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Date:   Wed, 9 May 2018 16:51:52 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, peterz@infradead.org,
        viro@zeniv.linux.org.uk, mingo@kernel.org,
        paulmck@linux.vnet.ibm.com, keescook@chromium.org, riel@redhat.com,
        tglx@linutronix.de, kirill.shutemov@linux.intel.com,
        marcos.souza.org@gmail.com, hoeun.ryu@gmail.com,
        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 2/2] memcg: Close the race between migration and
 installing bprm->mm as mm
Message-ID: <20180509145151.GB25742@redhat.com>
References: <20180503133338.GA23401@redhat.com>
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 <20180504162209.GB26573@redhat.com>
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On 05/04, Eric W. Biederman wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1044,6 +1044,8 @@ static int exec_mmap(struct mm_struct *mm)
>  		return 0;
>  	}
>  	mmdrop(active_mm);
> +	/* The tsk may have migrated before the new mm was attached */
> +	mm_sync_memcg_from_task(tsk);
>  	return 0;
>  }

call_usermodehelper(). perhaps it makes sense to change flush_old_exec()
to clear PF_KTHREAD/etc before exec_mmap().

Oleg.