---

yaml
---
r: 142788
b: refs/heads/master
c: ce9dbe2
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5e54f5986a579b8445aa1d5ad3435c2cf7568bed
+refs/heads/master: ce9dbe244bf2063c41792e40dae7745957b118e0

trunk/kernel/hung_task.c

@@ -17,9 +17,18 @@
 #include <linux/sysctl.h>
 
 /*
- * Have a reasonable limit on the number of tasks checked:
+ * The number of tasks checked:
  */
-unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
+unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
+
+/*
+ * Limit number of tasks checked in a batch.
+ *
+ * This value controls the preemptibility of khungtaskd since preemption
+ * is disabled during the critical section. It also controls the size of
+ * the RCU grace period. So it needs to be upper-bound.
+ */
+#define HUNG_TASK_BATCHING 1024
 
 /*
  * Zero means infinite timeout - no checking done:
@@ -109,6 +118,24 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
 		panic("hung_task: blocked tasks");
 }
 
+/*
+ * To avoid extending the RCU grace period for an unbounded amount of time,
+ * periodically exit the critical section and enter a new one.
+ *
+ * For preemptible RCU it is sufficient to call rcu_read_unlock in order
+ * exit the grace period. For classic RCU, a reschedule is required.
+ */
+static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
+{
+	get_task_struct(g);
+	get_task_struct(t);
+	rcu_read_unlock();
+	cond_resched();
+	rcu_read_lock();
+	put_task_struct(t);
+	put_task_struct(g);
+}
+
 /*
  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
  * a really long time (120 seconds). If that happens, print out
@@ -117,6 +144,7 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
 static void check_hung_uninterruptible_tasks(unsigned long timeout)
 {
 	int max_count = sysctl_hung_task_check_count;
+	int batch_count = HUNG_TASK_BATCHING;
 	unsigned long now = get_timestamp();
 	struct task_struct *g, *t;
 
@@ -131,6 +159,13 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 	do_each_thread(g, t) {
 		if (!--max_count)
 			goto unlock;
+		if (!--batch_count) {
+			batch_count = HUNG_TASK_BATCHING;
+			rcu_lock_break(g, t);
+			/* Exit if t or g was unhashed during refresh. */
+			if (t->state == TASK_DEAD || g->state == TASK_DEAD)
+				goto unlock;
+		}
 		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
 		if (t->state == TASK_UNINTERRUPTIBLE)
 			check_hung_task(t, now, timeout);