[PATCH net 1/2] net: xilinx: axienet: Enqueue Tx packets in dql before dmaengine starts

[Suraj Gupta]

Enqueue packets in dql after dma engine starts causes race condition.
Tx transfer starts once dma engine is started and may execute dql dequeue
in completion before it gets queued. It results in following kernel crash
while running iperf stress test:

kernel BUG at lib/dynamic_queue_limits.c:99!
<snip>
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
pc : dql_completed+0x238/0x248
lr : dql_completed+0x3c/0x248

Call trace:
  dql_completed+0x238/0x248
  axienet_dma_tx_cb+0xa0/0x170
  xilinx_dma_do_tasklet+0xdc/0x290
  tasklet_action_common+0xf8/0x11c
  tasklet_action+0x30/0x3c
  handle_softirqs+0xf8/0x230
<snip>

Start dmaengine after enqueue in dql fixes the crash.

Fixes: 6a91b846af85 ("net: axienet: Introduce dmaengine support")
Signed-off-by: Suraj Gupta <suraj.gupta2 at amd.com>
---
 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 273ec5f70005..0f4b02fe6f85 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -924,13 +924,13 @@ axienet_start_xmit_dmaengine(struct sk_buff *skb, struct net_device *ndev)
 	skbuf_dma->sg_len = sg_len;
 	dma_tx_desc->callback_param = lp;
 	dma_tx_desc->callback_result = axienet_dma_tx_cb;
-	dmaengine_submit(dma_tx_desc);
-	dma_async_issue_pending(lp->tx_chan);
 	txq = skb_get_tx_queue(lp->ndev, skb);
 	netdev_tx_sent_queue(txq, skb->len);
 	netif_txq_maybe_stop(txq, CIRC_SPACE(lp->tx_ring_head, lp->tx_ring_tail, TX_BD_NUM_MAX),
 			     MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS);
 
+	dmaengine_submit(dma_tx_desc);
+	dma_async_issue_pending(lp->tx_chan);
 	return NETDEV_TX_OK;
 
 xmit_error_unmap_sg:
-- 
2.25.1