[PATCH tip/core/rcu 10/17] rcu: Print per-CPU callback counts for forward-progress failures

["Paul E. McKenney" <paulmck@linux.ibm.com>]

This commit prints out the non-zero per-CPU callback counts when a
forware-progress error (OOM event) occurs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix a pair of uninitialized locals spotted by kbuild test robot. ]
---
 kernel/rcu/tree.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 67f2c7a055b6..cef7d9867508 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2672,6 +2672,10 @@ rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp)
  */
 void rcu_fwd_progress_check(unsigned long j)
 {
+	unsigned long cbs;
+	int cpu;
+	unsigned long max_cbs = 0;
+	int max_cpu = -1;
 	struct rcu_data *rdp;
 
 	if (rcu_gp_in_progress()) {
@@ -2682,6 +2686,20 @@ void rcu_fwd_progress_check(unsigned long j)
 		rcu_check_gp_start_stall(rdp->mynode, rdp, j);
 		preempt_enable();
 	}
+	for_each_possible_cpu(cpu) {
+		cbs = rcu_get_n_cbs_cpu(cpu);
+		if (!cbs)
+			continue;
+		if (max_cpu < 0)
+			pr_info("%s: callbacks", __func__);
+		pr_cont(" %d: %lu", cpu, cbs);
+		if (cbs <= max_cbs)
+			continue;
+		max_cbs = cbs;
+		max_cpu = cpu;
+	}
+	if (max_cpu >= 0)
+		pr_cont("\n");
 }
 EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
 
-- 
2.17.1