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stop_machine: introduce stop_machine_create/destroy.

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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>
This commit is contained in:
Heiko Carstens 2008-12-22 12:36:30 +01:00 • committed by Rusty Russell
parent c298be7449
commit 9ea09af3bd
3 changed files with 72 additions and 11 deletions
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6
kernel/cpu.c
View file

@ -269,8 +269,11 @@ out_release:
int __ref cpu_down(unsigned int cpu)
{
int err = 0;
int err;
err = stop_machine_create();
if (err)
return err;
cpu_maps_update_begin();
if (cpu_hotplug_disabled) {
@ -297,6 +300,7 @@ int __ref cpu_down(unsigned int cpu)
out:
cpu_maps_update_done();
stop_machine_destroy();
return err;
}
EXPORT_SYMBOL(cpu_down);