[Devel] [RFC] Fix get_exec_env() races

[Kirill Tkhai]

On 15.10.2015 14:15, Pavel Emelyanov wrote:
> 
>> @@ -130,6 +131,34 @@ struct ve_struct {
>>  #endif
>>  };
>>  
>> +static inline struct ve_struct *get_exec_env(void)
>> +{
>> +	struct ve_struct *ve;
>> +
>> +	if (++current->ve_attach_lock_depth > 1)
>> +		return current->task_ve;
>> +
>> +	rcu_read_lock();
>> +again:
>> +	ve = current->task_ve;
>> +	read_lock(&ve->attach_lock);
>> +	if (unlikely(current->task_ve != ve)) {
>> +		read_unlock(&ve->attach_lock);
>> +		goto again;
> 
> Please, no. 3.10 kernel has task_work-s, ask the task you want to
> attach to ve to execute the work by moving itself into it and keep
> this small routine small and simple.

cgroup_attach_task() is called under cgroup_mutex and threadgroup_lock(),
so we can't wait attaching task till it complete the task work (it may
execute any code; to be locking cgroup_mutex, for example).

Should we give a possibility (an interface) for userspace to get it know,
the task's finished ve changing?

 
>> +	}
>> +	rcu_read_unlock();
>> +
>> +	return ve;
>> +}
>> +
>