From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 3 Feb 2008 21:21:35 +0300 From: Oleg Nesterov Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting Message-ID: <20080203182135.GA5827@tv-sign.ru> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1201987065.9062.6.camel@localhost.localdomain> Sender: owner-linux-mm@kvack.org Return-Path: To: Matt Helsley Cc: Miklos Szeredi , Andrew Morton , Peter Zijlstra , William Lee Irwin III , Nick Piggin , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm List-ID: (remove stable@kernel.org from CC) On 02/02, Matt Helsley wrote: > > On Wed, 2008-01-30 at 20:26 +0300, Oleg Nesterov wrote: > > > > Offtopic. I noticed this problem while looking at this patch: > > > > http://marc.info/?l=linux-mm-commits&m=120141116911711 > > > > So this (the old vma could be removed before we create the new mapping) > > means that the patch above has another problem: if we are remapping the > > whole VM_EXECUTABLE vma, removed_exe_file_vma() can clear ->exe_file > > while it shouldn't (Matt Helsley cc'ed). > > > > Oleg. > > Looking at sys_remap_file_pages() it appears that the shared flag must > be set in order to remap. Executable mappings are always MAP_PRIVATE and > hence lack the shared flag so that any modifications to those areas > don't get written back to the executable. I don't think userspace can > change this flag Yes, userspace can't change it. But if MVFS changes ->vm_file it could also change vm_flags... But I think you are right anyway, we shouldn't care. 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)). Oleg. -- 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/ . Don't email: email@kvack.org