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mm: kmem: add lockdep assertion to obj_cgroup_memcg

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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 <songmuchun@bytedance.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Muchun Song 2024-08-14 17:34:15 +08:00 committed by Andrew Morton
parent 90a6f2a8f4
commit 02f4bbefca
2 changed files with 22 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
include/linux/memcontrol.h
View File

@ -366,11 +366,11 @@ static inline bool folio_memcg_kmem(struct folio *folio);
* After the initialization objcg->memcg is always pointing at
* a valid memcg, but can be atomically swapped to the parent memcg.
*
* The caller must ensure that the returned memcg won't be released:
* e.g. acquire the rcu_read_lock or css_set_lock.
* The caller must ensure that the returned memcg won't be released.
*/
static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
{
lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
return READ_ONCE(objcg->memcg);
}
@ -444,6 +444,19 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
return __folio_memcg(folio);
}
/*
* folio_memcg_charged - If a folio is charged to a memory cgroup.
* @folio: Pointer to the folio.
*
* Returns true if folio is charged to a memory cgroup, otherwise returns false.
*/
static inline bool folio_memcg_charged(struct folio *folio)
{
if (folio_memcg_kmem(folio))
return __folio_objcg(folio) != NULL;
return __folio_memcg(folio) != NULL;
}
/**
* folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
* @folio: Pointer to the folio.
@ -460,7 +473,6 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
unsigned long memcg_data = READ_ONCE(folio->memcg_data);
VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
WARN_ON_ONCE(!rcu_read_lock_held());
if (memcg_data & MEMCG_DATA_KMEM) {
struct obj_cgroup *objcg;
@ -469,6 +481,8 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
return obj_cgroup_memcg(objcg);
}
WARN_ON_ONCE(!rcu_read_lock_held());
return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
}

11
mm/memcontrol.c
View File

@ -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);