workqueue: Introduce show_freezable_workqueues

Currently show_all_workqueue is called if freeze fails at the time of
freeze the workqueues, which shows the status of all workqueues and of
all worker pools. In this cases we may only need to dump state of only
workqueues that are freezable and busy.

This patch defines show_freezable_workqueues, which uses
show_one_workqueue, a granular function that shows the state of individual
workqueues, so that dump only the state of freezable workqueues
at that time.

tj: Minor message adjustment.
Signed-off-by: Jungseung Lee <js07.lee@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/workqueue.h

@@ -472,6 +472,7 @@ 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_all_workqueues(void);
+extern void show_freezable_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

@@ -93,7 +93,7 @@ static int try_to_freeze_tasks(bool user_only)
 		       todo - wq_busy, wq_busy);
 
 		if (wq_busy)
-			show_all_workqueues();
+			show_freezable_workqueues();
 
 		if (!wakeup || pm_debug_messages_on) {
 			read_lock(&tasklist_lock);

kernel/workqueue.c

@@ -5065,8 +5065,7 @@ static void show_one_worker_pool(struct worker_pool *pool)
 /**
  * show_all_workqueues - dump workqueue state
  *
- * Called from a sysrq handler or try_to_freeze_tasks() and prints out
- * all busy workqueues and pools.
+ * Called from a sysrq handler and prints out all busy workqueues and pools.
  */
 void show_all_workqueues(void)
 {
@@ -5087,6 +5086,29 @@ void show_all_workqueues(void)
 	rcu_read_unlock();
 }
 
+/**
+ * show_freezable_workqueues - dump freezable workqueue state
+ *
+ * Called from try_to_freeze_tasks() and prints out all freezable workqueues
+ * still busy.
+ */
+void show_freezable_workqueues(void)
+{
+	struct workqueue_struct *wq;
+
+	rcu_read_lock();
+
+	pr_info("Showing freezable workqueues that are still busy:\n");
+
+	list_for_each_entry_rcu(wq, &workqueues, list) {
+		if (!(wq->flags & WQ_FREEZABLE))
+			continue;
+		show_one_workqueue(wq);
+	}
+
+	rcu_read_unlock();
+}
+
 /* used to show worker information through /proc/PID/{comm,stat,status} */
 void wq_worker_comm(char *buf, size_t size, struct task_struct *task)
 {