[PATCH net-next] r8169: change wmb to smb_wmb in rtl8169_start_xmit

[PATCH net-next] r8169: change wmb to smb_wmb in rtl8169_start_xmit

[Heiner Kallweit]

A barrier is needed here to ensure that rtl_tx sees the descriptor
changes (DescOwn set) before the updated tp->cur_tx value. Else it may
wrongly assume that the transfer has been finished already. For this
purpose smp_wmb() is sufficient.

No separate barrier is needed for ordering the descriptor changes
with the MMIO doorbell write. The needed barrier is included in
the non-relaxed writel() used by rtl8169_doorbell().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index ece899be9..bb8dcdb17 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4251,8 +4251,8 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
 
 	txd_first->opts1 |= cpu_to_le32(DescOwn | FirstFrag);
 
-	/* Force all memory writes to complete before notifying device */
-	wmb();
+	/* rtl_tx needs to see descriptor changes before updated tp->cur_tx */
+	smp_wmb();
 
 	tp->cur_tx += frags + 1;
 
-- 
2.26.1

Re: [PATCH net-next] r8169: change wmb to smb_wmb in rtl8169_start_xmit

[David Miller]

From: Heiner Kallweit <hkallweit1@gmail.com>
Date: Mon, 20 Apr 2020 22:52:59 +0200

> A barrier is needed here to ensure that rtl_tx sees the descriptor
> changes (DescOwn set) before the updated tp->cur_tx value. Else it may
> wrongly assume that the transfer has been finished already. For this
> purpose smp_wmb() is sufficient.
> 
> No separate barrier is needed for ordering the descriptor changes
> with the MMIO doorbell write. The needed barrier is included in
> the non-relaxed writel() used by rtl8169_doorbell().
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>

Applied, thanks.