linux-kernel - [PATCH AUTOSEL 5.10 077/217] r8169: use READ_ONCE in rtl_tx_slots

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Date:   Tue, 22 Dec 2020 21:14:06 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 077/217] r8169: use READ_ONCE in rtl_tx_slots_avail

From: Heiner Kallweit <hkallweit1@...il.com>

[ Upstream commit 95f3c5458dfa5856bb110e31d156e00d894d0134 ]

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>
Link: https://lore.kernel.org/r/5676fee3-f6b4-84f2-eba5-c64949a371ad@gmail.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 85d9c3e30c699..67918feed307e 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -4173,7 +4173,8 @@ 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;
-- 
2.27.0