From 02f4bbefcada38cab86b365e5c795e0f858356bc Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Wed, 14 Aug 2024 17:34:15 +0800 Subject: mm: kmem: add lockdep assertion to obj_cgroup_memcg obj_cgroup_memcg() is supposed to safe to prevent the returned memory cgroup from being freed only when the caller is holding the rcu read lock or objcg_lock or cgroup_mutex. It is very easy to ignore thoes conditions when users call some upper APIs which call obj_cgroup_memcg() internally like mem_cgroup_from_slab_obj() (See the link below). So it is better to add lockdep assertion to obj_cgroup_memcg() to find those issues ASAP. Because there is no user of obj_cgroup_memcg() holding objcg_lock to make the returned memory cgroup safe, do not add objcg_lock assertion (We should export objcg_lock if we really want to do). Additionally, this is some internal implementation detail of memcg and should not be accessible outside memcg code. Some users like __mem_cgroup_uncharge() do not care the lifetime of the returned memory cgroup, which just want to know if the folio is charged to a memory cgroup, therefore, they do not need to hold the needed locks. In which case, introduce a new helper folio_memcg_charged() to do this. Compare it to folio_memcg(), it could eliminate a memory access of objcg->memcg for kmem, actually, a really small gain. [songmuchun@bytedance.com: fix split_page_memcg()] Link: https://lkml.kernel.org/r/20240819080415.44964-1-songmuchun@bytedance.com Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@bytedance.com/ Link: https://lkml.kernel.org/r/20240814093415.17634-1-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Shakeel Butt Acked-by: Roman Gushchin Acked-by: Vlastimil Babka Cc: Johannes Weiner Cc: Michal Hocko Signed-off-by: Andrew Morton --- mm/memcontrol.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index cb2996d5d3f4..96f85fd0e5b3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2374,7 +2374,7 @@ void mem_cgroup_cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) { - VM_BUG_ON_FOLIO(folio_memcg(folio), folio); + VM_BUG_ON_FOLIO(folio_memcg_charged(folio), folio); /* * Any of the following ensures page's memcg stability: * @@ -3035,12 +3035,11 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void split_page_memcg(struct page *head, int old_order, int new_order) { struct folio *folio = page_folio(head); - struct mem_cgroup *memcg = folio_memcg(folio); int i; unsigned int old_nr = 1 << old_order; unsigned int new_nr = 1 << new_order; - if (mem_cgroup_disabled() || !memcg) + if (mem_cgroup_disabled() || !folio_memcg_charged(folio)) return; for (i = new_nr; i < old_nr; i += new_nr) @@ -3049,7 +3048,7 @@ void split_page_memcg(struct page *head, int old_order, int new_order) if (folio_memcg_kmem(folio)) obj_cgroup_get_many(__folio_objcg(folio), old_nr / new_nr - 1); else - css_get_many(&memcg->css, old_nr / new_nr - 1); + css_get_many(&folio_memcg(folio)->css, old_nr / new_nr - 1); } unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) @@ -4707,7 +4706,7 @@ void __mem_cgroup_uncharge(struct folio *folio) struct uncharge_gather ug; /* Don't touch folio->lru of any random page, pre-check: */ - if (!folio_memcg(folio)) + if (!folio_memcg_charged(folio)) return; uncharge_gather_clear(&ug); @@ -4752,7 +4751,7 @@ void mem_cgroup_replace_folio(struct folio *old, struct folio *new) return; /* Page cache replacement: new folio already charged? */ - if (folio_memcg(new)) + if (folio_memcg_charged(new)) return; memcg = folio_memcg(old); -- cgit v1.2.3