Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938853AbcJSOOq (ORCPT ); Wed, 19 Oct 2016 10:14:46 -0400 Received: from mail-lf0-f66.google.com ([209.85.215.66]:34786 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938790AbcJSOOj (ORCPT ); Wed, 19 Oct 2016 10:14:39 -0400 Date: Wed, 19 Oct 2016 10:13:52 +0200 From: Michal Hocko To: Jan Kara Cc: Lorenzo Stoakes , linux-mm@kvack.org, Linus Torvalds , Hugh Dickins , Dave Hansen , Rik van Riel , Mel Gorman , Andrew Morton , adi-buildroot-devel@lists.sourceforge.net, ceph-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, kvm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cris-kernel@axis.com, linux-fbdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-mips@linux-mips.org, linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-scsi@vger.kernel.org, linux-security-module@vger.kernel.org, linux-sh@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 08/10] mm: replace __access_remote_vm() write parameter with gup_flags Message-ID: <20161019081352.GB7562@dhcp22.suse.cz> References: <20161013002020.3062-1-lstoakes@gmail.com> <20161013002020.3062-9-lstoakes@gmail.com> <20161019075903.GP29967@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161019075903.GP29967@quack2.suse.cz> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1154 Lines: 25 On Wed 19-10-16 09:59:03, Jan Kara wrote: > On Thu 13-10-16 01:20:18, Lorenzo Stoakes wrote: > > This patch removes the write parameter from __access_remote_vm() and replaces it > > with a gup_flags parameter as use of this function previously _implied_ > > FOLL_FORCE, whereas after this patch callers explicitly pass this flag. > > > > We make this explicit as use of FOLL_FORCE can result in surprising behaviour > > (and hence bugs) within the mm subsystem. > > > > Signed-off-by: Lorenzo Stoakes > > So I'm not convinced this (and the following two patches) is actually > helping much. By grepping for FOLL_FORCE we will easily see that any caller > of access_remote_vm() gets that semantics and can thus continue search I am really wondering. Is there anything inherent that would require FOLL_FORCE for access_remote_vm? I mean FOLL_FORCE is a really non-trivial thing. It doesn't obey vma permissions so we should really minimize its usage. Do all of those users really need FOLL_FORCE? Anyway I would rather see the flag explicit and used at more places than hidden behind a helper function. -- Michal Hocko SUSE Labs