From 2a1d446019f9a5983ec5a335b95e8593fdb6fa2e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:36 +0000 Subject: kthread: Implement park/unpark facility To avoid the full teardown/setup of per cpu kthreads in the case of cpu hot(un)plug, provide a facility which allows to put the kthread into a park position and unpark it when the cpu comes online again. Signed-off-by: Thomas Gleixner Reviewed-by: Namhyung Kim Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Link: http://lkml.kernel.org/r/20120716103948.236618824@linutronix.de Signed-off-by: Thomas Gleixner --- include/linux/kthread.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 22ccf9dee177..8d816646f766 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -14,6 +14,11 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), kthread_create_on_node(threadfn, data, -1, namefmt, ##arg) +struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), + void *data, + unsigned int cpu, + const char *namefmt); + /** * kthread_run - create and wake a thread. * @threadfn: the function to run until signal_pending(current). @@ -34,9 +39,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), void kthread_bind(struct task_struct *k, unsigned int cpu); int kthread_stop(struct task_struct *k); -int kthread_should_stop(void); +bool kthread_should_stop(void); +bool kthread_should_park(void); bool kthread_freezable_should_stop(bool *was_frozen); void *kthread_data(struct task_struct *k); +int kthread_park(struct task_struct *k); +void kthread_unpark(struct task_struct *k); +void kthread_parkme(void); int kthreadd(void *unused); extern struct task_struct *kthreadd_task; -- cgit v1.2.3 From f97f8f06a49febbc3cb3635172efbe64ddc79700 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:36 +0000 Subject: smpboot: Provide infrastructure for percpu hotplug threads Provide a generic interface for setting up and tearing down percpu threads. On registration the threads for already online cpus are created and started. On deregistration (modules) the threads are stoppped. During hotplug operations the threads are created, started, parked and unparked. The datastructure for registration provides a pointer to percpu storage space and optional setup, cleanup, park, unpark functions. These functions are called when the thread state changes. Each implementation has to provide a function which is queried and returns whether the thread should run and the thread function itself. The core code handles all state transitions and avoids duplicated code in the call sites. [ paulmck: Preemption leak fix ] Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.352501068@linutronix.de Signed-off-by: Thomas Gleixner --- include/linux/smpboot.h | 43 +++++++++ kernel/cpu.c | 10 ++- kernel/smpboot.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++++ kernel/smpboot.h | 4 + 4 files changed, 285 insertions(+), 1 deletion(-) create mode 100644 include/linux/smpboot.h (limited to 'include') diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h new file mode 100644 index 000000000000..e0106d8581d3 --- /dev/null +++ b/include/linux/smpboot.h @@ -0,0 +1,43 @@ +#ifndef _LINUX_SMPBOOT_H +#define _LINUX_SMPBOOT_H + +#include + +struct task_struct; +/* Cookie handed to the thread_fn*/ +struct smpboot_thread_data; + +/** + * struct smp_hotplug_thread - CPU hotplug related thread descriptor + * @store: Pointer to per cpu storage for the task pointers + * @list: List head for core management + * @thread_should_run: Check whether the thread should run or not. Called with + * preemption disabled. + * @thread_fn: The associated thread function + * @setup: Optional setup function, called when the thread gets + * operational the first time + * @cleanup: Optional cleanup function, called when the thread + * should stop (module exit) + * @park: Optional park function, called when the thread is + * parked (cpu offline) + * @unpark: Optional unpark function, called when the thread is + * unparked (cpu online) + * @thread_comm: The base name of the thread + */ +struct smp_hotplug_thread { + struct task_struct __percpu **store; + struct list_head list; + int (*thread_should_run)(unsigned int cpu); + void (*thread_fn)(unsigned int cpu); + void (*setup)(unsigned int cpu); + void (*cleanup)(unsigned int cpu, bool online); + void (*park)(unsigned int cpu); + void (*unpark)(unsigned int cpu); + const char *thread_comm; +}; + +int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread); +void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread); +int smpboot_thread_schedule(void); + +#endif diff --git a/kernel/cpu.c b/kernel/cpu.c index 14d32588cccd..e615dfbcf794 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -280,12 +280,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) __func__, cpu); goto out_release; } + smpboot_park_threads(cpu); err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); if (err) { /* CPU didn't die: tell everyone. Can't complain. */ + smpboot_unpark_threads(cpu); cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu); - goto out_release; } BUG_ON(cpu_online(cpu)); @@ -354,6 +355,10 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out; } + ret = smpboot_create_threads(cpu); + if (ret) + goto out; + ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls); if (ret) { nr_calls--; @@ -368,6 +373,9 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out_notify; BUG_ON(!cpu_online(cpu)); + /* Wake the per cpu threads */ + smpboot_unpark_threads(cpu); + /* Now call notifier in preparation. */ cpu_notify(CPU_ONLINE | mod, hcpu); diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 98f60c5caa1b..9d5f7b04025d 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -1,11 +1,17 @@ /* * Common SMP CPU bringup/teardown functions */ +#include #include #include #include +#include +#include #include +#include #include +#include +#include #include "smpboot.h" @@ -65,3 +71,226 @@ void __init idle_threads_init(void) } } #endif + +static LIST_HEAD(hotplug_threads); +static DEFINE_MUTEX(smpboot_threads_lock); + +struct smpboot_thread_data { + unsigned int cpu; + unsigned int status; + struct smp_hotplug_thread *ht; +}; + +enum { + HP_THREAD_NONE = 0, + HP_THREAD_ACTIVE, + HP_THREAD_PARKED, +}; + +/** + * smpboot_thread_fn - percpu hotplug thread loop function + * @data: thread data pointer + * + * Checks for thread stop and park conditions. Calls the necessary + * setup, cleanup, park and unpark functions for the registered + * thread. + * + * Returns 1 when the thread should exit, 0 otherwise. + */ +static int smpboot_thread_fn(void *data) +{ + struct smpboot_thread_data *td = data; + struct smp_hotplug_thread *ht = td->ht; + + while (1) { + set_current_state(TASK_INTERRUPTIBLE); + preempt_disable(); + if (kthread_should_stop()) { + set_current_state(TASK_RUNNING); + preempt_enable(); + if (ht->cleanup) + ht->cleanup(td->cpu, cpu_online(td->cpu)); + kfree(td); + return 0; + } + + if (kthread_should_park()) { + __set_current_state(TASK_RUNNING); + preempt_enable(); + if (ht->park && td->status == HP_THREAD_ACTIVE) { + BUG_ON(td->cpu != smp_processor_id()); + ht->park(td->cpu); + td->status = HP_THREAD_PARKED; + } + kthread_parkme(); + /* We might have been woken for stop */ + continue; + } + + BUG_ON(td->cpu != smp_processor_id()); + + /* Check for state change setup */ + switch (td->status) { + case HP_THREAD_NONE: + preempt_enable(); + if (ht->setup) + ht->setup(td->cpu); + td->status = HP_THREAD_ACTIVE; + preempt_disable(); + break; + case HP_THREAD_PARKED: + preempt_enable(); + if (ht->unpark) + ht->unpark(td->cpu); + td->status = HP_THREAD_ACTIVE; + preempt_disable(); + break; + } + + if (!ht->thread_should_run(td->cpu)) { + preempt_enable(); + schedule(); + } else { + set_current_state(TASK_RUNNING); + preempt_enable(); + ht->thread_fn(td->cpu); + } + } +} + +static int +__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + struct smpboot_thread_data *td; + + if (tsk) + return 0; + + td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu)); + if (!td) + return -ENOMEM; + td->cpu = cpu; + td->ht = ht; + + tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, + ht->thread_comm); + if (IS_ERR(tsk)) { + kfree(td); + return PTR_ERR(tsk); + } + + get_task_struct(tsk); + *per_cpu_ptr(ht->store, cpu) = tsk; + return 0; +} + +int smpboot_create_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + int ret = 0; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry(cur, &hotplug_threads, list) { + ret = __smpboot_create_thread(cur, cpu); + if (ret) + break; + } + mutex_unlock(&smpboot_threads_lock); + return ret; +} + +static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + kthread_unpark(tsk); +} + +void smpboot_unpark_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry(cur, &hotplug_threads, list) + smpboot_unpark_thread(cur, cpu); + mutex_unlock(&smpboot_threads_lock); +} + +static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + if (tsk) + kthread_park(tsk); +} + +void smpboot_park_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry_reverse(cur, &hotplug_threads, list) + smpboot_park_thread(cur, cpu); + mutex_unlock(&smpboot_threads_lock); +} + +static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) +{ + unsigned int cpu; + + /* We need to destroy also the parked threads of offline cpus */ + for_each_possible_cpu(cpu) { + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + if (tsk) { + kthread_stop(tsk); + put_task_struct(tsk); + *per_cpu_ptr(ht->store, cpu) = NULL; + } + } +} + +/** + * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug + * @plug_thread: Hotplug thread descriptor + * + * Creates and starts the threads on all online cpus. + */ +int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) +{ + unsigned int cpu; + int ret = 0; + + mutex_lock(&smpboot_threads_lock); + for_each_online_cpu(cpu) { + ret = __smpboot_create_thread(plug_thread, cpu); + if (ret) { + smpboot_destroy_threads(plug_thread); + goto out; + } + smpboot_unpark_thread(plug_thread, cpu); + } + list_add(&plug_thread->list, &hotplug_threads); +out: + mutex_unlock(&smpboot_threads_lock); + return ret; +} +EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); + +/** + * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug + * @plug_thread: Hotplug thread descriptor + * + * Stops all threads on all possible cpus. + */ +void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) +{ + get_online_cpus(); + mutex_lock(&smpboot_threads_lock); + list_del(&plug_thread->list); + smpboot_destroy_threads(plug_thread); + mutex_unlock(&smpboot_threads_lock); + put_online_cpus(); +} +EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); diff --git a/kernel/smpboot.h b/kernel/smpboot.h index 6ef9433e1c70..72415a0eb955 100644 --- a/kernel/smpboot.h +++ b/kernel/smpboot.h @@ -13,4 +13,8 @@ static inline void idle_thread_set_boot_cpu(void) { } static inline void idle_threads_init(void) { } #endif +int smpboot_create_threads(unsigned int cpu); +void smpboot_park_threads(unsigned int cpu); +void smpboot_unpark_threads(unsigned int cpu); + #endif -- cgit v1.2.3