| Message ID | 20240724095307.81264-1-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm: kmem: add lockdep assertion to obj_cgroup_memcg | expand |
On 7/24/24 11:53 AM, Muchun Song wrote: > 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@bytedance.com/ > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > --- > v2: > - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt). > > include/linux/memcontrol.h | 20 +++++++++++++++++--- > mm/memcontrol.c | 6 +++--- > 2 files changed, 20 insertions(+), 6 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index fc94879db4dff..742351945f683 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -360,11 +360,11 @@ 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) > { > + WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_is_held(&cgroup_mutex)); Maybe lockdep_assert_once() would be a better fit? > return READ_ONCE(objcg->memcg); > } > > @@ -438,6 +438,19 @@ 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. > @@ -454,7 +467,6 @@ 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; > @@ -463,6 +475,8 @@ 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); > } > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 622d4544edd24..3da0284573857 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2366,7 +2366,7 @@ 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: > * > @@ -4617,7 +4617,7 @@ 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); > @@ -4662,7 +4662,7 @@ 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);
On Wed, Jul 24, 2024 at 05:20:09PM GMT, Vlastimil Babka (SUSE) wrote: > On 7/24/24 11:53 AM, Muchun Song wrote: > > 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@bytedance.com/ > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > --- > > v2: > > - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt). > > > > include/linux/memcontrol.h | 20 +++++++++++++++++--- > > mm/memcontrol.c | 6 +++--- > > 2 files changed, 20 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index fc94879db4dff..742351945f683 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -360,11 +360,11 @@ 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) > > { > > + WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_is_held(&cgroup_mutex)); > > Maybe lockdep_assert_once() would be a better fit? > So something like: lockdep_assert_once(rcu_read_lock_held() || lockdep_is_held(&cgroup_mutex));
On Wed, Jul 24, 2024 at 05:20:09PM +0200, Vlastimil Babka (SUSE) wrote: > On 7/24/24 11:53 AM, Muchun Song wrote: > > 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@bytedance.com/ > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > --- > > v2: > > - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt). > > > > include/linux/memcontrol.h | 20 +++++++++++++++++--- > > mm/memcontrol.c | 6 +++--- > > 2 files changed, 20 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index fc94879db4dff..742351945f683 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -360,11 +360,11 @@ 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) > > { > > + WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_is_held(&cgroup_mutex)); > > Maybe lockdep_assert_once() would be a better fit? 100%.
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index fc94879db4dff..742351945f683 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -360,11 +360,11 @@ 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) { + WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_is_held(&cgroup_mutex)); return READ_ONCE(objcg->memcg); } @@ -438,6 +438,19 @@ 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. @@ -454,7 +467,6 @@ 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; @@ -463,6 +475,8 @@ 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); } diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 622d4544edd24..3da0284573857 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2366,7 +2366,7 @@ 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: * @@ -4617,7 +4617,7 @@ 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); @@ -4662,7 +4662,7 @@ 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);
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@bytedance.com/ Signed-off-by: Muchun Song <songmuchun@bytedance.com> --- v2: - Remove mention of objcg_lock in obj_cgroup_memcg()(Shakeel Butt). include/linux/memcontrol.h | 20 +++++++++++++++++--- mm/memcontrol.c | 6 +++--- 2 files changed, 20 insertions(+), 6 deletions(-)