[PATCH net v3 4/4] gve: Fix link flap after ethtool ops

[Harshitha Ramamurthy <hramamurthy@google.com>]

From: Pin-yen Lin <treapking@google.com>

When modifying device features via ethtool, GVE causes a short link-down
after the ethtool command completes, which can break scripts that use
the network interface right after the ethtool command.

This issue was discovered and actually triggered by the
drivers/net/ping.py selftest. Modifying checksum offload features via
ethtool caused a transient carrier drop ("Lost carrier", DHCP lease lost),
causing the immediate ping invocation to fail.

Fix it by calling gve_turnup_and_check_status() in gve_queues_start()
instead of deferring the link status update to the service task, so the
carrier status is updated synchronously before returning to userspace.

This change was tested using the DQO RDA queue format.

Cc: stable@vger.kernel.org
Fixes: 3b7cc73628ff ("gve: Use link status register to report link status")
Signed-off-by: Pin-yen Lin <treapking@google.com>
Reviewed-by: Joshua Washington <joshwash@google.com>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
---

Changes in v3:
- Retitled from "gve: Make ethtool config changes synchronous"
- Fix the Fixes tag
- Refined the commit message

 drivers/net/ethernet/google/gve/gve_main.c | 61 +++++++++++-----------
 1 file changed, 30 insertions(+), 31 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 52c152a986eb..e2a016f4430a 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1423,6 +1423,35 @@ static void gve_queues_stop(struct gve_priv *priv)
 	gve_rx_stop_rings(priv, priv->rx_cfg.num_queues);
 }
 
+static void gve_handle_link_status(struct gve_priv *priv)
+{
+	bool link_up;
+
+	if (!gve_get_napi_enabled(priv))
+		return;
+
+	link_up = READ_ONCE(priv->link_up);
+	if (link_up == netif_carrier_ok(priv->dev))
+		return;
+
+	if (link_up) {
+		netdev_info(priv->dev, "Device link is up.\n");
+		netif_carrier_on(priv->dev);
+	} else {
+		netdev_info(priv->dev, "Device link is down.\n");
+		netif_carrier_off(priv->dev);
+	}
+}
+
+static void gve_turnup_and_check_status(struct gve_priv *priv)
+{
+	const struct gve_ctrl_ops *ops = priv->ctrl_ops;
+
+	gve_turnup(priv);
+	ops->report_link_status(priv);
+	gve_handle_link_status(priv);
+}
+
 /* The passed-in queue memory is stored into priv and the queues are made live.
  * No memory is allocated. Passed-in memory is freed on errors.
  */
@@ -1486,8 +1515,7 @@ static int gve_queues_start(struct gve_priv *priv,
 			  round_jiffies(jiffies +
 				msecs_to_jiffies(priv->stats_report_timer_period)));
 
-	gve_turnup(priv);
-	queue_work(priv->gve_wq, &priv->service_task);
+	gve_turnup_and_check_status(priv);
 	priv->interface_up_cnt++;
 	return 0;
 
@@ -1562,26 +1590,6 @@ static int gve_close(struct net_device *dev)
 	return err;
 }
 
-static void gve_handle_link_status(struct gve_priv *priv)
-{
-	bool link_up;
-
-	if (!gve_get_napi_enabled(priv))
-		return;
-
-	link_up = READ_ONCE(priv->link_up);
-	if (link_up == netif_carrier_ok(priv->dev))
-		return;
-
-	if (link_up) {
-		netdev_info(priv->dev, "Device link is up.\n");
-		netif_carrier_on(priv->dev);
-	} else {
-		netdev_info(priv->dev, "Device link is down.\n");
-		netif_carrier_off(priv->dev);
-	}
-}
-
 static int gve_configure_rings_xdp(struct gve_priv *priv,
 				   u16 num_xdp_rings)
 {
@@ -2056,15 +2064,6 @@ static void gve_turnup(struct gve_priv *priv)
 	gve_set_napi_enabled(priv);
 }
 
-static void gve_turnup_and_check_status(struct gve_priv *priv)
-{
-	const struct gve_ctrl_ops *ops = priv->ctrl_ops;
-
-	gve_turnup(priv);
-	ops->report_link_status(priv);
-	gve_handle_link_status(priv);
-}
-
 static struct gve_notify_block *gve_get_tx_notify_block(struct gve_priv *priv,
 							unsigned int txqueue)
 {
-- 
2.56.0.257.gf7497c7d27-goog