linux-kernel - Re: [PATCH] slub: assign refcount for kmalloc

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Message-ID: <CAAmzW4Nz6if==JjxLQGYwwQwKPDXfUbeioyPHWZQQFNu=xXUeQ@mail.gmail.com>
Date:	Wed, 26 Dec 2012 00:30:15 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Paul Hargrove <phhargrove@....gov>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <js1304@...il.com>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH] slub: assign refcount for kmalloc_caches

2012/12/26 Joonsoo Kim <js1304@...il.com>:
> commit cce89f4f6911286500cf7be0363f46c9b0a12ce0('Move kmem_cache
> refcounting to common code') moves some refcount manipulation code to
> common code. Unfortunately, it also removed refcount assignment for
> kmalloc_caches. So, kmalloc_caches's refcount is initially 0.
> This makes errornous situation.
>
> Paul Hargrove report that when he create a 8-byte kmem_cache and
> destory it, he encounter below message.
> 'Objects remaining in kmalloc-8 on kmem_cache_close()'
>
> 8-byte kmem_cache merge with 8-byte kmalloc cache and refcount is
> increased by one. So, resulting refcount is 1. When destory it, it hit
> refcount = 0, then kmem_cache_close() is executed and error message is
> printed.
>
> This patch assign initial refcount 1 to kmalloc_caches, so fix this
> errornous situtation.
>
> Cc: <stable@...r.kernel.org> # v3.7
> Cc: Christoph Lameter <cl@...ux.com>
> Reported-by: Paul Hargrove <phhargrove@....gov>
> Signed-off-by: Joonsoo Kim <js1304@...il.com>
>
> diff --git a/mm/slub.c b/mm/slub.c
> index a0d6984..321afab 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3279,6 +3279,7 @@ static struct kmem_cache *__init create_kmalloc_cache(const char *name,
>         if (kmem_cache_open(s, flags))
>                 goto panic;
>
> +       s->refcount = 1;
>         list_add(&s->list, &slab_caches);
>         return s;
>
> --
> 1.7.9.5
>

I missed some explanation.
In v3.8-rc1, this problem is already solved.
See create_kmalloc_cache() in mm/slab_common.c.
So this patch is just for v3.7 stable.
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