[PATCH] enc28j60: spend separate worker thread

[Christian Eisendle]

This patch modifies enc28j60 driver to use its own workqueue instead of 
the default events worker thread for two reasons:

- There is a race condition between fb_flashcursor and con_open (vt.c)
  when using framebuffer device, NFS as rootfs and enc28j60 as NIC:
  fb_flashcursor as well as con_open acquires the console semaphore.
  At system startup, when con_open is called, there are filesystem
  accesses (e.g. vcs_make_sysfs) while the console semaphore is
  being held.
  fb_flashcursor, which is a work_struct handler of the
  events worker thread, waits for the console semaphore to be
  released and blocks the events worker thread meanwhile.
  con_open will never return since NFS access will
  never be successful as the enc28j60 uses also
  the events worker thread.

- IMHO enc28j60 should anyway use its own worker thread since all
  work_structs in this driver (including tx work which always waits
  for SPI) are blocking the defaults worker thread.


Signed-off-by: Christian Eisendle <lkml@xxxxxxxxxxxx>
---

--- linux-2.6.29/drivers/net/enc28j60.c.orig	2009-03-25 
12:05:33.000000000 +0100
+++ linux-2.6.29/drivers/net/enc28j60.c	2009-03-25 12:05:46.000000000 +0100
@@ -23,6 +23,7 @@
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/netdevice.h>
+#include <linux/workqueue.h>
 #include <linux/etherdevice.h>
 #include <linux/ethtool.h>
 #include <linux/tcp.h>
@@ -61,6 +62,7 @@ struct enc28j60_net {
 	struct spi_device *spi;
 	struct mutex lock;
 	struct sk_buff *tx_skb;
+	struct workqueue_struct	*workqueue;
 	struct work_struct tx_work;
 	struct work_struct irq_work;
 	struct work_struct setrx_work;
@@ -1297,7 +1299,7 @@ static int enc28j60_send_packet(struct s
 	priv->netdev->trans_start = jiffies;
 	/* Remember the skb for deferred processing */
 	priv->tx_skb = skb;
-	schedule_work(&priv->tx_work);
+	queue_work(priv->workqueue, &priv->tx_work);

 	return 0;
 }
@@ -1322,7 +1324,7 @@ static irqreturn_t enc28j60_irq(int irq,
 	 * Remember that we access enc28j60 registers through SPI bus
 	 * via spi_sync() call.
 	 */
-	schedule_work(&priv->irq_work);
+	queue_work(priv->workqueue, &priv->irq_work);

 	return IRQ_HANDLED;
 }
@@ -1336,7 +1338,7 @@ static void enc28j60_tx_timeout(struct n

 	ndev->stats.tx_errors++;
 	/* can't restart safely under softirq */
-	schedule_work(&priv->restart_work);
+	queue_work(priv->workqueue, &priv->restart_work);
 }

 /*
@@ -1424,7 +1426,7 @@ static void enc28j60_set_multicast_list(
 	}

 	if (oldfilter != priv->rxfilter)
-		schedule_work(&priv->setrx_work);
+		queue_work(priv->workqueue, &priv->setrx_work);
 }

 static void enc28j60_setrx_work_handler(struct work_struct *work)
@@ -1567,6 +1569,11 @@ static int __devinit enc28j60_probe(stru
 	priv->msg_enable = netif_msg_init(debug.msg_enable,
 						ENC28J60_MSG_DEFAULT);
 	mutex_init(&priv->lock);
+	priv->workqueue = create_singlethread_workqueue(DRV_NAME);
+	if (priv->workqueue == NULL) {
+		dev_err(&spi->dev, "Unable to create work queue\n");
+		goto out_noqueue;
+	}
 	INIT_WORK(&priv->tx_work, enc28j60_tx_work_handler);
 	INIT_WORK(&priv->setrx_work, enc28j60_setrx_work_handler);
 	INIT_WORK(&priv->irq_work, enc28j60_irq_work_handler);
@@ -1616,6 +1623,8 @@ static int __devinit enc28j60_probe(stru
 error_register:
 	free_irq(spi->irq, priv);
 error_irq:
+	destroy_workqueue(priv->workqueue);
+out_noqueue:
 	free_netdev(dev);
 error_alloc:
 	return ret;
@@ -1627,6 +1636,7 @@ static int __devexit enc28j60_remove(str

 	if (netif_msg_drv(priv))
 		printk(KERN_DEBUG DRV_NAME ": remove\n");
+	destroy_workqueue(priv->workqueue);

 	unregister_netdev(priv->netdev);
 	free_irq(spi->irq, priv);
--
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