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Subject: Re: [PATCH 2/2] mm/slub: Fix slab_mutex circular locking problem in
 slab_attr_store()
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <20200424151225.10966-2-longman@redhat.com>
Date:   Fri, 24 Apr 2020 12:16:00 -0400
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>
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References: <20200424151225.10966-1-longman@redhat.com>
 <20200424151225.10966-2-longman@redhat.com>
To:     Waiman Long <longman@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Apr 24, 2020, at 11:12 AM, Waiman Long <longman@redhat.com> wrote:
>=20
> 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;
>=20
> 	err =3D attribute->store(s, buf, len);
> -#ifdef CONFIG_MEMCG
> -	if (slab_state >=3D FULL && err >=3D 0 && is_root_cache(s)) {
> -		struct kmem_cache *c;
> +#ifdef CONFIG_MEMCG_KMEM
> +	if (slab_state >=3D FULL && err >=3D 0 && is_root_cache(s) &&
> +	    !list_empty(&s->memcg_params.children)) {
> +		struct kmem_cache *c, **pcaches;
> +		int idx, max, cnt =3D 0;
> +		size_t size =3D s->max_attr_size;
> +		struct memcg_cache_array *arr;
> +
> +		/*
> +		 * Make atomic update to s->max_attr_size.
> +		 */
> +		do {
> +			if (len <=3D size)
> +				break;
> +		} while (!try_cmpxchg(&s->max_attr_size, &size, len));
>=20

try_cmpxchg() is only available on x86.

mm/slub.c: In function =E2=80=98slab_attr_store=E2=80=99:
mm/slub.c:5613:13: error: implicit declaration of function =
=E2=80=98try_cmpxchg=E2=80=99; did you mean =E2=80=98xa_cmpxchg=E2=80=99? =
[-Werror=3Dimplicit-function-declaration]
   } while (!try_cmpxchg(&s->max_attr_size, &size, len));
             ^~~~~~~~~~~
             xa_cmpxchg