Currently, when device mtu is updated, vmxnet3 updates netdev mtu, quiesces
the device and then reactivates it for the ESXi to know about the new mtu.
So, technically the OS stack can start using the new mtu before ESXi knows
about the new mtu.

This can lead to issues for TSO packets which use mss as per the new mtu
configured. This patch fixes this issue by moving the mtu write after
device quiesce.

Fixes: d1a890fa37f2 ("net: VMware virtual Ethernet NIC driver: vmxnet3")
Signed-off-by: Ronak Doshi <ronak.doshi@broadcom.com>
Acked-by: Guolin Yang <guolin.yang@broadcom.com>
---
 drivers/net/vmxnet3/vmxnet3_drv.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/vmxnet3/vmxnet3_drv.c b/drivers/net/vmxnet3/vmxnet3_drv.c
index 3df6aabc7e33..58027e82de88 100644
--- a/drivers/net/vmxnet3/vmxnet3_drv.c
+++ b/drivers/net/vmxnet3/vmxnet3_drv.c
@@ -3607,8 +3607,6 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
 	struct vmxnet3_adapter *adapter = netdev_priv(netdev);
 	int err = 0;
 
-	WRITE_ONCE(netdev->mtu, new_mtu);
-
 	/*
 	 * Reset_work may be in the middle of resetting the device, wait for its
 	 * completion.
@@ -3619,6 +3617,7 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
 	if (netif_running(netdev)) {
 		vmxnet3_quiesce_dev(adapter);
 		vmxnet3_reset_dev(adapter);
+		WRITE_ONCE(netdev->mtu, new_mtu);
 
 		/* we need to re-create the rx queue based on the new mtu */
 		vmxnet3_rq_destroy_all(adapter);
@@ -3638,6 +3637,8 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
 				   "Closing it\n", err);
 			goto out;
 		}
+	} else {
+		WRITE_ONCE(netdev->mtu, new_mtu);
 	}
 
 out:
-- 
2.45.2

On Tue, 13 May 2025 21:02:40 +0000 Ronak Doshi wrote:
> @@ -3619,6 +3617,7 @@ vmxnet3_change_mtu(struct net_device *netdev, int new_mtu)
>  	if (netif_running(netdev)) {
>  		vmxnet3_quiesce_dev(adapter);
>  		vmxnet3_reset_dev(adapter);
> +		WRITE_ONCE(netdev->mtu, new_mtu);
>  
>  		/* we need to re-create the rx queue based on the new mtu */
>  		vmxnet3_rq_destroy_all(adapter);

Maybe a nit pick but wouldn't it make the most sense to place the write
after all teardown related code? So after vmxnet3_rq_destroy_all() ?