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Message-ID: <cc088b05-7bc9-778e-30b9-4b8720314001@colorfullife.com>
Date: Sun, 23 Dec 2018 13:25:49 +0100
From: Manfred Spraul <manfred@...orfullife.com>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: syzbot+1145ec2e23165570c3ac@...kaller.appspotmail.com,
Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
ktsanaktsidis@...desk.com, LKML <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
Stephen Rothwell <sfr@...b.auug.org.au>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
Matthew Wilcox <willy@...radead.org>,
Davidlohr Bueso <dave@...olabs.net>
Subject: Re: general protection fault in put_pid
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
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