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 <[email protected]>
---
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);
--
1.7.0.4
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