Re: [PATCH] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug

[Zhang Qiao]

在 2022/1/21 20:43, Waiman Long 写道:
> On 1/21/22 05:12, Zhang Qiao wrote:
>> As previously discussed(https://lkml.org/lkml/2022/1/20/51),
>> cpuset_attach() is affected with similar cpu hotplug race,
>> as follow scenario:
>>
>>       cpuset_attach()                cpu hotplug
>>      ---------------------------            ----------------------
>>      down_write(cpuset_rwsem)
>>      guarantee_online_cpus() // (load cpus_attach)
>>                     sched_cpu_deactivate
>>                       set_cpu_active()
>>                       // will change cpu_active_mask
>>      set_cpus_allowed_ptr(cpus_attach)
>>        __set_cpus_allowed_ptr_locked()
>>         // (if the intersection of cpus_attach and
>>           cpu_active_mask is empty, will return -EINVAL)
>>      up_write(cpuset_rwsem)
>>
>> To avoid races such as described above, protect cpuset_attach() call
>> with cpu_hotplug_lock.
>>
>> Fixes: be367d099270 ("cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time")
>> Reported-by: Zhao Gongyi <zhaogongyi@xxxxxxxxxx>
>> Signed-off-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
>> ---
>>   kernel/cgroup/cpuset.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index dc653ab26e50..0af5725cc1df 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -2252,6 +2252,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>>       cgroup_taskset_first(tset, &css);
>>       cs = css_cs(css);
>>
>> +    cpus_read_lock();
>>       percpu_down_write(&cpuset_rwsem);
>>
>>       guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
>> @@ -2305,6 +2306,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
>>           wake_up(&cpuset_attach_wq);
>>
>>       percpu_up_write(&cpuset_rwsem);
>> +    cpus_read_unlock();
>>   }
>>
>>   /* The various types of files and directories in a cpuset file system */
>> -- 
>> 2.18.0
> 
> The locking sequence looks right.
> 
> Acked-by: Waiman Long <longman@xxxxxxxxxx>
> 
Thanks for your review!

Regards,
Qiao
.

> .