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

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Date:   Sun, 27 Mar 2022 13:43:03 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     kasan-dev@...glegroups.com,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: kfence: fix objcgs vector allocation

On Sun, Mar 27, 2022 at 1:19 PM Muchun Song <songmuchun@...edance.com> wrote:
>
> 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>

Since it cannot be compiled successfully when !CONFIG_MEMCG
(The following patch should be applied), I'll update this in the next
version if anyone agrees with this change.

Thanks.

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 9976b3f0d097..b5c4b62b5d2c 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -583,7 +583,9 @@ static bool __init kfence_init_pool(void)
                struct kfence_metadata *meta = &kfence_metadata[i];

                /* Initialize metadata. */
+#ifdef CONFIG_MEMCG
                slab->memcg_data = (unsigned long)&meta->objcg |
MEMCG_DATA_OBJCGS;
+#endif
                INIT_LIST_HEAD(&meta->list);
                raw_spin_lock_init(&meta->lock);
                meta->state = KFENCE_OBJECT_UNUSED;
@@ -940,7 +942,9 @@ 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 6f0e1aece3f8..9a6c4b1b12a8 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -89,7 +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
 };