linux-kernel - [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind spot

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Message-ID: <20241002145738.38226-4-frederic@kernel.org>
Date: Wed,  2 Oct 2024 16:57:38 +0200
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 <joel@...lfernandes.org>,
	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 3/3] rcu: Report callbacks enqueued on offline CPU blind spot

Callbacks enqueued after rcutree_report_cpu_dead() fall into RCU barrier
blind spot. Report any potential misuse.

Reported-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/tree.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a60616e69b66..36070b6bf4a1 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3084,8 +3084,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
 	head->func = func;
 	head->next = NULL;
 	kasan_record_aux_stack_noalloc(head);
+
 	local_irq_save(flags);
 	rdp = this_cpu_ptr(&rcu_data);
+	RCU_LOCKDEP_WARN(rcu_rdp_cpu_online(rdp), "Callback enqueued on offline CPU!");
+
 	lazy = lazy_in && !rcu_async_should_hurry();
 
 	/* Add the callback to our list. */
-- 
2.46.0