linux-kernel - [PATCH] rcu: Avoid invalid wakeup for rcuc kthreads in RCU_KTHREAD

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Message-Id: <20221115131926.3409974-1-qiang1.zhang@intel.com>
Date:   Tue, 15 Nov 2022 21:19:26 +0800
From:   Zqiang <qiang1.zhang@...el.com>
To:     paulmck@...nel.org, frederic@...nel.org, joel@...lfernandes.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] rcu: Avoid invalid wakeup for rcuc kthreads in RCU_KTHREAD_OFFCPU status

For CONFIG_PREEMPT_RT=y kernel, the "use_softirq=0" will be set, the
RCU_SOFTIRQ processing is moved to per-CPU rcuc kthreads which created
by smpboot_register_percpu_thread(). when CPU is going offline, the
corresponding rcu_data.rcu_cpu_kthread_status is set RCU_KTHREAD_OFFCPU,
and the rcuc kthreads enter TASK_PARKED state, kthreads in TASK_PARKED
state only accept kthread_unpark() to wakeup.

Therefore, This commit avoid invoke wake_up_process() to rcuc kthreads
in TASK_PARKED state.

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
---
 kernel/rcu/tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3ccad468887e..49dd87356851 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2375,7 +2375,8 @@ static void rcu_wake_cond(struct task_struct *t, int status)
 	 * If the thread is yielding, only wake it when this
 	 * is invoked from idle
 	 */
-	if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
+	if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) &&
+				status != RCU_KTHREAD_OFFCPU)
 		wake_up_process(t);
 }

-- 
2.25.1