On 2018/10/08 17:38, Yong-Taek Lee wrote:
>>
>> On 2018/10/08 15:14, Yong-Taek Lee wrote:
>>>> On 2018/10/08 10:19, Yong-Taek Lee wrote:
>>>>> @@ -1056,6 +1056,7 @@ static int __set_oom_adj(struct file *file, int
>>>>> oom_adj, bool legacy)
>>>>> struct mm_struct *mm = NULL;
>>>>> struct task_struct *task;
>>>>> int err = 0;
>>>>> + int mm_users = 0;
>>>>>
>>>>> task = get_proc_task(file_inode(file));
>>>>> if (!task)
>>>>> @@ -1092,7 +1093,8 @@ static int __set_oom_adj(struct file *file, int
>>>>> oom_adj, bool legacy)
>>>>> struct task_struct *p = find_lock_task_mm(task);
>>>>>
>>>>> if (p) {
>>>>> - if (atomic_read(&p->mm->mm_users) > 1) {
>>>>> + mm_users = atomic_read(&p->mm->mm_users);
>>>>> + if ((mm_users > 1) && (mm_users !=
>>>>> get_nr_threads(p))) {
>>>>
>>>> How can this work (even before this patch)? When clone(CLONE_VM without
>>>> CLONE_THREAD/CLONE_SIGHAND)
>>>> is requested, copy_process() calls copy_signal() in order to copy
>>>> sig->oom_score_adj and
>>>> sig->oom_score_adj_min before calling copy_mm() in order to increment
>>>> mm->mm_users, doesn't it?
>>>> Then, we will get two different "struct signal_struct" with different
>>>> oom_score_adj/oom_score_adj_min
>>>> but one "struct mm_struct" shared by two thread groups.
>>>>
>>>
>>> Are you talking about race between __set_oom_adj and copy_process?
>>> If so, i agree with your opinion. It can not set oom_score_adj properly for
>>> copied process if __set_oom_adj
>>> check mm_users before copy_process calls copy_mm after copy_signal. Please
>>> correct me if i misunderstood anything.
>>
>> You understand it correctly.
>>
>> Reversing copy_signal() and copy_mm() is not sufficient either. We need to
>> use a read/write lock
>> (read lock for copy_process() and write lock for __set_oom_adj()) in order
>> to make sure that
>> the thread created by clone() becomes reachable from for_each_process() path
>> in __set_oom_adj().
>>
>
> Thank you for your suggestion. But i think it would be better to seperate to
> 2 issues. How about think these
> issues separately because there are no dependency between race issue and my
> patch. As i already explained,
> for_each_process path is meaningless if there is only one thread group with
> many threads(mm_users > 1 but
> no other thread group sharing same mm). Do you have any other idea to avoid
> meaningless loop ?
Yes. I suggest reverting commit 44a70adec910d692 ("mm, oom_adj: make sure
processes
sharing mm have same view of oom_score_adj") and commit 97fd49c2355ffded ("mm,
oom:
kill all tasks sharing the mm").
>
>>>
>>>>> mm = p->mm;
>>>>> atomic_inc(&mm->mm_count);
>>>>> }
>>>
>>
>
