From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S934231AbdKQHbH (ORCPT <rfc822;w@1wt.eu>);
        Fri, 17 Nov 2017 02:31:07 -0500
Received: from mx1.redhat.com ([209.132.183.28]:39284 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S933991AbdKQHa5 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 17 Nov 2017 02:30:57 -0500
Subject: Re: [RFC PATCH 1/2] mm: introduce MAP_FIXED_SAFE
To: Michal Hocko <mhocko@kernel.org>, linux-api@vger.kernel.org
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org,
        Michal Hocko <mhocko@suse.com>
References: <20171116101900.13621-1-mhocko@kernel.org>
 <20171116101900.13621-2-mhocko@kernel.org>
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <a3f7aed9-0df2-2fd6-cebb-ba569ad66781@redhat.com>
Date: Fri, 17 Nov 2017 08:30:48 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
MIME-Version: 1.0
In-Reply-To: <20171116101900.13621-2-mhocko@kernel.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 17 Nov 2017 07:30:57 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 11/16/2017 11:18 AM, Michal Hocko wrote:
> +	if (flags & MAP_FIXED_SAFE) {
> +		struct vm_area_struct *vma = find_vma(mm, addr);
> +
> +		if (vma && vma->vm_start <= addr)
> +			return -ENOMEM;
> +	}

Could you pick a different error code which cannot also be caused by a 
an unrelated, possibly temporary condition?  Maybe EBUSY or EEXIST?

This would definitely help with application-based randomization of 
mappings, and there, actual ENOMEM and this error would have to be 
handled differently.

Thanks,
Florian