[NET]: Add netif_tx_lock

Various drivers use xmit_lock internally to synchronise with their
transmission routines.  They do so without setting xmit_lock_owner.
This is fine as long as netpoll is not in use.

With netpoll it is possible for deadlocks to occur if xmit_lock_owner
isn't set.  This is because if a printk occurs while xmit_lock is held
and xmit_lock_owner is not set can cause netpoll to attempt to take
xmit_lock recursively.

While it is possible to resolve this by getting netpoll to use
trylock, it is suboptimal because netpoll's sole objective is to
maximise the chance of getting the printk out on the wire.  So
delaying or dropping the message is to be avoided as much as possible.

So the only alternative is to always set xmit_lock_owner.  The
following patch does this by introducing the netif_tx_lock family of
functions that take care of setting/unsetting xmit_lock_owner.

I renamed xmit_lock to _xmit_lock to indicate that it should not be
used directly.  I didn't provide irq versions of the netif_tx_lock
functions since xmit_lock is meant to be a BH-disabling lock.

This is pretty much a straight text substitution except for a small
bug fix in winbond.  It currently uses
netif_stop_queue/spin_unlock_wait to stop transmission.  This is
unsafe as an IRQ can potentially wake up the queue.  So it is safer to
use netif_tx_disable.

The hamradio bits used spin_lock_irq but it is unnecessary as
xmit_lock must never be taken in an IRQ handler.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 9 deletions

diff --git a/drivers/net/forcedeth.c b/drivers/net/forcedeth.c
index feb5b223cd60..5a8651b4b01d 100644
--- a/drivers/net/forcedeth.c
+++ b/drivers/net/forcedeth.c
@@ -533,9 +533,9 @@ typedef union _ring_type {
  * critical parts:
  * - rx is (pseudo-) lockless: it relies on the single-threading provided
  *	by the arch code for interrupts.
- * - tx setup is lockless: it relies on dev->xmit_lock. Actual submission
+ * - tx setup is lockless: it relies on netif_tx_lock. Actual submission
  *	needs dev->priv->lock :-(
- * - set_multicast_list: preparation lockless, relies on dev->xmit_lock.
+ * - set_multicast_list: preparation lockless, relies on netif_tx_lock.
  */
 
 /* in dev: base, irq */
@@ -1213,7 +1213,7 @@ static void drain_ring(struct net_device *dev)
 
 /*
  * nv_start_xmit: dev->hard_start_xmit function
- * Called with dev->xmit_lock held.
+ * Called with netif_tx_lock held.
  */
 static int nv_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
@@ -1407,7 +1407,7 @@ static void nv_tx_done(struct net_device *dev)
 
 /*
  * nv_tx_timeout: dev->tx_timeout function
- * Called with dev->xmit_lock held.
+ * Called with netif_tx_lock held.
  */
 static void nv_tx_timeout(struct net_device *dev)
 {
@@ -1737,7 +1737,7 @@ static int nv_change_mtu(struct net_device *dev, int new_mtu)
 		 * Changing the MTU is a rare event, it shouldn't matter.
 		 */
 		nv_disable_irq(dev);
-		spin_lock_bh(&dev->xmit_lock);
+		netif_tx_lock_bh(dev);
 		spin_lock(&np->lock);
 		/* stop engines */
 		nv_stop_rx(dev);
@@ -1768,7 +1768,7 @@ static int nv_change_mtu(struct net_device *dev, int new_mtu)
 		nv_start_rx(dev);
 		nv_start_tx(dev);
 		spin_unlock(&np->lock);
-		spin_unlock_bh(&dev->xmit_lock);
+		netif_tx_unlock_bh(dev);
 		nv_enable_irq(dev);
 	}
 	return 0;
@@ -1803,7 +1803,7 @@ static int nv_set_mac_address(struct net_device *dev, void *addr)
 	memcpy(dev->dev_addr, macaddr->sa_data, ETH_ALEN);
 
 	if (netif_running(dev)) {
-		spin_lock_bh(&dev->xmit_lock);
+		netif_tx_lock_bh(dev);
 		spin_lock_irq(&np->lock);
 
 		/* stop rx engine */
@@ -1815,7 +1815,7 @@ static int nv_set_mac_address(struct net_device *dev, void *addr)
 		/* restart rx engine */
 		nv_start_rx(dev);
 		spin_unlock_irq(&np->lock);
-		spin_unlock_bh(&dev->xmit_lock);
+		netif_tx_unlock_bh(dev);
 	} else {
 		nv_copy_mac_to_hw(dev);
 	}
@@ -1824,7 +1824,7 @@ static int nv_set_mac_address(struct net_device *dev, void *addr)
 
 /*
  * nv_set_multicast: dev->set_multicast function
- * Called with dev->xmit_lock held.
+ * Called with netif_tx_lock held.
  */
 static void nv_set_multicast(struct net_device *dev)
 {