From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752365AbeC0G3m (ORCPT ); Tue, 27 Mar 2018 02:29:42 -0400 Received: from mx2.suse.de ([195.135.220.15]:44565 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750848AbeC0G3l (ORCPT ); Tue, 27 Mar 2018 02:29:41 -0400 Date: Tue, 27 Mar 2018 08:29:39 +0200 From: Michal Hocko To: Yang Shi Cc: adobriyan@gmail.com, willy@infradead.org, mguzik@redhat.com, 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: <20180327062939.GV5652@dhcp22.suse.cz> References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. I have just one more question. Now that you are touching this area, would you be willing to remove the following ugliness? > diff --git a/kernel/sys.c b/kernel/sys.c > index f2289de..17bddd2 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1959,7 +1959,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data > return error; > } > > - down_write(&mm->mmap_sem); > + down_read(&mm->mmap_sem); Why do we need to hold mmap_sem here and call find_vma, when only PR_SET_MM_ENV_END: is consuming it? I guess we can replace it wit the new lock and take the mmap_sem only for PR_SET_MM_ENV_END. Thanks! -- Michal Hocko SUSE Labs