From: Roman Gushchin roman.gushchin@linux.dev
mainline inclusion from mainline-v6.7-rc1 commit e86828e5446d95676835679837d995dec188d2be category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8YU7J
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Switch to a scope-based protection of the objcg pointer on slab/kmem allocation paths. Instead of using the get_() semantics in the pre-allocation hook and put the reference afterwards, let's rely on the fact that objcg is pinned by the scope.
It's possible because: 1) if the objcg is received from the current task struct, the task is keeping a reference to the objcg. 2) if the objcg is received from an active memcg (remote charging), the memcg is pinned by the scope and has a reference to the corresponding objcg.
Link: https://lkml.kernel.org/r/20231019225346.1822282-5-roman.gushchin@linux.dev Signed-off-by: Roman Gushchin (Cruise) roman.gushchin@linux.dev Tested-by: Naresh Kamboju naresh.kamboju@linaro.org Acked-by: Shakeel Butt shakeelb@google.com Reviewed-by: Vlastimil Babka vbabka@suse.cz Cc: David Rientjes rientjes@google.com Cc: Dennis Zhou dennis@kernel.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@kernel.org Cc: Muchun Song muchun.song@linux.dev Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com --- include/linux/memcontrol.h | 9 ++++++++ include/linux/sched/mm.h | 4 ++++ mm/memcontrol.c | 47 ++++++++++++++++++++++++++++++++++++-- mm/slab.h | 15 ++++++------ 4 files changed, 66 insertions(+), 9 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 370d02ebc3cc..fc6b7fd78209 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1861,6 +1861,15 @@ bool mem_cgroup_kmem_disabled(void); int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order); void __memcg_kmem_uncharge_page(struct page *page, int order);
+/* + * The returned objcg pointer is safe to use without additional + * protection within a scope. The scope is defined either by + * the current task (similar to the "current" global variable) + * or by set_active_memcg() pair. + * Please, use obj_cgroup_get() to get a reference if the pointer + * needs to be used outside of the local scope. + */ +struct obj_cgroup *current_obj_cgroup(void); struct obj_cgroup *get_obj_cgroup_from_current(void); struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio);
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index 8d89c8c4fac1..9a19f1b42f64 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -403,6 +403,10 @@ DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg); * __GFP_ACCOUNT allocations till the end of the scope will be charged to the * given memcg. * + * Please, make sure that caller has a reference to the passed memcg structure, + * so its lifetime is guaranteed to exceed the scope between two + * set_active_memcg() calls. + * * NOTE: This function can nest. Users must save the return value and * reset the previous value after their own charging scope is over. */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index abeb80a192dc..4b377611260f 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3193,6 +3193,49 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void) return objcg; }
+__always_inline struct obj_cgroup *current_obj_cgroup(void) +{ + struct mem_cgroup *memcg; + struct obj_cgroup *objcg; + + if (in_task()) { + memcg = current->active_memcg; + if (unlikely(memcg)) + goto from_memcg; + + objcg = READ_ONCE(current->objcg); + if (unlikely((unsigned long)objcg & CURRENT_OBJCG_UPDATE_FLAG)) + objcg = current_objcg_update(); + /* + * Objcg reference is kept by the task, so it's safe + * to use the objcg by the current task. + */ + return objcg; + } + + memcg = this_cpu_read(int_active_memcg); + if (unlikely(memcg)) + goto from_memcg; + + return NULL; + +from_memcg: + for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) { + /* + * Memcg pointer is protected by scope (see set_active_memcg()) + * and is pinning the corresponding objcg, so objcg can't go + * away and can be used within the scope without any additional + * protection. + */ + objcg = rcu_dereference_check(memcg->objcg, 1); + if (likely(objcg)) + break; + objcg = NULL; + } + + return objcg; +} + struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio) { struct obj_cgroup *objcg; @@ -3287,15 +3330,15 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order) struct obj_cgroup *objcg; int ret = 0;
- objcg = get_obj_cgroup_from_current(); + objcg = current_obj_cgroup(); if (objcg) { ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order); if (!ret) { + obj_cgroup_get(objcg); page->memcg_data = (unsigned long)objcg | MEMCG_DATA_KMEM; return 0; } - obj_cgroup_put(objcg); } return ret; } diff --git a/mm/slab.h b/mm/slab.h index 799a315695c6..3d07fb428393 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -484,7 +484,12 @@ static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s, if (!(flags & __GFP_ACCOUNT) && !(s->flags & SLAB_ACCOUNT)) return true;
- objcg = get_obj_cgroup_from_current(); + /* + * The obtained objcg pointer is safe to use within the current scope, + * defined by current task or set_active_memcg() pair. + * obj_cgroup_get() is used to get a permanent reference. + */ + objcg = current_obj_cgroup(); if (!objcg) return true;
@@ -497,17 +502,14 @@ static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s, css_put(&memcg->css);
if (ret) - goto out; + return false; }
if (obj_cgroup_charge(objcg, flags, objects * obj_full_size(s))) - goto out; + return false;
*objcgp = objcg; return true; -out: - obj_cgroup_put(objcg); - return false; }
static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, @@ -542,7 +544,6 @@ static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s, obj_cgroup_uncharge(objcg, obj_full_size(s)); } } - obj_cgroup_put(objcg); }
static inline void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,