On Thu, Jul 30, 2020 at 08:17:50PM -0700, Hugh Dickins wrote: > Moving tasks between mem cgroups with memory.move_charge_at_immigrate 3, > while swapping, crashes soon on mmotm (and so presumably on linux-next): > for example, spinlock found corrupted when lock_page_memcg() is called. > It's as if the mem cgroup structures have been freed too early. > > Stab in the dark: what if all the accounting is right, except that the > css_put_many() in __mem_cgroup_clear_mc() is now (worse than) redundant? > Removing it fixes the crashes, but that's hardly surprising; and stats > temporarily hacked into mem_cgroup_css_alloc() and mem_cgroup_css_free() > showed that mem cgroups were not being leaked with this change. > > Note: this removes the last call to css_put_many() from the tree; and > mm-memcg-slab-use-a-single-set-of-kmem_caches-for-all-accounted-allocations.patch > removes the last call to css_get_many(): now that their last references > have gone, I expect them soon to be freed from include/linux/cgroup.h. > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > --- > Fixes mm-memcontrol-decouple-reference-counting-from-page-accounting.patch > > mm/memcontrol.c | 2 -- > 1 file changed, 2 deletions(-) > > --- mmotm/mm/memcontrol.c 2020-07-27 18:55:00.700554752 -0700 > +++ linux/mm/memcontrol.c 2020-07-30 12:05:00.640091618 -0700 > @@ -5887,8 +5887,6 @@ static void __mem_cgroup_clear_mc(void) > if (!mem_cgroup_is_root(mc.to)) > page_counter_uncharge(&mc.to->memory, mc.moved_swap); > > - css_put_many(&mc.to->css, mc.moved_swap); > - > mc.moved_swap = 0; > } > memcg_oom_recover(from); Acked-by: Roman Gushchin <guro@xxxxxx> Good catch! Thank you, Hugh!
