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 <[email protected]> --- 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);
