From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752028AbeCZVKR (ORCPT ); Mon, 26 Mar 2018 17:10:17 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:49908 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107AbeCZVKQ (ORCPT ); Mon, 26 Mar 2018 17:10:16 -0400 Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct To: Cyrill Gorcunov , Matthew Wilcox Cc: Yang Shi , adobriyan@gmail.com, mhocko@kernel.org, mguzik@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> <20180326183725.GB27373@bombadil.infradead.org> <20180326192132.GE2236@uranus> From: Tetsuo Handa Message-ID: <0bfa8943-a2fe-b0ab-99a2-347094a2bcec@i-love.sakura.ne.jp> Date: Tue, 27 Mar 2018 06:10:09 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180326192132.GE2236@uranus> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/03/27 4:21, Cyrill Gorcunov wrote: > That said I think using read-lock here would be a bug. If I understand correctly, the caller can't set both fields atomically, for prctl() does not receive both fields at one call. prctl(PR_SET_MM, PR_SET_MM_ARG_START xor PR_SET_MM_ARG_END xor PR_SET_MM_ENV_START xor PR_SET_MM_ENV_END, new value, 0, 0); Then, I wonder whether reading arg_start|end and env_start|end atomically makes sense. Just retry reading if arg_start > env_end or env_start > env_end is fine?