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Message-ID: <20120314100240.GB4434@tiehlicka.suse.cz>
Date: Wed, 14 Mar 2012 11:02:41 +0100
From: Michal Hocko <mhocko@...e.cz>
To: Hugh Dickins <hughd@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Bob Liu <lliubbo@...il.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Johannes Weiner <jweiner@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] page_cgroup: fix horrid swap accounting regression
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 <hughd@...gle.com>
Thanks, this one looks really nasty.
Acked-by: Michal Hocko <mhocko@...e.cz>
> ---
>
> 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
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