From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PLEASE REVERT] "Add a WARN_ON_ONCE" at
 net/sched/sch_generic.c:
Date: Tue, 27 May 2008 06:14:42 -0700 (PDT)
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From: Komuro <komurojun-mbn@nifty.com>
Date: Tue, 27 May 2008 21:34:24 +0900

> I think the transmit timeout indicates 
> that the cable is not connected or the irq is conflict.

The MAC of the chip transmits and ACKs the packet in the hardware even
if the link is down.  The packet is simply dropped.

Also, when the link goes down, the driver should mark the device as
such.  In such a state, the generic networking does not pass new
packets to the driver.

Therefore, transmit timeouts in this case are a hardware
or driver error.

If there is an IRQ issue, that is an error that'd we would like to
have as much information as possible to diagnose.  So the warning is
still entirely appropriate.

I sense that you are seeing this warning triggered, and if so I
would suggest that you investigate it fully as it should not be
happening under normal circumstances.