i40e: fix race conditions on queuing skb for HW time stamp

i40e has a single set of TX time stamping resources per NIC.
Use a simple bit lock to avoid race conditions and leaking skbs
when multiple TX rings try to claim time stamping.
Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Tested-By: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e.h

@@ -134,6 +134,7 @@ enum i40e_state_t {
 	__I40E_EMP_RESET_REQUESTED,
 	__I40E_FILTER_OVERFLOW_PROMISC,
 	__I40E_SUSPENDED,
+	__I40E_PTP_TX_IN_PROGRESS,
 	__I40E_BAD_EEPROM,
 	__I40E_DOWN_REQUESTED,
 };

drivers/net/ethernet/intel/i40e/i40e_ptp.c

@@ -314,6 +314,7 @@ void i40e_ptp_tx_hwtstamp(struct i40e_pf *pf)
 	skb_tstamp_tx(pf->ptp_tx_skb, &shhwtstamps);
 	dev_kfree_skb_any(pf->ptp_tx_skb);
 	pf->ptp_tx_skb = NULL;
+	clear_bit_unlock(__I40E_PTP_TX_IN_PROGRESS, &pf->state);
 }
 
 /**
@@ -677,6 +678,7 @@ void i40e_ptp_stop(struct i40e_pf *pf)
 	if (pf->ptp_tx_skb) {
 		dev_kfree_skb_any(pf->ptp_tx_skb);
 		pf->ptp_tx_skb = NULL;
+		clear_bit_unlock(__I40E_PTP_TX_IN_PROGRESS, &pf->state);
 	}
 
 	if (pf->ptp_clock) {

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -1856,7 +1856,8 @@ static int i40e_tsyn(struct i40e_ring *tx_ring, struct sk_buff *skb,
 	 * we are not already transmitting a packet to be timestamped
 	 */
 	pf = i40e_netdev_to_pf(tx_ring->netdev);
-	if (pf->ptp_tx && !pf->ptp_tx_skb) {
+	if (pf->ptp_tx &&
+	    !test_and_set_bit_lock(__I40E_PTP_TX_IN_PROGRESS, &pf->state)) {
 		skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
 		pf->ptp_tx_skb = skb_get(skb);
 	} else {