linux-kernel - [PATCH] rcu: Cleanup RCU urgency state for offline CPU

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Date:   Thu, 26 May 2022 09:55:12 +0800
From:   Zqiang <qiang1.zhang@...el.com>
To:     paulmck@...nel.org, frederic@...nel.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] rcu: Cleanup RCU urgency state for offline CPU

When an RCU grace period starts and at this time the CPU is in
the process of going offline, if the RCU gp-fqs occurs during the
time period when the CPU has passed the stop-machine but has not
yet entered the idle loop, and this CPU have not report quiescent
state yet, its urgent flags maybe is set, for example due to cbovld
is true, but this CPUs rcu urgent flags is not cleanup in rcu_report_dead()
when report qs. however for CPU that have been report qs, its rcu
urgent flags should cleanup, so add rcu_disable_urgency_upon_qs()
in rcu_report_dead() when CPU report qs.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 02233b17cce0..6a01a48fe56d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4536,6 +4536,7 @@ void rcu_report_dead(unsigned int cpu)
 	rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
 	if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
 		/* Report quiescent state -before- changing ->qsmaskinitnext! */
+		rcu_disable_urgency_upon_qs(rdp);
 		rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	}
-- 
2.25.1