Re: [PATCH 08/10] rcu: Standardize explicit CPU-hotplug calls

From: Paul E. McKenney
Date: Mon Oct 02 2023 - 11:47:09 EST

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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@xxxxxxxxxx>

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

> ---
> .../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
>

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