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Subject: Re: general protection fault in put_pid
To:     Dmitry Vyukov <dvyukov@google.com>
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From:   Manfred Spraul <manfred@colorfullife.com>
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Date:   Sun, 23 Dec 2018 13:25:49 +0100
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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.


--

     Manfred