sfc: lock TX queues when calling netif_device_detach()

The assertion of netif_device_present() at the top of
efx_hard_start_xmit() may fail if we don't do this.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/efx.c

@@ -2279,7 +2279,7 @@ int efx_reset(struct efx_nic *efx, enum reset_type method)
 	netif_info(efx, drv, efx->net_dev, "resetting (%s)\n",
 		   RESET_TYPE(method));
 
-	netif_device_detach(efx->net_dev);
+	efx_device_detach_sync(efx);
 	efx_reset_down(efx, method);
 
 	rc = efx->type->reset(efx, method);
@@ -2758,7 +2758,7 @@ static int efx_pm_freeze(struct device *dev)
 	if (efx->state != STATE_DISABLED) {
 		efx->state = STATE_UNINIT;
 
-		netif_device_detach(efx->net_dev);
+		efx_device_detach_sync(efx);
 
 		efx_stop_all(efx);
 		efx_stop_interrupts(efx, false);

drivers/net/ethernet/sfc/efx.h

@@ -163,4 +163,17 @@ extern void efx_link_status_changed(struct efx_nic *efx);
 extern void efx_link_set_advertising(struct efx_nic *efx, u32);
 extern void efx_link_set_wanted_fc(struct efx_nic *efx, u8);
 
+static inline void efx_device_detach_sync(struct efx_nic *efx)
+{
+	struct net_device *dev = efx->net_dev;
+
+	/* Lock/freeze all TX queues so that we can be sure the
+	 * TX scheduler is stopped when we're done and before
+	 * netif_device_present() becomes false.
+	 */
+	netif_tx_lock(dev);
+	netif_device_detach(dev);
+	netif_tx_unlock(dev);
+}
+
 #endif /* EFX_EFX_H */

drivers/net/ethernet/sfc/selftest.c

@@ -722,7 +722,7 @@ int efx_selftest(struct efx_nic *efx, struct efx_self_tests *tests,
 	/* Detach the device so the kernel doesn't transmit during the
 	 * loopback test and the watchdog timeout doesn't fire.
 	 */
-	netif_device_detach(efx->net_dev);
+	efx_device_detach_sync(efx);
 
 	if (efx->type->test_chip) {
 		rc_reset = efx->type->test_chip(efx, tests);