mpc8349, gb ethernet, bridging

rje at rje at
Fri Apr 25 23:22:42 EST 2008

I think that I know what the immediate cause of the crash is.

In clean_tx_ring(),
GFAR_KFREE_SKBUF() is being given a NULL (0) for its skb argument

This is after a watchdog-timeout.  That timeout cause the driver to 
stop, and then restart.
The descriptior rings and the skbuffs are cleared, released, nulled.

Before anything gets put into the TX buffers, a NAPI poll causes 
clean_tx_ring() to be
called.  The check for empty vs. full ring says "FULL" (the current + 
dirty pointers (?)
are == and, for some reason, the queue is _not_ stopped), even though 
its empty.
The crash happens while processing the 1st buffer (whose zeroed status 
bits indiate it
should be reclaimed/freed).

Now ... _why_ this happens, is a good question.

I have tried bumping up the TIMEOUT value, but to no avail.
The timeout occured, and the issue happened.

Does anybody have any ideas?
Or has anybody seen anything similar?

We are running on an MCP8349E-based board.
Our base kernel and drivers were Freescale's BSP for their 8349emds 
evaluation board.
The ethernet driver is the gianfar driver from that BSP.

rje at wrote:

> Hi.
> Anybody have any idea what could cause the NETDEV WATCHDOG timeout?
> On the GB ethernet port?
> Could that happen if the other port was being overflowed?
> That watchdog timeout seems to be involved pretty much every time
> that the bridge goes down.  When the timeout occurs, the gianfar 
> driver stops
> and then (re)starts itself.
>> Hi.
>> We are having some issues regarding bridging the 2 ethernet ports of 
>> an mpc8349, and are
>> trying to determine what is going on.
>> We are attempting to daisy-chain several mpc8349-based boards via the 
>> 2 ethernet ports
>> on each 8349.  When we enable bridging for the units, we (sometimes) 
>> start seeing the following
>> on one of the interior bridge's (mostly on the root bridge) console(s):
>> NETDEV WATCHDOG: eth1 : transmit timed out
>> We then see the bridge output  messages that indicate that is is 
>> going through a topology
>> state change.
>> This situation keeps recurring.
>> At some point, the message from the bridge that it is entering a 
>> disabled state for port #2
>> (eth1) is followed by garbage (actually, it appears to be some 
>> pointers and/or memory
>> addresses printed out), and the system hangs.
>> We are using NAPI and the skbuff-recycling for the gianfar driver.
>> We use ring(s) of 32 buffers.
>> The gianfar's watchdog is set to  1Hz (once a seond ?)
>> We are not sure if/how affect things:
>> Port #1 of the 'root' bridge  is attached directly to our LAN
>> Port #1 of the 'root' bridge runs at 10 Mbs
>> Port #2 of the 'root' bridge runs at 1Gbs
>> All other ports in the chain are       1Gbs
>> We are using CAT-5 cables for all connections
>> We have an application on each bridge in the chain that periodically 
>> sends several hundred bytes
>> 'up the chain', towards its head (ie, towards our LAN).   This 
>> application is typically running
>> when the issue is seen.
>> Setting the bridge's forwarding delay to 0 and hellotime to 6,000 
>> helped, but did
>> not solve the issue.
>> ???


Sometimes I feel like a red shirt in the Star Trek episode of life.


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