/* CPU control. * (C) 2001, 2002, 2003, 2004 Rusty Russell * * This code is licenced under the GPL. */#include <linux/proc_fs.h>#include <linux/smp.h>#include <linux/init.h>#include <linux/notifier.h>#include <linux/sched.h>#include <linux/unistd.h>#include <linux/cpu.h>#include <linux/oom.h>#include <linux/rcupdate.h>#include <linux/export.h>#include <linux/bug.h>#include <linux/kthread.h>#include <linux/stop_machine.h>#include <linux/mutex.h>#include <linux/gfp.h>#include <linux/suspend.h> #include "smpboot.h" #ifdef CONFIG_SMP/* Serializes the updates to cpu_online_mask, cpu_present_mask */static DEFINE_MUTEX(cpu_add_remove_lock); /* * The following two API's must be used when attempting * to serialize the updates to cpu_online_mask, cpu_present_mask. */void cpu_maps_update_begin(void){ mutex_lock(&cpu_add_remove_lock);} void cpu_maps_update_done(void){ mutex_unlock(&cpu_add_remove_lock);} static RAW_NOTIFIER_HEAD(cpu_chain); /* If set, cpu_up and cpu_down will return -EBUSY and do nothing. * Should always be manipulated under cpu_add_remove_lock */static int cpu_hotplug_disabled; #ifdef CONFIG_HOTPLUG_CPU static struct { struct task_struct *active_writer; struct mutex lock; /* Synchronizes accesses to refcount, */ /* * Also blocks the new readers during * an ongoing cpu hotplug operation. */ int refcount;} cpu_hotplug = { .active_writer = NULL, .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock), .refcount = 0,}; void get_online_cpus(void){ might_sleep(); if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); }EXPORT_SYMBOL_GPL(get_online_cpus); void put_online_cpus(void){ if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); if (WARN_ON(!cpu_hotplug.refcount)) cpu_hotplug.refcount++; /* try to fix things up */ if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); }EXPORT_SYMBOL_GPL(put_online_cpus); /* * This ensures that the hotplug operation can begin only when the * refcount goes to zero. * * Note that during a cpu-hotplug operation, the new readers, if any, * will be blocked by the cpu_hotplug.lock * * Since cpu_hotplug_begin() is always called after invoking * cpu_maps_update_begin(), we can be sure that only one writer is active. * * Note that theoretically, there is a possibility of a livelock: * - Refcount goes to zero, last reader wakes up the sleeping * writer. * - Last reader unlocks the cpu_hotplug.lock. * - A new reader arrives at this moment, bumps up the refcount. * - The writer acquires the cpu_hotplug.lock finds the refcount * non zero and goes to sleep again. * * However, this is very difficult to achieve in practice since * get_online_cpus() not an api which is called all that often. * */static void cpu_hotplug_begin(void){ cpu_hotplug.active_writer = current; for (;;) { mutex_lock(&cpu_hotplug.lock); if (likely(!cpu_hotplug.refcount)) break; __set_current_state(TASK_UNINTERRUPTIBLE); mutex_unlock(&cpu_hotplug.lock); schedule(); }} static void cpu_hotplug_done(void){ cpu_hotplug.active_writer = NULL; mutex_unlock(&cpu_hotplug.lock);} #else /* #if CONFIG_HOTPLUG_CPU */static void cpu_hotplug_begin(void) {}static void cpu_hotplug_done(void) {}#endif /* #else #if CONFIG_HOTPLUG_CPU */ /* Need to know about CPUs going up/down? */int __ref register_cpu_notifier(struct notifier_block *nb){ int ret; cpu_maps_update_begin(); ret = raw_notifier_chain_register(&cpu_chain, nb); cpu_maps_update_done(); return ret;} static int __cpu_notify(unsigned long val, void *v, int nr_to_call, int *nr_calls){ int ret; ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call, nr_calls); return notifier_to_errno(ret);} static int cpu_notify(unsigned long val, void *v){ return __cpu_notify(val, v, -1, NULL);} #ifdef CONFIG_HOTPLUG_CPU static void cpu_notify_nofail(unsigned long val, void *v){ BUG_ON(cpu_notify(val, v));}EXPORT_SYMBOL(register_cpu_notifier); void __ref unregister_cpu_notifier(struct notifier_block *nb){ cpu_maps_update_begin(); raw_notifier_chain_unregister(&cpu_chain, nb); cpu_maps_update_done();}EXPORT_SYMBOL(unregister_cpu_notifier); /** * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU * @cpu: a CPU id * * This function walks all processes, finds a valid mm struct for each one and * then clears a corresponding bit in mm's cpumask. While this all sounds * trivial, there are various non-obvious corner cases, which this function * tries to solve in a safe manner. * * Also note that the function uses a somewhat relaxed locking scheme, so it may * be called only for an already offlined CPU. */void clear_tasks_mm_cpumask(int cpu){ struct task_struct *p; /* * This function is called after the cpu is taken down and marked * offline, so its not like new tasks will ever get this cpu set in * their mm mask. -- Peter Zijlstra * Thus, we may use rcu_read_lock() here, instead of grabbing * full-fledged tasklist_lock. */ WARN_ON(cpu_online(cpu)); rcu_read_lock(); for_each_process(p) { struct task_struct *t; /* * Main thread might exit, but other threads may still have * a valid mm. Find one. */ t = find_lock_task_mm(p); if (!t) continue; cpumask_clear_cpu(cpu, mm_cpumask(t->mm)); task_unlock(t); } rcu_read_unlock();} static inline void check_for_tasks(int cpu){ struct task_struct *p; write_lock_irq(&tasklist_lock); for_each_process(p) { if (task_cpu(p) == cpu && p->state == TASK_RUNNING && (p->utime || p->stime)) printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d " "(state = %ld, flags = %x)\n", p->comm, task_pid_nr(p), cpu, p->state, p->flags); } write_unlock_irq(&tasklist_lock);} struct take_cpu_down_param { unsigned long mod; void *hcpu;}; /* Take this CPU down. */static int __ref take_cpu_down(void *_param){ struct take_cpu_down_param *param = _param; int err; /* 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); return 0;} /* Requires cpu_add_remove_lock to be held */static int __ref _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; if (!cpu_online(cpu)) return -EINVAL; cpu_hotplug_begin(); err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err) { nr_calls--; __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL); printk("%s: attempt to take down CPU %u failed\n", __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)); /* * The migration_call() CPU_DYING callback will have removed all * runnable tasks from the cpu, there's only the idle task left now * that the migration thread is done doing the stop_machine thing. * * Wait for the stop thread to go away. */ while (!idle_cpu(cpu)) cpu_relax(); /* This actually kills the CPU. */ __cpu_die(cpu); /* CPU is completely dead: tell everyone. Too late to complain. */ cpu_notify_nofail(CPU_DEAD | mod, hcpu); check_for_tasks(cpu); out_release: cpu_hotplug_done(); if (!err) cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu); return err;} int __ref cpu_down(unsigned int cpu){ int err; cpu_maps_update_begin(); if (cpu_hotplug_disabled) { err = -EBUSY; goto out; } err = _cpu_down(cpu, 0); out: cpu_maps_update_done(); return err;}EXPORT_SYMBOL(cpu_down);#endif /*CONFIG_HOTPLUG_CPU*/ /* Requires cpu_add_remove_lock to be held */static int __cpuinit _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; if (cpu_online(cpu) || !cpu_present(cpu)) return -EINVAL; cpu_hotplug_begin(); idle = idle_thread_get(cpu); if (IS_ERR(idle)) { ret = PTR_ERR(idle); 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--; printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n", __func__, cpu); goto out_notify; } /* Arch-specific enabling code. */ ret = __cpu_up(cpu, idle); if (ret != 0) 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); out_notify: if (ret != 0) __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);out: cpu_hotplug_done(); return ret;} int __cpuinit cpu_up(unsigned int cpu){ int err = 0; #ifdef CONFIG_MEMORY_HOTPLUG int nid; pg_data_t *pgdat;#endif if (!cpu_possible(cpu)) { printk(KERN_ERR "can't online cpu %d because it is not " "configured as may-hotadd at boot time\n", cpu);#if defined(CONFIG_IA64) printk(KERN_ERR "please check additional_cpus= boot " "parameter\n");#endif return -EINVAL; } #ifdef CONFIG_MEMORY_HOTPLUG nid = cpu_to_node(cpu); if (!node_online(nid)) { err = mem_online_node(nid); if (err) return err; } pgdat = NODE_DATA(nid); if (!pgdat) { printk(KERN_ERR "Can't online cpu %d due to NULL pgdat\n", cpu); return -ENOMEM; } if (pgdat->node_zonelists->_zonerefs->zone == NULL) { mutex_lock(&zonelists_mutex); build_all_zonelists(NULL, NULL); mutex_unlock(&zonelists_mutex); }#endif cpu_maps_update_begin(); if (cpu_hotplug_disabled) { err = -EBUSY; goto out; } err = _cpu_up(cpu, 0); out: cpu_maps_update_done(); return err;}EXPORT_SYMBOL_GPL(cpu_up); #ifdef CONFIG_PM_SLEEP_SMPstatic cpumask_var_t frozen_cpus; int disable_nonboot_cpus(void){ int cpu, first_cpu, error = 0; cpu_maps_update_begin(); first_cpu = cpumask_first(cpu_online_mask); /* * We take down all of the non-boot CPUs in one shot to avoid races * with the userspace trying to use the CPU hotplug at the same time */ cpumask_clear(frozen_cpus); printk("Disabling non-boot CPUs ...\n"); for_each_online_cpu(cpu) { if (cpu == first_cpu) continue; error = _cpu_down(cpu, 1); if (!error) cpumask_set_cpu(cpu, frozen_cpus); else { printk(KERN_ERR "Error taking CPU%d down: %d\n", cpu, error); break; } } if (!error) { BUG_ON(num_online_cpus() > 1); /* Make sure the CPUs won't be enabled by someone else */ cpu_hotplug_disabled = 1; } else { printk(KERN_ERR "Non-boot CPUs are not disabled\n"); } cpu_maps_update_done(); return error;} void __weak arch_enable_nonboot_cpus_begin(void){} void __weak arch_enable_nonboot_cpus_end(void){} void __ref enable_nonboot_cpus(void){Lines 1–500 of 726. 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/* CPU control. * (C) 2001, 2002, 2003, 2004 Rusty Russell * * This code is licenced under the GPL. */ #include <linux/proc_fs.h> #include <linux/smp.h> #include <linux/init.h> #include <linux/notifier.h> #include <linux/sched.h> #include <linux/unistd.h> #include <linux/cpu.h> #include <linux/oom.h> #include <linux/rcupdate.h> #include <linux/export.h> #include <linux/bug.h> #include <linux/kthread.h> #include <linux/stop_machine.h> #include <linux/mutex.h> #include <linux/gfp.h> #include <linux/suspend.h> #include "smpboot.h" #ifdef CONFIG_SMP /* Serializes the updates to cpu_online_mask, cpu_present_mask */ static DEFINE_MUTEX(cpu_add_remove_lock); /* * The following two API's must be used when attempting * to serialize the updates to cpu_online_mask, cpu_present_mask. */ void cpu_maps_update_begin(void) { mutex_lock(&cpu_add_remove_lock); } void cpu_maps_update_done(void) { mutex_unlock(&cpu_add_remove_lock); } static RAW_NOTIFIER_HEAD(cpu_chain); /* If set, cpu_up and cpu_down will return -EBUSY and do nothing. * Should always be manipulated under cpu_add_remove_lock */ static int cpu_hotplug_disabled; #ifdef CONFIG_HOTPLUG_CPU static struct { struct task_struct *active_writer; struct mutex lock; /* Synchronizes accesses to refcount, */ /* * Also blocks the new readers during * an ongoing cpu hotplug operation. */ int refcount; } cpu_hotplug = { .active_writer = NULL, .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock), .refcount = 0, }; void get_online_cpus(void) { might_sleep(); if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); cpu_hotplug.refcount++; mutex_unlock(&cpu_hotplug.lock); } EXPORT_SYMBOL_GPL(get_online_cpus); void put_online_cpus(void) { if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); if (WARN_ON(!cpu_hotplug.refcount)) cpu_hotplug.refcount++; /* try to fix things up */ if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); } EXPORT_SYMBOL_GPL(put_online_cpus); /* * This ensures that the hotplug operation can begin only when the * refcount goes to zero. * * Note that during a cpu-hotplug operation, the new readers, if any, * will be blocked by the cpu_hotplug.lock * * Since cpu_hotplug_begin() is always called after invoking * cpu_maps_update_begin(), we can be sure that only one writer is active. * * Note that theoretically, there is a possibility of a livelock: * - Refcount goes to zero, last reader wakes up the sleeping * writer. * - Last reader unlocks the cpu_hotplug.lock. * - A new reader arrives at this moment, bumps up the refcount. * - The writer acquires the cpu_hotplug.lock finds the refcount * non zero and goes to sleep again. * * However, this is very difficult to achieve in practice since * get_online_cpus() not an api which is called all that often. * */ static void cpu_hotplug_begin(void) { cpu_hotplug.active_writer = current; for (;;) { mutex_lock(&cpu_hotplug.lock); if (likely(!cpu_hotplug.refcount)) break; __set_current_state(TASK_UNINTERRUPTIBLE); mutex_unlock(&cpu_hotplug.lock); schedule(); } } static void cpu_hotplug_done(void) { cpu_hotplug.active_writer = NULL; mutex_unlock(&cpu_hotplug.lock); } #else /* #if CONFIG_HOTPLUG_CPU */ static void cpu_hotplug_begin(void) {} static void cpu_hotplug_done(void) {} #endif /* #else #if CONFIG_HOTPLUG_CPU */ /* Need to know about CPUs going up/down? */ int __ref register_cpu_notifier(struct notifier_block *nb) { int ret; cpu_maps_update_begin(); ret = raw_notifier_chain_register(&cpu_chain, nb); cpu_maps_update_done(); return ret; } static int __cpu_notify(unsigned long val, void *v, int nr_to_call, int *nr_calls) { int ret; ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call, nr_calls); return notifier_to_errno(ret); } static int cpu_notify(unsigned long val, void *v) { return __cpu_notify(val, v, -1, NULL); } #ifdef CONFIG_HOTPLUG_CPU static void cpu_notify_nofail(unsigned long val, void *v) { BUG_ON(cpu_notify(val, v)); } EXPORT_SYMBOL(register_cpu_notifier); void __ref unregister_cpu_notifier(struct notifier_block *nb) { cpu_maps_update_begin(); raw_notifier_chain_unregister(&cpu_chain, nb); cpu_maps_update_done(); } EXPORT_SYMBOL(unregister_cpu_notifier); /** * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU * @cpu: a CPU id * * This function walks all processes, finds a valid mm struct for each one and * then clears a corresponding bit in mm's cpumask. While this all sounds * trivial, there are various non-obvious corner cases, which this function * tries to solve in a safe manner. * * Also note that the function uses a somewhat relaxed locking scheme, so it may * be called only for an already offlined CPU. */ void clear_tasks_mm_cpumask(int cpu) { struct task_struct *p; /* * This function is called after the cpu is taken down and marked * offline, so its not like new tasks will ever get this cpu set in * their mm mask. -- Peter Zijlstra * Thus, we may use rcu_read_lock() here, instead of grabbing * full-fledged tasklist_lock. */ WARN_ON(cpu_online(cpu)); rcu_read_lock(); for_each_process(p) { struct task_struct *t; /* * Main thread might exit, but other threads may still have * a valid mm. Find one. */ t = find_lock_task_mm(p); if (!t) continue; cpumask_clear_cpu(cpu, mm_cpumask(t->mm)); task_unlock(t); } rcu_read_unlock(); } static inline void check_for_tasks(int cpu) { struct task_struct *p; write_lock_irq(&tasklist_lock); for_each_process(p) { if (task_cpu(p) == cpu && p->state == TASK_RUNNING && (p->utime || p->stime)) printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d " "(state = %ld, flags = %x)\n", p->comm, task_pid_nr(p), cpu, p->state, p->flags); } write_unlock_irq(&tasklist_lock); } struct take_cpu_down_param { unsigned long mod; void *hcpu; }; /* Take this CPU down. */ static int __ref take_cpu_down(void *_param) { struct take_cpu_down_param *param = _param; int err; /* 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); return 0; } /* Requires cpu_add_remove_lock to be held */ static int __ref _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; if (!cpu_online(cpu)) return -EINVAL; cpu_hotplug_begin(); err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err) { nr_calls--; __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL); printk("%s: attempt to take down CPU %u failed\n", __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)); /* * The migration_call() CPU_DYING callback will have removed all * runnable tasks from the cpu, there's only the idle task left now * that the migration thread is done doing the stop_machine thing. * * Wait for the stop thread to go away. */ while (!idle_cpu(cpu)) cpu_relax(); /* This actually kills the CPU. */ __cpu_die(cpu); /* CPU is completely dead: tell everyone. Too late to complain. */ cpu_notify_nofail(CPU_DEAD | mod, hcpu); check_for_tasks(cpu); out_release: cpu_hotplug_done(); if (!err) cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu); return err; } int __ref cpu_down(unsigned int cpu) { int err; cpu_maps_update_begin(); if (cpu_hotplug_disabled) { err = -EBUSY; goto out; } err = _cpu_down(cpu, 0); out: cpu_maps_update_done(); return err; } EXPORT_SYMBOL(cpu_down); #endif /*CONFIG_HOTPLUG_CPU*/ /* Requires cpu_add_remove_lock to be held */ static int __cpuinit _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; if (cpu_online(cpu) || !cpu_present(cpu)) return -EINVAL; cpu_hotplug_begin(); idle = idle_thread_get(cpu); if (IS_ERR(idle)) { ret = PTR_ERR(idle); 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--; printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n", __func__, cpu); goto out_notify; } /* Arch-specific enabling code. */ ret = __cpu_up(cpu, idle); if (ret != 0) 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); out_notify: if (ret != 0) __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL); out: cpu_hotplug_done(); return ret; } int __cpuinit cpu_up(unsigned int cpu) { int err = 0; #ifdef CONFIG_MEMORY_HOTPLUG int nid; pg_data_t *pgdat; #endif if (!cpu_possible(cpu)) { printk(KERN_ERR "can't online cpu %d because it is not " "configured as may-hotadd at boot time\n", cpu); #if defined(CONFIG_IA64) printk(KERN_ERR "please check additional_cpus= boot " "parameter\n"); #endif return -EINVAL; } #ifdef CONFIG_MEMORY_HOTPLUG nid = cpu_to_node(cpu); if (!node_online(nid)) { err = mem_online_node(nid); if (err) return err; } pgdat = NODE_DATA(nid); if (!pgdat) { printk(KERN_ERR "Can't online cpu %d due to NULL pgdat\n", cpu); return -ENOMEM; } if (pgdat->node_zonelists->_zonerefs->zone == NULL) { mutex_lock(&zonelists_mutex); build_all_zonelists(NULL, NULL); mutex_unlock(&zonelists_mutex); } #endif cpu_maps_update_begin(); if (cpu_hotplug_disabled) { err = -EBUSY; goto out; } err = _cpu_up(cpu, 0); out: cpu_maps_update_done(); return err; } EXPORT_SYMBOL_GPL(cpu_up); #ifdef CONFIG_PM_SLEEP_SMP static cpumask_var_t frozen_cpus; int disable_nonboot_cpus(void) { int cpu, first_cpu, error = 0; cpu_maps_update_begin(); first_cpu = cpumask_first(cpu_online_mask); /* * We take down all of the non-boot CPUs in one shot to avoid races * with the userspace trying to use the CPU hotplug at the same time */ cpumask_clear(frozen_cpus); printk("Disabling non-boot CPUs ...\n"); for_each_online_cpu(cpu) { if (cpu == first_cpu) continue; error = _cpu_down(cpu, 1); if (!error) cpumask_set_cpu(cpu, frozen_cpus); else { printk(KERN_ERR "Error taking CPU%d down: %d\n", cpu, error); break; } } if (!error) { BUG_ON(num_online_cpus() > 1); /* Make sure the CPUs won't be enabled by someone else */ cpu_hotplug_disabled = 1; } else { printk(KERN_ERR "Non-boot CPUs are not disabled\n"); } cpu_maps_update_done(); return error; } void __weak arch_enable_nonboot_cpus_begin(void) { } void __weak arch_enable_nonboot_cpus_end(void) { } void __ref enable_nonboot_cpus(void) {