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Date:   Mon, 2 Oct 2023 08:47:02 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, rcu <rcu@vger.kernel.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH 08/10] rcu: Standardize explicit CPU-hotplug calls
Message-ID: <44e63790-0cdb-48e7-9c57-6f010a2358d7@paulmck-laptop>
Reply-To: paulmck@kernel.org
References: <20230908203603.5865-1-frederic@kernel.org>
 <20230908203603.5865-9-frederic@kernel.org>
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On Fri, Sep 08, 2023 at 10:36:01PM +0200, Frederic Weisbecker wrote:
> rcu_report_dead() and rcutree_migrate_callbacks() have their headers in
> rcupdate.h while those are pure rcutree calls, like the other CPU-hotplug
> functions.
> 
> Also rcu_cpu_starting() and rcu_report_dead() have different naming
> conventions while they mirror each other's effects.
> 
> Fix the headers and propose a naming that relates both functions and
> aligns with the prefix of other rcutree CPU-hotplug functions.
> 
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  .../Expedited-Grace-Periods.rst                      |  2 +-
>  .../RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg    |  4 ++--
>  .../RCU/Design/Memory-Ordering/TreeRCU-gp.svg        |  4 ++--
>  .../RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg   |  4 ++--
>  .../RCU/Design/Requirements/Requirements.rst         |  4 ++--
>  arch/arm64/kernel/smp.c                              |  4 ++--
>  arch/powerpc/kernel/smp.c                            |  2 +-
>  arch/s390/kernel/smp.c                               |  2 +-
>  arch/x86/kernel/smpboot.c                            |  2 +-
>  include/linux/interrupt.h                            |  2 +-
>  include/linux/rcupdate.h                             |  2 --
>  include/linux/rcutiny.h                              |  2 +-
>  include/linux/rcutree.h                              |  7 ++++++-
>  kernel/cpu.c                                         |  6 +++---
>  kernel/rcu/tree.c                                    | 12 ++++++++----
>  15 files changed, 33 insertions(+), 26 deletions(-)
> 
> diff --git a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
> index 93d899d53258..414f8a2012d6 100644
> --- a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
> +++ b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
> @@ -181,7 +181,7 @@ operations is carried out at several levels:
>     of this wait (or series of waits, as the case may be) is to permit a
>     concurrent CPU-hotplug operation to complete.
>  #. In the case of RCU-sched, one of the last acts of an outgoing CPU is
> -   to invoke ``rcu_report_dead()``, which reports a quiescent state for
> +   to invoke ``rcutree_report_cpu_dead()``, which reports a quiescent state for
>     that CPU. However, this is likely paranoia-induced redundancy.
>  
>  +-----------------------------------------------------------------------+
> diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
> index 7ddc094d7f28..d82a77d03d8c 100644
> --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
> +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg
> @@ -1135,7 +1135,7 @@
>         font-weight="bold"
>         font-size="192"
>         id="text202-7-5-3-27-6-5"
> -       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
> +       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead()</text>
>      <text
>         xml:space="preserve"
>         x="3745.7725"
> @@ -1256,7 +1256,7 @@
>         font-style="normal"
>         y="3679.27"
>         x="-3804.9949"
> -       xml:space="preserve">rcu_cpu_starting()</text>
> +       xml:space="preserve">rcutree_report_cpu_starting()</text>
>      <g
>         style="fill:none;stroke-width:0.025in"
>         id="g3107-7-5-0"
> diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
> index 069f6f8371c2..6e690a3be161 100644
> --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
> +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
> @@ -3274,7 +3274,7 @@
>           font-weight="bold"
>           font-size="192"
>           id="text202-7-5-3-27-6-5"
> -         style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
> +         style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead()</text>
>        <text
>           xml:space="preserve"
>           x="3745.7725"
> @@ -3395,7 +3395,7 @@
>           font-style="normal"
>           y="3679.27"
>           x="-3804.9949"
> -         xml:space="preserve">rcu_cpu_starting()</text>
> +         xml:space="preserve">rcutree_report_cpu_starting()</text>
>        <g
>           style="fill:none;stroke-width:0.025in"
>           id="g3107-7-5-0"
> diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
> index 2c9310ba29ba..4fa7506082bf 100644
> --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
> +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg
> @@ -607,7 +607,7 @@
>         font-weight="bold"
>         font-size="192"
>         id="text202-7-5-3-27-6"
> -       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_report_dead()</text>
> +       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcutree_report_cpu_dead()</text>
>      <text
>         xml:space="preserve"
>         x="3745.7725"
> @@ -728,7 +728,7 @@
>         font-style="normal"
>         y="3679.27"
>         x="-3804.9949"
> -       xml:space="preserve">rcu_cpu_starting()</text>
> +       xml:space="preserve">rcutree_report_cpu_starting()</text>
>      <g
>         style="fill:none;stroke-width:0.025in"
>         id="g3107-7-5-0"
> diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
> index f3b605285a87..cccafdaa1f84 100644
> --- a/Documentation/RCU/Design/Requirements/Requirements.rst
> +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> @@ -1955,12 +1955,12 @@ if offline CPUs block an RCU grace period for too long.
>  
>  An offline CPU's quiescent state will be reported either:
>  
> -1.  As the CPU goes offline using RCU's hotplug notifier (rcu_report_dead()).
> +1.  As the CPU goes offline using RCU's hotplug notifier (rcutree_report_cpu_dead()).
>  2.  When grace period initialization (rcu_gp_init()) detects a
>      race either with CPU offlining or with a task unblocking on a leaf
>      ``rcu_node`` structure whose CPUs are all offline.
>  
> -The CPU-online path (rcu_cpu_starting()) should never need to report
> +The CPU-online path (rcutree_report_cpu_starting()) should never need to report
>  a quiescent state for an offline CPU.  However, as a debugging measure,
>  it does emit a warning if a quiescent state was not already reported
>  for that CPU.
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index ce672cb69f1c..90c0083438ea 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -215,7 +215,7 @@ asmlinkage notrace void secondary_start_kernel(void)
>  	if (system_uses_irq_prio_masking())
>  		init_gic_priority_masking();
>  
> -	rcu_cpu_starting(cpu);
> +	rcutree_report_cpu_starting(cpu);
>  	trace_hardirqs_off();
>  
>  	/*
> @@ -401,7 +401,7 @@ void __noreturn cpu_die_early(void)
>  
>  	/* Mark this CPU absent */
>  	set_cpu_present(cpu, 0);
> -	rcu_report_dead();
> +	rcutree_report_cpu_dead();
>  
>  	if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
>  		update_cpu_boot_status(CPU_KILL_ME);
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index fbbb695bae3d..a132e3290e98 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1619,7 +1619,7 @@ void start_secondary(void *unused)
>  
>  	smp_store_cpu_info(cpu);
>  	set_dec(tb_ticks_per_jiffy);
> -	rcu_cpu_starting(cpu);
> +	rcutree_report_cpu_starting(cpu);
>  	cpu_callin_map[cpu] = 1;
>  
>  	if (smp_ops->setup_cpu)
> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> index f9a2b755f510..3e39a5e1bf48 100644
> --- a/arch/s390/kernel/smp.c
> +++ b/arch/s390/kernel/smp.c
> @@ -894,7 +894,7 @@ static void smp_start_secondary(void *cpuvoid)
>  	S390_lowcore.restart_flags = 0;
>  	restore_access_regs(S390_lowcore.access_regs_save_area);
>  	cpu_init();
> -	rcu_cpu_starting(cpu);
> +	rcutree_report_cpu_starting(cpu);
>  	init_cpu_timer();
>  	vtime_init();
>  	vdso_getcpu_init();
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index e1aa2cd7734b..d25b952a2b91 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -288,7 +288,7 @@ static void notrace start_secondary(void *unused)
>  
>  	cpu_init();
>  	fpu__init_cpu();
> -	rcu_cpu_starting(raw_smp_processor_id());
> +	rcutree_report_cpu_starting(raw_smp_processor_id());
>  	x86_cpuinit.early_percpu_clock_init();
>  
>  	ap_starting();
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index a92bce40b04b..d05e1e9a553c 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -566,7 +566,7 @@ enum
>   *
>   * _ RCU:
>   * 	1) rcutree_migrate_callbacks() migrates the queue.
> - * 	2) rcu_report_dead() reports the final quiescent states.
> + * 	2) rcutree_report_cpu_dead() reports the final quiescent states.
>   *
>   * _ IRQ_POLL: irq_poll_cpu_dead() migrates the queue
>   */
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index aa351ddcbe8d..f7206b2623c9 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -122,8 +122,6 @@ static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
>  void rcu_init(void);
>  extern int rcu_scheduler_active;
>  void rcu_sched_clock_irq(int user);
> -void rcu_report_dead(void);
> -void rcutree_migrate_callbacks(int cpu);
>  
>  #ifdef CONFIG_TASKS_RCU_GENERIC
>  void rcu_init_tasks_generic(void);
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 7f17acf29dda..04889a9602e7 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -169,6 +169,6 @@ static inline void rcu_all_qs(void) { barrier(); }
>  #define rcutree_offline_cpu      NULL
>  #define rcutree_dead_cpu         NULL
>  #define rcutree_dying_cpu        NULL
> -static inline void rcu_cpu_starting(unsigned int cpu) { }
> +static inline void rcutree_report_cpu_starting(unsigned int cpu) { }
>  
>  #endif /* __LINUX_RCUTINY_H */
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 7d75066c72aa..07d0fc1e0d31 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -109,7 +109,7 @@ void rcu_all_qs(void);
>  /* RCUtree hotplug events */
>  int rcutree_prepare_cpu(unsigned int cpu);
>  int rcutree_online_cpu(unsigned int cpu);
> -void rcu_cpu_starting(unsigned int cpu);
> +void rcutree_report_cpu_starting(unsigned int cpu);
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  int rcutree_dead_cpu(unsigned int cpu);
> @@ -121,4 +121,9 @@ int rcutree_offline_cpu(unsigned int cpu);
>  #define rcutree_offline_cpu NULL
>  #endif
>  
> +void rcutree_migrate_callbacks(int cpu);
> +
> +/* Called from hotplug and also arm64 early secondary boot failure */
> +void rcutree_report_cpu_dead(void);
> +
>  #endif /* __LINUX_RCUTREE_H */
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 86f08eafbd9f..a41a6fff3c91 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1368,10 +1368,10 @@ void cpuhp_report_idle_dead(void)
>  	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
>  
>  	BUG_ON(st->state != CPUHP_AP_OFFLINE);
> -	rcu_report_dead();
> +	rcutree_report_cpu_dead();
>  	st->state = CPUHP_AP_IDLE_DEAD;
>  	/*
> -	 * We cannot call complete after rcu_report_dead() so we delegate it
> +	 * We cannot call complete after rcutree_report_cpu_dead() so we delegate it
>  	 * to an online cpu.
>  	 */
>  	smp_call_function_single(cpumask_first(cpu_online_mask),
> @@ -1575,7 +1575,7 @@ void notify_cpu_starting(unsigned int cpu)
>  	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
>  	enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
>  
> -	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
> +	rcutree_report_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
>  	cpumask_set_cpu(cpu, &cpus_booted_once_mask);
>  
>  	/*
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 875f241db508..5698c3f30b1d 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4207,7 +4207,7 @@ bool rcu_lockdep_current_cpu_online(void)
>  	rdp = this_cpu_ptr(&rcu_data);
>  	/*
>  	 * Strictly, we care here about the case where the current CPU is
> -	 * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
> +	 * in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask
>  	 * not being up to date. So arch_spin_is_locked() might have a
>  	 * false positive if it's held by some *other* CPU, but that's
>  	 * OK because that just means a false *negative* on the warning.
> @@ -4436,8 +4436,10 @@ int rcutree_online_cpu(unsigned int cpu)
>   * from the incoming CPU rather than from the cpuhp_step mechanism.
>   * This is because this function must be invoked at a precise location.
>   * This incoming CPU must not have enabled interrupts yet.
> + *
> + * This mirrors the effects of rcutree_report_cpu_dead().
>   */
> -void rcu_cpu_starting(unsigned int cpu)
> +void rcutree_report_cpu_starting(unsigned int cpu)
>  {
>  	unsigned long mask;
>  	struct rcu_data *rdp;
> @@ -4491,8 +4493,10 @@ void rcu_cpu_starting(unsigned int cpu)
>   * Note that this function is special in that it is invoked directly
>   * from the outgoing CPU rather than from the cpuhp_step mechanism.
>   * This is because this function must be invoked at a precise location.
> + *
> + * This mirrors the effect of rcutree_report_cpu_starting().
>   */
> -void rcu_report_dead(void)
> +void rcutree_report_cpu_dead(void)
>  {
>  	unsigned long flags;
>  	unsigned long mask;
> @@ -5063,7 +5067,7 @@ void __init rcu_init(void)
>  	pm_notifier(rcu_pm_notify, 0);
>  	WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
>  	rcutree_prepare_cpu(cpu);
> -	rcu_cpu_starting(cpu);
> +	rcutree_report_cpu_starting(cpu);
>  	rcutree_online_cpu(cpu);
>  
>  	/* Create workqueue for Tree SRCU and for expedited GPs. */
> -- 
> 2.41.0
>