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b96d7e4f12
(cherry pick from commit 93ae4f978c)
The following method of CPU hotplug callback registration is not safe
due to the possibility of an ABBA deadlock involving the cpu_add_remove_lock
and the cpu_hotplug.lock.
get_online_cpus();
for_each_online_cpu(cpu)
init_cpu(cpu);
register_cpu_notifier(&foobar_cpu_notifier);
put_online_cpus();
The deadlock is shown below:
CPU 0 CPU 1
----- -----
Acquire cpu_hotplug.lock
[via get_online_cpus()]
CPU online/offline operation
takes cpu_add_remove_lock
[via cpu_maps_update_begin()]
Try to acquire
cpu_add_remove_lock
[via register_cpu_notifier()]
CPU online/offline operation
tries to acquire cpu_hotplug.lock
[via cpu_hotplug_begin()]
*** DEADLOCK! ***
The problem here is that callback registration takes the locks in one order
whereas the CPU hotplug operations take the same locks in the opposite order.
To avoid this issue and to provide a race-free method to register CPU hotplug
callbacks (along with initialization of already online CPUs), introduce new
variants of the callback registration APIs that simply register the callbacks
without holding the cpu_add_remove_lock during the registration. That way,
we can avoid the ABBA scenario. However, we will need to hold the
cpu_add_remove_lock throughout the entire critical section, to protect updates
to the callback/notifier chain.
This can be achieved by writing the callback registration code as follows:
cpu_maps_update_begin(); [ or cpu_notifier_register_begin(); see below ]
for_each_online_cpu(cpu)
init_cpu(cpu);
/* This doesn't take the cpu_add_remove_lock */
__register_cpu_notifier(&foobar_cpu_notifier);
cpu_maps_update_done(); [ or cpu_notifier_register_done(); see below ]
Note that we can't use get_online_cpus() here instead of cpu_maps_update_begin()
because the cpu_hotplug.lock is dropped during the invocation of CPU_POST_DEAD
notifiers, and hence get_online_cpus() cannot provide the necessary
synchronization to protect the callback/notifier chains against concurrent
reads and writes. On the other hand, since the cpu_add_remove_lock protects
the entire hotplug operation (including CPU_POST_DEAD), we can use
cpu_maps_update_begin/done() to guarantee proper synchronization.
Also, since cpu_maps_update_begin/done() is like a super-set of
get/put_online_cpus(), the former naturally protects the critical sections
from concurrent hotplug operations.
Since the names cpu_maps_update_begin/done() don't make much sense in CPU
hotplug callback registration scenarios, we'll introduce new APIs named
cpu_notifier_register_begin/done() and map them to cpu_maps_update_begin/done().
In summary, introduce the lockless variants of un/register_cpu_notifier() and
also export the cpu_notifier_register_begin/done() APIs for use by modules.
This way, we provide a race-free way to register hotplug callbacks as well as
perform initialization for the CPUs that are already online.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Bug: 24810447
Change-Id: I5f85fcb5cfaa5f5f04a29eefc361851e9c345a99
276 lines
8.4 KiB
C
276 lines
8.4 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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* and system devices are handled in drivers/base/sys.c.
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*
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* CPUs are exported via sysfs in the class/cpu/devices/
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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 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 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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extern int sched_create_sysfs_power_savings_entries(struct device *dev);
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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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#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
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extern int arch_cpu_uevent(struct device *dev, struct kobj_uevent_env *env);
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extern ssize_t arch_print_cpu_modalias(struct device *dev,
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struct device_attribute *attr,
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char *bufptr);
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#endif
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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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CPU_PRI_SMPBOOT = 9,
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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 __cpuinitdata = \
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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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void smpboot_thread_init(void);
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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 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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int cpu_down(unsigned int cpu);
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#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
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extern void cpu_hotplug_driver_lock(void);
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extern void cpu_hotplug_driver_unlock(void);
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#else
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static inline void cpu_hotplug_driver_lock(void)
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{
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}
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static inline void cpu_hotplug_driver_unlock(void)
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{
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}
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#endif
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#else /* CONFIG_HOTPLUG_CPU */
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#define get_online_cpus() do { } while (0)
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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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#define IDLE_START 1
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#define IDLE_END 2
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void idle_notifier_register(struct notifier_block *n);
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void idle_notifier_unregister(struct notifier_block *n);
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void idle_notifier_call_chain(unsigned long val);
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#endif /* _LINUX_CPU_H_ */
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