From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752315AbeC0Oba (ORCPT ); Tue, 27 Mar 2018 10:31:30 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:53676 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751122AbeC0Ob3 (ORCPT ); Tue, 27 Mar 2018 10:31:29 -0400 Date: Tue, 27 Mar 2018 16:31:23 +0200 From: Mateusz Guzik To: Michal Hocko Cc: Yang Shi , adobriyan@gmail.com, willy@infradead.org, gorcunov@openvz.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Message-ID: <20180327143122.rjgxjoj2adzvfck2@mguzik> References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> <20180327062939.GV5652@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180327062939.GV5652@dhcp22.suse.cz> User-Agent: Mutt/1.6.0.1 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 27, 2018 at 08:29:39AM +0200, Michal Hocko wrote: > On Tue 27-03-18 02:20:39, Yang Shi wrote: > [...] > The patch looks reasonable to me. Maybe it would be better to be more > explicit about the purpose of the patch. As others noticed, this alone > wouldn't solve the mmap_sem contention issues. I _think_ that if you > were more explicit about the mmap_sem abuse it would trigger less > questions. > >>From what I gather even with other fixes the kernel will still end up grabbing the semaphore. In this case I don't see what's the upside of adding the spinlock for args. The downside is growth of mm_struct. i.e. the code can be refactored to just hold the lock and relock only if necessary (unable to copy to user without faulting) -- Mateusz Guzik