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>

2 files changed, 5 insertions, 1 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;
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 564b8fef2a7e..9678cc3650f5 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -48,6 +48,7 @@
 
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
+DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DECLARE_PER_CPU(char, rcu_cpu_has_work);
 
 static char convert_kthread_status(unsigned int kthread_status)
@@ -75,7 +76,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                    rdp->dynticks_fqs);
 #endif /* #ifdef CONFIG_NO_HZ */
         seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
-        seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d b=%ld",
+        seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d ktl=%x b=%ld",
                    rdp->qlen,
                    ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
                         rdp->nxttail[RCU_NEXT_TAIL]],
@@ -88,6 +89,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                    convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
                                           rdp->cpu)),
                    per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
+                   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff,
                    rdp->blimit);
         seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
                    rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);