[PATCH net 3/3] igb: prepare TSO and checksum offloads before TX timestamps

[Paul Moses]

igb_xmit_frame_ring() takes an extra skb reference for TX timestamping
before transmit preparation. For GSO packets, igb_tso() calls
skb_cow_head(), which can reach pskb_expand_head() with a shared skb
when the header is cloned. Commit c7d8bc3dd511 ("net: skbuff: don't BUG()
on bad arguments to pskb_expand_head()") replaced the BUG_ON() with
-EINVAL, causing TSO preparation to fail and the packet to be dropped.

For non-GSO packets with CHECKSUM_PARTIAL, igb_tx_csum() falls back to
skb_checksum_help() for unsupported checksum offsets. This can also
reach pskb_expand_head() through skb_ensure_writable(). igb_tx_csum()
ignores the error, allowing transmission to continue without completing
the checksum.

Move TSO and checksum preparation before taking the timestamp reference.
Add the timestamp bit to first->tx_flags without overwriting the offload
flags.

Fixes: 1f6e8178d685 ("igb: Prevent dropped Tx timestamps via work items and 
interrupts.")
Fixes: 6e033700887b ("igb: Add support for generic Tx checksums")
Signed-off-by: Paul Moses <p...@1g4.org>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 31 ++++++++++++-----------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c 
b/drivers/net/ethernet/intel/igb/igb_main.c
index d4a897a8c82c..04c0053dbaae 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6559,6 +6559,21 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
        first->bytecount = skb->len;
        first->gso_segs = 1;
 
+       if (skb_vlan_tag_present(skb)) {
+               tx_flags |= IGB_TX_FLAGS_VLAN;
+               tx_flags |= (skb_vlan_tag_get(skb) << IGB_TX_FLAGS_VLAN_SHIFT);
+       }
+
+       /* record initial flags and protocol */
+       first->tx_flags = tx_flags;
+       first->protocol = protocol;
+
+       tso = igb_tso(tx_ring, first, &hdr_len);
+       if (tso < 0)
+               goto out_drop;
+       else if (!tso)
+               igb_tx_csum(tx_ring, first);
+
        if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)) {
                struct igb_adapter *adapter = netdev_priv(tx_ring->netdev);
 
@@ -6567,6 +6582,7 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
                                           &adapter->state)) {
                        skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
                        tx_flags |= IGB_TX_FLAGS_TSTAMP;
+                       first->tx_flags |= IGB_TX_FLAGS_TSTAMP;
 
                        adapter->ptp_tx_skb = skb_get(skb);
                        adapter->ptp_tx_start = jiffies;
@@ -6577,21 +6593,6 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
                }
        }
 
-       if (skb_vlan_tag_present(skb)) {
-               tx_flags |= IGB_TX_FLAGS_VLAN;
-               tx_flags |= (skb_vlan_tag_get(skb) << IGB_TX_FLAGS_VLAN_SHIFT);
-       }
-
-       /* record initial flags and protocol */
-       first->tx_flags = tx_flags;
-       first->protocol = protocol;
-
-       tso = igb_tso(tx_ring, first, &hdr_len);
-       if (tso < 0)
-               goto out_drop;
-       else if (!tso)
-               igb_tx_csum(tx_ring, first);
-
        if (igb_tx_map(tx_ring, first, hdr_len))
                goto cleanup_tx_tstamp;