netdev - [PATCH net-next] r8169: use READ_ONCE in rtl_tx_slots

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Date:   Wed, 11 Nov 2020 22:14:27 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next] r8169: use READ_ONCE in rtl_tx_slots_avail

tp->dirty_tx and tp->cur_tx may be changed by a racing rtl_tx() or
rtl8169_start_xmit(). Use READ_ONCE() to annotate the races and ensure
that the compiler doesn't use cached values.

Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/ethernet/realtek/r8169_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index aa6f8b16d..641c94a46 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4144,7 +4144,8 @@ static bool rtl8169_tso_csum_v2(struct rtl8169_private *tp,
 static bool rtl_tx_slots_avail(struct rtl8169_private *tp,
 			       unsigned int nr_frags)
 {
-	unsigned int slots_avail = tp->dirty_tx + NUM_TX_DESC - tp->cur_tx;
+	unsigned int slots_avail = READ_ONCE(tp->dirty_tx) + NUM_TX_DESC
+					- READ_ONCE(tp->cur_tx);
 
 	/* A skbuff with nr_frags needs nr_frags+1 entries in the tx queue */
 	return slots_avail > nr_frags;
-- 
2.29.2