linux-kernel - [PATCH] rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

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Message-ID: <20250318092336.5794-1-frederic@kernel.org>
Date: Tue, 18 Mar 2025 10:23:36 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	rcu <rcu@...r.kernel.org>
Subject: [PATCH] rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

When a stall is detected, the state of each NOCB CPU is dumped along
with the state of each NOCB group. The latter part however is
incidentally ignored if the NOCB group leader happens not to be
offloaded itself.

Fix this to make sure related precious informations aren't lost over
a stall report.

Reported-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree_nocb.h  | 3 +++
 kernel/rcu/tree_stall.h | 3 +--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 4a954ecf1c36..56baa78c6e85 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1564,6 +1564,9 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
 	if (rdp->nocb_gp_rdp == rdp)
 		show_rcu_nocb_gp_state(rdp);
 
+	if (!rcu_segcblist_is_offloaded(&rdp->cblist))
+		return;
+
 	nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp,
 					      &rdp->nocb_entry_rdp,
 					      typeof(*rdp),
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 56b21219442b..f96235d51642 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -927,8 +927,7 @@ void show_rcu_gp_kthreads(void)
 	for_each_possible_cpu(cpu) {
 		rdp = per_cpu_ptr(&rcu_data, cpu);
 		cbs += data_race(READ_ONCE(rdp->n_cbs_invoked));
-		if (rcu_segcblist_is_offloaded(&rdp->cblist))
-			show_rcu_nocb_state(rdp);
+		show_rcu_nocb_state(rdp);
 	}
 	pr_info("RCU callbacks invoked since boot: %lu\n", cbs);
 	show_rcu_tasks_gp_kthreads();
-- 
2.48.1