netdev - Re: Regression in net-2.6.24?

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Message-ID: <1192159036.6889.6.camel@dell>
Date:	Thu, 11 Oct 2007 20:17:16 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"David Miller" <davem@...emloft.net>
cc:	shemminger@...ux-foundation.org, takano@...-inc.co.jp,
	"netdev" <netdev@...r.kernel.org>, ilpo.jarvinen@...sinki.fi
Subject: Re: Regression in net-2.6.24?

On Thu, 2007-10-11 at 18:14 -0700, David Miller wrote:
> +       while (1) {
> +               work_done = tg3_poll_work(tp, work_done, budget);
> +
> +               if (unlikely(tp->tg3_flags & TG3_FLAG_TX_RECOVERY_PENDING))
> +                       goto tx_recovery;
> +
> +               if (unlikely(work_done >= budget))
> +                       break;
> +
> +               if (likely(!tg3_has_work(tp))) {
> +                       struct tg3_hw_status *sblk = tp->hw_status;
> +

--> new status block DMA

> +                       if (tp->tg3_flags & TG3_FLAG_TAGGED_STATUS) {
> +                               tp->last_tag = sblk->status_tag;
> +                               rmb();
> +                       } else
> +                               sblk->status &= ~SD_STATUS_UPDATED;

We need to read the sblk->status_tag before calling tg3_has_work().  If
a new status block DMA happens in between (shown above), tp->last_tag
will get the new tag and we will end up acknowledging work that we
haven't processed.

I'll go over this some more tonight and will send a patch to refine it.
Thanks.

> +
> +                       netif_rx_complete(tp->dev, napi);
> +                       tg3_restart_ints(tp);
> +                       break;
> +               }

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