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From:   "Zhang, Qiang1" <qiang1.zhang@intel.com>
To:     "Zhang, Qiang1" <qiang1.zhang@intel.com>,
        "paulmck@kernel.org" <paulmck@kernel.org>,
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CC:     "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] rcu: Add a warnings in sync_sched_exp_online_cleanup()
Thread-Topic: [PATCH] rcu: Add a warnings in sync_sched_exp_online_cleanup()
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Date:   Wed, 22 Jun 2022 23:43:26 +0000
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Add Cc=20

Currently, the sync_sched_exp_online_cleanup() is invoked in
cpuhp per-cpu kthreads when CPU is going online, so the CPU id
obtained by get_cpu() should always be equal to the CPU id of
the passed parameter, that is to say, the smp_call_function_single()
never be invoked, if be invoked, there may be problem with cpu-hotplug,
this commit add WARN_ON_ONCE() to remind everyone.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
 kernel/rcu/tree_exp.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index be667583a554..ae8dcfd4486c 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -865,6 +865,8 @@ static void sync_sched_exp_online_cleanup(int cpu)
 		put_cpu();
 		return;
 	}
+
+	WARN_ON_ONCE(my_cpu !=3D cpu);
 	/* Quiescent state needed on some other CPU, send IPI. */
 	ret =3D smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
 	put_cpu();
--=20
2.25.1