[PATCH rcu 11/12] rcu: Diagnose extended sync_rcu_do_polled_gp() loops

Paul E. McKenney
2022-06-20T22:52:10Z

This commit dumps out state when the sync_rcu_do_polled_gp() function
loops more than expected. This is a debugging aid.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_exp.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index f05a15b11fa0c..4c7037b507032 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -970,6 +970,7 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
static void sync_rcu_do_polled_gp(struct work_struct *wp)
{
unsigned long flags;
+ int i = 0;
struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
unsigned long s;

@@ -979,8 +980,12 @@ static void sync_rcu_do_polled_gp(struct work_struct *wp)
raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
if (s == RCU_GET_STATE_COMPLETED)
return;
- while (!poll_state_synchronize_rcu(s))
+ while (!poll_state_synchronize_rcu(s)) {
synchronize_rcu_expedited();
+ if (i == 10 || i == 20)
+ pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
+ i++;
+ }
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
s = rnp->exp_seq_poll_rq;
if (poll_state_synchronize_rcu(s))
--
2.31.1.189.g2e36527f23