gianfar: Fix race between gfar_error() and gfar_start_xmit()

gfar_error() can arrive at the middle of gfar_start_xmit() processing,
and so it can trigger transfers of BDs that we don't yet expect to
be transmitted.

Fix this by locking the tx queues in gfar_error().

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/gianfar.c

@@ -2943,14 +2943,22 @@ static irqreturn_t gfar_error(int irq, void *grp_id)
 		if (events & IEVENT_CRL)
 			dev->stats.tx_aborted_errors++;
 		if (events & IEVENT_XFUN) {
+			unsigned long flags;
+
 			if (netif_msg_tx_err(priv))
 				printk(KERN_DEBUG "%s: TX FIFO underrun, "
 				       "packet dropped.\n", dev->name);
 			dev->stats.tx_dropped++;
 			priv->extra_stats.tx_underrun++;
 
+			local_irq_save(flags);
+			lock_tx_qs(priv);
+
 			/* Reactivate the Tx Queues */
 			gfar_write(&regs->tstat, gfargrp->tstat);
+
+			unlock_tx_qs(priv);
+			local_irq_restore(flags);
 		}
 		if (netif_msg_tx_err(priv))
 			printk(KERN_DEBUG "%s: Transmit Error\n", dev->name);