From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx136.postini.com [74.125.245.136]) by kanga.kvack.org (Postfix) with SMTP id 2C5816B004A for ; Thu, 5 Apr 2012 16:35:37 -0400 (EDT) Received: from /spool/local by e1.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 5 Apr 2012 16:35:35 -0400 Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id 277C26E8057 for ; Thu, 5 Apr 2012 16:29:07 -0400 (EDT) Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q35KT6Gj3604630 for ; Thu, 5 Apr 2012 16:29:06 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q361xwMw015108 for ; Thu, 5 Apr 2012 21:59:59 -0400 Date: Thu, 5 Apr 2012 13:29:04 -0700 From: Matt Helsley Subject: Re: [PATCH 6/7] mm: kill vma flag VM_EXECUTABLE Message-ID: <20120405202904.GB7761@count0.beaverton.ibm.com> References: <20120331091049.19373.28994.stgit@zurg> <20120331092929.19920.54540.stgit@zurg> <20120331201324.GA17565@redhat.com> <20120402230423.GB32299@count0.beaverton.ibm.com> <4F7A863C.5020407@openvz.org> <20120403181631.GD32299@count0.beaverton.ibm.com> <20120403193204.GE3370@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120403193204.GE3370@moon> Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: Matt Helsley , Konstantin Khlebnikov , Oleg Nesterov , "linux-mm@kvack.org" , Andrew Morton , "linux-kernel@vger.kernel.org" , Eric Paris , "linux-security-module@vger.kernel.org" , "oprofile-list@lists.sf.net" , Linus Torvalds , Al Viro On Tue, Apr 03, 2012 at 11:32:04PM +0400, Cyrill Gorcunov wrote: > On Tue, Apr 03, 2012 at 11:16:31AM -0700, Matt Helsley wrote: > > On Tue, Apr 03, 2012 at 09:10:20AM +0400, Konstantin Khlebnikov wrote: > > > Matt Helsley wrote: > > > >On Sat, Mar 31, 2012 at 10:13:24PM +0200, Oleg Nesterov wrote: > > > >>On 03/31, Konstantin Khlebnikov wrote: > > > >>> > > > >>>comment from v2.6.25-6245-g925d1c4 ("procfs task exe symlink"), > > > >>>where all this stuff was introduced: > > > >>> > > > >>>>... > > > >>>>This avoids pinning the mounted filesystem. > > > >>> > > > >>>So, this logic is hooked into every file mmap/unmmap and vma split/merge just to > > > >>>fix some hypothetical pinning fs from umounting by mm which already unmapped all > > > >>>its executable files, but still alive. Does anyone know any real world example? > > > >> > > > >>This is the question to Matt. > > > > > > > >This is where I got the scenario: > > > > > > > >https://lkml.org/lkml/2007/7/12/398 > > > > > > Cyrill Gogcunov's patch "c/r: prctl: add ability to set new mm_struct::exe_file" > > > gives userspace ability to unpin vfsmount explicitly. > > > > Doesn't that break the semantics of the kernel ABI? > > Which one? exe_file can be changed iif there is no MAP_EXECUTABLE left. > Still, once assigned (via this prctl) the mm_struct::exe_file can't be changed > again, until program exit. The prctl() interface itself is fine as it stands now. As far as I can tell Konstantin is proposing that we remove the unusual counter that tracks the number of mappings of the exe_file and require userspace use the prctl() to drop the last reference. That's what I think will break the ABI because after that change you *must* change userspace code to use the prctl(). It's an ABI change because the same sequence of system calls with the same input bits produces different behavior. Cheers, -Matt -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org