[PATCH net v3 4/5] gve: Fix link flap after ethtool ops

[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() to
update the carrier status synchronously before returning to userspace,
and move the device_status register read into gve_handle_link_status()
so callers always check the current link status when NAPI is enabled.

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>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
---

Changes in v3:
- Retitled from "gve: Make ethtool config changes synchronous"
- Read device_status inside gve_handle_link_status()
- Fix the Fixes tag
- Refined the commit message

 drivers/net/ethernet/google/gve/gve_main.c | 63 +++++++++++-----------
 1 file changed, 31 insertions(+), 32 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 5bd6549e99b2..f1eb0c6e1f9b 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1442,6 +1442,34 @@ static void gve_queues_mem_remove(struct gve_priv *priv)
 	gve_queues_mem_free(priv, &tx_alloc_cfg, &rx_alloc_cfg);
 }
 
+static void gve_handle_link_status(struct gve_priv *priv)
+{
+	bool link_status;
+	u32 status;
+
+	if (!gve_get_napi_enabled(priv))
+		return;
+
+	status = ioread32be(&priv->reg_bar0->device_status);
+	link_status = GVE_DEVICE_STATUS_LINK_STATUS_MASK & status;
+	if (link_status == netif_carrier_ok(priv->dev))
+		return;
+
+	if (link_status) {
+		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)
+{
+	gve_turnup(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.
  */
@@ -1506,8 +1534,7 @@ 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;
 
@@ -1599,23 +1626,6 @@ static int gve_close(struct net_device *dev)
 	return 0;
 }
 
-static void gve_handle_link_status(struct gve_priv *priv, bool link_status)
-{
-	if (!gve_get_napi_enabled(priv))
-		return;
-
-	if (link_status == netif_carrier_ok(priv->dev))
-		return;
-
-	if (link_status) {
-		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)
 {
@@ -1634,7 +1644,6 @@ static int gve_set_xdp(struct gve_priv *priv, struct bpf_prog *prog,
 {
 	struct bpf_prog *old_prog;
 	int err = 0;
-	u32 status;
 
 	old_prog = READ_ONCE(priv->xdp_prog);
 	if (!netif_running(priv->dev)) {
@@ -1661,8 +1670,7 @@ static int gve_set_xdp(struct gve_priv *priv, struct bpf_prog *prog,
 		bpf_prog_put(old_prog);
 
 out:
-	status = ioread32be(&priv->reg_bar0->device_status);
-	gve_handle_link_status(priv, GVE_DEVICE_STATUS_LINK_STATUS_MASK & status);
+	gve_handle_link_status(priv);
 	return err;
 }
 
@@ -2090,15 +2098,6 @@ static void gve_turnup(struct gve_priv *priv)
 	gve_set_napi_enabled(priv);
 }
 
-static void gve_turnup_and_check_status(struct gve_priv *priv)
-{
-	u32 status;
-
-	gve_turnup(priv);
-	status = ioread32be(&priv->reg_bar0->device_status);
-	gve_handle_link_status(priv, GVE_DEVICE_STATUS_LINK_STATUS_MASK & status);
-}
-
 static struct gve_notify_block *gve_get_tx_notify_block(struct gve_priv *priv,
 							unsigned int txqueue)
 {
@@ -2427,7 +2426,7 @@ static void gve_service_task(struct work_struct *work)
 	gve_handle_status(priv, status);
 
 	gve_handle_reset(priv);
-	gve_handle_link_status(priv, GVE_DEVICE_STATUS_LINK_STATUS_MASK & status);
+	gve_handle_link_status(priv);
 }
 
 static void gve_set_netdev_xdp_features(struct gve_priv *priv)
-- 
2.56.0.385.gd3acb90ef8-goog