[PATCH v2] mm: kfence: fix objcgs vector allocation

[Muchun Song <songmuchun@bytedance.com>]

If the kfence object is allocated to be used for objects vector, then
this slot of the pool eventually being occupied permanently since
the vector is never freed.  The solutions could be 1) freeing vector
when the kfence object is freed or 2) allocating all vectors statically.
Since the memory consumption of object vectors is low, it is better to
chose 2) to fix the issue and it is also can reduce overhead of vectors
allocating in the future.

Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
v2:
 - Fix compiler error reported by kernel test robot <lkp@intel.com>.

 mm/kfence/core.c   | 11 ++++++++++-
 mm/kfence/kfence.h |  3 +++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 13128fa13062..d4c7978cd75e 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -555,6 +555,8 @@ static bool __init kfence_init_pool(void)
 	 * enters __slab_free() slow-path.
 	 */
 	for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
+		struct slab *slab = page_slab(&pages[i]);
+
 		if (!i || (i % 2))
 			continue;
 
@@ -562,7 +564,11 @@ static bool __init kfence_init_pool(void)
 		if (WARN_ON(compound_head(&pages[i]) != &pages[i]))
 			goto err;
 
-		__SetPageSlab(&pages[i]);
+		__folio_set_slab(slab_folio(slab));
+#ifdef CONFIG_MEMCG
+		slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
+				   MEMCG_DATA_OBJCGS;
+#endif
 	}
 
 	/*
@@ -938,6 +944,9 @@ void __kfence_free(void *addr)
 {
 	struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
 
+#ifdef CONFIG_MEMCG
+	KFENCE_WARN_ON(meta->objcg);
+#endif
 	/*
 	 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
 	 * the object, as the object page may be recycled for other-typed
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index 2a2d5de9d379..9a6c4b1b12a8 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -89,6 +89,9 @@ struct kfence_metadata {
 	struct kfence_track free_track;
 	/* For updating alloc_covered on frees. */
 	u32 alloc_stack_hash;
+#ifdef CONFIG_MEMCG
+	struct obj_cgroup *objcg;
+#endif
 };
 
 extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
-- 
2.11.0