Re: [PATCH v0 3/5] cgroup: Protect access to task_cls_classid() when built as module

[Li Zefan <lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

> +#if IS_ENABLED(CONFIG_NET_CLS_CGROUP)
> +extern struct static_key cgroup_cls_enabled;
> +#define clscg_enabled static_key_false(&cgroup_cls_enabled)
> +#endif
> +

If it's built-in, clscg_enabled is always true (after we call cgroup_subsys_init at
boot), so we don't need jump label at all.

>  extern void sock_update_classid(struct sock *sk);
>  
>  #if IS_BUILTIN(CONFIG_NET_CLS_CGROUP)
> @@ -52,7 +58,7 @@ static inline u32 task_cls_classid(struct task_struct *p)
>  	int id;
>  	u32 classid = 0;
>  
> -	if (in_interrupt())
> +	if (!clscg_enabled || in_interrupt())
>  		return 0;
>  
>  	rcu_read_lock();
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8f67ced..8d3a400 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -327,6 +327,11 @@ int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)
>  EXPORT_SYMBOL(__sk_backlog_rcv);
>  
>  #if defined(CONFIG_CGROUPS)
> +#if IS_ENABLED(CONFIG_NET_CLS_CGROUP)
> +struct static_key cgroup_cls_enabled = STATIC_KEY_INIT_FALSE;
> +EXPORT_SYMBOL_GPL(cgroup_cls_enabled);
> +#endif
> +
>  #if !defined(CONFIG_NET_CLS_CGROUP)
>  int net_cls_subsys_id = -1;
>  EXPORT_SYMBOL_GPL(net_cls_subsys_id);
> diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c
> index 7743ea8..f40086b 100644
> --- a/net/sched/cls_cgroup.c
> +++ b/net/sched/cls_cgroup.c
> @@ -44,12 +44,17 @@ static struct cgroup_subsys_state *cgrp_create(struct cgroup *cgrp)
>  
>  	if (cgrp->parent)
>  		cs->classid = cgrp_cls_state(cgrp->parent)->classid;
> +	else if (!clscg_enabled)
> +                static_key_slow_inc(&cgroup_cls_enabled);

It's not necessary to check if !clsg_enabled.

>  
>  	return &cs->css;
>  }
>  
>  static void cgrp_destroy(struct cgroup *cgrp)
>  {
> +	if (!cgrp->parent && clscg_enabled)
> +                static_key_slow_dec(&cgroup_cls_enabled);
> +

ditto.

>  	kfree(cgrp_cls_state(cgrp));
>  }
>  
>