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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 AA8EAC43441 for ; Tue, 9 Oct 2018 23:20:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 779AB214C4 for ; Tue, 9 Oct 2018 23:20:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 779AB214C4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726886AbeJJGjc (ORCPT ); Wed, 10 Oct 2018 02:39:32 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:47250 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725748AbeJJGjc (ORCPT ); Wed, 10 Oct 2018 02:39:32 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 96BCFAC9; Tue, 9 Oct 2018 23:20:13 +0000 (UTC) Date: Tue, 9 Oct 2018 16:20:12 -0700 From: Andrew Morton To: Jan Kara Cc: john.hubbard@gmail.com, Matthew Wilcox , Michal Hocko , Christopher Lameter , Jason Gunthorpe , Dan Williams , linux-mm@kvack.org, LKML , linux-rdma , linux-fsdevel@vger.kernel.org, John Hubbard , Al Viro , Jerome Glisse , Christoph Hellwig , Ralph Campbell Subject: Re: [PATCH v4 2/3] mm: introduce put_user_page*(), placeholder versions Message-Id: <20181009162012.c662ef0b041993557e150035@linux-foundation.org> In-Reply-To: <20181009083025.GE11150@quack2.suse.cz> References: <20181008211623.30796-1-jhubbard@nvidia.com> <20181008211623.30796-3-jhubbard@nvidia.com> <20181008171442.d3b3a1ea07d56c26d813a11e@linux-foundation.org> <20181009083025.GE11150@quack2.suse.cz> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 9 Oct 2018 10:30:25 +0200 Jan Kara wrote: > > Also, maintainability. What happens if someone now uses put_page() by > > mistake? Kernel fails in some mysterious fashion? How can we prevent > > this from occurring as code evolves? Is there a cheap way of detecting > > this bug at runtime? > > The same will happen as with any other reference counting bug - the special > user reference will leak. It will be pretty hard to debug I agree. I was > thinking about whether we could provide some type safety against such bugs > such as get_user_pages() not returning struct page pointers but rather some > other special type but it would result in a big amount of additional churn > as we'd have to propagate this different type e.g. through the IO path so > that IO completion routines could properly call put_user_pages(). So I'm > not sure it's really worth it. I'm not really understanding. Patch 3/3 changes just one infiniband driver to use put_user_page(). But the changelogs here imply (to me) that every user of get_user_pages() needs to be converted to s/put_page/put_user_page/. Methinks a bit more explanation is needed in these changelogs?