From: Muchun Song <[email protected]> [ Upstream commit eefbfa7fd678805b38a46293e78543f98f353d3e ]
The rcu_read_lock/unlock only can guarantee that the memcg will not be freed, but it cannot guarantee the success of css_get to memcg. If the whole process of a cgroup offlining is completed between reading a objcg->memcg pointer and bumping the css reference on another CPU, and there are exactly 0 external references to this memory cgroup (how we get to the obj_cgroup_charge() then?), css_get() can change the ref counter from 0 back to 1. Link: https://lkml.kernel.org/r/[email protected] Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") Signed-off-by: Muchun Song <[email protected]> Acked-by: Roman Gushchin <[email protected]> Reviewed-by: Shakeel Butt <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Vladimir Davydov <[email protected]> Cc: Joonsoo Kim <[email protected]> Cc: Yafang Shao <[email protected]> Cc: Chris Down <[email protected]> Cc: Christian Brauner <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- mm/memcontrol.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 74b85077f89ad..a717728cc7b4a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3247,8 +3247,10 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) * independently later. */ rcu_read_lock(); +retry: memcg = obj_cgroup_memcg(objcg); - css_get(&memcg->css); + if (unlikely(!css_tryget(&memcg->css))) + goto retry; rcu_read_unlock(); nr_pages = size >> PAGE_SHIFT; -- 2.27.0
