bcmgenet_netif_stop() and the Wake-on-LAN branch of bcmgenet_suspend()
both disable the Tx queues first and stop Tx NAPI several steps later. A
completion in flight calls netif_tx_wake_queue() in between, and nothing
stops the queue again, so a transmit can reach the rings after they have
been freed.

Close is safe because dev_deactivate_many() stops the qdisc first.
bcmgenet_suspend() does not, so stop Tx NAPI before the queues on both
paths.

KASAN on a Raspberry Pi CM4, driven from an MTU change because suspend
freezes user space before the callback runs:

  BUG: KASAN: use-after-free in bcmgenet_xmit+0x17f8/0x2258
  Write of size 8 at addr ffffff8055844a68 by task ksoftirqd/0/14
   bcmgenet_xmit+0x17f8/0x2258
   dev_hard_start_xmit+0x13c/0x588
   sch_direct_xmit+0x108/0x340
   __dev_queue_xmit+0x1190/0x3848

Fixes: 254f3239dd07 ("net: bcmgenet: revise suspend/resume")
Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
---
Found this, while I was preparing my jumbo frame series for genet.
The MTU change in my test comes from that series and is not in tree
yet.

v1: https://lore.kernel.org/netdev/20260921124435.974581-1-nb@tipi-net.de/

v2: also reorder the Wake-on-LAN branch of bcmgenet_suspend() (Clashiko)

 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index b916080f4ff1..ca62041efecd 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -3441,6 +3441,8 @@ static void bcmgenet_netif_stop(struct net_device *dev, bool stop_phy)
 {
 	struct bcmgenet_priv *priv = netdev_priv(dev);
 
+	/* Stop completion polling before it can wake a stopped queue */
+	bcmgenet_disable_tx_napi(priv);
 	netif_tx_disable(dev);
 
 	/* Disable MAC receive */
@@ -3455,7 +3457,6 @@ static void bcmgenet_netif_stop(struct net_device *dev, bool stop_phy)
 	/* Disable MAC transmit. TX DMA disabled must be done before this */
 	umac_enable_set(priv, CMD_TX_EN, false);
 
-	bcmgenet_disable_tx_napi(priv);
 	bcmgenet_disable_rx_napi(priv);
 	bcmgenet_intr_disable(priv);
 
@@ -4320,6 +4321,8 @@ static int bcmgenet_suspend(struct device *d)
 	netif_device_detach(dev);
 
 	if (device_may_wakeup(d) && priv->wolopts) {
+		/* Stop completion polling before it can wake a stopped queue */
+		bcmgenet_disable_tx_napi(priv);
 		netif_tx_disable(dev);
 
 		/* Suspend non-wake Rx data flows */
@@ -4348,7 +4351,6 @@ static int bcmgenet_suspend(struct device *d)
 			netdev_warn(priv->dev,
 				    "Timed out while disabling TX DMA\n");
 
-		bcmgenet_disable_tx_napi(priv);
 		bcmgenet_disable_rx_napi(priv);
 		disable_irq(priv->irq1);
 		bcmgenet_tx_reclaim_all(dev);
-- 
2.53.0