linux-kernel - Re: [PATCH] memcg: Replace mm->owner with mm->memcg

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Message-ID: <20180503133338.GA23401@redhat.com>
Date:   Thu, 3 May 2018 15:33:39 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, akpm@...ux-foundation.org,
        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>
Subject: Re: [PATCH] memcg: Replace mm->owner with mm->memcg

On 05/02, Eric W. Biederman wrote:
>
> +static void mem_cgroup_fork(struct task_struct *tsk)
> +{
> +	struct cgroup_subsys_state *css;
> +
> +	rcu_read_lock();
> +	css = task_css(tsk, memory_cgrp_id);
> +	if (css && css_tryget(css))
> +		task_update_memcg(tsk, mem_cgroup_from_css(css));
> +	rcu_read_unlock();
> +}

Why do we need it?

The child's mm->memcg was already initialized by mm_init_memcg() and we can't
race with migrate until cgroup_threadgroup_change_end() ?

Oleg.