linux-kernel - Re: [PATCH 1/4] rcu: Introduce rcu_cpu

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Message-ID: <CALm+0cVP+4ogirqUYMXp63vb7yisXCB0xpq+DSX9kqth0BpW6g@mail.gmail.com>
Date:   Wed, 25 Oct 2023 10:29:46 +0800
From:   Z qiang <qiang.zhang1211@...il.com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Neeraj Upadhyay <neeraj.upadhyay@....com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Uladzislau Rezki <urezki@...il.com>, rcu <rcu@...r.kernel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/4] rcu: Introduce rcu_cpu_online()

>
> Export the RCU point of view as to when a CPU is considered offline
> (ie: when does RCU consider that a CPU is sufficiently down in the
> hotplug process to not feature any possible read side).
>
> This will be used by RCU-tasks whose vision of an offline CPU should
> reasonably match the one of RCU core.
>
> Fixes: cff9b2332ab7 ("kernel/sched: Modify initial boot task idle setup")
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  kernel/rcu/rcu.h  | 2 ++
>  kernel/rcu/tree.c | 7 +++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index 0d866eaa4cc8..b531c33e9545 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -500,6 +500,7 @@ static inline void rcu_expedite_gp(void) { }
>  static inline void rcu_unexpedite_gp(void) { }
>  static inline void rcu_async_hurry(void) { }
>  static inline void rcu_async_relax(void) { }
> +static inline bool rcu_cpu_online(int cpu) { return true; }
>  #else /* #ifdef CONFIG_TINY_RCU */
>  bool rcu_gp_is_normal(void);     /* Internal RCU use. */
>  bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
> @@ -509,6 +510,7 @@ void rcu_unexpedite_gp(void);
>  void rcu_async_hurry(void);
>  void rcu_async_relax(void);
>  void rcupdate_announce_bootup_oddness(void);
> +bool rcu_cpu_online(int cpu);
>  #ifdef CONFIG_TASKS_RCU_GENERIC
>  void show_rcu_tasks_gp_kthreads(void);
>  #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 700524726079..fd21c1506092 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4202,6 +4202,13 @@ static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
>         return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
>  }
>
> +bool rcu_cpu_online(int cpu)
> +{
> +       struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>
>

Should 'struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu)' be used ?

Thanks
Zqiang


>
> +
> +       return rcu_rdp_cpu_online(rdp);
> +}
> +
>  #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
>
>  /*
> --
> 2.41.0
>