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

[Paul Moses <p@1g4.org>]

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;