netdev - Re: [PATCH v0 3/4] cgroup: net_cls: Pass in task to sock_update

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Date:	Wed, 17 Oct 2012 15:37:21 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Wagner <wagi@...om.org>
Cc:	netdev@...r.kernel.org, cgroups@...r.kernel.org,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	"David S. Miller" <davem@...emloft.net>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Glauber Costa <glommer@...allels.com>,
	Joe Perches <joe@...ches.com>,
	Neil Horman <nhorman@...driver.com>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v0 3/4] cgroup: net_cls: Pass in task to
 sock_update_classid()

On Wed, 2012-10-17 at 15:04 +0200, Daniel Wagner wrote:
> From: Daniel Wagner <daniel.wagner@...-carit.de>
> 
> sock_update_classid() assumes that the update operation always are
> applied on the current task. sock_update_classid() needs to know on
> which tasks to work on in order to be able to migrate task between
> cgroups using the struct cgroup_subsys attach() callback.
> 
...

>  
> -extern void sock_update_classid(struct sock *sk);
> +extern void sock_update_classid(struct sock *sk, struct task_struct *task);
>  
>  #if IS_BUILTIN(CONFIG_NET_CLS_CGROUP)
>  static inline u32 task_cls_classid(struct task_struct *p)
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8a146cf..68c2f3b 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1214,12 +1214,12 @@ static void sk_prot_free(struct proto *prot, struct sock *sk)
>  
>  #ifdef CONFIG_CGROUPS
>  #if IS_ENABLED(CONFIG_NET_CLS_CGROUP)
> -void sock_update_classid(struct sock *sk)
> +void sock_update_classid(struct sock *sk, struct task_struct *task)
>  {
>  	u32 classid;
>  
>  	rcu_read_lock();  /* doing current task, which cannot vanish. */
> -	classid = task_cls_classid(current);
> +	classid = task_cls_classid(task);
>  	rcu_read_unlock();


Comment is now misleading (since task might not be current) and
rcu_read_lock()/rcu_read_unlock() protects nothing here, but avoid a
lockdep splat...

Hey task_cls_classid() has its own rcu protection since commit
3fb5a991916091a908d (cls_cgroup: Fix rcu lockdep warning)

So we can safely revert Paul commit (1144182a8757f2a1)
(We no longer need rcu_read_lock/unlock here)

(BTW net-next is not opened yet, its content outdated, although I like
your patch series !)



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