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linux-next/include/linux/stop_machine.h
Heiko Carstens 9ea09af3bd stop_machine: introduce stop_machine_create/destroy.
Introduce stop_machine_create/destroy. With this interface subsystems
that need a non-failing stop_machine environment can create the
stop_machine machine threads before actually calling stop_machine.
When the threads aren't needed anymore they can be killed with
stop_machine_destroy again.

When stop_machine gets called and the threads aren't present they
will be created and destroyed automatically. This restores the old
behaviour of stop_machine.

This patch also converts cpu hotplug to the new interface since it
is special: cpu_down calls __stop_machine instead of stop_machine.
However the kstop threads will only be created when stop_machine
gets called.

Changing the code so that the threads would be created automatically
on __stop_machine is currently not possible: when __stop_machine gets
called we hold cpu_add_remove_lock, which is the same lock that
create_rt_workqueue would take. So the workqueue needs to be created
before the cpu hotplug code locks cpu_add_remove_lock.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2009-01-05 08:40:14 +10:30

73 lines
2.3 KiB
C

#ifndef _LINUX_STOP_MACHINE
#define _LINUX_STOP_MACHINE
/* "Bogolock": stop the entire machine, disable interrupts. This is a
very heavy lock, which is equivalent to grabbing every spinlock
(and more). So the "read" side to such a lock is anything which
disables preeempt. */
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <asm/system.h>
#if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
/**
* stop_machine: freeze the machine on all CPUs and run this function
* @fn: the function to run
* @data: the data ptr for the @fn()
* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
*
* Description: This causes a thread to be scheduled on every cpu,
* each of which disables interrupts. The result is that noone is
* holding a spinlock or inside any other preempt-disabled region when
* @fn() runs.
*
* This can be thought of as a very heavy write lock, equivalent to
* grabbing every spinlock in the kernel. */
int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
/**
* __stop_machine: freeze the machine on all CPUs and run this function
* @fn: the function to run
* @data: the data ptr for the @fn
* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
*
* Description: This is a special version of the above, which assumes cpus
* won't come or go while it's being called. Used by hotplug cpu.
*/
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus);
/**
* stop_machine_create: create all stop_machine threads
*
* Description: This causes all stop_machine threads to be created before
* stop_machine actually gets called. This can be used by subsystems that
* need a non failing stop_machine infrastructure.
*/
int stop_machine_create(void);
/**
* stop_machine_destroy: destroy all stop_machine threads
*
* Description: This causes all stop_machine threads which were created with
* stop_machine_create to be destroyed again.
*/
void stop_machine_destroy(void);
#else
static inline int stop_machine(int (*fn)(void *), void *data,
const struct cpumask *cpus)
{
int ret;
local_irq_disable();
ret = fn(data);
local_irq_enable();
return ret;
}
static inline int stop_machine_create(void) { return 0; }
static inline void stop_machine_destroy(void) { }
#endif /* CONFIG_SMP */
#endif /* _LINUX_STOP_MACHINE */