?? 2020/7/24 ????12:15, Andrew Morton ะด??:
> From: Hugh Dickins <[email protected]>
> 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/[email protected]
> Fixes: 615d66c37c75 ("mm: memcontrol: fix memcg id ref counter on swap charge move")
> Signed-off-by: Hugh Dickins <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Alex Shi <[email protected]>
> Cc: Shakeel Butt <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
> ---
Reviewed-by: Alex Shi <[email protected]>
>
> 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;
> _
>