PM: Allow wakeup events to abort freezing of tasks

If there is a wakeup event during the freezing of tasks, suspend or
hibernation will fail anyway.  Since try_to_freeze_tasks() can take
up to 20 seconds to complete or fail, aborting it as soon as a wakeup
event is detected improves the worst case wakeup latency.

Based on a patch from Arve Hjønnevåg.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>

include/linux/suspend.h

@@ -308,6 +308,8 @@ static inline int unregister_pm_notifier(struct notifier_block *nb)
 }
 
 #define pm_notifier(fn, pri)	do { (void)(fn); } while (0)
+
+static inline bool pm_check_wakeup_events(void) { return true; }
 #endif /* !CONFIG_PM_SLEEP */
 
 extern struct mutex pm_mutex;

kernel/power/process.c

@@ -40,6 +40,7 @@ static int try_to_freeze_tasks(bool sig_only)
 	struct timeval start, end;
 	u64 elapsed_csecs64;
 	unsigned int elapsed_csecs;
+	bool wakeup = false;
 
 	do_gettimeofday(&start);
 
@@ -78,6 +79,11 @@ static int try_to_freeze_tasks(bool sig_only)
 		if (!todo || time_after(jiffies, end_time))
 			break;
 
+		if (!pm_check_wakeup_events()) {
+			wakeup = true;
+			break;
+		}
+
 		/*
 		 * We need to retry, but first give the freezing tasks some
 		 * time to enter the regrigerator.
@@ -97,8 +103,9 @@ static int try_to_freeze_tasks(bool sig_only)
 		 * but it cleans up leftover PF_FREEZE requests.
 		 */
 		printk("\n");
-		printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "
+		printk(KERN_ERR "Freezing of tasks %s after %d.%02d seconds "
 		       "(%d tasks refusing to freeze, wq_busy=%d):\n",
+		       wakeup ? "aborted" : "failed",
 		       elapsed_csecs / 100, elapsed_csecs % 100,
 		       todo - wq_busy, wq_busy);
 
@@ -107,7 +114,7 @@ static int try_to_freeze_tasks(bool sig_only)
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
 			task_lock(p);
-			if (freezing(p) && !freezer_should_skip(p))
+			if (!wakeup && freezing(p) && !freezer_should_skip(p))
 				sched_show_task(p);
 			cancel_freezing(p);
 			task_unlock(p);