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 <imran.f.khan@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/tty/sysrq.c

@@ -296,7 +296,7 @@ static const struct sysrq_key_op sysrq_showregs_op = {
 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

@@ -469,7 +469,8 @@ extern bool workqueue_congested(int cpu, struct workqueue_struct *wq);
 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

@@ -94,7 +94,7 @@ static int try_to_freeze_tasks(bool user_only)
 		       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

@@ -375,6 +375,7 @@ EXPORT_SYMBOL_GPL(system_freezable_power_efficient_wq);
 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>
@@ -4447,7 +4448,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
 			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);
@@ -4797,25 +4798,14 @@ static void show_pwq(struct pool_workqueue *pwq)
 }
 
 /**
- * show_workqueue_state - dump workqueue state
- *
- * Called from a sysrq handler or try_to_freeze_tasks() and prints out
- * all busy workqueues and pools.
+ * show_one_workqueue - dump state of specified workqueue
+ * @wq: workqueue whose state will be printed
  */
-void show_workqueue_state(void)
+void show_one_workqueue(struct workqueue_struct *wq)
 {
-	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;
+	unsigned long flags;
 
 	for_each_pwq(pwq, wq) {
 		if (pwq->nr_active || !list_empty(&pwq->inactive_works)) {
@@ -4823,8 +4813,8 @@ void show_workqueue_state(void)
 			break;
 		}
 	}
-		if (idle)
-			continue;
+	if (idle) /* Nothing to print for idle workqueue */
+		return;
 
 	pr_info("workqueue %s: flags=0x%x\n", wq->name, wq->flags);
 
@@ -4843,16 +4833,23 @@ void show_workqueue_state(void)
 		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
+		 * sysrq-t -> show_all_workqueues(). Avoid triggering
 		 * hard lockup.
 		 */
 		touch_nmi_watchdog();
 	}
-	}
 
-	for_each_pool(pool, pi) {
+}
+
+/**
+ * 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)
@@ -4878,15 +4875,38 @@ void show_workqueue_state(void)
 	}
 	pr_cont("\n");
 	printk_deferred_exit();
-	next_pool:
+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
+	 * 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_all_workqueues(void)
+{
+	struct workqueue_struct *wq;
+	struct worker_pool *pool;
+	int pi;
+
+	rcu_read_lock();
+
+	pr_info("Showing busy workqueues and worker pools:\n");
+
+	list_for_each_entry_rcu(wq, &workqueues, list)
+		show_one_workqueue(wq);
+
+	for_each_pool(pool, pi)
+		show_one_worker_pool(pool);
 
 	rcu_read_unlock();
 }
@@ -5876,7 +5896,7 @@ static void wq_watchdog_timer_fn(struct timer_list *unused)
 	rcu_read_unlock();
 
 	if (lockup_detected)
-		show_workqueue_state();
+		show_all_workqueues();
 
 	wq_watchdog_reset_touched();
 	mod_timer(&wq_watchdog_timer, jiffies + thresh);