net: xilinx: axienet: Enqueue Tx packets in dql before dmaengine starts

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@amd.com>
Link: https://patch.msgid.link/20241030062533.2527042-2-suraj.gupta2@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index d940853acc0b637e3126c9a2e1d1a9e2464af011..1fcbcaa85ebdb4787457c0cdaec4112dee4c4a84 100644 (file)
--- 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: