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SubjectRe: [PATCH] mm: oom: Fix race condition between oom_badness and do_exit of task
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On 3/8/2018 2:26 AM, David Rientjes wrote:

> On Wed, 7 Mar 2018, Gaurav Kohli wrote:
>
>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
>> index 6fd9773..5f4cc4b 100644
>> --- a/mm/oom_kill.c
>> +++ b/mm/oom_kill.c
>> @@ -114,9 +114,11 @@ struct task_struct *find_lock_task_mm(struct task_struct *p)
>>
>> for_each_thread(p, t) {
>> task_lock(t);
>> + get_task_struct(t);
>> if (likely(t->mm))
>> goto found;
>> task_unlock(t);
>> + put_task_struct(t);
>> }
>> t = NULL;
>> found:
> We hold rcu_read_lock() here, so perhaps only do get_task_struct() before
> doing rcu_read_unlock() and we have a non-NULL t?

Here rcu_read_lock will not help, as our task may change due to below algo:

for_each_thread(p, t) {
task_lock(t);
+ get_task_struct(t);
if (likely(t->mm))
goto found;
task_unlock(t);
+ put_task_struct(t)


So only we can increase usage counter here only at the current task.

I have seen you new patch, that seems valid to me and it will resolve our issue.
Thanks for support.

Regards

Gaurav

>
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

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