Re: [PATCH 2/2] mm/slub: Fix slab_mutex circular locking problem in slab_attr_store()

[Qian Cai <cai@lca.pw>]

> On Apr 24, 2020, at 11:12 AM, Waiman Long <longman@redhat.com> wrote:
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 183ccc364ccf..255981180489 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5567,13 +5567,30 @@ static ssize_t slab_attr_store(struct kobject *kobj,
> 		return -EIO;
> 
> 	err = attribute->store(s, buf, len);
> -#ifdef CONFIG_MEMCG
> -	if (slab_state >= FULL && err >= 0 && is_root_cache(s)) {
> -		struct kmem_cache *c;
> +#ifdef CONFIG_MEMCG_KMEM
> +	if (slab_state >= FULL && err >= 0 && is_root_cache(s) &&
> +	    !list_empty(&s->memcg_params.children)) {
> +		struct kmem_cache *c, **pcaches;
> +		int idx, max, cnt = 0;
> +		size_t size = s->max_attr_size;
> +		struct memcg_cache_array *arr;
> +
> +		/*
> +		 * Make atomic update to s->max_attr_size.
> +		 */
> +		do {
> +			if (len <= size)
> +				break;
> +		} while (!try_cmpxchg(&s->max_attr_size, &size, len));
> 

try_cmpxchg() is only available on x86.

mm/slub.c: In function ‘slab_attr_store’:
mm/slub.c:5613:13: error: implicit declaration of function ‘try_cmpxchg’; did you mean ‘xa_cmpxchg’? [-Werror=implicit-function-declaration]
   } while (!try_cmpxchg(&s->max_attr_size, &size, len));
             ^~~~~~~~~~~
             xa_cmpxchg