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

[Cunhao Lu]

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. Account the frame as dropped and report the error. The
-ENOMEM and -EBUSY paths have already consumed the skb; explicitly free
it on -EINVAL, where ownership remains with the caller.

Fixes: b6661d73290c ("can: rockchip_canfd: add TX PATH")
Cc: stable at vger.kernel.org
Signed-off-by: Cunhao Lu <1579567540 at qq.com>
---
 drivers/net/can/rockchip/rockchip_canfd-tx.c | 14 ++++++++++++--
 1 file changed, 12 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..d2cbe25c46d6 100644
--- a/drivers/net/can/rockchip/rockchip_canfd-tx.c
+++ b/drivers/net/can/rockchip/rockchip_canfd-tx.c
@@ -125,8 +125,18 @@ 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) {
+		if (err == -EINVAL)
+			dev_kfree_skb_any(skb);
+
+		ndev->stats.tx_dropped++;
+		if (net_ratelimit())
+			netdev_err(ndev, "%s: failed to put echo skb: %pe\n",
+				   __func__, ERR_PTR(err));
+
+		return NETDEV_TX_OK;
+	}
+	netdev_sent_queue(priv->ndev, frame_len);
 
 	WRITE_ONCE(priv->tx_head, priv->tx_head + 1);
 

-- 
2.34.1