linux-kernel - [PATCH rcu 11/12] rcu: Diagnose extended sync_rcu_do_polled

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Message-Id: <20220620225128.3842050-11-paulmck@kernel.org>
Date:   Mon, 20 Jun 2022 15:51:27 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 11/12] rcu: Diagnose extended sync_rcu_do_polled_gp() loops

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@...nel.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