FAILED: patch "[PATCH] net: axienet: add missing memory barriers" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 95978df6fa328df619c15312e65ece469c2be2d2 Mon Sep 17 00:00:00 2001
From: Robert Hancock <robert.hancock@xxxxxxxxxx>
Date: Tue, 18 Jan 2022 15:41:27 -0600
Subject: [PATCH] net: axienet: add missing memory barriers

This driver was missing some required memory barriers:

Use dma_rmb to ensure we see all updates to the descriptor after we see
that an entry has been completed.

Use wmb and rmb to avoid stale descriptor status between the TX path and
TX complete IRQ path.

Fixes: 8a3b7a252dca9 ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
Signed-off-by: Robert Hancock <robert.hancock@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 53ff38cbc37b..fb486a457c76 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -632,6 +632,8 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
 		if (nr_bds == -1 && !(status & XAXIDMA_BD_STS_COMPLETE_MASK))
 			break;
 
+		/* Ensure we see complete descriptor update */
+		dma_rmb();
 		phys = desc_get_phys_addr(lp, cur_p);
 		dma_unmap_single(ndev->dev.parent, phys,
 				 (cur_p->cntrl & XAXIDMA_BD_CTRL_LENGTH_MASK),
@@ -645,8 +647,10 @@ static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
 		cur_p->app1 = 0;
 		cur_p->app2 = 0;
 		cur_p->app4 = 0;
-		cur_p->status = 0;
 		cur_p->skb = NULL;
+		/* ensure our transmit path and device don't prematurely see status cleared */
+		wmb();
+		cur_p->status = 0;
 
 		if (sizep)
 			*sizep += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
@@ -704,6 +708,9 @@ static inline int axienet_check_tx_bd_space(struct axienet_local *lp,
 					    int num_frag)
 {
 	struct axidma_bd *cur_p;
+
+	/* Ensure we see all descriptor updates from device or TX IRQ path */
+	rmb();
 	cur_p = &lp->tx_bd_v[(lp->tx_bd_tail + num_frag) % lp->tx_bd_num];
 	if (cur_p->status & XAXIDMA_BD_STS_ALL_MASK)
 		return NETDEV_TX_BUSY;
@@ -843,6 +850,8 @@ static void axienet_recv(struct net_device *ndev)
 
 		tail_p = lp->rx_bd_p + sizeof(*lp->rx_bd_v) * lp->rx_bd_ci;
 
+		/* Ensure we see complete descriptor update */
+		dma_rmb();
 		phys = desc_get_phys_addr(lp, cur_p);
 		dma_unmap_single(ndev->dev.parent, phys, lp->max_frm_size,
 				 DMA_FROM_DEVICE);