Re: general protection fault in put_pid

[Manfred Spraul]

On 1/3/19 11:18 PM, Shakeel Butt wrote:
> Hi Manfred,
>
> On Sun, Dec 23, 2018 at 4:26 AM Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> 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.

Nothing, it it just a question of implementing it.

I'll try to look at it.

--

ÂÂÂ Manfred