linux-kernel - Re: [PATCH] mm/slab: Fix a kmemleak in kmem_cache

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Date: Wed, 28 Feb 2024 08:34:00 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Xiaolei Wang <xiaolei.wang@...driver.com>, cl@...ux.com,
 penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
 akpm@...ux-foundation.org, roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slab: Fix a kmemleak in kmem_cache_destroy()

On 2/28/24 04:04, Xiaolei Wang wrote:
> For earlier kmem cache creation, slab_sysfs_init() has not been called.
> Consequently, kmem_cache_destroy() cannot utilize kobj_type::release to
> release the kmem_cache structure. Therefore, tweak kmem_cache_release()
> to use slab_kmem_cache_release() for releasing kmem_cache when slab_state
> isn't FULL. This will fixes the memory leaks like following:

So do I understand correctly the leak happens when a cache is destroyed
while slab_state < FULL? Do we ever destroy a cache that early?

> unreferenced object 0xffff0000c2d87080 (size 128):
>    comm "swapper/0", pid 1, jiffies 4294893428
>    hex dump (first 32 bytes):
>      00 00 00 00 ad 4e ad de ff ff ff ff 6b 6b 6b 6b .....N......kkkk
>      ff ff ff ff ff ff ff ff b8 ab 48 89 00 80 ff ff.....H.....
>    backtrace (crc 8819d0f6):
>      [<ffff80008317a298>] kmemleak_alloc+0xb0/0xc4
>      [<ffff8000807e553c>] kmem_cache_alloc_node+0x288/0x3a8
>      [<ffff8000807e95f0>] __kmem_cache_create+0x1e4/0x64c
>      [<ffff8000807216bc>] kmem_cache_create_usercopy+0x1c4/0x2cc
>      [<ffff8000807217e0>] kmem_cache_create+0x1c/0x28
>      [<ffff8000819f6278>] arm_v7s_alloc_pgtable+0x1c0/0x6d4
>      [<ffff8000819f53a0>] alloc_io_pgtable_ops+0xe8/0x2d0
>      [<ffff800084b2d2c4>] arm_v7s_do_selftests+0xe0/0x73c
>      [<ffff800080016b68>] do_one_initcall+0x11c/0x7ac
>      [<ffff800084a71ddc>] kernel_init_freeable+0x53c/0xbb8
>      [<ffff8000831728d8>] kernel_init+0x24/0x144
>      [<ffff800080018e98>] ret_from_fork+0x10/0x20
> 
> Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>
> ---
>  mm/slab_common.c | 8 ++++++--
>  mm/slub.c        | 6 ++----
>  2 files changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 238293b1dbe1..b6b35bcdd196 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -404,8 +404,12 @@ EXPORT_SYMBOL(kmem_cache_create);
>   */
>  static void kmem_cache_release(struct kmem_cache *s)
>  {
> -	sysfs_slab_unlink(s);
> -	sysfs_slab_release(s);
> +	if (slab_state >= FULL) {
> +		sysfs_slab_unlink(s);
> +		sysfs_slab_release(s);
> +	} else {
> +		slab_kmem_cache_release(s);
> +	}
>  }
>  #else
>  static void kmem_cache_release(struct kmem_cache *s)
> diff --git a/mm/slub.c b/mm/slub.c
> index 2ef88bbf56a3..9ba59d064b6d 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -6792,14 +6792,12 @@ static int sysfs_slab_add(struct kmem_cache *s)
>  
>  void sysfs_slab_unlink(struct kmem_cache *s)
>  {
> -	if (slab_state >= FULL)
> -		kobject_del(&s->kobj);
> +	kobject_del(&s->kobj);
>  }
>  
>  void sysfs_slab_release(struct kmem_cache *s)
>  {
> -	if (slab_state >= FULL)
> -		kobject_put(&s->kobj);
> +	kobject_put(&s->kobj);
>  }
>  
>  /*