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dd56af42bd
Currently, the expedited grace-period primitives do get_online_cpus(). This greatly simplifies their implementation, but means that calls to them holding locks that are acquired by CPU-hotplug notifiers (to say nothing of calls to these primitives from CPU-hotplug notifiers) can deadlock. But this is starting to become inconvenient, as can be seen here: https://lkml.org/lkml/2014/8/5/754. The problem in this case is that some developers need to acquire a mutex from a CPU-hotplug notifier, but also need to hold it across a synchronize_rcu_expedited(). As noted above, this currently results in deadlock. This commit avoids the deadlock and retains the simplicity by creating a try_get_online_cpus(), which returns false if the get_online_cpus() reference count could not immediately be incremented. If a call to try_get_online_cpus() returns true, the expedited primitives operate as before. If a call returns false, the expedited primitives fall back to normal grace-period operations. This falling back of course results in increased grace-period latency, but only during times when CPU hotplug operations are actually in flight. The effect should therefore be negligible during normal operation. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Tested-by: Lan Tianyu <tianyu.lan@intel.com>
271 lines
8.3 KiB
C
271 lines
8.3 KiB
C
/*
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* include/linux/cpu.h - generic cpu definition
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*
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* This is mainly for topological representation. We define the
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* basic 'struct cpu' here, which can be embedded in per-arch
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* definitions of processors.
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*
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* Basic handling of the devices is done in drivers/base/cpu.c
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*
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* CPUs are exported via sysfs in the devices/system/cpu
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* directory.
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*/
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#ifndef _LINUX_CPU_H_
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#define _LINUX_CPU_H_
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#include <linux/node.h>
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#include <linux/compiler.h>
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#include <linux/cpumask.h>
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struct device;
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struct device_node;
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struct cpu {
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int node_id; /* The node which contains the CPU */
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int hotpluggable; /* creates sysfs control file if hotpluggable */
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struct device dev;
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};
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extern int register_cpu(struct cpu *cpu, int num);
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extern struct device *get_cpu_device(unsigned cpu);
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extern bool cpu_is_hotpluggable(unsigned cpu);
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extern bool arch_match_cpu_phys_id(int cpu, u64 phys_id);
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extern bool arch_find_n_match_cpu_physical_id(struct device_node *cpun,
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int cpu, unsigned int *thread);
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extern int cpu_add_dev_attr(struct device_attribute *attr);
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extern void cpu_remove_dev_attr(struct device_attribute *attr);
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extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
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extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
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#ifdef CONFIG_HOTPLUG_CPU
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extern void unregister_cpu(struct cpu *cpu);
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extern ssize_t arch_cpu_probe(const char *, size_t);
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extern ssize_t arch_cpu_release(const char *, size_t);
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#endif
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struct notifier_block;
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/*
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* CPU notifier priorities.
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*/
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enum {
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/*
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* SCHED_ACTIVE marks a cpu which is coming up active during
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* CPU_ONLINE and CPU_DOWN_FAILED and must be the first
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* notifier. CPUSET_ACTIVE adjusts cpuset according to
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* cpu_active mask right after SCHED_ACTIVE. During
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* CPU_DOWN_PREPARE, SCHED_INACTIVE and CPUSET_INACTIVE are
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* ordered in the similar way.
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*
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* This ordering guarantees consistent cpu_active mask and
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* migration behavior to all cpu notifiers.
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*/
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CPU_PRI_SCHED_ACTIVE = INT_MAX,
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CPU_PRI_CPUSET_ACTIVE = INT_MAX - 1,
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CPU_PRI_SCHED_INACTIVE = INT_MIN + 1,
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CPU_PRI_CPUSET_INACTIVE = INT_MIN,
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/* migration should happen before other stuff but after perf */
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CPU_PRI_PERF = 20,
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CPU_PRI_MIGRATION = 10,
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/* bring up workqueues before normal notifiers and down after */
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CPU_PRI_WORKQUEUE_UP = 5,
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CPU_PRI_WORKQUEUE_DOWN = -5,
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};
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#define CPU_ONLINE 0x0002 /* CPU (unsigned)v is up */
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#define CPU_UP_PREPARE 0x0003 /* CPU (unsigned)v coming up */
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#define CPU_UP_CANCELED 0x0004 /* CPU (unsigned)v NOT coming up */
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#define CPU_DOWN_PREPARE 0x0005 /* CPU (unsigned)v going down */
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#define CPU_DOWN_FAILED 0x0006 /* CPU (unsigned)v NOT going down */
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#define CPU_DEAD 0x0007 /* CPU (unsigned)v dead */
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#define CPU_DYING 0x0008 /* CPU (unsigned)v not running any task,
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* not handling interrupts, soon dead.
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* Called on the dying cpu, interrupts
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* are already disabled. Must not
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* sleep, must not fail */
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#define CPU_POST_DEAD 0x0009 /* CPU (unsigned)v dead, cpu_hotplug
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* lock is dropped */
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#define CPU_STARTING 0x000A /* CPU (unsigned)v soon running.
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* Called on the new cpu, just before
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* enabling interrupts. Must not sleep,
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* must not fail */
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/* Used for CPU hotplug events occurring while tasks are frozen due to a suspend
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* operation in progress
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*/
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#define CPU_TASKS_FROZEN 0x0010
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#define CPU_ONLINE_FROZEN (CPU_ONLINE | CPU_TASKS_FROZEN)
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#define CPU_UP_PREPARE_FROZEN (CPU_UP_PREPARE | CPU_TASKS_FROZEN)
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#define CPU_UP_CANCELED_FROZEN (CPU_UP_CANCELED | CPU_TASKS_FROZEN)
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#define CPU_DOWN_PREPARE_FROZEN (CPU_DOWN_PREPARE | CPU_TASKS_FROZEN)
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#define CPU_DOWN_FAILED_FROZEN (CPU_DOWN_FAILED | CPU_TASKS_FROZEN)
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#define CPU_DEAD_FROZEN (CPU_DEAD | CPU_TASKS_FROZEN)
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#define CPU_DYING_FROZEN (CPU_DYING | CPU_TASKS_FROZEN)
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#define CPU_STARTING_FROZEN (CPU_STARTING | CPU_TASKS_FROZEN)
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#ifdef CONFIG_SMP
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/* Need to know about CPUs going up/down? */
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#if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
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#define cpu_notifier(fn, pri) { \
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static struct notifier_block fn##_nb = \
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{ .notifier_call = fn, .priority = pri }; \
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register_cpu_notifier(&fn##_nb); \
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}
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#define __cpu_notifier(fn, pri) { \
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static struct notifier_block fn##_nb = \
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{ .notifier_call = fn, .priority = pri }; \
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__register_cpu_notifier(&fn##_nb); \
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}
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#else /* #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */
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#define cpu_notifier(fn, pri) do { (void)(fn); } while (0)
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#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0)
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#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE) */
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#ifdef CONFIG_HOTPLUG_CPU
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extern int register_cpu_notifier(struct notifier_block *nb);
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extern int __register_cpu_notifier(struct notifier_block *nb);
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extern void unregister_cpu_notifier(struct notifier_block *nb);
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extern void __unregister_cpu_notifier(struct notifier_block *nb);
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#else
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#ifndef MODULE
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extern int register_cpu_notifier(struct notifier_block *nb);
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extern int __register_cpu_notifier(struct notifier_block *nb);
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#else
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static inline int register_cpu_notifier(struct notifier_block *nb)
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{
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return 0;
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}
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static inline int __register_cpu_notifier(struct notifier_block *nb)
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{
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return 0;
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}
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#endif
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static inline void unregister_cpu_notifier(struct notifier_block *nb)
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{
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}
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static inline void __unregister_cpu_notifier(struct notifier_block *nb)
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{
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}
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#endif
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int cpu_up(unsigned int cpu);
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void notify_cpu_starting(unsigned int cpu);
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extern void cpu_maps_update_begin(void);
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extern void cpu_maps_update_done(void);
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#define cpu_notifier_register_begin cpu_maps_update_begin
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#define cpu_notifier_register_done cpu_maps_update_done
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#else /* CONFIG_SMP */
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#define cpu_notifier(fn, pri) do { (void)(fn); } while (0)
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#define __cpu_notifier(fn, pri) do { (void)(fn); } while (0)
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static inline int register_cpu_notifier(struct notifier_block *nb)
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{
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return 0;
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}
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static inline int __register_cpu_notifier(struct notifier_block *nb)
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{
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return 0;
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}
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static inline void unregister_cpu_notifier(struct notifier_block *nb)
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{
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}
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static inline void __unregister_cpu_notifier(struct notifier_block *nb)
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{
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}
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static inline void cpu_maps_update_begin(void)
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{
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}
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static inline void cpu_maps_update_done(void)
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{
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}
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static inline void cpu_notifier_register_begin(void)
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{
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}
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static inline void cpu_notifier_register_done(void)
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{
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}
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#endif /* CONFIG_SMP */
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extern struct bus_type cpu_subsys;
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#ifdef CONFIG_HOTPLUG_CPU
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/* Stop CPUs going up and down. */
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extern void cpu_hotplug_begin(void);
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extern void cpu_hotplug_done(void);
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extern void get_online_cpus(void);
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extern bool try_get_online_cpus(void);
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extern void put_online_cpus(void);
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extern void cpu_hotplug_disable(void);
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extern void cpu_hotplug_enable(void);
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#define hotcpu_notifier(fn, pri) cpu_notifier(fn, pri)
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#define __hotcpu_notifier(fn, pri) __cpu_notifier(fn, pri)
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#define register_hotcpu_notifier(nb) register_cpu_notifier(nb)
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#define __register_hotcpu_notifier(nb) __register_cpu_notifier(nb)
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#define unregister_hotcpu_notifier(nb) unregister_cpu_notifier(nb)
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#define __unregister_hotcpu_notifier(nb) __unregister_cpu_notifier(nb)
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void clear_tasks_mm_cpumask(int cpu);
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int cpu_down(unsigned int cpu);
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#else /* CONFIG_HOTPLUG_CPU */
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static inline void cpu_hotplug_begin(void) {}
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static inline void cpu_hotplug_done(void) {}
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#define get_online_cpus() do { } while (0)
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#define try_get_online_cpus() true
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#define put_online_cpus() do { } while (0)
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#define cpu_hotplug_disable() do { } while (0)
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#define cpu_hotplug_enable() do { } while (0)
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#define hotcpu_notifier(fn, pri) do { (void)(fn); } while (0)
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#define __hotcpu_notifier(fn, pri) do { (void)(fn); } while (0)
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/* These aren't inline functions due to a GCC bug. */
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#define register_hotcpu_notifier(nb) ({ (void)(nb); 0; })
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#define __register_hotcpu_notifier(nb) ({ (void)(nb); 0; })
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#define unregister_hotcpu_notifier(nb) ({ (void)(nb); })
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#define __unregister_hotcpu_notifier(nb) ({ (void)(nb); })
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#endif /* CONFIG_HOTPLUG_CPU */
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#ifdef CONFIG_PM_SLEEP_SMP
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extern int disable_nonboot_cpus(void);
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extern void enable_nonboot_cpus(void);
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#else /* !CONFIG_PM_SLEEP_SMP */
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static inline int disable_nonboot_cpus(void) { return 0; }
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static inline void enable_nonboot_cpus(void) {}
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#endif /* !CONFIG_PM_SLEEP_SMP */
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enum cpuhp_state {
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CPUHP_OFFLINE,
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CPUHP_ONLINE,
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};
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void cpu_startup_entry(enum cpuhp_state state);
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void cpu_idle_poll_ctrl(bool enable);
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void arch_cpu_idle(void);
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void arch_cpu_idle_prepare(void);
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void arch_cpu_idle_enter(void);
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void arch_cpu_idle_exit(void);
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void arch_cpu_idle_dead(void);
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#endif /* _LINUX_CPU_H_ */
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