rcu: add tracing for RCU's kthread run states.

Add tracing to help debugging situations when RCU's kthreads are not
running but are supposed to be.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 10 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 198e4df7d83e..d8917401cbbc 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -91,8 +91,9 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  * handle all flavors of RCU.
  */
 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
-static DEFINE_PER_CPU(char, rcu_cpu_has_work);
+DEFINE_PER_CPU(char, rcu_cpu_has_work);
 static char rcu_kthreads_spawnable;
 
 static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
@@ -1563,11 +1564,13 @@ static int rcu_cpu_kthread(void *arg)
         int cpu = (int)(long)arg;
         unsigned long flags;
         int spincnt = 0;
+        unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
         wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
         char work;
         char *workp = &per_cpu(rcu_cpu_has_work, cpu);
 
         for (;;) {
+                *statusp = RCU_KTHREAD_WAITING;
                 wait_event_interruptible(*wqp,
                                          *workp != 0 || kthread_should_stop());
                 local_bh_disable();
@@ -1575,6 +1578,7 @@ static int rcu_cpu_kthread(void *arg)
                         local_bh_enable();
                         break;
                 }
+                *statusp = RCU_KTHREAD_RUNNING;
                 local_irq_save(flags);
                 work = *workp;
                 *workp = 0;
@@ -1587,10 +1591,12 @@ static int rcu_cpu_kthread(void *arg)
                 else
                         spincnt = 0;
                 if (spincnt > 10) {
+                        *statusp = RCU_KTHREAD_YIELDING;
                         rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
                         spincnt = 0;
                 }
         }
+        *statusp = RCU_KTHREAD_STOPPED;
         return 0;
 }
 
@@ -1637,10 +1643,12 @@ static int rcu_node_kthread(void *arg)
         struct task_struct *t;
 
         for (;;) {
+                rnp->node_kthread_status = RCU_KTHREAD_WAITING;
                 wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
                                                        kthread_should_stop());
                 if (kthread_should_stop())
                         break;
+                rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
                 raw_spin_lock_irqsave(&rnp->lock, flags);
                 mask = rnp->wakemask;
                 rnp->wakemask = 0;
@@ -1661,6 +1669,7 @@ static int rcu_node_kthread(void *arg)
                         preempt_enable();
                 }
         }
+        rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
         return 0;
 }