FreeBSD/Linux Kernel Cross Reference
sys/kernel/cpu.c

     /* 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;
   
           cpu_hotplug_begin();
   
           if (cpu_online(cpu) || !cpu_present(cpu)) {
                   ret = -EINVAL;
                   goto out;
           }
   
           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)
   {
           int cpu, error;
   
           /* Allow everyone to use the CPU hotplug again */
           cpu_maps_update_begin();
           cpu_hotplug_disabled = 0;
           if (cpumask_empty(frozen_cpus))
                   goto out;
   
           printk(KERN_INFO "Enabling non-boot CPUs ...\n");
   
           arch_enable_nonboot_cpus_begin();
   
           for_each_cpu(cpu, frozen_cpus) {
                   error = _cpu_up(cpu, 1);
                   if (!error) {
                           printk(KERN_INFO "CPU%d is up\n", cpu);
                           continue;
                   }
                   printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
           }
   
           arch_enable_nonboot_cpus_end();
   
           cpumask_clear(frozen_cpus);
   out:
           cpu_maps_update_done();
   }
   
   static int __init alloc_frozen_cpus(void)
   {
           if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
                   return -ENOMEM;
           return 0;
   }
   core_initcall(alloc_frozen_cpus);
   
   /*
    * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
    * hotplug when tasks are about to be frozen. Also, don't allow the freezer
    * to continue until any currently running CPU hotplug operation gets
    * completed.
    * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
    * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
    * CPU hotplug path and released only after it is complete. Thus, we
    * (and hence the freezer) will block here until any currently running CPU
    * hotplug operation gets completed.
    */
   void cpu_hotplug_disable_before_freeze(void)
   {
           cpu_maps_update_begin();
           cpu_hotplug_disabled = 1;
           cpu_maps_update_done();
   }
   
   
   /*
    * When tasks have been thawed, re-enable regular CPU hotplug (which had been
    * disabled while beginning to freeze tasks).
    */
   void cpu_hotplug_enable_after_thaw(void)
   {
           cpu_maps_update_begin();
           cpu_hotplug_disabled = 0;
           cpu_maps_update_done();
   }
   
   /*
    * When callbacks for CPU hotplug notifications are being executed, we must
    * ensure that the state of the system with respect to the tasks being frozen
    * or not, as reported by the notification, remains unchanged *throughout the
    * duration* of the execution of the callbacks.
    * Hence we need to prevent the freezer from racing with regular CPU hotplug.
    *
    * This synchronization is implemented by mutually excluding regular CPU
    * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
    * Hibernate notifications.
    */
   static int
   cpu_hotplug_pm_callback(struct notifier_block *nb,
                           unsigned long action, void *ptr)
   {
           switch (action) {
   
           case PM_SUSPEND_PREPARE:
           case PM_HIBERNATION_PREPARE:
                   cpu_hotplug_disable_before_freeze();
                   break;
   
           case PM_POST_SUSPEND:
           case PM_POST_HIBERNATION:
                   cpu_hotplug_enable_after_thaw();
                   break;
   
           default:
                   return NOTIFY_DONE;
           }
   
           return NOTIFY_OK;
   }
   
   
   static int __init cpu_hotplug_pm_sync_init(void)
   {
           /*
            * cpu_hotplug_pm_callback has higher priority than x86
            * bsp_pm_callback which depends on cpu_hotplug_pm_callback
            * to disable cpu hotplug to avoid cpu hotplug race.
            */
           pm_notifier(cpu_hotplug_pm_callback, 0);
           return 0;
   }
   core_initcall(cpu_hotplug_pm_sync_init);
   
   #endif /* CONFIG_PM_SLEEP_SMP */
   
   /**
    * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
    * @cpu: cpu that just started
    *
    * This function calls the cpu_chain notifiers with CPU_STARTING.
    * It must be called by the arch code on the new cpu, before the new cpu
    * enables interrupts and before the "boot" cpu returns from __cpu_up().
    */
   void __cpuinit 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);
   }
   
   #endif /* CONFIG_SMP */
   
   /*
    * cpu_bit_bitmap[] is a special, "compressed" data structure that
    * represents all NR_CPUS bits binary values of 1<<nr.
    *
    * It is used by cpumask_of() to get a constant address to a CPU
    * mask value that has a single bit set only.
    */
   
   /* cpu_bit_bitmap[0] is empty - so we can back into it */
   #define MASK_DECLARE_1(x)       [x+1][0] = (1UL << (x))
   #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
   #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
   #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
   
   const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
   
           MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
           MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
   #if BITS_PER_LONG > 32
           MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
           MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
   #endif
   };
   EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
   
   const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
   EXPORT_SYMBOL(cpu_all_bits);
   
   #ifdef CONFIG_INIT_ALL_POSSIBLE
   static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
           = CPU_BITS_ALL;
   #else
   static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
   #endif
   const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
   EXPORT_SYMBOL(cpu_possible_mask);
   
   static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
   const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
   EXPORT_SYMBOL(cpu_online_mask);
   
   static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
   const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
   EXPORT_SYMBOL(cpu_present_mask);
   
   static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
   const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
   EXPORT_SYMBOL(cpu_active_mask);
   
   void set_cpu_possible(unsigned int cpu, bool possible)
   {
           if (possible)
                   cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
           else
                   cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
   }
   
   void set_cpu_present(unsigned int cpu, bool present)
   {
           if (present)
                   cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
           else
                   cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
   }
   
   void set_cpu_online(unsigned int cpu, bool online)
   {
           if (online)
                   cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
           else
                   cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
   }
   
   void set_cpu_active(unsigned int cpu, bool active)
   {
           if (active)
                   cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
           else
                   cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
   }
   
   void init_cpu_present(const struct cpumask *src)
   {
           cpumask_copy(to_cpumask(cpu_present_bits), src);
   }
   
   void init_cpu_possible(const struct cpumask *src)
   {
           cpumask_copy(to_cpumask(cpu_possible_bits), src);
   }
   
   void init_cpu_online(const struct cpumask *src)
   {
           cpumask_copy(to_cpumask(cpu_online_bits), src);
   }

Cache object: 2eb734ce2bd0194ac3d53da06c179c6d