1 files changed, 37 insertions, 2 deletions

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index ba8ccd432963..481ca8b5c2bc 100644
--- a/kernel/hung_task.c
+++ b/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:
@@ -110,6 +119,24 @@ static void check_hung_task(struct task_struct *t, unsigned long now,
 }
 
 /*
+ * 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
  * a warning.
@@ -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);