The patch titled
Subject: mm: kmem: add lockdep assertion to obj_cgroup_memcg
has been added to the -mm mm-unstable branch. Its filename is
mm-kmem-add-lockdep-assertion-to-obj_cgroup_memcg.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmem-add-lockdep-assertion-to-obj_cgroup_memcg.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: kmem: add lockdep assertion to obj_cgroup_memcg
Date: Thu, 25 Jul 2024 17:43:30 +0800
The 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.
Link: https://lore.kernel.org/all/20240718083607.42068-1-songmuchun@xxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20240725094330.72537-1-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/memcontrol.h | 20 +++++++++++++++++---
mm/memcontrol.c | 6 +++---
2 files changed, 20 insertions(+), 6 deletions(-)
--- a/include/linux/memcontrol.h~mm-kmem-add-lockdep-assertion-to-obj_cgroup_memcg
+++ a/include/linux/memcontrol.h
@@ -366,11 +366,11 @@ static inline bool folio_memcg_kmem(stru
* 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_m
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_m
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_m
return obj_cgroup_memcg(objcg);
}
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
}
--- a/mm/memcontrol.c~mm-kmem-add-lockdep-assertion-to-obj_cgroup_memcg
+++ a/mm/memcontrol.c
@@ -2374,7 +2374,7 @@ void mem_cgroup_cancel_charge(struct mem
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:
*
@@ -4709,7 +4709,7 @@ void __mem_cgroup_uncharge(struct 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);
@@ -4754,7 +4754,7 @@ void mem_cgroup_replace_folio(struct fol
return;
/* Page cache replacement: new folio already charged? */
- if (folio_memcg(new))
+ if (folio_memcg_charged(new))
return;
memcg = folio_memcg(old);
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
mm-kmem-remove-mem_cgroup_from_obj.patch
mm-kmem-add-lockdep-assertion-to-obj_cgroup_memcg.patch
