Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable
From: Eric W. Biederman
Date: Mon Jun 04 2018 - 10:32:56 EST
Michal Hocko <mhocko@xxxxxxxxxx> writes:
> On Fri 01-06-18 10:25:59, Eric W. Biederman wrote:
>> Michal Hocko <mhocko@xxxxxxxxxx> writes:
>>
>> > On Fri 01-06-18 09:32:42, Eric W. Biederman wrote:
>> >> Michal Hocko <mhocko@xxxxxxxxxx> writes:
>> > [...]
>> >> > Group leader exiting early without tearing down the whole thread
>> >> > group should be quite rare as well. No question that somebody might do
>> >> > that on purpose though...
>> >>
>> >> The group leader exiting early is a completely legitimate and reasonable
>> >> thing to do, even if it is rare.
>> >
>> > I am not saying it isn't legitimate. But the most common case is the
>> > main thread waiting for its threads or calling exit which would tear the
>> > whole group down. Is there any easy way to achieve this other than tkill
>> > to group leader? Calling exit(3) from the leader performs group exit
>> > IIRC.
>>
>> pthread_exit from the group leader.
>
> Right, forgot to mention this one but this would be quite exotic,
> right?
Not exotic. It is easy to do and well defined.
It would be easy to do if you are running a thread pool and closing
unnecessary threads. Or frankly anything where the application is not
assigning a special role to the initial thread.
It does seem rare enough that no one has noticed how attrocious
mm_update_next_owner is until now.
My key point is that it is easy to trigger which makes the current
mm_update_next_owner a fundamentally flawed design, and something that
needs to be fixed.
Eric