Re: general protection fault in put_pid

[Shakeel Butt <shakeelb@google.com>]

Hi Manfred,

On Sun, Dec 23, 2018 at 4:26 AM Manfred Spraul <manfred@colorfullife.com> wrote:
>
> Hello Dmitry,
>
> On 12/23/18 10:57 AM, Dmitry Vyukov wrote:
> >
> > I can reproduce this infinite memory consumption with the C program:
> > https://gist.githubusercontent.com/dvyukov/03ec54b3429ade16fa07bf8b2379aff3/raw/ae4f654e279810de2505e8fa41b73dc1d77778e6/gistfile1.txt
> >
> > But this is working as intended, right? It just creates infinite
> > number of large semaphore sets, which reasonably consumes infinite
> > amount of memory.
> > Except that it also violates the memcg bound and a process can have
> > effectively unlimited amount of such "drum memory" in semaphores.
>
> Yes, this is as intended:
>
> If you call semget(), then you can use memory, up to the limits in
> /proc/sys/kernel/sem.
>
> Memcg is not taken into account, an admin must set /proc/sys/kernel/sem.
>
> The default are "infinite amount of memory allowed", as this is the most
> sane default: We had a logic that tried to autotune (i.e.: a new
> namespace "inherits" a fraction of the parent namespaces memory limits),
> but this we more or less always wrong.
>
>

What's the disadvantage of setting the limits in /proc/sys/kernel/sem
high and let the task's memcg limits the number of semaphore a process
can create? Please note that the memory underlying shmget and msgget
is already accounted to memcg.

thanks,
Shakeel