Re: [tip:smp/hotplug] cpu/hotplug: Restructure FROZEN state handling

["Srivatsa S. Bhat" <srivatsa@csail.mit.edu>]

On 3/1/16 2:51 PM, tip-bot for Thomas Gleixner wrote:
> Commit-ID:  090e77c391dd983c8945b8e2e16d09f378d2e334
> Gitweb:     http://git.kernel.org/tip/090e77c391dd983c8945b8e2e16d09f378d2e334
> Author:     Thomas Gleixner <tglx@linutronix.de>
> AuthorDate: Fri, 26 Feb 2016 18:43:23 +0000
> Committer:  Thomas Gleixner <tglx@linutronix.de>
> CommitDate: Tue, 1 Mar 2016 20:36:53 +0100
> 
> cpu/hotplug: Restructure FROZEN state handling
> 
> There are only a few callbacks which really care about FROZEN
> vs. !FROZEN. No need to have extra states for this.
> 
> Publish the frozen state in an extra variable which is updated under
> the hotplug lock and let the users interested deal with it w/o
> imposing that extra state checks on everyone.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-arch@vger.kernel.org
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>
> Cc: "Srivatsa S. Bhat" <srivatsa@mit.edu>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Sebastian Siewior <bigeasy@linutronix.de>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Paul Turner <pjt@google.com>
> Link: http://lkml.kernel.org/r/20160226182340.334912357@linutronix.de
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---

Reviewed-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>

Regards,
Srivatsa S. Bhat

>  include/linux/cpu.h |  2 ++
>  kernel/cpu.c        | 69 ++++++++++++++++++++++-------------------------------
>  2 files changed, 31 insertions(+), 40 deletions(-)
> 
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index d2ca8c3..f2fb549 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -118,6 +118,7 @@ enum {
>  
>  
>  #ifdef CONFIG_SMP
> +extern bool cpuhp_tasks_frozen;
>  /* Need to know about CPUs going up/down? */
>  #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
>  #define cpu_notifier(fn, pri) {					\
> @@ -177,6 +178,7 @@ extern void cpu_maps_update_done(void);
>  #define cpu_notifier_register_done	cpu_maps_update_done
>  
>  #else	/* CONFIG_SMP */
> +#define cpuhp_tasks_frozen	0
>  
>  #define cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
>  #define __cpu_notifier(fn, pri)	do { (void)(fn); } while (0)
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 5b9d396..41a6cb8 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -29,6 +29,8 @@
>  #ifdef CONFIG_SMP
>  /* Serializes the updates to cpu_online_mask, cpu_present_mask */
>  static DEFINE_MUTEX(cpu_add_remove_lock);
> +bool cpuhp_tasks_frozen;
> +EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
>  
>  /*
>   * The following two APIs (cpu_maps_update_begin/done) must be used when
> @@ -207,27 +209,30 @@ int __register_cpu_notifier(struct notifier_block *nb)
>  	return raw_notifier_chain_register(&cpu_chain, nb);
>  }
>  
> -static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
> +static int __cpu_notify(unsigned long val, unsigned int cpu, int nr_to_call,
>  			int *nr_calls)
>  {
> +	unsigned long mod = cpuhp_tasks_frozen ? CPU_TASKS_FROZEN : 0;
> +	void *hcpu = (void *)(long)cpu;
> +
>  	int ret;
>  
> -	ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
> +	ret = __raw_notifier_call_chain(&cpu_chain, val | mod, hcpu, nr_to_call,
>  					nr_calls);
>  
>  	return notifier_to_errno(ret);
>  }
>  
> -static int cpu_notify(unsigned long val, void *v)
> +static int cpu_notify(unsigned long val, unsigned int cpu)
>  {
> -	return __cpu_notify(val, v, -1, NULL);
> +	return __cpu_notify(val, cpu, -1, NULL);
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  
> -static void cpu_notify_nofail(unsigned long val, void *v)
> +static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
>  {
> -	BUG_ON(cpu_notify(val, v));
> +	BUG_ON(cpu_notify(val, cpu));
>  }
>  EXPORT_SYMBOL(register_cpu_notifier);
>  EXPORT_SYMBOL(__register_cpu_notifier);
> @@ -311,27 +316,21 @@ static inline void check_for_tasks(int dead_cpu)
>  	read_unlock(&tasklist_lock);
>  }
>  
> -struct take_cpu_down_param {
> -	unsigned long mod;
> -	void *hcpu;
> -};
> -
>  /* Take this CPU down. */
>  static int take_cpu_down(void *_param)
>  {
> -	struct take_cpu_down_param *param = _param;
> -	int err;
> +	int err, cpu = smp_processor_id();
>  
>  	/* Ensure this CPU doesn't handle any more interrupts. */
>  	err = __cpu_disable();
>  	if (err < 0)
>  		return err;
>  
> -	cpu_notify(CPU_DYING | param->mod, param->hcpu);
> +	cpu_notify(CPU_DYING, cpu);
>  	/* Give up timekeeping duties */
>  	tick_handover_do_timer();
>  	/* Park the stopper thread */
> -	stop_machine_park((long)param->hcpu);
> +	stop_machine_park(cpu);
>  	return 0;
>  }
>  
> @@ -339,12 +338,6 @@ static int take_cpu_down(void *_param)
>  static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  {
>  	int err, nr_calls = 0;
> -	void *hcpu = (void *)(long)cpu;
> -	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
> -	struct take_cpu_down_param tcd_param = {
> -		.mod = mod,
> -		.hcpu = hcpu,
> -	};
>  
>  	if (num_online_cpus() == 1)
>  		return -EBUSY;
> @@ -354,10 +347,12 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  
>  	cpu_hotplug_begin();
>  
> -	err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
> +	err = __cpu_notify(CPU_DOWN_PREPARE, cpu, -1, &nr_calls);
>  	if (err) {
>  		nr_calls--;
> -		__cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
> +		__cpu_notify(CPU_DOWN_FAILED, cpu, nr_calls, NULL);
>  		pr_warn("%s: attempt to take down CPU %u failed\n",
>  			__func__, cpu);
>  		goto out_release;
> @@ -389,10 +384,10 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  	/*
>  	 * So now all preempt/rcu users must observe !cpu_active().
>  	 */
> -	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> +	err = stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
>  	if (err) {
>  		/* CPU didn't die: tell everyone.  Can't complain. */
> -		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> +		cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
>  		irq_unlock_sparse();
>  		goto out_release;
>  	}
> @@ -419,14 +414,14 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  
>  	/* CPU is completely dead: tell everyone.  Too late to complain. */
>  	tick_cleanup_dead_cpu(cpu);
> -	cpu_notify_nofail(CPU_DEAD | mod, hcpu);
> +	cpu_notify_nofail(CPU_DEAD, cpu);
>  
>  	check_for_tasks(cpu);
>  
>  out_release:
>  	cpu_hotplug_done();
>  	if (!err)
> -		cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
> +		cpu_notify_nofail(CPU_POST_DEAD, cpu);
>  	return err;
>  }
>  
> @@ -485,10 +480,8 @@ void smpboot_thread_init(void)
>  /* Requires cpu_add_remove_lock to be held */
>  static int _cpu_up(unsigned int cpu, int tasks_frozen)
>  {
> -	int ret, nr_calls = 0;
> -	void *hcpu = (void *)(long)cpu;
> -	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
>  	struct task_struct *idle;
> +	int ret, nr_calls = 0;
>  
>  	cpu_hotplug_begin();
>  
> @@ -507,7 +500,9 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen)
>  	if (ret)
>  		goto out;
>  
> -	ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
> +	cpuhp_tasks_frozen = tasks_frozen;
> +
> +	ret = __cpu_notify(CPU_UP_PREPARE, cpu, -1, &nr_calls);
>  	if (ret) {
>  		nr_calls--;
>  		pr_warn("%s: attempt to bring up CPU %u failed\n",
> @@ -523,11 +518,11 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen)
>  	BUG_ON(!cpu_online(cpu));
>  
>  	/* Now call notifier in preparation. */
> -	cpu_notify(CPU_ONLINE | mod, hcpu);
> +	cpu_notify(CPU_ONLINE, cpu);
>  
>  out_notify:
>  	if (ret != 0)
> -		__cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
> +		__cpu_notify(CPU_UP_CANCELED, cpu, nr_calls, NULL);
>  out:
>  	cpu_hotplug_done();
>  
> @@ -719,13 +714,7 @@ core_initcall(cpu_hotplug_pm_sync_init);
>   */
>  void notify_cpu_starting(unsigned int cpu)
>  {
> -	unsigned long val = CPU_STARTING;
> -
> -#ifdef CONFIG_PM_SLEEP_SMP
> -	if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
> -		val = CPU_STARTING_FROZEN;
> -#endif /* CONFIG_PM_SLEEP_SMP */
> -	cpu_notify(val, (void *)(long)cpu);
> +	cpu_notify(CPU_STARTING, cpu);
>  }
>  
>  #endif /* CONFIG_SMP */
>