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

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Date:   Wed, 25 Oct 2023 12:32:05 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Z qiang <qiang.zhang1211@...il.com>
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()

Le Wed, Oct 25, 2023 at 10:29:46AM +0800, Z qiang a écrit :
> >
> > 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 ?

Oh! Good catch!

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