rcu: Add forward-progress diagnostic for per-CPU kthreads

Increment a per-CPU counter on each pass through rcu_cpu_kthread()'s
service loop, and add it to the rcudata trace output.

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, 2 insertions, 0 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 27b6d8de82f6..575d6414763e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -93,6 +93,7 @@ EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
+DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
 DEFINE_PER_CPU(char, rcu_cpu_has_work);
 static char rcu_kthreads_spawnable;
@@ -1625,6 +1626,7 @@ static int rcu_cpu_kthread(void *arg)
                         break;
                 }
                 *statusp = RCU_KTHREAD_RUNNING;
+                per_cpu(rcu_cpu_kthread_loops, cpu)++;
                 local_irq_save(flags);
                 work = *workp;
                 *workp = 0;