Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755113AbbEZNnN (ORCPT ); Tue, 26 May 2015 09:43:13 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41138 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753881AbbEZNnJ (ORCPT ); Tue, 26 May 2015 09:43:09 -0400 Date: Tue, 26 May 2015 14:33:20 +0200 From: Jan Kara To: Sergey Senozhatsky Cc: Daniel Phillips , Jan Kara , David Lang , Rik van Riel , linux-fsdevel@vger.kernel.org, tux3@tux3.org, linux-kernel@vger.kernel.org, OGAWA Hirofumi Subject: Re: [FYI] tux3: Core changes Message-ID: <20150526123320.GA22235@quack.suse.cz> References: <555D500B.4080901@phunq.net> <13c8bcdf-70e8-43d5-a05f-58ad839dbfd0@phunq.net> <5563F5C8.2040806@redhat.com> <67294911-1776-46b8-916d-0e5642a38725@phunq.net> <20150526070910.GA3307@quack.suse.cz> <20150526102239.GA466@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150526102239.GA466@swordfish> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1444 Lines: 33 On Tue 26-05-15 19:22:39, Sergey Senozhatsky wrote: > On (05/26/15 01:08), Daniel Phillips wrote: > > On Tuesday, May 26, 2015 12:09:10 AM PDT, Jan Kara wrote: > > > E.g. video drivers (or infiniband or direct IO for that matter) which > > >have buffers in user memory (may be mmapped file), grab references to pages > > >and hand out PFNs of those pages to the hardware to store data in them... > > >If you fork a page after the driver has handed PFNs to the hardware, you've > > >just lost all the writes hardware will do. > > > > Hi Jan, > > > > The page forked because somebody wrote to it with write(2) or mmap write at > > the same time as a video driver (or infiniband or direct IO) was doing io to > > it. Isn't the application trying hard to lose data in that case? It would > > not need page fork to lose data that way. > > > > Hello, > > is it possible to page-fork-bomb the system by some 'malicious' app? Well, you can have only two copies of each page - the one under writeout and the one in page cache. Furthermore you are limited by dirty throttling so I don't think this would allow any out-of-ordinary DOS vector... Honza -- Jan Kara SUSE Labs, CR -- 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/