Date:   Wed, 24 May 2017 09:25:38 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>
Subject: Re: [patch V3 01/32] cpu/hotplug: Provide cpus_read|write_[un]lock()

On Wed, May 24, 2017 at 10:15:12AM +0200, Thomas Gleixner wrote:
> The counting 'rwsem' hackery of get|put_online_cpus() is going to be
> replaced by percpu rwsem.
> 
> Rename the functions to make it clear that it's locking and not some
> refcount style interface. These new functions will be used for the
> preparatory patches which make the code ready for the percpu rwsem
> conversion.
> 
> Rename all instances in the cpu hotplug code while at it.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  include/linux/cpu.h |   32 ++++++++++++++++++--------------
>  kernel/cpu.c        |   36 ++++++++++++++++++------------------
>  2 files changed, 36 insertions(+), 32 deletions(-)
> 
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -99,26 +99,30 @@ static inline void cpu_maps_update_done(
>  extern struct bus_type cpu_subsys;
> 
>  #ifdef CONFIG_HOTPLUG_CPU
> -/* Stop CPUs going up and down. */
> -
> -extern void cpu_hotplug_begin(void);
> -extern void cpu_hotplug_done(void);
> -extern void get_online_cpus(void);
> -extern void put_online_cpus(void);
> +extern void cpus_write_lock(void);
> +extern void cpus_write_unlock(void);
> +extern void cpus_read_lock(void);
> +extern void cpus_read_unlock(void);
>  extern void cpu_hotplug_disable(void);
>  extern void cpu_hotplug_enable(void);
>  void clear_tasks_mm_cpumask(int cpu);
>  int cpu_down(unsigned int cpu);
> 
> -#else		/* CONFIG_HOTPLUG_CPU */
> +#else /* CONFIG_HOTPLUG_CPU */
> +
> +static inline void cpus_write_lock(void) { }
> +static inline void cpus_write_unlock(void) { }
> +static inline void cpus_read_lock(void) { }
> +static inline void cpus_read_unlock(void) { }
> +static inline void cpu_hotplug_disable(void) { }
> +static inline void cpu_hotplug_enable(void) { }
> +#endif	/* !CONFIG_HOTPLUG_CPU */
> 
> -static inline void cpu_hotplug_begin(void) {}
> -static inline void cpu_hotplug_done(void) {}
> -#define get_online_cpus()	do { } while (0)
> -#define put_online_cpus()	do { } while (0)
> -#define cpu_hotplug_disable()	do { } while (0)
> -#define cpu_hotplug_enable()	do { } while (0)
> -#endif		/* CONFIG_HOTPLUG_CPU */
> +/* Wrappers which go away once all code is converted */
> +static inline void cpu_hotplug_begin(void) { cpus_write_lock(); }
> +static inline void cpu_hotplug_done(void) { cpus_write_unlock(); }
> +static inline void get_online_cpus(void) { cpus_read_lock(); }
> +static inline void put_online_cpus(void) { cpus_read_unlock(); }
> 
>  #ifdef CONFIG_PM_SLEEP_SMP
>  extern int freeze_secondary_cpus(int primary);
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -235,7 +235,7 @@ static struct {
>  #define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
> 
> 
> -void get_online_cpus(void)
> +void cpus_read_lock(void)
>  {
>  	might_sleep();
>  	if (cpu_hotplug.active_writer == current)
> @@ -245,9 +245,9 @@ void get_online_cpus(void)
>  	atomic_inc(&cpu_hotplug.refcount);
>  	mutex_unlock(&cpu_hotplug.lock);
>  }
> -EXPORT_SYMBOL_GPL(get_online_cpus);
> +EXPORT_SYMBOL_GPL(cpus_read_lock);
> 
> -void put_online_cpus(void)
> +void cpus_read_unlock(void)
>  {
>  	int refcount;
> 
> @@ -264,7 +264,7 @@ void put_online_cpus(void)
>  	cpuhp_lock_release();
> 
>  }
> -EXPORT_SYMBOL_GPL(put_online_cpus);
> +EXPORT_SYMBOL_GPL(cpus_read_unlock);
> 
>  /*
>   * This ensures that the hotplug operation can begin only when the
> @@ -288,7 +288,7 @@ EXPORT_SYMBOL_GPL(put_online_cpus);
>   * get_online_cpus() not an api which is called all that often.
>   *
>   */
> -void cpu_hotplug_begin(void)
> +void cpus_write_lock(void)
>  {
>  	DEFINE_WAIT(wait);
> 
> @@ -306,7 +306,7 @@ void cpu_hotplug_begin(void)
>  	finish_wait(&cpu_hotplug.wq, &wait);
>  }
> 
> -void cpu_hotplug_done(void)
> +void cpus_write_unlock(void)
>  {
>  	cpu_hotplug.active_writer = NULL;
>  	mutex_unlock(&cpu_hotplug.lock);
> @@ -773,7 +773,7 @@ static int __ref _cpu_down(unsigned int
>  	if (!cpu_present(cpu))
>  		return -EINVAL;
> 
> -	cpu_hotplug_begin();
> +	cpus_write_lock();
> 
>  	cpuhp_tasks_frozen = tasks_frozen;
> 
> @@ -811,7 +811,7 @@ static int __ref _cpu_down(unsigned int
>  	}
> 
>  out:
> -	cpu_hotplug_done();
> +	cpus_write_unlock();
>  	return ret;
>  }
> 
> @@ -893,7 +893,7 @@ static int _cpu_up(unsigned int cpu, int
>  	struct task_struct *idle;
>  	int ret = 0;
> 
> -	cpu_hotplug_begin();
> +	cpus_write_lock();
> 
>  	if (!cpu_present(cpu)) {
>  		ret = -EINVAL;
> @@ -941,7 +941,7 @@ static int _cpu_up(unsigned int cpu, int
>  	target = min((int)target, CPUHP_BRINGUP_CPU);
>  	ret = cpuhp_up_callbacks(cpu, st, target);
>  out:
> -	cpu_hotplug_done();
> +	cpus_write_unlock();
>  	return ret;
>  }
> 
> @@ -1424,7 +1424,7 @@ int __cpuhp_state_add_instance(enum cpuh
>  	if (sp->multi_instance == false)
>  		return -EINVAL;
> 
> -	get_online_cpus();
> +	cpus_read_lock();
>  	mutex_lock(&cpuhp_state_mutex);
> 
>  	if (!invoke || !sp->startup.multi)
> @@ -1453,7 +1453,7 @@ int __cpuhp_state_add_instance(enum cpuh
>  	hlist_add_head(node, &sp->list);
>  unlock:
>  	mutex_unlock(&cpuhp_state_mutex);
> -	put_online_cpus();
> +	cpus_read_unlock();
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
> @@ -1486,7 +1486,7 @@ int __cpuhp_setup_state(enum cpuhp_state
>  	if (cpuhp_cb_check(state) || !name)
>  		return -EINVAL;
> 
> -	get_online_cpus();
> +	cpus_read_lock();
>  	mutex_lock(&cpuhp_state_mutex);
> 
>  	ret = cpuhp_store_callbacks(state, name, startup, teardown,
> @@ -1522,7 +1522,7 @@ int __cpuhp_setup_state(enum cpuhp_state
>  	}
>  out:
>  	mutex_unlock(&cpuhp_state_mutex);
> -	put_online_cpus();
> +	cpus_read_unlock();
>  	/*
>  	 * If the requested state is CPUHP_AP_ONLINE_DYN, return the
>  	 * dynamically allocated state in case of success.
> @@ -1544,7 +1544,7 @@ int __cpuhp_state_remove_instance(enum c
>  	if (!sp->multi_instance)
>  		return -EINVAL;
> 
> -	get_online_cpus();
> +	cpus_read_lock();
>  	mutex_lock(&cpuhp_state_mutex);
> 
>  	if (!invoke || !cpuhp_get_teardown_cb(state))
> @@ -1565,7 +1565,7 @@ int __cpuhp_state_remove_instance(enum c
>  remove:
>  	hlist_del(node);
>  	mutex_unlock(&cpuhp_state_mutex);
> -	put_online_cpus();
> +	cpus_read_unlock();
> 
>  	return 0;
>  }
> @@ -1587,7 +1587,7 @@ void __cpuhp_remove_state(enum cpuhp_sta
> 
>  	BUG_ON(cpuhp_cb_check(state));
> 
> -	get_online_cpus();
> +	cpus_read_lock();
> 
>  	mutex_lock(&cpuhp_state_mutex);
>  	if (sp->multi_instance) {
> @@ -1615,7 +1615,7 @@ void __cpuhp_remove_state(enum cpuhp_sta
>  remove:
>  	cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
>  	mutex_unlock(&cpuhp_state_mutex);
> -	put_online_cpus();
> +	cpus_read_unlock();
>  }
>  EXPORT_SYMBOL(__cpuhp_remove_state);
> 
> 
> 

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