Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932547AbYBGAlU (ORCPT ); Wed, 6 Feb 2008 19:41:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933403AbYBGAQq (ORCPT ); Wed, 6 Feb 2008 19:16:46 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:49848 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763802AbYBGAQo (ORCPT ); Wed, 6 Feb 2008 19:16:44 -0500 Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting From: Matt Helsley To: Hugh Dickins Cc: Oleg Nesterov , Miklos Szeredi , Andrew Morton , Peter Zijlstra , William Lee Irwin III , Nick Piggin , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm In-Reply-To: References: <20080130142014.GA2164@tv-sign.ru> <1201712101.31222.22.camel@tucsk.pomaz.szeredi.hu> <20080130172646.GA2355@tv-sign.ru> <1201987065.9062.6.camel@localhost.localdomain> <20080203182135.GA5827@tv-sign.ru> Content-Type: text/plain Organization: IBM Linux Technology Center Date: Wed, 06 Feb 2008 16:16:38 -0800 Message-Id: <1202343398.9062.253.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.12.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2414 Lines: 57 On Wed, 2008-02-06 at 20:33 +0000, Hugh Dickins wrote: > On Sun, 3 Feb 2008, Oleg Nesterov wrote: > > > > So I have to try to find another bug ;) Suppose that ->load_binary() does > > a series of do_mmap(MAP_EXECUTABLE). It is possible that mmap_region() can > > merge 2 vmas. In that case we "leak" ->num_exe_file_vmas. Unless I missed > > something, mmap_region() should do removed_exe_file_vma() when vma_merge() > > succeds (near fput(file)). > > Or there's the complementary case of a VM_EXECUTABLE vma being > split in two, for example by an mprotect of a part of it. > > Sorry, Matt, I don't like your patch at all. It seems to add a fair > amount of ugliness and unmaintainablity, all for a peculiar MVFS case I thought that getting rid of the separate versions of proc_exe_link() improved maintainability. Do you have any specific details on what you think makes the code introduced by the patch unmaintainable? > (you've tried to argue other advantages, but not always convinced!). Yup -- looking at how the VM_EXECUTABLE flag affects the vma walk it's clear one of my arguments was wrong. So I can't blame you for being unconvinced by that. :) I still think it would help any stacking filesystems that can't use the solution adopted by unionfs. > And I found it quite hard to see where the crucial difference comes. > I guess it's that MVFS changes vma->vm_file in its ->mmap? Well, if Yup. > MVFS does that, maybe something else does that too, but precisely to > rely on the present behaviour of /proc/pid/exe - so in fixing for > MVFS, we'd be breaking that hypothetical other? I'm not completely certain that I understand your point. Are you suggesting that some hypothetical code would want to use this "quirk" of /proc/pid/exe for a legitimate purpose? Assuming that is your point, I thought my non-hypothetical java example clearly demonstrated that at least one non-hypothetical program doesn't expect the "quirk" and breaks because of it. Frankly, given /proc/pid/exe's output in the non-stacking case, I can't see how its output in the stacking case we're discussing could be considered anything but buggy. Cheers, -Matt Helsley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/