[PATCH v4 1/3] can: rockchip_canfd: prevent TX stall on echo skb failure

rkcanfd_start_xmit() advances tx_head and requests transmission even when
can_put_echo_skb() fails. This creates a pending TX entry without the echo
skb that the RXSTX completion path needs to match the self-received frame.
The entry cannot be completed, and the netdev TX queue can remain stopped
after the two-entry software FIFO fills.

Do not advance tx_head or request transmission if the echo skb cannot be
installed, and account the frame as dropped.

This depends on the standalone can_put_echo_skb() ownership fix. It makes
the remaining -EINVAL path consume the skb and was posted at:

Link: https://lore.kernel.org/linux-can/[email protected]
Fixes: b6661d73290c ("can: rockchip_canfd: add TX PATH")
Cc: [email protected]
Signed-off-by: Cunhao Lu <[email protected]>
---
Changes in v4:
- Split the can_put_echo_skb() ownership fix into a standalone patch.
- Rely on the standalone patch for error-path skb ownership.
- Drop the redundant error message from rkcanfd_start_xmit().
---
 drivers/net/can/rockchip/rockchip_canfd-tx.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/can/rockchip/rockchip_canfd-tx.c b/drivers/net/can/rockchip/rockchip_canfd-tx.c
index 12200dcfd338..b1954b72560c 100644
--- a/drivers/net/can/rockchip/rockchip_canfd-tx.c
+++ b/drivers/net/can/rockchip/rockchip_canfd-tx.c
@@ -125,8 +125,11 @@ netdev_tx_t rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 
 	frame_len = can_skb_get_frame_len(skb);
 	err = can_put_echo_skb(skb, ndev, tx_head, frame_len);
-	if (!err)
-		netdev_sent_queue(priv->ndev, frame_len);
+	if (err) {
+		ndev->stats.tx_dropped++;
+		return NETDEV_TX_OK;
+	}
+	netdev_sent_queue(priv->ndev, frame_len);
 
 	WRITE_ONCE(priv->tx_head, priv->tx_head + 1);
 

-- 
2.34.1