linux-kernel - Re: [PATCH 2/2] mm/slub: Fix slab_mutex circular locking problem in slab_attr

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Message-Id: <0A3C34CA-F514-41C2-AC3F-E5925C7C0F9A@lca.pw>
Date:   Fri, 24 Apr 2020 12:16:00 -0400
From:   Qian Cai <cai@....pw>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH 2/2] mm/slub: Fix slab_mutex circular locking problem in
 slab_attr_store()



> On Apr 24, 2020, at 11:12 AM, Waiman Long <longman@...hat.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