linux-kernel - [PATCH 2/2] mm: kfence: fix objcgs vector allocation

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Date:   Sun, 27 Mar 2022 13:18:53 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     torvalds@...ux-foundation.org, glider@...gle.com, elver@...gle.com,
        dvyukov@...gle.com, akpm@...ux-foundation.org, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        vbabka@...e.cz, roman.gushchin@...ux.dev
Cc:     kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH 2/2] mm: kfence: fix objcgs vector allocation

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@...edance.com>
---
 mm/kfence/core.c   | 3 +++
 mm/kfence/kfence.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 13128fa13062..9976b3f0d097 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -579,9 +579,11 @@ static bool __init kfence_init_pool(void)
 	}
 
 	for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
+		struct slab *slab = virt_to_slab(addr);
 		struct kfence_metadata *meta = &kfence_metadata[i];
 
 		/* Initialize metadata. */
+		slab->memcg_data = (unsigned long)&meta->objcg | MEMCG_DATA_OBJCGS;
 		INIT_LIST_HEAD(&meta->list);
 		raw_spin_lock_init(&meta->lock);
 		meta->state = KFENCE_OBJECT_UNUSED;
@@ -938,6 +940,7 @@ void __kfence_free(void *addr)
 {
 	struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
 
+	KFENCE_WARN_ON(meta->objcg);
 	/*
 	 * 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..6f0e1aece3f8 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -89,6 +89,7 @@ struct kfence_metadata {
 	struct kfence_track free_track;
 	/* For updating alloc_covered on frees. */
 	u32 alloc_stack_hash;
+	struct obj_cgroup *objcg;
 };
 
 extern struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS];
-- 
2.11.0