linux-kernel - Re: [PATCH v5 27/45] vmw_balloon: dynamically allocate the vmw-balloon shrinker

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Message-ID: <a7f13bb5-4344-e3db-1b2f-7edfbe6dae94@bytedance.com>
Date:   Fri, 25 Aug 2023 10:27:00 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Nadav Amit <namit@...are.com>
Cc:     Qi Zheng <zhengqi.arch@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "david@...morbit.com" <david@...morbit.com>,
        "tkhai@...ru" <tkhai@...ru>, "vbabka@...e.cz" <vbabka@...e.cz>,
        "roman.gushchin@...ux.dev" <roman.gushchin@...ux.dev>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "tytso@....edu" <tytso@....edu>,
        "steven.price@....com" <steven.price@....com>,
        "cel@...nel.org" <cel@...nel.org>,
        "senozhatsky@...omium.org" <senozhatsky@...omium.org>,
        "yujie.liu@...el.com" <yujie.liu@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Muchun Song <songmuchun@...edance.com>,
        Pv-drivers <Pv-drivers@...are.com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v5 27/45] vmw_balloon: dynamically allocate the
 vmw-balloon shrinker

Hi Nadav,

On 2023/8/24 23:28, Nadav Amit wrote:
> 
> 
>> On Aug 23, 2023, at 8:42 PM, Qi Zheng <zhengqi.arch@...edance.com> wrote:
>>
>> In preparation for implementing lockless slab shrink, use new APIs to
>> dynamically allocate the vmw-balloon shrinker, so that it can be freed
>> asynchronously via RCU. Then it doesn't need to wait for RCU read-side
>> critical section when releasing the struct vmballoon.
>>
>> And we can simply exit vmballoon_init() when registering the shrinker
>> fails. So the shrinker_registered indication is redundant, just remove it.
> 
> ...
> 
> Ugh. We should have already moved to OOM notifier instead...
> 
>> static void vmballoon_unregister_shrinker(struct vmballoon *b)
>> {
>> -	if (b->shrinker_registered)
>> -		unregister_shrinker(&b->shrinker);
>> -	b->shrinker_registered = false;
>> +	shrinker_free(b->shrinker);
>> }
> 
> If the patch goes through another iteration, please add:
> 
> 	b->shrinker = NULL;
> 
> Not that this is a real issue, but I prefer it so in order to more easily
> identify UAF if the function is called elsewhere.

OK, will add it.

> 
> Otherwise, LGTM. Thanks.

Thanks for your review!

Qi

>