From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id C3E926B0003 for ; Tue, 27 Mar 2018 02:29:44 -0400 (EDT) Received: by mail-pl0-f70.google.com with SMTP id f19-v6so4527344plr.23 for ; Mon, 26 Mar 2018 23:29:44 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d2-v6si624719plh.44.2018.03.26.23.29.43 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 26 Mar 2018 23:29:43 -0700 (PDT) Date: Tue, 27 Mar 2018 08:29:39 +0200 From: Michal Hocko 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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