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

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Date:	Sun, 15 May 2016 20:07:34 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Shuyu Wei <wsy2220@...il.com>
Cc:	wxt@...k-chips.com, davem@...emloft.net, heiko@...ech.de,
	linux-rockchip@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH] ethernet:arc: Fix racing of TX ring buffer

Shuyu Wei <wsy2220@...il.com> :
[...]
> 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