On Mon, Dec 14, 2020 at 02:37:16PM -0800, Yang Shi wrote: > The shrink_slab_memcg() races with mem_cgroup_css_online(). A visibility of > CSS_ONLINE flag > in shrink_slab_memcg()->mem_cgroup_online() does not guarantee that we will > see > memcg->nodeinfo[nid]->shrinker_maps != NULL. This may occur because of > processor reordering > on !x86. > > This seems like the below case: > > CPU A CPU B > store shrinker_map load CSS_ONLINE > store CSS_ONLINE load shrinker_map > > So the memory ordering could be guaranteed by smp_wmb()/smp_rmb() pair. > > The memory barriers pair will guarantee the ordering between > shrinker_deferred and CSS_ONLINE > for the following patches as well. > > Signed-off-by: Yang Shi <shy828...@gmail.com>
As per previous feedback, please move the misplaced shrinker allocation callback from .css_online to .css_alloc. This will get you the necessary ordering guarantees from the cgroup core code. Thanks
