Subject: Re: atl1 warn_on_slowpath help

From: Patrick McHardy <[email-masked]>
Date: Wed, 29 Oct 2008 11:17:09 +0100

Patrick McHardy wrote:
> Jarek Poplawski wrote:
>> On 29-10-2008 01:08, Jay Cliburn wrote:
>>> [   27.779463] ------------[ cut here ]------------
>>> [   27.779509] WARNING: at kernel/softirq.c:136 
>>> local_bh_enable+0x37/0x81()
>> ...
>>> [   27.782520]  [<c0264755>] netif_nit_deliver+0x5b/0x75
>>> [   27.782590]  [<c02bba83>] __vlan_hwaccel_rx+0x79/0x162
>>> [   27.782664]  [<f8851c1d>] atl1_intr+0x9a9/0xa7c [atl1]
>>>>
>>> warn_on_slowpath stuff well enough to know what to look for. Can someone
>>> please take a quick look at drivers/net/atlx/atl1.c around line 2017
>>> and see if there's an obvious error?  I'd really appreciate it.
>>
>> It looks to me like vlan_hwaccel_rx() is to blame: I doubt we can do
>> netif_nit_deliver() in hard irq context. (Patrick Cc-ed.)
> 
> Crap, I didn't think of that, all drivers I tested with support
> NAPI. I can't think of a clean way to fix it right now, but I'll
> look into it.

This is the best I could come up with, short of simply restoring
the old behaviour for non-polling drivers.

The __vlan_hwaccel_rx function only does the device lookup and
stores it in the cb. The remaining processing is done in a new
function that is invoked by netif_receive_skb(), in the proper
context. Unfortunatly this needs vlan-specific handling in
netif_receive_skb().

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 9e7b49b..a5cb0c3 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -114,6 +114,8 @@ extern u16 vlan_dev_vlan_id(const struct net_device *dev);
 
 extern int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
 			     u16 vlan_tci, int polling);
+extern int vlan_hwaccel_do_receive(struct sk_buff *skb);
+
 #else
 static inline struct net_device *vlan_dev_real_dev(const struct net_device *dev)
 {
@@ -133,6 +135,11 @@ static inline int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
 	BUG();
 	return NET_XMIT_SUCCESS;
 }
+
+static inline int vlan_hwaccel_do_receive(struct sk_buff *skb)
+{
+	return 0;
+}
 #endif
 
 /**
diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index 916061f..68ced4b 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -3,11 +3,20 @@
 #include <linux/if_vlan.h>
 #include "vlan.h"
 
+struct vlan_hwaccel_cb {
+	struct net_device	*dev;
+};
+
+static inline struct vlan_hwaccel_cb *vlan_hwaccel_cb(struct sk_buff *skb)
+{
+	return (struct vlan_hwaccel_cb *)skb->cb;
+}
+
 /* VLAN rx hw acceleration helper.  This acts like netif_{rx,receive_skb}(). */
 int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
 		      u16 vlan_tci, int polling)
 {
-	struct net_device_stats *stats;
+	struct vlan_hwaccel_cb *cb = vlan_hwaccel_cb(skb);
 
 	if (skb_bond_should_drop(skb)) {
 		dev_kfree_skb_any(skb);
@@ -15,23 +24,35 @@ int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
 	}
 
 	skb->vlan_tci = vlan_tci;
+	cb->dev = vlan_group_get_device(grp, vlan_tci & VLAN_VID_MASK);
+
+	return (polling ? netif_receive_skb(skb) : netif_rx(skb));
+}
+EXPORT_SYMBOL(__vlan_hwaccel_rx);
+
+int vlan_hwaccel_do_receive(struct sk_buff *skb)
+{
+	struct vlan_hwaccel_cb *cb = vlan_hwaccel_cb(skb);
+	struct net_device *dev = cb->dev;
+	struct net_device_stats *stats;
+
 	netif_nit_deliver(skb);
 
-	skb->dev = vlan_group_get_device(grp, vlan_tci & VLAN_VID_MASK);
-	if (skb->dev == NULL) {
-		dev_kfree_skb_any(skb);
-		/* Not NET_RX_DROP, this is not being dropped
-		 * due to congestion. */
-		return NET_RX_SUCCESS;
+	if (dev == NULL) {
+		kfree_skb(skb);
+		return -1;
 	}
-	skb->dev->last_rx = jiffies;
+
+	skb->dev = dev;
+	skb->priority = vlan_get_ingress_priority(dev, skb->vlan_tci);
 	skb->vlan_tci = 0;
 
-	stats = &skb->dev->stats;
+	dev->last_rx = jiffies;
+
+	stats = &dev->stats;
 	stats->rx_packets++;
 	stats->rx_bytes += skb->len;
 
-	skb->priority = vlan_get_ingress_priority(skb->dev, vlan_tci);
 	switch (skb->pkt_type) {
 	case PACKET_BROADCAST:
 		break;
@@ -43,13 +64,12 @@ int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
 		 * This allows the VLAN to have a different MAC than the
 		 * underlying device, and still route correctly. */
 		if (!compare_ether_addr(eth_hdr(skb)->h_dest,
-					skb->dev->dev_addr))
+					dev->dev_addr))
 			skb->pkt_type = PACKET_HOST;
 		break;
 	};
-	return (polling ? netif_receive_skb(skb) : netif_rx(skb));
+	return 0;
 }
-EXPORT_SYMBOL(__vlan_hwaccel_rx);
 
 struct net_device *vlan_dev_real_dev(const struct net_device *dev)
 {
diff --git a/net/core/dev.c b/net/core/dev.c
index d9038e3..9174c77 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2218,6 +2218,9 @@ int netif_receive_skb(struct sk_buff *skb)
 	int ret = NET_RX_DROP;
 	__be16 type;
 
+	if (skb->vlan_tci && vlan_hwaccel_do_receive(skb))
+		return NET_RX_SUCCESS;
+
 	/* if we've gotten here through NAPI, check netpoll */
 	if (netpoll_receive_skb(skb))
 		return NET_RX_DROP;