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Subject[ 69/82] r8169: fix early queue wake-up.
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Francois Romieu <romieu@fr.zoreil.com>

[ Upstream commit ae1f23fb433ac0aaff8aeaa5a7b14348e9aa8277 ]

With infinite gratitude to Eric Dumazet for allowing me to identify
the error.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/ethernet/realtek/r8169.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
index 5104d76..5f3fa32 100644
--- a/drivers/net/ethernet/realtek/r8169.c
+++ b/drivers/net/ethernet/realtek/r8169.c
@@ -5561,7 +5561,18 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
RTL_W8(TxPoll, NPQ);

if (TX_BUFFS_AVAIL(tp) < MAX_SKB_FRAGS) {
+ /* Avoid wrongly optimistic queue wake-up: rtl_tx thread must
+ * not miss a ring update when it notices a stopped queue.
+ */
+ smp_wmb();
netif_stop_queue(dev);
+ /* Sync with rtl_tx:
+ * - publish queue status and cur_tx ring index (write barrier)
+ * - refresh dirty_tx ring index (read barrier).
+ * May the current thread have a pessimistic view of the ring
+ * status and forget to wake up queue, a racing rtl_tx thread
+ * can't.
+ */
smp_mb();
if (TX_BUFFS_AVAIL(tp) >= MAX_SKB_FRAGS)
netif_wake_queue(dev);
@@ -5663,6 +5674,13 @@ static void rtl8169_tx_interrupt(struct net_device *dev,

if (tp->dirty_tx != dirty_tx) {
tp->dirty_tx = dirty_tx;
+ /* Sync with rtl8169_start_xmit:
+ * - publish dirty_tx ring index (write barrier)
+ * - refresh cur_tx ring index and queue status (read barrier)
+ * May the current thread miss the stopped queue condition,
+ * a racing xmit thread can only have a right view of the
+ * ring status.
+ */
smp_mb();
if (netif_queue_stopped(dev) &&
(TX_BUFFS_AVAIL(tp) >= MAX_SKB_FRAGS)) {



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