On 12/11/2012 07:47 PM, Chuansheng Liu wrote:
>
> When one CPU is going down, and smpboot_register_percpu_thread is called,
> there is the race issue below:
> T1(CPUA): T2(CPUB):
> _cpu_down()
> smpboot_register_percpu_thread()
> smpboot_park_threads() ...
> __stop_machine()
> __smpboot_create_thread(CPU_Dying)
> [Currently, the being down
> CPU is online yet]
> take_cpu_down()
> smpboot_unpark_thread(CPU_Dying)
> __cpu_disable() ....
> native_cpu_disable()
> .... Here the new kthread will
> get running
> based on the CPU_Dying
> set_cpu_online(cpu, false)
> ....
> cpu_notify(CPU_DYING)
>
> After notified the CPU_DYING, the new created kthead for dying CPU will
> be migrated to another CPU in migration_call().
>
> Here we need use get_online_cpus()/put_online_cpus() when calling
> function smpboot_register_percpu_thread().
>
> Signed-off-by: liu chuansheng <chuansheng....@intel.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
Regards,
Srivatsa S. Bhat
> ---
> kernel/smpboot.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/smpboot.c b/kernel/smpboot.c
> index d6c5fc0..3fe708a 100644
> --- a/kernel/smpboot.c
> +++ b/kernel/smpboot.c
> @@ -266,6 +266,7 @@ int smpboot_register_percpu_thread(struct
> smp_hotplug_thread *plug_thread)
> unsigned int cpu;
> int ret = 0;
>
> + get_online_cpus();
> mutex_lock(&smpboot_threads_lock);
> for_each_online_cpu(cpu) {
> ret = __smpboot_create_thread(plug_thread, cpu);
> @@ -278,6 +279,7 @@ int smpboot_register_percpu_thread(struct
> smp_hotplug_thread *plug_thread)
> list_add(&plug_thread->list, &hotplug_threads);
> out:
> mutex_unlock(&smpboot_threads_lock);
> + put_online_cpus();
> return ret;
> }
> EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
>
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