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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 17 May 2022 07:07:37 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Shida Zhang <starzhangzsd@gmail.com>
Cc:     lizefan.x@bytedance.com, hannes@cmpxchg.org, zhangshida@kylinos.cn,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org
Subject: Re: [PATCH] cgroup: fix potential null pointer risk
Message-ID: <YoPWWfoZ+6PrHuJl@slm.duckdns.org>
References: <20220517073106.1704628-1-zhangshida@kylinos.cn>
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In-Reply-To: <20220517073106.1704628-1-zhangshida@kylinos.cn>
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On Tue, May 17, 2022 at 03:31:06PM +0800, Shida Zhang wrote:
> We previously assumed 'parent' could be null,
> so null pointer judgment should be added.
> 
> Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
> ---
>  kernel/cgroup/cgroup.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index adb820e98f24..7f230b0ab644 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -5701,7 +5701,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
>  	}
>  	spin_unlock_irq(&css_set_lock);
>  
> -	cgroup1_check_for_release(parent);
> +	if (parent)
> +		cgroup1_check_for_release(parent);

The function is never called for a root cgroup. The parent check up above in
the same function is superflous. So, maybe remove that?

Thanks.

-- 
tejun