Actually this is a known bug. Ive had a patch for a long time. Only
problem is noone cares about CONFIG_NET_HW_FLOWCONTROL anymore.
Summary, apply the patch for legacy reasons. The patch i had is slightly
different; but this one looks sane too.
cheers,
jamal
On Mon, 2003-09-29 at 15:37, Andrew Morton wrote:
> Begin forwarded message:
>
> Date: Mon, 29 Sep 2003 14:08:54 +0200
> From: dfages@xxxxxxxxxx
> To: linux-kernel@xxxxxxxxxxxxxxx
> Subject: [BUG/PATCH] CONFIG_NET_HW_FLOWCONTROL and SMP
>
>
>
>
> Hi,
> by testing the CONFIG_NET_HW_FLOWCONTROL (NIC Hardware throttling) on
> a SMP system, I found a bug in net/core/dev.c : the netdev_dropping
> variable can be set to a negative value (the result is that a CPU can
> be locked in "throttle" state).
> This bug seems to exist in 2.4 and in 2.6 kernels.
>
> Here's a typical scenario :
>
> - Throttling --> (CPU 0)queue->throttle==1 && (CPU 1)queue->throttle==1
> && netdev_dropping == 2
> - 1st packet Unthrottle ( in net_rx_action() ), received by CPU 0
> --> (CPU 0)queue->throttle==1 && (CPU 1)queue->throttle==1
> && netdev_dropping == 1
> - 2nd packet Unthrottle ( in net_rx_action() ), received by CPU 0
> --> (CPU 0)queue->throttle==0 && (CPU 1)queue->throttle==1
> && netdev_dropping == 0
> - 3nd packet Unthrottle ( in net_rx_action() ), received by CPU 1
> --> (CPU 0)queue->throttle==0 && (CPU 1)queue->throttle==0
> && netdev_dropping == -1
>
> and so on...
>
> The problem is that the (CPU)queue->throttle should be set to zero every
> time the netdev_dropping variable is decremented.
>
>
> Here's a patch for the 2.4.19 kernel (tested with success) :
>
> --- linux-2.4.19/net/core/dev.c.orig Mon Sep 29 12:49:14 2003
> +++ linux-2.4.19/net/core/dev.c Tue Sep 23 18:35:35 2003
> @@ -1519,8 +1519,8 @@
>
> #ifdef CONFIG_NET_HW_FLOWCONTROL
> if (queue->throttle && queue->input_pkt_queue.qlen < no_cong_thresh ) {
> + queue->throttle = 0;
> if (atomic_dec_and_test(&netdev_dropping)) {
> - queue->throttle = 0;
> netdev_wakeup();
> goto softnet_break;
> }
>
>
>
>
> I haven't done a patch for 2.4.22 (as we currently use 2.4.19) but the same
> modification should be applied around lines 1572 to 1577 of net/core/dev.c
>
> For 2.6.0-test5, the lines to modified are arount 1631 to 1637.
>
> Regards,
> ---
> Daniel FAGES
> ARKOON Network Security http://www.arkoon.net
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>
>
>
|