Re: [PATCH] ethernet:arc: Fix racing of TX ring buffer

[Francois Romieu <romieu-W8zweXLXuWQS+FvcfC7Uqw@public.gmane.org>]

Shuyu Wei <wsy2220-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> :
[...]
> I still have a question, is it possible that tx_clean() run
> between   priv->tx_buff[*txbd_curr].skb = skb   and   dma_wmb()?

A (previous) run can take place after priv->tx_buff[*txbd_curr].skb and
before *info = cpu_to_le32(FOR_EMAC | FIRST_OR_LAST_MASK | len).

So, yes, the driver must check in arc_emac_tx_clean() that 1) either
txbd_dirty != txbd_curr or 2) "info" is not consistent with a still-not-used
status word. Please be patient with me and get rid of the useless "i"

diff --git a/drivers/net/ethernet/arc/emac_main.c b/drivers/net/ethernet/arc/emac_main.c
index a3a9392..337ea3b 100644
--- a/drivers/net/ethernet/arc/emac_main.c
+++ b/drivers/net/ethernet/arc/emac_main.c
@@ -153,9 +153,8 @@ static void arc_emac_tx_clean(struct net_device *ndev)
 {
 	struct arc_emac_priv *priv = netdev_priv(ndev);
 	struct net_device_stats *stats = &ndev->stats;
-	unsigned int i;
 
-	for (i = 0; i < TX_BD_NUM; i++) {
+	while (priv->txbd_dirty != priv->txbd_curr) {
 		unsigned int *txbd_dirty = &priv->txbd_dirty;
 		struct arc_emac_bd *txbd = &priv->txbd[*txbd_dirty];
 		struct buffer_state *tx_buff = &priv->tx_buff[*txbd_dirty];

-- 
Ueimor