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

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Message-ID: <9fee780e-2c32-bb6a-08c0-cae8fdc58e9f@redhat.com>
Date:   Mon, 27 Apr 2020 14:16:18 -0400
From:   Waiman Long <longman@...hat.com>
To:     Qian Cai <cai@....pw>
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 4/24/20 12:16 PM, Qian Cai wrote:
>
>> 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
>
Oh, sorry about that. Will fix it and send out v2.

Cheers,
Longman