From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7B2CC10F14 for ; Thu, 18 Apr 2019 18:23:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 990532064A for ; Thu, 18 Apr 2019 18:23:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="oCZtbd8w" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391689AbfDRSX0 (ORCPT ); Thu, 18 Apr 2019 14:23:26 -0400 Received: from mail-lf1-f67.google.com ([209.85.167.67]:41735 "EHLO mail-lf1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390479AbfDRSXY (ORCPT ); Thu, 18 Apr 2019 14:23:24 -0400 Received: by mail-lf1-f67.google.com with SMTP id t30so2328247lfd.8 for ; Thu, 18 Apr 2019 11:23:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=vC2agpd/yeTIjkC+tv6Q0HWjOpOqDC0mbvCHm0eBf4Y=; b=oCZtbd8wbvAsIKhSYoUJZQVeVFzI9LhVk5xw5A9aYv70oTCxPDa6CUjfhq+7Ko97Yw 5EBuW7fdsXGgA4duhAS6WpIwtYcQqgAk9n2TFWUG9A7Guuq6Wjh96ylkUMKabdIy43a6 8DlL8MSTSorKUkzsLvIHVbj17K+BG/zixxqBZhZOCrrzOYOTMKXRFKWY3xzHa5FX0FnE N6PJsM8S5vsd0FFiKD5cO1kUvacWe5/8AigkrFKVHcH1e2gmueli4YEM7P5c4pgH8ojH IXmHDGo8zSl1fe/FBh+n8Fy+4L+B3KeT+Qf9JY48R+SfJhpOvzSGNTMAIWBWK6bhaoHX t7lA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=vC2agpd/yeTIjkC+tv6Q0HWjOpOqDC0mbvCHm0eBf4Y=; b=VgH6eNXtgng+J9tSr3StlyQdvN+gqTpdO+/SwT/ceiQTcZpBWN460dBXeMfR+BII0t kfMw2LC0FcomSzG1BfeKFZ5on7DS+3UHfznMHDttBlRhdXr1L3hDGi7OwqW5C7uYljOB hUExL7cS6jZZUZoZQwLs3NCS9ccZFgWKkKyZ2QJMb+nhgze3JyHzZGgmGo3t3iEKX7ru oepYEtpYUPOHwU3/juMtM8e53zhlXny4HmKofFmmBomQYW5iAMTmfEFmH6hJloKJH4ka DezBadSQhKQpL37AsxpPrZH8Ard0Pdb1urxAR27xaZJ6pnaceaq+k6bRJejglFjmV40k mQhQ== X-Gm-Message-State: APjAAAXpI30dMc8EGMN/OZei4Lo8pJX02XxdrT7ZClliZyCIZPddnYzk WrrMcBgdsB9FhwlW3iGiuh0= X-Google-Smtp-Source: APXvYqyBjDf0Lb5iqi1H4sy3SWYyTORWzsqfNAlBTaJ1dtcbk6DdNBZyJ36/uSTPPp/2Mrwa4eR7NA== X-Received: by 2002:a19:c51a:: with SMTP id w26mr50367270lfe.59.1555611802703; Thu, 18 Apr 2019 11:23:22 -0700 (PDT) Received: from uranus.localdomain ([5.18.103.226]) by smtp.gmail.com with ESMTPSA id n28sm90162lfi.79.2019.04.18.11.23.21 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 18 Apr 2019 11:23:22 -0700 (PDT) Received: by uranus.localdomain (Postfix, from userid 1000) id B8D49460E21; Thu, 18 Apr 2019 21:23:21 +0300 (MSK) Date: Thu, 18 Apr 2019 21:23:21 +0300 From: Cyrill Gorcunov To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: mhocko@kernel.org, akpm@linux-foundation.org, arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mguzik@redhat.com, rppt@linux.ibm.com, vbabka@suse.cz, Laurent Dufour Subject: Re: [PATCH] prctl_set_mm: downgrade mmap_sem to read lock Message-ID: <20190418182321.GJ3040@uranus.lan> References: <20190417145548.GN5878@dhcp22.suse.cz> <20190418135039.19987-1-mkoutny@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190418135039.19987-1-mkoutny@suse.com> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 18, 2019 at 03:50:39PM +0200, Michal Koutný wrote: > I learnt, it's, alas, too late to drop the non PRCTL_SET_MM_MAP calls > [1], so at least downgrade the write acquisition of mmap_sem as in the > patch below (that should be stacked on the previous one or squashed). > > Cyrill, you mentioned lock changes in [1] but the link seems empty. Is > it supposed to be [2]? That could be an alternative to this patch after > some refreshments and clarifications. > > > [1] https://lore.kernel.org/lkml/20190417165632.GC3040@uranus.lan/ > [2] https://lore.kernel.org/lkml/20180507075606.870903028@gmail.com/ > > ======== > > Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect > arg_start|end and env_start|end in mm_struct") we use arg_lock for > boundaries modifications. Synchronize prctl_set_mm with this lock and > keep mmap_sem for reading only (analogous to what we already do in > prctl_set_mm_map). > > Also, save few cycles by looking up VMA only after performing basic > arguments validation. > > Signed-off-by: Michal Koutný Reviewed-by: Cyrill Gorcunov As Laurent mentioned we might move vma lookup before the spinlock, but this might be done on top of the series.