Re: general protection fault in oom_unkillable_task

[Tetsuo Handa]

On 2019/06/16 6:33, Tetsuo Handa wrote:
> On 2019/06/16 3:50, Shakeel Butt wrote:
>>> While dump_tasks() traverses only each thread group, mem_cgroup_scan_tasks()
>>> traverses each thread.
>>
>> I think mem_cgroup_scan_tasks() traversing threads is not intentional
>> and css_task_iter_start in it should use CSS_TASK_ITER_PROCS as the
>> oom killer only cares about the processes or more specifically
>> mm_struct (though two different thread groups can have same mm_struct
>> but that is fine).
> 
> We can't use CSS_TASK_ITER_PROCS from mem_cgroup_scan_tasks(). I've tried
> CSS_TASK_ITER_PROCS in an attempt to evaluate only one thread from each
> thread group, but I found that CSS_TASK_ITER_PROCS causes skipping whole
> threads in a thread group (and trivially allowing "Out of memory and no
> killable processes...\n" flood) if thread group leader has already exited.

Seems that CSS_TASK_ITER_PROCS from mem_cgroup_scan_tasks() is now working.
Maybe I was confused due to without commit 7775face207922ea ("memcg: killed
threads should not invoke memcg OOM killer"). We can scan one thread from
each thread group, and remove

	/* Prefer thread group leaders for display purposes */
	if (points == oc->chosen_points && thread_group_leader(oc->chosen))
		goto next;

check.