From: Eric Pilmore epilmore@gigaio.com
[ Upstream commit 5f7d78b2b12a9d561f48fa00bab29b40f4616dad ]
TX/RX callback handlers (ntb_netdev_tx_handler(), ntb_netdev_rx_handler()) can be called in interrupt context via the DMA framework when the respective DMA operations have completed. As such, any calls by these routines to free skb's, should use the interrupt context safe dev_kfree_skb_any() function.
Previously, these callback handlers would call the interrupt unsafe version of dev_kfree_skb(). This has not presented an issue on Intel IOAT DMA engines as that driver utilizes tasklets rather than a hard interrupt handler, like the AMD PTDMA DMA driver. On AMD systems, a kernel WARNING message is encountered, which is being issued from skb_release_head_state() due to in_hardirq() being true.
Besides the user visible WARNING from the kernel, the other symptom of this bug was that TCP/IP performance across the ntb_netdev interface was very poor, i.e. approximately an order of magnitude below what was expected. With the repair to use dev_kfree_skb_any(), kernel WARNINGs from skb_release_head_state() ceased and TCP/IP performance, as measured by iperf, was on par with expected results, approximately 20 Gb/s on AMD Milan based server. Note that this performance is comparable with Intel based servers.
Fixes: 765ccc7bc3d91 ("ntb_netdev: correct skb leak") Fixes: 548c237c0a997 ("net: Add support for NTB virtual ethernet device") Signed-off-by: Eric Pilmore epilmore@gigaio.com Reviewed-by: Dave Jiang dave.jiang@intel.com Link: https://lore.kernel.org/r/20221209000659.8318-1-epilmore@gigaio.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/ntb_netdev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/ntb_netdev.c b/drivers/net/ntb_netdev.c index 33974e7519ce..ca0053775d3f 100644 --- a/drivers/net/ntb_netdev.c +++ b/drivers/net/ntb_netdev.c @@ -140,7 +140,7 @@ static void ntb_netdev_rx_handler(struct ntb_transport_qp *qp, void *qp_data, enqueue_again: rc = ntb_transport_rx_enqueue(qp, skb, skb->data, ndev->mtu + ETH_HLEN); if (rc) { - dev_kfree_skb(skb); + dev_kfree_skb_any(skb); ndev->stats.rx_errors++; ndev->stats.rx_fifo_errors++; } @@ -195,7 +195,7 @@ static void ntb_netdev_tx_handler(struct ntb_transport_qp *qp, void *qp_data, ndev->stats.tx_aborted_errors++; }
- dev_kfree_skb(skb); + dev_kfree_skb_any(skb);
if (ntb_transport_tx_free_entry(dev->qp) >= tx_start) { /* Make sure anybody stopping the queue after this sees the new