Subject: Re: [net-next PATCH 2/3] net: sched: cls_u32 add missing rcu_assign_pointer and annotation

From: John Fastabend <[email-masked]>
Date: Mon, 15 Sep 2014 23:25:20 -0700

On 09/15/2014 07:48 PM, John Fastabend wrote:
> Add missing rcu_assign_pointer and missing  annotation for ht_up
> in cls_u32.c
> 
> Caught by kbuild bot,
> 
>>> net/sched/cls_u32.c:378:36: sparse: incorrect type in initializer (different address spaces)
>    net/sched/cls_u32.c:378:36:    expected struct tc_u_hnode *ht
>    net/sched/cls_u32.c:378:36:    got struct tc_u_hnode [noderef] <asn:4>*ht_up
>>> net/sched/cls_u32.c:610:54: sparse: incorrect type in argument 4 (different address spaces)
>    net/sched/cls_u32.c:610:54:    expected struct tc_u_hnode *ht
>    net/sched/cls_u32.c:610:54:    got struct tc_u_hnode [noderef] <asn:4>*ht_up
>>> net/sched/cls_u32.c:684:18: sparse: incorrect type in assignment (different address spaces)
>    net/sched/cls_u32.c:684:18:    expected struct tc_u_hnode [noderef] <asn:4>*ht_up
>    net/sched/cls_u32.c:684:18:    got struct tc_u_hnode *[assigned] ht
>>> net/sched/cls_u32.c:359:18: sparse: dereference of noderef expression
> 
> Signed-off-by: John Fastabend <[email-masked]>
> ---
>  net/sched/cls_u32.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 8cffe5a..19b2808 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -375,7 +375,7 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
>  {
>  	struct tc_u_knode __rcu **kp;
>  	struct tc_u_knode *pkp;
> -	struct tc_u_hnode *ht = key->ht_up;
> +	struct tc_u_hnode *ht = rtnl_dereference(key->ht_up);
>  
>  	if (ht) {
>  		kp = &ht->ht[TC_U32_HASH(key->handle)];
> @@ -607,7 +607,8 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
>  		if (TC_U32_KEY(n->handle) == 0)
>  			return -EINVAL;
>  
> -		return u32_set_parms(net, tp, base, n->ht_up, n, tb,
> +		return u32_set_parms(net, tp, base,
> +				     rtnl_dereference(n->ht_up), n, tb,
>  				     tca[TCA_RATE], ovr);
>  	}
>  
> @@ -681,7 +682,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
>  #endif
>  
>  	memcpy(&n->sel, s, sizeof(*s) + s->nkeys*sizeof(struct tc_u32_key));
> -	n->ht_up = ht;
> +	rcu_assign_pointer(n->ht_up, ht);

also believe this should be RCU_INIT_POINTER() the rcu_assign_pointer() to attach
n to the hash table happens below so there are no concurrent readers until after
the assign.

however while reviewing this I realize there is a 'copy'/'update' pattern I
missed in the u32_set_parms case when the classid and ifindex is changed. So
a fix coming for that shortly.

>  	n->handle = handle;
>  	n->fshift = s->hmask ? ffs(ntohl(s->hmask)) - 1 : 0;
>  	tcf_exts_init(&n->exts, TCA_U32_ACT, TCA_U32_POLICE);
> 
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