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Date: Tue, 21 Dec 2004 23:58:31 +0100
From: Francois Romieu <romieu@fr.zoreil.com>
To: Matt Mackall <mpm@selenic.com>
Cc: Mark Broadbent <markb@wetlettuce.com>, linux-kernel@vger.kernel.org,
       netdev@oss.sgi.com
Subject: Re: Lockup with 2.6.9-ac15 related to netconsole
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Matt Mackall <mpm@selenic.com> :
[...]
> I think it's the promiscuous mode message itself that's the problem

Yes. dev_mc_add takes dev->xmit_lock and the game is over.

Marc, if the patch below happens to work, it should not drop messages
like the previous one (it is an ugly short-term suggestion).

--- net/core/netpoll.c	2004-12-21 13:09:51.000000000 +0100
+++ net/core/netpoll.c	2004-12-21 23:35:25.000000000 +0100
@@ -22,6 +22,7 @@
 #include <net/tcp.h>
 #include <net/udp.h>
 #include <asm/unaligned.h>
+#include <net/pkt_sched.h>
 
 /*
  * We maintain a small pool of fully-sized skbs, to make sure the
@@ -184,11 +187,19 @@ void netpoll_send_skb(struct netpoll *np
 
 repeat:
 	if(!np || !np->dev || !netif_running(np->dev)) {
 		__kfree_skb(skb);
 		return;
 	}
 
-	spin_lock(&np->dev->xmit_lock);
+	while (!spin_trylock(&np->dev->xmit_lock)) {
+		if (np->dev->xmit_lock_owner == smp_processor_id()) {
+			struct Qdisc *q = dev->qdisc;
+
+			q->ops->enqueue(skb, q);
+			return;
+		}
+	}
+
 	np->dev->xmit_lock_owner = smp_processor_id();
 
 	/*