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@xxxxxxxxxx> Thanks, this one looks really nasty. Acked-by: Michal Hocko <mhocko@xxxxxxx> > --- > > 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@xxxxxxxxx. 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>