netdev - Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone

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Date:   Sat, 20 Jun 2020 10:48:06 +0800
From:   Zefan Li <lizefan@...wei.com>
To:     Roman Gushchin <guro@...com>
CC:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Cameron Berkenpas <cam@...-zeon.de>,
        Peter Geis <pgwipeout@...il.com>,
        Lu Fengqi <lufq.fnst@...fujitsu.com>,
        Daniël Sonck <dsonck92@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone_lock()

>>> If so, we might wanna fix it in a different way,
>>> just checking if (!(css->flags & CSS_NO_REF)) in cgroup_bpf_put()
>>> like in cgroup_put(). It feels more reliable to me.
>>>
>>
>> Yeah I also have this idea in my mind.
> 
> I wonder if the following patch will fix the issue?
> 

I guess so, but it's better we have someone who reported this bug to
test it.

> --
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 4598e4da6b1b..7eb51137d896 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -942,12 +942,14 @@ static inline bool cgroup_task_frozen(struct task_struct *task)
>  #ifdef CONFIG_CGROUP_BPF
>  static inline void cgroup_bpf_get(struct cgroup *cgrp)
>  {
> -       percpu_ref_get(&cgrp->bpf.refcnt);
> +       if (!(cgrp->self.flags & CSS_NO_REF))
> +               percpu_ref_get(&cgrp->bpf.refcnt);
>  }
>  
>  static inline void cgroup_bpf_put(struct cgroup *cgrp)
>  {
> -       percpu_ref_put(&cgrp->bpf.refcnt);
> +       if (!(cgrp->self.flags & CSS_NO_REF))
> +               percpu_ref_put(&cgrp->bpf.refcnt);
>  }
>  
>  #else /* CONFIG_CGROUP_BPF */
>