r8169: fix early Tx queue wake-up.

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

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Hayes Wang <hayeswang@realtek.com>
---
 I'll address Michał's remarks and add unrelated comments after some sleep.

 drivers/net/ethernet/realtek/r8169.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

Le mardi 31 janvier 2012 à 00:16 +0100, Francois Romieu a écrit :
> With infinite gratitude to Eric Dumazet for allowing me to identify
> the error.
> 
> Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Hayes Wang <hayeswang@realtek.com>
> ---
>  I'll address Michał's remarks and add unrelated comments after some sleep.
> 
>  drivers/net/ethernet/realtek/r8169.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
> index d039d39..f994606 100644
> --- a/drivers/net/ethernet/realtek/r8169.c
> +++ b/drivers/net/ethernet/realtek/r8169.c
> @@ -5559,7 +5559,18 @@ static netdev_tx_t rtl8169_start_xmit(struct sk_buff *skb,
>  	mmiowb();
>  
>  	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);
> @@ -5659,6 +5670,14 @@ static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp)
>  
>  	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)) {


Thanks !

Acked-by: Eric Dumazet <eric.dumazet@gmail.com>



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