linux-kernel - Re: [PATCH] slab: add a check for the first kmem

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Date:   Tue, 17 Jan 2017 10:33:00 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     Kyunghwan Kwon <kwon@...nyone.net>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: add a check for the first kmem_cache not to be
 destroyed

On Mon, Jan 16, 2017 at 04:04:59PM +0900, Kyunghwan Kwon wrote:
> The first kmem_cache created at booting up is supposed neither mergeable
> nor destroyable but was possible to destroy. So prevent it.
> 
> Signed-off-by: Kyunghwan Kwon <kwon@...nyone.net>
> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 1dfc209..2d30ace 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -744,7 +744,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
>  	bool need_rcu_barrier = false;
>  	int err;
>  
> -	if (unlikely(!s))
> +	if (unlikely(!s) || s->refcount == -1)
>  		return;

Hello, Kyunghwan.

Few lines below, s->refcount is checked.

if (s->refcount)
        goto unlock;

Am I missing something?

Thanks.