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 in
dev_hard_start_xmit().

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 32 insertions, 36 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 5902426ef585..7f390b52caab 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1895,6 +1895,22 @@ static inline void skb_orphan_try(struct sk_buff *skb)
                 skb_orphan(skb);
 }
 
+/*
+ * Returns true if either:
+ *      1. skb has frag_list and the device doesn't support FRAGLIST, or
+ *      2. skb is fragmented and the device does not support SG, or if
+ *         at least one of fragments is in highmem and device does not
+ *         support DMA from it.
+ */
+static inline int skb_needs_linearize(struct sk_buff *skb,
+                                      struct net_device *dev)
+{
+        return skb_is_nonlinear(skb) &&
+               ((skb_has_frags(skb) && !(dev->features & NETIF_F_FRAGLIST)) ||
+                (skb_shinfo(skb)->nr_frags && (!(dev->features & NETIF_F_SG) ||
+                                              illegal_highdma(dev, skb))));
+}
+
 int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
                         struct netdev_queue *txq)
 {
@@ -1919,6 +1935,22 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
                                 goto out_kfree_skb;
                         if (skb->next)
                                 goto gso;
+                } else {
+                        if (skb_needs_linearize(skb, dev) &&
+                            __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;
+                        }
                 }
 
                 rc = ops->ndo_start_xmit(skb, dev);
@@ -2089,22 +2121,6 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
         return rc;
 }
 
-/*
- * Returns true if either:
- *      1. skb has frag_list and the device doesn't support FRAGLIST, or
- *      2. skb is fragmented and the device does not support SG, or if
- *         at least one of fragments is in highmem and device does not
- *         support DMA from it.
- */
-static inline int skb_needs_linearize(struct sk_buff *skb,
-                                      struct net_device *dev)
-{
-        return skb_is_nonlinear(skb) &&
-               ((skb_has_frags(skb) && !(dev->features & NETIF_F_FRAGLIST)) ||
-                (skb_shinfo(skb)->nr_frags && (!(dev->features & NETIF_F_SG) ||
-                                              illegal_highdma(dev, skb))));
-}
-
 /**
  *      dev_queue_xmit - transmit a buffer
  *      @skb: buffer to transmit
@@ -2137,25 +2153,6 @@ int dev_queue_xmit(struct sk_buff *skb)
         struct Qdisc *q;
         int rc = -ENOMEM;
 
-        /* GSO will handle the following emulations directly. */
-        if (netif_needs_gso(dev, skb))
-                goto gso;
-
-        /* Convert a paged skb to linear, if required */
-        if (skb_needs_linearize(skb, dev) && __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;
-        }
-
-gso:
         /* Disable soft irqs for various locks below. Also
          * stops preemption for RCU.
          */
@@ -2214,7 +2211,6 @@ gso:
         rc = -ENETDOWN;
         rcu_read_unlock_bh();
 
-out_kfree_skb:
         kfree_skb(skb);
         return rc;
 out: