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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Tue, 12 Dec 2023 18:22:33 -0500
Message-ID: <CAEXW_YQSPfv50=KNKp-rBVNDPw+XkQ5tUxbVZUL5TW0VVUvVuA@mail.gmail.com>
Subject: Re: [PATCH rcu 3/3] rcu: Force quiescent states only for ongoing
 grace period
To:     "Neeraj Upadhyay (AMD)" <neeraj.iitr10@gmail.com>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, rostedt@goodmis.org, paulmck@kernel.org,
        Neeraj.Upadhyay@amd.com, Zqiang <qiang.zhang1211@gmail.com>
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On Tue, Dec 12, 2023 at 12:40=E2=80=AFPM Neeraj Upadhyay (AMD)
<neeraj.iitr10@gmail.com> wrote:
>
> From: Zqiang <qiang.zhang1211@gmail.com>
>
> If an rcutorture test scenario creates an fqs_task kthread, it will
> periodically invoke rcu_force_quiescent_state() in order to start
> force-quiescent-state (FQS) operations.  However, an FQS operation
> will be started even if there is no RCU grace period in progress.
> Although testing FQS operations startup when there is no grace period in
> progress is necessary, it need not happen all that often.  This commit
> therefore causes rcu_force_quiescent_state() to take an early exit
> if there is no grace period in progress.
>
> Note that there will still be attempts to start an FQS scan in the
> absence of a grace period because the grace period might end right
> after the rcu_force_quiescent_state() function's check.  In actual
> testing, this happens about once every ten minutes, which should
> provide adequate testing.
>
> Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
> ---
>  kernel/rcu/tree.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 3ac3c846105f..1ae851777806 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2338,6 +2338,8 @@ void rcu_force_quiescent_state(void)
>         struct rcu_node *rnp;
>         struct rcu_node *rnp_old =3D NULL;
>
> +       if (!rcu_gp_in_progress())
> +               return;

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>

(Probably no need to resend with the tag, just update the patch in the PR).

Thanks.