在 2020/7/24 下午12:15, Andrew Morton 写道: > From: Hugh Dickins <hughd@xxxxxxxxxx> > Subject: mm/memcg: fix refcount error while moving and swapping > > It was hard to keep a test running, moving tasks between memcgs with > move_charge_at_immigrate, while swapping: mem_cgroup_id_get_many()'s > refcount is discovered to be 0 (supposedly impossible), so it is then > forced to REFCOUNT_SATURATED, and after thousands of warnings in quick > succession, the test is at last put out of misery by being OOM killed. > > This is because of the way moved_swap accounting was saved up until the > task move gets completed in __mem_cgroup_clear_mc(), deferred from when > mem_cgroup_move_swap_account() actually exchanged old and new ids. > Concurrent activity can free up swap quicker than the task is scanned, > bringing id refcount down 0 (which should only be possible when > offlining). > > Just skip that optimization: do that part of the accounting immediately. > > Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2007071431050.4726@eggly.anvils > Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap charge move") > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> > Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- Reviewed-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx> > > mm/memcontrol.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > --- a/mm/memcontrol.c~mm-memcg-fix-refcount-error-while-moving-and-swapping > +++ a/mm/memcontrol.c > @@ -5669,7 +5669,6 @@ static void __mem_cgroup_clear_mc(void) > if (!mem_cgroup_is_root(mc.to)) > page_counter_uncharge(&mc.to->memory, mc.moved_swap); > > - mem_cgroup_id_get_many(mc.to, mc.moved_swap); > css_put_many(&mc.to->css, mc.moved_swap); > > mc.moved_swap = 0; > @@ -5860,7 +5859,8 @@ put: /* get_mctgt_type() gets the page > ent = target.ent; > if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) { > mc.precharge--; > - /* we fixup refcnts and charges later. */ > + mem_cgroup_id_get_many(mc.to, 1); > + /* we fixup other refcnts and charges later. */ > mc.moved_swap++; > } > break; > _ >
