linux-kernel - Re: [PATCH 0/2] mm->owner to mm->memcg fixes

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Message-ID: <87vab3en5v.fsf@xmission.com>
Date:   Thu, 31 May 2018 12:43:24 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, peterz@...radead.org,
        viro@...iv.linux.org.uk, mingo@...nel.org,
        paulmck@...ux.vnet.ibm.com, keescook@...omium.org, riel@...hat.com,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com,
        marcos.souza.org@...il.com, hoeun.ryu@...il.com,
        pasha.tatashin@...cle.com, gs051095@...il.com, dhowells@...hat.com,
        rppt@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Balbir Singh <balbir@...ux.vnet.ibm.com>,
        Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 0/2] mm->owner to mm->memcg fixes

Michal Hocko <mhocko@...nel.org> writes:

> On Wed 23-05-18 14:46:43, Eric W. Biederman wrote:
> [...]
>> As two processes sharing an mm is useless and highly unlikely there is
>> no need to handle this case well, it just needs to be handled well
>> enough to prevent an indefinite loop.  So when css_tryget_online fails
>> just treat the mm as belong to the root memory cgroup.
>
> Does that mean that a malicious user can construct such a task and
> runaway from its limits?

Unfortunately if the memory cgroup is delegated than yes that can
happen.  So removing the loop in get_mem_cgroup_from_mm won't work.

Eric