netdev - [PATCH net-next v2 2/3] r8169: replace dma_rmb with READ_ONCE in rtl

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Date:   Sun, 19 Apr 2020 20:15:29 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next v2 2/3] r8169: replace dma_rmb with READ_ONCE in
 rtl_rx

We want to ensure that desc->opts1 is read before desc->opts2.
This doesn't require a full compiler barrier. READ_ONCE provides
the ordering guarantee we need.

Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index dd6113fd7..2fc65aca3 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -1548,7 +1548,7 @@ static inline u32 rtl8169_tx_vlan_tag(struct sk_buff *skb)
 
 static void rtl8169_rx_vlan_tag(struct RxDesc *desc, struct sk_buff *skb)
 {
-	u32 opts2 = le32_to_cpu(desc->opts2);
+	u32 opts2 = le32_to_cpu(READ_ONCE(desc->opts2));
 
 	if (opts2 & RxVlanTag)
 		__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), swab16(opts2 & 0xffff));
@@ -4490,16 +4490,11 @@ static int rtl_rx(struct net_device *dev, struct rtl8169_private *tp, u32 budget
 		struct RxDesc *desc = tp->RxDescArray + entry;
 		u32 status;
 
-		status = le32_to_cpu(desc->opts1);
+		/* Use READ_ONCE to order descriptor field reads */
+		status = le32_to_cpu(READ_ONCE(desc->opts1));
 		if (status & DescOwn)
 			break;
 
-		/* This barrier is needed to keep us from reading
-		 * any other fields out of the Rx descriptor until
-		 * we know the status of DescOwn
-		 */
-		dma_rmb();
-
 		if (unlikely(status & RxRES)) {
 			netif_info(tp, rx_err, dev, "Rx ERROR. status = %08x\n",
 				   status);
-- 
2.26.1