();
+			show_pwq(pwq);
+			printk_deferred_exit();
+		}
+		raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
+		/*
+		 * We could be printing a lot from atomic context, e.g.
+		 * sysrq-t -> show_all_workqueues(). Avoid triggering
+		 * hard lockup.
+		 */
+		touch_nmi_watchdog();
+	}
+
+}
+
+/**
+ * show_one_worker_pool - dump state of specified worker pool
+ * @pool: worker pool whose state will be printed
+ */
+static void show_one_worker_pool(struct worker_pool *pool)
+{
+	struct worker *worker;
+	bool first = true;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&pool->lock, flags);
+	if (pool->nr_workers == pool->nr_idle)
+		goto next_pool;
+	/*
+	 * Defer printing to avoid deadlocks in console drivers that
+	 * queue work while holding locks also taken in their write
+	 * paths.
+	 */
+	printk_deferred_enter();
+	pr_info("pool %d:", pool->id);
+	pr_cont_pool_info(pool);
+	pr_cont(" hung=%us workers=%d",
+		jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
+		pool->nr_workers);
+	if (pool->manager)
+		pr_cont(" manager: %d",
+			task_pid_nr(pool->manager->task));
+	list_for_each_entry(worker, &pool->idle_list, entry) {
+		pr_cont(" %s%d", first ? "idle: " : "",
+			task_pid_nr(worker->task));
+		first = false;
+	}
+	pr_cont("\n");
+	printk_deferred_exit();
+next_pool:
+	raw_spin_unlock_irqrestore(&pool->lock, flags);
+	/*
+	 * We could be printing a lot from atomic context, e.g.
+	 * sysrq-t -> show_all_workqueues(). Avoid triggering
+	 * hard lockup.
+	 */
+	touch_nmi_watchdog();
+
+}
+
+/**
+ * show_all_workqueues - dump workqueue state
  *
  * Called from a sysrq handler or try_to_freeze_tasks() and prints out
  * all busy workqueues and pools.
  */
-void show_workqueue_state(void)
+void show_all_workqueues(void)
 {
 	struct workqueue_struct *wq;
 	struct worker_pool *pool;
-	unsigned long flags;
 	int pi;
 
 	rcu_read_lock();
 
 	pr_info("Showing busy workqueues and worker pools:\n");
 
-	list_for_each_entry_rcu(wq, &workqueues, list) {
-		struct pool_workqueue *pwq;
-		bool idle = true;
+	list_for_each_entry_rcu(wq, &workqueues, list)
+		show_one_workqueue(wq);
 
-		for_each_pwq(pwq, wq) {
-			if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
-				idle = false;
-				break;
-			}
-		}
-		if (idle)
-			continue;
-
-		pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
-
-		for_each_pwq(pwq, wq) {
-			raw_spin_lock_irqsave(&pwq->pool->lock, flags);
-			if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
-				/*
-				 * Defer printing to avoid deadlocks in console
-				 * drivers that queue work while holding locks
-				 * also taken in their write paths.
-				 */
-				printk_deferred_enter();
-				show_pwq(pwq);
-				printk_deferred_exit();
-			}
-			raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
-			/*
-			 * We could be printing a lot from atomic context, e.g.
-			 * sysrq-t -> show_workqueue_state(). Avoid triggering
-			 * hard lockup.
-			 */
-			touch_nmi_watchdog();
-		}
-	}
-
-	for_each_pool(pool, pi) {
-		struct worker *worker;
-		bool first = true;
-
-		raw_spin_lock_irqsave(&pool->lock, flags);
-		if (pool->nr_workers == pool->nr_idle)
-			goto next_pool;
-		/*
-		 * Defer printing to avoid deadlocks in console drivers that
-		 * queue work while holding locks also taken in their write
-		 * paths.
-		 */
-		printk_deferred_enter();
-		pr_info("pool %d:", pool->id);
-		pr_cont_pool_info(pool);
-		pr_cont(" hung=%us workers=%d",
-			jiffies_to_msecs(jiffies - pool->watchdog_ts) / 1000,
-			pool->nr_workers);
-		if (pool->manager)
-			pr_cont(" manager: %d",
-				task_pid_nr(pool->manager->task));
-		list_for_each_entry(worker, &pool->idle_list, entry) {
-			pr_cont(" %s%d", first ? "idle: " : "",
-				task_pid_nr(worker->task));
-			first = false;
-		}
-		pr_cont("\n");
-		printk_deferred_exit();
-	next_pool:
-		raw_spin_unlock_irqrestore(&pool->lock, flags);
-		/*
-		 * We could be printing a lot from atomic context, e.g.
-		 * sysrq-t -> show_workqueue_state(). Avoid triggering
-		 * hard lockup.
-		 */
-		touch_nmi_watchdog();
-	}
+	for_each_pool(pool, pi)
+		show_one_worker_pool(pool);
 
 	rcu_read_unlock();
 }
···
 	rcu_read_unlock();
 
 	if (lockup_detected)
-		show_workqueue_state();
+		show_all_workqueues();
 
 	wq_watchdog_reset_touched();
 	mod_timer(&wq_watchdog_timer, jiffies + thresh);