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Date: Tue, 31 Jan 2012 00:16:41 +0100 From: Francois Romieu <romieu@...zoreil.com> To: netdev@...r.kernel.org Cc: David Miller <davem@...emloft.net>, Eric Dumazet <eric.dumazet@...il.com>, Michał Mirosław <mirqus@...il.com>, Hayes Wang <hayeswang@...ltek.com> Subject: [PATCH] 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@...zoreil.com> Cc: Eric Dumazet <eric.dumazet@...il.com> Cc: Hayes Wang <hayeswang@...ltek.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)) { -- 1.7.6.5 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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