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Subject: Re: general protection fault in put_pid
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
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From:   Manfred Spraul <manfred@colorfullife.com>
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Date:   Mon, 7 Jan 2019 19:04:55 +0100
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On 1/3/19 11:18 PM, Shakeel Butt wrote:
> 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.

Nothing, it it just a question of implementing it.

I'll try to look at it.

--

     Manfred