/* 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/module.h> #include <linux/kthread.h> #include <linux/stop_machine.h> #include <linux/mutex.h> /* Serializes the updates to cpu_online_map, cpu_present_map */ static DEFINE_MUTEX(cpu_add_remove_lock); static __cpuinitdata 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; 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; wait_queue_head_t writer_queue; } cpu_hotplug; #define writer_exists() (cpu_hotplug.active_writer != NULL) void __init cpu_hotplug_init(void) { cpu_hotplug.active_writer = NULL; mutex_init(&cpu_hotplug.lock); cpu_hotplug.refcount = 0; init_waitqueue_head(&cpu_hotplug.writer_queue); } #ifdef CONFIG_HOTPLUG_CPU 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); cpu_hotplug.refcount--; if (unlikely(writer_exists()) && !cpu_hotplug.refcount) wake_up(&cpu_hotplug.writer_queue); mutex_unlock(&cpu_hotplug.lock); } EXPORT_SYMBOL_GPL(put_online_cpus); #endif /* CONFIG_HOTPLUG_CPU */ /* * The following two API's must be used when attempting * to serialize the updates to cpu_online_map, cpu_present_map. */ void cpu_maps_update_begin(void) { mutex_lock(&cpu_add_remove_lock); } void cpu_maps_update_done(void) { mutex_unlock(&cpu_add_remove_lock); } /* * 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_maps_update_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) { DECLARE_WAITQUEUE(wait, current); mutex_lock(&cpu_hotplug.lock); cpu_hotplug.active_writer = current; add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait); while (cpu_hotplug.refcount) { set_current_state(TASK_UNINTERRUPTIBLE); mutex_unlock(&cpu_hotplug.lock); schedule(); mutex_lock(&cpu_hotplug.lock); } remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait); } static void cpu_hotplug_done(void) { cpu_hotplug.active_writer = NULL; mutex_unlock(&cpu_hotplug.lock); } /* Need to know about CPUs going up/down? */ int __cpuinit 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; } #ifdef CONFIG_HOTPLUG_CPU EXPORT_SYMBOL(register_cpu_notifier); void 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); 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 && (!cputime_eq(p->utime, cputime_zero) || !cputime_eq(p->stime, cputime_zero))) 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 take_cpu_down(void *_param) { struct take_cpu_down_param *param = _param; int err; raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod, param->hcpu); /* Ensure this CPU doesn't handle any more interrupts. */ err = __cpu_disable(); if (err < 0) return err; /* Force idle task to run as soon as we yield: it should immediately notice cpu is offline and die quickly. */ sched_idle_next(); return 0; } /* Requires cpu_add_remove_lock to be held */ static int _cpu_down(unsigned int cpu, int tasks_frozen) { int err, nr_calls = 0; struct task_struct *p; cpumask_t old_allowed, tmp; 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 = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls); if (err == NOTIFY_BAD) { nr_calls--; __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL); printk("%s: attempt to take down CPU %u failed\n", __FUNCTION__, cpu); err = -EINVAL; goto out_release; } /* Ensure that we are not runnable on dying cpu */ old_allowed = current->cpus_allowed; tmp = CPU_MASK_ALL; cpu_clear(cpu, tmp); set_cpus_allowed(current, tmp); p = __stop_machine_run(take_cpu_down, &tcd_param, cpu); if (IS_ERR(p) || cpu_online(cpu)) { /* CPU didn't die: tell everyone. Can't complain. */ if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, hcpu) == NOTIFY_BAD) BUG(); if (IS_ERR(p)) { err = PTR_ERR(p); goto out_allowed; } goto out_thread; } /* Wait for it to sleep (leaving idle task). */ while (!idle_cpu(cpu)) yield(); /* This actually kills the CPU. */ __cpu_die(cpu); /* CPU is completely dead: tell everyone. Too late to complain. */ if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod, hcpu) == NOTIFY_BAD) BUG(); check_for_tasks(cpu); out_thread: err = kthread_stop(p); out_allowed: set_cpus_allowed(current, old_allowed); out_release: cpu_hotplug_done(); return err; } int cpu_down(unsigned int cpu) { int err = 0; cpu_maps_update_begin(); if (cpu_hotplug_disabled) err = -EBUSY; else err = _cpu_down(cpu, 0); cpu_maps_update_done(); return err; } #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; if (cpu_online(cpu) || !cpu_present(cpu)) return -EINVAL; cpu_hotplug_begin(); ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls); if (ret == NOTIFY_BAD) { nr_calls--; printk("%s: attempt to bring up CPU %u failed\n", __FUNCTION__, cpu); ret = -EINVAL; goto out_notify; } /* Arch-specific enabling code. */ ret = __cpu_up(cpu); if (ret != 0) goto out_notify; BUG_ON(!cpu_online(cpu)); /* Now call notifier in preparation. */ raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu); out_notify: if (ret != 0) __raw_notifier_call_chain(&cpu_chain, CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL); cpu_hotplug_done(); return ret; } int __cpuinit cpu_up(unsigned int cpu) { int err = 0; if (!cpu_isset(cpu, cpu_possible_map)) { 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) || defined(CONFIG_X86_64) || defined(CONFIG_S390) printk(KERN_ERR "please check additional_cpus= boot " "parameter\n"); #endif return -EINVAL; } cpu_maps_update_begin(); if (cpu_hotplug_disabled) err = -EBUSY; else err = _cpu_up(cpu, 0); cpu_maps_update_done(); return err; } #ifdef CONFIG_PM_SLEEP_SMP static cpumask_t frozen_cpus; int disable_nonboot_cpus(void) { int cpu, first_cpu, error = 0; cpu_maps_update_begin(); first_cpu = first_cpu(cpu_online_map); /* 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 */ cpus_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) { cpu_set(cpu, frozen_cpus); printk("CPU%d is down\n", cpu); } 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 enable_nonboot_cpus(void) { int cpu, error; /* Allow everyone to use the CPU hotplug again */ cpu_maps_update_begin(); cpu_hotplug_disabled = 0; if (cpus_empty(frozen_cpus)) goto out; printk("Enabling non-boot CPUs ...\n"); for_each_cpu_mask(cpu, frozen_cpus) { error = _cpu_up(cpu, 1); if (!error) { printk("CPU%d is up\n", cpu); continue; } printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error); } cpus_clear(frozen_cpus); out: cpu_maps_update_done(); } #endif /* CONFIG_PM_SLEEP_SMP */