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![Linus Torvalds](/assets/img/avatar_default.png)
SLAB uses get/put_online_cpus() which use a mutex which is itself only initialized when cpu_hotplug_init() is called. Currently we hang suring boot in SLAB due to doing that too late. Reported by James Bottomley and Sachin Sant (and possibly others). Debugged by Benjamin Herrenschmidt. This just removes the dynamic initialization of the data structures, and replaces it with a static one, avoiding this dependency entirely, and removing one unnecessary special initcall. Tested-by: Sachin Sant <sachinp@in.ibm.com> Tested-by: James Bottomley <James.Bottomley@HansenPartnership.com> Tested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
564 lines
14 KiB
C
564 lines
14 KiB
C
/* CPU control.
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* (C) 2001, 2002, 2003, 2004 Rusty Russell
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*
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* This code is licenced under the GPL.
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*/
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#include <linux/proc_fs.h>
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#include <linux/smp.h>
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#include <linux/init.h>
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#include <linux/notifier.h>
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#include <linux/sched.h>
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#include <linux/unistd.h>
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#include <linux/cpu.h>
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#include <linux/module.h>
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#include <linux/kthread.h>
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#include <linux/stop_machine.h>
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#include <linux/mutex.h>
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#ifdef CONFIG_SMP
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/* Serializes the updates to cpu_online_mask, cpu_present_mask */
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static DEFINE_MUTEX(cpu_add_remove_lock);
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static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
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/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
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* Should always be manipulated under cpu_add_remove_lock
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*/
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static int cpu_hotplug_disabled;
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static struct {
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struct task_struct *active_writer;
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struct mutex lock; /* Synchronizes accesses to refcount, */
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/*
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* Also blocks the new readers during
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* an ongoing cpu hotplug operation.
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*/
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int refcount;
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} cpu_hotplug = {
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.active_writer = NULL,
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.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
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.refcount = 0,
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};
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#ifdef CONFIG_HOTPLUG_CPU
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void get_online_cpus(void)
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{
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might_sleep();
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if (cpu_hotplug.active_writer == current)
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return;
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mutex_lock(&cpu_hotplug.lock);
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cpu_hotplug.refcount++;
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mutex_unlock(&cpu_hotplug.lock);
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}
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EXPORT_SYMBOL_GPL(get_online_cpus);
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void put_online_cpus(void)
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{
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if (cpu_hotplug.active_writer == current)
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return;
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mutex_lock(&cpu_hotplug.lock);
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if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
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wake_up_process(cpu_hotplug.active_writer);
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mutex_unlock(&cpu_hotplug.lock);
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}
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EXPORT_SYMBOL_GPL(put_online_cpus);
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#endif /* CONFIG_HOTPLUG_CPU */
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/*
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* The following two API's must be used when attempting
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* to serialize the updates to cpu_online_mask, cpu_present_mask.
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*/
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void cpu_maps_update_begin(void)
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{
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mutex_lock(&cpu_add_remove_lock);
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}
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void cpu_maps_update_done(void)
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{
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mutex_unlock(&cpu_add_remove_lock);
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}
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/*
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* This ensures that the hotplug operation can begin only when the
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* refcount goes to zero.
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*
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* Note that during a cpu-hotplug operation, the new readers, if any,
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* will be blocked by the cpu_hotplug.lock
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*
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* Since cpu_hotplug_begin() is always called after invoking
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* cpu_maps_update_begin(), we can be sure that only one writer is active.
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*
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* Note that theoretically, there is a possibility of a livelock:
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* - Refcount goes to zero, last reader wakes up the sleeping
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* writer.
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* - Last reader unlocks the cpu_hotplug.lock.
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* - A new reader arrives at this moment, bumps up the refcount.
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* - The writer acquires the cpu_hotplug.lock finds the refcount
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* non zero and goes to sleep again.
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*
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* However, this is very difficult to achieve in practice since
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* get_online_cpus() not an api which is called all that often.
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*
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*/
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static void cpu_hotplug_begin(void)
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{
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cpu_hotplug.active_writer = current;
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for (;;) {
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mutex_lock(&cpu_hotplug.lock);
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if (likely(!cpu_hotplug.refcount))
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break;
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__set_current_state(TASK_UNINTERRUPTIBLE);
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mutex_unlock(&cpu_hotplug.lock);
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schedule();
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}
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}
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static void cpu_hotplug_done(void)
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{
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cpu_hotplug.active_writer = NULL;
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mutex_unlock(&cpu_hotplug.lock);
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}
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/* Need to know about CPUs going up/down? */
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int __ref register_cpu_notifier(struct notifier_block *nb)
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{
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int ret;
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cpu_maps_update_begin();
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ret = raw_notifier_chain_register(&cpu_chain, nb);
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cpu_maps_update_done();
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return ret;
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}
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#ifdef CONFIG_HOTPLUG_CPU
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EXPORT_SYMBOL(register_cpu_notifier);
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void __ref unregister_cpu_notifier(struct notifier_block *nb)
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{
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cpu_maps_update_begin();
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raw_notifier_chain_unregister(&cpu_chain, nb);
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cpu_maps_update_done();
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}
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EXPORT_SYMBOL(unregister_cpu_notifier);
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static inline void check_for_tasks(int cpu)
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{
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struct task_struct *p;
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write_lock_irq(&tasklist_lock);
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for_each_process(p) {
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if (task_cpu(p) == cpu &&
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(!cputime_eq(p->utime, cputime_zero) ||
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!cputime_eq(p->stime, cputime_zero)))
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printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
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(state = %ld, flags = %x) \n",
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p->comm, task_pid_nr(p), cpu,
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p->state, p->flags);
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}
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write_unlock_irq(&tasklist_lock);
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}
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struct take_cpu_down_param {
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unsigned long mod;
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void *hcpu;
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};
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/* Take this CPU down. */
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static int __ref take_cpu_down(void *_param)
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{
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struct take_cpu_down_param *param = _param;
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int err;
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/* Ensure this CPU doesn't handle any more interrupts. */
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err = __cpu_disable();
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if (err < 0)
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return err;
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raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
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param->hcpu);
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/* Force idle task to run as soon as we yield: it should
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immediately notice cpu is offline and die quickly. */
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sched_idle_next();
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return 0;
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}
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/* Requires cpu_add_remove_lock to be held */
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static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
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{
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int err, nr_calls = 0;
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cpumask_var_t old_allowed;
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void *hcpu = (void *)(long)cpu;
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unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
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struct take_cpu_down_param tcd_param = {
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.mod = mod,
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.hcpu = hcpu,
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};
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if (num_online_cpus() == 1)
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return -EBUSY;
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if (!cpu_online(cpu))
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return -EINVAL;
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if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
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return -ENOMEM;
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cpu_hotplug_begin();
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err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
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hcpu, -1, &nr_calls);
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if (err == NOTIFY_BAD) {
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nr_calls--;
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__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
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hcpu, nr_calls, NULL);
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printk("%s: attempt to take down CPU %u failed\n",
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__func__, cpu);
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err = -EINVAL;
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goto out_release;
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}
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/* Ensure that we are not runnable on dying cpu */
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cpumask_copy(old_allowed, ¤t->cpus_allowed);
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set_cpus_allowed_ptr(current,
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cpumask_of(cpumask_any_but(cpu_online_mask, cpu)));
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err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
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if (err) {
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/* CPU didn't die: tell everyone. Can't complain. */
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if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
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hcpu) == NOTIFY_BAD)
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BUG();
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goto out_allowed;
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}
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BUG_ON(cpu_online(cpu));
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/* Wait for it to sleep (leaving idle task). */
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while (!idle_cpu(cpu))
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yield();
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/* This actually kills the CPU. */
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__cpu_die(cpu);
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/* CPU is completely dead: tell everyone. Too late to complain. */
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if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
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hcpu) == NOTIFY_BAD)
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BUG();
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check_for_tasks(cpu);
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out_allowed:
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set_cpus_allowed_ptr(current, old_allowed);
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out_release:
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cpu_hotplug_done();
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if (!err) {
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if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
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hcpu) == NOTIFY_BAD)
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BUG();
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}
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free_cpumask_var(old_allowed);
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return err;
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}
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int __ref cpu_down(unsigned int cpu)
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{
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int err;
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err = stop_machine_create();
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if (err)
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return err;
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cpu_maps_update_begin();
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if (cpu_hotplug_disabled) {
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err = -EBUSY;
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goto out;
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}
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set_cpu_active(cpu, false);
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/*
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* Make sure the all cpus did the reschedule and are not
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* using stale version of the cpu_active_mask.
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* This is not strictly necessary becuase stop_machine()
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* that we run down the line already provides the required
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* synchronization. But it's really a side effect and we do not
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* want to depend on the innards of the stop_machine here.
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*/
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synchronize_sched();
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err = _cpu_down(cpu, 0);
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if (cpu_online(cpu))
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set_cpu_active(cpu, true);
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out:
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cpu_maps_update_done();
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stop_machine_destroy();
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return err;
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}
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EXPORT_SYMBOL(cpu_down);
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#endif /*CONFIG_HOTPLUG_CPU*/
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/* Requires cpu_add_remove_lock to be held */
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static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
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{
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int ret, nr_calls = 0;
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void *hcpu = (void *)(long)cpu;
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unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
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if (cpu_online(cpu) || !cpu_present(cpu))
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return -EINVAL;
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cpu_hotplug_begin();
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ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
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-1, &nr_calls);
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if (ret == NOTIFY_BAD) {
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nr_calls--;
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printk("%s: attempt to bring up CPU %u failed\n",
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__func__, cpu);
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ret = -EINVAL;
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goto out_notify;
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}
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/* Arch-specific enabling code. */
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ret = __cpu_up(cpu);
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if (ret != 0)
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goto out_notify;
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BUG_ON(!cpu_online(cpu));
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set_cpu_active(cpu, true);
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/* Now call notifier in preparation. */
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raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
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out_notify:
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if (ret != 0)
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__raw_notifier_call_chain(&cpu_chain,
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CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
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cpu_hotplug_done();
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return ret;
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}
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int __cpuinit cpu_up(unsigned int cpu)
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{
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int err = 0;
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if (!cpu_possible(cpu)) {
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printk(KERN_ERR "can't online cpu %d because it is not "
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"configured as may-hotadd at boot time\n", cpu);
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#if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
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printk(KERN_ERR "please check additional_cpus= boot "
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"parameter\n");
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#endif
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return -EINVAL;
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}
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cpu_maps_update_begin();
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if (cpu_hotplug_disabled) {
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err = -EBUSY;
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goto out;
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}
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err = _cpu_up(cpu, 0);
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out:
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cpu_maps_update_done();
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return err;
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}
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#ifdef CONFIG_PM_SLEEP_SMP
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static cpumask_var_t frozen_cpus;
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int disable_nonboot_cpus(void)
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{
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int cpu, first_cpu, error;
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error = stop_machine_create();
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if (error)
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return error;
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cpu_maps_update_begin();
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first_cpu = cpumask_first(cpu_online_mask);
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/* We take down all of the non-boot CPUs in one shot to avoid races
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* with the userspace trying to use the CPU hotplug at the same time
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*/
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cpumask_clear(frozen_cpus);
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printk("Disabling non-boot CPUs ...\n");
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for_each_online_cpu(cpu) {
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if (cpu == first_cpu)
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continue;
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error = _cpu_down(cpu, 1);
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if (!error) {
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cpumask_set_cpu(cpu, frozen_cpus);
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printk("CPU%d is down\n", cpu);
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} else {
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printk(KERN_ERR "Error taking CPU%d down: %d\n",
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cpu, error);
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break;
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}
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}
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if (!error) {
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BUG_ON(num_online_cpus() > 1);
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/* Make sure the CPUs won't be enabled by someone else */
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cpu_hotplug_disabled = 1;
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} else {
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printk(KERN_ERR "Non-boot CPUs are not disabled\n");
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}
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cpu_maps_update_done();
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stop_machine_destroy();
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return error;
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}
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void __ref enable_nonboot_cpus(void)
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{
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int cpu, error;
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/* Allow everyone to use the CPU hotplug again */
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cpu_maps_update_begin();
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cpu_hotplug_disabled = 0;
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if (cpumask_empty(frozen_cpus))
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goto out;
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printk("Enabling non-boot CPUs ...\n");
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for_each_cpu(cpu, frozen_cpus) {
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error = _cpu_up(cpu, 1);
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if (!error) {
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printk("CPU%d is up\n", cpu);
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continue;
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}
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printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
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}
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cpumask_clear(frozen_cpus);
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out:
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cpu_maps_update_done();
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}
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static int alloc_frozen_cpus(void)
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{
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if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
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return -ENOMEM;
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return 0;
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}
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core_initcall(alloc_frozen_cpus);
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#endif /* CONFIG_PM_SLEEP_SMP */
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/**
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* notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
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* @cpu: cpu that just started
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*
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* This function calls the cpu_chain notifiers with CPU_STARTING.
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* It must be called by the arch code on the new cpu, before the new cpu
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* enables interrupts and before the "boot" cpu returns from __cpu_up().
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*/
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void __cpuinit notify_cpu_starting(unsigned int cpu)
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{
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unsigned long val = CPU_STARTING;
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#ifdef CONFIG_PM_SLEEP_SMP
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if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
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val = CPU_STARTING_FROZEN;
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#endif /* CONFIG_PM_SLEEP_SMP */
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raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
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}
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#endif /* CONFIG_SMP */
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/*
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* cpu_bit_bitmap[] is a special, "compressed" data structure that
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* represents all NR_CPUS bits binary values of 1<<nr.
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*
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* It is used by cpumask_of() to get a constant address to a CPU
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* mask value that has a single bit set only.
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*/
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/* cpu_bit_bitmap[0] is empty - so we can back into it */
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#define MASK_DECLARE_1(x) [x+1][0] = 1UL << (x)
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#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
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#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
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#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
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const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
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MASK_DECLARE_8(0), MASK_DECLARE_8(8),
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MASK_DECLARE_8(16), MASK_DECLARE_8(24),
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#if BITS_PER_LONG > 32
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MASK_DECLARE_8(32), MASK_DECLARE_8(40),
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MASK_DECLARE_8(48), MASK_DECLARE_8(56),
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#endif
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};
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EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
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const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
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EXPORT_SYMBOL(cpu_all_bits);
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#ifdef CONFIG_INIT_ALL_POSSIBLE
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static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
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= CPU_BITS_ALL;
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#else
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static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
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#endif
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const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
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EXPORT_SYMBOL(cpu_possible_mask);
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static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
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const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
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EXPORT_SYMBOL(cpu_online_mask);
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static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
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const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
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EXPORT_SYMBOL(cpu_present_mask);
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static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
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const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
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EXPORT_SYMBOL(cpu_active_mask);
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void set_cpu_possible(unsigned int cpu, bool possible)
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{
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if (possible)
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cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
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else
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cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
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}
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void set_cpu_present(unsigned int cpu, bool present)
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{
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if (present)
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cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
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else
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cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
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}
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void set_cpu_online(unsigned int cpu, bool online)
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{
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if (online)
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cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
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else
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cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
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}
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void set_cpu_active(unsigned int cpu, bool active)
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{
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if (active)
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cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
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else
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cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
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}
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void init_cpu_present(const struct cpumask *src)
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{
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cpumask_copy(to_cpumask(cpu_present_bits), src);
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}
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void init_cpu_possible(const struct cpumask *src)
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{
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cpumask_copy(to_cpumask(cpu_possible_bits), src);
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}
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void init_cpu_online(const struct cpumask *src)
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{
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cpumask_copy(to_cpumask(cpu_online_bits), src);
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}
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