From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:35710 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728404AbfHBMlv (ORCPT ); Fri, 2 Aug 2019 08:41:51 -0400 Date: Fri, 2 Aug 2019 14:41:46 +0200 From: Jan Kara Subject: Re: [PATCH 00/34] put_user_pages(): miscellaneous call sites Message-ID: <20190802124146.GL25064@quack2.suse.cz> References: <20190802022005.5117-1-jhubbard@nvidia.com> <20190802091244.GD6461@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190802091244.GD6461@dhcp22.suse.cz> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Michal Hocko Cc: john.hubbard@gmail.com, Andrew Morton , Christoph Hellwig , Dan Williams , Dave Chinner , Dave Hansen , Ira Weiny , Jan Kara , Jason Gunthorpe , =?iso-8859-1?B?Suly9G1l?= Glisse , LKML , amd-gfx@lists.freedesktop.org, ceph-devel@vger.kernel.org, devel@driverdev.osuosl.org, devel@lists.orangefs.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-block@vger.kernel.org, linux-crypto@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-media@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, linux-xfs@vger.kernel.org, netdev@vger.kernel.org, rds-devel@oss.oracle.com, sparclinux@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org, John Hubbard On Fri 02-08-19 11:12:44, Michal Hocko wrote: > On Thu 01-08-19 19:19:31, john.hubbard@gmail.com wrote: > [...] > > 2) Convert all of the call sites for get_user_pages*(), to > > invoke put_user_page*(), instead of put_page(). This involves dozens of > > call sites, and will take some time. > > How do we make sure this is the case and it will remain the case in the > future? There must be some automagic to enforce/check that. It is simply > not manageable to do it every now and then because then 3) will simply > be never safe. > > Have you considered coccinele or some other scripted way to do the > transition? I have no idea how to deal with future changes that would > break the balance though. Yeah, that's why I've been suggesting at LSF/MM that we may need to create a gup wrapper - say vaddr_pin_pages() - and track which sites dropping references got converted by using this wrapper instead of gup. The counterpart would then be more logically named as unpin_page() or whatever instead of put_user_page(). Sure this is not completely foolproof (you can create new callsite using vaddr_pin_pages() and then just drop refs using put_page()) but I suppose it would be a high enough barrier for missed conversions... Thoughts? Honza -- Jan Kara SUSE Labs, CR