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Message-ID: <20100104102153.11639.48828.stgit@localhost.localdomain>
Date: Mon, 04 Jan 2010 10:21:53 +0000
From: John Fastabend <john.r.fastabend@...el.com>
To: netdev@...r.kernel.org
Subject: [RFC PATCH] net: consolidate netif_needs_gso() checks
netif_needs_gso() is checked twice in the TX path once,
before submitting the skb to the qdisc and once after
it is dequeued from the qdisc just before calling
ndo_hard_start(). This opens a window for a user to
change the gso/tso or tx checksum settings that can
cause netif_needs_gso to be true in one check and false
in the other.
Specifically, changing TX checksum setting may cause
the warning in skb_gso_segment() to be triggered if
the checksum is calculated earlier.
This consolidates the netif_needs_gso() calls so that
the stack only checks if gso is needed after the skb
is dequeued from the qdisc. Or if the device has no
queue then before dev_hard_start_xmit() in dev_queue_xmit().
Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
---
net/core/dev.c | 88 +++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 58 insertions(+), 30 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index c36a17a..91077df 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1808,12 +1808,39 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
{
const struct net_device_ops *ops = dev->netdev_ops;
int rc = NETDEV_TX_OK;
+ int need_gso = netif_needs_gso(dev,skb);
+
+ if (!need_gso) {
+ if (skb_has_frags(skb) &&
+ !(dev->features & NETIF_F_FRAGLIST) &&
+ __skb_linearize(skb))
+ goto out_kfree_skb;
+
+ /* Fragmented skb is linearized if device does not support SG,
+ * or if at least one of fragments is in highmem and device
+ * does not support DMA from it.
+ */
+ if (skb_shinfo(skb)->nr_frags &&
+ (!(dev->features & NETIF_F_SG) ||
+ illegal_highdma(dev, skb)) &&
+ __skb_linearize(skb))
+ goto out_kfree_skb;
+ /* If packet is not checksummed and device does not support
+ * checksumming for this protocol, complete checksumming here.
+ */
+ if (skb->ip_summed == CHECKSUM_PARTIAL) {
+ skb_set_transport_header(skb, skb->csum_start -
+ skb_headroom(skb));
+ if (!dev_can_checksum(dev, skb) && skb_checksum_help(skb))
+ goto out_kfree_skb;
+ }
+ }
if (likely(!skb->next)) {
if (!list_empty(&ptype_all))
dev_queue_xmit_nit(skb, dev);
- if (netif_needs_gso(dev, skb)) {
+ if (need_gso) {
if (unlikely(dev_gso_segment(skb)))
goto out_kfree_skb;
if (skb->next)
@@ -2006,6 +2033,35 @@ int dev_queue_xmit(struct sk_buff *skb)
struct Qdisc *q;
int rc = -ENOMEM;
+ /* Disable soft irqs for various locks below. Also
+ * stops preemption for RCU.
+ */
+ rcu_read_lock_bh();
+
+ txq = dev_pick_tx(dev, skb);
+ q = rcu_dereference(txq->qdisc);
+
+#ifdef CONFIG_NET_CLS_ACT
+ skb->tc_verd = SET_TC_AT(skb->tc_verd, AT_EGRESS);
+#endif
+ if (q->enqueue) {
+ rc = __dev_xmit_skb(skb, q, dev, txq);
+ goto out;
+ }
+
+ /* The device has no queue. Common case for software devices:
+ loopback, all the sorts of tunnels...
+
+ Really, it is unlikely that netif_tx_lock protection is necessary
+ here. (f.e. loopback and IP tunnels are clean ignoring statistics
+ counters.)
+ However, it is possible, that they rely on protection
+ made by us here.
+
+ Check this and shot the lock. It is not prone from deadlocks.
+ Either shot noqueue qdisc, it is even simpler 8)
+ */
+
/* GSO will handle the following emulations directly. */
if (netif_needs_gso(dev, skb))
goto gso;
@@ -2035,34 +2091,6 @@ int dev_queue_xmit(struct sk_buff *skb)
}
gso:
- /* Disable soft irqs for various locks below. Also
- * stops preemption for RCU.
- */
- rcu_read_lock_bh();
-
- txq = dev_pick_tx(dev, skb);
- q = rcu_dereference(txq->qdisc);
-
-#ifdef CONFIG_NET_CLS_ACT
- skb->tc_verd = SET_TC_AT(skb->tc_verd, AT_EGRESS);
-#endif
- if (q->enqueue) {
- rc = __dev_xmit_skb(skb, q, dev, txq);
- goto out;
- }
-
- /* The device has no queue. Common case for software devices:
- loopback, all the sorts of tunnels...
-
- Really, it is unlikely that netif_tx_lock protection is necessary
- here. (f.e. loopback and IP tunnels are clean ignoring statistics
- counters.)
- However, it is possible, that they rely on protection
- made by us here.
-
- Check this and shot the lock. It is not prone from deadlocks.
- Either shot noqueue qdisc, it is even simpler 8)
- */
if (dev->flags & IFF_UP) {
int cpu = smp_processor_id(); /* ok because BHs are off */
@@ -4869,7 +4897,7 @@ unsigned long netdev_fix_features(unsigned long features, const char *name)
printk(KERN_NOTICE "%s: Dropping NETIF_F_SG since no "
"checksum feature.\n", name);
features &= ~NETIF_F_SG;
- }
+}
/* TSO requires that SG is present as well. */
if ((features & NETIF_F_TSO) && !(features & NETIF_F_SG)) {
--
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