[PATCH -mm 0/3] Freezer: Use wait queue instead of busy looping

@@ -227,18 +227,21 @@ int freeze_processes(void)
 {
 	int error;
 
-	printk("Stopping tasks ... ");
+	printk("Freezing user space processes ... ");
 	error = try_to_freeze_tasks(FREEZER_USER_SPACE);
 	if (error)
-		return error;
+		goto Exit;
+	printk("done.\n");
 
+	printk("Freezing remaining freezable tasks ... ");
 	error = try_to_freeze_tasks(FREEZER_KERNEL_THREADS);
 	if (error)
-		return error;
-
-	printk("done.\n");
+		goto Exit;
+	printk("done.");
+ Exit:
 	BUG_ON(in_atomic());
-	return 0;
+	printk("\n");
+	return error;
 }
 
 static void thaw_tasks(int thaw_user_space)

@@ -19,6 +19,12 @@
  */
 #define TIMEOUT	(20 * HZ)
 
+/*
+ * Time to wait until one or more tasks enter the refrigerator after sending
+ * freeze requests to them.
+ */
+#define WAIT_TIME (HZ / 5)
+
 #define FREEZER_KERNEL_THREADS 0
 #define FREEZER_USER_SPACE 1
 

@@ -43,6 +49,18 @@ static inline void frozen_process(void)
 	clear_freeze_flag(current);
 }
 
+/*
+ * Wait queue head used by try_to_freeze_tasks() to wait for tasks to enter the
+ * refrigerator.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(refrigerator_waitq);
+
+/*
+ * Used to notify try_to_freeze_tasks() that the refrigerator has been entered
+ * by a task.
+ */
+static int refrigerator_called;
+
 /* Refrigerator is place where frozen processes are stored :-). */
 void refrigerator(void)
 {

@@ -58,6 +76,10 @@ void refrigerator(void)
 		task_unlock(current);
 		return;
 	}
+
+	refrigerator_called = 1;
+	wake_up(&refrigerator_waitq);
+
 	save = current->state;
 	pr_debug("%s entered refrigerator\n", current->comm);
 

@@ -170,6 +192,7 @@ static int try_to_freeze_tasks(int freez
 	unsigned int todo;
 
 	end_time = jiffies + TIMEOUT;
+	refrigerator_called = 0;
 	do {
 		todo = 0;
 		read_lock(&tasklist_lock);

@@ -189,7 +212,16 @@ static int try_to_freeze_tasks(int freez
 				todo++;
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
-		yield();			/* Yield is okay here */
+
+		if (todo) {
+			unsigned long ret;
+
+			ret = wait_event_timeout(refrigerator_waitq,
+					refrigerator_called, WAIT_TIME);
+			if (ret)
+				refrigerator_called = 0;
+		}
+
 		if (time_after(jiffies, end_time))
 			break;
 	} while (todo);

@@ -190,6 +190,11 @@ static int try_to_freeze_tasks(int freez
 	struct task_struct *g, *p;
 	unsigned long end_time;
 	unsigned int todo;
+	struct timeval start, end;
+	s64 elapsed_csecs64;
+	unsigned int elapsed_csecs;
+
+	do_gettimeofday(&start);
 
 	end_time = jiffies + TIMEOUT;
 	refrigerator_called = 0;

@@ -226,6 +231,11 @@ static int try_to_freeze_tasks(int freez
 			break;
 	} while (todo);
 
+	do_gettimeofday(&end);
+	elapsed_csecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);
+	do_div(elapsed_csecs64, NSEC_PER_SEC / 100);
+	elapsed_csecs = elapsed_csecs64;
+
 	if (todo) {
 		/* This does not unfreeze processes that are already frozen
 		 * (we have slightly ugly calling convention in that respect,

@@ -233,10 +243,9 @@ static int try_to_freeze_tasks(int freez
 		 * but it cleans up leftover PF_FREEZE requests.
 		 */
 		printk("\n");
-		printk(KERN_ERR "Freezing of %s timed out after %d seconds "
+		printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "
 				"(%d tasks refusing to freeze):\n",
-				freeze_user_space ? "user space " : "tasks ",
-				TIMEOUT / HZ, todo);
+				elapsed_csecs / 100, elapsed_csecs % 100, todo);
 		show_state();
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {

@@ -247,6 +256,9 @@ static int try_to_freeze_tasks(int freez
 			task_unlock(p);
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
+	} else {
+		printk("(elapsed %d.%02d seconds) ", elapsed_csecs / 100,
+			elapsed_csecs % 100);
 	}
 
 	return todo ? -EBUSY : 0;