linux-kernel - [PATCH] rcu: Fix rcu_read_unlock

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Date:   Thu, 16 Jun 2022 21:53:47 +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: Fix rcu_read_unlock_strict() strict QS reporting

When running a kerenl with CONFIG_PREEMPT=n and
CONFIG_RCU_STRICT_GRACE_PERIOD=y, the QS state will be reported
directly after exiting the last level of RCU critical section and
in non irqs-disable context, but maybe the CPU's rcu_data
structure's ->cpu_no_qs.b.norm is not cleared, as a result the
rcu_report_qs_rdp() will exit early, and not report QS state.

This commit will clear CPU's rcu_data structure's ->cpu_no_qs.b.norm
before invoke rcu_report_qs_rdp().

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

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index b2c01919b92c..dc78726b993f 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -824,6 +824,7 @@ void rcu_read_unlock_strict(void)
 	if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
 		return;
 	rdp = this_cpu_ptr(&rcu_data);
+	rdp->cpu_no_qs.b.norm = false;
 	rcu_report_qs_rdp(rdp);
 	udelay(rcu_unlock_delay);
 }
-- 
2.25.1