[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>

4 files changed, 24 insertions, 29 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 6bfa78c66c2..1b09f1cae46 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1282,15 +1282,13 @@ int __skb_linearize(struct sk_buff *skb, gfp_t gfp_mask)
 
 #define HARD_TX_LOCK(dev, cpu) {			\
 	if ((dev->features & NETIF_F_LLTX) == 0) {	\
-		spin_lock(&dev->xmit_lock);		\
-		dev->xmit_lock_owner = cpu;		\
+		netif_tx_lock(dev);			\
 	}						\
 }
 
 #define HARD_TX_UNLOCK(dev) {				\
 	if ((dev->features & NETIF_F_LLTX) == 0) {	\
-		dev->xmit_lock_owner = -1;		\
-		spin_unlock(&dev->xmit_lock);		\
+		netif_tx_unlock(dev);			\
 	}						\
 }
 
@@ -1389,8 +1387,8 @@ int dev_queue_xmit(struct sk_buff *skb)
 	/* The device has no queue. Common case for software devices:
 	   loopback, all the sorts of tunnels...
 
-	   Really, it is unlikely that xmit_lock protection is necessary here.
-	   (f.e. loopback and IP tunnels are clean ignoring statistics
+	   Really, it is unlikely that netif_tx_lock protection is necessary
+	   here.  (f.e. loopback and IP tunnels are clean ignoring statistics
 	   counters.)
 	   However, it is possible, that they rely on protection
 	   made by us here.
@@ -2805,7 +2803,7 @@ int register_netdevice(struct net_device *dev)
 	BUG_ON(dev->reg_state != NETREG_UNINITIALIZED);
 
 	spin_lock_init(&dev->queue_lock);
-	spin_lock_init(&dev->xmit_lock);
+	spin_lock_init(&dev->_xmit_lock);
 	dev->xmit_lock_owner = -1;
 #ifdef CONFIG_NET_CLS_ACT
 	spin_lock_init(&dev->ingress_lock);
diff --git a/net/core/dev_mcast.c b/net/core/dev_mcast.c
index 05d60850840..c57d887da2e 100644
--- a/net/core/dev_mcast.c
+++ b/net/core/dev_mcast.c
@@ -62,7 +62,7 @@
  *	Device mc lists are changed by bh at least if IPv6 is enabled,
  *	so that it must be bh protected.
  *
- *	We block accesses to device mc filters with dev->xmit_lock.
+ *	We block accesses to device mc filters with netif_tx_lock.
  */
 
 /*
@@ -93,9 +93,9 @@ static void __dev_mc_upload(struct net_device *dev)
 
 void dev_mc_upload(struct net_device *dev)
 {
-	spin_lock_bh(&dev->xmit_lock);
+	netif_tx_lock_bh(dev);
 	__dev_mc_upload(dev);
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 }
 
 /*
@@ -107,7 +107,7 @@ int dev_mc_delete(struct net_device *dev, void *addr, int alen, int glbl)
 	int err = 0;
 	struct dev_mc_list *dmi, **dmip;
 
-	spin_lock_bh(&dev->xmit_lock);
+	netif_tx_lock_bh(dev);
 
 	for (dmip = &dev->mc_list; (dmi = *dmip) != NULL; dmip = &dmi->next) {
 		/*
@@ -139,13 +139,13 @@ int dev_mc_delete(struct net_device *dev, void *addr, int alen, int glbl)
 			 */
 			__dev_mc_upload(dev);
 			
-			spin_unlock_bh(&dev->xmit_lock);
+			netif_tx_unlock_bh(dev);
 			return 0;
 		}
 	}
 	err = -ENOENT;
 done:
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 	return err;
 }
 
@@ -160,7 +160,7 @@ int dev_mc_add(struct net_device *dev, void *addr, int alen, int glbl)
 
 	dmi1 = kmalloc(sizeof(*dmi), GFP_ATOMIC);
 
-	spin_lock_bh(&dev->xmit_lock);
+	netif_tx_lock_bh(dev);
 	for (dmi = dev->mc_list; dmi != NULL; dmi = dmi->next) {
 		if (memcmp(dmi->dmi_addr, addr, dmi->dmi_addrlen) == 0 &&
 		    dmi->dmi_addrlen == alen) {
@@ -176,7 +176,7 @@ int dev_mc_add(struct net_device *dev, void *addr, int alen, int glbl)
 	}
 
 	if ((dmi = dmi1) == NULL) {
-		spin_unlock_bh(&dev->xmit_lock);
+		netif_tx_unlock_bh(dev);
 		return -ENOMEM;
 	}
 	memcpy(dmi->dmi_addr, addr, alen);
@@ -189,11 +189,11 @@ int dev_mc_add(struct net_device *dev, void *addr, int alen, int glbl)
 
 	__dev_mc_upload(dev);
 	
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 	return 0;
 
 done:
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 	kfree(dmi1);
 	return err;
 }
@@ -204,7 +204,7 @@ done:
 
 void dev_mc_discard(struct net_device *dev)
 {
-	spin_lock_bh(&dev->xmit_lock);
+	netif_tx_lock_bh(dev);
 	
 	while (dev->mc_list != NULL) {
 		struct dev_mc_list *tmp = dev->mc_list;
@@ -215,7 +215,7 @@ void dev_mc_discard(struct net_device *dev)
 	}
 	dev->mc_count = 0;
 
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 }
 
 #ifdef CONFIG_PROC_FS
@@ -250,7 +250,7 @@ static int dev_mc_seq_show(struct seq_file *seq, void *v)
 	struct dev_mc_list *m;
 	struct net_device *dev = v;
 
-	spin_lock_bh(&dev->xmit_lock);
+	netif_tx_lock_bh(dev);
 	for (m = dev->mc_list; m; m = m->next) {
 		int i;
 
@@ -262,7 +262,7 @@ static int dev_mc_seq_show(struct seq_file *seq, void *v)
 
 		seq_putc(seq, '\n');
 	}
-	spin_unlock_bh(&dev->xmit_lock);
+	netif_tx_unlock_bh(dev);
 	return 0;
 }
 
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index e8e05cebd95..9cb78183038 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -273,24 +273,21 @@ static void netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 
 	do {
 		npinfo->tries--;
-		spin_lock(&np->dev->xmit_lock);
-		np->dev->xmit_lock_owner = smp_processor_id();
+		netif_tx_lock(np->dev);
 
 		/*
 		 * network drivers do not expect to be called if the queue is
 		 * stopped.
 		 */
 		if (netif_queue_stopped(np->dev)) {
-			np->dev->xmit_lock_owner = -1;
-			spin_unlock(&np->dev->xmit_lock);
+			netif_tx_unlock(np->dev);
 			netpoll_poll(np);
 			udelay(50);
 			continue;
 		}
 
 		status = np->dev->hard_start_xmit(skb, np->dev);
-		np->dev->xmit_lock_owner = -1;
-		spin_unlock(&np->dev->xmit_lock);
+		netif_tx_unlock(np->dev);
 
 		/* success */
 		if(!status) {
diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index c23e9c06ee2..67ed14ddabd 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2897,7 +2897,7 @@ static __inline__ void pktgen_xmit(struct pktgen_dev *pkt_dev)
 		}
 	}
 
-	spin_lock_bh(&odev->xmit_lock);
+	netif_tx_lock_bh(odev);
 	if (!netif_queue_stopped(odev)) {
 
 		atomic_inc(&(pkt_dev->skb->users));
@@ -2942,7 +2942,7 @@ static __inline__ void pktgen_xmit(struct pktgen_dev *pkt_dev)
 		pkt_dev->next_tx_ns = 0;
 	}
 
-	spin_unlock_bh(&odev->xmit_lock);
+	netif_tx_unlock_bh(odev);
 
 	/* If pkt_dev->count is zero, then run forever */
 	if ((pkt_dev->count != 0) && (pkt_dev->sofar >= pkt_dev->count)) {