Re: [PATCH] slab: add a check for the first kmem_cache not to be destroyed

[kwon]

> On Jan 17, 2017, at 10:33 AM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> 
> 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@xxxxxxxxxxxx>
>> ---
>> 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.

Hello, Joonsoo.

In case it is called the number of int size times. refcount would finally reach
to 0 since decreased every time the function called.

When refcount is -1, the count will not change in the patch so no lock would be
need to be taken prior, I believe.

Thanks.