linux-kernel - [PATCH rcu 1/2] rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

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Message-Id: <20250709104641.15699-2-neeraj.upadhyay@kernel.org>
Date: Wed,  9 Jul 2025 16:16:40 +0530
From: neeraj.upadhyay@...nel.org
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	paulmck@...nel.org,
	joelagnelf@...dia.com,
	frederic@...nel.org,
	boqun.feng@...il.com,
	urezki@...il.com,
	rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com,
	jiangshanlai@...il.com,
	qiang.zhang1211@...il.com,
	neeraj.iitr10@...il.com,
	neeraj.upadhyay@....com,
	"Neeraj Upadhyay (AMD)" <neeraj.upadhyay@...nel.org>
Subject: [PATCH rcu 1/2] rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

From: Frederic Weisbecker <frederic@...nel.org>

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>
Reviewed-by: "Paul E. McKenney" <paulmck@...nel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@...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 b473ff056f49..cb29b6bb0ed4 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 486c00536207..4fa64c959083 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -953,8 +953,7 @@ 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();
-- 
2.40.1