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Date:   Fri, 4 May 2018 18:22:09 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, akpm@linux-foundation.org,
        peterz@infradead.org, viro@zeniv.linux.org.uk, mingo@kernel.org,
        paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com,
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        pasha.tatashin@oracle.com, gs051095@gmail.com, dhowells@redhat.com,
        rppt@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        Balbir Singh <balbir@linux.vnet.ibm.com>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] memcg: Replace mm->owner with mm->memcg
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On 05/04, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> > I'd vote for the change in exec_mmap(). This way mm_init_memcg() can just
> > nullify mm->memcg.
>
> There is at least one common path where we need the memory control group
> properly initialized so memory allocations don't escape the memory
> control group.
>
> do_execveat_common
>    copy_strings
>       get_arg_page
>          get_user_pages_remote
>             __get_user_pages_locked
>                __get_user_pages
>                   faultin_page
>                      handle_mm_fault
>                         count_memcg_event_mm
>                         __handle_mm_fault
>                           handle_pte_fault
>                              do_anonymous_page
>                                 mem_cgroup_try_charge
>
> I am surprised I can't easily find more.   Apparently in load_elf_binary
> we call elf_mmap after set_new_exec and install_exec_creds, making
> a gracefull recovery from elf_mmap failures impossible.
>
> In any case we most definitely need the memory control group properly
> setup before exec_mmap.

Confused ...

new_mm->memcg has no effect until exec_mmap(), why it can't be NULL ?

and why do you think mem_cgroup_try_charge() can use the wrong memcg
in this case?

Oleg.