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Date: Fri, 4 May 2018 16:54:35 +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>,
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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:
>
> > OK, what about exec() ? mm_init_memcg() initializes bprm->mm->memcg early in
> > bprm_mm_init(). What if the execing task migrates before exec_mmap() ?
>
> We need the the cgroup when the mm is initialized.  That way we have the
> cgroup information when initializing the mm.

Yes, we need to initialize new_mm->memcg but iiuc mostly for the error path,

> I don't know if a lock preventing changing the cgroup in exec or just
> a little bit of code in exec_mmap to ensure mm->memcg is properly set
> is the better approach.

I'd vote for the change in exec_mmap(). This way mm_init_memcg() can just
nullify mm->memcg.

> This does look like a very good place for an incremental patch to close
> that race.

Hmm. I think v2 makes more sense, but I won't argue.

Oleg.