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Message-ID: <56D76AA4.5010709@csail.mit.edu>
Date: Wed, 2 Mar 2016 17:35:16 -0500
From: "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>
To: tj@...nel.org, akpm@...ux-foundation.org, rusty@...tcorp.com.au,
linux-kernel@...r.kernel.org, rostedt@...dmis.org,
paulmck@...ux.vnet.ibm.com, peterz@...radead.org, mingo@...nel.org,
arjan@...ux.intel.com, tglx@...utronix.de,
rafael.j.wysocki@...el.com, pjt@...gle.com, riel@...hat.com,
bigeasy@...utronix.de, oleg@...hat.com,
torvalds@...ux-foundation.org, srivatsa@....edu, hpa@...or.com,
linux-tip-commits@...r.kernel.org
Subject: Re: [tip:smp/hotplug] cpu/hotplug: Restructure FROZEN state handling
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@...utronix.de>
> AuthorDate: Fri, 26 Feb 2016 18:43:23 +0000
> Committer: Thomas Gleixner <tglx@...utronix.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@...utronix.de>
> Cc: linux-arch@...r.kernel.org
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Rafael Wysocki <rafael.j.wysocki@...el.com>
> Cc: "Srivatsa S. Bhat" <srivatsa@....edu>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Cc: Sebastian Siewior <bigeasy@...utronix.de>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Paul Turner <pjt@...gle.com>
> Link: http://lkml.kernel.org/r/20160226182340.334912357@linutronix.de
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
Reviewed-by: Srivatsa S. Bhat <srivatsa@...il.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 */
>
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