From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx169.postini.com [74.125.245.169]) by kanga.kvack.org (Postfix) with SMTP id 2AFE26B004D for ; Wed, 14 Mar 2012 06:02:44 -0400 (EDT) Date: Wed, 14 Mar 2012 11:02:41 +0100 From: Michal Hocko Subject: Re: [PATCH] page_cgroup: fix horrid swap accounting regression Message-ID: <20120314100240.GB4434@tiehlicka.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Linus Torvalds , Bob Liu , KAMEZAWA Hiroyuki , Johannes Weiner , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon 05-03-12 20:52:55, Hugh Dickins wrote: > Why is memcg's swap accounting so broken? Insane counts, wrong ownership, > unfreeable structures, which later get freed and then accessed after free. > > Turns out to be a tiny a little 3.3-rc1 regression in 9fb4b7cc0724 > "page_cgroup: add helper function to get swap_cgroup": the helper > function (actually named lookup_swap_cgroup()) returns an address > using void* arithmetic, but the structure in question is a short. > > Signed-off-by: Hugh Dickins Thanks, this one looks really nasty. Acked-by: Michal Hocko > --- > > mm/page_cgroup.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > --- 3.3-rc6/mm/page_cgroup.c 2012-01-20 08:42:35.320020840 -0800 > +++ linux/mm/page_cgroup.c 2012-03-05 19:51:13.535372098 -0800 > @@ -379,13 +379,15 @@ static struct swap_cgroup *lookup_swap_c > pgoff_t offset = swp_offset(ent); > struct swap_cgroup_ctrl *ctrl; > struct page *mappage; > + struct swap_cgroup *sc; > > ctrl = &swap_cgroup_ctrl[swp_type(ent)]; > if (ctrlp) > *ctrlp = ctrl; > > mappage = ctrl->map[offset / SC_PER_PAGE]; > - return page_address(mappage) + offset % SC_PER_PAGE; > + sc = page_address(mappage); > + return sc + offset % SC_PER_PAGE; > } > > /** -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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