From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753826AbeDWA1p (ORCPT ); Sun, 22 Apr 2018 20:27:45 -0400 Received: from mx2.suse.de ([195.135.220.15]:45430 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753791AbeDWA1m (ORCPT ); Sun, 22 Apr 2018 20:27:42 -0400 Date: Sun, 22 Apr 2018 18:27:38 -0600 From: Michal Hocko To: vcaputo@pengaru.com Cc: Pavel Machek , Ferry Toth , linux-kernel@vger.kernel.org Subject: Re: DOS by unprivileged user Message-ID: <20180423002738.GF16083@dhcp22.suse.cz> References: <9023506.UBh6vynRGa@delfion> <20180422101654.GA26243@amd> <20180422174300.srzhf3veqxfigqhg@shells.gnugeneration.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180422174300.srzhf3veqxfigqhg@shells.gnugeneration.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 22-04-18 10:43:00, vcaputo@pengaru.com wrote: > On Sun, Apr 22, 2018 at 12:16:54PM +0200, Pavel Machek wrote: > > On Thu 2018-04-19 21:13:35, Ferry Toth wrote: > > > It appears any ordinary user can easily create a DOS on linux. > > > > > > One sure way to reproduce this is to open gitk on the linux kernel repo > > > (SIC) on a machine with 8GB RAM 16 GB swap on a HDD with btrfs and quad core > > > + hyperthreading. But I will be easy enough to get the same effect with more > > > RAM, other fs etc. > > > > You may want to disable swap. > > > > I run without swap on my laptops, and still observe long periods of > thrashing on the road towards OOM. What seems to occur is the active > file-backed mappings of executables/libraries become a sort of swap > area, repeatedly being discarded and faulted back in as the context > switches occur. > > If there's any good way to prevent this, I'd like to know. I am afraid there is none yet. Johannes had some ground work for page cache trashing detection https://marc.info/?i=20170727153010.23347-1-hannes%40cmpxchg.org but there was no version of the patchseries for quite some time and there was no integration into the oom detection which would be non-trivial as well. I realize this sucks. But the reality is that this is far from trivial to resolve without introducing pre-mature OOM killer invocations. -- Michal Hocko SUSE Labs