Re: [PATCH v2 net-next 4/4] net/sched: act_mirred: Implement ingress actions

Hi,

On Tue, 27 Sep 2016 14:27:13 -0700 Eric Dumazet [off-list ref] wrote:

On Tue, 2016-09-27 at 23:59 +0300, Shmulik Ladkani wrote:

quoted

Up until now, 'action mirred' supported only egress actions (either
TCA_EGRESS_REDIR or TCA_EGRESS_MIRROR).

This patch implements the corresponding ingress actions
TCA_INGRESS_REDIR and TCA_INGRESS_MIRROR.  

quoted

-		if (m->tcfm_mac_header_xmit)
+	/* If action's target direction differs than filter's direction,
+	 * and devices expect a mac header on xmit, then mac push/pull is
+	 * needed.
+	 */
+	if (at != tcf_mirred_act_direction(m->tcfm_eaction) &&  

Note that m->tcfm_eaction is read here.

quoted

+	    m->tcfm_mac_header_xmit) {
+		if (at & AT_EGRESS) {
+			/* caught at egress, act ingress: pull mac */
+			mac_len = skb_network_header(skb) - skb_mac_header(skb);
+			skb_pull_rcsum(skb2, mac_len);
+		} else {
+			/* caught at ingress, act egress: push mac */
 			skb_push_rcsum(skb2, skb->mac_len);
+		}
 	}
 
 	/* mirror is always swallowed */
-	if (m->tcfm_eaction != TCA_EGRESS_MIRROR)
+	if (tcf_mirred_is_act_redirect(m->tcfm_eaction))
 		skb2->tc_verd = SET_TC_FROM(skb2->tc_verd, at);
 
 	skb2->skb_iif = skb->dev->ifindex;
 	skb2->dev = dev;
-	err = dev_queue_xmit(skb2);  

Note that m->tcfm_eaction is read another time here.

quoted

+	if (tcf_mirred_act_direction(m->tcfm_eaction) & AT_EGRESS)
+		err = dev_queue_xmit(skb2);
+	else
+		netif_receive_skb(skb2);
   

Since this runs lockless, another cpu might change m->tcfm_eaction in
the middle, and you could call dev_queue_xmit(skb2) while the skb2 was
prepared for the opposite action.

Thanks Eric.

I assume adding a READ_ONCE(m->tcfm_eaction) at beggining of section,
and using the read value, will solve this specific inconsistency?