On Thu, Feb 25, 2010 at 07:53:30PM -0500, Paul Gortmaker wrote:
[...]

I was able to reproduce it on an 8641D and bisected it down to this:

-----------
commit a3bc1f11e9b867a4f49505ecac486a33af248b2e
Author: Anton Vorontsov [off-list ref]
Date:   Tue Nov 10 14:11:10 2009 +0000

    gianfar: Revive SKB recycling

Thanks for the bisect. I have a guess why tx hangs in
SMP case. Could anyone try the patch down below?

[...]

...which probably explains why you weren't seeing it on non-SMP.
I'd imagine it would show up on any of the e500mc boards too.

Yeah.. Pity, I don't have SMP boards anymore. I'll try
to get one though.

diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c
index 8bd3c9f..3ff3bd0 100644
--- a/drivers/net/gianfar.c
+++ b/drivers/net/gianfar.c

@@ -2614,6 +2614,8 @@ static int gfar_poll(struct napi_struct *napi, int budget)
 			tx_queue = priv->tx_queue[rx_queue->qindex];
 
 			tx_cleaned += gfar_clean_tx_ring(tx_queue);
+			if (!tx_cleaned && !tx_queue->num_txbdfree)
+				tx_cleaned += 1; /* don't complete napi */
 			rx_cleaned_per_queue = gfar_clean_rx_ring(rx_queue,
 							budget_per_queue);
 			rx_cleaned += rx_cleaned_per_queue;