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

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Date:   Thu, 24 Aug 2023 15:28:54 +0000
From:   Nadav Amit <namit@...are.com>
To:     Qi Zheng <zhengqi.arch@...edance.com>
CC:     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



> 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.

Otherwise, LGTM. Thanks.