From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Fw: [BUG/PATCH] CONFIG_NET_HW_FLOWCONTROL and SMP Date: Mon, 29 Sep 2003 12:37:34 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <20030929123734.5bd97a47.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: dfages@arkoon.net Return-path: To: netdev@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Begin forwarded message: Date: Mon, 29 Sep 2003 14:08:54 +0200 From: dfages@arkoon.net To: linux-kernel@vger.kernel.org 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